what gear ratio to run?

[klutz51]

S Once again i find myself unsure of a choice and hoping for some help.here is the set up 454 with lots of hp, 400 turbo trans, now the issue is do i run a 3.08 or a 3.42 since i don't have overdrive. Need some help from someone who maybe has run into this.
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[papastrk]

It would help if we had a tire size. What rpm range do you want to run your engine? The 3.08 and the th400 should be nice on the street. The 3.42 will work great as a performance gear for the street also, but the rpm range will be up there if you run a short tire. A stout long stroke 454 can hide the fact you have a tall 3.08 gear, and light up street tires with the 3.42.

[1958Warrior]

Here is a link to a good calculator for the gear, need to know what your tire size is , or you can play with it to find out how tall of a tire you need for example if you have a 25 inch tall tire, 3.42gear, you will be running at 3000rpm and going 65mph
http://www.angelfire.com/fl/procrastination/rear.html
3.08 and a 25" tire 2700rpm ,65mph
All depends on the use street/ hwy , race only ect.

[mr48chev]

Two really good answers.
The 3.08's would give it longer legs out on the highways and help with fuel mileage while the 3.42 gears would be more friendly with with off the line acceleration and more fun if you occasionally want to run it at the drags.

The biggest difference is most likely going to be the difference in potential gas mileage. That might not be a big deal if you stick to car shows within a hundred miles of home and only hit one or two a year that are further or if it's a trailer queen that you don't drive to out of town events. It is a big deal if you decide to jump in the truck and head to Dallas or Oklahoma City or some other place hundreds if not thousands of miles away for an event.

[1project2many]

Mr48's got good advice.

Is this a street driver or a racer? Cruising long distances or just down to the local diner? A 454 makes power "all over" but what's the rpm range of the cam? You should think about how the truck will be used, look at the engine power band, and pick the gears that will best fit.

[klutz51]

it is a 37 Lincoln zepher I came across and the 454 is rated with proof at 750 hp. now it is going to be a cruiser and all around vehicle but I know at that hp fuel mileage can't be a factor, but would like to get the most possible. I had no intension of buying another project with out finishing my 51, but to good of a deal to pass up.

[Speedbumpauto]

If the 750 number has real proof, there's no way that engine is going to like anywhere near a 3.08 gear, or even a converter without near 3500 stall unless it has a blower. If it's already part of a project, hopefully the former builder took some of this into consideration. To make this work well, I'd suggest doing what I did and bolt an overdrive on the back of the 400. I'm running a 31" tire with a 4.11 gear and a 30% US Gear OD + a 4K stall converter and my WAG at the HP of the engine I built(505cid) is 600 HP. It's still a couple of months away from running so I can't give you hard driving manners but hopefully this will give you an idea of where you are.

[papastrk]

750 Wow! Then I would decide at what speeds I think I would be cruising at and then look at rpm's to pick a gear ratio. Tire size is going to be a big influence. A low profile tire may force you to run the 3.08 if you intend to drive 70's speeds. The 3.42 will make the car more drivable at lower speeds with a large cam, which you surely must have to get the 750 hp. A high stall converter will most likely be a must for this combination too. Do you know what stall you have? Keep in mind that the late model trucks have a tall 17" tire, 3.42 rear gear and .70 overdrive trans (2.39 final ratio)and turn 1800 rpm at 70 mph with a small V6. Your rpm with either of these gears is going to be substantially higher than that, so calculate rpm's before deciding. Some of the big block guys need to throw in their two cents worth here. Just read the most recent post above and added following. 4.11 with overdrive is 2.89. 31" tall is a large rear tire! The overdrive gives him the best of both worlds. The TH400 makes it difficult when you try to have both.

[_Ogre]

Originally Posted by klutz51

the 454 is rated with proof at 750 hp.

insert eye roll here

[1project2many]

750 naturally aspirated, without nitrous? Carb'ed? Any idea how heavy the vehicle is? Chances are it's going to want a bit more rpm than the average farm truck. Look into a 4L80E with standalone controller or one of the new six speed automatics. You'll be able to run the right rear gear for that engine and still have an overdrive.

[klutz51]

if the paper work is correct for this motor it says 748 hp. however haven't drove it causing the rear end has a broken pinion gear, and don't even know what gears are in it, causing the ring gear is locked up and the pinion is nonexistent. I got the thirdmember out and it is a mess. I don't even know if there is a stall in it or not.

[Speedbumpauto]

There will be a number sequence stamped on the edge of the ring gear along with a part number. The numbers that matter will look like 41:11, or along those lines. Divide the little number into the big number and that's the gear ratio that was in the car. In this case, 3.73:1.