BenM's M5X/S5X Frankenmotor build

[M-technik-3]

No it was this year either pay extra for track side parking or park on the crazy tiny lot right after you cross the bridge. Both M3's got hung up trying to park.

[Fidhle007]

Thanks man. Hope the new shell for the S50 is coming along...

It's getting paint and some minor fender modification as we speak... I'm also pulling the motor from my old car today and tomorrow, my plan is to have everything together by the spring for track season. :) I'm so bored without a car though, I spend all my time acting like an angry old man on the internet!

[BenM]

Here is another link on BFC for calculating displacement and compression ratio that I found - http://forums.bimmerforums.com/forum...5&postcount=31


It's pretty good, but I don't think its entirely accurate.

[dude8383]

Thanks man, I'd like to chat about it sometime if you ever have a minute.

To be honest, I'm still figuring it out myself. The short answer is that its a ratio of volume at BDC to volume at TDC. Someone from Brazil over on BFC recommended this combination and figured I'd try it. Here is a good calculator I found with google - http://www.csgnetwork.com/compcalc.html

The issue is trying to find the proper info to input, as well as the stock s52 piston specs.

Sure man, feel free to hit me up on AIM or google talk. Shoot me a PM, I'm online all day at work :)

Here is another link on BFC for calculating displacement and compression ratio that I found - http://forums.bimmerforums.com/forum...5&postcount=31


It's pretty good, but I don't think its entirely accurate.

Man, I still can't calculate some of the data because I don't have much to work with :(

That has some decent info about the M52 which more closely resembles my build. I bored my block out to 84.5 so I think the numbers will change a tiny amount.

http://www.usautoparts.net/bmw/engines/m52.htm

Found this as well:

http://www.secondchancegarage.com/public/165.cfm

^not bad

[BenM]

I've been in contact with a member from Brazil on BFC who has an excel formula on calculating compression ratio. I've already measured the dish volume and compression height of the S52US Piston I have, so I will post up that info in the next week or so.

I'm also opening up the M50TU in the next couple of days so I'll be measuring the M50 engine deck height, piston dish volume and piston compression height. This will help others who want to do odd M5x/S5x combinations for calculating compression ratio.

Also, if anyone has any spare S50US or M52 pistons laying around that they need the compression height and dish volume of, I'd be happy to measure it for them.

[Fidhle007]

FWIW an M52 has flat pistons. I'm not sure about the S50US though.

[BenM]

FWIW an M52 has flat pistons. I'm not sure about the S50US though.

Hmm, thats good to know. I know the M50TU is flat top too, but I believe it has a greater compression height because of the shorter stroke and 10.5:1 compression ratio. I just need to find someone with an S50 piston to get a little more info.

BTW, does anyone know if the 86.415mm rings that are available through AutohausAZ, Pelican, etc. work with the 86.365mm pistons? There's only a .002" difference, and I plan on having the block honed out that much anyways. I really don't want to buy the 86.365mm ones through BMW since they run around $115 per piston.