When Spoolin and I put his engine back together after his 'methanol incident', we left the pistons as they were, melted crowns and all lol. That was 7 years ago. He doesn't really drive it much, but it still runs fine.

I try to stick to stock parts as much as possible for the oiling system. But at 7500 you're probably better served by aftermarket stuff. Especially with high lobe lift/high valvetrain loads. If you really want oil pressure, the high volume GM pump is gnarly. I currently run one, which I found is excessive for my setup. High RPM is always 100psi+, overflowing the bypass I assume. Even on 0w20 oil. But doesn't seem to be causing issues, even with the turbo.

 

opinion time! Is it worth $900 to replace the dinged up pistons to drop compression from 10.39:1 compression to 9.44:1 compression? I run pump 93 with meth injection and plan to pour more boost to the engine. I was running 13-14lbs boost before the chain let go.

also, if anyone is bored, would you mind confirming my compression calculations?

bore: 4.030
Stroke: 4.0
Rods: 6.125
piston cc: -10
comb. chamber cc: 68
ls9 gasket: (.054/4.10?)
deck: 9.232

 

I just got off the phone with TSP and they said to go with the high pressure pump and not the high volume unless i have an 8qt pan. He said the HV would suck a 6qt pan dry. anyone ever seen this happen?

 

Hmm...maybe if you're running heavy weight oil and its cold. I have not had this happen with my 6qt pan, however I always let my engine reach operating temp and get some heat into the oil before beating on it.

 

I get 10.50006 assuming your piston/rod combo puts piston height at zero on stock deck height (ie 0.008 out of the hole)

Hard to say on the pistons without seeing them but gut feeling is they will be fine as long as they are not fractured and the sharp edges on the dings are smoothed out.

I have heard of oil starvation with high volume pumps on stockish bearing clearances and stock pans running at high rpm for prolonged periods of time. Since you are not road racing, I doubt this would be an issue for you considering the setup. However I also don't feel you need a high volume pump either unless you intend to open up the bearing clearances from what you had.

 

The calculator I used uses a formula to determine the Piston/Deck. it calculated .003. If you still have it up, what do you get for a -20cc piston?

 

For -20cc pistons 0.003 out of the hole, I get 9.447:1. FYI, that is very close to my 371 @ 9.480:1 When I originally spec'ed everything out, heads were supposed to be 68cc for 9.68:1 with 11cc pistons but were built with 70cc.

BTW.. my spreadsheet calculates the same as yours with 0.003 out of the hole on 10cc pistons at 10.38857:1. If you weren't having any detonation issues previously and you don't intend to increase the boost, I would stick with this setup.

 

You just Idle around the neighborhood so that doesn't really count...

 

I didnt intend to increase boost from 13-14lbs because the top ring gap was only .019. I intend to open the gap and pulley down

 

What is your current pulley ratio making 13-14psi?