e30 316 and 318i piston differences?

[Stevin]

I was looking at some new pistons for my car which is is a 1989 316 (note not fuel injected).

I see the pistons listed for this motor are different than the ones listed for the 318i. I checked and the crank and rods are the same part no's so it's not due to a difference in stroke.

I'm busy building the motor for FI and Boost, so I'm just curious as to what the difference is between the 2 pistons.

Unfotunatley I haven't pulled the motor yet as I'm still mocking up the FI and Turbo stuff.

[Stevin]

Oh, I forgot to add that the diameter is also the same across the 2 motors.

[m8782538]

I am looking into doing a turbo conversion on my 316i M10 1786cc. good source is on here, someone used cosworth pistons and other parts, the block and head are good, its just about everything else that needs replacing.

[Stevin]

Well we have a couple boosted motors here, just everyone is very hush hush.

I plan on just dropping the CR with gasket and offset small end bearings. Doesn't need much as far as I can tell. Max 1mm offset on the small ends.

I could also remove some material on the combustion chamber. Right now I'm just looking to order pistons and noticed that the part no's differed.

Guess I'll hold off until I have the motor in pieces.

[peeweemad]

I think the compression and valve size is the only difference between the 2 engines, the 1.6 being 1766cc high comp and the 1.8 being 1796cc low comp with larger valves.

I would also recommend contacting fritz bits as they will be able to help you.

Hope that helps

[Stevin]

What gives the engine the different displacement?

I looked on BMW fans website, and the cranks, rods and bore are the same.

[eta]

Both the 316i and 318i have the same capasity of 1766cc. If the bore and stroke are the case this has to be true. The pistons appear to be the same as you indicated.

Be careful about removing material from the head as remove it from the wrong place and you could end up provoking detonation.

[m8782538]

from what i can tell the 316i M10 has a cat in the exhuast and the 318i doesn't which gives the different BHP figures. my M10 316i has a de-cat stainless system and should be running more BHP than a stock 318i or an M40 316i

[Jhonno]

Is yours LHD then...?

The M10 318i came with and without a cat.

[Olie]

The 316 and 318 are same blobk crank pistons etc. but its the injecton or carbs that alter the power, esstially its like modern engine where you spec what PS you want, its all the same stuff just with a different mapping on their ECU's,