General > Naturally Aspirated Tuning

Understanding how to tune according to octane.

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Pierre3400:
Hey guys,

I have an e36 coupe with an M50B20 engine, running the 403 ecu with the war chip.
The engine is running a crank from a 325, so its stroked to 2,2liters.

It has been about 2 years since the car actually ran on the road, due to lack of time and money, its been sitting.

Last time it ran, i ran with an miller tune for ignition, but re adjusted fuel mapping. The car was only able to run on octane 98.

I want to be able to run on 95. But i need to understand how i should be changing the mapping to make this possible.

As of right now, i think i have a blown head gasket, and the head is coming off soon to be tuned and fitted with 325 intake. But i want to start learning how i need to tune my car for it to run on 95.

The compression is higher due to being stroked, and measures out at around 18bar per cylinder.

millerperformance:
That is quite high in compression. Our 11.5:1 engine with suitable aftermarket cams for the application is only making 205 PSI.

You need to reduce your timing. How much, you will have to determine that. With such high compression like that, I would venture to guess you will need to pull at least 4 to 5 degrees of timing under high load areas.

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