rob wild Posted July 16, 2008 Share Posted July 16, 2008 (edited) Hey Guys Just in the middle of calculating my compression ratio for a new project using a spreadsheet a made a while ago but I cant find (and i have search) the Piston volume for a 86.5mm piston. Anyone got a build sheet for one with it on i'm sort of thinking 15cc or something like that but want to be sure before i start buying HG's Cheers in advance Edited July 17, 2008 by rob wild (see edit history) Link to comment Share on other sites More sharing options...
Chris Wilson Posted July 17, 2008 Share Posted July 17, 2008 Did a quick search myself, even CP's own site and catalogue fail to reveal the dish volume. Doesn't surprise me, they don't mention the *rap material that expands like hell, or the fact they supply generic ring packs that need hand filing as they cover various bore sizes (most incorrectly). If you want a cheap piston I have found Wiseco to be a better bet myself. I would say from the specs on the CP site they will have about a 14 cc dish volume including valve reliefs. Link to comment Share on other sites More sharing options...
rob wild Posted July 17, 2008 Author Share Posted July 17, 2008 Interesting that Chris i always though CP pistions were ok and had a fairly good reputation and are very light 322g. Back in the day when i was building a few engines I would only really ever use cosworth pistons and through a couple of seasons i never saw a piston failure. If the CP pistons are not right in the engine im rebuilding I think i read somewhere that Cosworth do a 87mm piston that would be ok for the 2JZ engine. I think your right with about 14cc just put it back in my spreadsheet: Enter Bore 8.65 Enter Stroke 8.6 Total in CC 505.3792608 Gasket bore hole 8.6 Compressed gasket width 0.12 Total in CC 6.970515516 Piston volume 14CC Combustion Chamber Volume 45.7 66.67051552 Compression Ratio 8.580251284:1 Just in your opinion Chris what CR would you aim for with a single turbo application? I know its a compromise but was think as close to the stock 8.5:1 as possible using a stock HG which I believe is 1.2mm? Cheers Rob Link to comment Share on other sites More sharing options...
Wez Posted July 17, 2008 Share Posted July 17, 2008 Cosworth make the JUN pistons, they even come in a cosworth box Link to comment Share on other sites More sharing options...
bolarbag Posted July 17, 2008 Share Posted July 17, 2008 Subscribed, I'm interested in comp ratio as Terminators build intrigues me, isnt he running 9.5:1 now? The response on a relative midsize single would be immence at that ratio!!Can't wait to see it mapped! Link to comment Share on other sites More sharing options...
rob wild Posted July 17, 2008 Author Share Posted July 17, 2008 (edited) Cosworth make the JUN pistons, they even come in a cosworth box Ahh right Subscribed, I'm interested in comp ratio as Terminators build intrigues me, isnt he running 9.5:1 now? The response on a relative midsize single would be immence at that ratio!!Can't wait to see it mapped! I've changed the title although it doesn't seem to have updated Maybe a mod could sort it Yeah I thought that was an interesting way to go as well. I would have thought that using 9.5:1 would have required a fair amount of retard and low afr to stop det? unless Phill plans to run water/meth and Race fuel i.e. 118 at which point im sure he could have a considerable amount of HP. Personally in the build im doing the maximum CR i would use is 8.5:1 which is stock but I have been considering slightly lower to allow me to run more boost. Edited July 17, 2008 by rob wild (see edit history) Link to comment Share on other sites More sharing options...
bondango Posted July 17, 2008 Share Posted July 17, 2008 Rob the CP .040 is 15.5cc, think i have a .020 over set in work so will check the sheets today Link to comment Share on other sites More sharing options...
Chris Wilson Posted July 17, 2008 Share Posted July 17, 2008 I have found CP pistons to be made of a high expansion alloy and need a lot of bore clearance to be sure of them not picking up. The Cosworth made JUN pistons are lovely, but pricey. It's a shame that Omega have nothing off the shelf for the "JZ-GTE (they don't, I asked Fred there a bit ago...). As for CR, as you say, it's a compromise. If you are happy to run a fast spooling turbo with a low boost level you can mimic these modern low pressure turbo engines, with great low end and no lag, but if you want to up the boost and have some real top end power you are probably going to have to dual map it and run race fuel for serious power. I'd go for about 8.5 to 8.75 ish to 1 CR and allow some boost headroom on pump fuel. Try and keep the HG as thin as available, clearances permitting, I think some decent squish allows a lot more timing and peak torque boost without det. Machine the chambers or pistons to drop CR if needed, DON'T use a thicker head gasket. It works of course, but kills squish. Link to comment Share on other sites More sharing options...
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