Author Topic: High compression 1.9 project thread (Read 12291 times)

2002maniac · « **on:** March 20, 2006, 10:56:49 AM »

Ok. Since my motor burns oil, and has relatively low compression, I have been wanting to build up a motor for some time.

I originally wanted to do the M47n crankshaft but I realized that custom pistons would definately be needed and that doesnt quite fit in my budget. I bought 5 S52 pistons from a guy on bimmerforums who broke a valve and damaged one piston. Since it was an incomplete set (for the 6-cyl guys) I got them for almost nothing!

I am going to go pick up a high mileage motor as soon as the guy get it out of his totalled car.

The S52 has a 89.6mm stroke and uses a 135mm rod. The M42 of course has a 81mm stroke and uses a 140mm rod. If the deck height is the same in both motors we can calculate the pin height (EDIT it isnt so we cant!). It turns out to be 179.8 for the S52 and 180.5mm for our beloved M42. From this we can see that the S52 piston sits .7mm higher in the bore than the M42. (EDIT this was all great in theory, but it doesnt work) I doubt there will be any valve contact in this configuration, but as you will see, the CR will be a bit too high for street use anyway.

I'll be using the M44 headgasket which comes in 2 different thicknesses from the dealer.

I'll have to wait until I get my pistons and head so I can know for sure how much to mill off the pistons but I think it will be between 1.5-2mm off the squish ring. I am shooting for 11:1 CR since a lot of S14 guys run that on California gas at sea level with no problems.

If you have any questions, shoot...

m42 fan · « **Reply #1 on:** March 20, 2006, 11:17:20 AM »

Just one question. Is this going to be a race only engine, or will it see significant ammounts of street time? Just wondering

Brian

bmwman91 · « **Reply #2 on:** March 20, 2006, 11:20:36 AM »

Sounds like a neat project. As always, I have to know what engine management you will be using. The Motronic could work fine if you put in injectors that are of a higher flow rate proportional to the increase in displacement. The only real worry is in the open-loop operation at WOT, and with the properly sized injectors it should not really be an issue. The ignition timing would seem to need some modifications since the CR is going up, but I have heard of folks making changes like this w/o software modification. Keep us posted!

2002maniac · « **Reply #3 on:** March 20, 2006, 02:54:20 PM »

Quote from: m42 fan

Just one question. Is this going to be a race only engine, or will it see significant ammounts of street time? Just wondering

Brian

This is my daily driver. I expect it to run with no detonation on 91 octane. The S14 guys are fine at sea level so I think I should be ok at 5000ft elevation.

Air will be metered by a 2.75" MAF and controlled by an SMT6 piggyback.

nickmpower · « **Reply #4 on:** March 20, 2006, 08:43:53 PM »

f that. Just do it right with the m47 crank. Save up as long as you need, in not like you need the motor right now. And didnt the guy on bimmerforums just shave the top of his pistons?

2002maniac · « **Reply #5 on:** March 20, 2006, 11:48:43 PM »

Quote from: nickmpower

didnt the guy on bimmerforums just shave the top of his pistons?

Almost 4mm. That is alittle too much for my comfort. That method makes for a small space between the piston face and the ring lands.

Custom forged pistons are ~$450-600

e9nine · « **Reply #6 on:** March 21, 2006, 06:48:58 AM »

Quote from: nickmpower

f that. Just do it right with the m47 crank. Save up as long as you need, in not like you need the motor right now. And didnt the guy on bimmerforums just shave the top of his pistons?

AS some of us have stated on r3v, don't think what he did is a simple plug and play. There is a descrepancy with the diesel cranks, they rare as heck and there's more machine work involved with his process than you can see.

Not trying to rain on your parade for the m47 set up as it will most likely just end up being another project that never makes it to fruition. Nothing wrong with being the innovator but it comes at a huge cost. If you do get the SAME exact crank and can confirm with the overseas shipper, rock on. We all know that's never the case with most overseas or even local parts dealings.

Back on topic; rock on with this 1.9l high compression mission

1991318is · « **Reply #7 on:** March 21, 2006, 04:47:31 PM »

Sounds awesome, let us know how it ends up and goes along the way.

bmwman91 · « **Reply #8 on:** March 21, 2006, 11:29:06 PM »

Yeah, I second the first idea for doing this. Getting an M47 crank is tough, and there is some hard machining that needs doing. Let's see if we can come up with some sort of home-brew solution, that is nice & reputable as well!

kowalski · « **Reply #9 on:** March 22, 2006, 01:54:39 AM »

Quote from: bmwman91

Yeah, I second the first idea for doing this. Getting an M47 crank is tough, and there is some hard machining that needs doing. Let's see if we can come up with some sort of home-brew solution, that is nice & reputable as well!

how much would a custom crank cost? i'm sure you can get one CNC'd or somthing... that might defeat the whole cost idea, but atleast you wouldn't have to find one then?

bmwman91 · « **Reply #10 on:** March 22, 2006, 03:09:57 PM »

Machining one would not be cost effective by any means. And, you want a forged one anyway. Not saying the M4 crank is a bad idea, but it isn't the easiest.

kowalski · « **Reply #11 on:** March 22, 2006, 03:16:04 PM »

you can get a forged block, and machine it out of that. i guess oil journals would be hard to machine...

bmwman91 · « **Reply #12 on:** March 22, 2006, 06:01:50 PM »

Hehe, quite the optimist. Hell, if you can find a way to pull it off, hats off to you! The thing is that it must be forged into its shape. Machining cuts grain boundaries and does other stuff like heat/anneal the metal, and can lead to crack propagation in the metal. The M47 crank is sounding better by the minute lol.

tim_s · « **Reply #13 on:** March 28, 2006, 08:13:47 AM »

nice project! be interesting to see what you get from this. what HG are you going to run? and just out of interest, why this route rather than m44?
oh and i've said it before but if anyone wants an m47 crank i'd imagine i could find one over here without too many problems, the issue is cost, as these are expensive, heavy to post and then require mods to fit.

m42 fan · « **Reply #14 on:** March 28, 2006, 08:25:34 AM »

I'm def. watching this one with interest also. Even though I don't have any plans for the immediate future, it's always nice to have options for when rebuild time comes around.