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Hello all,

In the words of Austin Powers, allow myself to introduce, myself:

 

Smooth, handsome and wealthy, with a penchant for exotic cars. Well, that’s quite enough about 007. As for me, I’m a highly mechanically competent privateer with an unhealthy obsession for carbs and extracting every last pony out of vintage cars.* In short, a middle aged man in suburbia, living the dream! 

 

I’m currently helping my BIL with the challenges bestowed upon him by his gorgeous TR6 PI running the Lucas Injection system - which I have been learning a lot about of late.

Here’s a great read that I’m certain is old hat to the 6-enthusiast.

http://www.lucasinjection.com/index.html

 

336E7475-ADFE-4F0F-A145-A636EA20BFE5.thumb.jpeg.d78ab3a14d0195df70ac8ca458787fce.jpeg

 

The car was running beautifully but then began having issues starting and bogging down / fouling plugs / stalling.


We identified the MU as the underlying issue which was sent away and rebuilt by an expert. But sadly the garage who fitted it for him haven’t dialled it in on a RR or with a gas analyser. I cannot imagine it’s set up correctly for the car. Frankly I don’t believe they understand it well enough and gave it their best shot.

 

Since getting it back from the garage the car is running very rough, popping through the intake when blipped and slightly reluctant to rev / down on power. Doing the old school test: WOT then turn engine off and into neutral / coast to the side of the road, the plugs look lean to me. I can even smell the leanness - anyone else sad enough to know that smell? So potentially we have two issues of mix and injection timing both being off. If it was on multiple carbs I would say it’s akin to them being out of balance and overly lean.

 

410FD14E-727C-4758-8468-D0EDC151AAC4.thumb.jpeg.2dbd9850f80d4aea3a083f43bdfeaf3b.jpeg

 

The car is on electronic ignition (no vac) with ROCK SOLID timing which I’ve checked - 17degrees @idle (850-900rpm) and maxing out at 27 @2.5k ish which was only as far as I took it to ensure it was sufficiently advancing. Plugs, leads, coil are all new. Cant recall the plug gaps but they are all even. Vac hose to MU is new, brake booster hose is good and there are no known false air sources / leaks. Butterflies balanced with air-flow meter.
 

We know the car has a stage 3 head (whatever that means) but not sure if the cam is totally stock. So next, I’m going to check the cam profile - using one DTI over the rockers and another I have which confirms TDC through the spark plug hole; it’s a very useful bit of kit.

 

So, now we have the long intro out of the way, please allow me to gain the benefit of your insights / experience:

 

1. Firstly, does anyone know what the crank damper OD is on these cars? I need to get stick on 360degree marks to be able to properly check the cam profile / LSA / lift / etc with the DTI and a spreadsheet.

 

2. I read everywhere that the voodoo magic of the MU is not to be touched by mortal hands, otherwise we shall all perish - most horribly!!! So are there any recommended garages in the South East (or even up to the Midlands) whom we trust with good knowledge of dialling in MUs / understand Lucas injection system well?

 

3. Let’s be controversial - is it really beyond the wit of man to adjust the 3 rings of the MU with an o2 sensor / AFR gauge and get it right? Seriously, I don’t see any magic in the schematics. Except for setting up the correct injection timing, it doesn’t “look” any more involved than setting up triple DCOEs!! Am I missing something? 


I’d be most grateful for your kind advice / pointers.

Thanks in advance,

Ali

 

Ps. *My NA Datsun Z on twin 1.75” SUs (with custom needles) is currently doing 245BHP @6.5k and low 13 quarter miles; now tell me “them SUs just won’t flow” ;)! Oh and with two TRs in the family we regularly talk about my Jap-*rap!! So feel free to have a good dig, my skin has been somewhat thickened!

F3DA5C63-755D-47FA-8AEB-D01835A67716.thumb.jpeg.c5731884e47804b5053e2fded6210f34.jpeg

Edited by FastNCurious
Typos, courtesy of iOS autocorrect!
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Welcome !

the tr6 on PI is a Great Thing, and can be made to run beautifully amd reliably.

i bought my current tr6 in december 2012 and after some initial work it has run perfectly ever since.

if you had the MU set up by a reputable rebuilder then it should be good to go, no need for tuning to at least get the engine running well.

the thing that sticks out from the above is the timing, 17btdc is too advanced at idle, try 8-10 as a starting point.

good luck!

steve

Edited by Steves_TR6
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One other thing on timing, the timing marks can slip !

the timing marks are on the damper and these are old now and can slip, mine were 7deg out!

so ideally measure tdc with a tool and check the timing marks first

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Quick way to set timing that does not depend upon the crank damper marks is to find the fastest idle by rotating the disy slightly to and fro, engine running, taking care to avoid shocks.

Peter

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Posted (edited)

Thank you gentlemen, much appreciated.

