pi v su v webbers

[rpurchon]

i have SUs on my car.and im very happy with them .however am i missing out ?

can any one tell me how much power each set up puts out.

from owners who have been on a rolling road, not hear say.

my 6 has SUs 6 branch manifold- standard exhaust. big valve high comp head. cam unknown.

whot will it be putting out? i was hovering around the rolling road at malvern last year .

and a dutch chap with a gt6 got 150bhp on SUs. a tr5 pi on the other hand got 128bhp ish.

 

richard

[robgeev]

Stop hovering!

 

Strap the damn thing down and know for sure!

 

 

Webbers Gona win though.

 

 

Rob (had all the choices)

[Red 6]

I have su's on my car and get 160+ at the rear wheels, the improvements came from the exhaust, head and cams not the carbs

[rpurchon]

I have su's on my car and get 160+ at the rear wheels, the improvements came from the exhaust, head and cams not the carbs

 

 

whot cam do you have in your 6. thanks richard

[boxer]

I have su's on my car and get 160+ at the rear wheels, the improvements came from the exhaust, head and cams not the carbs

would be interested to know the spec in more detail of your engine as i,ve done very similar to mine and i dont think i,m getting anywhere near that figure,but i would like to think i could

bob

[trt74]

Red Six,

 

I think you've made a lot of 6C owners curious! Could you tell us a bit more about how exactly you squeezed 160 BHP + out of your 2,5 liters?

 

Tim

[marvmul]

Don't forget that SU's are performance carburettors.

Only at very high rpm (>6000 rpm), DCOE Webers will have the edge, very marginally. I.e. 175 bhp

on SU and 180 bhp on Webers at 6500/'.

Webers are looking better of course, and SU's are very common, so the SU's don't get the status they deserve. SU carbs are a very simple but very clever design. Webers have lot's of jet's, orifices, ducts etc. yet the metering of the fuel is very poor at part trottle and the presence of an auxiliary venturi doesn't help much. An SU can do with just 1 needle and jet and a variable ventury and yet is able to

meter the fuel very efficiently on cold start, acceleration, overrun, and all other circumstances.

[Red 6]

Hi trt74,

 

My engine (which is now very old) has very sraightforward mods. The head has been flowed but the valve sizes left standard albeit with the standard valves modified as per the triumph tune/ kas kastner design.

 

The cam has been changed to a 285 duration which gives a normal tickover and peak power about 6200 rpm, so the power is noticably better but it pulls from low down, i experimented here with different advance and retard positions to give more power or more torque, (it is all covered in David Vizards book on tuning a series engines).

 

The car is a tr250 and it has the origional head so i was limited to using the std stromberg manifold but adding the su' s to it. As you may or may not know the tr250 has different inlet port spacings to the UK models which is a bit of a pain as with a different inlet length i could release more power.

 

The next issue was the exhaust manifold. Origionally it had a GT6 type cast manifold which appeared to be not too good but was far better than the Moss twin system which did nothing to improve the power at all. After several years i fitted a phoenix bigbore system and the improvement in mid range was startling, but i felt was still inhibiting performance.

 

When i modified my tr6 race car (225+) i used the manifold on the tr250 and again because of the long primary pipes another noticable improvement, to mid range and it revved higher and more easily, the trouble was i i couldnt be bothered to get a proper gas tight seal and with the hood up we ended up a bit "gassed" so off it came.

 

The final part was getting cold air to the carbs. I have seen so many su installations with K+N's breathing from the engine bay. This is not good, an engine needs fresh cold (or cooler) air. I experimented with ducting and creating a cold air zone and again noticable improvements.

 

So there you have it a sweet smooth engine running on su's capable of blowing off 5's and 6's with ease. Tony Lindsay Dean put me on to su's years ago, he said he was getting over 200 using them in his race car.

 

I am prepearing my next engine as i write this, i am aiming for the same drivability but with more rev's, it might incude efi and a supercharger! (that was for Harry)

[marvmul]

RED6

I'm interested in the retard and advnce positions of the cam : did you notice much difference? I only tried to 5° retard and advance in respect to the recommended installation figure on a 2 camshafts and found no difference to speak of.

[Red 6]

RED6

I'm interested in the retard and advnce positions of the cam : did you notice much difference? I only tried to 5° retard and advance in respect to the recommended installation figure on a 2 camshafts and found no difference to speak of.

 

I have to say that there wasnt that much difference on the 285 cam, i was looking for more torque and got it to pull better. On the race car it was much more noticable right down to being difficult to pull away at low speed! But there were other factors that made a difference such as i was using a higher ratio roller rocker and i needed the max torque quite high up the rev range.

 

I also remember that i was only moving it 2or3 degrees either way

[Tom Fremont]

Testimony before and after a switch between Webers and S.U.s is what's missing on this thread.

