Move away from SU's to ........

[tr6wilts]

So, I have a 1971 PI and the PO removed all of the PI system, just leaving the Dissy Pedestal, and plumbing in the boot (but with a cheap electric pump) and installed twin SU's.

 

Car runs well now that I have removed the waxstat jets, but look to get a bit more sparkle back.

 

So options seem to be :

 

Go back to PI keep it original, but will need lots of parts Professionally fitted.

 

Go the Weber route seems to be a good option but seems expensive and complex to set up.

 

Or the Moss Super Charger - that although the outright purchase is much higher "seems" simpler to install (i.e. I could do it, single carb linkage, swap out the waterpump..).

 

Priorities are in order reliability, performance, cost, originality.

 

Answers on a postcard.... ;o)

 

Rich

Edited July 5, 2014 by tr6wilts

[RobinTR6]

Just done this, and following inputs went back to Pi. Lucas pump, eBay inlet manifolds with linkage, eBay MU and injectors. All then refurbished by our own man on this forum Neil Raven Smith. Not much difference in cost if you add in refurb costs. You may get lucky and get the whole lot in one go at a reduced cost. Getting CP manifolds wasn't easy as they ate much harder to find than the CR ones.£500 to £1000 is what I'd budget, so as I said not much in it against Webers. I really wanted to go that way but many in the TR world want the original injection, so decided to be original ish.

[Peter Cobbold]

Rich,

Supercharger, no contest.

And before anyone says it wont fit a RHD TR6:

http://ccfsdealerportalimagesupplier.azurewebsites.net/Image/GetImage/ad2eae2d-f249-4fe9-a545-2baeab88cced?container=ccfslistingimages&width=880&height=880&fixAspect=1

 

Peter

[peejay4A]

I really fancy one for my 4a.

[tr6wilts]

Would the CR manifold, provide less power than the original CP ones?

 

Peter, as you are the expert all things supercharged, have many put them on RHD CP with higher compression, and is the Moss kit as simple as it seems, bolt on with new waterpump, tune the single carb and sort timing?

 

Rich

Edited July 5, 2014 by tr6wilts

[RobinTR6]

The CR manifolds have smaller ports so presumably, not sure hoe much. I thought the Moss supercharger wasn't suited to the higher compression on a Pi engine, so it says in the catalogue Xu have. TRGB have a yellow RHD TR6 with a supercharger for sale and the guys really rate how it drives.

[Peter Cobbold]

have many put them on RHD CP with higher compression, and is the Moss kit as simple as it seems, bolt on with new waterpump, tune the single carb and sort timing?

 

Rich

Rich,

It'll work fine on a standard PI head with 9.5:1 compression. The blower is geared to give 6 psi boost at 5000-ish rpm , so it gives around 3psi at 2500-ish rpm. Thats equivalent to 10.5 CR , within the detonation limit of the TR6 head. You'll need to use 97RON fuel but it will be safe. Moss do a higher boost pulley - I would avoid that, its really only suitable for late USA=spec heads with 8.5:1 CR.

The Moss kit follows the rules that Alan Allard wrote decades ago in his book.

 

The Moss kit seems to cover everything. It is enormously simpler than starting from scratch with an Eaton M62 blower and building your own. Austin Branson has done that - see his recent TRAction article. I have no experience of the Moss kit: it certainly looks comprehensive. Maybe try the USA fora.

 

I dont know what Moss recommend re spark timing. My guess is standard PI curve will be OK, Maybe slightly less swing. Unlike with PI you will be able to connect up the vac advance capsule to give better cruise economy.

 

The percentage gain in power and torque from a blower are across the rpm range. There's no waiting to come on cam or rebuilding an engine to give an extra 1000rpm. It is normal- quite correct - to fit a blower to a standard tune engine in good fettle without altering the stock camshaft. PI or Webers wont come near to a blower's 'grunt' at low rpm. Supercharged engines are the least fussy engine to drive- highly 'roadable'. I drive mine a gear higher than normal, theres so much torque available.

A blower that maxes out at 6psi boost gives a percentage gain in power and torque of about 35 to 55% ( Allard).A poor-breathing engine gets bigger gains. So the 6 on twin SUs will get around 40% gain at a guess. With torque gains to match- that's what gives acceleration. Ask to see Moss' dyno data for a 9.5 head.

 

Peter

[Peter Cobbold]

I really fancy one for my 4a.

And why not?

A whole new car to drive, for a weekend's work.

