Crate engine specs
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Have you got results with 2 different engine HP levels that vary by about 200hp? Tony Mamo's results, which I actually trust, are showing about an 70hp engine change and they point more towards either a fixed or mixed loss than a straight percent loss. Still, it's not enough of a difference to really differentiate between fixed or % drivetrain losses and I can't find any test result posts on his newest engine.
You have to even consider than unless you put the exact same full intake and exhaust system and accessories onto the engine when it's on the engine dyno that the engine HP measured on the dyno is not the engine HP once it's installed in the car. So, in the end, there are so many variables between the 2 tests that can change between vehicles and test methods that it's easiest to just say "it's 20%" and move on.
Le Mans Master
Joined: May 2007
Posts: 5,007
Likes: 1,114
From: North tonawanda NY
Yup I've read the same thing on many forums including the serious gear head forums like speed talk were its commonly accepted. While it varies a bit its a good guideline to use the percentage. The th350 is lighter and more efficient with less power loss (as I stated early in this thread) than the th400 but the th400 is stronger (capable of supporting up 800hp so I've read)
