Maximum power from a stock M42.

[avt007]

Hi everyone,

I'm new to the M42 world, and I've been looking around at various forums, trying them out.

This forum looks very good, so I'll post here what I posted on M42club, in the hopes of getting the most advice and feedback.

"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

[anthonymax007]

Hey man, welcome! I'm not an expert by any means, and hopefully others will chime in but here's my two cents.

The stock air box works best, no need to run a cold air intake if you don't have to. For your flywheel, I'd say to go the route of the lightened M20 flywheel. That seems to be the most common flywheel upgrade. I'm hoping to get that done soon for my car.

People recommend the MarkD chip, although I run a Squid chip in mine and I personally love it. I haven't had my car on a dyne to record any numbers though. Some guys adjust the cams to get a little more out of the top end, but I have no experience with that.

Give the link below a read. It highlights some of what you're asking. Are you able to change out your differential for one with gearing that would better suit your needs? That might be another consideration as well.

http://www.r3vlimited.com/tech/318is/318is.htm

[avt007]

Hey Anthony,

I haven't decided, but I figure on running some kind of large diameter intake runner with a K&N drawing air from the nose somewhere (I run a composite nose meant to be a Dodge Challenger).

The chip, I like the sounds of the Mark D, but I haven't been able to contact him about it. I will probably dyno this when it's done, and compare stock vs whatever chip I get.

I haven't figured out what diff I have yet, but I'd like to drop 5% or so to raise my rpm. Currently I run about 4800-6700 rpm, with the diff and tires I have now. Higher rpm would reduce bog out of the corner.

Since I run a short track (1/4 mile) everything is about 2nd gear acceleration in that rpm band.

The flywheel is a big issue, and a bit confusing too. Our rules call for a stock flywheel and clutch, so aftermarket aluminum is out.

Thanks for the link, it's very interesting.

[bmwman91]

Yup, the stock air box is best. Don't touch it. I have a 2.1L ~205bhp m42 and I did a bunch of datalogging on it that showed ZERO performance gain with a MAF and M30 air box (60% more filter surface area).

The same goes for the exhaust. On an internally stock engine, just leave the exhaust alone.

Chips...MarkD 93 octane if you have access to the gas. Otherwise a MarkD or Conforti 91 octane chip is good.

As mentioned above, the only other bolt-on worth a damn is a lighter flywheel. That assumes that you can change that and still meet the racing class rules. The M42 was prettymuch optimized from the factory, with the exception of the weak ECU chip tune. Back in 2003, I put down 131whp with an internally stock M42 and Conforti chip on an Dynojet. After wrecking that car, I put down ~120whp with another 1991 318iS and the same chip in 2006. A very clean, low mileage M42 with a good chip is going to make 150hp at the crank, tops. No amount of bolt-ons or other trickery will change that.

BMW knew what they were doing when they designed this engine (and all of them for that matter). There is nothing that any of us are going to do or think of that was not already considered in the design...except the chip tune. The general thought is that they used a weak ass tune on the 318iS so that it would not be as competitive with the more expensive M20-based 325 models and eat into their bottom line. It was also the most technologically advanced engine they put into the E30, so maybe they were just playing things safe.

[avt007]

Thanks for the reply. The rules call for all stock internals and injection, but I can run any BMW flywheel.

The exhaust has no cat, and is large diameter back to a very loud and free flowing muffler, exiting in front of the RR wheel.

So all I can do is exhaust (done), cold air intake, chip, and in the M42's case, adjust the cam timing.

Trying to find definitive cam timing results, backed up by dyno numbers, is impossible.

The stock airbox goes fairly far forward, so maybe I'll retain it, and run a pipe to a hole in the nose to pull cold air.

Thanks guys, I only joined this forum a couple hours ago, and already I'm getting good helpful information!

