Butterfly or butterflies

[ijonsson]

Has anyone skipped the butterflies on a PI and substituted them with a single butterfly in front of the air plenum? I guess those who are fiddling with EFI and supercharging has, but has anyone done it without those additions? If so, what donor car/s and what are the pros and cons? I guess you need a bit of DIY mechanics to fix the choke but as I see it there is a lot to gain not needing the throttle linkage and the pain in balancing the butterflies.

[peejay4A]

This has been discussed in the dim and distant past on the forum.

[Ade_TR6]

This has been discussed before. No reason why it shouldn't work but you will need to make sure the plenum is well secured coz if it comes adrift for any reason you will have 6 wide open throttle bodies feeding 6 hungry cylinders and very brown trousers...

[ijonsson]

This has been discussed in the dim and distant past on the forum.

Yes I made a Google search for "TR register forum TR6 EFI" and learned a bit there. I'm more interested if there is something to gain with a single throttle body without going all the way wit EFI, and also experiences from people who's been using single TB.

/Inge

[Tony Millward]

Hi Inge,

 

This has certainly been discussed before but so has everything else. We may as well close the forum if we just reply 'discussed before'.

 

To get back to your question and hopefully instigate a healthy debate amongst the newer forum members who aren't aware of this subject, there is no reason it couldn't be done. As Ade mentioned, the plenum has to have a secure fixing. You are probably aware that I did indeed use a single butterfly on my car but that was using EFT (electronic fuel injection for the newbies). I have since gone back to individual butterflies with K&N filters on. I like the sound that the intakes make..very similar to Webers.

I don't have many challenges balancing my butterflies as I have fitted a throttle linkage of my own design. You will need a butterfly in the region of 50 - 55 mm in diameter and a Ford one would work well. Let us know how you go....then start looking at EFI...

 

Cheers

 

Tony

[peejay4A]

Sorry if my reply upset you Tony. It wasn't meant to cause any offence.

[ijonsson]

Hi Inge,

 

This has certainly been discussed before but so has everything else. We may as well close the forum if we just reply 'discussed before'.

 

To get back to your question and hopefully instigate a healthy debate amongst the newer forum members who aren't aware of this subject, there is no reason it couldn't be done. As Ade mentioned, the plenum has to have a secure fixing. You are probably aware that I did indeed use a single butterfly on my car but that was using EFT (electronic fuel injection for the newbies). I have since gone back to individual butterflies with K&N filters on. I like the sound that the intakes make..very similar to Webers.

I don't have many challenges balancing my butterflies as I have fitted a throttle linkage of my own design. You will need a butterfly in the region of 50 - 55 mm in diameter and a Ford one would work well. Let us know how you go....then start looking at EFI...

 

Cheers

 

Tony

Yes, EFI is interesting, before the TR6 I built a Miata powered Westfield and later fitted a supercharger so I know there are interesting possibilities, as well possibilities going all wrong mapping the thing. Or, go your way just fitting filters, Weber sound is special!

[Peter Cobbold]

The plenum would need to be redesigned not only to stop it dropping off the manifold - an absolute necessity - but to avoid mixture distribution issues.

A Graham Bell gives sizing.

The butterfly diameter is important. I disagree with Inge, it's no good fitting one cut off a 2" SU, that'd only be good for about 100hp. A 2" would be good for 200hp when feeding a blower, but not normally aspirated. At a guess you'd need about 75mm diameter, or two 2" butterflies.

Peter

[Nick Jones]

I tried this with my 2.5 PI. Partly because the standard linkage was shot to bits and impossible to balance and partly because I was going EFI anyway and wanted a single. I used a 62mm throttle body from a Nissan Primera 2.0. This later proved sufficient for 146 bhp from a standard bottom end with "132" PI cam and some head work plus TR6 exhaust manifold.

 

While still on the PI the single throttle instantly cured the dreadful idle, constant plug fouling and poor part throttle running (entirely due to the balance issues being cured). The car ran too lean generally at this point with some flat spots, but the PI system was badly in need of a fettle.