 

Steve, I will be sure to check that. It's interesting how engines can be so different, the Datsun LOVES timing. It idles at 17, with 34-36 all-in being plenty safe on RON 95 - so I made a silly assumption that 17 was also OK on the 6. I guess head design, compression, cams etc all play their parts. I replaced my 40+ year old one with an ATi Super Racing damper, having 360 degree timing marks - if it's acceptable in TR circles, I recommend it, it's a fantastic bit of kit.  

ati-917122e_w.jpg.ba2b548e39043d650347902ae260a4c1.jpg

Stuart, thank you for the recommendation. I just discovered that, coincidentally, my brother-in-law spoke with them today. He was mightily impressed with their client centric / friendly approach. So it's great to hear them being called out here also.

 

Peter - thanks for that, it's a good method. Oh and for the link. I was just reading your presentation on ‘mixture spread‘. Great to find people that truly understand SUs. I see so many cars on carbs that aren't properly tuned or over-carbed, but I guess the common understanding of carbs has been in decline with modern EFi coming to the fore. We could speak for days on this topic!! My new bad obsession is Inlet tract tuning to take advantage of the pulses ;). That and doing some Vizzard style mods to my spare SUs - would love to hear your thoughts are on SU modding (and I am conscious I'm taking my own thread way off topic now, so maybe in a new thread then). Here's something I took off 'tinter and started scribbling on - I can't take credit for the photo. It's from a chap in Lancashire who does these mods commercially.

 

vizzard.JPG.4112fc780afc03466362afa82d32f58e.JPG

Edited by FastNCurious
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You do need to be careful in smoothing the inlet tract on an SU as you do need some turbulence in the airflow to get a good mixture of fuel/air.

Stuart

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Ali,   Tks for the plaudits re SU functioning. It took a year, on and off, to reverse engineer, as no records survive. Even textbooks say they work as a venturi but that is wrong.  It works as a gate valve and shmfering to ramp and leading edge of the piston is a no-no. "Gas flowing" the butterfly is OK.  Mixture quality - atomisation- is a function of the spring: more downforce increases depression and atomisation.  Recontouring the entry to the carb or fitting a trumpet can change the metering, because the less pressure dropped at the entry means the piston does not lift so much to maintain as it must constant depression at the jet. Result: a mixture change to weaker, but impossible to calculate. UEGO to the rescue !

My motive for writing the talk was the result of trying to work out how to Allard,a supercharging guru, got 220 hp metered by one HS8 ( 2 inch) SU. I think I now know how best to do it. Despiite  using EP 140 diff oil in the damper my blown engine would stumble upon modestyl rapid throttle opening. I cured that with Allard's trick of lead added to the piston, but the result was 22 mpg.  That worked, it runs very smooooth, but was "wrong" to my thnking. The plan now is to ditch the lead and cover up one of the transfer ports to slow the piston rise.

==

Witha 8.5:1 compression r my 6 runs best with 18 BTDC tick-over.

Peter

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Well lots of us have tried David Vizards flowing of the SU and although it’s counter intuitive... it doesn’t give an advantage.
As Stuart says and Peter Cobbold endorses altering the inside of a SU by chamfered edges on the piston front reduces the turbulence which reduces the ‘carry’ mixture of the flow making it a weaker mix and less flow results.

I had a badinage with our much lamented  Badfrog friend about 6-7 years ago before his passing. He’d machined his pistons as described and after I’d told him my experiences ( back in winter of 86) his dismay was apparent, but he still fitted them... and found out it was true. 
I’d turned up at Peter Burgess home with a collection of 5 x SUs ( 1 3/4) modified as per Vizard ( and other) which I contributed to Peter as he was testing variations of the same on 3 of his own SU carbs on his flow bench ( only way to tell without track time).
 

I had the whole collection, advance ramp flowed and reduced by araldite, both advance and depart... less flow. Radiused leading piston edges... less flow, Leading piston edge chamfered... less flow, blending the edges in of the jet bridge in with araldite ... less flow etc etc. The only small increases were made by the thinning of the butterfly spindle with countersunk screws fitted and chamfered edges on the advance  edge of the butterfly. 
Mr Skinner did a better job than many think when he came up with this design, I think some tuners feel aggrieved because so many obvious flow enhancers don’t deliver the power on this carb. The only mod I’ve heard of that gives more power is a complete machine removal of the jet bridge but leaving the jet standing in the middle, it just gives a large increase in hole volume but at the cost of enormous part throttle power losses and flexibility where the gas speed is reduced until the larger numbers come in.

Mick Richards

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6 minutes ago, Motorsport Mickey said:

Well lots of us have tried David Vizards flowing of the SU and although it’s counter intuitive... it doesn’t give an advantage.
As Stuart says and Peter Cobbold endorses altering the inside of a SU by chamfered edges on the piston front reduces the turbulence which reduces the ‘carry’ mixture of the flow making it a weaker mix and less flow results.

I had a badinage with our much lamented  Badfrog friend about 6-7 years ago before his passing. He’d machined his pistons as described and after I’d told him my experiences ( back in winter of 86) his dismay was apparent, but he still fitted them... and found out it was true. 
I’d turned up at Peter Burgess home with a collection of 5 x SUs ( 1 3/4) modified as per Vizard ( and other) which I contributed to Peter as he was testing variations of the same on 3 of his own SU carbs on his flow bench ( only way to tell without track time).
 

