I recently had a stock TB bored to 2" and am planning to bore the GM Performance Parts TBI-Vortec manifold to match. Given the cost of the manifold, I am concerned about boring into the water jacket that surrounds the bores, ruining the manifold. Am wondering if anyone on the boards has bored out a GMPP Vortec-TBI manifold. I searched but came up with nothing. If I missed the thread please point me in the right direction- Gracias. S-D

How did you manage to bore out a stock tb to 2 inches?

ShiftyCapone has bored his Performer TBI intake to 2" bores and had no problems running into water jackets. I don't see the 2 intakes having much different layouts, so I say you should be fine.

I noticed a post where Shifty shows a photo of his bored intake. There is a weird looking spot on the left bore (approximately the 1:00 to 2:00 position in the left bore). I can't tell if that is a EGR opening or a shadow or what. I will pm him.

http://www.thirdgen.org/techbb2/show...former+AND+tbi

Also, 25th, the intake was bored by Tom Bishop (eBay). I am reserving comment on the work until the unit is on and right. I should also mention that I told a big fat fib. It is not 2", it is 1.96". From now on, I call it 2" "nominal".

S-D

The holes are the EGR provisions. I am not familiar with the GMPP vortec intake but I thought it already came with 2" bores. I am almost positive it does. I know you can bore the stock intake as well as the edelbrock intake to 2".

Shifty-
Thanks for the clear pic.

It seems there are some differences between the Edlebrock and GMPP Vortec-TBI intakes.

The bores on mine are 1.75" (stock) and the EGR enters the A/F stream from the small (~0.25") holes at the bottom of the TBI bore. These holes are seen in the photo.

Photo attached:

Thanks for all replies- still wondering if anyone has bored a 2" GMPP Vortec-TBI?

Thanks-
S-D

You may want to send a letter/question/email to CHP. I believe they bored their intake on their vortec TBI buildup. They should get back with you if they realize part of their story was unclear.

shifty,

you were correspomding with the author ... do you still have his email address?

You have a PM

If either of you (Shift or Sean) have the authors e-mail and can shoot it to me, I will get in touch with him.
It would be much appreciated-
Thanks,
S-D

I see in the Sept. 04 issue of CHP, page 142, note 2, that the unit they use is a Turbocity 1-13/16" (stock noted as 1-11/16").

I don't see any reference to them boring the GMPP TBI intake.

Believe it or not, my bored TBI , when bolted to the 1.75" GMPP manifold will open and close, it just kind of defeats the purpose of having a bored TBI when the intake constricts the bore down to 1.75". There is also the chance that the butterfly could get hung up at WOT. Bad.

S-D

I bored my GMPP manifold to 2". No problem.

There is no water running through the intake around the throttle bores. Bore away!

Thanks Walter-

Damon-
I was under the impression that that the "box" around the throttle bores was a water jacket that helped keep bores at a suitable operating temp?

I will thread a piece of water up in there tonite and 2x check-

Thanks all for posting.

S-D

I can say for sure that there -is- a path from the thermostat hole, through the water jacket to the underside of where the TB mounts. I see nothing preventing water from circulating around the bores.
How old is your GMPP Vortec-TBI intake? Part#? Maybe they are different?

However, in doing this, I found that it does appear that the walls of this jacket are thick enough to handle the ~0.125" loss of material required to bore to 2.0".

Will post post-machining results-

S-D

I let this one slip for a while. I was able to machine the GMPP vortec-TBI manifold bores to 2" with plenty of meat left.
S-D

The difference in bore size by no means restricts the flow. It is the injector placement that reduces the flow. Even if there is a difference the injector hanging over the bore restricts the flow alot worse.

Like you said there is always the possibility that it will get a little carbon on it and stick.

Injectors are spaced up 0.25" to help with that. Time will tell how much it helps.
S-D

what is the GM unit rated for on rpms? it appears to be $350 at Pace Chev plus the cost to bore. A Holley Unit is 2.00 inch and is $190.00(summit) rated for 6000 rpms and has EGR. throttle/cruise cable was easy. i have photos if you like.

Do you have a part number for the Holley TBI-Vortec Manifold (summit# if possible)?
I am unable to locate it on the summit site.

HLY-300-49 out of summit catalog.

The 300-49 is for 87-later aluminum heads, not vortecs. I believe 87-later heads had the same bolt pattern as pre 87 cast iron heads. The 300-66 fits the 87-later cast iron heads.

But, neither of them fit vortec heads.

my screwup. did not read vortec!