pistons

[sinisterfuzzy]

hey has anyone else gone .5 over? and if so what sort of pistons did you use?

[bobafett]

the temptation to just lock this thread right now is overwhelming.

read about my build. i am the only person that i know of who HAS gone .050" over.

but are you talking .5mm or .050"? there is a big difference.

almost any company that makes pistons will make you custom pistons. there are 2 catches to this, 1) they need specific specs, 2) they cost money - usually 350-600 in that range.

why do you want to go that large of an overbore? FYI the only reason i did go as big as i did was cause i needed to go .040 to get rid of scarring, and they had some awesome rings available if i was willing to take a chance and jump up to .050" :)

you need to specify your question a hell of a lot more before its really feasable to answer it though...

[sinisterfuzzy]

well it it's a lower bore than .050" is it even worth the money of new pistons and boring? what would be a better route?

[bobafett]

it depends what you are trying to do....

for a stockish rebuild i wouldnt bother with custom pistons. if your going for a specific compression ratio, or need lighter/stronger pistons, or plan on using something wierd like B-series rods, you will need pistons made.

why would you be considering a bore and piston upgrade in the first place? its not like the 50cc that you gain will make a noticable amount of power without increasing the compression. :) so if u just want bigger pistons just for the heck of it i would say you are wasting your money.

:)

[sinisterfuzzy]

alright, so where can i read something about different compressions? i don't really know what I want as far as that goes. But isn't it true that higher compressions are best for Nitrous and getting the best NA power? and lower compressions are beter for turbocharging?

[bobafett]

http://en.wikipedia.org/wiki/Compression_ratio

in most forced induction applications, lower CR is safer, but of course you can tune anything to work. using a higher CR the result is usually retarding the timing so much that the overall power is less than if you had stayed with a lower compression ratio and been able to keep more agressive timing. :)

NA = higher compression
FI = lower compression, even nitrous....

the caveat is with a nitrous setup you are not usually running the gas, so you can use a higher CR to enable your car to have better power and response.

it just depends on how you want to run the nitrous. with a large jet, and high compression, you will be running rediculously retarded timing. :)

its all in the tuning i guess, there is a million different scenarios that could take place. you can do whatever you want in the end, but be prepared to tune appropriately, and the lower your CR, the more lax your margin for error.

EDIT: diesel motors run really high CR, but don't use spark plugs to ignite the mixture... so diesels don't really apply to this post. :D