BC

Doing some re-thinking here on what I want to do with the engine and in what time frame.

Kinda getting tired of driving a chevy - I'm thinking about maybe speeding up the process - MAYBE.

I will still sleeve a block to 106 and use a stock crank, forged rods from the 944 (or early S4 or whatever other 928 had them), and custom JE pistons built to 9:1 compression.

BUt I could also just put this block together with the forged rods that I can get, and put the original pistons back in (maybe shave them ala Tony), and slap a Murph supercharger on, and have 500rwhp SOONER then my 650 or more with my more robust buildup.

Here's the catch - My cylinder walls are ALMOST perfect still at 75k, except for a few SCRATCHES. These scratches are what started me on the quest to do a different engine bore material, (as well as wanting a 5.6).

This below is the driver's rear cylinder bore. I can catch my finger nail in these.


This below is the passenger rear bore. I can also just catch my finger nail in these.


So anybody put together an engine with these scratches and have bad leakdown?

Mongo

I would definitely bore and steel sleeve that engine to support the supercharger. with 9.5:1 compression on the build up, you can run more boost on the supercharger. I haven't seen a Murph setup before but do they have an intercooler? If so, I'm sure you can run a high boost on the car, probably around 10-12 psi and get away with it if there's an intercooler to keep the charge temperature down.. Take your time on your decisions as well as on the engine, so it will surely be a durable heartstopper.

Good Luck

Andy

BC

The current murph-charged people have between 8 and 14psi I think, and none of them have sleeves, and all of them have whatever compression the 928S4 MAY be in thier year, thogh many think its down around 9.5 or less to 1 anyway.

Yes, all murph's kits have big intercoolers.

I'd probably go to 15psi or so if I slapped it back together stock. I was going to do 20psi if I sleeved.

heinrich

Well, I am no engine guru Brendan, but seems to me, if you're going to put it all back together with those scratches, you may want to just drive it and not load it with a supercharger. No?

Mongo

BTW anyone know if the cylinders are NikaSil coated from the factory like on the 944s???

Andy

UKKid35

If those scratches are significant then my engine must leak like a sieve

BC

Stig - the cylinders are ALUSIL. A process that uses a special set of pastes and felt pads that wear back the aluminum to let the silicon in the aluminum stand proud, microscopically. Thats what the rings slide on - silicon crystals. Quite a good idea.

BC

...Well thats the thing. I don't like the idea of doing it half assed. If these scratches will represent some sort of leak down issue, then I will continue with my plan and simply not be able to drive my car for a longer time. But if I put this together stock like this, I will get the murph kit during this time and drive it with a stock engine at about 14 or 15psi. At the same time I will slowely build my other engine.

Mongo

the scratches could get worse and you could have oil blowing by the rings eventually and a compression loss. Do something about the scratches definitely.

Andy

Jim bailey - 928 International

Brendan I believe your engine ran well before you took it apart it should run well if you put it back together . It would be nice if there were no scratches BUT nearly every engine we pull apart has some . It would have been interesting if you had done a leak down prior to taking it apart . The scratches are not that significant in my opinion . It really matters little if you might be down 2 % in power and have slightly more oil consumption than if " perfect " .

BC

Yeah my engine ran great before I took it apart for no real reason.

It put down 276/291 hp/tq in 2000 at a dyno meet in Chicago.

The LH that died that I sent to you Jim didn't just "die" - it had to have been "dying"

Oh - and the EZK that I sold as well turned out to be *1986* guts in the 89 EZK with a BAD chip or two, per Walt, who was the unfortunate buyer of that unit.

What kind of problems did these units cause that I never really noticed except for some slight loss of power going past 4k SOMETIMES? IT never lasted but a split second, and never happened repeatedly.

Tony

Four letter principle : "KISS"

Throw it all back together with some stock machined pistons yielding 8.7-9.1:1 CR, a good multi layer gasket, new gaskets, bearings, seals where applicable , run low teens boost and be done with it all. Put the money you save into a rear fender project so you can run 315s and add LSD

The sleeving is an ambitious project with many unknowns on this motor, but if those scratches are the reason for sleeving, save your money. IMHO. I thought you had a toasted block or something? I found a couple of scratches in my cylinders and assoc piston skirt but the great thing is, i did a leak down prior to tear down and the strongest cylinder was the one with the scratches!! ..so go figure!!

Chris

So here is a thought, there would be far more leak coming from the end gap on the piston rings than there would be from one tiny scratch. True ?

Chrus

BC

I love it that your so positive Tony. And your pilot, which makes that fact so much more....uplifting.

I wanted to sleave to have a 400hp NA engine that could take 20psi of boost before I even PUT the supercharger on. Its a good plan. I'm just getting REAL tired of having to NOT drive this car!

How much was it to machine your pistons?

I would still do the motor I want, but it would be DURING the driving of the current car.

BC

As that blue tractor thing in "Bob the Builder" always says:

"Um, I think so!"