Author Topic: M42 head work (Read 35980 times)

unome · « **on:** November 13, 2011, 12:07:22 PM »

Hi, has anyone documented a proper port and polish of an M42? Everyone has stroked or turbo'd or bored these engines, but I'm looking for whatever I can do basically for free. ( no, I'm not going to just start grinding)

I've read comments like "port aggressively" or "don't touch the ports" but nobody ever goes into detail. I know Metric Mechanic ports these with success but as you would expect, they share no details. Since I want to spend nothing, a MM head is not going to happen.

I've got a 318is E30 that is track-only, so streetability is not a concern. It will live at the red line. The entire car is brilliant on the track, so I'm not going to swap etc. but as long as I've got it apart I'd like to help it breathe a bit better. Specifics would be very appreciated!

Thanks

Nelson_40 · « **Reply #1 on:** November 13, 2011, 03:10:43 PM »

I have never seen anyone go past the "I was thinking about P&P for my M42, but I don't want to spend a bundle" stage. Perhaps you can be the first. I can say that MM claims a 6% gain in flow, "Our M42/M44 heads flow 6% over stock. These heads have our patented Surface Turbulence concentric grooves machined into the back side of the intake valve and the heads o both the intake and exhaust valves. This helps to reduce detonation in a boosted engine. It also helps prevent head cracking, increases fuel mileage and helps reduce emissions."

VAC has a picture of their stage 3 ports. http://store.vacmotorsports.com/vac---m42-stage-3-performance-cylinder-head-p1019c278.aspx?Thread=True

Perhaps the best thing to do on a budget is to make sure your intake runners, head to intake, and head to exhaust ports are close to matched as possible at home with no gasket overhang. In the end, although I base this on nothing more than personal feeling, I think there is nothing really useful to be gained from a P&P on the M42 without spending big bucks. Then again, on the track every single thousandth HP/lb/second counts.

Maybe you can find a ruined/cracked head locally and practice on that to see what you would like to change? Good luck however you proceed!

unome · « **Reply #2 on:** November 13, 2011, 05:27:31 PM »

Yes, nobody seems to get past the "I'm going to do this" stage. Well, the motor is apart, and it's going to go back together, so we'll see what gets done to it. I'll report back, but in the meantime if anyone has done this before, I'd love to hear about it.

dsm2002 · « **Reply #3 on:** November 13, 2011, 09:11:58 PM »

Look at my engine-in-build thread: Link. I have flow figures on the head before and after. The ports are 29mm although this maybe quite aggressive for a less experience engine porter.

wazzu70 · « **Reply #4 on:** November 13, 2011, 11:56:21 PM »

Keep in mind that M50 ports are very similar, so what works for them can work here too.

Overall the M42 head is very decent flowing. Depending on what tools you have access to, you can do a multi-angle valve job.

Other than that you can blend the valve seat to the head casting better and remove the protruding valve guide material.

On most heads, blending the seat to the head, smoothing out the short radius, and removing/tapering the valve guides gets you majority of the gains.

Boyracer · « **Reply #5 on:** November 14, 2011, 07:39:30 AM »

I think with some effort bit of gains can be found without having deep understanding of porting.

There is noticeable step where cast surface and machined surface meet on intake port. There is also small step between machined surface and valve seat. Also, combustion chamber can be blended more smoothly to valve seat, there is not some steps.

More involved is to remove valve guide that protrudes to intake port but that should yield nice gain.

I think I will try these basic things myself. Ports are quite generously sized compared to many other similar engines as they are.

Warsteiner · « **Reply #6 on:** November 14, 2011, 11:05:32 AM »

Once I get home from my wedding/honeymoon in Thailand I will be finishing my M42 stroker. I ported the head myself with the watchful eye of my buddy who is a BMW Master Mechanic. Just to give you an idea of power, my S14 is making 320+HP on 11.25:1 compression that we built.

I changed my head to 6mm valves along with 33mm buckets!

The pic in the VAC ad is a S14 head.....