Peter

[PaulAA]

Rich,

It'll work fine on a standard PI head with 9.5:1 compression. The blower is geared to give 6 psi boost at 5000-ish rpm , so it gives around 3psi at 2500-ish rpm. Thats equivalent to 10.5 CR , within the detonation limit of the TR6 head. You'll need to use 97RON fuel but it will be safe. Moss do a higher boost pulley - I would avoid that, its really only suitable for late USA=spec heads with 8.5:1 CR.

The Moss kit follows the rules that Alan Allard wrote decades ago in his book.

 

The Moss kit seems to cover everything. It is enormously simpler than starting from scratch with an Eaton M62 blower and building your own. Austin Branson has done that - see his recent TRAction article. I have no experience of the Moss kit: it certainly looks comprehensive. Maybe try the USA fora.

 

I dont know what Moss recommend re spark timing. My guess is standard PI curve will be OK, Maybe slightly less swing. Unlike with PI you will be able to connect up the vac advance capsule to give better cruise economy.

 

The percentage gain in power and torque from a blower are across the rpm range. There's no waiting to come on cam or rebuilding an engine to give an extra 1000rpm. It is normal- quite correct - to fit a blower to a standard tune engine in good fettle without altering the stock camshaft. PI or Webers wont come near to a blower's 'grunt' at low rpm. Supercharged engines are the least fussy engine to drive- highly 'roadable'. I drive mine a gear higher than normal, theres so much torque available.

A blower that maxes out at 6psi boost gives a percentage gain in power and torque of about 35 to 55% ( Allard).A poor-breathing engine gets bigger gains. So the 6 on twin SUs will get around 40% gain at a guess. With torque gains to match- that's what gives acceleration. Ask to see Moss' dyno data for a 9.5 head.

 

Peter

 

... or have the head uprated to Stage 3 and swap to a fast road cam..? It does appear (since I am still doing my cost analysis of the two options) that the head and cam change is cheaper than the Moss kit.

 

Question is, which give more bangs per buck?

 

Cheers

 

Paul

[stuart]

And why not?

A whole new car to drive, for a weekend's work.

Peter

The 4 cyl cars dont take so well to supercharging, there are a few around but I believe the 6 version is probably better.

Stuart.

[Peter Cobbold]

Paul

There's no comparability between naturally aspirated and forced induction.....chalk and cheese.

 

A worked head might get a bit more volumetric efficiency, up from around 83% to perhaps 90+%. Even that is doubtful with the carb manifold. But the blower takes VE up to 120+% !!

To get more power normally aspirated needs more rpm and that gets expensive and time consuming. And to get VE to 100% needs a trick cam that operates effectively only over a narrow rpm range and that peakiness is cr*p for road driving.

There isn't a cam on the planet that will get a TR6 to to 120%VE. That blower will, in a weekend. Granted, the cost is greater than a small gain in VE by conventional routes. But when comparing the same power gain the blower wins.

And there's no way conventional tuning gives 40% more torque at road rpm. To do that needs a bigger engine.

The Moss kit turns a 2.5litre into a 3.5 litre. That's what mine feels like, and its not had the benefit of professional design and development..

 

Peter

Edited July 5, 2014 by Peter Cobbold

[Peter Cobbold]

The 4 cyl cars dont take so well to supercharging, there are a few around but I believe the 6 version is probably better.

Stuart.

Wet liners shifting?

Peter

 

 

200+hp does seem a bit greedy.....

Wiki:

"The standard engine produced 105 bhp (78 kW) SAE but, supercharged and otherwise performance-tuned, a 2.2-litre I4 version could produce in excess of 200 bhp (150 kW) at the flywheel."

Edited July 5, 2014 by Peter Cobbold

[tr6wilts]

Thanks, the other important factor is I want some omph, but maintain driveability in traffic, so going back to standard PI or Super Charging seem best route..

 

Rich

[GT6M]

If, ye bung 1 3/4 SUs,or even 2inchers, with some porting work on the inlet manifold, a little bit of head work, and with the early PI cam fitted, then 170+ is quite dooable, as has been done quite a few times

 

other optionee,s are to bung EFI on it.

either going the OE lucas manifold way, or by bunging injectors into the carb mani close to the head.

taking all the gubbins oot of the carb,bar the throttles

 

my self, if yer not experienced with PI, want to constantly be plagued by niggles, cos it aint been put in reet

want to constantly give yer loot to so called specialists, then go for Lucas

 

EFI will be as cheeper route, and will pay for itself in 10-15 mpg moer than yer Lucas set up.

