250 i6 fuel economy w/o sacrificing HP

[68gmsee]

Originally Posted by markallen

a guy my dad works with said that if you put a performance cam in a 6 cylinder the motor will not hold up bc it is not made to do things like that with...is there any truth to this

Way back in the 50's and 60's there were quite a few of them in drag and speedway circle racing. I've seen some of these sixes out run V8's in the 1/4.

These engines can hold up pretty well if built right. Check this Youtube video. Chevy 250 on a dyno.

http://www.youtube.com/watch?v=5uVNQFkIZXc

[longbed67]

Depending on whether your tranny is a standard t5 with the .63 OD gear or the close ratio t5 with the .74 OD gear this is what your RPM bands look like with a 3.07 rear and 255/60R15 tires for a total tire height of 27.05" If it is the standard t5 the ~1300 rpm at highway speed would explain the low fuel econ. because you dont have enough power to push it down the road.

[longbed67]

Same setup as above except this is what happens when you change to a 3.73 rear end! The lower rpm in 5th gear is the standard t5 the higher rpm 5th is the close ratio T5