The competition and gear ratios

[rcdice]

In my never ending quest to drive myself crazy as to exactly which rear gear ratio to swap to in the Spring, I've been noticing what's been coming out lately on newer "performance" cars. A few interesting observations:

C6 Vette 3.42
Porsche Carrera S 3.44
New Mustang 3.55
New 400hp GTO 3.46

See a pattern developing here?

Anyway, then I read in the latest Car & Driver that the new Ferrari F430 has a 4.30. Are you kidding me? 4.30:1 Wow! I suppose the fact that the car redlines at 8,500 rpms makes that doable. Still. Also interesting to note that according to C&D, this car will do 0-60 in 3.5 and the 1/4 in 11.7. All this with "only" 483 hp and a measly 343 torque. Also interesting to note that at 123 mph in the quarter, the car would have just shifted into 5th gear.

Very interesting.

 

[ruckdr]

rcdice,
Remember, as you are aware, it is not just the differential ratio, but the combination of 1st, 2nd, 3rd, 4th, 5th, 6th, in combination with the rear end ratio, and also the tire diameter that effects the OVERALL ratio to the ground. As you know the Viper top speed is recorded in 5th gear with stock 3.07, and stock trans ratios. There are (can't remember where or the exact ratios) a 5th and 6th gear replacement for the Viper trans that brings the 5th closer to 4th, and 6th closer to 5th. This might be a good combination if you are running in excess of 140 mph, now done in 4th gear with stock 3.07.
You said: "Also interesting to note that at 123 mph in the quarter, the car would have just shifted into 5th gear."
Not necessarily, depends on the 1,2,3,4,(5,6,(7)) gear ratios + being able to stretch each gear to 8500 rpm; could possibly have only taken 3 gears. Remember the Viper will do 123 mph in 4th (stock 3.07) at only 5000 rpm.
Later,

 

[phiebert]

I switched to 3.55s from the stock 3.07 and love it. I actually use 6th gear occasionally now when cruising long distances at high speeds. Before I only used 5th. It is just a little nicer to have first and second gear a little shorter. You always feel like you are in a position to take off instead of making sure you are ready for a challenge. Of course, you'll have to shift a little more often. I think going higher than 3.55s might be a little much for the torque of a Viper but then I don't know, I haven't tried it.

 

[PhoenixGTS]

I think a good way to look at ratios is the top speeds in gears. For example, I believe the top speed in second with stock height tires is 70 mph (compared to a 4:10 which = 64 mph). This sounds like an optimal gear for making 0-60 mph runs. And the top 4th gear speed with 3:73 should be 125 (compared to 114 with a 4:10) which should cover most mildly modded cars in the quarter mile so they do not have to shift to 5th. Sounds like 3:73 is good with stock height tires (and maybe a 4:10 is in order with 19-20" tires). Now, to just get some traction!

 

[rcdice]

It really makes you wonder why DC didn't put a little shorter gear in from the factory. It would seem that something in the 3.33, 3.45, 3.55 range would be about perfect for a stock to moderately modified car. For my wants and desires, anything at or above 3.73 would be too much. I want it to pull hard off the line and at the low end, but I don't want to give up too much flexibility in the triple digits either. Maybe 3.33 or 3.45 is the way to go. Who knows? Like I said, I'm driving myself crazy with this.

Whatever I end up doing, I'm now thinking I should do the half shafts at the same time. At least that's any easy decision.

 

[IEATVETS]

I am with you Bob, I was going nuts trying to figure out which gears to go with but I made up my mind. I am going with 3.55 gears. I rode in a friends car with these gears and what a difference! You launch so much better vs the 3.07's. You do more shifting but who cares, the fun factor is worth it.

 

[joe117]

Does anyone think that DC might put in the 3.07 for CAFE gas mileage reasons?

I don't know, but it might be the reason.

Aside from that,
When comparing the Viper rear and overall ratio with other cars,
remember that the big 488 V10 might have more area under the curve than other engines with about the same hp peak.