I had the whole collection, advance ramp flowed and reduced by araldite, both advance and depart... less flow. Radiused leading piston edges... less flow, Leading piston edge chamfered... less flow, blending the edges in of the jet bridge in with araldite ... less flow etc etc. The only small increases were made by the thinning of the butterfly spindle with countersunk screws fitted and chamfered edges on the advance  edge of the butterfly. 
Mr Skinner did a better job than many think when he came up with this design, I think some tuners feel aggrieved because so many obvious flow enhancers don’t deliver the power on this carb. The only mod I’ve heard of that gives more power is a complete machine removal of the jet bridge but leaving the jet standing in the middle, it just gives a large increase in hole volume but at the cost of enormous part throttle power losses and flexibility where the gas speed is reduced until the larger numbers come in.

Mick Richards

Mick, Fascinating that flow falls with chamfering the piston and/or filling in the leading edge of the bridge. I am now, having worked though the fluid mechanics, confident why you got that ( counterintutive) effect. Those mods will create a venturi effect that will result in low pressure between bridge and piston. Result: the piston is pulled down. The transfer ports will not see that ventri-depression so the depression thre loses out in piston-lifting. Imprtantly, a venturi needs smooth laminar flow to work. In umolested SUs ( and Strombergs) the sharp ramp-up to the bridge and sharp edge to the piston destroy the laminer flow and the device no longer works as a venturi.

We should combine forces and write it up for TRA: your data. my theory.

Peter

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Posted (edited)

To bring the thread back on track before I upset moderators too much ;) - Mark of Enginuity saw my BIL last night and instantly knew what was wrong: Injector no.2 is dead. The poppet valve (is that what you call it?) at the end has no spring and can be pulled out easily by hand, therefore just dribbling fuel instead of atomising. As already mentioned above by @Steves_TR6 , Mark also thought the car had too much timing. 

With the wonders of modern tech, otherwise known as FaceTime, I walked my BIL through using a timing light and we determined that all-in, the dizzy was hitting the poor car with 37 degrees! So we dialled it back to a safe 27/28 degrees@3.5Krpm. It may seem conservative but I'm not familiar with TR nuances and not entirely sure what a "stage 3 head" means! Is it a port and polish or the full works with enlarged valves, raised compression etc.? I therefore thought losing a few degrees below optimal power will keep him on the safe side and allow headroom for poor quality fuels he may be limited to at some point on the road. Lo and behold, no more popping through the inlet on blipping. The idle settled to around 12 degrees at 850-900 rpm (the timing light pickup was noisy so it was jumping about a little at idle). 

When he was up here yesterday, I didn't get to properly test the car, as we spend 90% of our available time troubleshooting dodgy earths, an intermittent brake light switch and renewing crusty spade connectors. At least now he has headlights, tail / brake lights which work again and are much brighter. But now I wish I had gone over the dizzy properly - I feel a little foolish there. 

 

As for Enginuity and Mark - WHAT AN ABSOLUTE TOP MAN!!! He is sorting BIL out with a recon injector after work this evening, so he should be driving again at the weekend. Honestly, it is so very nice to find people who are knowledgeable, helpful and delight their customers. He just gained two very loud advocates and a customer for life!  

I will update you in due course as to the full outcome of the car's troubles. 

Now to go back off track and onto carbs! :D

Thanks gentlemen for sharing your thoughts! This is really interesting stuff to read!!! I recall as a child in the 70s watching my father for HOURS dismantling and rebuilding carbs, but in all honesty, no matter how much I feel I know, every day is a school day! VERY VERY interesting to read your findings on the "Vizzard" mods. It is, as you say, COMPLETELY counter intuitive.

Here's a slowed down video of my carb standoff, which I thought some of you may find interesting. After installing a new exhaust system with larger equal length primaries, I'm sporting two noticeable torque holes at 2.1K and 3.2K rpm (after which it's just woaaaaaaaaah to the 6.8K limiter). So I was investigating the piston position at different revs/MAP (I strongly suspect the primaries are just that little bit too large and I will have to revert to the old one). My timing light rev counter wasn't playing ball though and I never got the time to repeat it with a proper chronometer installed in the view of the webcam. I had marked the piston at 3mm intervals which also washed off rather quickly with standoff juices. Anyway, I thought this may be an interesting video even if not on a TR engine; the principles are the same regardless.

 

Also if it is of interest, here's my thread on playing with the SUs and my spreadsheet modelling of needles. It's a little out of date now but it may make for some entertainment if you are bored. 

On inlet tract tuning: permit me to caution against buying the ITG trumpets for HS6 carbs - I found them to make the car feel flat EVERYWHERE in the rev range. Not only are they extremely poor quality / poorly finished, but the opening is 40mm v the Hitachi SU (HS6 based) carbs that are 44mm. So it felt like going a carb size down!! Not to mention the dreadful step inside the opening (visible in the photo) that causes more turbulence just before the carb mouth. To their credit, Merlin Motorsport are willing to refund without a single word of quibble and a year after my purchase.

