Gear/Tire Size/Motor/Tranny Combo

[Honky Kong jr]

they are there, you dont see them?

Now I do last night it was the broken image kitten

 

[QBuff02]

Anyone in this discussion know the difference in final drive ratios between a 4 speed and a th400? I don't off the top of my head but pretty sure they're both 1.1 final, and the reason I bring it up.. my 82 with 454/th400/4.10 and 33's turns 2,600rpm at lets just say 55-60. my buddy with his '84 that's a 350/4speed/3.73 and 33's turns 1,800ish at 55-60. Those are two real world sets of numbers. now I get these are 30-something year old trucks, but that's driving right with each other and our speedos are within 1-2mph of each others. point I'm trying to make that if final drive ratios were pretty much in line with each other, that would equate to a roughly 800ish rpm difference between 3.73's and 4.10's at speed with 33's. I know sometimes the "calculators" aren't exactly spot on.

 

[4WDKC]

Anyone in this discussion know the difference in final drive ratios between a 4 speed and a th400? I don't off the top of my head but pretty sure they're both 1.1 final, and the reason I bring it up.. my 82 with 454/th400/4.10 and 33's turns 2,600rpm at lets just say 55-60. my buddy with his '84 that's a 350/4speed/3.73 and 33's turns 1,800ish at 55-60. Those are two real world sets of numbers. now I get these are 30-something year old trucks, but that's driving right with each other and our speedos are within 1-2mph of each others. point I'm trying to make that if final drive ratios were pretty much in line with each other, that would equate to a roughly 800ish rpm difference between 3.73's and 4.10's at speed with 33's. I know sometimes the "calculators" aren't exactly spot on.

Tires sizes vary also one set of 33s might be 32.1 tall the other might really be a 33, also speedos could be off.

 

[QBuff02]

Tires sizes vary also one set of 33s might be 32.1 tall the other might really be a 33, also speedos could be off.

I get that and i'll be honest my tires are realistically 32 inches tall or less at this point.. Lol And he's got fancy new meats on his, that even if they are 34" tall, when we're driving down the road and he's in front of me, or I'm in front of him, doesn't matter the order, if we're pacing each other and keeping the same distance between us, our speedos are within a mile an hour or two of each other. and we're basically 800 rpm off. I could see a couple hundred maybe based off of tire variations. So even if we factor that in, that's still 500ish rpms difference between gear ratios. Mine is an original th400/4.10 truck, and his is a very unmolested, 68,000 original miles, all factory drivetrain 4speed/3.73 (minus what we've done to engine and exhaust) truck.

 

[4WDKC]

I get that and i'll be honest my tires are realistically 32 inches tall or less at this point.. Lol And he's got fancy new meats on his, that even if they are 34" tall, when we're driving down the road and he's in front of me, or I'm in front of him, doesn't matter the order, if we're pacing each other and keeping the same distance between us, our speedos are within a mile an hour or two of each other. and we're basically 800 rpm off. I could see a couple hundred maybe based off of tire variations. So even if we factor that in, that's still 500ish rpms difference between gear ratios. Mine is an original th400/4.10 truck, and his is a very unmolested, 68,000 original miles, all factory drivetrain (minus what we've done to engine and exhaust) truck.

Tires size aside you have 400 rpm difference between the two, now you have to factory in tire height as installed and the last remaining factory is slippage chances are the torque converter is slipping a little while the 4speed is not. Download gps speedo on your phone and check your speeds just for curiosity.

 

[bucket]

Anything without overdrive and a cruise rpm of 2200 is going to be a slug.

What is the purpose in wanting the tall gearing anyway?

 

[hirschdalechevy]

I have 4.88's in my crew cab with 44's and a 450hp 454 , turbo 400 and it is great all around. My blazer has 4.56's with 38's , 400 sbc. , turbo 400 , and same thing , good gear on hwy. and off road. I will say that the 4.88's cook the gear oil pretty good when going down the hwy. for longer road trips. I will say that when you get into low gears the pinion gets pretty small and starts to turn your gear oil into cooking oil with a lot of hwy. miles , so that might be a factor to think about if you do a lot of hwy. driving. I think you have to find a happy medium for what you use your square for.

 

[shiftpro]

4.88's cook the gear oil pretty good when going down the hwy.

Good point! Don't skimp on the Royal Purple gear oil. Also a drain plug in the diff cover will help to keep up on oil changes. Thanks for reminding me as my build has 4.88s and overdrive and I'll be doing my share of highway driving.

 

[hirschdalechevy]

Go for a bigger diff cover , more oil = a bit cooler or a finned aluminum cover like magnatech.

 

[Honky Kong jr]

I got these......

You must be registered for see images attach

They are for a 70 though. Haven’t decided on a price yet that’s why they aren’t in the “for sale” thread yet.

 

[454-k10]

My 1980 swb had a mildly built 454/th350/np205/35s/4.10s. I could cruise all day at 80-85 mph, 3,000-3,300 rpms. It was locked front and rear and in 4 low it would smoke all 4 tires down the street. I had rear disc so I couldn't brake and light em up. Either way I wanted lower gears and taller tires. My next big build like that will be 38s-40s with 4.88s-5.13s.

 

[Blazin890]

In my experience, running 35’s with the 4.10 rear gears is a great combo. Running 38’s or larger with the 3-speed 400 (considering your power output) I’d suggest 4.56’s to be an all-around driveable gear.