A comparison of gear multiplied torque at the rear wheels at various rpm and in different gears, might show what's going on with the gears in a Viper vs. ZO6 and others.

 

[Steve 00RT/10]

I think C-5 vettes were also a 3:42 rear end. In other words....no change for the C-6. The transmission gearing is different in the Corvette even though the Corvette transmission is the same as ours(jointly developed by GM and Dodge). I would guess the higher rear ends for these has to do with displacement issues. I think Joe is on the right track with CAFE gas mileage being an issue. The 3:07 was plenty enough in 1992 for a 8 liter engine. The skip-shift feature and a .5 6th gear ratio also stuck a balance for power and gas mileage with an engine of that size.

Steve

Steve

 

[rcdice]

My guess on the "why 3.07 from the factory" issue is a combination of CAFE mileage, enough (is there ever enough?) torque from the V10 AND DC wanted to be able to say the car will do 180+ mph. Since I personally have no intention of taking the car anywhere near that high limit, lowering that number doesn't bother me in the least.

What I am concerned with is what a gear swap might do to acceleration numbers at say 60 to 120 or say 100 to 130. My understanding is that a shorter gear, like 3.55 will give you tons of power to the ground in the low end but you'll feel a drop once you get in the triple digits. Am I off on this? A buddy of mine has a built, NA, GTS with 3.73's in it. He says that once he gets over 100 mph he feels the ability to accelerate from there die off as compared to his bone stock ACR.

If the above is accurate, that is why I'm considering 3.33 or perhaps 3.45 to kind of hit a happy medium.

 

[SUN RA KAT]

A Roe Supercharger solves the problem. Big time torque above 2000 RPMs makes 6th gear very usable above 60 MPH, even though 60 MPH is well below 2000 RPMs. In lower gears, just be careful about loss of traction. 3rd gear is the first gear that almost to full power can be done on the street - the lower gears (1st & 2nd) will spin - and 4th and 5th gears are d*mn fast at part to full throttle.

 

[Steve 00RT/10]

What I am concerned with is what a gear swap might do to acceleration numbers at say 60 to 120 or say 100 to 130. My understanding is that a shorter gear, like 3.55 will give you tons of power to the ground in the low end but you'll feel a drop once you get in the triple digits. Am I off on this? A buddy of mine has a built, NA, GTS with 3.73's in it. He says that once he gets over 100 mph he feels the ability to accelerate from there die off as compared to his bone stock ACR.

I looked into the examples you mention before buying a 3:45 rear end last year. I bought a software program on line to figure this out. Cartest 2000.
The program may not be the gospel, but it works real slick for what I wanted to find out. You can create your vehicle and input your own data. It also comes with around 1400 cars already in the data base.

With a 3:45 gear, the acceleration is still a little stronger with the 2 examples you mention. I believe a 3:55 gear will top out under 130 in 4th. Once you hit the .74 gear at 125 or so in 4th gear, the stock rear end still in a 1:1 ratio will start to gain. It doesn't top out till around 152.

Even with gears, there will be a see saw effect all the way up as the lower gears shift sooner in each gear. The stock rear end car will gain a little each time you shift your 3:55 and then, conversely, lose a little when it shifts.

I am very happy with my 3:45, although I will say that from a SOTP measure, the stock rear end 'feels' like it pulls harder from 115 or so to my 3:45 redline in 4th of about 132. This is probably because the 3:45 gear is nearing redline and quickly moving out of the power band of the engine while the stock rear end is in prime power territory at that speed. As I am at lower speeds more of the time, I enjoy the power more in the lower gears. I also have a lightened flywheel. Between the 2 mods, it produces much more snap for autocrossing.

Steve

 

[Hisserman]

We all know you have plenty of "snap", Steve. Merry Christmas from downstate!

 

[FE 065]

I still have a new Unitrax 3.45 r&p w/speedo recalibration box for sale..