[Jason977]

New owner here, just picked up a GXP with M6. I love the car, but the gearing is really strange to me. I'm coming from a C5 w/ M6 which has both a higher ratio rear end and higher gears in every position except 4th (both 1:1). Driving casually and shifting at 3k, for example, in 2nd gear the vette is at 40mph, vs 30mph for the GXP.

With the GXP being such a powerful car and able to pull higher gears, it really confuses me as to why they would put such a low rear end in it, and also not include a "highway gear" in the 6th position. My car will pretty much be a daily driver on my short commute, with a few track days and road trips thrown in. No drag racing.

Any downsides to the Camaro SS 3.27 rear end? It will still be slower in every gear than my C5 (except 4th), but should open up the ratios enough that 1st and 2nd aren't so abrupt, and will drop my rpms at 75mph from 2k to 1750. Seems full of win, except for a bit more clutch slipping on take-off, and a small gap between 4th and 5th.

Seems like everyone wants to swap to lower gears for a better launch, but I'm going the other way...
Thoughts?

 

[danlewis]

The auto GXP has 3.27 gears as well. I don't know what the diff is between the Camaro SS 3.27 and the auto GXP 3.27.

I've thought about it too, especially with the engine upgrades I've done, I'd like to have a little bit longer gears.

 

[Jason977]

When we do an axle swap, do we need to have the ECM programmed to fix the speedo/ odometer, or is that read at the wheel speed sensors rather than the tranny?

 

[STAGEUP]

If you want higher gears, i would consider the camaro 3.45 rear for your Gxp. It would offer better mpg, and still keep your car in its rpm band. Remember the Gxp is about 800 lbs heavier than a Corvette. So lower gearing helps with acceleration

 

[Silver Bullet]

If you want higher gears, i would consider the camaro 3.45 rear for your Gxp. It would offer better mpg, and still keep your car in its rpm band. Remember the Gxp is about 800 lbs heavier than a Corvette. So lower gearing helps with acceleration

I agree. I think swaping to the 3.45 would be a better choice in the case of lengthening the gears in an M6 GXP.

 

[camoeto]

I agree in general. I think the GXP is geared too low for optimal street driving. I'm not sure the 3.45 would make that much difference though. It's about a 7% difference from the 3.70. The 3.27 however is about 11.5% difference.

Taking 80 MPH cruise as an example:

3.70: 2122 RPM
3.45: 1979 RPM
3.27: 1875 RPM

The 3.45 is probably optimal for 6th, but the 3.27 may actually make 2nd usable while making 6th more of a pure overdrive

If you're going to shell out upwards of $1k to do this you might as well go with the 3.27.

This site is good for playing around with the numbers:

http://www.kabamus.com/garage/gears.html

 

[Bo White]

The gearing in the tranny is different too c5 to gxp as well too I believe. I would like more gear myself but that's just me lol. The reason why the gearing is steeper in the gxp is because of the extra 1000lbs its carrying around compared to the vette.

 

[Jason977]

I have a spreadsheet made up showing speed vs RPM in all gears for the GXP and C5. Since 4th is the same ratio in both trannys, it's interesting to see how different rear end ratios change the gear spacing.

With 3.27s, the GXP is still slower in every gear, but with nice spacing. With the 2.92s, 1st and 6the are almost identical. The gap between 3rd and 4th gets really big though

What I really need to do is thrust curves in every gear.

 

[Bo White]

Figure tire diameter on both vehicles?

 

[Bo White]

Never mind. Reread what you posted.
What are your goals? I take you are going for top speed and very low cruise rpm.

 

[Jason977]

Not even top speed, as I'm not sure more gear would get you there anyway without more power.

I think taller gears would make it a better daily driver, both in town and on the highway. Higher 1st would be nice for pulling into traffic without shifting or reving the engine out, and higher 6th would bring cruising rpms down, hopefully netting a little mpg gain.

 

[Bo White]

I'm a gear head lol. 3500rpm @ 70mph is no big deal to me even. I didn't own a street car with an overdrive until I was in my mid 20s and went back to a STD tranny on my next one.
First gear doesn't bother me since I shift no sooner than 2500rpm into second and I only downshift into first if I'm at a complete stop.

 

[camoeto]

One interesting aspect of this I haven't thought about previously is the top speed in 3rd at the 6600 rpm redline on the different diffs. It calculates out to be:

3.70: 99 MPH
3.27: 112 MPH

Depending on how much power you have, it may be that on the strip a 3-4 shift is not necessary.

 

[SRM6]

Personally I think the 3.70 rear with the 6 speed ratio spread is just right. I've driven an lot of combinations over the years and I would have loved to have had a 0.5 sixth gear in my 69 Chevelle 396/375 with a 3.73 rear. 3500 rpm at 70 mph in 4th gear (M22 rock crusher). I eventually sold the M22 with a 2.20 first gear and put in an M21 with a 2.52 first gear. It was like a new car in everyday driving, much more fun! Everyone has to do what suits their personal driving needs. For me, I think they got this one right the first time!