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Dyno torque

  
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Dyno torque

 
Socorro59 Socorro59
New User | Posts: 2 | Joined: 05/13
Posted: 05/20/13
12:19 PM

I've googled everything I can think of, and still can't find an answer that explains dyno torque numbers to me in a way my old ***** can understand. Question started when I went to re-gear my rear end. Going from 3:08s to 4:11s. I did a pre maintenance dyno and got peak HP of 255 and peak torque of 298. I'm putting a bigger motor (400 little M bored .030 over) to go along with the gears, so I know both numbers, torque and HP, will be much higher. My question is though; would my dyno'd torque numbers go up with just the gear change? I understand physics and gears. The purpose of steeper gears is to multiply torque. Big trucks have low gears so they can pull big loads. This is done at the expense of top end speed. I can't go 80 on the highway without the engine running at 4000 rpm if I have low gears (unless I have an overdrive). I get all that. But how does this come in to play on the dyno? Every tech I've asked says I will not show more RWTQ on the dyno with just a gear change. They say that the dyno just looks at how fast the drum is spinning and how long it took to spin it that fast. I'm confused.

Matt  

redneckjoe69 redneckjoe69
Addict | Posts: 2337 | Joined: 03/10
Posted: 05/20/13
02:32 PM

theoretically, the tech's would be correct.    woulda been cool if you got the "after" results with the same set-up.     i dont know if you would see any gain, but it wouldnt surprise me if you did.    after all, a factor of RWHP is driveline loss.  a customer at the local parts store told me he picked up 7 RWHP on a chassis dyno with his mustang, just by changing to royal purple synthetic fluid in the rear.     sounds kinda hard to believe, but anything that saves driveline loss is a good thing.  

   interesting topic! Cool  

Dave632 Dave632
Addict | Posts: 2219 | Joined: 07/08
Posted: 05/20/13
04:04 PM

Very interesting question.
I imagine the dyno would have some way of compensating for the difference in torque when multiplied by a lower gear ratio. Otherwise the rear wheel dyno numbers would be meaningless. I do not know the method used to do this.
What Joe is saying is very true. Drive train losses are magnified by heavier stronger components. This is also true with high stall converters.
Some drive trains will pull 30+ percent away from flywheel ratings. I have seen tests that confirm this. A 700 flywheel hp BB made 495 at the rear wheels due to a high stall converter and a heavy duty Ford 9" rear.
Removing rotating weight gives the biggest advantage when taking weight off a car. That is why Pro Stock cars use Titanium axles, spools, etc. Most bang for the buck.  
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Socorro59 Socorro59
New User | Posts: 2 | Joined: 05/13
Posted: 05/27/13
10:26 AM

Check out this article I just read. Makes sense to me.

http://www.nrhsperformance.com/tech_power.shtml

Matt