 

No problems keeping the plenum on. I formed a small lip on the end of each plenum tube and used jubilee clips on both ends of all 6 rubber link tubes. Modifying the plenum to eliminate the link tubes and make it bolt-on was on my wish list, but as the car is now sold it won't be happening.

 

Don't understand the comment about mixture distribution. Can only assume this is a reference to the theory that the plenum to too small and causes 5 & 6 to run rich due to less air reaching them. Not convinced this is the case except on very high power engines.

 

Nick

 

[Tony Millward]

No offense taken Pete, all's good.

 

Tony

[GT6M]

If ye can get it to work as throttle opens then great.

BUTT, I fear that it will not run as you may think

As Lucas works in a diff way to EFI.

 

I did this, because of v worn spinnals, and spent great time / effort fitting a BMW 3 litre one.

But what I found was it idled great, but the least amount of throttle opening, it would die.

 

it would nae die wid 3/4 or moer choke, as it was the fueling that was the prob

I think it was that the MU took its vac feed of the OE TBs, v v close to the throttles on OE set up

so when OE throttle was opened, the links in MU dropped,and gave a rich mix

 

Nick kem across this prob too, so said it might help if he took the MU feed, nearer the new throttle,

He said it helped, but was still not right. think it needed a much bigger feed to MU, to let vac drop faster !!

Butt, another 2.5 PI bloke, said he got it to work OK

nooo, whether his ..work ok.. is same as my ..work ok.. is a diff matter !!!

 

But also, when on the single throttle, all the logg was under high vac, and I think it was this high vac that

made the links in MU stay up, so med it run weak as throttle opened,

totally opposit wot yer want,n to happen.

 

I farted aboot for a while, and had one rubber joint split after a while, and engine went red lining.

so put steel rings in to hoses to support em, as they can be seen to get sucked in quite alott

when under vac,or high rev slow doon,with throttle shut.then bulge oot when no vac,

never could get it to run ok, so scrapped the idea. and sorted the OE spinnals oot

 

Note, its the brass that wears, not the softer alloy of the manis,

reason, the ali, in cohoots with the brass, turns into ali oxide, which is tuffer than the ali

thus wears the brass away.

It helps if the spinnals are oiled on a regular basis, hands up how many of you ladds have oiled yer spindals on a reg basis.!!!

 

may be of some help

 

M

Edited June 21, 2014 by GT6M

[ijonsson]

Thanks GT6M, a lot of useful info. I also had an idea using a BMW throttle body, but maybe I'll just settle for filters on the TB to make it sound like Webers sound make a lot for the imagination of speed.

[michaeldavis39]

Question for Tony Millward- how have you fixed your TPS onto the throttle body and how have you overcome the problem of pulsation affecting TPS readings and idle?

[TR6GAZ]

Very interesting, ill be watching this thread! Going onto the subject of individual k&n filters I too was after that induction suck, but so far I've read that the under bonnet heat from the exhaust messes up the back 2-3 pots...anyone shed any light on this?

[TriumphV8]

When driving I would not expect hotspots in some very local areas

but the whole part over the exhaust will be a little bit hotter than the

air outside the car.

This reduces power but the sound of the K&N open filters

and a hotter cam is better.

 

As it is original and it is a pretty good solution I would keep the

original PI air intake.

Today many people pay a lot of money to establish a cold air intake system

at their modern cars.

[Stanpartmanpartwolf]

Thanks GT6M, a lot of useful info. I also had an idea using a BMW throttle body, but maybe I'll just settle for filters on the TB to make it sound like Webers sound make a lot for the imagination of speed.

Weber used to make angled 75mm trumpets that would fit into the PI bodies' outer counterbore (48mm diameter).

I put a set on the TR5- the noise was phenomenal at >3000rpm & snapping the throttles open would get Lake District sheep leaping out of the road instantly; they do not respond to any kind of car horn!

Hot vs cold air feeds: a load of hot air in my experience, no difference in dyno hp or real-world performance.

Go make some noise

[TR6GAZ]

Awesome...right, I think I'll order some of those up then! I did put some trumpets on once and it ran like a sack of spuds, but since then I have had many faults with my pi gear so I guess I cant blame them! When balancing the throttle bodies I just cant get enough of the induction GASP!