Triple Webers or PI?

[Tom Fremont]

Shall we speculate on what the cars would be worth today had they originally been outfitted with Webers instead of LUCAS P.I. ?

 

2X I posit, apart from TR5s whose values are finally approaching their " peers " if you can call them that ( Alfa spiders, Porsche 356 series, etc. ). The sheer fright of the LUCAS P.I. to the main market today ( here in the 'States ) overwhelms what value boost might accrue to its rarity and wonder factor. The P.I. system, while distinguishing the TRs that came with them from the rest of the world, did nothing Webers wouldn't have done with utter reliability, instead saddling them with the well known stigma of " black box " mystery and unreliability, however debatable today. Moreover, DCOEs were always a rare fitment and then to the most highly regarded sports cars of the era - ever a value boost, then as now.

 

Cheers,

Tom

[Alec Pringle]

Of course you have the correct tin, Andy !!

 

It's the PI label that counts . . . . .

 

If we'd sold PI cars to the States Tom, then the Lucas system might not be such a mystery to y'all . . . . . and even better if it had been fitted with a pukka engine-driven fuel pump and retained the electric pump for starting only . . . . . as per the competition systems.

 

Nothing wrong with Webers, and I know you love 'em, but they don't have the exclusivity of Lucas PI !

 

Cheers

 

Alec

[Guest ntc]

As most of you know I have both types and all the parts to use and swap,would I swap the webered car back to Pi ( no chance )

[cp25616]

Have to agree with Alec here, the Lucas PI is what the car is all about really. Its a defining feature in the "all things great TR5 and Tr6".

At the end of the day its your choice and you will get many people saying go with triple carbs over PI and vice versa. I have triple downdraft Weber 42 DCNF's on my oh so genuine Capri X pack and boy are they thirsty....... or is it just the way I drive the blessed thing? No, for me it would be PI every time.

Alan G

[Tim D.]

Interesting the different views of how PI handles altitude..

I wonder whether those that handle it fine are set up leaner at sea level.

Following other PI cars it is clear that the standard setting is rather rich (undoubtably to cover the lack of a richening device to cover rapid opening of the throttles.). I tested my own newly set up PI on an AFR and found it pretty rich. Turned it down a tad and now closer to perfect without any bogging on rapid throttle opening. Am now wondering whether it would be good in the alps.. Perhaps time to do the 10CR rally!

Tim

[peejay4A]

I think I'm right in saying that the Lucas race setup doesn't use manifold depression to govern fuelling but a mechanical connection between throttle sliders and the metering unit.

[k_raven_smith]

Only on racing applications

[Madmal]

Well, I can understand the bias towards PI, part of the history of the car, one of the first in production etc etc but we've purchased these cars to enjoy. I have not driven a 6 on triple webers but i have had triple carbs on other cars and the induction roar and performance is great. Obviously driveability is important, as is fuel consumption and at the end of day, we all want something that we look forward to taking out. I guess there will always be a lively debate, which is what drew me to this forum in the first place!

[peejay4A]

Only on racing applications

 

Erm, yes. As I said, the race setup.

[pinky]

 

 

,hi my friends

 

 

what we need to do is go to santana pod, and see what runs the best,

 

I am running webers I have on occasion nearly binned them ,

however now they are set up properly they are the dogs boliks

 

pink

[Nick Jones]

Neither, EFI based on the PI inlets. Best of all worlds.

 

To follow up on an earlier question - PI can work Ok-ish up to 2000m even 2500m if running on the lean side at sea level, though they will be running very rich at altitude. As many, if not most, are set on the richer side they can really struggle over 2000m. I've followed (then overtaken) TR6's and PI saloons limping up passes chuffing out clouds of evil smelling black smoke.

 

Nick

[Tom Fremont]

EFI? Like I told Neil Revington years ago when he pitched his " If I wanted all that technology I'd buy a Z3! "

 

EFI ain't period, that's for sure; way out of sync with the '50s technology in the TR engine ( to be generous, some say ). What it would gain over properly set up DCOEs is scant by all indications, but admittedly not zero.

