12560688....that is the # cast into the manifold that I have, NO-ONE has been able to tell me what this came off of and the only reference I have been able to find is on NHRA's tech spec web site relating to allowable parts for the '00 Chevrolet/Pontiac engines, and GM has been no help because they have NO part that matches that # !!
The circumstances behind me recieving this manifold were kinda strange too, I didn't explain it in my other post but a friend of mine bought it off of ebay day before yesterday (he hasn't even recieved it yet), he realized it was an LS1 manifold after he had bid on it an so he decided to give it to me as a late birthday present (only a month late), he said that the guy he bought it from used it on a flowbench to test LS1 head porting with a stock manfold

is this some kind of race-only manifold or a flow-bench only manifold ??

here is a picture of it....


I'm also going to double post this in the Truck Peformance section...sorry for the double post , I normally NEVER duoble post but I REALLY need an answer

 

That is a 98-00 F-body LS1 intake. You can tell because it has the EGR provision on top, right behind where the T/B would mount. All 97-00 LS1 Vette manifolds do not have EGR, and all 01-03 F-bodies and Vettes, both LS1 and LS6 use the LS6 intake and do not have EGR. Hope he didn't pay too much for it. They are not worth a whole lot.

 

he paid $11.95 for it.....
My MAJOR concern is: Will I LOSE power if I switch from the truck manifold to the LS1 manifold ??
Also, is it possible to port this manifold to improve mid-range flow??, and can the EGR port be blocked off??, because when I have my LS1Edit tuning done I am having the EGR deleted

 

Couple guys in our Truck section are or have done this. Moving this thread over there.