The Stovebolt Site Forums The Shop Area The HiPo Shop What rear end to use?

The Toad now has a 305 engine, TH400 and a 9" Fjord rear end. Just wondering on what would be an appropriate gear ratio for highway running? Right now they are 3:25 gears. Thanks in advance.

I have 3,23 gears in my mopars. 3.25 should be good

Drive it first and see if you like what you have or want something faster or slower.
You're in the ballpark, next is just personal preference depending on your use for the truck and the roads and hills where you drive.

Mine has a 3.08 with a 250 inch engine. It likes the higher rpm on the highway ( 2400 ish @ 70 mph ). I had a 3.42 for a while that was to much. Around town is not a peppy, but the trade off on the highway is worth it to me.

I'm with Chaz, that is what I have in my Barracuda and it seems just about right. Any lower and it winds too fast on the freeway, any higher ratio and it may be a bit of a slug. I have wanted to try maybe some 3.55 gears but the trade-off is not worth the money since I have a good set of 3.23's in it now!

The best gear ratio depends on a lot of variables.
A few of the important ones are tire diameter, vehicle weight plus wind resistance, and engine characteristics.

Whatever ratio is great or best in one situation won't necessarily transfer over to another situation unless all these variables are the same, or different variables offset such that the answer could be the same.

This gear calculator will help with those comparisons
http://www.onlineconversion.com/bigger_tires.htm

Say you and your buddy have identical trucks and ratios except one has 28" tires and the other has 33" tires. One of you really likes how their truck drives and the other not so much. What ratio might the second truck need to drive like the nice one?
Or perhaps you have a slow old Stovebolt 6 happy at 2,500 rpm and your buddy has a v8 that likes to cruise at 3,200 RPM, you can account for those differences with some math or the gear calculator website/program and get an idea what ratio one might like knowing what the other is and how that behaves.

Not the exact subject of this thread but gear ratio related; I think a common mistake at least with old trucks with old engines is believing that because the gear calculator says with a quick axle gear ratio that you can go 110 MPH or cruise at 2,000 rpm at 65.. However you might not have power enough to do either.
To fast a gear is as bad or worse for driving than one that is too slow for your liking.

All that calculating, comparing, and guessing is no substitute for finally trying a ratio, see how you like it, and adjust from there if you can.

In my panel, with the 305 reman engine/700r4 I'm running a 3:38 and it loves it.

As side note to my above post, and related to what Gregg mentions, my '37 is considered a pretty small truck. Frontal area is narrow but it has big fenders and sets pretty tall. Weight is only 3200 lbs. On windy days my mileage drops two mpg. I can tell by how much throttle it takes, and with so few hp to work with (120 @ flywheel ) strong winds eat them right up. This goes back to gear selection, ideal rpm range, and driving style.

I would drive the truck for a season and see how it acts on the road and in town. 9" Fords are easy to change out the ratio if you have a whole third member to swap out with, so ask around, maybe you could find one to borrow for a road trip or two.

Joe

Second what Joe said, nothing beats real life driving experience. I knew my 37 Buick with a 52 263 straight eight was a torque monster so after doing away with the torque tube rear I went with a 2.73 GM 10 bolt and was very pleased with my choice-- IN TEXAS. Got almost 16 mpg(great for a straight 8) and cruised 63mph at 2100 rpm. Then I made a trip through Missouri and it was a PIG in the hills; heating, pinging, and under constant lugging condition in high and second was too low of gearing. Now going with a 4.11 rear and overdrive transmission to make it much more versatile. Will have a 2.88 final in OD and the deeper gear for climbing in straight drive. This is the exact same set up all the cars back in the overdrive days used so I guess even the engineers without computers were not dummies.