 

Here in Ohio near the turn of the century a fellow named Chris Petch in a Webered TR5 smoked a pair of EFI'd TR6s at the Mid-Ohio vintage races, after wrecking the car the day before and getting it patched together for the race!

 

Still, an original P.I. car deserves to stay that way - for better or worse! And I do love that air plenum, had to get one for my collection. I'd like nothing more than to come up with an equally appealing airbox for my DCOEs that fits in the early wheelarch.

 

Cheers,

Tom

[westaj]

Hi Mal,

 

The triple carb option doesn't have to be expensive.

For converting my TR250, my starting point was the Goodparts manifold kit from the States and I then sourced some second hand SU carbs from eBay .

 

I chose SU4 s as used on MGB s rather than SU6s, as I wanted drivability and torque rather than top end power. SU 4 carbs are very easy to obtain.

The engine in my TR250 is an ex- Pi from a saloon car with about 9.5:1 compression and a Newman 280 duration camshaft, and could probably be considered to be in fast road spec.

 

The SU4s should be able to give around 48 bhp per carb, and for this output, I believe, an airflow rate of around 80 ft/s is expected. Fitting the larger SU6s would drop the airflow to around 58 ft/s, for the same power, which is probably a bit low for good mixing.

 

(I think from memory some of the 3 litre Austin Healeys were originally fitted with three SU4s, possibly for the same airflow mixing reason)

 

Due to space constraints and aesthetics I decided to use 3 identical carbs each with right handed (front mounted ) float chambers. The Goodparts manifold inlets are sized at 1-3/4 inch so I fabricated tapering transition pieces to match the 1-1/2 inch size of the SU4 outlet and simple support plates for the throttle linkage control rod.

Lever arms and linkage rods were bought from Burlem Fuel systems.

 

Choke mechanisms are non standard, but cold starts are fine with just 2 individual choke cables fitted.

 

The carbs were fitted with FX designation needles, as used on later MGBs, and simply balanced with a flow meter.

Tuning SUs is fairly straightforward and low cost, especially compared to Webers.

 

The engine runs very well through the full rev range and is smoother and crisper than with the earlier 2 x SU6 setup.

Trips to Classic Le Mans and Laon earlier this year returned over 35 mpg and after an Autumn TR register track day at Castle Coombe, power improvement is estimated to be around 15%. I will need to complete a rolling road test at some point to establish actual power values.

 

 

In summary I am very pleased with the simplicity and performance of this triple SU arrangement.

 

Hope that the above is of some help.

 

Jerry

[westaj]

Hi Mal,

 

The triple carb option doesn't have to be expensive.

For converting my TR250, my starting point was the Goodparts manifold kit from the States and I then sourced some second hand SU carbs from eBay .

 

I chose SU4 s as used on MGB s rather than SU6s, as I wanted drivability and torque rather than top end power. SU 4 carbs are very easy to obtain.

The engine in my TR250 is an ex- Pi from a saloon car with about 9.5:1 compression and a Newman 280 duration camshaft, and could probably be considered to be in fast road spec.

 

The SU4s should be able to give around 48 bhp per carb, and for this output, I believe, an airflow rate of around 80 ft/s is expected. Fitting the larger SU6s would drop the airflow to around 58 ft/s, for the same power, which is probably a bit low for good mixing.

 

(I think from memory some of the 3 litre Austin Healeys were originally fitted with three SU4s, possibly for the same airflow mixing reason)

 

Due to space constraints and aesthetics I decided to use 3 identical carbs each with right handed (front mounted ) float chambers. The Goodparts manifold inlets are sized at 1-3/4 inch so I fabricated tapering transition pieces to match the 1-1/2 inch size of the SU4 outlet and simple support plates for the throttle linkage control rod.

Lever arms and linkage rods were bought from Burlem Fuel systems.

 

Choke mechanisms are non standard, but cold starts are fine with just 2 individual choke cables fitted.

 

The carbs were fitted with FX designation needles, as used on later MGBs, and simply balanced with a flow meter.

Tuning SUs is fairly straightforward and low cost, especially compared to Webers.

