Gears and Dyno Numbers

[Shelby3]

What's the formula for factoring gears into dyno numbers for comparison? I'm runing 3.73 gears in my GTS. How do I factor what the dyno numbers would be if I had stock gearing in the car? Thanks

 

[Torquemonster]

Good question - I'm not sure there is a set formula as different dyno's would be slightly different.

There have been posts of back to back runs with a gear swap - and the steeper gears lose power on the dyno - which drives people crazy - because they have the OPPOSITE effect on the road - as you know!

The car will feel (and be) a LOT quicker thru the gears with the 3.7's than with the 3.07's. It may not do better 0-60, or even 1/4 mile times because of the extra gear changes - but the acceleration in each gear will be significantly better.

Stating the obvious I know - but this was for the benefit of those that are confused by rolling road dyno figures that drop off when you run steeper gears - it's not real world power loss.

 

[Ulysses]

what percentage of power loss are we talking here?

 

[Torquemonster]

what percentage of power loss are we talking here?

I can't recall the specific amounts. I do remember Jason Heffner telling me the drops he had witnessed on his own dyno. If he sees this post - maybe he can chime in.

Or maybe other tuners can indicate the differences they've seen.

If enough results are gathered it may be possible to apply a rule of thumb (aproximate) factor to gross the power back up so it equates to running a 3.07 stock gear.

 

[Shelby3]

Gary Almond was present watching Macedo tune my car. Gary remarked that Jason Heffner was talking to Larry on the phone and asked if the car he had on the dyno had gears in it. Good ears huh? I'm guessing he (Heffner)has done a few with gears and could add to this post. Everyone says there is a difference, nobody I've talked to so far has quantified how much that difference is.

 

[Big Medicine]

http://www.viperclub.org/faq/techgears.html

 

[Martin D]

There is a 2-3% loss from 3.07 to 3.55. So do the math!

Regards,

 

[Simms]

Shelby3, I thought your car put down some good numbers?

 

[Shelby3]

Shelby3, I thought your car put down some good numbers?

The initial tune was around 635 rwhp and 670 rwtq on blower only, 798 rwhp and 908 rwtq with the juice added. Timing had to be pulled due to detonation and now it's making 613 rwhp and 650 rwtq. The blower only numbers seem low to me based on what is on the car. There's lots of forged piston cars with 8lb pulleys making those kind of numbers without heads and cam. I'm in the process of trying to find out if there is more in the tuning or the dyno numbers are low due to the rear 3.73 gears.

 

[Simms]

Shelby3, I thought your car put down some good numbers?

The initial tune was around 635 rwhp and 670 rwtq on blower only, 798 rwhp and 908 rwtq with the juice added. Timing had to be pulled due to detonation and now it's making 613 rwhp and 650 rwtq. The blower only numbers seem low to me based on what is on the car. There's lots of forged piston cars with 8lb pulleys making those kind of numbers without heads and cam. I'm in the process of trying to find out if there is more in the tuning or the dyno numbers are low due to the rear 3.73 gears.

Interesting, I sent you a pm.

 

[Shelby3]

Simms, Sent you a PM back. Let me know how your cars does after it's tuned.