|
|
Posted by Chriscase [75.36.36.87] on Wednesday, September 22, 2010 at 17:49:48 :
I don't think I posted this print out from a dyno run, for my 230 with headers and intake. Go to the link for a bigger pic, much more detail visible. The wiggles are due to big lugs on the tires.
Anyways, I'm cogitating it. I calculate that it does about 60 mph at 3000 rpm. (5.83, 11.00 Michelins XZLs) That speed is still near the peak horse power. And, the hp curve is pretty flat, from about 2,300 to 3,000. Any faster than t6hat, and the hp drops quickly, making these trucks pretty self governing- on flat ground anyhow.
So, an overdrive ratio of between 17 - 23% would still keep it in the power band. Now most vehicles don't gain as much MPG with an overdrive as the ratio- usually about half.(20% overdrive ~ 10% gain) But these flat head trucks do seem to make a full percentage gain. I'm thinking it is because of that flat power curve, where in a 20% drop in speed still leaves us with full power, where as in a modern engine, a 20% drop puts the engine off it's power band, necessitating more foot into the carb, making the engine run richer, decreasing the gains of the overdrive.
Discuss?
Follow Ups: