Maximum power from a stock M42.

[avt007]

Hi everyone. I currently race an E30 with a modified M10. I have purchased an M42 from a 92 318i convertible and I am looking for max HP at the top end for track purposes.

The class rules call for a stock engine, so all I can do is run a chip (which one?) a very open exhaust (no cat, and not much of a muffler) any cold air intake and filter I want, and any valve timing.

The engine internals and injection must be stock, so I'm looking for the best I can get on 94 octane pump gas.

I can run any flywheel, too. Based on these rules, what should I run? Bottom end and midrange are unimportant, eveything I do is 4500 rpm and up.

Ideas?

Thanks

[Darky]

Hi

E36 m42?

For that the e30 inlet manifold would be a better choice.
But perhaps itbs could be used, if so have a look at the stuff here from Rama and lambertus.

Also the later e36 m42 s had smaller valve stems.

As far as flywheel as light as possible, for that application!

Have a look around on this site though there are heaps of upgrades

Hope this helps Rohan

[avt007]

Thanks Rohan,

It is an E30 M42, and I have to use the stock intake. I weighed the flywheel today at 28 lbs without the clutch. I'd rather not have to buy an M20 flywheel and change the starter, so I'm sure which way to go. 

Flywheel weight and the overall weight of the car are a big concern though.

BTW, the rules also call for pump gas only, so no race gas. Another help is that I don't run an alternator or power steering, so the only belt is the water pump.

[DesktopDave]

Can you run solid lifters? You could gain a few HP and some more top end that way. M3 cam trays can be modified to fit, along with the M3-ish cam profiles. Warsteiner did it, he has a few great threads around.

I'd pick and choose between the M44 and M42 bits to build the best motor. They look identical, so you wouldn't get flagged for rule violations. I've heard that the best parts are the late M42 or M44 cam chain case, chain tensioner, and larger M44 oil pump with the late M42 head and rods. The later M42 head has skinnier valve stems, the late M42 rods are lighter.

I believe the smaller M40 or the M42 non-A/C flywheel are your best bet for weight loss, but they may not be durable on the top end. Here's a few details. You could save weight with a small diff, what ratio are you running?

[avt007]

Hi Dave,

Solid lifters- I could run an M44 complete if I had one, but the M42 is more plentiful, and I've got one already. The rules say I can't touch the internals, although no one would notice.

I like the looks of the M40 flywheel, but availability and price will drive that choice too. It'd be nice to machine my existing flywheel but I'd need data to back that up before trying it.

I'm not sure of my current diff ratio. I will be checking though, as I may want to go 5% shorter to hit max revs on the straights.

I've just spent tonight going over the wiring requirements to hook this engine up. The list of things to measure and test fit is rather long! Good thing i have all winter to do it.

Thanks
Rob

[benz-tech]

You would want the 91 e30 cams since they have about 7deg more duration. Double check with real oem about the part numbers but I think the early ones ended with the e30 manifolds. Late cams should be all DISA engines but there could be some crossover in '92, however.

[avt007]

The engine I've picked up is from a 91, so that part is good. The valve timing settings for track use is a hard one to pin down, though.

[the white guy]

I weighed the flywheel today at 28 lbs without the clutch. I'd rather not have to buy an M20 flywheel and change the starter.

You can remove the starter ring gear from the M42 flywheel and put it on the M20 flywheel to retain the M42 starter.
This is how Metric Mechanic does it for their M42 flywheel conversion. Once you have removed the old M20 starter ring gear you can freeze the M20 flywheel in a freezer and heat the M42 starter ring in an oven and the M42 ring gear will slide on the M20 flywheel with little resistance.

 Thanks,
        Stan

[benz-tech]

I weighed the flywheel today at 28 lbs without the clutch. I'd rather not have to buy an M20 flywheel and change the starter.

You can remove the starter ring gear from the M42 flywheel and put it on the M20 flywheel to retain the M42 starter.
This is how Metric Mechanic does it for their M42 flywheel conversion. Once you have removed the old M20 starter ring gear you can freeze the M20 flywheel in a freezer and heat the M42 starter ring in an oven and the M42 ring gear will slide on the M20 flywheel with little resistance.

 Thanks,
        Stan

That would be true if they were the same diameter. They, however,  are not. The m20 flywheel will require machining to accept the m42 ring gear.

[Warsteiner]

bez-tech is correct. The M20 FW will need to be machined in order to accept the M42 ring gear. It's not a direct swap no matter how cold you get the FW. The ring gear will still need to be heated if done correctly. It's not a difficult task but the FW is a very hard material and will eat expensive bits, hence the reason for the cost of them being so high as compared to the JB aluminum ones.

Cheers,
~Ralph

[avt007]

thanks for the info, guys. I am stuck with using an original BMW FW, no aftermarket allowed, but I can lighten it.

[benz-tech]

Source a late m20 starter. I honestly think it's the easiest way. Plus it's spins an m42 over very quickly.