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Old Subaru and Apexi Power FC

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Hi folks! First time posting in this forum. I've done some of my tuning course but I want to make sure my understanding are right!

First, I have a GC8 Impreza with STI Version 4 engine (EJ20K, 2.0L). Car have been previously tuned with the stock 440cc injectors.

This winter I put a brand new engine in my car. Same setup but 2.2L instead. The stroke is the same, only bore size increases. Also I installed new-age WRX STI 550cc injectors instead.

I found that old injectors are 440cc with 0.69ms latency, new injectors are 550cc with 0.74ms latency.

So with my Datalogit cable I can make these adjustment for the base map:

440cc/550cc = 80% Injectors

0.74ms - 0.69ms = +0.05ms

And since my engine is 0.2L bigger, increasing the fuel map by 10%?

Thanks for your answer!

You'll probably find fuelling is much lower than that, with part throttle being very close to the same and increasing to, perhaps, 5% extra at full throttle and load.

At light and part throttle the same torque will require around the same air mass and hence fuel for that output. As rpm and load increases the airflow will still be restricted by the heads/camshaft breathing and the capacities of the intake and exhaust system for airflow.

So since I have to do a proper break in of the engine at first you would leave it has it is and then when the break in is done adjusting the fuel trim after doing some pull to aquire some data?

Except for the injectors adjustment for sure.

Salut Anthony,

Yes, I would scale the injector as you said, your math is correct. You should be in the ball park after that.

And as Gord said, you probably won't need to scale the fuel map that much in order to compensate for the 0.2L. You will need to do some logging and adjust your fuel map as required in order to optimize your fuel map. It doesn't need to be 100% optimized if it's for the break in, you could do it on the road. But be careful not to be too rich or too lean.

Hope it helps,


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