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"10th Year" Silver Supporting Member
Loc: Williamsport, Pa. USA
05-10-08 08:01 PM - Post#1430477
Hi Guys , I haven't been around for a while ,too busy hanging out in the 1949-1954 Chevy forum ,doing over 1950 Styleline 2 door sedan but I'm still running the truck to some shows and cruise-ins. Which brings up my question, 3 years ago I was gettin 14-15 Mpg. with the original 454 cu.in. motor ,normal driving 55-60 mph, fresh re-build ,now I have about 15,000 miles on it and last fall we realized the timing had become retarded so my mechanic advanced it and we were looking for some improvement . We got some,,, retarded we were only getting 8-10 mpg but now we still are only getting 10-12 mpg. My mechanic works with "total timing " it suppose to be much more accurate of a way to set your timing.I think he set mine at 31. He's into racing and can do it with his timing light . So anyway , does anyone have any suggestions for timing setting or how to improve my mileage ??
14-15mpg at these prices is a lot better then 10-11mpg. Thanks
I thought perhaps I should include some more information, 454 cu.in, bored 20 over ,flat-top pistons , RV cam ,headers ,3" dual exhaust, TH400 ,Holley 750 double -pumper. Oil changed over 4000 miles or ever fall before getting put away. Spark plugs are still from the re-build,about 15000 miles on them. Thanks
Edited by super_cheyenne on 05-10-08 08:30 PM. Reason for edit: No reason given.
"13th Year" Gold Supporting Member
Loc: Colorado Springs, CO
05-10-08 09:42 PM - Post#1430514
In response to super_cheyenne
Total timing is important in racing, but less so in street driven vehicles. If the distributor was recurved (means that the advance weights/springs were changed) then you would want to look at total timing fairly closely.
But, if it has stock weights and springs, you would want to stick with an initial timing of no more than 12 degrees - which works out to about 36 degrees total.
You can get a good amount of low RPM power out of a set of different advance weights and springs, but the trouble is - it kills low speed fuel economy. If the weights/springs were changed, that is where your fuel economy went.
Also, if the vacuum advance routing was changed or disconnected, this will contribute to your fuel economy problem. The stock thermo-vacuum valve on top the thermostat housing has to be in place also - this often gets thrown out.
I see that you are using a Holley in place of the Q-jet. The Holley isn't the best for consistent fuel mileage, they have a tendency to change settings and require constant fiddling to keep them in the best state of tune. They are great for power, but are only average when it comes to fuel economy. Check float settings (important), look for bowl leaks, check all vacuum lines.