So i would like to buy a spread bore, vortec, intake manifold and bolt a BB-TBI unit onto it. My concern is that BB-TBI units have 2" bores, and i cant seem to find any information that would indicate the size of the secondary bore of a spreadbore manifold?

Has anyone installed a BB-TBI unit on a spreadbore manifold before? I realize a simple adaptor will be necessary, but i would like to avoid having to bore out the manifold, or weld in new material.

-Zander

 

Spreadbore as in a quadrajet carb? It will have 4 holes and you're trying to adapt a TBI with 2 holes on it. You're going to need an adapter and boring out holes isn't an issue.

The BBC TBI, although it has 2" butterflies, it also has a slightly larger bolt pattern than a SBC TBI meaning it isn't a direct bolt on swap to a SBC manifold and it isn't designed for use with SBC TBI adapters.

If you want to know the bolt pattern of a q-jet carb, go to PNP and take a q-jet carb gasket.

 

I can use an adaptor like this one

http://store.summitracing.com/partdetail.asp?autofilter=1∂=TRD-2207&N=700+115&autoview=sku

from transdapt, but it will all be for nothing if the holes in a spreadbore manifold are too small to allow the 2" butterflies to open all the way. obviously i will try to center the BB-TBI over the secondary bores in the manifold, as they are much larger, but are they 2"?

-Zander

 

I believe that adapter might use the smaller bolt pattern SBC TBI and may also have the smaller butterfly holes. It doesn't specifically say it's designed for the BBC TBI but the wording of the description seems to indicate it's designed to use the OEM TBI on a Q-jet manifold when you do a BBC manifold swap.

That adapter positions the TBI over the secondary butterfly holes. The Q-jet uses 1-3/8" primaries and 2-1/4" secondaries so the 2" TBI butterflies will never touch the sides of the holes in the manifold.

 

Excellent, worse case scenario is that i would have to have a custom adapter plate machined. So given that q-jet secondaries are 2-1/4" diameter can i assume all spread bore manifolds have openings large enough to fit a q-jet? Obviously other manufactures make spread bore carbs with different sized bores. Of course manifold manufactures like edelbrock only "recommend" the use of their bars with their manifolds. Is that just a corporate policy or do edelbrock spread bore manifolds not fit q-jets?

Are you sure that the bolt pattern for the BB-TBIs is different from the SBC variant? I dont have a BB-TBI unit (yet) so all i have to go on are pics from transdapt and summit's website. Check out the two pics below, both adapt TBI to spread bore, the one listed as intended for a big block looks to have larger diameter bores and, judging by the position relative to the spread bore mounting holes, the same TBI bolt pattern.

What do you think?

http://static.summitracing.com/globa...trd-2206_w.jpg
http://static.summitracing.com/globa...trd-2207_w.jpg

-Z

 

I have a 91 454SS with a TBI. I bought a TBI riser plate (carb spacer for TBI) that was for a SBC TBI. The butterflies fit but the bolt spacing wasn't the same. I had to drill out the mount holes in the riser plate to bolt it onto the TBI manifold.

Just did some searching. This is the adapter you need Transdapt 2207 adapts a BBC TBI to a q-jet manifold. http://www.jegs.com/i/Trans+Dapt/969/2207/10002/-1. This puts the TBI at the rear. You can also use the 2209 http://www.jegs.com/i/Trans+Dapt/969/2209/10002/-1 which puts the TBI at the front.

The opening in the manifold is never an issue with the butterflies. The picture in the first link, you can see the size of the opening from the q-jet gasket. Even the q-jet butterflies never get close to the manifold. The inlet on a carb manifold isn't like the inlet on a TBI manifold.

 

I bolted a BBC 454 TBI unit right onto a SBC intake manifold that I bored to 2". The BOLT patter on both units is the SAME.

There are TWO factory TBI-Spreadbore adapters floating around out there too. One for a TBI 454 Truck and the other for a Marine application.

 

Thanks Stephen, that the adaptor i suspected i would need.

Fast355, I would do the same thing, except that only GMPP offers a TBI manifold with a vortec intake pattern. And there is no way i'm going to pay my local dealership $500 for a manifold, that's highway robbery. Thus my solution is to use a spreadbore edelbrock performer, with an adaptor plate, and a 454 TBI.

-Z

 

You could definately do that. Although I have run the adapters, I personally like the Mercruiser Crusader TBI Vortec intake manifold for a daily driver. Those engines ran Vortec heads and 2" bore 454 TBI units as FACTORY equipment. The "MARINE" roller cam they ran is now being used as the Ramjet 350/HT383 cams.

 

That manifold is exactly what i have been looking for! So where can i get one? Summit and eBay searches yield nothing.

-Z