I bought a HSR kit from someone and they dont know the part number but are pretty sure it is the 7540. The only things I was able to pull off it was 701R-126 on the lower intake, 701R122 on upper intake and a casting date of 6/16/03. I am bolting this onto a ZZ4 shortblock with Trick Flow TFS 30400002 heads (perimeter bolt style) My car is a 91 Z28, which had centerbolt style heads. I just want to make sure that these heads,block and intake are going to be a match before I start bolting things up. Doing a rought test fit, it appears everything lines up correctly. I am unclear as to what the difference is in the 67-86 heads and the 87-95 heads. I know the 7542 is for vortec heads. The difference between the pre 87 heads, 87+ heads and vortec heads confuses me. Basically I need to find out what intake model I have and if it will bolt up to the pre 87' perimeter heads I have and my ZZ4 shortblock. I thought I was ordering centerbolt heads but these arrived instead. Any reason I cant use one or the other or a reason I would want to choose one over the other? Thanks in advance... -Ray

pre 86 heads are perimeter bolts 87 and up to 92 are center bolts our cars never came with vortec heads the vortec heads only use 8 bolts to bolt the intake up as where reg heads use the reg 12 hope that helps pre 86 heads use intake bolts that are all the same direction 97 -up use the 4 bolts closest to the center at a different angle but alot of intake companies make them so they fit both ways u would just have to get different valve covers since your center bolts wont work anymore

Is there anything about my HSR I could look at and see "hey this must be the 7540 non-vortec one because of blah blah?"

the center bolts on my HSR are elongated, from what I can find, they did that on early castings to make it work on different head types.

nevermind, I think I got my answer by doing some searching. The vortec style intake only came out in mid 2005 and mine has a casting from 2003.

Also, it only has eight bolt holes provisioned for the vortec heads while my intake has 12. So I def have the 7540 non vortec intake.


Now my final question is, given that I have the 7540, which is said to work with 67-86 perimeter bolt heads and ALUMINUM 87-95 centerbolt heads, is there a reason why I would want one style over the other on my 91.

My car came with centerbolt obviously, what I got from Summit was 67-86 perimeter bolt Trick Flow heads. Playing devil's advocate, is there any reason I would want one style over the other in my car?

I must say that being able to run perimeter bolt does give me some much better valve cover options. Like these for my Ultra Blue Metallic car:

the only difference is gm changed the design that's all the centerbolt's i think seal better other then that that's GM 's decision and i was gonna say just count how many intake holes u have good luck

no real difference. there are a bunch more aftermarket products for the perimiter bolt valve covers over centerbolt. both seal the same. centerbolt valve covers require narrow body rocker arms tho. and i believe self aligning as well. unless you are gona use guide plates then u cant use self aligning rockers. if u use centerbolt valve covers ur have to use narrow body rockers and prob self aligning unless u use guide plates then regular narrow body rockers work. if u use perimeter valve covers u can use whatever u want but might need self aligning but u dont have the prob with the centerbolts needed narrow body rocker.

the prob with your intake is that its a 2003 is that its the older style HSRs vs the newer believe after 2006/2007. they fixed the sealing problem with the larger intake gaskets like the 1205 vs the 1206, they fixed it by adding alot more material to the intake sealing surface. allowing porting and the use of felpro 1206 intake gaskets for 195cc and larger heads. u wont be able to do that with yours, if u need a 1206 then u need material welded/added to those areas inorder to be ported.

they also fixed some other things i believe. elongated the center bolts more for use of more/different styles of heads. i believe the older style "yours" has a problem when bolting to newer style heads. and u need to get a angled bolt washer/wedge to correct this for the center bolts.