The MM head gains 6% flow from changing over to 6mm valves from the 7mm ones. I have never seen or heard of any info that MM has ported a M42 head and stated any flow statistics. If they have done so, I would love to see it, I'm curious.

"The Power is in the Head"!! Port it and have fun. Not rocket science. There's a lot of meat to remove in there. I think I must have spent 4-5 hours porting mine. NO polishing Required. It's a myth. Just port it. I'll have pics and a write up when I get back home. Porting also gains you torque down low, just don't go overboard on cams unless of course like you said it will stay at redline. The engine only breathes if all components work together. Open the ports, ditch AFM, increase compression, increase cam duration, increase exhaust flow.

Have fun with it. Mark D or Midnight can tune a chip for you or go stand alone.

Lots you can do and have fun at the same time!

Cheers,
~Ralph

unome · « **Reply #7 on:** November 14, 2011, 05:54:52 PM »

Thanks for the replies! Lots of food for thought...

2002Harv · « **Reply #8 on:** November 19, 2011, 04:29:12 PM »

I would be careful here. When dealing with older designs it's easy to make improvments by using your eye and motor theory, but working with something as modern as an M42 it's very possible to make it worse not better.

If it were me and I wasn't paying someone with vast experience with these heads, I would go for the thinner valve stems and try to taper the guides a bit. Then maybe smooth out any irregularities.

If MM is getting a 6% improvement with all their resources, I'm sure the potential to do harm is high.

John

Warsteiner · « **Reply #9 on:** November 19, 2011, 10:18:21 PM »

John, MM gets 6% increase in flow from only changing over to the 6mm valves and guides. Stock M42 before '93 was 7mm. They never mention head porting whatsoever.....so the potential is very significant! More air+ more fuel= More power.....

As long as you compliment all the parts, cams, head, intake, fuel, exhaust, bore, stroke, and engine management, you will always make more power than stock.

I just met with a master mechanic here in Thailand that worked for Schnitzer. I saw M42's making 300+ HP with slide throttles and carbon air boxes running 8 inj's etc.....he showed me the ported heads!

I will be getting a complete set of the intake from the air box to the head. I might be making up sets if people are interested. These kits are very "street able" and run perfectly. These are replicas of the original Motorsport ones. So there is a lot of potential even for street cars not just race cars. But for race cars....it's awesome when you get all the parts right!

Cheers,
Ralph

wazzu70 · « **Reply #10 on:** November 20, 2011, 08:53:42 PM »

Ralph, no pictures? Come on!

Excited to see your setup!

For what its worth, I don't think there is a ton to be gained from head porting with the stock ECU. I really think you need larger cams and ECU tuning to make much of it.

Warsteiner · « **Reply #11 on:** November 21, 2011, 04:20:30 AM »

Yeah I had no camera can you frigging believe it!!

Yes you're correct in needing to retune a chip if you port the head and change cams. That's if you want full potential.

I'll be running the Dbilas setup for a bit until I get the ore setup sent to me. It's very cool!!

Cheers,
Ralph

bwawuz02 · « **Reply #12 on:** November 21, 2011, 05:06:52 PM »

Quote from: Warsteiner;108205

I'll be running the Dbilas setup for a bit until I get the ore setup sent to me. It's very cool!!

care to share the details of this "ore setup"?

wazzu70 · « **Reply #13 on:** November 21, 2011, 11:04:17 PM »

Quote from: Warsteiner;108205

Yeah I had no camera can you frigging believe it!!

Yes you're correct in needing to retune a chip if you port the head and change cams. That's if you want full potential.

I'll be running the Dbilas setup for a bit until I get the ore setup sent to me. It's very cool!!

Cheers,
Ralph

If that Dbilas set needs a home when you get your new kit, let me know. I would absolutely love a set of individual throttle bodies.

Warsteiner · « **Reply #14 on:** November 21, 2011, 11:45:33 PM »

That was "other" set up....sorry

The other setup is the Motorsport one that you've all seen in the pics for the S42. Carbon fiber airbox with arihorns and 8 inj's, slide throttles, and intake adapters to the head.

When I get ready to get rid of the Dbilas, I will keep you in mind.

Cheers,
~Ralph