Replacing carbs for PI

[knapman]

Hi all

Have a 4A with 6 engine on SU's (tired) & wondering whether its worth fitting a PI system. Has anyone out there

fitted one from scratch & if so was it worth all the work & expense? I know fitting Webers is an alternative but

i can't lay out that kind of money in one lump but could slowly accumulate all the parts required over time for a PI system.

Have always shied away from the PI system because of its notoriety but am assured all its foibles are now sorted.

Am just thinking it over for now before i take the plunge!

What good S/hand parts are OK (E'Bay) & what new/rebuilt parts are a definate requirment?

 

Bob K

[jemgee]

Hi Bob

 

First off speak to Malcolm at Prestige who will give you the answers.

 

You will need to get s/h units for him to do it on an exchange basis for the metering unit and injectors.but he may be able to give you a complete price eg including Bosch pump and dizzie together with throttle bodies and linkages.

 

Webbers with all the extras would be a heck of a price and then they would need tune & dyno to get them on song.

[david ferry]

Bob,

 

Don't forget that you will also possibly need to change your fuel tank and play around with petrol pipes running the length of the car, also adding wiring for new fuel pump.

 

Would it not be simpler, and possibly cheaper to go down the weber route?

 

David

Edited July 3, 2007 by david ferry

[Rob Salisbury]

Well Triumph thought it was worth it when they took a 4A and created the 5, if it was good enough for them......

if you go for the hands on approach and learn just how the system works it's a darn sight easier to adjust than a bunch of webbers. It was designed for the 2.5 six pot after all, best to use the 150BHP cam and dizzy to match, oh and don't forget to change the 3.7 diff for a 3.45 unless you already have one.... ummm I'm warming to this idea already!!

Cheers, Rob

[knapman]

Hi

Thanks for the input lads, looked at Prestige's web site, all looked impressive but costly especially

when its all on an exchange basis meaning i would have to pay out for bits just to swap for

replacement ones. Will still mull it over & may be discuss it with some suppliers.

Thanks again.

Bob K

[boxer]

hi bob.b malcolm at prestige has just finished converting my us6 to pi alot of work on top of which head cam dizzy has to be soughted to get the benefit but i can only say from my expierence the conversion although expensive is well worth the money always felt the twin hs6,s were holding the beast in the car back and this conversation has more than confirmed this dont waste your money buying up old parts spend your money on malcolm,s parts from the off he will probally tell you that anyway because alot of parts on ebay are non servicable

bob

[marvmul]

Sorting the SU's (fitting the right needles, matching the ports and manifolds,...) and fitting a sprint cam, a stage 2 or preferably a stage 3 lead free cylinderhead and a 6 into 3 into 1 exhaust system, will get you a car that is fun to drive, leaving every standard PI TR5/TR6 behind. And the parts you buy for this set up are necessary anyway when you like to fit Webers or a PI system later on.

[knapman]

Hi Marvmul

That idea sounds intersting as i could buy parts piecemeal & add them as i can find funds,

the cylinder head might be pricey especially as i already have an unleaded one.

Not too keen on stripping engine to change cam, i presume as its a CP engine

it will have the 150 cam in as standard & thought that would suffice.

If i buy separatley, in what order would you buy & fit the parts?

I'm talking spreading the costs over maybe a year or more.

As you can see i dont have an open cheque book as some seem to have!

Regards

Bob K

[Tom Fremont]

Hi Bob,

 

This is all in the archives somewhere, but here's the real deal about Webers:

 

1. Used are fine - I've got 70,000 miles on a set of 60s vintage 40s with no problems, and the engine could hardly run sweeter. Point being you can buy a 2nd hand set for a fraction of the new cost ( last one I saw with manifold and linkage sold for ~$800 recently on ebay ). I'd say with the various jets, air filters and miscellaneous bits you could be done for under 1000 GBP.

 

The reason you can buy these reasonably 2nd hand has to do with frustrated attempts to calibrate them, at least partly.

 

2. Calibration is the only nut to crack, and if you're in the UK apparently there are plenty of rolling roads with Weber experience who can get them just right. Here in the 'states I've been on my own, and achieved a very nice result with trial and error after getting some baseline guidance at no charge from the Weber source.