 

ITG.thumb.JPG.ae775ad57dbdb9097fdaa344e619d6b6.JPG

 

I have learned that much of classic car ownership, for many, is about things "looking good" and / or being "shiny" - and they do "look" good on the car.

 

ITG2.JPG.8b5a94098177898c0dedd330d58cb358.JPG

 

So I do wonder how many people have thought "Ooooh shinyyyyy", installed them as open trumpets for sound / looks and in the process lost power / economy!? What percentage of owners take out their callipers and think to themselves, "I wonder"!? I knew they were a little restrictive just by looking at them but I hadn't realised just how much! Either way, I wanted to test them out and see the effect given they are twice the height of stock trumpets. Now I'm about to spend $120 on a fully radiused set made for these carbs in the US. Unlike you very fortunate TR owners, there isn't a UK / European network of new parts for us "ricers". 

 

In fact, are you chaps aware of a supplier of fully radiused SU / HS6 trumpets in the UK which google hasn't shown me yet?

 

Thank you again for your support and insights!

Ali

Edited by FastNCurious
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Ali,  The  reversion is probably not going to happen when the engien is loaded as the mass air flow will be much greater and particle velocity over the jjet mcuh greater. In your video I  think it starts when the throttle lever is about half way down. It is known that at 30deg opening or less the air flow past a butterlfy valve is sonic. That meanas that pulses of retrograde air flow cannot pass from the iv to the carb. Late iv closing is probably causing pulsing at >30 dge butterfly openings, and low intake mass flows. Once the egnine is loaded the momentum of the inflowing air will counter the retrograde pulsing but a rolling road would be needed to check.

Peter

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47 minutes ago, FastNCurious said:

To bring the thread back on track before I upset moderators too much ;) - Mark of Enginuity saw my BIL last night and instantly knew what was wrong: Injector no.2 is dead. The poppet valve (is that what you call it?) at the end has no spring and can be pulled out easily by hand, therefore just dribbling fuel instead of atomising. As already mentioned above by @Steves_TR6 , Mark also thought the car had too much timing. 

With the wonders of modern tech, otherwise known as FaceTime, I walked my BIL through using a timing light and we determined that all-in, the dizzy was hitting the poor car with 37 degrees! So we dialled it back to a safe 27/28 degrees@3.5Krpm. It may seem conservative but I'm not familiar with TR nuances and not entirely sure what a "stage 3 head" means! Is it a port and polish or the full works with enlarged valves, raised compression etc.? I therefore thought losing a few degrees below optimal power will keep him on the safe side and allow headroom for poor quality fuels he may be limited to at some point on the road. Lo and behold, no more popping through the inlet on blipping. The idle settled to around 12 degrees at 850-900 rpm (the timing light pickup was noisy so it was jumping about a little at idle). 

When he was up here yesterday, I didn't get to properly test the car, as we spend 90% of our available time troubleshooting dodgy earths, an intermittent brake light switch and renewing crusty spade connectors. At least now he has headlights, tail / brake lights which work again and are much brighter. But now I wish I had gone over the dizzy properly - I feel a little foolish there. 

 

As for Enginuity and Mark - WHAT AN ABSOLUTE TOP MAN!!! He is sorting BIL out with a recon injector after work this evening, so he should be driving again at the weekend. Honestly, it is so very nice to find people who are knowledgeable, helpful and delight their customers. He just gained two very loud advocates and a customer for life!  

I will update you in due course as to the full outcome of the car's troubles. 

Now to go back off track and onto carbs! :D

Thanks gentlemen for sharing your thoughts! This is really interesting stuff to read!!! I recall as a child in the 70s watching my father for HOURS dismantling and rebuilding carbs, but in all honesty, no matter how much I feel I know, every day is a school day! VERY VERY interesting to read your findings on the "Vizzard" mods. It is, as you say, COMPLETELY counter intuitive.

Here's a slowed down video of my carb standoff, which I thought some of you may find interesting. After installing a new exhaust system with larger equal length primaries, I'm sporting two noticeable torque holes at 2.1K and 3.2K rpm (after which it's just woaaaaaaaaah to the 6.8K limiter). So I was investigating the piston position at different revs/MAP (I strongly suspect the primaries are just that little bit too large and I will have to revert to the old one). My timing light rev counter wasn't playing ball though and I never got the time to repeat it with a proper chronometer installed in the view of the webcam. I had marked the piston at 3mm intervals which also washed off rather quickly with standoff juices. Anyway, I thought this may be an interesting video even if not on a TR engine; the principles are the same regardless.

 

Also if it is of interest, here's my thread on playing with the SUs and my spreadsheet modelling of needles. It's a little out of date now but it may make for some entertainment if you are bored. 

