Help with 2004 LS1 5.7 Corvette Rebuild

Hello all,

As I posted in my introduction, I know nothing about computer controlled engines, but I have a friend with a 2004 Corvette in need of a rebuild and he doesn't speak english.

I do build engines, mostly carburated small block chevys. So many things about this engine are not familiar to me.

My friend had a problem which seems to be frequent with LS1's, he "fried" pistons 7 and 8, so he needs to rebuild the engine.

we are looking for help on the engine configuration, the idea is to install a little more agressive camshaft than standard (around the 1500-6500 range), something that can be used with the original torque converter and to be drivable as a daily driver car.

The engine now has been pulled apart, the non-stock parts he already has are:

BBK intake manifold
80MM BBK Throttle Body
BBK Cold Air Intake
JET Performance MASS sensor.
removed catalitic converter

Other questions are:

So, if you could help me out with the setup it would be awesome, I've been looking in the Comp Cams XFI and XFI RPM cams families. The idea would be to buy a complete (K) kit.

options for cams, pistons, injectors, etc would be welcome.

thanks in advance.

We finally went for the following:

Comp Cams XR275HR complete kit
36 lb/hr fuel injectors
Mahle LS1314898F04 flat top pistons


any advice or caution about this setup?

I've never heard of "frying" pistons 7 & 8 as a problem that frequents the LS1.

I would recommend replacing the Jet mass air flow sensor with the stock GM one. Aftermarket MAFs are notorious for causing problems with the LS1. You will also want to make sure to have the car "tuned" before startup, meaning proper adjustments are made to the PCM. Frost - a site sponser - is very well known and recommended for his mail order tunes. He can get you close, if you don't have a local shop that handles tuning, so the car can be started. Otherwise, have a shop tune it for the componants you've installed.

frying piston 7 or 8 is common on ls1's and is usually due to pre detonation or running lean. the mahle pistons you selected arent a bad choice I didnt have luck finding them on google but mahle is a good brand and actually supplied the original pistons for the ls1 to gm.

The only thing I am going to address here is your cam choice. It looks like its 222/224 with a 112 lsa honestly that cam is pretty tiny for an ls1 usually people go atleast 224/224. The average would be around a 228 duration cam you can keep good street manners with a 228/232 cam and make much more power than a smaller grind. However I can assure you with the stock converter your friends corvette will probably slower with the stock converter and the cam you selected. Ls1's are under stalled already and will pick up around .7 in the 1/4 with a 3600 stall (good size for a stock motor) add in a cam that moves the powerband further up and you will get a car that will push through the brakes at a stop and will generally be a dog down low.

My advice is if you guys must keep the cam you have then get a 3200 stall atleast for the car and call it a day. If not then tell us a little more about the car and we can recommend a better cam choice and perhaps a 3600 stall. Also you will need new springs and pushrods. Standard hardened pushrods from comp or texas speed will be fine. and if your going tokeep the cam under 235ish on the duration and under .620 on the lift I'd just do a good beehive like a pac 1218 or pac 1518. Just stay away from comp 918's the had a bad batch a couple years back where they were always breaking under use but I've seen quite a few since then that have still been breaking and destorying engines.

You might want to think about getting some pistons with a -2cc valve relief. That way you can shave the heads a little and pickup some compression!. Thats a power across the whole powerband. If he put the Jet MAF on without a tune then thats probally what leaned out 7 & 8.

No need to have valve releases unless he mills them way down and uses a big cam. A cam specd in the ballpark of 228/230 with under .600 lift should have no issue clearing flat top pistons. Milling .04 off the heads will yield 11:1 compression and really is the max you can take off with running into problems with the intake not bolting up. Even at that height I still don't see where you would need valve reliefs with a med size cam. As always check to be sure though.

Thanks all for your replies, the parts I listed is what we had bought, so we can't change anything there now. (sadly, my original message was up for a few days before somebody answered).


Knight: thanks for the advice about the sensor, as far as I understand the original one was back in place already.

redbird: we got a complete set from comp cams which included the cam, pushrods, beehive springs, timing set, etc. My friend likes to do some rolling and "high speed highway races". It will still be his daily driver and grocery getter.

PFM: as far as I understand, valve reliefs on this pistons are 4cc's


Parts arrived in Chile yesterday, parts are at the shop and I hope my friend can get it together in a couple weeks. I really hope redbird555 is wrong about the car being slower! But it shows me that I need to learn a lot about LS1's, as I can see the cam selection is WAY different to what you do for a Gen I small block.

I will keep you updated and thanks for your help.


any comments about the injectors selection?

I'm sorry man but that car will need a stall. Ls1's in stock form will benefit .5 secs or more in the quarter due to their higher revving powerband. By putting the larger cam in there you ill have to raise the idle a tad to get it to want to idle good which will make it want to push through the brakes a bit and the cam will also push the powerband even higher making the stock stall even more inefficient.
I bet the car may gain a mph or two in the quarter but will run slower because it will bog off the line and drop to many rpms after shifts.... Sorry man but thats the honest truth do some searches on here or other ls sites and you'll see everyone either does a stall before a cam or with a cam. A 3200 stall or higher would really compliment that build and to put it all together now only to take the tranny out again to put a stall in it sounds like a PITA. Circle D, PTC, and Yank all make budget converters around 400 that would work great for that build

thanks redbird555,

I have discussed the subject with the car owner and he will "see" once the car is on the streets. Sadly he is rebuilding the engine at some other place, I just helped him to select the parts and brought them down to Chile.

Looks like I will still have a shot to beat him with my old Camaro :P

i just put a 3600 stall in mine and tis a night and day difference. spend the extra cash on the stall now or spend alot more later when that cam kills the stock convertor now.

Well, I messed it up.

Found out "the hard way" that there are different tastes for the "5.7 LS1" engine for 2004. I bought pistons with .927 pin diameter and the engine happens to be "the other one" with .945 pin. We knew it was a "switch" year, but some sellers refer to it as 2003 and some others to 2004.

I bought now a set of standard replacement hypereutectic keith black pistons from summit.

I finally convinced the owner to change the stall, it will be done in a couple months though.

If anybody needs a mahle set of forged pistons with a .927 pin diameter down in Chile, let me know.