Question about TBI

[Cyclone03.1]

In the cost thread on the main page a mention is made about the cooling effect an emusified mixture creates in the runner. Lowers inlet temp at the valve.

DG has responded in my MegaSquirt thread below about TBI having poor mixture distribution over port injectors.

My question is can the mixture problem be lessoned with a split plenum type (dual plane,) mainfold?

Does TDI have the same or near,cooling effect on the mixture?

Does cranking up the preasure help break up the fuel more?

[dieselgeek]

Re: Question about TBI

I will add that, I believe the claim about "cooler mixture from a carb" is bogus to begin with, because it causes an equal impedance in the incoming air charge. They don't put slide throttles on motorcycle IR intakes just for kicks.

I don't think you can or want to crank up the fuel pressure on the TBI only because it'll exceed specs for the injectors rapidly. The injectors will atomize as fine, or more fine, than any carburetor. The problem is keeping that suspended mix evenly distributed in the incoming air charge.

My gut says a dual plane intake manifold will help a lot, but the bulk of the effect comes from cam profile (from what I've observed in testing). Aggressive cam, high compression, puts greater shockwaves into the intake runners, and this is what causes distribution problems.

TBIs are more sensitive to this than carburetors. This I know for sure.

That's about all I can offer.

[Cyclone03.1]

Re: Question about TBI

I've changed my set up from below, I put less cam in it and I like it much more now.

I guess I just want a 4brl TBI to work.

So even batch firing 4 big injectors in a tbi doesn't get the fuel where it needs to be?

[dieselgeek]

Re: Question about TBI

I've changed my set up from below, I put less cam in it and I like it much more now.

I guess I just want a 4brl TBI to work.

So even batch firing 4 big injectors in a tbi doesn't get the fuel where it needs to be?

It'll work fine with an OEM cam grind. Or, close to OEM... the only way to find out, is to try.

[Matt Cramer]

Re: Question about TBI

I've changed my set up from below, I put less cam in it and I like it much more now.

I guess I just want a 4brl TBI to work.

So even batch firing 4 big injectors in a tbi doesn't get the fuel where it needs to be?

I suspect the problem with aftermarket TBIs is in some ways similar to what you get when you run a carburetor on an intake designed for someone else's carb. We found that a Holley 4 barrel TBI on our Nova didn't get any better fuel distribution than a stock GM TBI - this was on a Torker II manifold, using an adapter for the TBI.