On inlet tract tuning: permit me to caution against buying the ITG trumpets for HS6 carbs - I found them to make the car feel flat EVERYWHERE in the rev range. Not only are they extremely poor quality / poorly finished, but the opening is 40mm v the Hitachi SU (HS6 based) carbs that are 44mm. So it felt like going a carb size down!! Not to mention the dreadful step inside the opening (visible in the photo) that causes more turbulence just before the carb mouth. To their credit, Merlin Motorsport are willing to refund without a single word of quibble and a year after my purchase.

 

ITG.thumb.JPG.ae775ad57dbdb9097fdaa344e619d6b6.JPG

 

I have learned that much of classic car ownership, for many, is about things "looking good" and / or being "shiny" - and they do "look" good on the car.

 

ITG2.JPG.8b5a94098177898c0dedd330d58cb358.JPG

 

So I do wonder how many people have thought "Ooooh shinyyyyy", installed them as open trumpets for sound / looks and in the process lost power / economy!? What percentage of owners take out their callipers and think to themselves, "I wonder"!? I knew they were a little restrictive just by looking at them but I hadn't realised just how much! Either way, I wanted to test them out and see the effect given they are twice the height of stock trumpets. Now I'm about to spend $120 on a fully radiused set made for these carbs in the US. Unlike you very fortunate TR owners, there isn't a UK / European network of new parts for us "ricers". 

 

In fact, are you chaps aware of a supplier of fully radiused SU / HS6 trumpets in the UK which google hasn't shown me yet?

 

Thank you again for your support and insights!

Ali

Topic drift for Velocity Stacks fitted to  SU carbs

A good read if you are interested

https://mgaguru.com/mgtech/power/pp104.htm

Cheers

Peter W

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Posted (edited)

Update on the 6:

 

Injector no.2 was replaced at the weekend and with the timing set correctly now, my BIL was saying that the 6 has NEVER ran so smoothly in his ownership. He commented that it felt a lot less raw and a lot more refined / modern - that was right up until injector no.5 decided to let go in short order!!! I suspect he has always had weak injectors on their way out which got worse with time and that the engine has always been intermittently running on 5.5 cyls. Fortunately, thanks to Mark being such a total gentleman, he is planning on replacing that one and all 3 ball linkages this evening. The current links are not great and one is completely different to the other two. So more of that anon. 

 

It seems from what we've read that injectors 2 & 5 are very susceptible to failures - something to do with the banjo fittings on the MU and a non-return valve. It just doesn't seem to make logical sense to me? Am I missing something obvious? 

 

Does a long winter layup with ethanol encourage these failures? I personally add a shot of Millers VSPe to my last tank of the summer but I understand Esso has brought out ethanol free unleaded which I have yet to sample. 

 

On the topic of carbs: 

Thanks Peter C - that is interesting indeed. Like I said, it's always a school day! BTW the webcam video was with me going uphill at WOT in 2nd. Interestingly though, with the plenum fitted, the AFRs around the torque holes become a lot more civilised - albeit still too rich. I suspect the moving column of air standing above the carbs is smoothing out some of the pulsation, maybe? Or the pulses in the plenum cancel each other out a bit? Or both?

Peter W - thanks also for the link. I had come across that one previously and ordered some "shorties" to experiment with based on the article. Once more, they went straight back as an eBay return - despite the flanges being correct, the openings at 38.5mm were way smaller than HS6 mouth size!

For info, this is the listing: https://www.ebay.co.uk/itm/1-3-4-Pair-Stub-Stacks-for-K-N-or-Other-Pancake-Air-Filter-SU-HS6/200962949913

The ones that fit the carbs absolutely perfectly (which I've borrowed from another Z club member and tested before spending more money) are the ones below from the US. They measure to within 1/4 mm of the carb mouths. At $69 each before delivery, they are a little eye watering but it doesn't seem possible for me to find well built HS6 sized and fully radiused trumpets in the UK. Having said that, these have something like 270 degree radii but are much better than anything I've seen available so far for HS6.

zstorestacks.jpg.90b4257b29190cfde029f57ae55d8241.jpg

The DCOE ones below on eBay are actually fully radiused and made from a single billet. But with 65mm centres, they won't bolt up to the HS6 72mm centres. Having said that, I have a custom backplate for my plenum whereby I can add North-South (or at 45 degrees) studs to make them fit. I would also have to open / taper the carb mouths, or in fact the backplate holes, by about a mm to avoid a "step" into the carbs. Why am I sharing all this nonsense? Well, I thought it may be of interest to anyone else sporting HS6 carbs on their 6, with an unhealthy airflow obsession and going through my current dilemma ;) . Also hoping that someone will slap me and tell me to go to "Harry in Devon" who makes them for BL cars :P

s-l500.jpg.4c302b8a8b3caf4d8c7edca24ec3c977.jpg
 

Edited by FastNCurious
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Ali, So the standoff is at wot fully loaded. In that situation it is possible for inlet tract pulsing to occur. It is complex and impossible to calculate but does have to effect of richening the mixture. SU company found that the balance pipe plays an important role in sharing the pulses between carbs. See talk, but it is difficult to follow. The original manfold design will have been a joint  effort, Triumph with SU ,I suspect and with the standard cam. With a wilder cam and late iv closing and greater mass air flow the balance pipe may no longer be big enough to share the pulsing between carbs. Welding in a bigger bore balance pipe might be worth trying.

