2.7i compared to m20b25

[5Toes]

I searched, but couldnt find much. I need a new motor soon. I have a m20b25 now, but I believe it has an AMC head and is not original to the car. I say this because the harness above the engine has been cut and the head has a stamp that says "2.5 2.7" on it underneatht he 1st cylinder spark plug hole.

When I do swap I am contemplating putting in another b25 or doing a mild stroker build using all oem parts. I want to keep my automatic for now, and I know the e36 autos are a pain to wire in with all the computers, etc. I ahve heard rumors that the e30 auto wont work with a 24valve because it wont like the 15 degree or so tilt?

So what does a eta bottom end with an i head put out? Ive read into the stroker thing quite a bit, but I am unclear what factory parts combination will have the highest compression ratio. I have no intent to boost this motor

[tH16]

325i pistons shaved is the best or custom built. This is what you need http://www.strictlyeta.net/technical/328i_1.html

[5Toes]

It all depends on the setup. It's tough to talk straight numbers because there is so much variance between engines in terms of modifications, but figure that a conservative 2.7 liter setup with '88 325 pistons and stock 325i fuel injection, cam, and exhaust may yield around 180 horsepower and 190 lb-ft of torque at the crankshaft.

So shaved i pistons would mean maybe 185 crank? Also I would use vanos m50b25 rods, because they are factory forged and the same length as m20b25 ones. Ive seen them for $100 for the whole set

http://www.daham.org/16vt/technical/bmwm20/

Looks like there is a good deal on them now - http://www.ebay.com/itm/Bmw-M50-vano...#ht_500wt_1361

[e30trooper]

oem euro eta pistons with eta crank/rods.

[5Toes]

^ just was researching that combination!

And that will work on motronic 1.3?

Found this good thread - http://www.e30tech.com/forum/showthread.php?t=103356

[acolella76]

My current M20B27 is putting down 150whp/148wtq without a tune. All stock except for the 272˚ cam, headers, and M50 injectors.



You can build an M20B28 with all OEM parts, which is what I am currently doing. M52 crank, 325e rods, and M20B25 pistons will fit. All that needs to be done is machine the crank down to clear the pistons and machine a front oil seal spacer, neither of which are very expensive.

What is your budget?

[e30trooper]

^ just was researching that combination!

And that will work on motronic 1.3?

Found this good thread - http://www.e30tech.com/forum/showthread.php?t=103356

motronic 1.3 is the DME and harness. yes

[5Toes]

My budget will be $700 or so, plus what I can sell off my current motor.

I have the intake manifold and all the i bits, though my head is an AMC head I believe so... I will need a proper i head.

I figure a $300 engine and then $150 for i head. Ill "part out" my current motor or sell as a whole for atleast $150

Also, trooper do you know of any build threads that used the early euro eta pistons? Like I said I have no plans to boost, so a 9.5:1 C/R or 10:1 would be ideal

[acolella76]

I'm not so sure you have an AMC head just because it says 2.5 2.7. I have seen a few BMW heads that say that. Look at the intake side of the head and see what it says... instead of a casting number it should just say 'AMC'.

[5Toes]

Hmm I had the intake mani off for my starter, but cant remember.

Ill investigate this more

[5Toes]

Is there any build threads that use the euro 325i pistons and rods? they are 9.7:1 compression ratio stock with an "i" head. I dont know how to calculate the new C/R, bu ti I would guess it is around 9.5:1 in the eta block?

[Wishno87]

I'm not so sure you have an AMC head just because it says 2.5 2.7. I have seen a few BMW heads that say that. Look at the intake side of the head and see what it says... instead of a casting number it should just say 'AMC'.

+1 it seems to be on later model heads. I have one sitting on a stand from a 90 IIRC with that stamp.

[5Toes]

Well I am happy now! Woohoo!

[TurboJake]

I'm not so sure you have an AMC head just because it says 2.5 2.7. I have seen a few BMW heads that say that. Look at the intake side of the head and see what it says... instead of a casting number it should just say 'AMC'.

+1
Both the 89 325i's in my driveway have 2.5/2.7 on them, Neither are AMC heads.

[5Toes]

Thank you Jake. I figured it would be an AMC head, because the AMC's are made to fit etas and i cars. Thus it would say 2.5/2.7

Awesome, that makes my budget even better.

So anybody able to point me to some build threads that used euro eta high comp pistons? And also can anybody explain how the euro m20b25s only made 1 more hp, even though the engine compression is much higher??