 

The engine runs very well through the full rev range and is smoother and crisper than with the earlier 2 x SU6 setup.

Trips to Classic Le Mans and Laon earlier this year returned over 35 mpg and after an Autumn TR register track day at Castle Coombe, power improvement is estimated to be around 15%. I will need to complete a rolling road test at some point to establish actual power values.

 

 

In summary I am very pleased with the simplicity and performance of this triple SU arrangement.

 

Hope that the above is of some help.

 

Jerry

[Peter Cobbold]

Hi Mal,

 

The triple carb option doesn't have to be expensive.

For converting my TR250, my starting point was the Goodparts manifold kit from the States and I then sourced some second hand SU carbs from eBay .

 

I chose SU4 s as used on MGB s rather than SU6s, as I wanted drivability and torque rather than top end power. SU 4 carbs are very easy to obtain.

The engine in my TR250 is an ex- Pi from a saloon car with about 9.5:1 compression and a Newman 280 duration camshaft, and could probably be considered to be in fast road spec.

 

The SU4s should be able to give around 48 bhp per carb, and for this output, I believe, an airflow rate of around 80 ft/s is expected. Fitting the larger SU6s would drop the airflow to around 58 ft/s, for the same power, which is probably a bit low for good mixing.

 

(I think from memory some of the 3 litre Austin Healeys were originally fitted with three SU4s, possibly for the same airflow mixing reason)

 

Due to space constraints and aesthetics I decided to use 3 identical carbs each with right handed (front mounted ) float chambers. The Goodparts manifold inlets are sized at 1-3/4 inch so I fabricated tapering transition pieces to match the 1-1/2 inch size of the SU4 outlet and simple support plates for the throttle linkage control rod.

Lever arms and linkage rods were bought from Burlem Fuel systems.

 

Choke mechanisms are non standard, but cold starts are fine with just 2 individual choke cables fitted.

 

The carbs were fitted with FX designation needles, as used on later MGBs, and simply balanced with a flow meter.

Tuning SUs is fairly straightforward and low cost, especially compared to Webers.

 

The engine runs very well through the full rev range and is smoother and crisper than with the earlier 2 x SU6 setup.

Trips to Classic Le Mans and Laon earlier this year returned over 35 mpg and after an Autumn TR register track day at Castle Coombe, power improvement is estimated to be around 15%. I will need to complete a rolling road test at some point to establish actual power values.

 

 

In summary I am very pleased with the simplicity and performance of this triple SU arrangement.

 

Hope that the above is of some help.

 

Jerry

Jerry, Neat.

I agree with the logic of your design. And to confound the doubters:

Triple 11/2" SU are OK for 175bhp:

http://www.sw-em.com/SU_vs_disp.jpg

 

The quality of the fuel mixture is very important - the smaller the droplets the better combustion. And carbs will out-perform low pressure (100-150psi) injectors. The butterfly contributes a great deal to fuel atomisation as the air velocity around it becomes sonic up to modest openings.

Some data on carb vs PI droplets here:

http://papers.sae.org/885015/

(I've seen a figure from Lenz book somewhere, will try to find it)

This work was done 20+ years after Triumph opted for Lucas PI: they simply did not know. Had they access to Lenz' work I doubt triple SUs would have been ignored for a sports car driven 95% of the time at less than full throttle. And if they had kown they would not have expected the PI to help pass smog legislation on unburned HC.

Peter

Edited December 14, 2016 by Peter Cobbold

[TR NIALL]

Hi Mal,

The triple carb option doesn't have to be expensive.

For converting my TR250, my starting point was the Goodparts manifold kit from the States and I then sourced some second hand SU carbs from eBay .

I chose SU4 s as used on MGB s rather than SU6s, as I wanted drivability and torque rather than top end power. SU 4 carbs are very easy to obtain.

The engine in my TR250 is an ex- Pi from a saloon car with about 9.5:1 compression and a Newman 280 duration camshaft, and could probably be considered to be in fast road spec.

