Manifold balance pipes?

[aborris]

Newbie alert!

Starting to convert a Triumph 6 cylinder to MS and very nervous, EFI is very outside my comfort zone!

I think I'm lucky though, I'm in touch with a few people who have already installed and they don't seem to mind my dumb questions, always staying polite and helpful!

But it's not fair to overload them with all my dumb questions, that's what the forums are for, right?

The install will use converted Triumph/Lucas mech petrol injection manifolds, these manifolds have several external air balance pipes between each set (3 sets of manifolds, 2 runners in each set).
They also have much smaller air bleeds between each runner of each set (make sense?)

Should I leave all these balance pipes/ air bleeds open? While I think the larger pipes which run between the manifold bodies are OK to leave open, what about the smaller ones between each runner?
Will these cause uneven flow pulses? Or doesn’t that matter, because only carbs suffer from this?

Thanks
Andy

[Stag76]

Are you using the individual butterflies or a throttle body. The balance pipes are plumbed into the throttle body after the butterfly, and I think they're designed to enable the idle valve to allow air into the throttle body when the buttterfly is closed. We removed the butterflies and attached a Ford throttle body to the existing plenum, and so all balance pipes etc. are still open, but not really doing anything.

[aborris]

I've also removed the butterflies and using a TB.

Thanks, was pretty sure that they wouldn't make a difference, may just block them off.

Andy

[jcarruthers]

Andy - you don't need to leave them open - at least I have blocked mine off.

You have a massive great big plenum to do the balancing

http://www.youtube.com/watch?v=bjfx4QMILoE

[Stag76]

We originally attached a Ford 65mm throttle body to the existing PI Plenum. The volume of this plenum is 2.5 litres, and we were getting a bit of lag on throttle opening and closing, and having a lot of trouble tuning the over-run and acceleration enrichments. The runner length from plenum to valve was also a bit short, so I made a plenum from 76mm ID exhaust piping, and replaced the stubs with 60mm long pipes to fit between the plenum and the injector bodies (made from 1.875 inch exhaust piping). This made a really big difference in power and drivability. We were running spark via a locked distributor, which we upgraded to EDIS6 which also gave us a big improvement.

[jcarruthers]

Hi there,

Do you have a photo?

I am running a 52mm throttle body on my 2 litre - even at 6krpm I had atmospheric pressure so the body is not too small.

I thought the existing plenum is 76mm?

It is something I have thought about to improve the plenum but it's working for now.

James

[Stag76]

The original PI Plenum is 78mm ID, with a capacity of 2.5 litres. The pipe I used is 76mm OD or 72mm ID. This gives a plenum capacity of 1.77 litres. The Ford 65mm throttle body is probably right on the upper limit for this 2.5 litre engine,
but is a really good unit incorporating TPS and Idle Valve. Your 52mm throttle body will be ideal for a 2 litre engine.

There are some pictures at this link

http://s991.photobucket.com/albums/af32 ... =slideshow

[jcarruthers]

Ohh I see you made the plenum smaller— for some reason I thought you would want to make it bigger!

As mine is smaller capacity, though tuned up a lot, maybe it's worth considering. I need to get it all tuned properly before so I can identify any issues.


James

[Stag76]

With the larger plenum, we got slow and exaggerated throttle response. Blipping the throttle slightly would produce a flare to a RPM way above what it should have (eg. throttle opening should produce a rise to 1500 rpm for .5 second, where it actually flared to 2000 rpm for 1.5 seconds). There was also a lag of about .5 second after blipping the throttle before the engine responded. The smaller plenum and longer runners cured this completely. While we were trouble-shooting it, we placed a plastic bottle in the plenum to reduce its capacity, and immediately noticed the difference. It is a stock standard 2.5 PI motor.