3.08 to 3.55 what does it cost you on a dyno?
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IEATVETS
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We all know you meant 3.07 but who cares! I talked with Cory at Snake Oyl about this very thing and he said that you do indeed pick up some tq but not hp. It isn't a lot mind you, but an increase none the less.
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RWHP loss on the dyno is about 10 to 15 with the 3.55s. RW Torque loss is the same, or at least is was with my car.
Probably depends on may variables, as usual.
Yes, I've done it.
Dan
Probably depends on may variables, as usual.
Yes, I've done it.
Dan
Vic
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Interesting...Gears affect rear wheel horsepower and torque, but not crank hp or torque. Thats understandable, since the power is being measured after the diff.
On an inertial dyno lower gears (higher numerical) lose hp because they are accelerating the wheels and driveline more rapidly. That means the wheels and driveline are "consuming" more power than if done at a higher gear ratio (lower numerically).
The effect is more with vehicles that have higher horsepower, thus accelerate the drum facter. It does not really affect the horsepower applied at the rear wheels, just what is measured. If you have a static dyno (like a Mustang running at a steady speed), the gear ratio will have almost no impact.
Peak torque is less impacted as the inertial effect goes up with the square of the speed (driveline & wheels) and peak torque occurs at a lower speed.
The effect is more with vehicles that have higher horsepower, thus accelerate the drum facter. It does not really affect the horsepower applied at the rear wheels, just what is measured. If you have a static dyno (like a Mustang running at a steady speed), the gear ratio will have almost no impact.
Peak torque is less impacted as the inertial effect goes up with the square of the speed (driveline & wheels) and peak torque occurs at a lower speed.
ViperJames
Enthusiast
WOW...Thats it? on a car that has stock HP over 400 that is not much.....
KenH
Enthusiast
I have heard similar numbers of about 10HP loss on the dyno with the 3.55 gears. I did not measure mine before and after however.
What seems less clear is whether it is an actual HP loss due to more frictional losses because of the different gear mesh or if it tends to throw the dyno off a little due to spinning the drum up faster resulting in a different measurement. I have heard it argued both ways, though I think it is probably a true HP loss. I have heard that the 3:55 gears run hotter (requiring more frequent gear oil changes) which would indicate that there is at least some HP loss with them.
What seems less clear is whether it is an actual HP loss due to more frictional losses because of the different gear mesh or if it tends to throw the dyno off a little due to spinning the drum up faster resulting in a different measurement. I have heard it argued both ways, though I think it is probably a true HP loss. I have heard that the 3:55 gears run hotter (requiring more frequent gear oil changes) which would indicate that there is at least some HP loss with them.
Paul Hawker
Enthusiast
Interesting. On a dyno the lower gears produce lower numbers, but on a highway roll on in 4th gear the 3:55's will pull away from the stocker every time.
Kinda like that Mystery Hill where water runs uphill.
Kinda like that Mystery Hill where water runs uphill.
That's because the car with 3.55's is developing more power than the 3.08 car at the same speed/same gear. It's not a fair race assessment. I got suckered into a similar race situation with a 3.55 geared car. He pulled me in the beginning, but as we reached the end of 4th, I was catching him, then he lifted after he hit 5th (but I was still in 4th).
The best way I found to "counter" this was to set the starting speed where it benefited me, for example I am in 3rd around 3.5 to 4K rpm. The 3.55 geared car, is still in 3rd, but at a higher rpm. Once the race starts, he has to shift into 4th within seconds, as he is making the shift I am flying by him because now he is at lower rpms, thus generating less power/thrust than me. By the time the advantage shifts back to the 3.55 geared car, the race is over.
Dimitrios
Enthusiast
agreed with john, used to race charlie with 355's and he used to pull on me in lower gears but every time he shifted i would gain on him cause i didnt have to.
joe117
Enthusiast
A car with 3.55 will get off the line better, if he can get traction.
That is because the 3.55 car has more torque to the rear wheels in first gear because of the mechanical advantage of those gears.
As you go up through the gears there will be points where the 3.55 has an advantage and points where the 3.08 has an advantage.
This is because the overall gear ratio, trans and rear, changes with the shift points.
The only change in the horsepower will be due to the increase in gear friction loss in the 3.55 and that is probably not much over the 3.08.
You can increase torque with gears but you can't increase horsepower with gears.
Horsepower is calculated by measuring torque and rpm.
When you increase torque with gears, you reduce rpm and so the formula will give you the same horsepower number.
In other words, you don't have more horsepower at the rear wheels at 5000 rpm in first gear than you do at 5000 rpm in second gear.
You have more torque at the rear wheels in first gear at 5000 rpm but the rear wheels are turning slower than in second at the same 5000 engine rpm.
Any dyno that shows a change in horsepower because of rear end gear ratio change, is only showing an artifact of how that dyno makes it's measurement.
This is aside from the small loss due to increased gear friction.
That is because the 3.55 car has more torque to the rear wheels in first gear because of the mechanical advantage of those gears.
As you go up through the gears there will be points where the 3.55 has an advantage and points where the 3.08 has an advantage.
This is because the overall gear ratio, trans and rear, changes with the shift points.
The only change in the horsepower will be due to the increase in gear friction loss in the 3.55 and that is probably not much over the 3.08.
You can increase torque with gears but you can't increase horsepower with gears.
Horsepower is calculated by measuring torque and rpm.
When you increase torque with gears, you reduce rpm and so the formula will give you the same horsepower number.
In other words, you don't have more horsepower at the rear wheels at 5000 rpm in first gear than you do at 5000 rpm in second gear.
You have more torque at the rear wheels in first gear at 5000 rpm but the rear wheels are turning slower than in second at the same 5000 engine rpm.
Any dyno that shows a change in horsepower because of rear end gear ratio change, is only showing an artifact of how that dyno makes it's measurement.
This is aside from the small loss due to increased gear friction.
V 10 MAFIA
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Very true, D was always able to pull me down upstairs when I made the shift from 4th to 5th.
Marc Lublin
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Charlie, you just need to learn how to shift quickly. Granny!
v10sloboy
Enthusiast
I have 3.55 gears and I am taking them out because my car is going to make over 700rwhp. At 565rwhp right now it is still not that great, traction limited with drag radials. I think 3.07 is best with boost and 3.55 gears for all motor and close to stock.