The SU4s should be able to give around 48 bhp per carb, and for this output, I believe, an airflow rate of around 80 ft/s is expected. Fitting the larger SU6s would drop the airflow to around 58 ft/s, for the same power, which is probably a bit low for good mixing.

(I think from memory some of the 3 litre Austin Healeys were originally fitted with three SU4s, possibly for the same airflow mixing reason)

Due to space constraints and aesthetics I decided to use 3 identical carbs each with right handed (front mounted ) float chambers. The Goodparts manifold inlets are sized at 1-3/4 inch so I fabricated tapering transition pieces to match the 1-1/2 inch size of the SU4 outlet and simple support plates for the throttle linkage control rod.

Lever arms and linkage rods were bought from Burlem Fuel systems.

Choke mechanisms are non standard, but cold starts are fine with just 2 individual choke cables fitted.

The carbs were fitted with FX designation needles, as used on later MGBs, and simply balanced with a flow meter.

Tuning SUs is fairly straightforward and low cost, especially compared to Webers.

The engine runs very well through the full rev range and is smoother and crisper than with the earlier 2 x SU6 setup.

Trips to Classic Le Mans and Laon earlier this year returned over 35 mpg and after an Autumn TR register track day at Castle Coombe, power improvement is estimated to be around 15%. I will need to complete a rolling road test at some point to establish actual power values.

In summary I am very pleased with the simplicity and performance of this triple SU arrangement.

Hope that the above is of some help.

Jerry

Hi Gerry a few Pics of your Set Up would be nice as I'm playing with HS6s at the moment on a CP Engine in a Spitfire but like the idea of the 3 Carb Set Up,Cheers.

[TriumphV8]

EFI? Like I told Neil Revington years ago when he pitched his " If I wanted all that technology I'd buy a Z3! "

 

EFI ain't period, that's for sure; way out of sync with the '50s technology in the TR engine ( to be generous, some say ). What it would gain over properly set up DCOEs is scant by all indications, but admittedly not zero.

 

Here in Ohio near the turn of the century a fellow named Chris Petch in a Webered TR5 smoked a pair of EFI'd TR6s at the Mid-Ohio vintage races, after wrecking the car the day before and getting it patched together for the race!

 

First let me say that an EFI can be more or less identical to a PI

except the fuel transport to the inlet.

It does all what the PI has done before and if EFI set properly and

the PI was not before it will perform better and/or need less fuel.

 

If it would be a Bugatti I would understand to keep original but as its my fun car,

also used for vacation and in the Alps under high altitude and sharp cornering,

I am happy with the benefits I have got and its now a reliable EFI that works

with no hesitation or trouble.

 

To be honest if somebody claims for original I would expect he does that with all

the rest, too like colour, tires, steering wheel and seats, fuel pickup in the trunk with

the original pump, shocks and springs. Thats not typical for TR6 owners.

 

Often people loving oldtimer are older and simply do not want to learn new

things as electronics is. Revington may not, Racetorations does a very modern

twin injector system on their race car.

 

The EFI itself is not necessarily better than other systems regarding performance,

its just a tool easy to use and setup to make the best out of what you have.

Its up to the tuner to do so, even if its easier than all other systems its just the chance

to do so, not the ticket to get all the advantages automatically.

 

The only thing that can be told to the race cars is that the winners would have

also won the race if their carbs would be changed to EFI -not more-

 

And to be honest the differences between the systems became smaller because

many people do a good job on their favorite system like Neil on the PI or Viktor Günther

did formerly on the Weber and Dimitry Bilas does on Weber and EFI and many more.....

 

The individual setups will overlap the advantage of the individual systems.

Only the best system with the perfect setup will be the best and a pain if

an idiot does the setup. Look at the Weber DCOE that was sold in thousands

in the Alfa Romeos without much trouble noticed. They are daily drivers, often

used by ladies in those days and they have been happy. If they are claimed to

be unreliable thirsty monsters in the TR there is something badly done in setup.

It can be fully different like Tom reports.