The richness from pulsing cannot be tuned out on the needle as the same needle-position is used to meter cruise miixture.  Pulsing richens the mixture because the depression at the jet also pulses, the inertia of the piston in the carb preventing it responding to pulses. 

I have not seen any tuner palying with the balance pipe. But considerations of mpg at wot are not high on their list of objectives. And  bit rich at full load helps avoid detonaiton. As long  as the standoff re-enters the carb and does not escape the plenum I would not worry overmuch. But is is an interesting phenomenon.

Peter

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10 hours ago, FastNCurious said:

Update on the 6:

 

Injector no.2 was replaced at the weekend and with the timing set correctly now, my BIL was saying that the 6 has NEVER ran so smoothly in his ownership. He commented that it felt a lot less raw and a lot more refined / modern - that was right up until injector no.5 decided to let go in short order!!! I suspect he has always had weak injectors on their way out which got worse with time and that the engine has always been intermittently running on 5.5 cyls. Fortunately, thanks to Mark being such a total gentleman, he is planning on replacing that one and all 3 ball linkages this evening. The current links are not great and one is completely different to the other two. So more of that anon. 

 

It seems from what we've read that injectors 2 & 5 are very susceptible to failures - something to do with the banjo fittings on the MU and a non-return valve. It just doesn't seem to make logical sense to me? Am I missing something obvious? 

 

Does a long winter layup with ethanol encourage these failures? I personally add a shot of Millers VSPe to my last tank of the summer but I understand Esso has brought out ethanol free unleaded which I have yet to sample. 

 

On the topic of carbs: 

Thanks Peter C - that is interesting indeed. Like I said, it's always a school day! BTW the webcam video was with me going uphill at WOT in 2nd. Interestingly though, with the plenum fitted, the AFRs around the torque holes become a lot more civilised - albeit still too rich. I suspect the moving column of air standing above the carbs is smoothing out some of the pulsation, maybe? Or the pulses in the plenum cancel each other out a bit? Or both?

Peter W - thanks also for the link. I had come across that one previously and ordered some "shorties" to experiment with based on the article. Once more, they went straight back as an eBay return - despite the flanges being correct, the openings at 38.5mm were way smaller than HS6 mouth size!

For info, this is the listing: https://www.ebay.co.uk/itm/1-3-4-Pair-Stub-Stacks-for-K-N-or-Other-Pancake-Air-Filter-SU-HS6/200962949913

The ones that fit the carbs absolutely perfectly (which I've borrowed from another Z club member and tested before spending more money) are the ones below from the US. They measure to within 1/4 mm of the carb mouths. At $69 each before delivery, they are a little eye watering but it doesn't seem possible for me to find well built HS6 sized and fully radiused trumpets in the UK. Having said that, these have something like 270 degree radii but are much better than anything I've seen available so far for HS6.

zstorestacks.jpg.90b4257b29190cfde029f57ae55d8241.jpg

The DCOE ones below on eBay are actually fully radiused and made from a single billet. But with 65mm centres, they won't bolt up to the HS6 72mm centres. Having said that, I have a custom backplate for my plenum whereby I can add North-South (or at 45 degrees) studs to make them fit. I would also have to open / taper the carb mouths, or in fact the backplate holes, by about a mm to avoid a "step" into the carbs. Why am I sharing all this nonsense? Well, I thought it may be of interest to anyone else sporting HS6 carbs on their 6, with an unhealthy airflow obsession and going through my current dilemma ;) . Also hoping that someone will slap me and tell me to go to "Harry in Devon" who makes them for BL cars :P

s-l500.jpg.4c302b8a8b3caf4d8c7edca24ec3c977.jpg
 

These are the best ones I've found in the UK.

https://www.med-engineering.co.uk/ancillaries/stub-stacks/med-stub-stacks

They work well inside a deeper airfilter.

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Damn...You can work on my car anytime Bob.

Mick Richards

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1 hour ago, Lebro said:

Or make your own:  

198416558_Studsfitted.thumb.jpg.ab59157ce8ccdcaf88344b1c538b9628.jpg  1276876417_Oncar3.thumb.jpg.950fde869f588c4467f19443a89c4470.jpg  2102081423_Afterpolishing.jpg.84d11ca753fc77f69ffbfe6ac4f50bfb.jpg

Bob.

I wish I had the facilities to do so!

