Rear Gears

[HIZNHRZ]

Okay, next questions for the experts. With roughly 425Hp and and 410ftlbs at the rear wheels, would you go with 3.90 rear gears or 4.10s?

I'm looking for a nice compromise between highway pleasure cruising and rear gears that optimize my engines Hp and torque numbers at the drag strip.

[jonszr1]

I am about the same hp as you i have 410 but would go to 373s of i did it over took the 373s out of my yellow car thats stk and just loved them in the black car . if your looking for the best of both worlds thats what i would go with . 410s gas mileage goes down to 20 with 373s 24 -26. hope this helps

[Aurora40]

I've thought 3.73:1's would be a nice gear also. And the speedo correction gear is like a $10 GM part vs a $140 custom part.

The only thing is 3.73:1 isn't a huge change. It costs the same for the gears as 4.10:1, and costs as much to install. But for less "improvement".

A 3.90:1 might be a good in-between. A fair amount of change, but not quite so gear-shortening as the 4.10's. I thought 3.90:1 gears were hard to find? Or maybe it was the speedo correction gears?

If you math it out on the LT5 vs the L98, with a 3.33:1 rear and a 5,500 rpm redline, to have the same shift points in MPH at 7,100 rpm, the LT5 should have a 4.30:1 rear end. In reality the L98 shifts earlier, giving it even shorter gear ranges than that.

Not sure what that is worth, though.

As an aside, guess you decided to go with the 500hp package?

[jonszr1]

very nice and thought provocking post. heck i wish a gear vendors od wasnt so expencive. that would be the best of both worlds . put 430s in and have the gear vendors to reduce 22% to 335s now that would be cool plus you would have an 11 speed .it uses a timed selinoid to shift extreamly fast.wouldnt that freek people out . i can hear the shifts now

[kenthompson]

Originally Posted by jonszr1

very nice and thought provocking post. heck i wish a gear vendors od wasnt so expencive. that would be the best of both worlds . put 430s in and have the gear vendors to reduce 22% to 335s now that would be cool plus you would have an 11 speed .it uses a timed selinoid to shift extreamly fast.wouldnt that freek people out . i can hear the shifts now

I have a GV unit that I'm thinking about selling. The adapter is for a 4l80e though. Do they make an adapter to a ZF 6 speed?


KT

[HIZNHRZ]

Bob,

I'm clearly leaning towards the top end package. While a stroker is the dream, I'm going to have to dream some more as I've got one more college education to bank role.

I've done the rear gear math and certainly have my own opinion. I've never been much of a drag racer but because my reflexes are not as sharp as they once were I'm not all that interested in track day at Summit Point unless I take a class or two. I feel like my stock ZR1s performance pushed me beyond what I was confident with.

With drag racing, I do'nt have a good feel for the time impact of shifting other than to say that every .01 of a second wasted is included in your timeslip. As far as gears, I'm looking for opinions based on a combination of theory and practical experience. I'm also not sure I'm following your cpmparison to a L98. You have both knowledge of the theory and practical experience; what does you gut tell you?

[Aurora40]

Originally Posted by HIZNHRZ

I'm also not sure I'm following your cpmparison to a L98.

Sorry. I'm not sure what exactly I draw as a conclusion from it either. But, gears are chosen for a reason. Part of it is what fits in the tranny/diff. But mainly, you have a set of gears, 6 in this case. And you want to balance performance with economy with drivability.

In the case of the LT5 vs L98, you have one engine with a very limited rpm range, vs one with a very wide range and which is substantially stronger up top.

So partly what I mean is that in terms of drivability and having to shift, going with 4.10:1's is no worse than the amount an L98 owner must shift with stock gears. Except that you are making one hell of a lot more power and will have one hell of a lot more torque at the wheels due to the higher torque of the LT5 plus the mechanical advantage of 4.10:1 vs 3.33:1 rear gears.

So that is a positive thing to be said for the 4.10's I think. The amount of shifting can't be that bad, as a base Corvette shifted that often from the factory. Plus it gets you into the meat of the powerband quicker.

