2017 diff swap

[venturaII]

Originally Posted by mrg666

Let me ask this way. Suppose you are not drag racing but you will try to brake a speed record for your car and you have access to a very long straight track. The length of the track is not going to limit your end speed. What final drive gear would you choose for your 700+ hp car? I would choose the smallest final drive I can, i.e. less than 4.1. Am I wrong?

You'd pick the final drive that allowed the engine to be at (or just past...) it's peak horsepower at the same time the car arrives at it's drag-limited (both aerodynamic and parasitic) top speed for the power produced. This, however, does not necessarily produce a vehicle that is relaxing to drive and fuel efficient under normal conditions. This why our gearing allows for a theoretical top speed of something like 170mph in 6th based on gearing alone, but the stock car would never ever achieve that unless it was pushed off a cliff. Stock gearing is too tall to pull peak rpm in 6th with the power it produces.

[BirdTRD]

Originally Posted by FRS Justin

weir performance in American canyon cali sells anything you need for gearing and does installs, Ive used them and never been disappointed. Mark Spencer in NH also does gear setups if on the east coast and he's awesome too.

Both of these guys (Spence Weir and Mark Spencer) are awesome but Mark doesn't do diff's any longer.

[FRS Justin]

Originally Posted by mrg666

Let me ask this way. Suppose you are not drag racing but you will try to brake a speed record for your car and you have access to a very long straight track. The length of the track is not going to limit your end speed. What final drive gear would you choose for your 700+ hp car? I would choose the smallest final drive I can, i.e. less than 4.1. Am I wrong?

to a degree yes you are correct but you cant just say the lowest number you can find like a 2.73. example. car one is a stock N/A frs 148whp bone stock in the salt flats to reach top speed you would need a 3.55 gear ratio and 10m miles of track to hit 175mph (totally hypothetical numbers)car 2 is a turbo frs with 700hp on same track you could use a 2.73 and hit 300mph both the cars have the same aero same weight same everything except hp rating. my point is drag v/s hp will depend on the gear ratio needed to obtain max speed. yes lower number ratio has the POETENTIAL for higher mph but factors such as drag and hp dictate the limits for the ratio best suited.

[mrg666]

Originally Posted by FRS Justin

to a degree yes you are correct but you cant just say the lowest number you can find like a 2.73. example. car one is a stock N/A frs 148whp bone stock in the salt flats to reach top speed you would need a 3.55 gear ratio and 10m miles of track to hit 175mph (totally hypothetical numbers)car 2 is a turbo frs with 700hp on same track you could use a 2.73 and hit 300mph both the cars have the same aero same weight same everything except hp rating. my point is drag v/s hp will depend on the gear ratio needed to obtain max speed. yes lower number ratio has the POETENTIAL for higher mph but factors such as drag and hp dictate the limits for the ratio best suited.

I agree, I don't know why we had to disagree in the beginning. Thanks for stopping by.

[ermax]

10 million mile track. 😉

[ermax]

Originally Posted by mrg666

I agree, I don't know why we had to disagree in the beginning. Thanks for stopping by.

You are obviously still confused.

[ermax]

Originally Posted by venturaII

You'd pick the final drive that allowed the engine to be at (or just past...) it's peak horsepower at the same time the car arrives at it's drag-limited (both aerodynamic and parasitic) top speed for the power produced. This, however, does not necessarily produce a vehicle that is relaxing to drive and fuel efficient under normal conditions. This why our gearing allows for a theoretical top speed of something like 170mph in 6th based on gearing alone, but the stock car would never ever achieve that unless it was pushed off a cliff. Stock gearing is too tall to pull peak rpm in 6th with the power it produces.

Well explained. So all but one person in this thread is on the same page.

[nikitopo]

Originally Posted by FRS Justin

EDIT
You want facts here you go, My N/A car 13.74 @ 101mph 4:10 gears 13.47 @ 104 mph with 4:56 gears in the quarter,

Did you have a higher rev limiter in this N/A car? Let's say @7600?

[ermax]

Originally Posted by nikitopo

Did you have a higher rev limiter in this N/A car? Let's say @7600?

That isn’t really relevant to the stock power output. We will never hit redline in top gear with stock output. Not on the 4.3 gear that this thread was originally discussing.

[gtengr]

As an aside, and maybe something else we can all argue about, my calcs indicate that it would take ~280 rwhp to redline 6th with the 4.30's. That is based on rolling resistance and aero drag that fits the stock top speed, but the usual disclaimers that come with using the same rolling resistance and drag coefficients at different speeds.

[nikitopo]

I was asking for the 1/4-mile times and more specifically the redline limiter of 4th gear. Not about the top speed. Just curious..

[gtengr]

Yeah that would've been higher redline or non-stock tire diameter. Doubt he was shifting to 5th.

[FRS Justin]

Originally Posted by nikitopo

Did you have a higher rev limiter in this N/A car? Let's say @7600?

I don't remember my final rpm in the qtr but it wasn't at redline, man that's been awhile lol

[FRS Justin]

Originally Posted by gtengr

Yeah that would've been higher redline or non-stock tire diameter. Doubt he was shifting to 5th.

ya I was in 4th