88porsche928

The car did run for a week before the fuel injectors lost power. i heard a pining but not a pounding sound. From what I understand 91 octaine gas is not enough to run the current setup and i would need racing fuel if I where to use the current compression.

Giovanni

Will that be safe with our fuel tank and rubber lines though?

88porsche928

man he seemed so honest he even told me that in mid 89 they changed the engines around and thats why he had to take most of the stuff off the old block and put it on the new one. and he did mention he had problem with the flex plate.

Imo000

Did you talked to him since you found out the engine is not an S4? Also, have you compared the two block numers?

danglerb

Get all the numbers, motor ID, casting on the heads, check back with us, and give the guy a chance to fix his mistake.

OTOH seeming honest is a key skill of those who aren't.

namasgt

He already posted the number from the engine in his car. And his old block is there in the pictures in post #2 with the original S4 pistons still in the block, and you can tell from that same picture the knock sensor plug was removed to be used on the 85/86 block, since they only have one not 2 like the S4.

BC

Not long term. But once he goes back to regular gas he'll be fine. Ethanol softens rubber - it does not destroy it.

88porsche928

why didnt he just use the 85/86 cylinder heads and give me the orginal cylinder heads?

dr bob

None of the intake pieces would interchange, and as Jim B points out there are other differences around the flywheel and starter too.

Let your mechanic know that the 'change' in the S4 engines was in mid '86 for the '87 model year. The block he put in is a pre-change block from the earlier "S3" series US 32V car.

The 'pinging' you heard is what pinging sounds like. The effect is the same as pounding on the piston tops with a hammer, but not the sound. A few taps aren't usually fatal, but the continuous banging from detonation will make short work of ring lands and eventually the whole metal tops of the pistons. That top land gets hammered down to the point where it pinches the top ring. The ring woun't move any more in the groove and ends up leaking combustion gasses down, letting some more oil stay on the cylinder walls so there's even more detonation, and eventually beating the pistons and rod bearings to mush.

Comparing to the BMW with the high factory compression, the management systems on those cars is able to adjust mixture and timing over a much wider range than the LH/EZK combo in the 928, and is therefore able to compesate for the effects a lot better than what we have right now. With better FI, ignition, and variable cam timing, you could probably get those high compression numbers to work most of the time. The rest of the time it would be like pounding on the piston tops with a hammer.

Fabio421

Sorry, typo. The #'s are correct. I mistyped when I wrote S3. I meant S3pistons and S4 heads. The comp. ratio I stated was correct. I will edit the mistake above.

Vilhuer

S3 heads have casting number in them same way as S4 have. It can have ...2R ending but previous numbers are not same.

Imo000

I know for sure the '85 32Vs don't have any knock sensor at all and pretty certain the '86s were without one too. If the S4 had two then I'm not sure what that block is from?