DIY TBI Set-up

[Steven]

hello
i need to fabricate a horizontal TBI setup, i have a throttle body from a LS truck engine and 4 x 60lb injectors that should suffice for 400hp. does anyone have any experience with this type of setup?

Regards Steven

[Bernard Fife]

Steven,

I have done this on a 1.5 litre Honda 4 cylinder engine in a Prelude using a TBI from a Corvette cross-fire but in a horizontal configuration (I also have a Corvette with a 406 SBC that had a Holley 4bbl TBI only it, but that has since been converted to port injection).

It worked better than I thought it might. I thought fuel might spit back out of the TBI while running, or run back out on shut-down, but it did spit only slightly and only at occasional times, and negligible fuel run back on shut down, and either were easily contained by the air cleaner.

The fuel pressure regulator worked fine, and there were no issues at all (it probably helped that the manifold the TBI was adapted to was a wet-flow manifold original mounting a side draft carb).

Be sure to read the manual regarding PWM current limiting for the low-impedance TBI injectors (mine worked best with about 22% PWM% and a 0.7 msec opening time).

Lance.

[Matt Cramer]

hello
i need to fabricate a horizontal TBI setup, i have a throttle body from a LS truck engine and 4 x 60lb injectors that should suffice for 400hp. does anyone have any experience with this type of setup?

Regards Steven

This seems like it could easily turn into a fuel distribution nightmare if you're not careful. Here are some general notes about TBIs.

1. Any setup I've seen tested that put the injectors below the throttle blades had severe fuel distribution issues - I'm talking "Four black header pipes and four red ones" type issues in many cases.

2. All successful TBI implementations kept the individual throttle bores under 2". At light throttle, TBIs often rely on how the air speeds up around the edges of the throttle plate to atomize the fuel. A throttle over 3" may have problems.

3. If this is a V type engine, I have concerns about the intake manifold if the air/fuel mixture is entering horizontally from a single point. This would be a pretty challenging manifold to set up correctly. An inline engine may do somewhat better.

[Steven]

Lance / Matt
thanks for the input i did post on the subject earlier but i didn't get a reply maybe too much verbiage. the engine is a 250 GM straight six with Siamese ports and i originally went with a port injection but that didn't work out too well. i have three inlet runners coming into a common plenum where i need to get the fuel to atomize and distribute. runners are 2" and feed two cylinders each, i went with 4 injectors to try and get some fuel spread. i currently have a common plenum that will be going in the trash see photo and be replaced with the 3d model contraption you see attached (shows six injectors not four). i did kick up the throttle bore into the common plenum to try and create some turbulence at the injection point. basically i want this engine to run this summer so i have time to work on the head to try and separate the siamese inlet bores before going back to port injection.

p.s. i was struggling with detonation on the last set-up.

Regards Steven

[Steven]

just had another thought, what about injecting into the sides as it is a flatish section?

[Matt Cramer]

I suspect fuel distribution with that setup will be VERY sensitive to the injector location and spray pattern.

[Steven]

Matt
which one the side or top injection, or both?

Regards Steven

[Matt Cramer]

Both.

I strongly do not recommend a TBI type setup locating the injectors downstream of the throttle body.

[Steven]

Matt, i appreciate the advice but why is it that you dont recommend doing this? I cannot use port injection on this engine because of the siamese ports 240-480deg firing order (i learnt this the hard way) and i don't know of any horizontal TBI setups commercially available.

I would love to go with a constant flow PWM injection but as far as i know i cant do this with Microsquirt.

My strategy is to inject at two places down stream and into a turbulent flow area to try and ensure a consistent as possible fuel air mixture.

also the cross sectional area is reducing from the throttle to the plenum and same again into the three inlet port runners, i.e the flow is speeding up at each point.

Regards Steven

[Steven]

Steven,

I have done this on a 1.5 litre Honda 4 cylinder engine in a Prelude using a TBI from a Corvette cross-fire but in a horizontal configuration (I also have a Corvette with a 406 SBC that had a Holley 4bbl TBI only it, but that has since been converted to port injection).

It worked better than I thought it might. I thought fuel might spit back out of the TBI while running, or run back out on shut-down, but it did spit only slightly and only at occasional times, and negligible fuel run back on shut down, and either were easily contained by the air cleaner.

The fuel pressure regulator worked fine, and there were no issues at all (it probably helped that the manifold the TBI was adapted to was a wet-flow manifold original mounting a side draft carb).

Be sure to read the manual regarding PWM current limiting for the low-impedance TBI injectors (mine worked best with about 22% PWM% and a 0.7 msec opening time).

Lance.

Lance
i just re-read your post, did you use PWM or just the injectors firing in the usual way?

Regards Steven