SurlyOldManMN Posted November 17, 2011 Share Posted November 17, 2011 n00b question, I know... Everything I understand about torque says I should have more mechanical advantage (and subsequently more torque) in lower gears. Whereas gear decreases in size as we row from 1st-6th, mechanically speaking I should see progressively less torque. In preschool terms, it's easier to use a big gear to spin a little gear than it is to use a little gear to spin a little gear. What else am I not considering here? This has been bothering the piss out of me ever since my car was mistakenly dyno'd in 4th (should be 3rd even though it's a 6 speed, due to gearing) and put down higher numbers than 3rd. I'm sure it's something that's going to cause a massive, epic facepalm, but I just can't wrap my head around this. Link to comment Share on other sites More sharing options...
Types4 Posted November 17, 2011 Share Posted November 17, 2011 The transmission is a torque multiplier. However a dyno compensates for that so it doesn't matter if you dyno in 3rd, 4th or 5th it should net similar results. A dyno knows your rpms and the speed at which the rollers are spinning so it can calculate and compensate for any torque multiplication that is happening. With turbo cars on a dyno you will see higher torque/boost in the higher gears as the higher load on the engine really gives the turbo a chance to built boost better as the revs are climbing slower. Just like how in first gear you probably won't hit full boost because there just isn't enough time. Hope that makes sense. Link to comment Share on other sites More sharing options...
Spec B Posted November 17, 2011 Share Posted November 17, 2011 How much higher were the numbers? I always thought the peak should be about the same (3rd or 4th), but the torque curve would come on sooner in 4th. Link to comment Share on other sites More sharing options...
SurlyOldManMN Posted November 17, 2011 Author Share Posted November 17, 2011 How much higher were the numbers? I always thought the peak should be about the same (3rd or 4th), but the torque curve would come on sooner in 4th. 315/250 for 3rd 336/263 for 4th The curve did indeed shift earlier for 4th. The transmission is a torque multiplier. However a dyno compensates for that so it doesn't matter if you dyno in 3rd, 4th or 5th it should net similar results. A dyno knows your rpms and the speed at which the rollers are spinning so it can calculate and compensate for any torque multiplication that is happening. I suspected some kind of calculation coming in to play that makes sense of it all... If compensation is correct, I would expect almost identical numbers between 3rd and 4th barring heat soak/boost/some-other-differentiating-factor. If there is going to be a delta, I expect to see it increase as we move to lower gears. That's not what happened though. supwidat? With turbo cars on a dyno you will see higher torque/boost in the higher gears as the higher load on the engine really gives the turbo a chance to built boost better as the revs are climbing slower. Just like how in first gear you probably won't hit full boost because there just isn't enough time. Hope that makes sense. I could see that. I hit peak boost before 3k in both gears though. VF54 means a very early hit and then immediate death. There was a .1 psi difference in 3rd (17.9 vs 18.0 in 4th). I can't see 1/10 psi sucking 26wtq, maybe it does? Here's the plot just for gits and shiggles: http://i53.tinypic.com/jq12c7.jpg Link to comment Share on other sites More sharing options...
Types4 Posted November 17, 2011 Share Posted November 17, 2011 Could be that the dyno doesn't do a great job at calculating and compensating for the gear. Link to comment Share on other sites More sharing options...
bmx045 Posted November 17, 2011 Share Posted November 17, 2011 gear ratios are suppose to be input into the dyno software before pulls. you need the specific gear ratio and the final drive. of course you need to change these values if you're going to change the gear you're pulling in. Link to comment Share on other sites More sharing options...
Legend Posted November 17, 2011 Share Posted November 17, 2011 Should make the same power. I ran my car going WOT from 35mph to 125mph in 3rd and 4th and the whp is identical. See below. (torque not plotted). You might get more torque sooner in 4th gear when plotted versus rpm because of the higher load on the engine but more likely because of poor boost control and some overboost in high gears when going WOT at low rpms. http://beeez.com/lgt/dynogears.jpg My '05 LGT My '07 Supercharged Shelby Link to comment Share on other sites More sharing options...
RabidWombat Posted November 17, 2011 Share Posted November 17, 2011 The dyno shouldn't care what gear you're in, that's why its WHP and WT. The dyno should be able to know exactly the gear multiplier since it know roller speed and engine speed. If the dyno is deriving engine speed based on gearing multipliers your RPM curves would be shifted and you get the wrong red-line. The dyno should be directly measuring road speed and taking the derivative to get the applied torque. Torque and HP are related by a simple multiplier, so the curves should be equivalent. My guess is that you're looking at natural variation between the runs, due to things changing. Link to comment Share on other sites More sharing options...
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