Fast 95 Z28

Looking to buy some TSP PRC Stage 2.5 5.3L 62cc heads for my 2000 Z28 with a bone stock LS1. Will the car still run fine on 91 pump gas or will I run into detonation problems at sea level? I currently live at 4500 ft though. I'm assuming this will put the engine around 11.1 compression.

Thanks

Fast 95 Z28

Has no one slapped aftermarket heads on a stock engine before? Or does everyone do heads/cam at the same time?

G Atsma

Go use Summit's compression calculator to find out where you are compression-wise.

65lsx

My heads are 60cc with 11.8-1 compression and it runs fine on 92-93 octane.

grubinski

Depends on the IVC closing event (at .002" lift, not .050"), and also on the altitude. 4500 ft. will help the car tolerate a higher CR ... until you take a road trip to sea level. Later IVC helps lower dynamic compression.

I run 11.8:1 on my car, the Wallace Racing dynamic compression ratio calculator has me at 8.7 or 8.8 DCR. I've been running at sea level with 92 octane, no problems.

Fast 95 Z28

The car has the stock 2000 LS1 fbody cam 198/208 .500' lift. I did enter the info on summits calculator and depending on how far my piston is out of the hole from .005"-.010". The compression would either be 10.98:1 or max of 11.12:1, with a .051" stock headgasket.

Fast 95 Z28

Does anyone happen to know the IVC ABDC of the stock 98-00 LS1 cam? I'm trying to figure it out and its not making sense on the dynamic compression that the calculator is giving me. Its up around 10.7:1 which is way to high for pump gas.

grubinski

Cams with 'fast' ramps typically have around 25 degrees of ramp on each side from .002" to .050". If you can't find the .002" number, adding 25 degrees (or 27-28 for a factory cam, probably) to the .050" number should get you in the ballpark.

Fast 95 Z28

Hmm doing my math with that added 28, is still putting a stock LS1 at 9.0:1 DCR. After reading some prior forums, Pat G had mentioned the stock DCR for a 98-00 LS1 was 6.97:1. Can anyone else confirm this? So, if I understand this correctly going from 10.2:1 SCR to 11.1:1 SCR would increase my DCR from 6.97:1 to 7.87:1? Which should be plenty suitable for pump 91 still since I've read 8.5:1 DCR is about max for pump 91.

grubinski

I confirmed on the Wallace Racing website, which says you'd be at a DCR of 8.97:1 with the stock LS1 cam (198/209 119.5+2.5 LSA, according to what I found online) and 11.2 static CR. This cam has an IVC of 36 degrees ABDC at .050", so I added 28 to get to 64 ABDC for the IVC at .002".

According to the Wallace Racing calculator, it looks like the static CR has to be 10.8 or so to keep the DCR under 8.7:1.

I'd suggest running a thinner (.040") head gasket and adding a few cc to the chambers. The thinner head gasket will improve quench, which helps prevent detonation.

Using the stock static CR of 10.2:1 for the LS1, I get 8.19:1 DCR.

Bspeck82

Probably a bit tight for pump but the car will pull timing if it pings anyways.

Bspeck82

Those heads will want some cam anyways. Put a small street cam in it and run it. You'll have to tune anyways