Switch rear gears?

[Daryl]

Thank you, everyone, for your input and feedback. When the budget allows, I will have 3.08’s installed.

Cheers and Happy New Year!!

 

[Daryl]

looking for a CARB compliant set…

 

[Mr horsepower]

Based on the updated tire info, you have 3:73 rear gears, so you could consider 3.27's as well as 3.08's. I don't think gears some into play when considering CARB inspections as that is not something that can be "inspected" (same as inspector cannot tell if you have 302 or 347)

Your car came stock with 3.08 gears, so going back there, puts you back to stock.

 

[Snorky]

3.27s would only be maybe 200-300rpm difference at 80 mph in 5th gear with that .68 5th gear ratio. The 3.08s will be noticeable. The 2.73s would probably be a little too much

 

[Mr horsepower]

3.27s would only be maybe 200-300rpm difference at 80 mph in 5th gear with that .68 5th gear ratio. The 3.08s will be noticeable. The 2.73s would probably be a little too much

He has a .72 5th gear.

 

[Snorky]

More or less the same story on The outcome

 

[Daryl]

I’m well aware of what rear gears I have as I ordered them, received them, took them personally to the shop and watched as were installed and they are not 3.73’s. They are 3.55’s.

I appreciate everyone’s input and feedback. I will speak to the shop that ordered and installed the transmission when they return from vacation next week. Figure out my next step.

 

[joemomma]

Typically, one "step" in gearing change isn't worth the cost for the change or improvement. You want to go at least 2 "steps" for it to be worth the cost.

 

[lwarrior1016]

3.55 down to 3.08 would be two steps. He’s skipping over 3.27 or 3.31

 

[joemomma]

Yeah the 3.55 > 3.08 would be a good change if you're concerned about highway cruising. Can confirm 3.73 on the highway are about as steep as I'd want to go for any extended highway driving. My commute is about 30 minutes with 3/4 of it highway - any more gear and I'd be taking the "old road" to work rather than highway/interstate.

 

[Daryl]

I talked to a tech from Tremec today. He initially said 3.27’s but when I reminded him it’s a 347 stroker, he said 3.08’s would be “okay”. So, the 2-step down would be 3.27’s, but only 150-200rpm difference in 5th.The max step down would be 3.08’s

 

[joemomma]

What would the RPM drop be with the 3.08s? 3-400?

 

[Daryl]

What would the RPM drop be with the 3.08s? 3-400?

Yes

 

[joemomma]

That would be noticeable for sure, almost like another OD. Cruising at 75 @ 2000RPM would be much more agreeable than 2500.

EDIT: and with the torque of the 347, you could still pass with ease.

 

[Daryl]

Started shopping around. Would I need just the ring & pinion or the whole 3.08 rear gear kit?

 

[lwarrior1016]

Started shopping around. Would I need just the ring & pinion or the whole 3.08 rear gear kit?

Gears and a bearing kit. Your gears haven’t been in there very long, but the inner pinion bearing will likely be destroyed during removal. At the very least you’ll need the inner pinion bearing and a shim kit for the carrier.

 

[Daryl]

Gears and a bearing kit. Your gears haven’t been in there very long, but the inner pinion bearing will likely be destroyed during removal. At the very least you’ll need the inner pinion bearing and a shim kit for the carrier.

So May as well get the whole gear set; err on the side of caution + all the innards will marry up.

 

[Daryl]

With the 3.55 rear gear kit in there now, I'm not even sure what I have as far as traction: traction lock? Posi? or ??? If I want to keep rpm's low, does one type of gearing affect that differently? ie, does Posi-traction make more rpm's? Or are 3.08's 3.08's regardless of the traction type?

 

[Snorky]

Posi/lsd is the differential carrier. The gears are the gears. Open is 1 wheel peal,a posi makes both spin when one slips, and a locker does both the same speed all the timr no matter what. So yeah.. 3.08s are 3.08s regardless of the carrier.

 

[Daryl]

Thx, Snorky. That was my understanding. Just wanted to make sure I was on the right page still!

I guess my focus regarding traction is: Does either choice (Posi/LSD) affect mpg and/or rpm's?

I'm guessing "no" based on the "3.08's are 3.08"s" element of the equation, but again... just want to clarify and reassure! Any thoughts on where to get? Which brands are best? Which to avoid? I'm running Ford Performance now but have Googled and found Yukon and Moser so far...

Appreciate and await your feedback. Thx again ++