Interest in a 2.56" bore TBI?

[1BadAction]

Out of curiousity, how much interest do you guys think there would be in a "reasonably" priced 2.375" to 2.56" bore throttle body, that uses GM injector pod, IAC, and TPS? It would use the factory TBI bolt pattern but would obviously need to have the intake bores adjusted...

[dave w]

Out of curiousity, how much interest do you guys think there would be in a "reasonably" priced 2.375" to 2.56" bore throttle body, that uses GM injector pod, IAC, and TPS? It would use the factory TBI bolt pattern but would obviously need to have the intake bores adjusted...

I don't foreseen a SBC truly needing a TBI bore of 2.375" to 2.560". I can foresee a 7.4 liter or bigger engine truly needing bores of 2.375" to 2.56" if truly making more than 1 HP per cubic inch.

I'll make a flow matched adapter plate, 1" thick, to fit the intake. The pics below are for a TBI to Square Bore, "D" port design for dual plane intake.

dave w

[1BadAction]

Yea, I don't think it would be something an SBC guy needs, I'm speaking strictly of the higher compression modified big blocks. I'm "thinking" about making a 2.375" bore TB for my 3764 intake and was curious if anyone else may need one. Throttle plates are easily available in both diameters.

On a similar note, have you ever tried notching a TBI intake below the throttle bores? Similar to this but maybe not as drastic.

[dave w]

Yea, I don't think it would be something an SBC guy needs, I'm speaking strictly of the higher compression modified big blocks. I'm "thinking" about making a 2.375" bore TB for my 3764 intake and was curious if anyone else may need one. Throttle plates are easily available in both diameters.

On a similar note, have you ever tried notching a TBI intake below the throttle bores? Similar to this but maybe not as drastic.

No, I have not notched an intake. I tend to work with 4x4 applications (rock crawler) where low RPM is the primary focus. It's my understanding the notch helps high RPM performance.

Is it actually possible to bore a 454 TBI to the 2.56" diameter? Based on my CAD model, I'm thinking the maximum diameter is about 2.10".

dave w

[Nasty-Z]

Is it actually possible to bore a 454 TBI to the 2.56" diameter? Based on my CAD model, I'm thinking the maximum diameter is about 2.10".

dave w

2.244" (57mm) is basically the absolute max throttle bore on a factory 454 TBI unit, this is after boaring the unit to 2.291 (58.2mm) and installing sleeves to get to the 2.244 final diameter , any more than that and you cut the throttle shaft bearing off of the drivers side of the TB.

Throttle blades are custom made and the shaft is thinned on these units, a gentleman on our 454SS site used to make these and I have done a few myself , not for the faint of heart as bleed holes need to be drilled (one of which is square) and lined up perfectly for it to function properly.

I have a few 56mm BBC TBI's that I run on my junk , work well and I have made well over 1 hp/CID with them on top of a good single plane.

Out of curiousity, how much interest do you guys think there would be in a "reasonably" priced 2.375" to 2.56" bore throttle body, that uses GM injector pod, IAC, and TPS? It would use the factory TBI bolt pattern but would obviously need to have the intake bores adjusted...

Care to share details on how you plan to reach that bore ?? I am curious .


TOM

[Nasty-Z]

I'm "thinking" about making a 2.375" bore TB for my 3764 intake and was curious if anyone else may need one.

If you end up actually fabricating a 2.375" bore TBI unit , you will want to swap to a single plane intake , the 3764 is a restriction with a stock 2" TBI unit on top of it .

TOM

[1BadAction]

As Tom said, it's not possible to bore a stock TB nearly that big. The one I'm talking about would be a custom machined part with throttle bores on different hole centers compared to stock. I would also be grinding new shafts. The reasoning behind the 2.375 and 2.56 sizes is mostly because I can easily get throttle blades in those sizes, but also because the increased bore makes the jump worthwhile. 2.12" (what is available now) to a custom 2.25" isn't that big of an increase for the cost, but 2.375+ might be worth it to someone who wants to run a stealthy 502+ in their original BBC truck.

I already have some preliminary models done to figure out how many operations this is going to take on the CNC, between the time intensity of the machining, and how big I can safely go with the intake, I may not even be able to do one for myself, let alone for other people. TBI throttle bodies aren't quite as simple as MPFI TBs.

If you end up actually fabricating a 2.375" bore TBI unit , you will want to swap to a single plane intake , the 3764 is a restriction with a stock 2" TBI unit on top of it .

TOM

Boring of the intake is a given, hole centers are offset two ways from stock. If the 3764 can't go to size because of it's water jacket, then it isn't worth sticking with the TBI bolt pattern. Currently, my 3764 is getting bored for the 54mm bore factory casting that I'm using on my 454, I'm just getting some measurements off of it for when I drop a 502 in the truck. lol.

[1BadAction]

BTW, I probably wouldn't even have started fooling with this CNCd TB if JimD was still doing his TBs. :( One of his would have been perfect for my current application.

[dave w]

I'm thinking there is a cost point that makes using a 2 barrel TBI cost ineffective for performance? There are aftermarket 4 barrel square bore Throttle Bodies available, most with 4 injectors. I'm thinking, 4 barrels with 4 injectors would show better performance vs. the cost of modifying a 2 barrel Throttle Body with 2 Injectors? I'm thinking someone looking for the best overall performance for the money would find outstanding performance from a 4 barrel 4 injector Throttle Body mounted on an Off-The-Shelf square bore intake.

dave w

[Nasty-Z]

BTW, I probably wouldn't even have started fooling with this CNCd TB if JimD was still doing his TBs. :( One of his would have been perfect for my current application.

He will still do them , just need to ask VERY nicely

Boring of the intake is a given, hole centers are offset two ways from stock. If the 3764 can't go to size because of it's water jacket, then it isn't worth sticking with the TBI bolt pattern. Currently, my 3764 is getting bored for the 54mm bore factory casting that I'm using on my 454, I'm just getting some measurements off of it for when I drop a 502 in the truck. lol.

What I am saying , is the 3764 is worthless to make any real power with a TBI , one it is a dual plane and two it flows no better than the later factory TBI intakes .

I'm thinking there is a cost point that makes using a 2 barrel TBI cost ineffective for performance? There are aftermarket 4 barrel square bore Throttle Bodies available, most with 4 injectors. I'm thinking, 4 barrels with 4 injectors would show better performance vs. the cost of modifying a 2 barrel Throttle Body with 2 Injectors? I'm thinking someone looking for the best overall performance for the money would find outstanding performance from a 4 barrel 4 injector Throttle Body mounted on an Off-The-Shelf square bore intake.

dave w

100% correct Dave , except where Emission compliance is concerned , the originator of the design lives in the Peoples republic of California......

Also , for me it was just neat to see the look on the dyno operators face after he chuckled at the fact it was a 2bbl TBI , he didn't chuckle after the pulls .....


TOM

[1BadAction]

Verdict is: not going to happen anyways. I think boring the intake to the size and location needed would put the holes into the cast in water jacket. Oh well, guess I'll find another way to do it or swap ECMs and go MPFI when the time comes.