Piston - Bore gap?

[mcandmar]

Now thats an old thread. I have since had the opportunity to have a block machined to suit my pistons, for interest this is what my original block clearances looked like (block machined locally to 81.5mm before i bought the JE pistons)

1 - 0.107mm / 0.0042in
2 - 0.104mm / 0.0041in
3 - 0.104mm / 0.0041in
4 - 0.109mm / 0.0043in
5 - 0.100mm / 0.0039in

New block was machined by JP to suit my pistons, think they are all ~.0035 now.

Mark.

P.S. Yes i know its going on five years now, ill get it done eventually

[JP]

Depends on the boresize as the bigger the bore the greater the clearance. Likewise it depends on the use of the engine the higher the boost it will run/power the bigger the clearance. I usually go between 3.25 and 3.5 thou on an 82mm piston 400+hp. If its a JE. Wossner and supertech I'll run .25thou less

[JP]

^^^^macandmar finish that engine already!

[Thuppu]

Target is to max out a HX40S, so say 600+hp. Bore size is 82,5mm.

[JP]

On a set of Je's 3.5-3.75 for 700+ I'd go for 4. Which is about the max I'd want unless an out and out track car.

[Thuppu]

Yesturday I carry the block to the machine shop. We decide to use 0.00355(0.09mm) clearance. Hope it's good..?

How about the piston ring end gap clearance? 0.012-0.016"(0.3-0.4mm) usable?

[Billman]

I had this from CP-Pistons

Nitrous/Turbo Top ring Bore x .0065/.007”, Second ring Bore x .007/.008”, Min .015 oil rail end gaps”

[JP]

16thou for oil control ring. 1st and 2nd bigger. 2nd ring is always 1thou bigger than the 1st ring. Depending on application 1st ring range from 17-19thou. More boost more heat = bigger gap.

Bigger gap = also less vacuum at idle

[Thuppu]

Ok, those are quite big gaps. How does this sound if I use 0.01772"(0.45mm) on the first ring, 0.020"(0.50mm) on the second and 0.016"(0.40mm) on the oilring? Or can I use 0.05mm smaller gap in first and second? My feeler gage is only in 0.05mm steps.

[J_ones]

I used these calculations to measure right gaps to my Supertech rings. The moderate turbo part
Note: These measurements are USA model, not millimetre

Page 39

http://issuu.com/fabreaus/docs/2010supertech_pdf

[Thuppu]

Wow, those are quite tight gaps..?

Edit. oops it was ring gap per inch of bore. Ok, thats close to the measures above.