Rolling Road Stats

[sheldricka]

I'm after some thoughts and forum wisdom at the attached results of my 72 150BHP

 

Having refurbished/replaced the entire PI system, new injectors, refurb'd Lucas pump, new PRV, refurb'd metering unit, new nylon pipes, Phoenix standard format exhaust system, new head and exhaust gasket and rubber vacuum hoses. Fuel pressure measured at 108. I have standard inlet manifolds and linkages but have put on new poly bushes to pick up any play I still have poor drivability, very hard to start cold and the exhaust smells so much so that when I get out of the car I smell of it.

 

The engine itself is in standard spec, generally in good order, good oil pressure (except a possible small end bearing as noted) it does not smoke, manifold pressures fluctuate when measured but remain in tolerance.

 

Since coming back I have fettled with the butterfly balance (were slightly adrift but now reset to 3 using an air meter @ 800 rpm) and low drivability has improved but it still smells on tick over and has the sense of hesitation when running at a steady speed. The HC on the rolling road were 2000 odd and fuelling very lean at tickover

 

Any thoughts, do I need to richen things up a bit on the metering unit? It was refurb'd in the summer so should be OK. On the power run, when floored the performance falls away as you can see

[Nigel Triumph]

That power trace does look odd.

 

Having said that, not all rolling roads give the same result but I would have expected the power curve to keep climbing to around 5,000 rpm for a healthy CP-series engine, with a peak well above 100 bhp at the flywheel. One point, surely Lambda less than 1 is rich, not weak? The highish CO figures and smelly exhaust also suggest rich mixture but that shouldn't be enough to cause the power to tail off so much at high revs.

 

I wouldn't expect adjusting the throttle butterfly synchronisation to make any difference at the top end, but as you found, it will smooth things out at low throttle/low revs.

 

For comparison, my CP-series 6 gave 126 bhp at the flywheel on the Aldon Automotive's rolling road a few years ago. It's standard except for a K&N air filter, electronic ignition and 6-3-1 exhaust manifold with big bore silencer. Roger (Aldon's RR guru) commented it was the best he had seen from a near-standard TR6, as they tend to make 110 - 120 bhp on their rolling road.

 

Have you looked closely at the ignition? Is the timing correct using a strobe at tickover? The book says 10 deg BTDC but my car is better with a touch more advance at 12 deg BTDC. And is the centrifugal advance working? Seized advance weights will stop the timing advancing as it should as revs rise and that would certainly cause an early tail off in power; the effect of retarded ignition at high revs would probably cause mixture to appear rich and CO high due to incomplete combustion. A good rolling road technician should go right through ignition and fuelling while the car is on the rollers. I would want to be certain the ignition system including the distributor were perfect before touching the injection MU settings.

 

 

Nigel

[Steves_TR6]

That doesnt look to be running properly at all.

 

I suggest a methodical review of the engine is needed :

 

Compression

Cam timing

Ignition timing

Fuel timing

Valve clearances, correct for the cam in use

 

Perhaps engage with a local TR expert / garage

 

Steve

Ps, being so badly out of tune i suspect there will be a ready fix and a big improvement

Pps, Nigel's answer more comprehensive, you should be WELL above 100bhp at the flywheel, ideally at the wheels !

Edited May 3, 2017 by SDerbyshire

[Nigel Triumph]

+1 for Steve's reply.

 

Make sure everything he suggests is checked/adjusted.

 

For comparison, a compression test on my 6 shows 145 - 150 psi on every cylinder, fast cranking with all plugs out and throttle held wide open.

 

And I agree, you'll find and fix something and suddenly all that lost power will be back!

 

One other thought about Lambda... I'm a chemist by training and so tend to think more of Air/Fuel Ratio than Lambda, though it's the same thing expressed in a different way. Your lowest Lambda reading, or richest mixture, was about 0.85. That equates to AFR of 12.75:1. That's a reasonable reading at full throttle, when classics engines are intended to run at a mixture richer than the stoichiometrically ideal 15:1 AFR or Lambda = 1. A slightly richer mixture is desirable to get the best power output though leaner mixtures are best for cruising economy at part-throttle. Apologies if I'm stating the obvious.

 

 

Nigel

[Guest ntc]

You did not have a rr setup just a power run, go to a good un.

[sheldricka]

Thanks for your comments, I meant to add that the distributor has recently had the full Dr treatment. The MU is timed for port 6 just opening at TDC, compression is 140+ on all as described, One was 10% lower, I'm guessing it maybe the one with the recently knocking bearing.

 

Camshaft timing has been checked with 1&2 on the rock at TDC, values set to10 thou. Ignition steady at 12 before at 800. Number one is firing at about 8 o'clock on the distributor

 

It's been like this since I've owned it and nothing done has materially changed anything. I've recently put in new NGK bpr6es plugs and have new magnecor leads in the post. It revs freely, at tick over it hunts a bit but holds fairly steady

 

The only thing that has ever struck me as odd is that when I time the valves against the repair manual I have to push the car in gear backwards to time in the order of the book, 1&3 then 8&11 etc. Maybe nothing just struck me as odd

[sheldricka]

Neil, they were reluctant to mess with it as at steady throttle they suggest all was in order with respect to the numbers. TR6 injection and all that ...

[stephen cooper]

Something badly amiss here.

 

Have you checked the throttles are opening fully?

 

Have you checked the ignition is advancing properly? What is max advance?

 

What do the plugs look like?

 

If still struggling definitely take it to a specialist, I don't know many with rolling roads who mess with PI and while he doesn't alter PI, Peter Burgess at Alfreton is very good for general tuning.

