87 D100 225 833 OD 8 1/4 3.55

I want to do a gear swap in the future for my truck and am trying to decide on which gears. Right now with the 3.55's and 27" tires its basically a 3 speed unless im going 65 mph or over which I never do,I cant really use 4th. This truck is mostly driven around town with 50-60 mph speed limits.

I plan on going with a 235/70/15 when I replace my tires which will bump me up to a 28" tall tire.

Using this http://www.kabamus.com/garage/gears.html it looks like I will be at about 2600 rpm at 65 with a 4.56 and 28" tire which sounds good to me. I am wondering if I go with a 4.56 if my first gear will become useless? Anyone have any experience? THis is my daily driver but also my toy to mess with. I will be putting on a super six intake with a 2300 350 cfm holley and HEI by the end of january,and then plan on doing some head work and putting in a erson 270 cam by the summer.

Tried doing a search,but only found some snippets about DI using a 4.56 in one of his cars.

Jared

Oh ya,I have been talking to hantayo13 through pm about his truck which has 4.11's and he really likes it,but he is only running 25" tires.

I am going to just order the 4.56's,I can always correct with a 29 or 30" tire if need be,it is a truck.

moparts used to have a couple of Excel spreadsheets that you can download that would allow you to enter in your tires, your tranny ratios, and it would spit out the speedogear you needed along with looking at rpms and speeds at various gears/rpms... I use it when I look at one of my dusters and try to keep the highway cruise in the rpm power band.
Your cam choice and build will help determine what you should and should not do...Personally I'd get your engine where you want it first then make the gear change since there will be a possible change in powerband between now and then which may help you better determine whether you 'need' the 4.56's or opt for the 4.11's... One thing I have found is when you go with "steep" ratios you can get up to rpm and speed pretty fast, but you start to limit what your top speed will be when your at the end of the engine and cams ability (2600 rpm at 70 mph or 2600 at 90 mph).

Good luck on making an "educated" guess...

-D.Idiot

Thanks Rob.

I will be using the erson 270 cam which is 2000-5000 range,and the stock is 800-4500 range so it will be close either way. My max rpm will be 5-5500. Im thinking with the 28" tire that it will work out,with either the stock cam or the erson I will be in the power band at 60+ in 4th. Im not trying to go over 80 mph at any time. Its a truck and the tires have a low speed rating,but I want to be able to have some "fun" getting up to 60-70,maybe take some cars off the line,but not breaking the speed limit.

Jared