What gears are you running?

[Mick Je]

I'm in the middle of building a 454 engine for my 70 GMC, I currently run 3.73s but going on the freeway it screams at 3k. I have a TH-400 with 30in tire's on the back, I'm trying to decide to put 3.42s and use 3rd like an overdrive or put 3.55s. Just wonder what some of you guys were running and what rpms you are running at 70.

[Tkmadone]

I am currently running a 3.54 Dana 60 in my C20 and I was turning about 3k at 65 with the T400. I just installed a 2004R and now it's 1800 rpm at 65, about 2000 at 70. So now I'm looking for a 4.10 rear!

If you put in a 3.54 it will only drop you from 3k to 2850 rpm. Your best bet would be 3.07, which will drop you to 2450 rpm from 3k, or an overdrive transmission.

[CST10]

I'm running a 454 with a T350 tranny. Rear gear is 3.07. Runs about 2500 rpms at 70 mph.

[Fldawg]

Like you i had 3:73's in mine went to 3:42's and only lost 200 rpm maybe 300

[GASoline71]

The engine will handle 3,000 RPM's all day long. But will your wallet handle it as that BBC is drinking fuel?

If it's an engine "longevity" issue you're worried about... I would think it's a non issue. But if you want better MPG's then I'd look into an overdrive transmission that will handle BBC TQ.

Gary

[Mick Je]

Originally Posted by Fldawg

Like you i had 3:73's in mine went to 3:42's and only lost 200 rpm maybe 300

Do you have to drive it in second around town (under 50 mph)?

[Fldawg]

Originally Posted by Mick Je

Do you have to drive it in second around town (under 50 mph)?

no, mine is fine, i'm running a stall converter i have no probelms

[jocko]

Get the best of both worlds - 3.42 (or stock big block gear of 3.54) and WITH an od trans. Highway cruising without earplugs and more bottom end torque multiplication that you'll ever want or need. Just the gear change alone won't net much of a difference cruising rpm-wise. If that's all you're concerned with, o/d trans is the way to go.

[Mick Je]

Im sticking to the TH-400 there good solid trans, and maybe later on bolt a gear vendor to it. The only 4 speed trans I would consider is a 4l80e and put the MSD or B&M electric controller on it. I still pull boats and haul stuff with my truck, and never have been a fan of the 700r. For now I'm just going to change the gears.

[CST10]

Like I said earlier. I have 3.07's and can roast the tires a good 50-60 feet and still have to let off to hook up. Just so much torque that 454 will make is unbelievable.

[CST10]

I had thought of changing to 3.42's at one time but it won't hook with 3.07's. It will be worst going lower for me.

[In The Ten Ring]

I have a 4.11 rear end. Terrible gas mileage but dad says my truck "will pull WV hills easily."

How can I add an overdrive gear to my 3OTT?

[Mick Je]

What are the diameter of your rear wheels?

[enigma]

3:73 with 700r4 1800 rpm at 60.

[special-K]

I run 4.10s and run 65 mph all day long. In my newer vehicle with overdrive (& 4.10s) I also run at 65. I use overdrive for it's intended purposes, reduced wear & tear and better mileage, not to go faster. On my '67 I have 3.42 with an M22. That is as tall as I would go for a manual trans. It will accept an overdrive well and will be fine in case that never happens. The '72 has a mild 350 and the '67 has a ht little 327.

Figure these trucks in 1/2t came with 3.08s behind a 402/TH400 and 3/4t came with 3.54s. 3.08s rare lanky for my taste but certainly fine behind a 454. The more torque, the taller gear you can get away with

[Tom Vogel]

Originally Posted by Mick Je

Im sticking to the TH-400 there good solid trans, and maybe later on bolt a gear vendor to it. The only 4 speed trans I would consider is a 4l80e and put the MSD or B&M electric controller on it. I still pull boats and haul stuff with my truck, and never have been a fan of the 700r. For now I'm just going to change the gears.

Very Wise.

[Fitz]

Originally Posted by Mick Je

I'm in the middle of building a 454 engine for my 70 GMC, I currently run 3.73s but going on the freeway it screams at 3k. I have a TH-400 with 30in tire's on the back, I'm trying to decide to put 3.42s and use 3rd like an overdrive or put 3.55s. Just wonder what some of you guys were running and what rpms you are running at 70.

I run a turbo 400 backed up by a gear vendors overdrive which gives 2300 RPM at 70 mph.

This link will take you to a gear ratio calculator which will help you figure this out.
http://www.grimmjeeper.com/gears.html

[Mick Je]

Originally Posted by Fitz

I run a turbo 400 backed up by a gear vendors overdrive which gives 2300 RPM at 70 mph.

This link will take you to a gear ratio calculator which will help you figure this out.
http://www.grimmjeeper.com/gears.html

Sweet!
We have one on our Motorhome and it's nice!!! That's what made me think about putting one on my truck. They are pricey but are worth the money to me!

[Fitz]

Originally Posted by Mick Je

Sweet!
We have one on our Motorhome and it's nice!!! That's what made me think about putting one on my truck. They are pricey but are worth the money to me!

With my truck it's a necessity. The torque from the ZZ572 up front would grenade a 700R or a 2004R so, 4.10 gears for quick starts and a 0.7:1 overdrive is just the ticket.