Manual trans dyno, what gear?

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georgboy

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I asked the guy who dynoed my truck what gear he had it in, g56 trans he told me that he dynoed it in 6 th gear! Now my question wouldn't a 1:1 be more accurate on the dyno as far as engine horsepower output? If my memory serves me correct then a g56s 6 th gear is .76. That means the trans was in overdrive and the engine was not dynoed to it full potential right?
 
and too add to your question, would running in 4th gear with a 6 spd show a higher hp then running in 5th?
 
Depends on the dyno type. Inhertia dynos like 6th. More load on the dyno to spool the turbo. Load dyno takes care of that for ya, so you can get a way with 1:1. Also, I bet a load dyno can make short work of 6th gear and leave ya walking
 
The dyno I was on was a dynajet248h. I guess I can just Dyno again. Makes more sense to me to dyno in a 1:1 setup.
 
georgboy said:
The dyno I was on was a dynajet248h. I guess I can just Dyno again. Makes more sense to me to dyno in a 1:1 setup.
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You can possibly get a way with it on the stock turbo. The key here is, during the run do you boost numbers reflect the same acceleration on the road? Do you make full boost that is in 5th on the dyno as you should on the road with a stock turbo? If not, you need to dyno in 6th.
 
I always Dyno in 6th, only way to get it loaded up enough, Im usually 20 hp or so low in direct.
 
so I was at a dyno competition, on a load dyno, and a guy with a 6 speed came in and redynoed cause the first time he dynoed in 5th, and then said that it should have been in 4th. Well he laid down some better numbers and then he bumped me out of third place!! wasnt too happy that he got to redyno and i didnt, cause i could of done some tuning and laid down some better numbers.

So would runnin in 4th give you just a tad bit higher readings then 5th?
 
It's the amount of acceleration (0-30,0-50,0-100,0-120mph) of a set mass over time. Those three factors is what determine your hp. From hp, they calculate probable torque at that rpm where you made that specific hp.

So for example, If you dyno in 2nd gear in a manual, your top speed is like 35mph or so.

So 15mph to 35mph. You can turn that set mass very fast to 35mph. Say that time is 2 seconds. However, you never make any boost since the run is over very fast. top out at 25psi of 50. you accelerated the mass 20mph faster in 2 seconds might translate to 400hp.

The next run is in 6th. 70mph to 110. you do the same run in 3 seconds. you are able to make 50psi on the run now due to the gearing that translates into more preload on the motor right.. Now you accelerate the same mass 40mph. your HP is now 600hp. you where able to accelerate it much "further" in just a little more time.. Therefore you need more hp to do that task.

thats why you dyno on a inhertia dyno in a higher gear, so you can get push that roller as fast and as far as you can.

Ever wonder why guys with 600hp trucks take for ever to spin the dynojet while the 1200hp trucks spool and shut down almost in the same instant?


Now the guy that just dynoed 1088 on BDP's load dyno, that was a near 10 second run, mainly because the dyno was holding back on the truck. In theory, the dyno could stall the truck at peek HP if the operated wanted to. I'm sure the tires would rip apart first, however, it's possible. With that dyno, the amount of current required to hold back the truck translates into hp with some magical pixie dust.
 
I am always lower on boost in 6th at WOT vs the same speed in 5th at WOT. -example- pulling at 60MPH in 6th I push WOT and sit at 28 PSI vs drop to 5th at 50MPH and WOT gets 34 PSI- I used 60 and 50 as a approx. b/c the RPM at about 1700 or so in both scenarios-- I don't have a ton of mods done, but it seems that keeping in 5th gives the best pull, but I do get the issue with the inertia dyno- so why even mess with one of those, wouldn't those really be more suited to gas engines than a turbo charged diesel that needs more load to get to max output?
 
Most dynos will give you multiple runs so why not make a few in 5th and then make a few in 6th and see which is higher. My guess is that 6th will make the highest numbers.
 
georgboy said:
No LOL I meant 1:1 on he transmission LOL
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i know so ur motor and tranny r goin to be 1 to 1 but when it gets to ur rear end its goin to be 3.55, 4.10 etc... to 1 so y should the the tranny have to be 1 to 1. plus ur tire size will make a diff. And ur goin to make more power in ur highest gear.
 
You know there are so many different variables to look at. I am pretty happy with 551 hp on my very mild setup
 
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