 

3. Webers can be successfully applied to anything from stock to full race engines, and be set up to operate flawlessly. Don't expect a major performance increase on a stock motor, though unless you've got a P.I. engine running on other carbs. You'll see the most increase in power when the fuel/air delivery system is the bottleneck before switching to Webers ( or P.I. per the previous post ).

 

Be forewarned - if you succeed with Webers you'll never again consider the alternatives, except for originality's sake

[harrytr5]

On a Holiday to Italy going through France and then Swiss Alps and back again after two weeks the difference between my TR5 injected car and my best mates Webber 45s on his TR6, MPG was surpisingly in fact not a lot in it.My TR5 ran like a pig in the high altitude due to lack of density of air,where his on webbers although suffered, was so much better.I of course know why my TR5 ran like this in high altitude but the overaul MPG between the cars was a revelation.Both cars were tuned on the same rolling road in Cambridge.My TR5 has a 28% reduction overdrive and was designed for better MPG on touring and at 70mph equals 2200 on the rev counter.

Regards Harry.

[jonlar]

Hi Harry, unless I'm missing something here - what was the revelation on the mpg - and also the performance differences. PI cars can be quite easily tweaked for higher altitudes, I believe?

[marvmul]

Hi Marvmul

That idea sounds intersting as i could buy parts piecemeal & add them as i can find funds,

the cylinder head might be pricey especially as i already have an unleaded one.

Not too keen on stripping engine to change cam, i presume as its a CP engine

it will have the 150 cam in as standard & thought that would suffice.

If i buy separatley, in what order would you buy & fit the parts?

I'm talking spreading the costs over maybe a year or more.

As you can see i dont have an open cheque book as some seem to have!

Regards

Bob K

 

I would buy a good exhaust system in the first place and service kits with needles BAE for the SU's(if possible, have the spindles of the carbs rebushed). The 150 PI cam will work very well together with the exhaust and a stage 3 cylinderhead, so you can leave the engine block alone. I think there is no way around a modified cylinderhead if you want a real performance boost.

[Guest Wyn]

Jonlar,

 

I may be wrong, but I think Harry was saying that there was very little difference in mpg whereas some may have expected the weber 45s TR6 to be thirstier, espectially with Harry's car having a 28% reduction overdrive.

 

Wyn

[Tom Fremont]

It seems to me the P.I. system will go rich at lower pressure ( higher alititude ) via the metering unit, across the rpm range. The Webers will be too rich at the pump jets but might otherwise self-adjust to the lower air velocities

 

Having crossed the Rocky Mountains in 1979 in a TR250 with emission type Strombergs uneventfully, I suspect the " constant depression " S.U.s and Strombergs may cope with altitude best of all...

[john.r.davies]

Tom,

Quite right about Pi at altitude. We only just made it over the Col d'Iseran on the 10CR two years ago. 3K metres, and it would only climb the last 100 in first gear, though it was not steep. I'm told that Lucas made 'altitude' versions for the metering unit, but have no idea what that meant. I've also heard of a Swiss owner who kept his car adjusted lean, so that it ran correctly at altitude. What that did when he came down on a vist, I don't like to think off, unless he kept the choke lever out all the time.

 

John

[jonlar]

Hi Wyn, that's what confused me, I was expecting the PI to be thirstier, having managed less than 12mpg in a 2.5PI saloon.

 

Hi John, you're right the MUs for higher altitudes had a different colour conical cover (Green?). I think the MU meters the fuel according to the difference in air pressure in the throttle bodies. I'm sure I've seen somewhere that the fuelling is quite easily altered - not messing around with the calibration - for higher altitudes.

[harrytr5]

Yes it is very easy to adjust the metering unit to run at high altitudes.Undo the bottom ring under the cap on the metering unit and turn the unit anti clockwise to weaken off.I was enjoying myself along with my wife and Alan/Lou (wife) so much up in the Swiss mountains with all the 180% chicanes I just did not want to stop despite it running like a pig.You guys and girls just have to do it as it is just one big F***ing buzz and we will never forget it.I thought my mates Webbered TR6 would be more thirsty than my injected TR5.