 

SP,s carbed engine results, so very dooable

 

M

[Ade_TR6]

Supercharging is great. I don't have experience on my 6 which is PI, but I have supercharged a relatively modern car with amusing results, one of which is diesel torque from diesel RPM figures (240 lbft from 2500 rpm up from 160 at 7600 rpm!). My question for Peter is, assuming a roots type blower is used in the Moss kit, why the rising rate boost. My experience is full boost at any rpm I.e a constant 7 psi from tick over. I know the centrifugal blowers are rising rate so is there something in the moss kit I am missing? Also, the latest project I am playing with is water injection to cool the charge and up the boost a little which is probably possible on the moss kit if you are creative and brave.

 

Here is a little vid of the boost gauge in my last project to demonstrate the instant boost available with a supercharger... http://youtu.be/YM3RcimR4ew

[PaulAA]

Paul

There's no comparability between naturally aspirated and forced induction.....chalk and cheese.

 

A worked head might get a bit more volumetric efficiency, up from around 83% to perhaps 90+%. Even that is doubtful with the carb manifold. But the blower takes VE up to 120+% !!

To get more power normally aspirated needs more rpm and that gets expensive and time consuming. And to get VE to 100% needs a trick cam that operates effectively only over a narrow rpm range and that peakiness is cr*p for road driving.

There isn't a cam on the planet that will get a TR6 to to 120%VE. That blower will, in a weekend. Granted, the cost is greater than a small gain in VE by conventional routes. But when comparing the same power gain the blower wins.

And there's no way conventional tuning gives 40% more torque at road rpm. To do that needs a bigger engine.

The Moss kit turns a 2.5litre into a 3.5 litre. That's what mine feels like, and its not had the benefit of professional design and development..

 

Peter

 

Thanks, Peter

 

Good point well made.

 

Paul

[Austin Branson]

Hi, Rich, you are likely to get a lot of response to this. I can only advise on the Supercharger. I fitted one a couple of years ago (see TRaction 273). It may not be so simple - your compression ratio could be too high. Also, you need to check that there is clearance for your steering column. The Moss kit was, I believe, designed for the Left Hand Drive, low compression engines in North America. The TR guru of supercharging is Peter Cobbold (North Wales Group), and he will be able to steer you if you go ahead. I know that he sourced a low compression (North American) cylinder head when he fitted his blower. Having said all this, I still think its worth you taking a look at it. It's transformed the performance of mine.

Let us know what you decide to do. The 4th alternative, of course, is to go Efi. Several guys have done this, or you could go to Revington TR, or possibly Racetorations for a bolt-on kit.

Austin

[Peter Cobbold]

If, ye bung 1 3/4 SUs,or even 2inchers, with some porting work on the inlet manifold, a little bit of head work, and with the early PI cam fitted, then 170+ is quite dooable, as has been done quite a few times

 

other optionee,s are to bung EFI on it.

either going the OE lucas manifold way, or by bunging injectors into the carb mani close to the head.

taking all the gubbins oot of the carb,bar the throttles

 

my self, if yer not experienced with PI, want to constantly be plagued by niggles, cos it aint been put in reet

want to constantly give yer loot to so called specialists, then go for Lucas

 

EFI will be as cheeper route, and will pay for itself in 10-15 mpg moer than yer Lucas set up.

 

SP,s carbed engine results, so very dooable

 

M

M,

Adding a blower to that engine will get you to over 200hp. Gas-flowed heads, big valves etc improve power on blown engines too, although high overlap cams are undesirable.

Peter

[Peter Cobbold]

Supercharging is great. I don't have experience on my 6 which is PI, but I have supercharged a relatively modern car with amusing results, one of which is diesel torque from diesel RPM figures (240 lbft from 2500 rpm up from 160 at 7600 rpm!). My question for Peter is, assuming a roots type blower is used in the Moss kit, why the rising rate boost. My experience is full boost at any rpm I.e a constant 7 psi from tick over. I know the centrifugal blowers are rising rate so is there something in the moss kit I am missing? Also, the latest project I am playing with is water injection to cool the charge and up the boost a little which is probably possible on the moss kit if you are creative and brave.

 

Here is a little vid of the boost gauge in my last project to demonstrate the instant boost available with a supercharger... http://youtu.be/YM3RcimR4ew

Ade,

For old motors that constant boost level would be highly unusual. Usually with a Roots blower boost starts at ca 1000rpm and rises linearly with rpm, the slope depending upon the drive ratio, which is fixed by the pulleys (All approximately)

 

You constant 7psi is puzzling. What supercharger is it- an Eaton? - and belt driven? If so on a simple engine the boost would rise with rpm. But many moderns have complicated engine inlet and exhaust valve controls. if your engine has those I can well imagine the inlet valves being altered in their openings to allow boost to build up in the engine manifold at lower rpm. I'm not sure why- maybe its to get best possible swirl as the boost rushes past the inlet valve- good in a direct injection engine. Enough of this reverse engineering guesswork - tell us what you've fitted, I'm intrigued! ***

 

So why the rise in boost with rpm in a 6?