Now cruising rpm will of course be higher than an L98, and fuel economy will suffer.

It would almost be like having an L98 that has had it's power output doubled and its sound improved.

On the flip side, the stock gears. They show off the engines wide flexible power band better. I mean, you can about hit 60mph in 1st gear. In a 6-speed transmission, that is insane. 4-speeds didn't have gears that tall.

Fuel economy is great, driveability is great, and the engine is flexible enough to work with the tall gears. Plus you don't have to shift much, and it is harder to blow the tires away in 1st and 2nd.

I haven't looked at the numbers, but I believe this is the kind of gearing cars like the Countach had. Tall gears so it could run fast. And a big motor that could pull it off. To me the 3.45 gears are sort of exotic. They let you savor the engine as it pulls through the rev range.

I asked Mark about 3.73's at BG. He mentioned the 4.10's are probably good for a .5 second improvement in the 1/4, and that you give back .2-.3 seconds for the extra shift. 3.73's will also require an extra shift, but will not have the same gain. So the net effect may be a wash in the 1/4. 3.90's, I don't know.

As to my gut, well I think now it is telling me, stick with the stock gears. While the 1/4 mile improvement would be nice, I don't really drag race the car that much, and I mainly just do it to have fun and to go fast. I probably won't trap any faster because of the gears, so who cares. I do love how long the cars legs are on the street. I do still think 3.73's would be cool, but it's just a very small change for the same amount of cost. So I probably never will do it.

And in the back of my head, I don't want to give up any top end. Sure, the car will probably never see 150mph, let alone 180. But still, it's nice to know it can do it. 5th gear @ 7300rpm with 4.10's would be good for about 175mph. 3.90's put it at 185mph. 3.73's top out at 195. And the stock gearing, if the motor could pull it, would run to almost 210mph @ 7300 rpm (about 200mph at 7000rpm). On a ported car, 3.73's would probably enable the highest top speed just because the power peaks around 7,000 (or at least my car does).

So to me, 3.45:1 or 4.10:1 makes sense depending on whether you like the sort of gentlemanly exotic aspect, or the tire burning 1/4 mile monster aspect. 3.73's and 3.90's fall somewhere in-between. So maybe the answer depends on where you fall between those ends? Hope that's helpful and not just rambling.

P.S. an upshot of 4.10:1 gears is if you want to do some 3rd gear pulls for datalogging, you only have to hit 97mph on Great Seneca instead of 115mph!

P.P.S to answer the question asked, if it were my car, the cost were the same, and I had a choice of 3.90's vs 4.10's, I would go 3.90:1.

[Tim]

Wow, Great posts. Learned a lot. I went with 4.09:1 based mostly on the useability of 6 th gear at highway speeds as the rpms were so low I sometimes had to downshift to pass. I have not noticed much diff in milage. Plus I enjoy the pull in 1st and 2nd.

[blackjack]

when i changed my rear end ratio,my first choice was 3:90..because it wasnt readily available,i went with 4:10...and now with 2 summers of driving the z with the new ratio,i still would like to try the 3:90,as i find first gear almost useless...too much wheelspin,even with yokos avs sport...we must not forget that in the great white north,the asphalt is often colder than down south,except maybe for july and august,and spinning the tires is a lot easier on cool pavement...im also curious to know how the onboard computer figures my gas mileage,in relation with the gear change...is it lying to me??
i still get 25 mpg,according to the oracle.
bj
91/1735
ported plenum & ih
2.5'' exhaust with x pipe,no resonator
lucas injectors
haibeck chip

[DaveK]

Blackjack

I'm the same. Have 4.10s in mine and 1st is gone almost before you can think about it. I also get 24/25mpg usually.

I wouldn't think that the computer knows anything about the gears when it does the calculation - it's likely to be just simply miles travelled/fuel used.

The gear wouldn't affect that, unless you didn't do the odometer correction, in which case it would be sending too many pulses and recording more miles than were physically travelled.