How to dyno - Diesel Truck Forum -
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post #1 of 7 (permalink) Old 12-30-2008, 10:59 PM Thread Starter
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How to dyno

I thought it would be nice for some of us who have never dyno'd (myself included) to have a instructional post on what to do when dynoing to get the best numbers on the rollers. I do plan to dyno in the future and would hate to waste my money because i'm not doing something right.


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post #2 of 7 (permalink) Old 12-30-2008, 11:15 PM
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I'm interested in this as well...never really heard a description of how to go about it...

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post #3 of 7 (permalink) Old 12-30-2008, 11:17 PM
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give dyno operator your truck keys, stand back and watch while drinkin' a's that simple and easy..........


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post #4 of 7 (permalink) Old 12-31-2008, 08:38 AM
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Here's a little dyno check list:

1) - Make sure the tires are inflated properly. Low pressure increases rolling resistance and lowers power numbers.

2) - Make sure the dyno operator runs your truck in Drive or your 1:1 gear. If you have a programmer, or if you are having tuning done, make sure the converter is locked and the truck doesn't downshift.

3) - My experience is that load dynos are better only because they light the turbo at lower rpm and give you more representative data. But make sure that the dnyo shop you use is familiar with diesels otherwise it could end up being an expensive waste of time.

4) - Finally, run the truck with th same tun you drive it around with the most. That's the tune you want to know the power ratings for. Race tunes, Looney tunes, Insanity tunes, whatever you want to call them, they migh lay down a big number, but if you never go to the track or sled pull, then those tunes are just feel good numbers for when you dyno and are otherwise impractical.

I've probably made close to 200 pulls on the dyno with my truck now, it's never hurt the truck, so don't be affraid to do it.

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post #5 of 7 (permalink) Old 12-31-2008, 10:22 AM
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Check out the graphs at the end of Post #13 here...

...and note that if you use an inertial dyno you'll typically get a higher RWHP reading in an overdrive gear compared to direct gear. However the resulting MPH will exceed the speed rating of LT type tires so it's not the safest thing to do, and if your chip didn't remove the speed limiter you can't use OD anyway!

Ask the operator what atmospheric correction factor and smoothing factor he's using and see if he can explain why he choose the ones he did! I suggest also getting an uncorrected curve with no or little smoothing and no atmospheric correction because the SAE atmospheric correction that's commonly used is a compromise that's more appropriate for gassers than diesels! Make note of the barometric pressure and ambient temperature, and I might be able to provide a more realistic atmospheric correction factor for your diesel. Also if the dyno uses a temperature probe it should be positioned so as to get a true reading of the air intake temperature.

Warm the engine and driveline fluids enough to reduce their viscosity, but don't over warm the engine because for most dyno setups there's typically either no cooling air or an insufficient supply of it to effective remove engine heat like when driving down the road, and a hot intake manifold and engine heat leads to hotter than normal air intake temperatures which results in a lower maximum engine HP than you'd normally get when doing a hard acceleration run down the road. Before long I'll be posting a simple road test procedure you can use to check the accuracy of your dyno results.

I'm always nervous about EGT and when I've asked to sit in the passenger seat to watch the gauges it's always been ok with the operator, but these were on ground level dynos not the portable drive up elevated types.

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post #6 of 7 (permalink) Old 01-04-2009, 07:53 PM
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Originally Posted by O2ShootTheJ View Post
I thought it would be nice for some of us who have never dyno'd (myself included) to have a instructional post on what to do when dynoing to get the best numbers on the rollers. I do plan to dyno in the future and would hate to waste my money because i'm not doing something right.

on your truck 5th is the 1 to 1 gear. tell them to load the piss out of the dyno cause thats the only way these trucks make power. and put it to the rug at about 1200-1300rpm. let off at about 3200-3300. any higher than that and your wasting your time.

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post #7 of 7 (permalink) Old 01-05-2009, 12:47 AM
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from what I have seen on the rollers of portable dyos the the dyno jets you get higher numbers in od. the best way to not get a downshift is to run up to about 65 then have them start the sampling. mine doesn't downshift from that point.

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