External links now open in a new browser tab - turn this off in your UCP - Read more here.
Compression ratio's
-
- Posts: 37
- Joined: Jun 18, 2007 3:32 PM
- Location: SW Michigan
Compression ratio's
I hope that this is in the right section......
I want to start prepping for FI in the near future ( less than 6 months) Still using the M20 engine, I want to do the 2.7i conversion first. Does anyone know what the compression will be if I use an B27 short block with the B25 head and related parts. Reading from the strictlyeta website , all that was said was the compression would be low. How low??
I want to start prepping for FI in the near future ( less than 6 months) Still using the M20 engine, I want to do the 2.7i conversion first. Does anyone know what the compression will be if I use an B27 short block with the B25 head and related parts. Reading from the strictlyeta website , all that was said was the compression would be low. How low??
Exactly how low is hard to say. I do know theres a guy on an e30 forum with a standard eta block and pistons with a standard 325i head thats running about 20 psi of boost. You would probably be around 8 or 7.5 to 1. Apparently, off boost driveability isn't a concern. I would do it if I had the parts sitting around ready to go.
-
- Posts: 415
- Joined: Feb 12, 2006 12:00 PM
- Location: Charlotte, NC
this doesn't answer your question, but may be helpful in coming to a conclusion.
this fella has done a fair amount of research on the topic of M20 compression.
http://www.bmwccn.no/rogaland/Mahle_m20.html
this fella has done a fair amount of research on the topic of M20 compression.
http://www.bmwccn.no/rogaland/Mahle_m20.html
He's not quite right on super e pistons. I dont know about his numbers, but the diagram is way off. They are pretty much 2.5i pistons with a deeper dish and different dimensions for the 81mm stroke. They do slightly protrude above the deck at TDC, unlike standard e pistons. They do not have a symmetrical bowl as the diagram shows.
-
- Posts: 415
- Joined: Feb 12, 2006 12:00 PM
- Location: Charlotte, NC
weird. i wonder how he came up with that stuff.
goes to show you that you can't believe everything you read on the web. i'd have figured that stuff was from some factory manual or something.
given the title of the page (Mahle Pistons or whatever), might all of these designs be aftermarket parts with slightly different characteristics?
goes to show you that you can't believe everything you read on the web. i'd have figured that stuff was from some factory manual or something.
given the title of the page (Mahle Pistons or whatever), might all of these designs be aftermarket parts with slightly different characteristics?
Im actually happy with that CR being this is the first turbo motor I will be building. It will provide an extra margin of error against detonation with a slight loss of off boost power.I'd go with it. Thats a wee bit low, but I dont think you'll have any problems with it. Boost the hell out of it.
Can I ask how you came up with 7.9 to 1?
I didn't come up with the 7.9:1 CR. Several people from other different BMW forums seem to agree on this one. At first it was going to be between 7.5-8:1 was the answer. Then it was wittled down to the 7.9:1 from someone who measured the 885 head volume and eta piston volume, etc., etc.