pro's and con's on engine conversions.

[raj1980]

i currently have a 320 convertible, its a solid engine but fancy something a little faster. i was looking to pick up a m20b25 engine as it would be a cheap and easy swap, i have seen someone selling a 3.5 m30 engine on here.

i wanted to know the pros and cons on both conversions, i have listed a few questions below.

reliablilty?

power?

any easy mods to release more power and expected output? (im not after the fastest car, i just want something faster than i already have)

MPG? (not a deciding factor but would be nice to know)

weight of engines?


just like to say thanks in advance for any advice.

[baptie0]

if you opt for a 2.5 you will notice a big difference compared to 2.0 in power.

[raj1980]

would i need to change the diff and gearbox too?

[Speedtouch]

Properly done, any conversion should be reliable. the M20B25 gives 165-171bhp while the M30B35 is 211-218bhp. The 3.5 M30 engine weighs around 40kg more than the M20.

The M30B35 is a bit heavy on fuel: in my 1988 E34 535iSE, it gave low 20s mpg around town, with 30mpg achievable on a long motorway run. In a lighter E30, it would probably be a little more economical.

You would certainly need to change the gearbox and probably the diff (to the large case unit) if fitting the 3.5

I can supply a chip to improve the driveability and power of either 2.0, 2.5 or 3.5 units for £30 posted.

[raj1980]

that sounds like the m30 and the b25 will have nearly the same acceleration giving the extra weight of the engine and larger diff.

might be better chucking in a 2.5 and chip it.

[Speedtouch]

The M30B35 is a stonking grunt monster, with serious torque over the M20B25, but a good 2.5 certainly doesn't lack punch.

Most good M30B35 conversions will give a 0-60mph time of around 6 seconds and top out at 150mph, while the M20B25 is good for 0-60 in around 7-7.5sec and tops out at 135mph approx.

If fitting a 2.5, try to get the earlier pre-1988 25 6E high compression version; the later 25 6K low compression isn't as responsive or perky, nor as economical.

[ImysE30]

If it's your daily driver i would go with the 2.5, not expensive to do and better than the 2.0.

If it's not, then M30 or even M52 it. M30 is easier and cheaper to do, M52 is a more modern engine with better fuel economy

[raj1980]

whats the M52 engine from? if i can get about 25mpg i would be happy with that. the 320 is very good on fuel, i get about 250miles to a tank but painfully slow.

[ImysE30]

M52 is the 2.8 engine from the E36 328. Can produce 200BHP plus with a few mods

I'm still undecied on weather to get an M30 or M52 for mine

[dips346]

m52 mate ,easy to do ,weighs less and looks much better

[dips346]

M52 is the 2.8 engine from the E36 328. Can produce 200BHP plus with a few mods

235/240 bhp with a extra grand spent on a standard engine set up

[raj1980]

whats involved with the m52 conversion?

[ImysE30]

Check out the mammoth M50 Development thread

Main issue is the manifold, need to be a competent welder or pay around £700 for a ready made one

Think you use the M42 gearbox as well

[raj1980]

that sounds expensive. i want a cheap conversion. lol.

[ImysE30]

It's not expensive if you can do most of the work yourself. How competent are you?

[raj1980]

im happy swaping engine and wiring but would not be able to do the welding.

[ImysE30]

Dips isn't too far from you (i think), give him a shout

[snakebrain]

If it's your daily driver i would go with the 2.5, not expensive to do and better than the 2.0.

What's the going rate for an m20b25 put into a 320 cabbie with labour etc, because I'm a useless numpty when it comes to such things and couldn't possibly do it myself?

[Speedtouch]

Try SPADGE on here; he's done quite a few of these conversions for other Zoners.

[snakebrain]

lol thanks, i've already messaged him, just waiting to hear back