A Roots blower is a 'positive displacement' air pump, it has no ability to compress air. What it does is pump air (mixture in our case) into the engine inlet manifold faster than the engine can use it when fed atmospheric air. So air accumulates in the engine inlet manifold and pressure rsies above atmospheric - which is the boost. Things even out when the air sucked in by the blower is used by the engine equally fast. All the above happens in about one tenth of a second - ie too fast to see on the gauge. And only at wide open throttle.

All that might lead us to think that if the air flows equalise at say 3psi boost at 2000rpm the flows still equalise at 3psi boost at 4000rpm. After all, the blower turns twice as fast so does the engine. BUT there is twice as much mass of air accumulated in the manifold so that gives double the boost. Three other complications: the blower continues to breathe well as rpm rise, the engine less so - so boost rises. At higher rpm the air blown out by the bower is hotter, and the extra boost makes things hotter still - so boost rises ( but not power so much). At low rpm the blower tends to leak so boost is low at very low rpm. And at higher boost around 10+psi Roots leak back air. The overall result is rising boost with rpm. The percentage gain in power and torque works out to be moreorless the same over say 1500-5000rpm. As the Moss curves show.

 

Water injection needs proepr atomisation- and expensive kit. It can be done. I tried a windcreen washer squirter years ago and it had no effect on temperature of boost that i could see!

 

Peter

 

 

**** Ah I see you have a Mitsubishu FTO. which does have variable valves:

http://en.wikipedia.org/wiki/MIVEC

It can advance inlet valve closure, so could the constnat boost be related to that? -did you fit another ECU chip as well as the blower ?

Edited July 6, 2014 by Peter Cobbold

[Peter Cobbold]

Hi, Rich, you are likely to get a lot of response to this. I can only advise on the Supercharger. I fitted one a couple of years ago (see TRaction 273). It may not be so simple - your compression ratio could be too high. Also, you need to check that there is clearance for your steering column. The Moss kit was, I believe, designed for the Left Hand Drive, low compression engines in North America. The TR guru of supercharging is Peter Cobbold (North Wales Group), and he will be able to steer you if you go ahead. I know that he sourced a low compression (North American) cylinder head when he fitted his blower. Having said all this, I still think its worth you taking a look at it. It's transformed the performance of mine.

Let us know what you decide to do. The 4th alternative, of course, is to go Efi. Several guys have done this, or you could go to Revington TR, or possibly Racetorations for a bolt-on kit.

Austin

Hi Austin,

We were greedy with boost, about 9-10psi, so the low compression heads were needed.The Moss kit maxes out at 6psi so I reckon it will be safe with 9.5:1

Allard gives a rule of thumb of 3.7psi of boost is equal to 1 on the compression ratio. The peak in detonation risk is at peak torque rpm around 3000-3500 where Moss delivers about 3psi, so the ratio rises to around 10.5 - should be safe. The effCR does rise to around 11 at 6psi/5000rpm but combustin is so fast and turbulent that detonation is unlikely.

Anyone with a low compression head can use the higher boost pulley that Moss supply!

Peter

[cp25616]

Nothing wrong with the standard CP PI set up and thats the way I would go, not webers and not supercharger either. At least you will have your "standard" car back and at less cost than the others too.

Just my tuppence and all that rubbish

Alan

[Peter Cobbold]

I drove standard PI for over 200k miles. No way at all I'd go back to that after experiencing driving supercharged !!

 

Peter

[dingle]

I don't know what needle/spring combo you are using with the SUs, but I have found that the usual recommendation of BAE or BAG with yellow springs is too lean. With the 9.5 cr PI head that is used with the better flowing later intake manifold, early PI cam, and dual exhaust manifold, there may be more hp available with richer needles. Maybe not comparable with PI or supercharging, but better than the stock US carb cars.

Berry

[Guest ntc]

I drove standard PI for over 200k miles. No way at all I'd go back to that after experiencing driving supercharged !!

 

Peter

Peter

I found very little difference between the two.Moss kit btw

[tr6wilts]

So super charge or back to PI then, probably need to talk to moss about fitting to Rhd and clearance around steering column.....