Shoaf85

iTrader: (9)

Just wondering if it is a big difference going from a 3.42 to a 3.90 car has around 450 rwhp! Ordering next week and was wondering if the 3.90 would be a good choice?

Cgillies86

iTrader: (1)

Go with a 4.10. Gears was one of the best mods I did to my car. My car had 419 rwhp on a mustang dyno I think that is around 450 on a dynojet. Second gear will be one hell of a blast with 4.10 gears as long as you can hook. When it was really hot outside my car hooked in second from a 40 roll with 4.10 gears and it was well worth it.

allngn_c5

iTrader: (3)

I rode in Chris's car and I can vouch for how it pulls a lot harder now then it ever did !! Very hard to get traction, but once he did the power was put to the ground and I was pressed into my seat.

Shoaf85

iTrader: (9)

The only thing is I am installing a 100 shot soon. so I'll probably stick with the 3.90! I have bfg d/r so w/o the nitrous it should hook but I seriously doubt it will w/ the spray!

allngn_c5

iTrader: (3)

I just noticed that you have a 2000 FRC, what color ??

Take a look at my sig, my FRC is hooked up and makes sick N/A stock cubed power.

mdhmi

iTrader: (1)

Only worth it if you upgrade your tires to take advantage of it.

allngn_c5

iTrader: (3)

+1 ........

I went from Goodyear OEM's to Michelin PS2's (c5 zo6 size) to take advantage of the extra horsepower. Tires are everything if you got the power to utilize the extra traction they provide.


POST A PIC OR 2 OF YOUR RIDE....

99C5JA

Another thing to consider is how high you want to rev it. If you are planning to keep it at or below 6500rpm 4.10's give you very little if any cushion in the 1/4 mile. With the shot of nitrous you'll likely be trapping higher than 123mph and that is where 4th tops out at with a 6500rpm limit and 4.10's. And you know you don't want to use 5th.

Cgillies86

iTrader: (1)

Assuming he has stock tires sizes and adequate inflation he would be able to get to 126 in 4th @ 6500 rpm. My car's redline was at 6800 and that is 132 mph. With 450 rwhp 4.10s are perfect. 450 rwhp + nitrous then 4.10s may be a bit much.

silver01z06

personally i am not a big fan of gears. if you are always running from a stop or at the track then i guess so. but more often than not people are doing gears to make up for the lack of power. that is why mustang gt's love gears so much.

BitViper

iTrader: (63)

And only if your drag racing..on a road track 4.10 will be WAT too high!...3.90's are pushing it

99C5JA

Hmm. The calculator I'm using lists 123mph for a 26.1" tire height and 6500rpm. So either you are running taller tires, the calculator is off, or your tach is slow. Even 126mph is to close IMO. With gears costing what they do, I want more than a 6mph cushion in case I want to throw more mods at the car.

Cgillies86

iTrader: (1)

Stock C5 Tire size:
275/40/18

To calculate tire height one uses the rim size and adds the wall thickness multiplied by two. A person multiplies by two in order to account for the wall above and below the rim.

Wall Thickness:
275mm * 0.4 = 110mm = 4.33 inches

Total Tire Diameter or Height:
18 + 4.33*2 = 26.66 inches

Cgillies86

iTrader: (1)

To calculate a speed of a car:

(RPM*60*Diameter*pi*(1.578283*10^-5))/(trans ratio*final drive ratio)

Explanation:
(1.578283*10^-5)): converts inches to miles
60: converts minutes to hours
Diameter*pi: circumference of tire
RPM/(trans ratio * final drive ratio): Number of times the tire turns

Basically one just multiplies the number turns of the tire by its circumference.

Example:
C5 with stock tires with 4.10s in 4th gear @ 6500 rpm

(6500*60*26.66*3.14*(1.578283*10^-5))/4.1 = 125.67 MPH

99C5JA

So to quickly summarize: you are running taller tires.

And I was aware of the process of figuring out the tire height. I'm running 295/35 tires with gives an overall diameter of 26.1". The Nitto 305/35's I am switching to soon will have a height of 26.4". My opinion still stands that for a car that will be knocking on 120mph trap speeds, 3-6mph simply isn't enough cushion for me.

BTW the calculations for speed is nice to know. Thanks!

Cgillies86

iTrader: (1)

No problem

Here is a new version of the formula, that gets rid of the nasty scientific notation:

(RPM*60*Diameter*pi)/(trans ratio*final drive ratio*12*5280)

Dividing by 12*5280 does the same thing as multiplying by (1.578283*10^-5).

mdhmi

iTrader: (1)

There are a few pics on my CarDomain site --> www.cardomain.com/id/mdhmi.

The car looks better in street trim (purdier rims/tires), but those pics should give you an idear.

Sigforty

A 3.90 will make the car seem like a different animal. With heads and cam you really need to put some more gear into the car. I am pushing close to 500 rwhp and have the M12 trans with 3.90s and it rocks. Even on the road course the car is great.

Blacked Out

I was looking into the 3.90 gear for my car as well. I am in the 430hp range and I thought the 4.10s might be a bit much for all the street running I do. Plus I plan on road coursing the car once in a while.

marlowchris

Like said, calculate your estimated trap speed and determine the gear from there. I am running 3.90s with a MN12 and cross at 6500 and 130 mph. If I turn the boost up any higher, then I will need to step down to 3.73 gears. 3.90s + MN12 are a blast to drive around town, mash the gas and instant tire smoke.