cant used domed pistons or weld up combustion chamber.

bige 0412 864 741

you know there are quite easy ways to work that out. im sure you can find an online compression ratio calculator that will actually take into account all of your particular engine variables. as no one else will be able to accurately answer that question without knowing more info

can you get domed pistons? can you weld up the combustion chamber? both of these will effect the comp ratio alot more than shaving a whole heap off the head

pistons are allowed up to 10 thou above the block.But mine are currently level.Wondering how much 10 thou will increase my compression ratio.

what i meant by much safer ways to increase power, were getting more air in rather than compressing the air more. as there was no mention of speedway regs or anything when i made that reply

but i guess, ask a vague question, get a vague answer

what you need to do is dilute 98 down to 97 by mixing it with 91 (i don't know the ratios)

then skim it until it starts to ping on the 97 and thats your safe limit

I always thought sunny02 and GG-datsun were the same person?

There isn't much else to do hey (without breaching the rules).

I don't know what your regulations actually are but things like thinner head gaskets, flat faced valves would be the go.

Not sure if you can try and take a bit more volume with a deeper sitting spark plug- and I don't even know if those are available.

Second thing would be to take a good look at what combustion chambers shapes are available to you, the H75 head holds alot of it's volume in the very last part of the combustion chamber (closest to the deck). Taking that large open circle of volume off may yield a lower volume at the 60 thou surface milling limit, compared to if you were to machine say a H89/GX. But having said that the H75 holds approx 2cc more than the H89 so maybe it won't work out as well, worth a look though?

Also surface milling on an angle that would remove most of the larger side of the combustion chamber (on a H89/GX) may result in a lower volume but I haven't looked into that. Coming to think of it that may not work either.

Are there regulations against having the pistons proud of the deck height?

I know mate, I'm not having a stab at you, I'm just wondering what Pigdogs 'much better and safer ways of increasing the engine power' ideas are, considering you drive a speedway car and are limmited in what engine machining you can actually do. Cheers.

exactly but you can get real thin head gaskets

Well the rule with junior sedans is - no more than 60 thou off the head. Clearly some of those compettitors are shaving more off if they are reaching over 10.5:1 So Clyons8, what more can he do to increase compression?