Rear gear question

[Slimpickens]

I've got a 99 obs k1500 suburban
350 l31/4l60e g80 with 3.73's front and rear.
I recently upgraded to 18" wheels and 32" bfg at ko tires. They are load range e. Anyways when I went to the bfg's I definitely lost some bottom end. I want to put gears in my truck. Front and rear. I'm wanting something in a 4.30, but cannot find any. So I'm thinking of going to 4.56's. If my math is correct it would actually be somewhere around 4.27 final drive. I drive my truck daily and on the highway a lot.
Do you guys think that's to much gear? I think it would be a waste of time and resources to go from 3.73's to 4.10's...
Any input and real world experience would be greatly appreciated. And if you can point me in the direction to a vendor that has 4. 30's that would be greatly appreciated.
Leo

 

[5spd Z71]

Too much gear on the highway for 32" tires. I have 4.56 gears, 35" tires, I'm running almost 2300rpm at 65mph. If you really wanna spend the $1200+ on regear, I'd stay around 4.10.

Personally I'd leave it alone. I ran stock 265/75/16 with 3.42 gears for years and never had any issues. Even when I had to tow or haul with it.



Sent from my iPhone

 

[Jorge6.5]

I would also just leave it since you do lots of highway driving. The taller tires will help bring down cruise rpm.

 

[slowburb]

You are getting answers that are OPINION here. Here is another OPINION.

Driving with 3.73:1 gearsets and taller-than-stock tires SUCKS. I used to do it, with 285/70/17's, and with 295/65/18's. These were both around 32"-33" tall mounted and on the truck. It sucked. I taxed the **** out of the drivetrain trying to propel the truck in stop/go traffic driving it every day. While running the 295/65/18's, I swapped gears for a couple pairs of 4.56:1 ring & pinion sets. "Night and day" is cliche now, but son lemme tell you, it was night and day. The truck would actually get out of its own way. It suddenly became easier to pull away from a stop light, and some (not all, but some) of the transmission stalking/hunting for gears was suppressed. Cruising rpm's obviously and expectedly increased, but as the majority of my daily driving is in a city setting, this was factored in beforehand as acceptable. With the 296/65/18's, (around 33"), the truck was revving at about 2600-2700 at 70 mph with the converter locked. Where I live, the interstate system in undeveloped areas is 70, and people drive like complete morons, so if you're not running 80 mph, you risk life and limb. At 80, the truck revved almost 3000 rpm's. As those tires started to wear out, and in anticipation of an upcoming 3000+ mile trip to be made with this truck, I installed a set of 295/70/18's, which are just shy of 35" tall. New cruising rpm's at 70 dropped to around 2500 with the converter locked. This is *almost* equivalent to a "stock" 245/75/16 tire and a set of 4.10:1 gears. I can't remark exactly towards launching ease because I have a looser-than-stock torque converter (B29/4.3L S10), a built 4L60E (with shift kit/hot servo/etc/etc) and a ramjet/HT383/marine 350 cam, and these take away any shot at an apples to apples comparison between our rigs.


It is up to you to decide what is too much gear and too much cruising rpm. I'm fine with mine the way it is, and I'm fine with the fact that my truck isn't a TURD any more.

 

[Slimpickens]

I'm running 275/65/18's on 18x9" rims.
Here are my mods on my truck
Pro flash tune.. Currently on 89 tune
.030" over 350 9.5:1 cr
062 heads with z28 springs
Stock lt1 cam
Comp 1.52 roller tips
S10 converter
Corvette servo
Dual 2.25" exhaust
Hi flow cats
Magna flow Dual in dual out muffler.

I had street tires on the 18's before going to AT and it liked the slightly shorter tire. Plus it was less rotating mass. Didn't notice a difference from 265/75/16's to that size in a 18.
The truck runs great it just lost that snap down low. Don't get me wrong it will chirp the tires if I hit it at 10mph or so. But it just lost a little and I'd like it back.
I do plan on going withh long tune headers and a volant cai here in the future to compliment my other mods. Plus I want the extra torque from the long tubes.
As far as gear costs go. I have a couple of buddies who own shops. So getting them installed and paying out the arse is not going to happen. More like the cost of the gears and a 12 pack of beer...lol
I appreciate your real world experience. Seems like you can relate to how a larger off road tire affects these trucks. Plus I'm close to 6k pounds in my suburban. So extra bottom 32nd would be a benefit. I plan to tow with this rig. When I got it I wanted to make it the best daily/tow rig it could be.

I'm not sure if I want to turn that much rpm on the highway though. To be honest I live in Texas and the speed limit where I live on the interstate is 75. Well it's like what you said. You have to do 80--90 mph to keep from getting ran over.
I think if I can find 4 30:1 I would be in great shape.

Btw how does that 383 run?

 

[slowburb]

I'm running a 350 with enough overbore to make it round again. No extra stroke. It runs great.
Here are a couple tools to use for comparative purposes:

This is for 1:1 final transmission ratio, and where you'd be towing in 3rd gear, you want to be in the orange.

You must be registered for see images attach

This is a nifty calculator:

http://tri-5.chevyrides.com/rpm.php


I'll leave you with this. Marine 350's sustain rpm's WAAAYYYYY higher than what most people think is OK in a vehicle. Those motors go for a long time. Don't fear the gear.

 

[Slimpickens]

I'm running a 350 with enough overbore to make it round again. No extra stroke. It runs great.
Here are a couple tools to use for comparative purposes:

This is for 1:1 final transmission ratio, and where you'd be towing in 3rd gear, you want to be in the orange.

You must be registered for see images attach

This is a nifty calculator:

http://tri-5.chevyrides.com/rpm.php


I'll leave you with this. Marine 350's sustain rpm's WAAAYYYYY higher than what most people think is OK in a vehicle. Those motors go for a long time. Don't fear the gear.

Sorry, I see my error. You're running the 395 cam. I saw 383 When you were describing your camshaft.
I agree with you on not fearing the gear! I had a few mustangs that I would race in my twenties. 5spd and 4.11's is a blast to drive!
If I can't find 4.30's I'm going 4.56's ... Get this big girl moving down the road better.

Do you have an exhaust clip of your 395 cam? How does it rev?​

 

[slowburb]

I don't think you're going to find 4.30's. I don't have an exhaust clip. I haven't taken one, because it sounds so stockish that I don't really see a point. The narrowed LSA of the 395 cam that would normally offer some chop is overshadowed by the short seat to seat duration of the cam profile, so it has a very similar blub blub blub blub to that of the L31 stocker cam. It revs as quickly as my ring pack will let it. I'm still running on the stock tune, and can't manage to find time to set up an appointment at EPS to tune and dyno it.