[MVincken]

i´m not sure you get a lot of profit from a lighter flywheel.
like you say yourself, the car is only used above 4000 rpm, and if you want to accelerate again at this rpm, some inertia would be welcome.
Edit: i´m not saying the standard fly would be best, you will have to test this to get the best one. euro single mass m42 fly is possibly the best one to start. for the m20 fly you also need a m20 starter or starterpin and m20 clutch

further you can play around with the variable camshaft gears. increasing the intake angle will get you more horsepower at higher rpm, but would lose you a lot at lower rpm, but again: the car isn´t used here so you don´t care.
when you have done that, you can set your exhaust cam later, again increasing your top-end horsepower.

also a possibility to increas fullthrottle horsepower is increasing the diameter of the throttle valve. i´ve read you can increase this with 3mm, but honestly i dont know what´s exactly possible and which throttlevalve you have to put in to clear the extra gap created.

a faster chip will definately get you the first couple of horsepower, but after these upgrades you better get a custom chip to get the maximum out of your "stock" engine

[bmwman91]

Messing with the cam timing is sort of pointless unless you plan to take the car to a dyno shop for a custom tune. Trust me on this, it will run like shit if you adjust the cams without getting the ECU retuned for it. There's just no way around it. If you do plan to run the car only at high RPMs then maybe you could optimize the cam timing for that, at the expense of mid-range torque. An engine with electronic ignition and fuel control is not going to respond well to physical changes to its operating parameters because the software was tuned around the original parameters.

That wide-open exhaust is probably not helping things. It is almost guaranteed to kill low end torque and some midrange, which might not be an issue for you. The M42 doesn't really rev all that high so I would bet that the benefit at higher RPMs is also negligible.

Leave the throttle body alone. The engine builder I worked with even told me to leave it alone on my very not-stock M42. Again, I am making 205bhp from a 2.1L M42 with a stock intake and mostly stock exhaust (Supersprint catback only because it sounds and looks better than the rusted-out stock one). I did data logs with different intakes, including a MAF conversion, and it did precisely ZERO for power at any point in the RPM range, and the engine goes up to 7700RPM. BMW optimized the M42 for what it was and if you are racing in a stock class then there is very little you can do that will improve performance. Most of the "common sense" bolt on items like straight exhausts and open air filters will just hurt performance overall. Seriously, I have owned and modded M42's for almost 16 years and there's no low-hanging fruit other than a good chip and lighter flywheel. Every other bolt-on is a big fat waste of time and money. The only way to get more power from an M42 is to increase displacement, higher compression and hotter cams with some head work...which are obviously not options for the class you are participating in.

My advice is to do a season with the stock engine and then go from there. And to at least put stock diameter exhaust pipes back on. A stock M42 just is not flowing enough air to see a benefit from a wide open exhaust, even at its limit of 6700RPM (or 7200RPM with a chip).

Your bigger focus should be on engine reliability if you plan to beat on it. The timing chain setup in the E30 M42 actually has a big flaw (IMO) in the design. The deflector sprocket that deflects the timing chain around the water pump and thermostat is prone to failure, and the timing case itself is known to break there, causing the timing chain to come loose. I am not sure if this would be allowed by your class, but you should SERIOUSLY consider finding a 1994-1995 M42 timing case and sticking that in because they got rid of the deflector sprocket and used a stationary plastic guide rail there. It is MUCH more reliable. It makes no difference to performance, so maybe it would be a legal swap. While you are in there, you should think about completely overhauling the timing chain setup anyway since it might be somewhat worn. There is one other major reliability issue too. If you drop your lower oil pan, there is a good chance that you will find some bolts in it (and maybe pieces of the timing chain and guides). The bolts that hold the upper pan to the timing case (inside the pan) are known to fall out. You should reinstall them to the specified torque with some red loc-tite after cleaning the oil out of the threads. The big issue here is that the bolts fall out and the gasket around the oil sump loses compression, imploding and causing the oil pump to suck air.

