Posted by Matt Wilson [172.69.68.132] on Friday, February 21, 2020 at 12:14:23 :
In Reply to: Re: Probably answering my own question but... posted by Kaegi [162.158.107.164] on Friday, February 21, 2020 at 11:10:08 :
Yep, cams probably have a fair amount to do with the power increases. Afyer I posted the above comments on compression ratios, I did a Google search on "power increase with compression ratio" and found a couple of articles that confirmed my suspicions. A rule of thumb is that you gain 4 - 5% Power for every point of compression ratio increase. One example they gave is that going from 8:1 to 9:1 will net you about 4 - 5% gain, everything else being equal. One article has a table for a theoretical engine, which indicates about a 3.5% increase when going from 8:1 to 9:1. At higher compression ratios, going up by one point gains less than that, for example going from 12:1 to 13:1 only provides about 2 or 2.5%. They said real-world engines, not the theoretical engine, actually gain a little bit more tuan that, but still not a 20 or 25% increase shown in the flathead six manuals. Something else was going on there to provide such big gains. Of course, as these articles pointed out, there are plenty of ways to shoot yourself in the foot when trying to make power by increasing compression, and you'll end up with less gain or even some loss of power.