[sheldricka]

Yes, butterflies opening together, full and even at max throttle, a cigarette paper drags in all 6 when closed. I've attached shots of the exhaust colour, a plug just pulled and the distributor graph from the rebuild in Nov

[Graham]

Alan possibly a bit to far north for you but Enginuity have a rolling road and have loads of experience with PI I also think at least one of their team live in your area, or used to anyway if you get stuck might be worth giving them a call

[stephen cooper]

Sure looks lean! I would still want to see what max advance is doing dynamically with a timing light.

 

Hope you get to the bottom of it.

 

Cheers

[sheldricka]

All, thanks for your input, it is a bit of a puzzle, at the weekend I'll validate the advance and post the value. I'll try calling Enginuity too.

[Nigel Triumph]

A Distributor Doctor dizzie will be spot on. Enginuity look after my brother's TR5. Top guys by all accounts so they are sure to get to the bottom of the problem.

 

Good luck, and please let us know the outcome.

 

 

Nigel

[oldtuckunder]

Slightly confused about the dissy advance curve for a CP 150bhp when compared to the charts

 

http://www.tr-register.co.uk/forums/index.php?/topic/24915-tr6-ignition-timing/page-2post 26

 

But I don't know what you asked for?

 

One question I would ask is what coil do you have fitted? 6 and above cyl engines suffer way more than 4 cyls if the impedance of the coil is too high, the dwell time is shorter and they struggle to get fully charged at higher rpm's and a diving off of power at higher rpm's is a typical symptom. As from your list about the only thing you don't mention changing is the coil, just made me wonder.

 

Alan

[Steves_TR6]

Slightly confused about the dissy advance curve for a CP 150bhp when compared to the charts

 

http://www.tr-register.co.uk/forums/index.php?/topic/24915-tr6-ignition-timing/page-2post 26

 

But I don't know what you asked for?

 

One question I would ask is what coil do you have fitted? 6 and above cyl engines suffer way more than 4 cyls if the impedance of the coil is too high, the dwell time is shorter and they struggle to get fully charged at higher rpm's and a diving off of power at higher rpm's is a typical symptom. As from your list about the only thing you don't mention changing is the coil, just made me wonder.

 

Alan

 

Good thinking Alan.

 

And as '90% of fuel problems are actually ignition' i'd question the lumenition.

 

Theyre very reliable, mine is 20 years old, but i believe can be fragile and not like being disturbed.

Maybe try points ?

 

Steve

Ps, am intrigued now and looking forward the the answer to this puzzle!

[sheldricka]

Hi Alan, I replaced the coil in the autumn with the standard Lucas 12v from Rimmers, it also has the standard points set up

 

With respect to the curve I did advise the car spec but looking at the documents on the attached link and my plotted curve there is a difference.

 

I have the 22D6 41298B 768 distributor. Comparing mine to that it is comparable to 1600 rpm where it remains at 8.

 

Question, should it be advancing 12-16 at 2700 upwards as suggested?

 

I'll check what's actually happening with a strobe tomorrow evening or over the weekend and report back. The magnecor leads have also arrived today

[oldtuckunder]

If you have or can borrow a multi meter and your in testing mode, I would test the coil. There is no guarantee that even a new one these days is any good.

 

Just google measuring resistance of a 12v coil

 

However all that really tells you if its bad, but not if its good. Some coils start faltering when they start getting warm. I have noticed several new "Lucas Badged" coils over the last couple of years seem both smaller and when shaken don't appear to have anywhere near as much cooling oil in them.

 

Its a complete long shot, but hey you have been methodically working through the more likely causes, so if you can see if you can borrow a known good coil just to try, but make sure is a points one not one for electronic ignition.

 

As to the advance figure hopefully a PI expert will chip in, I do know there is some confusion in some references between dissy advance and crank shaft advance which is dissy x 2. So if you have 10/11 static and your distributor from the charts is giving 7.5 mechanical advance, that means your maximum crank advance is 25/26 degrees. To me that seems a low figure but maybe PI's don't like the advance that carb 6's do?

 

Alan

[sheldricka]

I'll check the coil as part of the weekend review, I've still got the old one that I could compare to as well

 

I've also dropped the distributor Dr an email on the advance subject, I'm sure he'll confirm.

 

Thanks again

[stephen cooper]

I didn't understand the dizzy map but you should be advancing once off tickover. I've heard 30 deg max suggested before but engines do vary and timing marks can slip.

 

Mine doesn't like anything above mid 20s but it's high compression.

I have a 123 tune and you can see how it's dialled in on the attached image.

[sheldricka]

Stephen, the distributor curve figures I shared are half those of the normally viewed crankshaft figures.

 

So , for example a CP strobed @ 12 BTDC @ idle circa 700rpm, before the centrifugal advance starts , will @ 2600 rpm be yielding 12 + 14 centrifugal , circa 26 degrees.

[sheldricka]

Coil results are 3.2 and 10.27, I've rechecked the compression and the results are 145, 127, 145, 127, 145, 145 looks like I need to have it all to bits to sort those 2 cylinders out and the small end that appears to be knocking before looking elsewhere...

[Peter Cobbold]

Nigel gets my vote - too little spark advance. The timing marks on the pulley may be off - it happens when the rubber annulus deteriorates with age. So what you think is 12 BTDC static is actually a lot less. So check the TDC position with a piston stop. A rough and ready way is to set the tickover to its best setting by slowly turning the disy a few mm to and fro with engine running. Beware of HT shocks.

Peter

[Stanpartmanpartwolf]

[stuart]

IMG_0762.PNG

:lol:

Stuart.

[Alec Pringle]

Surely any rolling road operator worth his salt could have worked that one out Jon, even if he didn't know PI from L-Jetronic ?

 

Cheers,

 

Alec