Finally, there is the engine oil. I highly recommend Mobil 1 15W-50 with a Mahle filter. This will offer the best longevity for the M42 since it is a strung-out 4 cylinder. This oil also has the highest ZDDP content of any non-race oil, which is absolutely critical for flat-tappet applications like ours.

[avt007]

Very good points, thanks. I can't touch the throttle body, although changing the timing chain setup would be ok.


I think a lighter flywheel can only help, not just from the acceleration point of view, but also overall weight. I'm trying to cut down every pound of unnecessary weight on the car. It will still be above the minimum weight no matter what I do, but every bit helps.

I'm not averse to changing the muffler, but again, without data, any change is pointless. Dyno time is pricey as it is without trying all sorts of different mods.

As for oil, the rules say no synthetics since they can't be soaked up by cement dust. They don't know what you're running, until you leak and they try to clean it up.

Keep the ideas coming, thanks.

Oh yes, the oil pan. I've already had to modify my M10, since all turns are to the left, the oil sloshes right, and starves. I fixed that, but the M42 has a very different pickup, so I've got more work to do there, too.

[econti]

Lighter flywheel will help with faster gearshifts. I find that the thing that contributes the most for gearchange speed with mine is waiting for the engine to drop enough in RPM to not grind.

My 2 cents, anyway.

[avt007]

Thanks econti,

The funny thing about running a short track oval is that I don't shift. Once I'm in 2nd, that's it. But I am constantly (every 7.5 seconds) accelerating from 5,000 to 6,700.

[digger]

can you get custom burnt chips?

[avt007]

can you get custom burnt chips?

There's a local speed shop, specializing in ECU tunes, but I don't know if they can handle the older technology here. I had them dyno the car last spring to jet the carb.

[anthonymax007]

Back in 2003, I put down 131whp with an internally stock M42 and Conforti chip on an Dynojet. After wrecking that car, I put down ~120whp with another 1991 318iS and the same chip in 2006. A very clean, low mileage M42 with a good chip is going to make 150hp at the crank, tops. No amount of bolt-ons or other trickery will change that.

I just participated in a dyno day here and put down 115whp and 107tq on a dynojet. I'm running a Squid tuning chip and am stock everywhere else. I assumed my motor was well worn and in need of some maintenance, but after reading your numbers it looks like I've got some work to do.

[bmwman91]

I just participated in a dyno day here and put down 115whp and 107tq on a dynojet. I'm running a Squid tuning chip and am stock everywhere else. I assumed my motor was well worn and in need of some maintenance, but after reading your numbers it looks like I've got some work to do.

When I dyno'ed the first car, it had ~95,000 miles and the previous owner had been meticulous about maintenance. The second car was dyno'ed with ~150,000 miles and the previous owner had not taken great care of it. So, aside from whatever differences two M42 engines have out the door from the factory (and I am willing to bet that there is at least a 5WHP tolerance between engines), age and condition are also a factor. The first M42 had slightly better compression numbers too, IIRC. Then, there is also the fact that you will see a couple of HP differences between runs on the same dyno on the same day. Comparing numbers between dynos across a decade is also going to add some uncertainty.

So, all in all, there may very well be nothing wrong with your M42 and 115WHP is what that particular dyno told you on that day. You can try to get a hold of a MarkD or Conforti chip and try one of those to see if it makes a difference, too. If you have fairly easy access to a dyno, I can mail you my Conforti chip to borrow for the dyno (if I can find it) since it is of no use to me on my 2.1L M42. Heck, any chance you could do a couple of pulls with all 3 chips (stock, Ssquid, Conforti) and post the results?

[avt007]

I done a lot of electronic board repairs and chip replacements over the years, and I've been wondering about trying different chips in a dyno environment.

It can be fiddly, installing chips without bending pins, etc. I've considered buying a second ECU, so that on the (expensive) dyno, I could plug in a different ECU with a different chip. Thoughts?

Also, I just got a reply from the shop, they have no BMW OBD1 ECU tuning experience, however they do have the dyno files from the spring, so I'd have a comparison between engines.