GregBBRD

I'm not sure what the grey coating on the Ross Pistons is (I didn't do it), but it didn't keep the pistons from digging into the bores and turning both into trash. It may indeed be Krylon. Worked like it.

BTW--There is a set of rods that were attached to the crank. i could measure them, if anyone gets interested. Pretty sure they are Oliver Rods...I would need to look.

Yes, the crank thing is just a personal issue between Scat vs. Moldex.

greg brown

BC

We need to find out what grey coating it was guys. This is important. Lindsey racing has done Wiseco pistons with swaintech PC9 coating in alusil with no problems.

If this was a non-solution, we need to know what it was.

slate blue

I would like to know what the personal issue is scat versus moldex? Also the 6 counterweight versus 8. Personally I know I have got myself out there but I went with 8, the reason being high rpms that this engine will turn and maybe any other later 4 valve engine I may build with it. The fully countered weighted engine have better balance and should cause less harmonics/flex in the engine.

I am aware however that Nascar and Supercar guys use the lighter cutdown cranks, they do change their cranks more often than I intend to, which is never. I would also hope that my Honda journeled crank despite its 8 counterweights will be lighter than the ones with cut down centres.

The coating I am commited to is Ferroprint by Mahle, that with low expansion pistons and a decent rod to stroke (1 to 1:75) should hopefully not cause excessive wear on the skirts, time will tell.

Greg

GregBBRD

Not sure we should be telling Scat/Moldex stories out here in public. Scat might not like it. I guess I could give someone (or 8 of you) a piston to have checked. Or you could do a bit of detective work and ask the guy who built the engine the first time.

greg brown

Louie928

I've got a set of Wiseco 104mm pistons & rings to use with stock S4 crank and rods. They are coated with a dark grey coating that's about 0.001" thick. I got them from a central California 928 developer (not Devek). I've been afraid to use them. Would this coating be similar to what was on the pistons from this engine? I don't know what the coating is. Posssibly from Swain.

Mike Simard

Something that may be a factor in these trashed piston skirt cases could be the edge break at the bottom of the cylinder bore. It's rarely considered and many engine builders think a minimal edge break is desired for oil control. A stroker has the skirt poking out of the bore even more and if the piston rocks at a greater angle than the edge allows it's going to scrape. I've even seen that on non-928 stroker builds that don't have materials issues, in one case I scrubbed the edge with a bunch of 400 grit but after a teardown you could still see gouging on the bottom of the skirt. IMHO a big, gentle edge break is desired. Greg, do you have any thoughts on this?

Vilhuer

Can 928 pistons even come below bottom of bore as some of the 360 degrees is blocked by block?

Rick Carter

Why not use pistons forged from 4032 alloy with Ferrocoat? At least this has been proven to work. An interesting read, scroll down about half a page: http://www.freepatentsonline.com/4395442.html

atb

When I told my local machinest that I was using a Scat stroker crank, he said to make sure that turns true. He has had Scat cranks come out of the box "bent". Have you seen this issue Greg?

brutus

From what I have seen Scat makes a number of cranks from various materials the basic chevy small block crank is made in China by chinese machinists using Chinese steel and quality control is suspect.

GregBBRD

I have not seen a Scat crank for a 928 that came "bent". I have not seen very many, however. I did have a friend with a Pontiac engine whose Scat crank came with taper on the rods and such a severe surface on the thrust that it took out 3 sets of main bearings (and the rest of the engine, due to the debris) before he had it checked and machined. The Pontiac guys say that the cranks are "good cores" that need to be re-machined before they can be used.

greg brown

Fastest928

We designed the DEVEK 8CW crank to handle over 700 crank hp. We broke two 6 CW cranks at around that level and the factory confirmed that the block is not stiff enough to support high hp, even designing the GTS crank with 8 CW for that reason. Longer stroke = increased harmonics = increased stresses = increased bore distortion = loss of power

I know from a series of tests at 8000 rpms (and making less than 100 hp), that a stock 6 CW crank will result in uneven bearing wear.

Based on what I know, and confirmed by the factorys decision to go with a 8 CW crank, even at a cost increase, my opinion (supported by designing & building high hp 928 engines) is that a 8 CW crank is a better design for the 928 block/engine.

Cheers,
Marc

John Veninger

Good! Since Louie is very close and I'm right behind.

SwayBar

Rumor has it that the coating on the pistons came from the same person who claims that he can plasma-coat camshafts and re-grind into a new profile (..Phil Threshie); ask Don Hanson how all that went. Also, ask Dennis Wilson how his then newly built stroker engine ran with PT's camshafts, horribly, and continued to do-so until he replaced PT's camshafts with GT ones.

So I wouldn't use those pistons with that coating, or else you may be selling a crankshaft too.

On the other hand, somone can take the coating off the pistons and have the block nikasiled, so it's not a complete loss.

atb

JV wrote:

Hand raised.