can you do this to lower comp slightly does it work ok and how much do u take off??

 

You can, but obviously it weakens them like skimming any pistons

Its not really "skimming" though as that would just take material off the crown at the edges where its highest, which isnt what you want, they need machining in a slightly more involved what that that.

How much you take off depends on how much you want to lower the CR by?

 

am i right think CnB Skimmmed there psitons on the fisrt engine or am i wrong

 

Cant comment on that im afraid mate, i dont even know who CnB are!

 

....and I don't know who Chip is.

Roosie. Mine were machined from when Harvey rebuilt my engine. They were taken down by enough to virtually lose the Valve Cut-outs.

I can't say that its ideal, but you know what I threw at mine. They saw up to 32psi and 160mph.

 

LOL

didnt realise that was short for yuo mate!

 

No worries mate. I only a mere 5k Poster, so I'm not really surprised!!

 

Well if he reffered to me as "c" would you have known who it was?

 

No, but had he referred to you as 'C-3dr' I might have.

 

what compresion ratio did that give you CnB?

 

for me


ouch

 

Fook knows to be honest. Somewhere around 7.5:1 I would say.

 

harvey SCS engine C?

if so, the one he built me was 7.8:1 I think

 

Upto 40 thou is ok on these, but re chip - after 230hp id use low comp mahles. I did once havea skimmed piston fail (ring land) BUT i was running over 20psi and 8.5:1 comp, so was under a lot of stress - lasted 20k though.

 

Just an advise, don't remove material form the edges, but only the central area. Leave the first ~8mm intact. I once measured the material thickness to be around 7mm. 0.5mm reduction is usually considered very safe. On the other hand I wouldn't touch the original CR of 8.3:1 unless going for over 20psi pressures. IMO people go low comp far too early just because it sounds good in the spec.

 

im ruuniing 24psi so i do need low comp lol