compression ratio vs needed fuel

Nistune topics specific to the 6802 cpu

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bsdkllr
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compression ratio vs needed fuel

Post by bsdkllr » Sun Oct 06, 2019 4:00 am

i cant seem to find this info anywhere. its not really nistune specific but. how does increasing compression ratio effect the needed fueling.

so if i raised the compression ratio from 7.8 to 9.0 would it require more or less fuel?

Matt
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Re: compression ratio vs needed fuel

Post by Matt » Tue Oct 08, 2019 10:56 pm

Compression ratio is more about amount of static pressure in the cylinder. Higher pressure usually resulting in more torque. Compared to adjusting ignition timing (where the fuel is ignited before piston hits top dead centre) which is dynamic pressure (can be adjusted by the ECU). This doesn't take into account turbo applications which force pressure into the cylinder

So tuning for compression ratio is more about timing than fuel. Sure you might have a little less space in the cylinder and a little less, fuel but you will see that with your AFRs when tuning and drop your total fuel multiplier (or in the fuel trim maps)

bsdkllr
Posts: 25
Joined: Wed Mar 09, 2016 5:32 am
Location: Boston, MA

Re: compression ratio vs needed fuel

Post by bsdkllr » Wed Oct 09, 2019 3:07 pm

I was always under the assumption that if you increase the compression ratio it would need more fuel. But it does make since that the same volume of air is entering the cylinder. Just getting squashed down just a bit more.

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