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Cyls 2 and 5 do indeed have a deserved bad rep, they use different fittings at the MU to the other 4 and the o-rings do cause problems as they disintegrate.

i recommend a set of 6 reconditioned injectors be fitted, i did this in 2012 and they are still working perfectly today!

good luck getting the ‘6 running perfectly, they’re a joy to drive when right !

steve

Edited by Steves_TR6
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On 4/8/2021 at 8:54 PM, FastNCurious said:

3. Let’s be controversial - is it really beyond the wit of man to adjust the 3 rings of the MU with an o2 sensor / AFR gauge and get it right? Seriously, I don’t see any magic in the schematics. Except for setting up the correct injection timing, it doesn’t “look” any more involved than setting up triple DCOEs!! Am I missing something? 

 

No it's not, and no you're not. But the addition of a vacuum calibration rig would make tuning more repeatable, i.e., a vacuum generator + accurate vacuum gauge(s) to allow you to measure/ adjust cam follower gap (aka fuel delivery) at different vacuum settings. Even better, the means to log vacuum and AFR while driving, for later analysis. Cheaper and more fun than a RR. Oh, and as well as the three rings, there is max fuel and datum track gradient. But all are simple. Just require care because very little adjustment does a lot. But all totally do-able.

John 

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Manifold vacuum at cruise when butterflies are less than 30deg open is always half atmospheric, or you cn use a dashborad manifold vac gauge. For mixture a UEGO  probe in the exhaust is ideal. However although the PI mixtureat cruise could be adjsuted weaker using  those tools, the engine will stumble badly upob going to full throttle. The PI lacks a  throttle pump to transiently supply more fuel so has to be run rich to avoid the "lean spike". Also the lack of vac advance on the disy menas that optimum advance at cruise cannot be set.( it was never connected by Triumph with good reason; if the cruise mixture is not ruuning weak then there is no need for more advance)

There is a lot of scope for experimentation to win more mpg and "green" the PI.

Peter

 

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On 4/15/2021 at 10:58 PM, Peter Cobbold said:

Manifold vacuum at cruise when butterflies are less than 30deg open is always half atmospheric, or you cn use a dashborad manifold vac gauge. For mixture a UEGO  probe in the exhaust is ideal. However although the PI mixtureat cruise could be adjsuted weaker using  those tools, the engine will stumble badly upob going to full throttle. The PI lacks a  throttle pump to transiently supply more fuel so has to be run rich to avoid the "lean spike". Also the lack of vac advance on the disy menas that optimum advance at cruise cannot be set.( it was never connected by Triumph with good reason; if the cruise mixture is not ruuning weak then there is no need for more advance)

There is a lot of scope for experimentation to win more mpg and "green" the PI.

Peter

Hi Peter (and others),

Thought you might be interested to see data from a UEGO sensor, which clearly shows opportunities for improvement as you suggest. The car runs a standard CP cam, with PI set up per the Lucas manual for a TR5. Head is gas-flowed but standard exhaust. Sensor is AEM 30-4110 wide-band; Data are logged using an Innovate LMA-3 Auxbox and PL-1 data logger. Also logged but not shown here are RPM, acceleration and sideforce.

The 3D chart has vacuum along the long axis, and AFR on the short axis. Height is the frequency of reading. You can see that during the log period the car spent a lot of time at idle vacuum (about 11.5"Hg in this case), with a peak at WOT and another set of peaks at over-run vacuum.

The 2D chart is simply AFR vs manifold vacuum. The three lines are average AFR, average-1 Standard Deviation, and avg+1 SD.

As you can see, WOT AFR is a little rich at 12:1, but the mixture rapidly gets richer as soon as you back off, until the weak spring starts to compress at about 1.5"Hg/11.2:1. Then it quickly gets leaner until the weak spring is fully compressed at about 3.5"/13:1. Thereafter the mixture gets steadily richer as airflow is reduced faster than fuel supply until just after idle at about 13"Hg/11:1. After the throttles are closed the fuel supply reduces faster than air flow does and the mixture leans out to the point of min fuel at 18"Hg/14:1. After that the mixture gets richer as the fuel supply stays constant but demand continues to reduce.

My next steps in "greening" this car will be:

  1. Reduce pre-load (A1) so that the initial richening stops sooner (I'm leaving max fuel as-is for the time being)
  2. Maybe adjust the A2 stop to allow the cruise AFR peak to be a little leaner. But, as you say, I want to avoid a lean spike causing poor pickup (not present currently)
  3. Switch to a slightly weaker "strong" spring to increase the rate at which fuel flow reduces with vacuum, to flatten the gradient of the line from cruise peak to idle. I could do that by tweaking the datum track as well of course.

John

Image 21-4-21 at 10.00 am.jpg

Image 21-4-21 at 09.58 am.jpg

Edited by JohnC
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Posted (edited)

Apologies for being AWOL gents, been pretty occupied on other matters. Also my apologies for the long reply to follow.

 

Wow! Thanks for all the responses – I greatly appreciate your support and wisdom! As a moderator in another forum, I feel rather guilty of walking my thread here off track between the 6 and carbs! ;) So mods, please feel free to rename the topic to add a reference to carbs as you see fit (I’m not certain I can).

