Cam timing for MPG

[80Stang]

Just some facts needed in my learning curve for better MPG.

Retarding a cam will give
- better vacuum = thus will help fuel atomize better
- better low end torgue

??

Any idea what a typical about 4 degrees retard would do? Small change, not worth it? Big change, nice gains?

Well, this is pretty easy to test anyway as it is so easy to change the timing on this little six.

 

[JackFish]

: Advancing the cam gives more bottom-end torque, lower top-end, doesn't it?

 

[80Stang]

Yes, I read some books meanwhile to refresh my memory and that way it is; advancing the cam will boost mid-range and give better MPG. According to some book.

Anyway, is there a dramatic change or is it not just worth the trouble?

 

[JackFish]

Well, mine's in at 4* advanced on an otherwise stock motor.
It definitely is about 4-5mph slower than before, and the seat of the pants torque is great, maybe even a bit too much, depending on your driving needs.
I think it should be considered as part of a package, and the dizzy should be recurved as well, although I don't yet have the means. But it's quite drivable anyway.
Next time I pull things apart, in the spring, I will probably set the valve timing back, because I need more top-end, and the bottom-end on this motor is already quite good. I would even consider retarding it maybe 2* next time.

 

[robbinsj]

I just rebuilt a 250 for my '69 Mustang and put in the 264/274 cam from FSPP. Unfortunately the 250 cam set has only one keyway and can't be advanced or retarded. The shortblock I had was a 1978 and, according to the Falcon Performance handbook, had about 7* of retard built into the timing set. The engine ran very well but I had wanted to install the cam 4* advanced per Mike's advice since I use this car as a daily driver. So I was a total of 11* retarded from where I wanted to be. After about 500 miles I installed the timing set from 1969 which does not have the 7* retard built in. Holy crap what a difference. I'm still in the break in period and I'm fooling around with the jets in the Weber 38/38, but the car is more fun to drive around town. I hardly have to press the accelerator to get the car moving well and I've got to believe that's going to help MPG. Bottom line is that it depends on where YOU want your power band.

I have a T-5 and at 70 MPH it's running around 1850 - 1900 RPM. I hope to test the mileage on the road soon.
-Joey

 

[80Stang]

Robbinsj, that is encouraging.

If somebody is thinking what cam and timing set I have just check my website for details. Well, the cam is a FSPP 274/274 and timing set is from Comp Cams (non-adjustable). The marks were just aligned while buildup.

 

[rbohm]

8) the general rule is advancing the cam improves low end torque, and retarding the cam improves top end horse power. most engines fall with in the boundries of this rule, BUT, there are combinations that are just the opposite, and there are combinations where advancing the cam improves both low end torque, and top end hp. other combinations you retard the cam and improve both areas. the only way to know for sure is to put the engine on a dyno and test it.