Stock 4g with mpi

[niss720]

Hey I was searching to see what people have found the max power a sohc 4g63 will make on standard pistons. I found a thread from tomsun from back in 2004 but it didn't really go too far into it!

Can any one help me with what sort of power to expect with mpi and what max boost and revs it would handle on stock internals.

Thanks

[thrash]

I have no practical experience in this, so this may just count as internet rumours, but when I purchased my first starion and was doing research into this, it seemed that the max power to expect from mpi on a stock motor would be around the 170 rwkw mark.

I cannot remember if this was with or without a cam - I have a feeling adding a ralliart copy cam or similar allows for a little bit more.

Max boost on stock pistons should be about 1 bar with an intercooler to be safe.

My old car used to run 11psi with no supporting mods, not even an intercooler (this was not on purpose, we just measured it with a calibrated boost gauge one day). It ran fine like this for the entire period of time i had it working, which was a few years. It had a damaged crank key groove from when i first bought it, so the timing would have been off every now and then, but it still didn't blow up on 11 psi, so the sohc are still not overly weak motors. The motor is still running fine now with the crank replaced in robert26t's car.

[thrash]

http://www.beyondthelimit.com.au/

talk to these guys, they seem to love their sohcs, and have a number of high powered builds completed, so they would probably be able to give you a very difinitive answer on where the limits of the oem stuff lie.

[4gpwr]

boost or power will not hurt pistons , detonation breaks pistons

[niss720]

Yea thanks for the replys, i will be getting it tuned properly I just dont want to push it too far as it will be a daily, was hoping for maybe 150-170kw and 6500rpm.

[enthuzed]

boost or power will not hurt pistons , detonation breaks pistons

Well said!

[redzone]

Normally i'd agree with 4gpwr but cylinder pressure also breaks 4g63 starion standard pistons, if you want it to live then don't go over 15psi & get a really good tune. Rad was running 18psi for years with a very good tune & ceramic coated pistons.

The stock starion pistons use very thick rings with very thin ring lands which break off easily. The favoured dohc type pistons use thin rings & thick lands, which explains why even cast dohc pistons will take a pizzling...