M30 head

[Jose]

Anyone out there had any experience skimming of the head of an M30 engine in order to raise compression ratio from 9:1 up to 10:1 ?

[632 Regal]

wow.

[MSM]

Hi Jose,

Did you manage to find any more useful information with respect to your question?

Were you planning to run 10:1 with the standard cam or with a longer duration one? A longer duration cam should drop the effective compression ratio, so you can, in theory, get away with more static compression.

[Martin in Bellevue]

would throw the cam timing out the window.

Hi Jose,

Did you manage to find any more useful information with respect to your question?

Were you planning to run 10:1 with the standard cam or with a longer duration one? A longer duration cam should drop the effective compression ratio, so you can, in theory, get away with more static compression.

[MSM]

Hi Martin,

Emmissions could certainly be an issue, depending on your locality.

I would assume that the available fuel octane would also have been taken into consideration before such changes were implemented.

Cam timing could be sorted out reasonably easily, and you would expect it to be addressed on any engine being changed that much.

My quick calculations worked out that for a 0.010" skim you would see a 0.26 degree advance in cam timing. Another quick calc reckons on needing a 0.044 thou skim to obtain a 9.99:1 CR assuming the motor started off as spot on 9:1. A 0.044" skim would advance the timing by 1.15 degrees. Assuming I haven't messed up the calcs too much, the cam timing adjustment required is not that big. In fact, assuming no interference issues, a slightly advanced cam would, as I understand it, tend to help improve bottom end and midrange power at the expense of a small bit of top end.

I would also assume that valve drop clearance would also have been addressed in such a build, especially if the cam in use is running a higher lift as well as longer duration.

I would also assume that the engine management would be remapped to properly manage the new configuration.

Personally, I like the idea of a higher than 9:1 CR M30B35. Alpina ran a hotter cam and a 9.5:1 CR in the B10 non-turbo car. This car made more power than the factory 535 and, as I understand it, returned better fuel economy too. The throttle response woulld also benefit from higher compression. I suspect that the B10 non-turbo also had to pass exactly the same emmissions standards that the factory 535 would have.

So, other than cam timing, internal clearances, fuel octane, and emmissions issues, what are the other big issues that need to be considered when running more than 9:1 CR on an M30B35 motor?

Cheers.

msm

[Martin in Bellevue]

I have the Ireland 284 regrind in my '89 535. It has a little something; Ireland offers a 292 which would require oversized eccentrics. It would seem to be what you are looking for, at a hella good price. https://secure9.nexternal.com/shared...unt2=854896187

I think custom pistons would be the way to higher compression. There was a set of m88 pistons on ebay recently that a few of us were watching; I question the wisdom of a rebuild with used pistons, but they looked very good in the auction. Most bmw tuners/rebuilders want at least $1,200 for a set of high compression pistons.

I do agree that more compression should really wake up the m30.

[MSM]

Hi Martin,

Thanks for the recommendations. However, I am currently in the process of sorting a failed headgasket, and I have already replaced the worn cam and associated bits. With any luck, I may get the chance to put the head back on this weekend.

I was actually interested to expand on the discussion of running higher compression on the M30B35, as there doesn't seem to be very much in the way of technical information about this on the forum as yet. Personally, I feel that 10:1 from a skim is pushing it a bit far, however, I cannot see why ~9.5:1 (through a skim) would necessarily cause massive problems, assuming, of course, it is balanced with appropriate supporting changes.

msm

[Craig]

I do agree that more compression should really wake up the m30.

I got yer compression right here!



Seriously though, from what I've seen on dynos and heard anecdotally it's pretty damn hard to get much more power NA from an M30.

A point higher compression will yield about 4% more power, or maybe 10hp on the high end. That's not much, for a lot of work and money. You'd see similar gains with just a MAF conversion, with a lot less work and money. Even throwing the kitchen sink at the car (MAF, head, cams, etc) would probably not get you much more than 240-250hp, at least based on what I'd seen from this board and local cars.

[Jose]

Skimmed it 0.65 mm with a 288 degree cam Omega forged pistons custom headgasket , tubular manifold, de-catted it, open HKS Skyline muffler and chipped the hell out of it. Nothing more than 254 bhp at the wheels. Just crap if you ask me.After cranking it every day to see if it would hold, the head cracked in 5 places after only 600 miles.
That made me decide to just build a whoop-ass turbo M5 slaying machine. No more fussing about with the M30 engine, it's a torque motor not a revs machine.It will never be real fast if you don't turbo it. If you don't believe,read this; 9 of our customers have E30 M3's of which one is a rare Alpina M3 B6 3.5s with 260 bhp. This thing is not quicker then a standard M3, just because it takes too long to rev. Turbo is the solution for real power.

[MSM]

Craig,

LOL!

Good point about forced induction, however, in my case, I already have a silly fast turbo car as a toy, I bought my 535 as the sensible grown up car to rely on whatever state I leave my turbo car in. I am currently building an experimental engine up for the toy, so the 535 seemd a good idea (used to have an E30 M3 for the same reasons). Naturally, the 535 decided to spit out its headgasket before the new engine for the toy was finished. Such is life.

Anyways, I wanted a decent sized NA motor with RWD to play with and to help with my M3 withdrawal symptoms. I want to keep it NA and enjoy the good points of NA motors. I have enough fun playing around with turbo lag and suchlike on the toy.


Jose,

I'm sorry to hear that the NA tune didn't last long for you. How high a compression did you end up running on it? An instantly responding non laggy 254hp at the wheels must have been pretty impressive, at least for a while.

msm