rear gear opinions?

[DustinsDuster]

copied from Facebook:

alright car guys, i need some opinions. turns out the 4.56 gears i bought for my truck are actually 4.88's. as steep as those sound for a street car, it might still be doable thanks to T56's .50 6th gear, which my truck can't push with 4.10 gears now. my main concern is highway cruising RPM, and what i'd be going through the traps at in the neighborhood of 110-120mph. my street tires are 25.5" tall, and the circle track slicks i have at the moment are 25" tall.

with 4.56's=

at 70mph(25.5" tire) 5th gear = 3112rpm, 6th gear = 2103rpm

at 115mph(25" tire) 7048rpm in 4th gear

with 4.88's=

at 70mph(25.5" tire) 5th gear = 3331rpm, 6th gear = 2251rpm

at 115mph(25" tire) 7548rpm in 4th gear

i could try to pick up some outside circle track tires that i believe are around 27" tall, in which case 4.56@115= 6526rpm, 4.88@115= 6984rpm.

if i got 28" ET streets, it'd be 4.56@115= 6293rpm, 4.88@115= 6734rpm.

so now the 4.88's aren't looking quite so aggressive anymore. opinions? remember, this is a turbo 2.0L in a 2600lb truck, and that motor was originally geared to pull almost 3500rpm at 70mph.

good god, i can't believe i'm trying to figure out how much RPM to ADD at highway speeds...

[McKeever]

How useful is your first gear with 4.88's?

[DustinsDuster]

How useful is your first gear with 4.88's?


i could barely even get my street tires to break loose at the track with 30psi in them, even slipping the clutch from 5500rpm. it would hook and bog, BAD. even when i did get a decent launch, the best 60' i pulled was like 2.2 or 2.3. damn 2.66 first gear.

i imagine 4.88's would make it a lot easier to launch.

[McKeever]

Dang, sounds to me like you need more gearing then what you have now, especially if you go up in tire size.

[DustinsDuster]

Pretty much decided it. Going with the 4.88's and I'm picking up a pair of used 28" slicks to run at the track. 6500rpm should give me around 115-117mph that way, and I should be just about high enough to use 6th gear at 70-75mph with my street tires

[Drifte]

So the truck class has someones boosted 80's gmc, your truck, a tuned explorer (I assume eco boost) kitch's diesel, and finally myself. And I imagine the places go something like that, although I should be close to Kitch I think? No trophies for me :/

And if you want to up the boost dustin, ryans got some manual ones that seemed to work pretty well.

[DustinsDuster]

I'm performing g a wedding that day and won't be at the shootout. Have fun guys!