 

To begin with the 6:

With no.5 injector replaced, the 6 is purring like a kitten!! My brother-in-law was utterly stunned at the difference. He surprised himself while heading up the slip road of his local motorway - he is now reaching speeds not previously possible when joining the fast-moving traffic. The “butt-dyno” and speedo are telling him the car is running well at last.

 

As is the case with our old cars, no sooner is one issue resolve, that another crops up to keep us interested! So now third gear has started a “knocking” noise that increases in frequency with the revs. The car is booked in for Ingenuity to rebuild the ‘box for him. Not one of those fun repairs but one that is an absolute necessity and will improve the rest of the ‘box no end with new synchros and bearings.

 

@Steves_TR6 – thank you for the explanation. To your point, he did pull out some black rubbery stuff out of no.2!! I concur with your very sensible suggestion of replacing all 6 – at least you KNOW they will be more equal in operation and less likely to fail.  We’re also going to be installing some new link rods he has bought which look superb for fine adjustments even if a little expensive.

Capture.JPG.67d073f69448ef24d64f9666c6968874.JPG

@JohnC: I appreciate your feedback on this and TOTALLY agree with the "more fun than RR" remark! Exactly why I installed my AEM AFR! The way I look at it is: regardless of Petrol, Diesel, carbs, EFi etc, EVERY ICE engine has 5 phases of fuelling – Cold start, Idle, Cruise, transition/pick up/acceleration and WOT. From what I read about the MU, it has an adjustment for each of those phases (much like DCOEs with their 5 circuits). As you say, you just need some tools, patience and small incremental adjustments. I absolutely LOVE your data logging post / data and frankly most envious!!! I really need to expand my ecosystem to include the rest of the sensors / logger.

 

Now onto carbs again!

Peter C – thank you again for your advice. I have a feeling we will talk a lot further on carbs in the future. I went out last night on my local dual carriageway (that is flat, straight and virtually deserted at 20:30) for experimentation with the borrowed Zstore trumpets and a head torch! They pushed the AFRs one whole number down! I can only assume that they are significantly improving air velocity across the bridge. Both carbs had to be backed off half a turn to get sensible AFRs. KD needles with 4oz springs are delivering WOT AFRs of 12.2-12.8 from 3.5K to 6.6K rpm. Briefly touching mid 10s in the torque holes below 3.5K, but it’s better than low 9s!! ;) Cruise is now at 14-16 depending on how flat the road is! A lengthy downhill on the overrun is 20+. FYI the engine is an OHC 6 cyl 2.8, 10.5:1 static comp (205PSI comp test), 270 degree Kent fast road cam with 0.48” lift and a fully ported head. It’s probably thirstier than most mildly modified TR straight 6s but I wonder if this info is of some use to the TR community? I have found though that MC needles on 2oz springs produce superb throttle response and perfect AFRs all round (but the torque holes become more pronounced due to the lighter springs). 

 

While doing my WOT pulls in second, I caught the attentions of a 2021 Porsche Cayenne Turbo S. He was clearly holding back, toying with me side by side from 10mph to 60 mph which is where I always back off to avoid silly antics. The Z is doing 60 in around 5secs - a 4x4 THAT big and heavy has no right to be so much quicker. At 60, he pulled alongside, gave the beep / wave of appreciation. Then as his two turbos spooled, he virtually folded space-time, disappeared into the distance at some ridiculous speed and made me look like I had selected reverse. Modern cars are just so effortlessly quick these days and will only get quicker with the advent of electric motors. It’s a wonder more people aren’t banned for speeding or admitted to hospital for detaching their retinas!!

 

@Lebro – WOW Bob! That is a seriously impressive creation. I utterly love the fact that you have eliminated any disruption to airflow with your studs and grooves! Big thumbs up. I have a friend with a CNC machine and will now have to hit the CAD to duplicate your ideas for my application + buy him lots of Kit-Kats.

 

@DRD – thank you for the link!! Now why is it google never showed that one up!? They seem great value and well built. If I don’t buy them and manage to convince my friend to have a go on his CNC to create something similar to Bob’s, I will be sure to let you know. I wonder if we can do a “batch run” and some variations in total heights for experimentation. What is the ideal / rule of thumb best length for a TR 6 engine? For all-round best performance it's 40-50mm for a Z engine on twin SUs. 

 

On the antipodean Z scene there is Norm, who is pulling high 12s ¼ miles - calling himself “The 12s dual SU dude” !!! His solution to the velocity stack challenge is …… don't laugh .........  a baby ring toss toy modified and glued onto his backplate with JB weld! Not exactly a thing of beauty but all that expense and engineering can simply be matched with some creativity and modifying an inexpensive toy! (It does look like he has modified that piston also).

 

ring1.jpg.0b4f318c3fe928e3b823be3612b94c6e.thumb.jpg.26442afb8201180a2df9d6a96710b514.jpg

ring2.jpg.5df1921c2395e250b6b08c24194c8851.thumb.jpg.81742177d54ba7e14f972ccb74830bc8.jpg

 

Edited by FastNCurious
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