Join Date: Jan 2008
Location: Seattle, WA area
Re: 3rd gear vs. 4th gear dyno pull
Results depend on the type of dyno and software. Some are reactive dynos, and others are inertial, and every company has it's own way of calculating. Effectively, it doesn't make much difference overall as lower gearing accelerates an [example] inertial dyno faster, but to a lower speed, giving a calculation result similar to a higher gear accelerating slower but to a higher speed. However, I won't go into that as it doesn't matter for what a chassis dyno is for. Chassis dynos are NOT for measuring horsepower, and should never be used for that - even though that's the most popular use.
Chassis dynos are for tuning with more chassis variables than an engine dyno. It would be much better if the output was in letters or Greek, as it would be just as useful as HP numbers for the intended purpose. For example, if you did a pull and got "J" power at one RPM, then made an adjustment and got "K" power at the same RPM, that's tuning. More power relative to other pulls, under the same conditions on the same dyno is the point. Raise your tire pressure or align your U-joints and make 20 hp more. It's all relative.
So, my most useful suggestion is to ignore the gear, but always use the same gear so you get relative results. I prefer higher gears only because they give a longer and more readable pull on an inertial dyno, or less jitter on a load cell. Otherwise I don't care. Just always do it the same, ignore the HP, and tune to increase the average numbers across the useful RPM range. Hope that helps.
-=≡ If it was easy everyone would do it ≡=-
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Last edited by PSIG; 05-31-2014 at 10:20 PM.