So I thought I'd try something I haven't ever seen before. If you're at all familiar with the GM TBI unit, people do what's called the "ultimate TBI" mods. Shaving down and giving the throttle bores a more aerodynamic radius and adding an injector pod spacer to lift the pod for more air flow.

Well..... I decided to go a step further and smooth down and streamline the injector pod itself. It sits directly above the TBI unit and impedes on airflow in stock form. I smoothed the pod down as far as I felt safe doing so and it definitely looks more aerodynamic. Whether or not it makes a big difference is up in the air. I won't know until I test it out but anything free is worth it in my eyes. Tell me what you think

 

Good work

 

Looks good!

 

Visually streamliined, and actually aerodynamic are two different things.

Until someone shows me flow-bench or (better yet) dyno-proven horsepower improvements, I'm skeptical of the entire "Ultimate TBI mods"; in fact I suspect it's a total hoax. At best, perhaps some of the modifications do some little good, while others are completely useless or counterproductive. And it may be that if any of the "Ultimate" mods genuinely work at WFO--high rpm, they may create driveability issues at part-throttle.

Every time someone wants to make power with a TBI, the first thing they do is increase the fuel delivery. Tells me that airflow is not the major problem, fuel flow is.

Raising the injector pods with a quarter-inch "spacer" on stock-sized throttle blades seems especially silly. GM goes to the trouble to get the spray from the injectors to flare out in a certain-diameter cone to match the throttle size, and hot-rodders make the fuel-cone wider by raising the injectors so the spray ends up wetting the side of the throttle bores.

GM did use the spacer on the 454 throttle body, but that had larger throttle blades; so the taller injector pod produced a wider cone to match the bigger throttle bore.

 

I can tell you that it is NOT silly to raise the injector pod out of the bore hole. We did a lot of testing back in the day on a flow bench with a lot of TB sizes from stock to 2.25" bores and you would be surprised on the flow difference there is on these size TBs with different sizes of spacers under the pod makes from stock spacer to 3/8" spacer. Jus sayin'.

 

From messing with them back in the day. Stock bore big block TBI I tested lost nearly 100 cfm at 28 in/h20 removing the spacer. Gained an additional 50ish cfm with two spacers. Big block large base TBI gained 40 cfm with the IAC wide open vs closed. You want the IAC wide open using throttle follower at high rpm especially on a performance engine with a smaller throttle body. Stock TBI units gain a ton of flow with the injector pod removed entirely. Edelbrock MPFI setup on a MTC1 cammed 350 dropped nearly a full second off the 1/4 mile time.

Also tested back in the day. Stock choker ring of death cost about 25% CFM. Hypertech power bowl or stock big block air cleaner base worked better than a flat base air cleaner base. Caddy TBI bonnet also had better cfm than the stock air cleaner spacer ring. Unshrouding the area around the injectors helps alot with flow.

 

Does this increase the the RPM range or does the fuel limit it? Seems like going from 450cfm to 500cfm would make the most difference at higher rpm right. Is the TBI useable to something like 5500 after this if you had better heads

 

Airflow wise a stock small block TBI is good to around 320-330 hp before it starts getting restrictive. A big block TBI can handle 425-450 without becoming restrictive. I was at 370 wheel at 5,900 rpm with a double spaced big block TBI on a victor jr single plane. With a dual TBI setup the sky is the limit for a small block. Ran dual stock bore small block TBIs on a tunnel ram on a 406 with a solid roller cam. Making roughly 500 rwhp at 6,700. Did a Mercury 575SCI 502 with an 8-71 conversion using dual big block TBIs. Was around 750 hp.

 

My TBs are 2.13" and flow great and I take it to 6k or more with no issues. Hoping to get into the 11s with my new tune and Robs help.

 

2.13" TBIs...Must be a Crossfire. Going against the grain a little there but I like it.

A little off topic, but I am doing the same thing here with going against the grain. Shooting for a 12.99 or better with my current build. 1997 Express conversion van with full 1 ton suspension and running gear with a ~500 hp 383 on E85 with a ported Vortec truck manifold just because people claim you cannot make power with them. They were fuel limited at one point with 23 lbs/hr spiders but they make 36, 48 and 62 lb/hr MPFI spiders for them now. Just installed an 80mm throttle body on a ported intake base with a 48 lb/hr spider and a plenum opened up to match the 80mm throttle body as well as a 4" air intake and 4" MAF on the thing. Van has a 4L85E with a hard hit high STR 2,800 converter and 5.13 gears.

Working on dialing in the P59 LS PCM but it is beast of a little small block.

 

My engine is basically a stock L98 with a lil head porting, bored stock TBI intake, 46 MM TBI. Pulls hard to 5200-5400.