-All mainly a question of skill when doing the setup-

[Peter Cobbold]

Older triple SU thread here:

http://www.tr-register.co.uk/forums/index.php?/topic/43950-are-triple-carbs-rubbish/

-richer running on centre carb due to 153624 firing order.

Peter

[TR NIALL]

Older triple SU thread here:

http://www.tr-register.co.uk/forums/index.php?/topic/43950-are-triple-carbs-rubbish/

-richer running on centre carb due to 153624 firing order.

Peter

Thanks Peter,I can find nothing with the Search Button.

[westaj]

Hi Niall,

 

Picture of my 3 x SU4s arrangement attached.

 

I have no issues with the Triumph engine firing order and its uneven stagnation periods, ie. with 1,2 and 5,6 on uneven pulses and 3,4 on even.

 

There is some intake balancing across the 3 carburetters, achieved by interconnecting the 3 low pressure connection ports just upstream of the throttle plates to the rocker box breather. I believe that this lowers the pressure in the engine which helps to minimise oil leaks.

 

For about 95%+ of my driving I am not at full throttle, so the 3 x 1-1/2 inch set up provides sprightly performance, simplicity and good economy.

 

Hope the picture helps.

 

 

Jerry

[TR NIALL]

Hi Niall,

Picture of my 3 x SU4s arrangement attached.

I have no issues with the Triumph engine firing order and its uneven stagnation periods, ie. with 1,2 and 5,6 on uneven pulses and 3,4 on even.

There is some intake balancing across the 3 carburetters, achieved by interconnecting the 3 low pressure connection ports just upstream of the throttle plates to the rocker box breather. I believe that this lowers the pressure in the engine which helps to minimise oil leaks.

For about 95%+ of my driving I am not at full throttle, so the 3 x 1-1/2 inch set up provides sprightly performance, simplicity and good economy.

Hope the picture helps.

Jerry

Thanks Gerry,more Studying and Head Scratching.

[Andy Moltu]

Hi Mal,

 

I have to agree with the points that Tom made! Altitude is a real problem for the standard PI metering unit, as a number of our Group found out on their Swiss Trip All 6 cars suffered plug trouble.

.But, in my view before deciding which way to go. What is the condition of your engine, regarding compression and inlet manifold vacuum, etc.? These are key points for the Lucas PI system to work properly. Do you know why that owner went over to Carbs?

 

Bruce.

 

They do run rich at altitude but a properly set up 6 will still get up Stelvio without problems.

If they are not set up well then perhaps an issue.

 

 

As long as you carry a spare injector, a bag of frozen peas and stay away from mountains the PI is very dependable.

 

Fit a Bosch pump and eat the peas. The Lucas pump is a weak point that is better replaced with a new Bosch for less money than a rebuilt Lucas.

[Guest ntc]

You are so wrong Andy sorry.

[Peter Cobbold]

Agree with Neil. I carried a spare Lucas pump in the boot for 150k miles. It was only needed when the original started to weep fuel onto the ground, but it was still pumping fine. Never needed peas.

Peter

[Stephen Jones]

Hello everyone

I did a bike carb conversion a few months ago and I am really pleased with the results. I bought 2 sets of motorcycle carbs from the wreckers (8 carbs in total). They were Keihin cvk, off a '95 Kawasaki zx6r. I split and re spaced them to suit the triumph head, and made all the manifolds and velocity stacks myself. I own a small machining business, so I have access to lathes and milling machines. The car was originally a US import, which had a triple stromberg conversion on it. It was never a PI, so I had no problem with originality. Bike carbs are fairly cheap and plentiful. All 8 carbs cost me AU$350 and the aluminium for the manifolds was just material out of the scrap bin so it was an inexpensive conversion. They were easy to set up, requiring re jetting and a little adjustment of the needle height. The engine was rebuilt 2000 miles ago with a fast road cam and a ported head. Fitting these carbs has made the engine feel much more awake than it was before. The revs come on much quicker than before under hard acceleration and the induction noise is gorgeous. I also like the look of them. I was careful not to make them look botched and too homemade. There is loads of information on the internet about bike carb conversions and I know of a couple of UK companies that specialise in this.Please see attached pic