why do some recommend running the tranny in the 1:1 gear when dynoing? is it purely comparison reasons? something else im not thinking of at the moment?


thanks, Pat

 

1:1 doesn't have the parasitic losses that running most vehicles in overdrive has. However, on these trucks you're much better off in overdrive because it provides a load for the turbo to spool against. Back to back 4th and 5th gear runs displayed below graphically show the results:



brandon.

 

On a Dynojet 246C (inertial dyno), I ran 320/650 in 5th (1:1) and 347/762 in 6th. Even in 6th, my 4.10 gears were a hindrance. The taller gearing in 6th means that rotational inertia of engine-speed-related components doesn't sap as much power from the rollers since the pull takes longer to make, and the turbo has more time to "get its shoulder under the load" and spool in the higher gear. Although no one would ever do it, think how the engine would dyno if you made a pull in 1st - it wouldn't even know the rollers were there!

Rusty

 

yeah, i always thought the highest gear possible would be the best bet for the sake of loading the motor and spooling the turbo, atleast on diesels. my '02 made ~100 ft*lbs more torque in 6th vs. 5th.

 

Have you ever ran on a Mustang M250?

If you have under 1200 HP that dyno will bring your truck to its breaking point. I have seen a HT3B used as a single on a 12v and it spooled just fine.

If you run in anything but 1:1 on a M250 you will post lower numbers.

 

I believe the 1:1 might well be more efficient on a load dyno like the Mustang, but the highest gear possible seems to be more efficient on an inertial dyno like the Dynojet. Horses for courses........

Rusty