burnt pistons!
 

what causes pistons to be burnt on the only on the intake side of the pistons? a little on to top, most on the top of the first compression ring. could it be timing? fuel? or ring did not seal properly?

Re: burnt pistons!
 

thats where the detonation started

Re: burnt pistons!
 

yeah but not always detonation - it could simply be over heating. But yeah if its wrapping around the ring land area thats knock potential and thats when you start breaking ----

Re: burnt pistons!
 

Most of the time when you melt a piston, it starts on the intake side. usually you have had high EGTs and prolonged detonation. High speed highway runs + lean condition + high EGT's = Fail. Turbo Mr2's are the worst for it. They have shitty intercoolers and poor engine management to begin with, toss in a half dead knock sensor and there you go.

Re: burnt pistons!
 

no pings what so ever. egt is around 1500f fullboost. afr is 11 at fullboost. its a toyota 4agze turbocharged with greddy emanage ultimate, walbro and 750cc. could it be over rich mixture or oil goes to the side of the piston and heats up?

Re: burnt pistons!
 

By chance, did you put the engine together yourself? If so, what sort of piston-to-wall clearance did you have?

I ASSume this is in an FX by your screen name. ------- sweet. At this moment I own an 87 MR2 and an 89 Supra thats in the process of a 2JZ-GE swap.

Re: burnt pistons!
 

i'm not the mad scientinst, but i don't think you can burn pistions up with a rich a/f ratio and no detonation.

and usually the hottest part of the combustion chamber is the exhaust valve. intake valves have the air charge to cool them off as air enters the cyl. exhaust don't have ---- to help cool them. i've always read that the exhaust valves are a good place for the preignition to start at, but never heard about the intake.

do you have any pictures of said pistons?

Re: burnt pistons!
 

yes i did build the engine. as far as i could remember piston to wall clearance is at 0.004in with the stock 4agze pistons.

its an fx 16 front on a sedan. still tyring to find out what happened. to make the story short. it was on the dyno. made 291whp 240tq lb. on like the 12th run. sunddenly stop. the sleeves gave. ok. no bent con rod. only the number 3 cyclinder gave. but i cant understand why all four piston are burnt on the intake side part.


picture will follow soon.

any inputs.

Re: burnt pistons!
 

burnt, or just carbon build up?

Re: burnt pistons!
 

Ugh. Thats too tight for that kind of power. Factory wants quiet, smooth engines. We want loud, reliable ones. 0.004" is too tight. Thermal expansion owned your piston. That sucks. Bet the skirts are gauled up pretty bad huh? Id say you might have had a tuning issue, but im willing to bet the lack of clearance was the real problem. You see it all the time in the 2jz-ge N/A-Turbo cars, they bust around 350hp and the pistons are done. The piston-to-wall wear spec on a 2jz-ge is where the tolerances start on a GTE. 4A-GZE is the same 7rib block as the GE, with dished pistons. Get the idea?

Nice power though, get some pics up here.

Valve temp has little to do with the piston's ability to transfer heat from itself. Every engine Ive torn apart that melted a piston, started on the intake side.