Bopcat

Anyone know the max (redline) speed in each gear for a GT w/automatic tranny?

don_w

That would depend on a lot of things... don't think there is an answer for that.

Bopcat

Wrong...there's a definite answer...it just takes a bit of calculation and I'm asking if anyone has found the numbers in a magazine or figured it out. Assume a 6250rpm redline, stock gearing and tire size.
Road & Track, etc. have listed the max speed in gears for manual tranny GTs but I haven't seen any numbers for autos.

Stangers

Do a search on autos that have had dynos.Theres plenty of info on it.
No two cars are the same.

Cleveland

the only thing I can tell ya is that I regularly hit 60mph when it shifts to 2nd gear under WOT. It got me my first ticket.

-Dan

don_w

Uh.. no there isn't. You might be able calculate a thoretical number, but it's has no bearing on reality. Atmospheric conditions affect hp. Wind speed and direction will affect drag. And probably a dozen other variables to consider. None of which I care to spend any time trying to determine.

Weedo

You're exactly right, and I know what you're looking for. Every magazine you read tests cars this way, showing max speed in each gear (manuals are shown shifting at redline, autos are shown shifting where they shift when in D).

Anyway, I don't know the numbers and haven't found them either. I'm curious as well. No need to talk about "variables, weather, different cars, etc..." he's looking for some numbers from a magazine, or numbers someone has seen on their actual car. Magazine numbers are sometimes based on the manufacturer claims as well...

don_w

Well, if all your looking for is someone's best guess (like a magazine's), then you could probably assume the auto would be very similar to the manual. The slight loss of powertrain efficiency for the automatic, would likely be compensated by the higher rear end ratio (3.31 vs. 3.55).

2MFF

I made a gear ratio calculator when I was planning my 6 speed swap in my 66 mustang. If you want a chart similar to this one

http://www.2mfffabshop.com/mycar.htm

let me know and I'll run the numbers and post the chart.

Bopcat

Thanks, I'll look up the numbers and get back to you. I know how to do this by working it out one by one, but if you have a program that would be faster.


Obviously these are theoretical speeds in gears. The manual (and prob the auto as well) is electronically limited to 143. Lots of cars can't pull redline in top gear (or even the top two gears) because they are drag/hp limited. Our Miata will pull redline in fifth (118) but tops out at 122, which is a long from top gear redline because of its crappy aerodynamics.

Bopcat

hey 2MFF, here's the numbers for 2005 auto
thanks

1st 3.22
2nd 2.29
3rd 1.54
4th 1.00
5th 0.71

rear end 3.31

tire 235
aspect 55
wheel dia. 17"

2MFF

Here ya go

CHART

Bopcat

The link is broken for me. Anyone else able to get it to work?

2MFF

OK, try it now

Bopcat

Thanks, that's just what I was looking for.
I've done this once before with a different car. Took me all day doing it with a calculator.

Ben

Weedo

That's a great "best guess"!

Kidding of course, thanks for the chart, good to know!

don_w

Yep.. good to know... for what reason, I have no clue... but it is sure good to know. LOL

2MFF

Well, I originally designed the program to compare different combinations of transmissions/transmission gear sets/rear end ratio/tire sizes when I swapped a 6 speed into my 66 Mustang. I wanted to pick the right combination to keep within the power band of my cam when racing(open track), and still have a nice low cruising RPM on the freeway. When you are comparing 3 different transmissions, with at least 2 gear set choices per transmission, 3 rear end ratios, and multiple tire sizes a program like this comes in real handy.

Gearhead

Peak Power for the V8 is at 5,750 RPM, and maximum upshift engine speed is 6,250 RPM
The rear axle ratio for the automatic is 3.31:1
Transmission Ratios: 1st = 3.22:1, 2nd = 2.29:1, 3rd = 1.54:1, 4th = 1:1, 5th = 0.71:1
If you care to calculate speed at RPM, here is how you do it:
Tire Diameter (stock) = (23.5 cm)(1/2.54 in/cm)(0.55)(2) + 17" = 27.18 in
Circumference = (3.14159)(27.18 in)(1/12 ft/in)(1/5,280 mile/ft) = 0.0013477 mile/rev
1st Gear Speed = (6,250 rev/min)(60 min/hr)(1/3.22 1st gear)(1/3.31 axle ratio)(0.0013477 mile/rev) = 47 MPH
2nd Gear Speed = (6,250 rev/min)(60 min/hr)(1/2.29 1st gear)(1/3.31 axle ratio)(0.0013477 mile/rev) = 67 MPH
3rd Gear Speed = (6,250 rev/min)(60 min/hr)(1/1.54 1st gear)(1/3.31 axle ratio)(0.0013477 mile/rev) = 99 MPH
4th Gear Speed = (6,250 rev/min)(60 min/hr)(1/1.00 1st gear)(1/3.31 axle ratio)(0.0013477 mile/rev) = 153 MPH
5th Gear Speed = (6,250 rev/min)(60 min/hr)(1/0.71 1st gear)(1/3.31 axle ratio)(0.0013477 mile/rev) = 215 MPH
It would be advisable to be going down hill with a strong tail wind if you hope to hit the maximum speed in 5th gear.
Brian.

Weedo

If I wasn't so tired right now, I'd probably figure this out with my 4.10's...