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# How do I apply this calculation to my own engine?

### Tech Articles

Discussion and questions related to the course EFI Tuning Fundamentals

EDIT: I just watched the "Volumetric Efficiency" lesson and I have a question.

Hi, I have a Subaru Impreza GC8 with a built motor.

From what I know the the crank has a different stroke from the stock one, the block has been bored out to a slightly larger size and the compression ratio has been changed.

So my question is:

Do I need to open the engine to do this calculation or is there a way of doing this with knowing the Bore size, crank stroke? I'm very inexperienced so I don't even know if Piston size and Rod length effect this as well.

Thank you!

ET

Please clear up which "calculation" you are asking about. The calculation of displacement (you would just substitute the your engines values)? Or something else.

If using VE model for fuel you want to have a fairly good estimate of rngine displacement to start with, especially if using ecu manufacturer of injector supplier flow tables, however it will all just get absorbed in the maps in the end.

Yes, I mean finding the engine capacity (volume of all cylinders combined).

How important is knowing the correct amount of true air flow when tuning the engine? Can I discover it through other parameters when tuning or is this info critical in order to target\calculate the perfect tune?

I might be asking this question too early on. I haven't finished the course yet so I don't know if this question will be answered in a later stage.

Thanks,

ET

Engine capacity = bore [original plus oversize] x bore x pi [approximately 3.142] /4 x stroke x number of cylinders.

It seems you do have the engine's bore and stroke, but if you aren't able to find out the actual bore and stoke from the builder/person you bought the vehicle from/invoices, there should be a couple of ways of establishing them. If you buy a cheap vernier caliper, you can use it to measure the stroke by putting it through the spark plug hole and comparing the distance to the piston at TDC and BDC. If it is a simple rebore, it will normally be the next oversize, which will usually be 20 thou'(0.5mm) but can be 40/1.0 - it won't make a significant difference, but if you can get hold of a boroscope, you may be able to still read the piston markings through the spark plug hole, to confirm it.

Ahh, wonderful info!

Thank you!

ET

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