 

I switched to triple Webers from dual Stromberg 175s with no other changes, and the difference was hugely noticeable. I was persuaded to make the switch principally for the tuneablility of the Webers vs. the emissions-type Strombergs ( which ran fine over 2000 rpm, they just wouldn't give good idle quality with the Kent TH2 cam ). No one will easily convince me that Strombergs or SUs will perform equivalently to Webers. Of course, one can make up the difference with other modifications, and of course TR heads in standard form don't make full use of Webers either.

 

Ideally we would hear from someone who can report the dyno results of such a switch.

 

 

My 1st set of triples ( now with 70,000+ trouble-free miles since installing them second-hand ) will soon be joined by a set of NOS vintage Italian 40DCOE18s on the current project

[Red 6]

Tom,

 

Thats why i switched to su's, i just could not get the engine to idle with the emmission strombergs.

 

Not only that but I have a complete set of triple webbers with the correct twm manifold and i cant fit them because of the port spacing of the 250 head so i cant contribute to your question.

[Tom Fremont]

Not only that but I have a complete set of triple webers with the correct twm manifold and i cant fit them because of the port spacing of the 250 head

 

Maybe TWM don't offer it, but Cannon make a manifold for the early head; this is what I started with myself. www.piercemanifolds.com. Interestingly, I was later told not to waste my time with the early head ( porting, polishing etc. ) so I got ( now 2 ) the later type and let go cheap a '250 manifold which I had machined for O-rings.

 

The only hitch with TR5/250 and early TR6 and triple Webers is the clearance with the wheel arch is barely enough to fit air cleaners of the recommended depth for the short trumpets. Doable, however.

 

I'm betting you'll find a dramatic difference if you make the switch. Pierce can give jetting advice if you go that route. Your report following will be of great interest, especially if dyno figures are included.

[Red 6]

Maybe TWM don't offer it, but Cannon make a manifold for the early head; this is what I started with myself. www.piercemanifolds.com. Interestingly, I was later told not to waste my time with the early head ( porting, polishing etc. ) so I got ( now 2 ) the later type and let go cheap a '250 manifold which I had machined for O-rings.

 

The only hitch with TR5/250 and early TR6 and triple Webers is the clearance with the wheel arch is barely enough to fit air cleaners of the recommended depth for the short trumpets. Doable, however.

 

I'm betting you'll find a dramatic difference if you make the switch. Pierce can give jetting advice if you go that route. Your report following will be of great interest, especially if dyno figures are included.

Tom, the problem with all but one webber set up i have seen is that they were breathing engine bay air! What a waste of power.

 

The 1 that was done correctly had a complicated cold air zone set up within the engine bay

[Tom Fremont]

Tom, the problem with all but one weber set up i have seen is that they were breathing engine bay air! What a waste of power.

 

Racetoration's cars have a duct feeding cold air to the zone - but they don't use air cleaners ( " It's not so dusty here in the UK...").

 

TR250s and TR5s get plenty of cold air in the intake zone since they don't have radiator cowls. When the car is moving nicely it should be quite a blast - I can live with the power losses when stopped .

[Red 6]

Racetoration's cars have a duct feeding cold air to the zone - but they don't use air cleaners ( " It's not so dusty here in the UK...").

 

TR250s and TR5s get plenty of cold air in the intake zone since they don't have radiator cowls. When the car is moving nicely it should be quite a blast - I can live with the power losses when stopped .

 

 

Ha Ha,

 

In the UK the roads are so congested we dont get a chance to go fast

[jellison]

i have SUs on my car.and im very happy with them .however am i missing out ?

can any one tell me how much power each set up puts out.

from owners who have been on a rolling road, not hear say.

my 6 has SUs 6 branch manifold- standard exhaust. big valve high comp head. cam unknown.

whot will it be putting out? i was hovering around the rolling road at malvern last year .

and a dutch chap with a gt6 got 150bhp on SUs. a tr5 pi on the other hand got 128bhp ish.

 

richard

All depends what trick or standard bit you have in the car engine as to whether each is of any benefit.

 

No point putting 1500 quids worth of webbers on a std engine! But then I think the twin carbs look rubbish.

 

Alot of work to change from fi to carbs and vice versa - so if on carbs and you have some trick bits in it then pop on some webbers (40's or 42's if you can find them or 45 if rull RACE!). If fi then you can do alot with this up to about 220bhp (at the fly). I'd stick with Fi if that is what you have. We used to run our 6 on a fast road cam and blueprinted and made about 175 - 180 at the fly.

 

If you really want to switch to Fi - we have every thing you need! Better pumps, remapped fuel pumps fi dissy, everything.

 

Oh and Webbers make a FANTASTIC NOISE!!!!