Author Topic: General Questions on M42 Builds (Read 3068 times)

flyingbrickperformance · « **on:** March 13, 2011, 06:48:05 PM »

So I've posted here in the past regarding building up the M42 and I've recently decided to start my project. The car is not a daily and has been in storage but its time to see if I can get things going.

A key detail is the car - this is not going into a BMW. I'm starting to build one of these:

http://www.bruntonauto.com/gallery/gallery.htm

So, I have a complete M42, an M44 crank, S52 pistons, and a supercharger. Drivetrain is a 240 Getrag linked to a 4.10 Diff. Total weight of the car will be around 1800lbs, so pretty light.

Is there any value in building this with the M44 and S52 pistons, or would it make more sense to just throw the supercharger on a clean and rebuilt M42 and call it a day. Even if I could get my hands on an M47 crank is there sufficient benefits with a stroker and supercharger to make the extra work worthwhile? What do I gain by stroking and supercharging - I'm thinking I'm just going to supercharge the thing and call it a day.

I'm familiar with M20s and haven't done anything with the M42 so it'll be a bit new to me, but an engine is an engine so I'll figure it out. However, I'm having a hard time on justifying costs for machine work on the internals if I can just slap the supercharger on a rebuilt M42.

Thoughts?

Hey-u · « **Reply #1 on:** March 13, 2011, 07:54:49 PM »

What are you going to use the car for and how much HP do you want?

DesktopDave · « **Reply #2 on:** March 13, 2011, 07:57:47 PM »

At 1800 pounds with a 4.10 I'd just do a straight M42, no need for the extra power IMHO. The chain drive on the M42 is finicky compared to the M20 belt, and the M42 is far more sensitive to overheats. Otherwise you're right, a motor is just a motor.

The crank and S/C is a little work there, especially if it needs a bit of tweaking to get right. You'd get some massive power gains though, I'll bet. A conservative blower setup can easily get you 200rwhp with a tweak or two on a 1.8.

I love the seven. Great car, way ahead of it's time. But I've often wondered why so few try an eleven? Almost the same frame, nice envelope chassis...now that'd be something to see!

flyingbrickperformance · « **Reply #3 on:** March 13, 2011, 08:19:27 PM »

Quote from: Hey-u;102241

What are you going to use the car for and how much HP do you want?

I'll be using it as a daily driver - just kidding.

I may take it for a summer spin periodically, but primarily, its going to be a track rat.

In terms of power, I'm not too worried about getting it beyond 200hp. These cars hit a brick wall at 100mph without a complete body make-over so it goes to waste once you're well out of the turns. As light as these cars are, it doesn't take much to get it to rocket through turns.

flyingbrickperformance · « **Reply #4 on:** March 13, 2011, 08:21:50 PM »

Quote from: DesktopDave;102243

At 1800 pounds with a 4.10 I'd just do a straight M42, no need for the extra power IMHO. The chain drive on the M42 is finicky compared to the M20 belt, and the M42 is far more sensitive to overheats. Otherwise you're right, a motor is just a motor.

The crank and S/C is a little work there, especially if it needs a bit of tweaking to get right. You'd get some massive power gains though, I'll bet. A conservative blower setup can easily get you 200rwhp with a tweak or two on a 1.8.

I love the seven. Great car, way ahead of it's time. But I've often wondered why so few try an eleven? Almost the same frame, nice envelope chassis...now that'd be something to see!

Not sure about the eleven but suspect it has to do with the widely accessible plans to diy a chassis for the seven and body components that are available.

I have a good little S/C from the Mini-Cooper S, and the space requirements are what I make it, no power steering or ac, alternator is the only item that'll be running off the belts. I'm leaning this direction, but am always easily persuaded to increase displacement.

B318M42W · « **Reply #5 on:** March 13, 2011, 09:19:15 PM »

don't forget to add an intercooler for the s/c! with that small blower, it will generate some heat and limit psi. without it, i doubt you can acheve 200rwhp on just 7psi.

great looking car by the way! good luck with your project!

Hey-u · « **Reply #6 on:** March 13, 2011, 10:21:07 PM »

Quote from: flyingbrickperformance;102245

I'll be using it as a daily driver - just kidding.

I may take it for a summer spin periodically, but primarily, its going to be a track rat.

In terms of power, I'm not too worried about getting it beyond 200hp. These cars hit a brick wall at 100mph without a complete body make-over so it goes to waste once you're well out of the turns. As light as these cars are, it doesn't take much to get it to rocket through turns.

I think you might be better off building a na 2.1 stroker for track use. Around 200 bulit proof hp.

M42_Zach · « **Reply #7 on:** March 15, 2011, 08:44:16 AM »

i too am thinking on building a similar setup, at least 86mm pistons, with an M44 crank that a mate was selling cheep.
Only problem i am having is the problem of con rods, and am unsure what ones to use, if anyone could enlighten me on that problem, i would have owe many thanks to them.