how much can a stock shortblock take?

[DustinsDuster]

before i start, i want you all to know that im not much of an import guy, im more into domestics, but my friend is in need of some advice, and me loving any kind of car knowledge i can get my hands on, im asking for him. so please excuse me if i sound stupid with some of this. ok, here goes:

my friend has an 89 Supra with the 7MGTE inline 6 single turbo. this is where details got a little sketchy, the turbo hes got to put on his car now has aparently been reworked, has a different impeller and what not, i heard the words "60 trim" and "TOE upgrade" said a few times. it uses the stock CT26 housing. ok, from what he is told, the turbo is currently set up to run somewhere over 20psi of boost, but wanting to run on pump gas, he realizes(after i talked to him a bit about it) that hes gonna have to drop the boost a bit. im not gonna pretend i know a lot about turbos, because i dont, i have the basic concept down, but different motor designs can take more static compression than others, so thats why im asking you guys. hes having the headgasket changed, but doesnt want to dig into the shortblock yet. so im curious, how much boost could a stock shortblock take? could he run thicker headgaskets to drop the compression a bit? the shop said they could install O-ring headgaskets for a bit more money(although i thought theyd have to have the motor out and disassembled for that), should he go with that? how much hp can the stock bottom end take before he should be all that worried about it? thanks for all the help guys.

Dustin

[repinS]

I think it'd be relatively safer if he had thicker head gaskets.

IIRC, the R154 transmission (considered how much power it can take?) can take 350-400hp to the wheels. Safely, the 7M-GTE should be about the same on your plans. Don't take my word for it, though, many factors can make this safety threshold increase of decrease

[bgrieger]

The engine has to come out to do a metal gasket. Anything over 12-15ra finish and longevity becomes a bit of a question mark.

As for the stock block, the generally accepted threashold is 500 RWHP, if he keeps it a little rich. Upgrades to safely walk beyond: balance, stress relieved stock rods and new pistons (forged or hyperhueretic). That will carry him as far as anyone else has ever gone. No need to change the compression. 24psi is run on 94 octane street fuel if you richen it up a little (cool charge a bit more and cut detonation).

That CT-peashooter in any trim ain't gonna cut it beyond mid 300's (efficiently). Some enterprising souls determined the efficiency is gone beyond about 15 (measured charge intake temps) , and it is the hot side that is the restriction. There are hybrids available with larger hot wheels that bolt to the CT applications, but they are hybrids, and early models had a few problems with the internal wastegate doors. Best to look to a new manifold and a true built turbo for maximum life and power. The stock cast manifold is a bit of a restriction as power climbs.

Tranny...depends on how he drives. 700hp machines use stock 5 speeds all day, and some 300hp guys grenade them weekly. Clutch has a bit to do with it, and thrust bearings in the motor have been known not to like heavy pressure plates when starting. Bypassing the clutch safety switch is one way around the problem.

All in all, the headgasket from Toyota is the only weakness of this motor, and is an easy problem to get around. Actually, it is the torque spec. Should be 70-80 lbs/ft, Toyota says 54.

Bob