NA Compression Ratio

[MrMike990]

What's an ideal range and can too much be a bad thing?

[Jay Allen]

What's an ideal range and can too much be a bad thing?
Are you running a class that has a spec fuel? If so then you may need to limit the ratio. If you just have a high horsepower engine and are not limited by a spec fuel, then more is better IMHO.

Thanks.

[ROB]

Along with detonation resistance in fuels,

Too much compression will impare airflow if excessively large piston domes are required in order to acheive your targeted ratio. Large domes add mass to pistons and they can potentially mask charge mixture in the end gas regions of the chamber. This will aggrevate/cause detonation.

Increasing compression ratio is a diminishing return so keep in mind you're only going to see leaps & bounds when increases from, say 11 to 1 up to 14 to 1 are made. Beyond that gains are slim.

If you're running current cylinder heads with active chambers the gains from increasing compression aren't as significant as they would be with a lazy chamber.

In general, you will see a 1% torque output increase per 4% compression ratio increase.

[MrMike990]

I've made my mind up on a new cylinder head and was just wondering whether to choose a flat top or reverse dome piston. With a 6cc FT, the static CR will be 15.62(using Fel Pro 1144 MLS) with the piston .013 in the hole. If the block is "0" decked the CR will increase to 16.33. Also, I'm thinking about switching to an alum rod maybe Groden as well.

thanks for the replies guys

Mike

[Jay Allen]

I've made my mind up on a new cylinder head and was just wondering whether to choose a flat top or reverse dome piston. With a 6cc FT, the static CR will be 15.62(using Fel Pro 1144 MLS) with the piston .013 in the hole. If the block is "0" decked the CR will increase to 16.33. Also, I'm thinking about switching to an alum rod maybe Groden as well.

thanks for the replies guys

Mike
There are a lot of theories concerning compression. Then there is the dome vs F/T vs reverse dome deal. Compression will help the engine to accelerate. Use an aluminum rod at about .0125" to .015" in the hole with a F/T and go have fun!