California M42 Upgraded cam shafts

[OSAH racing]

Short version of a semi long story: new to me 1991 318i, M50 S52 swapped, Track day build, California car registerer out of state, Metal in the oil pan and filter. I want to drive it on street and AX/ track day so I am Moon walking this thing back to an M42. I have a potential 123K engine in decent condition ( heard this before ). I think too avoid a repeat disappointment new bearings, seals and a valve job are in order. I have read that the M20 single mass, exhaust and a quality chip are solid upgrades.

The trip to DMV the 318 will have all the California emissions on it. Which leads me to the camshaft question. Will the Cat Cams 279/274 run on a stock ECU. More importantly do cam upgrades produce any power on stock bottom ends? Does the engine characteristics improve ( pulling harder to redfine) ? 15 to 20 horse power is good enough for me but less than that and it is money not worth spending.

signed Old, Slow and Happy.

[bmwman91]

279/274 is getting a bit hot for the street IMO. My 2.1L runs well on a 272/258 combo, and it didn't have problems back when it was on a mostly-stock tune. I cannot say for certain, but I'd think that the stock ECU would run the engine with the hotter cams you are considering, although I am not sure that they would provide as much benefit to a stock displacement M42. Give Metric Mechanic a call and ask about their cam recommendations...they design their own profiles with a focus on improving top end flow without sacrificing mid-range torque. For a street car, you want to avoid prioritizing top-end performance too much since it kills drivability the rest of the time. Since you want to also do events with the car here and there, maybe streetability does not apply, in which case go for it and build a top-end screamer.

As far as exhausts, I do not think that they do all that much. The stock header is well designed and I still run it on my 2.1L. I have a welded in Magnaflow cat since that is one of the only CA-legal options available for replacements, and I have a Supersprint cat-back which sounds fun but I am not sold on the idea that it is making more power for me. Basically, stick a muffler on it that you like is my position.

Chips...this is the single biggest improvement you can make to the M42. I highly recommend Sssquid tuning. They have a lot of M42 experience and their chips are complete tunes...all maps (idle, part throttle, WOT) along with some other timing constants that improve drivability. If you go with hotter cams, they can also work up a tweaked tune to capture more of the gains.

I'd say that cams and a chip will easily net you more than 20bhp, with the chip doing most of the work.

The flywheel...two options:
1. You can go with 100% stock M20 parts (you also need the shorter M20 FW bolts) as long as they are for the 1989+ M20. The other thing you need is either the matching starter, or you can swap the pinion gear assembly from an M20 starter into your M42 starter. You will notice a little bit of transmission rattle in neutral.
2. RHD 8.5lb flywheel. It uses the M20 clutch parts (FW bolts too), but has the starter ring machined to work directly with the M42 starter. This is probably the cheaper option in the end since you do not need to find an M20 starter. Do note that you will get a lot of transmission rattle in neutral, and I think that you will also be guaranteed to need a bit more of a custom tune to get proper idle stability. The FW is LIGHT and on a stock tune the engine might stall coming off the throttle lol...I had that issue at first until I got the tune sorted out. Despite that hassle, the engine revs like a champ, rev-matching is almost effortless, and the car engine-brakes a lot better too.
https://racehead.com.au/product/bmw-...254-m40424344/


Be sure to post pics as you overhaul the engine! It is always good to see someone reviving one of these!

[OSAH racing]

Bmwman91, i see you have a lot of time with your M42 car. Your response is much appreciated. if the M42 is designed to make Top end power that's fine with me. I will give MM a call as a decent idle for the street would be nice. The plan with this car is to be dual purpose ( yes i know there are compromises with dual purpose ) its more track car than street car. it won't be a daily as I am a general contractor and pulling a 8K trailer will not suit the e30. Cisco is meant for fun and a top end screamer sounds perfect. I too busy to do the engine rebuild, but I do get involved and if its okay here I will post pictures while the shop progress through the process. I do plan to do a bunch od other work myself.

Current specs on the car 91, sunroof delete sedan, AST coilers, massive brakes, 4.10 LSD, G250,DSSR, poly everywhere., M3 rack, M3 radiator, reinforced front and rear subframes, 15 x 7s, gutted, m50 S52 head. bolt in half cage.

Plans.

M50 out M42 in by BMW Pro independent

weld in 1/2 cage moved back and up tied into the rear shock towers
Lexan door windows and rear window
power wind delete to cranks
Porsche RS style interior
front end splitter / oil pan skid plate custom made
spare tire delete muffler center exit with rear defuser custom made

[bmwman91]

Aah, ok yeah forget my words of caution then lol. Depending on your budget, you might want to talk to MM about having an engine built...not sure if you are racing in a class with strict governance or not, but it would be a mostly turn-key way to get a reliable new engine that makes good power and is fun as hell to drive. I have their 2.1L 'Rally' engine with the RHD flywheel I mentioned & a Sssquid tune, and it is a blast. It makes good midrange power, and also pulls hard right up to 7500RPM. MM said that I could run it higher, but I want to get 100K miles from it, and power starts tapering off a little above 7000RPM. Since you are building a (mostly) track car, they might have hotter cam profiles for you too.