HP question

[BeemerDan]

I just bought a 1991 318i convertible with an M42, but it needs a new engine. I want to stay with a 4-cylinder, but would like to get good performance out of it. My question is how many HP is that engine? and how many HP was the 318is?
I have found several different numbers for it.

Thanks in advance!

[DesktopDave]

Spec for the '91 M42 was 138hp, IIRC.  It's the same motor in the coupe, sedan or 'vert.  However, your car originally has a 4.27 diff to compensate (stock is a 4.10).  Later E36 M42's had an improved intake manifold that improved the torque curve.  The very similar 1.9 liter M44 motor had slightly more power as well, 141 HP IIRC.

One ticket for a powerful M42 is the M47 crank & M3 pistons.  Metric Mechanic sells drop-in motors from 2.0L on up, and they claim from 170hp to over 200hp.  Those are not cheap motors though, starting cost is about $7.5K.  A used Downing Atlanta supercharger can also be a good deal.  There was one of those for sale here recently, and not for too much cash IIRC.

IMHO given the heavier weight of the 'vert you might be best off with a later six-cylinder motor all together.  The alu-block M52 from the 530i is lighter than the M42 from what I've heard.

I'd stick with the four-banger myself just for the sheer reliability and economy of it.  Small changes you can make to perk the motor up include a DME chip, lighter flywheel, hose delete mod, or COP mod.

[BeemerDan]

Thats what I thought, I had just found a few places that said like 113HP for the vert.
The 4.27 gives it better acceleration right? whereas the 4.10 is geared a little more for faster speeds?
And do you know if I can put the newer intake manifold on the 91?

Thanks!

[DesktopDave]

For sheer acceleration, the higher-numbered diff rules.  But if it's too "short" it ends up being buzzy on the highway and makes first gear essentially useless.

My 4.10 was bad when I bought the car, so I swapped it for a 325is 3.73 limited slip unit.  I prefer the lower ratio - the car is much better for highway use.

I'm not sure the later manifold would fit under the e30 hood - and it's a lot of work for very little gain, IMHO.  I would go for a DASC in a second though - they're a very reliable 200hp and aren't too hard on gas.