FSTPRSH

Me and some friends are in the process of rebuilding a 1983 944 from bumper shock to bumper shock. I'm needing to know what the maximum safe bore for the cylinders are. I know the tech manuals say that 100.5mm is the only option over stock, but I was wondering how far I could cut it without needing to resleeve. Or, could I actually bore the sleeve cylinders out then resleeve with over sized sleeves? I've always worked with cast iron Chevy's, so the whole aluminum thing is kinda different and I don't wanna mess it up too bad. <img src="graemlins/c.gif" border="0" alt="[ouch]" /> Would appreciate any help anyone can offer.

--Brad

Perry 951

Garrity took my origional block to 102mm without sleeves. He said that is about as big as you can get to be safe, and I have heard others say that 102mm is way too big.

Of course you will need custom pistons if you go bigger than factory replacements.

Your bore size will be determined by how out of round the bores are. I would have it machiened to round, then see what size pistons are availible. Once you have a piston close to what the round bore is, do a final boring, polishing, and silicate treatment to match the pistons perfectly.

Robby

If Garrity said 102mm, then I would listen, and I agree completely w/what Perry951 just said. There's been a LOT of debate over this issue the last year or two, and I would rather be on the cautious side myself. SFR and other's are going to 106mm, but they are using sleeves- this is the largest overall, that I have heard of for one of these blocks- 968's & S2's could go larger, since they start larger I'm sure...

FSTPRSH

Perry, just so I understand you correctly (I'm over cautious when it comes to engine building) they did NOT use sleeves when going to 102mm? I figured it up and that comes to about .076+ on the bore diameter...I'll just send Ross an old piston and tell them to use it as a template and just make it larger. But I was just wanting to make sure that's what you said, NO SLEEVES. Just out of curiosity, does having no sleeves have any negative effects on the engine? Thanks for you help.

--Brad

Danno

No sleeves also means you need to have iron-coated pistons like the stock ones.

Perry 951

To clerify, Garrity took my block to a 102mm bore with no sleeves. He ordered a set of custom pistons with the coatings and special rings and scrapers to make it just like stock.

Unfortunately, since the block was dropped off the back of a UPS truck, I will not be running that motor. Garrity said he has done several that large before without sleeves. He did not mention any problems as of yet.

I would imagine that if you went a lot larger than 102mm, you could crack a cylinder pretty easy with extra boost or a quick overheat.

A side note, and I tried to mention this above, go only as big as needed to get the bores round again. My thrust on the crank was toast, and I ovaled the bores pretty good. 102mm was the finish size and we knew we could get pistons for it. (Although the pistons took more than 8 months to arrive). Be sure that the person you select to machiene the bores knows the proper finish process and tools outlined in the factory manuals. The alumasyl needs to be treated unlike most cast aluminum, iron, or steel blocks.