325e M20B27 -> M20B25

[lateracer]

A B27 bottom with a B25 head that is milled makes more power than a B25. So a B25 swap is pointless *unless* you are trying to run Spec E30 which has guidelines requiring a stock B25 motor.

Not quite. A b27 bottom with a b25 head makes more power than a b27, but not a b25. Seems to be a common rumor here, but it's incorrect. Every time someone actually posts a dyno chart of a 2.7i, it's not as strong as a b25.

In the end, long term planning and some honest answers should be your guide. What are your plans for the car and how long do you plan to keep it?

A 2.7i is a good street motor for the price and will last quite a while if you take care of it. You get the low end torque that's actually useful on the street and pick up some top end as well. It's also manageable in your driveway without any special tools outside of torx sockets. If you're planning on keeping it for a while, the M50 swap is better than the 2.5/2.7/2.7i but is a little more costly and labor intense.

My 2.5 build is for my track car (spends most of its time at 3K+ RPM) and I don't expect it to live for more than 2 years. If I was streeting it, I would have probably just done the 2.7i build. Metal chunks on my magnetic drain plug sort of pointed me in another direction.

Can't agree more with what rc said about a remanufactured head. I actually have an extra 885 head after coming to my senses about it....lmk if you wanna buy it :)

[rcfanatic]

A b27 bottom with a b25 head makes more power than a b27, but not a b25.

You're right, but that's not what I said. This is what I said:

A B27 bottom with a B25 head that is milled makes more power than a B25.

Here's Mitch's dyno to prove it. Take the integral of the power curve and it trumps a b25.

[lateracer]

That's a strong 2.7i build. It's stronger than most of the other dyno sheets people post for what they see from the swap, which makes me wonder if that motor is running all stock components. That is, what would this same motor put down with everything like it is here except using the b27 head? My guess is probably more than a normal b27.

Yeah, the torque output at the bottom end does mean an integral increase in output, but is it worth all that effort? I'm not trying to say I'm right and you're wrong; I'm totally open to the notion of being wrong here. I just think that if you were to put as much effort into that kind of build with a 2.5, you would see a greater return than producing the same amount of horsepower a stock motor puts out, which is what your chart shows.

[rcfanatic]

Right, it's not about winning an argument, it's just about getting the right info to Andy348.

I spoke to Mitch, maybe he can chime in, but I spoke to him over the phone and the engine dyno'd there is otherwise entirely stock. Even the exhaust. Compression ratio has a large impact on power, and a bump is easily achieved by milling as long as you are mindful of piston-valve clearance.

[Andy348]

Thanks for all the info everyone. Sorry its taken me so long to respond.

The engine's erratic idle has made me busy for the past couple days. Its nice to consider modding it but I want it to run well first.

Ill read this over again and do some more reading after I figure this problem out.

[Andy348]

Okay I think I've fixed the idle, but that's not important right now.

My plans for this car was originally an S50 swap, but somewhat limited $$$ and 1 way insurance (if I crash, there goes all my money) kind of stopped me. Now I haven't really driven my 325e that much, so it's either keep it stock w/chip, make it into a 327i, swap M20 or swap M50. I'm really not sure what I should do.

Any ideas? Money is an issue, but lets say I've budgeted roughly 3K.

[e30huh]

i did my 2.7i build on a $250 budget with a used machine head and all fresh internals (Febi). If you have the patient, then troll around for some new parts other don't need or want and you can get it on the cheap. $275.89 is the total i spend on the 2.7i including Goetze HG and VR gaskets for all other. Napa has the Goetze for $27.99 and with your AAA, it's, $22.78. Do it..........................JUST DO IT.

In then long run, it's cheaper to maintain an M20 head then a M/S50 and slap a turbo on there if you want extra HP.

[lateracer]

If money is a concern and it's a street car, my vote is for the 2.7i build. Two reasons:

1) You'll keep the e's low end torque, and torque is what really makes for power on the street. The additional HP on the upper range is fun too. Toss in a chip, some rebuilt injectors and a good exhaust and you're looking at easily noticeable gains.

2) It's a low introductory budget price to going faster, and the motors aren't what slow these cars down. Spending some of your motor money on suspension upgrades and a differential swap will have you going faster as well.

Finally, it's an old car. Stuff breaks...constantly. It won't be long before you find some where else to spend whatever money you've got left. If it's like mine, about 1/3 of the stuff you take off (belts, hoses, seals, gaskets) dies when it's removed.

Let us know how it goes

[rcfanatic]

I wouldn't throw any more money on that idle problem until after doing the Motronic 1.3 swap (if it still exists)

Also don't get your hopes up on cheap parts. Just don't want you to be dissapointed/make a reckless purchase. Sounds like e30huh got lucky, plus living in California probably helps. Not sure how popular they are in Canada.

The biggest thing is to be wary about used parts purchased over the internet at least for the head. Unless you can obtain very good photos it's completely hit or miss because a cylinder head is a high wear item and you generally don't want to take it back apart anytime soon so getting quality parts is important.

[e30huh]

I wouldn't throw any more money on that idle problem until after doing the Motronic 1.3 swap (if it still exists)

Also don't get your hopes up on cheap parts. Just don't want you to be dissapointed/make a reckless purchase. Sounds like e30huh got lucky, plus living in California probably helps. Not sure how popular they are in Canada.

The biggest thing is to be wary about used parts purchased over the internet at least for the head. Unless you can obtain very good photos it's completely hit or miss because a cylinder head is a high wear item and you generally don't want to take it back apart anytime soon so getting quality parts is important.

Pick-A-Part is my friend and Cali is awesome for e30 parts. I agree, i did get lucky, spend the extra money on the internals and a good head.

[lateracer]

Pick-A-Part is my friend and Cali is awesome for e30 parts. I agree, i did get lucky, spend the extra money on the internals and a good head.

SoCal is definitely good for parts from people, but all (4) of the yards I've been to (South of OC) have been picked clean for parts...except for fenders and things like that. Where are you finding stuff?

Eventually I stumbled upon a BMW shop that stock piled old parts for pretty cheap, but that was more dumb luck. Would be cool to know where I could score stupid things like check valves and master cylinders on the cheap.

[e30huh]

pick-a-pull off of Katella ave (Stanton) and there's one off of Beach blvd. GL.

[Andy348]

I might be able to pick up an M20 for $150.

What parts should I inspect specifically if I'm looking to do the 2.7i stroker? Other than the head of course.

Thanks

[digger]

Compression ratio has a large impact on power, and a bump is easily achieved by milling as long as you are mindful of piston-valve clearance.

Actually CR has less impact than what you think.

I still think the B28 option using M52 84mm crank is better.

[ForcedFirebird]

Actually CR has less impact than what you think.

I still think the B28 option using M52 84mm crank is better.

THIS!

Think about it for one second. The 2.5i has 8.5:1 and the 2.7i has 8.3:1. It takes several whole points to make a real difference in power, not tenths of a point.