head trouble

[badboygem]

yes there are a shite load of posts about this but im still confused.

i have a g200 block, am a lil scared to put a g161 head on it because i cant afford valve recesses in the pistons, because i want to run a pretty crazy cam. i have been told that i could get away with a g180 head on it without the valve recesess. my understanding of a g180 head is that it is the same compression as a g161 but with valves the size of a big valve head.

wouldnt this mean that the g180 heads valves come the same or closer distance to the pistons because the valves are greater in diameter?? i have also been told that g200 heads have stainless valves?? is it worth the worry of pinging with a g161 or g180 head on it if it does go ~10:1 compression(block been decked)in 35 degree heat(i live in townsville) or is it just a better idea that i put a g200 head on it?? as it goes im already getting a custom alloy radiator made up and twin 12" thermo fans(got factory aircon so need some good cooling).

which ever way i go im going to have to order the head thru an importer because neither g180 or g200 heads r available here....bloody backwards town.

any help is much abliged, been stuffed around for way too long plus current engine had just done headgasket, cant be bothered fixing it.

[Ben Wight]

I dont know for sure what heads have what size valves and what they are made of, but I can tell you that a 1600, 1800 and 2 litre heads have the cam in the same position, and thus the vales should be in the same position.

Keeping that in mind, a bigger diameter valve will be physically closer to the crown of the piston as you have said. Therefore, if you need valve reliefs in the pisons with a 1600 head, you are going to need them with a 2 litre head, and vice versa.

THe material of the valve wont really change the compression ratio you can run before detonation occurs, thats more to do with the fuel used.

Keep in mind though that to run high compression, like a 1600 head on a 2 litre, you really need a big cam, as the overlap with the big cam will let your compression escape out of your exhaust valve, effectively lowering your compression ratio, or you will have to retard you igntion timing to stop it pinging, and when you have to retard your timing, you are throwing power out the window.

Therefore, to make decent power, a high compression engine needs a big cam, and vice versa. And a high lift cam usually needs valve reliefs.

[badboygem]

yeah thats exactly why i bought a custom made cam. but yes thanks for the help, no room for trial and error on a tight budget.