Larger factory TBI? - SOLVED

[cdoggwsu]

OK, question for you TBI gurus. A few years ago a buddy of mine had an '88 K5 (5.7L) and I helped him install a TBI that he said was bigger than the stock TBI. I seem to remember something about the stock being 340 cfm and the new one was 370 or something. I have no idea where he got this thing from but it did come with wiring instructions and stuff. We put in a TBI spacer as well because the butterflies on the new TBI were too big for the stock intake manifold. Was there ever multiple sizes available for the 5.7L or did it come off of a different engine?

 

[b454rat]

They were bigger than 340/370, IIRC 670. Still not large enough if you have a healthy motor. 454s use the bigger TB, they will bolt on to a 350, but looks like you already found out what won't clear...

 

[cdoggwsu]

Yeah I thought maybe it was a 454 TBI. I think those are the oval-bore too which might account for the need to use the spacer.

 

[NEK5]

They were bigger than 340/370, IIRC 670. Still not large enough if you have a healthy motor. 454s use the bigger TB, they will bolt on to a 350, but looks like you already found out what won't clear...

I actually believe they're 590 CFM. I`m sure Thunder will chime in eventually...

 

[Thunder]

Stock SBC TBI flows aprox 500 CFM 1 11/16" bore

Stock 454 flows aprox 670 CFM 2" Bore

Need the adapter plate to bolt 454 TB to SBC manifold. Or have the manifold bored out to 2"

Holley sells a 670 cfm TB which will work on SBC with the adapter plate.

You can get high flow TBs here:http://www.xtremefi.com/
and here: http://www.strokerengine.com/TBIkit.html

IMO it is better to use a bored 1 11/16 SBC TB, than a 454 or Holley TB on a SBC.

 

[cdoggwsu]

Now that I think about it I believe it was the 670 I was thinking of, not 370 as I stated before and it was a factory part so most likely not the holley. We used a knockoff TBI spacer and ground it out with a dremel for "proper" fitment. Anyway...glad to get it sorted out. Thanks Thunder and all for the replies!

 

[BGKYK5]

IMO it is better to use a bored 1 11/16 SBC TB, than a 454 or Holley TB on a SBC.

Why? Is it hard to get the 454 TB to work right on a SBC?

 

[cdoggwsu]

Why? Is it hard to get the 454 TB to work right on a SBC?

If it was in fact a 454 TBI that we swapped on, it wasn't hard at all, just used the TBI spacer as an adapter (the 454 TBI is a larger bore) and wired up a different sized injector harness. We put in an MSD 6AL when we did it, but I would assume the factory ignition would be fine.

 

[Thunder]

Why? Is it hard to get the 454 TB to work right on a SBC?

454 TB have different IAC connection, No provision for the TV cable if you have a 700R4. 2" bores require an adapter plate or boring your manifold. Depending on year of TB the TPS connector may need to be changed. Depending on year of TB idle air passage will not seal right requiring grinding out the passages the get the idle air equal to both sides if the intake.
The Holley 670 cfm have all the right connections to hook up. But need the adapter plate and usually need a lot of playing around with the fuel pressure to make them run right. Even then they get bad fuel milage compaired to a smaller TB.
Most TRUCK SBC, even 383s AND 400s, dont really need a 670cfm TB.
A bored 46mm TB flows aprox 600 cfm. With the right fuel pressure and or bigger injectors that is plenty big enough for any SBC that does not see much time over 5000 RPM.
They are an easy plug and play install Plus you will keep good fuel economy. But you should get an adjustable fule pressure regulator to get the most out of it.

If it was in fact a 454 TBI that we swapped on, it wasn't hard at all, just used the TBI spacer as an adapter (the 454 TBI is a larger bore) and wired up a different sized injector harness. We put in an MSD 6AL when we did it, but I would assume the factory ignition would be fine.

If it came with the instructions wiring and spacer it was Prolly the Holley TB. They are a fairly simple install but IMO are overkill unless you have a very healthy build on a SBC.

 

[cdoggwsu]

Err...what he said...

Once again thanks for the great info Thunder. If that's the case than it must have been the Holley. It probably was overkill and as far as I know it did nothing to the performance of the motor but it was something to do .

 

[BGKYK5]

Once again thanks for the great info Thunder.

x2!