Regards Harry, a very happy veteran of the Alps

[jonlar]

Hi Alec,

 

The particular occasion I had in mind, was an Easter Bank Holiday Monday 1974 or 5. I was just ready to go off duty (re-fuelled the beast - a K reg 2.5 non O/D) at home station Frome, when I was called and asked if I'd consider a very urgent Ambulance from Yeovil to Frenchay. Well, that's not a challenge you can refuse is it? I hammered down the A361, then down the A37, meeting the Yeovil car escorting the Amb. north bound at Lydford Cross, it took some distance to stop, turn and get back up to speed north-bound, I would think probably the best part of 2 miles, before I caught back up and passed the Ambulance, the Yeovil crew, just pulled over and returned to base to go off-duty. The run up the A37 was rather uneventful bar the excessive speed. When I hit Bristol, I was joined by 4 lads on bikes, who played leap-frog on the junctions and lights all the way to Frenchay, which we reached at 1423, the Ambulance (I think it was a Range Rover based one) had averaged just under 70mph from YDH to Frenchay, I poodled (still at a fair rate of knots - to keep the brakes hot) back to Frome, re-fuelled, I can't remember if it was 12 gallons, for 98 miles or 8 gallons, so it was an average mpg for the run of either 8 or 12 mpg.. I immediately put the car on Defect Notice on return, for the pads to be changed and discs checked - in chase and very fast driving conditions, we found that the pads would craze and break up on cooling, and sometimes the discs would warp (wheel bearings would always be checked as well). And to think, I was being paid to enjoy myself by the Tax payer! On the run down to Lydford, I was very nearly a wipe out, there was the usual Easter Monday scramble going on at Leighton (just east of Foster Yeoman's Torr Works Merehead Quarry), as I was approaching, a Special directing traffic turning into the field, had 3 or 4 vehicles waiting to turn right, he started waving me through and as I went by the queue, the lead vehicle started moving and turning in front of me, I took to the lay-by on my off-side, when I looked in the mirror, all I could see was a big cloud of dust! Talking of Foster Yeoman's quarry, I remember one year in the mid 70s, a RAC Rally Special Stage was routed around the quarry (I dug out the pics I took the other day - Stig Blomqvist in a Saab - he rolled it in this particular year, and complained bitterly that the spectators took too long - about 40 seconds - to get him back on his wheels and on his way, he retired later - does that ring any bells with anyone as to the year) - my crew-mate and I had a quietish (about 50% more time than the top competitors took) drive around the course in a PI before it was actually used. Oh Happy Days!

 

And to get back on the thread, Webers sound nice, but the Lucas PI is what the car was made for....................

Edited July 6, 2007 by jonlar

[Tom Fremont]

Here's a set of triple Webers for a pittance - the exact type I use on both my '250s, Italian made:

 

http://cgi.ebay.com/ebaymotors/Triple-Webe...131907329QQrdZ1

 

 

...and another set with everything else included:

 

http://cgi.ebay.com/ebaymotors/Triumph-TR6...134225575QQrdZ1

 

( Manifold is correct for P.I. heads )

 

Cost is arguably competitive against all comers for the performance potential gained

[jonlar]

Talking of Foster Yeoman's quarry, I remember one year in the mid 70s, a RAC Rally Special Stage was routed around the quarry (I dug out the pics I took the other day - Stig Blomqvist in a Saab - he rolled it in this particular year, and complained bitterly that the spectators took too long - about 40 seconds - to get him back on his wheels and on his way, he retired later - does that ring any bells with anyone as to the year)

 

As a matter of interest, I've had a dig around the 'net, and confirmed the year as 1975, the RAC GB Rally, won by T. Mäkinen, Brian Culceth and J Syer came in 16th in a Dolly. If I can find the negatives, I will try to find out how to upload them to the 'net for others to access. Avengers came in 18th and 36th!

Edited July 14, 2007 by jonlar

[jellison]

Bob - I have sent you a PM - I have all this - just come off our race car (the whole lot just sitting on a shelf).

 

Jon