S50b32 psitons with M44 crank

[IlovM42]

Hi everyone

As i said in an another post, i'm looking to build a little N/A M42 for my 318is e30

I have been thinking on 2 different simple setup

First setup is to use M42 crank with 86mm bore S50b30 pistons (but haven't find them yet) to make a 1881cc M42 with higher compression ratio.
this avoid a lot of work, only things to do is bore the block, change rod bearing and M44 head gasket as I know.

Second setup is to go with M44 crank and 86,5mm bore S50b32 pistons (already find them) to make a 1957cc M42 as I'm keeping the M42 head, but i don't know if the M44 head gasket can be use, also i didn't find a lot of information about M44 crankshaft. Engine is not going to revs past 7200rpm so there will no problem with the M44 crank right? the fact that is cast and not forged like the M42 one is really a problem on such a little N/A engine? I guess problem come with boost.


So if you have some ideas/answers/remarks about this two setup feel free to post

I also have an M47 crank but this involve much more manufacturing and i want to keep the engine a square one (bore > stroke) and don't go long stroke (bore < stroke)

All this will be going to power my stripped out 318is e30, with E36 gearbox and 3,45 LSD

Thanks in advance!

[bme30]

Sounds good!

Im keeping mine real simple... Just going to swap in m50tub25 pistons.

[IlovM42]

what is the benefit of using M50b25TU pistons than M44 pistons if both of them are 84mm diameter?

[bme30]

Piston design.. Higher compression.

[IlovM42]

do you use those pistons on a M42 or M44?

[bme30]

do you use those pistons on a m42 or m44?

m42

[bme30]

Here are some helpful links if you didnt come across them yet..

http://www.motortraders.net/groups/attachments/1_35_m42.pdf

http://www.e30zone.net/e30zonewiki/index.php/M42

M50 piston chart..

http://www.e30zone.net/e30zonewiki/index.php/M5x#Pistons

Enjoy

[bme30]

Here are some helpful links if you didnt come across them yet..

http://www.motortraders.net/groups/attachments/1_35_m42.pdf

http://www.e30zone.net/e30zonewiki/index.php/M42

M50 piston chart..

http://www.e30zone.net/e30zonewiki/index.php/M5x#Pistons

Enjoy

[bme30]

Sorry about the double post

[IlovM42]

thanks for the links

[wazzu70]

Excellent links. I havent seen the M50 piston chart.

I would go with the M44 crank. Might as well add some stroke to the equation. I dont think forged versus cast really matters here! I don't think it matters for most FI builds either.

Not sure which pistons to use. Personally I would just use custom ones to make sure I get the bore and CR correct.

[accota]

Sounds good!

Im keeping mine real simple... Just going to swap in m50tub25 pistons.

Have you already done this?

Doesnt the piston slap the valves? Because the M50TUB25 piston with lowest compression height has cr: 32.55

This gives a piston that sits (32.55-31.65)=0.9mm higher. Standard deck height is 0.15 above.  This makes about 1.05mm above deck hight.

The head gasket is 1.75mm compressed, giving you only 0.7mm to spare.

The valve pockets from the M50TUB25 are 0.87 and 2.24. If u subtract 0.9mm from these pockets. U get 0(+.03) and 1.34mm. Comparing this to the standard m42 pockets of 1.65 and 1.85. So thats seems like a recipe for disaster. If you want higher CR, that asks for higher duration, higher lift cam...

[bme30]

Working on it and yes i have taken all that in consideration.  I will have the pistons decked and have new slots to make up for the valve clearance.  

As for the cams.. I will go with a longer duration intake and leave the exhaust cam stock.  Im already running itbs from a gsxr 750 tuning with tunerpro rt/ ostrich 2.0

With most of my time and funds going to my new born this build will be a long one... I hope to have most of it if not all of it done fall 2013.

[accota]

You could find urself some s50b30us pistons, also wrist pin 22m.
CR 32.8
VT 0.52 and 3.11

s50b32us is 86.4mm but CR 31, so never high enough.

If you go through the hassle of pocketing and decking pistons w new rings, why not bore to 86mm? Its an extra cost of about €300, the rings are also more expensive. That would make a great short stroke high revving, with your itbs and assymetric cam profiles. A dream come true :p

Also the M3 pistons are forged, so lighter, designed for the job and less weakened by pocketing and decking. That makes for all forged internals (drool)

Your next limitation must be the hydraulic lifters.

Congrats with the family expension, a future m42 enthousiast

[bme30]

Thanks for the added info!  Im going to look into it.  If im going to upgrade the valve-train i might as well get the crank balanced and harmonic balancer to match so i can rev past 7200rpm without any crank walk