Not the normal gear question

pimpstar00 said:

Does anyone know the exact science of picking gear ratios for maximum performance? I have a supercharger and was debating between 3.73, or the 4.10's. If i have to shift into 4th (in the quarter mile) with the 3.73's, then i might as well get the 4.10's right? One of the magazines had a formula based on peak dyno numbers to find the best ratio, just looking for some info.

Thanks

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I am curious as well, I am planning on either going the HCI route or a Paxton Novi 2000 blower, either way i am planning on ending up around 350-400hp. Would i better off either way going with 3.73's or 4.10's??

Whatever your decision, make sure you take into consideration street performance. (That is if you drive the car daily or on the street a lot) I have 3.73's and have trouble keeping the tires from spinning on the street and on the track. With street radials, I have to pedal through first then on a power shift, i have to pedal through second. If you plan on running at the track, are going to run DR's or Slicks and dont care too much about street performance, go with the 4.10's. If you want a more streetable ride with street radials go with the 3.73's. I guess there are give and takes to all gear decisions. Its the drivers preferance. Since I run street radials all the time, 4.10's would slow me down on the track or on the street due to spinning worse than I do now. Once you start spinning with the supercharger, as the power comes on, it only gets worse...

Here is some info I was given when making my choise. I dont know if it will answer your question exactly, but it could give you a means to figure it out.

Ex:
Use 95 mph as your speed.
Take your rpms divided by stock gear. Then multiply that number by what your new gear will be.

Say a car is at 95 at 2500 rpm, with stock 3.27 gears(switched to 4.10s) So here's the math:
2500 rpm / 3.27(stock gear) X 4.10(new gear) = 3100 rpm at 95 mph

I was also told this, Im not sure how accurate it is.

With the 4.10's you will redline in 4th gear at 110 MPH, vs. 137 MPH with the stock 3.27's. With the 3.73's redline in 4th is about 121 MPH

I know with my 3.73's the other day I redlined 3rd at around 97-98mph, I didnt redline 4th since traffic was picking up on the hw.

Hope this helps some

Im happy with my 3.73's. I know a lot of people on here are all gung ho about 4.10's, but my 3.73's work perfectly well for all my daily driving, and give me some added ummph on the hw. IMO I run out of 2nd to quickly as it is, I can imagine how quickly I would run out of it with 4.10's.

pimpstar00 said:

That doe help stanglou, i should hopefully be past 110 in the quarter so i guess i should get the 3.73s? dont want to shift into fifth.

Roush, you have the positive displacement blower, so traction is an issue, but with the centrifugal, i dont have all the bottom end torque that you do, so i might be ok with a little higher gear. what do you think?

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I think it all comes down to tires. I have seen the n/a guys having traction issues with 4.10's and street radials. If your running on the street a lot, the 3.73's will be nicer to drive around on and will make life easier for the occasional times when the tricked out ricer pulls up next to you. I would look through a few posts and look at the many members sig's see if you can find a few guys with similar setups as yours and private message them. You are right my blower puts out max torque real early in the powerband so it is quite different from a centrifugal which will make max power later in the rpm range.

gears

Hey man, if you have a supercharger, don't go with 410's. You will be shifting into 5th before the 1/4 mile ends. Top speed in 4th with 410's is about 108 mph. You should be able to trap at a higher speed than 108 being blown. 373's redline at about 125 mph, vs. 108 mph with the 410's. Plus 410's suck on the highway. I ran a Z4 from about 60 mph to 130 mph on Rt. 80 in NJ and beat him up pretty good. I have also beaten a 350Z and a Porsche Boxster on the highway. Running out of gear at 108 sucks on the highway! My wifes Chrysler 300M has beaten some Mustangs on Rt. 80. I don't know what gears they had, but from the sound of their revs, I bet they where rowing through 410's. Bogus for the highway.