So I've been out on the highway several times now.  I tend to keep up with traffic at 1500 to 2000rpm.  Around here people do about 80.  I'm concerned that that may be too low for the engine.  I hear no knocks or weird noises but it's hard to hear anything over the wind noise.  In the other gears, 1500rpm feels like the start of the power band so lugging is the concern.   I'm thinking I should gear it a little shorter to get into the 2000 to 2500 range.  What do y'all think.  The engine is 318ci, 9.5:1, cam 226 @ 50, 274 adv, 112 Separation, .295 lift.


Lawrenceville, GA

I know I would like it to rev a little higher, mine with a 3.50:1 rear ratio and short tires turns 2500 @ 70 mph and feals real nice. I've got about the same spec engine as yours, it has real good low end torque, but I don't think I'd want to lug it all day.

Tim

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias

  Tim  ,what's the overall height of your rear tires 25"-26"?   Charlie, maybe you or a friend might have a set of tires the height of Charlies that you could try at 70mph to see what RPM your turning? If it's a comfortable rpm for the motor then stay with the tire size or go lower gears in the rear end. I know you have already thought of this but I've already done ebay,sooo! Any way my 94 flareside runs 31"s and an aode with 3:73's cruises all day at 70 mph. KID

Charlie.  Any idea what gear ratio is in the truck now?  Ideally, a mininum cruise rpm of 2000-2250 would be ideal but as Kid mentions, tire diameter is a key player here.

Lorena, Texas (South of Waco)

It should be a 3.70.  It hasn't been verified, though.  I can't read the tag on the axle housing.  Tires are 225/70-15 which work out to about 27.4" tall.


Lawrenceville, GA

The tires I run on the truck now are 26" tall, when I put my camper on the 6 ply tires I have for the extra load are 29" tall and I still get a comfortable cruise. With the taller tires my speedo dosen't read correctly, but I indicate 60 and the RPM is still the same. Also on the funny side, the old "Alaskan" is a heavy load, but with the taller tires I seem to get the same mileage as I do unloaded.

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias

Charlie, if you can cruise 70 mph at 2000 + rpms and not lugging ( rocking back and forth ) with the engine feeling like it's in its power band then I feel you're good to go with the cam you're using, and your gear ratio sounds about right on.

-Gary Burnette-

I would like 2000rpm minimum when cruising.  So I guess first thing I need to do is to check the final drive ratio.  Then find out how fast I'm going at a given RPM and start doing some math.  The speedo's been reading fast since the trans swap.  The drive gear in the tranny must be bigger.


Lawrenceville, GA

It's not a cure all, but I like to put a vacumn gauge on and see what I'm pulling at cruise, compared to idle, one gear lower etc.  If nothing else, it'll tell you how close you are to opening the power valve (or step up rod, or whatever the carb has) 'cause that really kills the mileage.  Learned that in a motor home on a day with a headwind.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Miker is dead on in his comments on the engine vacuum.  I had a 352 in a pickup in which I had changed the gearing from 3.89 to 3.00 and the fuel mileage took a dump.  I did have a permanently mounted vacuum gauge on that pickup and it told the story as the vacuum also took a dump at the cruising rpm.  Put the 3.89’s back in and the fuel mileage went back up accordingly.

Lorena, Texas (South of Waco)