dyno question
Thread Starter
TECH Apprentice
Joined: Nov 2005
Posts: 304
Likes: 0
From: Newmarket, Ontario
dyno question If running a turbo car on a dynojet (vs. mustang) why not dyno it in 5th gear if it is not loaded properly in 4th? From what I understand the dyno doesn't know what rear end gear you have, it just checks how fast you spin the weight and your RPM's.
Why won't this work (dyno in 5th to load turbo better)?
Why won't this work (dyno in 5th to load turbo better)?
TECH Enthusiast
Joined: Sep 2004
Posts: 564
Likes: 0
From: Omaha, NE
That is a good idea, providing that the 5th gr can handle the extra power and the tires and dyno can handle the extra MPH. Doing this would better simulate the extra load that the engine would see on the street. If this is an inertia only Dynojet, it simulates a 2500 Lb load on the car with no provision for simulating air resistance as MPH increases. This would prevent normal turbo spool-up and not expose real detonation that shoud be tuned out. ABeasst states, "you'd be skewing the dyno", I think that it needs to be skewed if it does not provide the proper load for tuning purposes. Actually, aren't we un-skewing it?
Thread Starter
TECH Apprentice
Joined: Nov 2005
Posts: 304
Likes: 0
From: Newmarket, Ontario
I have 4.11 gears, SO, if I run in 5th it is like running in 4th with a 3.08 gear in the back.
4.11 rear end gear in 5th final ratio -> ~3.04
3.08 rear end gear in 4th final ratio -> ~3.08
Any thoughts why this will not work to help load up the car properly on a dyno and get the tune more accurate?
4.11 rear end gear in 5th final ratio -> ~3.04
3.08 rear end gear in 4th final ratio -> ~3.08
Any thoughts why this will not work to help load up the car properly on a dyno and get the tune more accurate?
TECH Enthusiast
Joined: Sep 2004
Posts: 564
Likes: 0
From: Omaha, NE
You got it, this will better emulate real world engine loads for better mapping of fuel and spark on an inertia dyno. I would rather error on too much load while tuning, you may race someone up a hill.
Peak numbers won't be as high as you would have more drive train loss, as you are not running 1:1 though the trans in 5th gear causing more friction with gears turning at different speeds..
Trending Topics
TECH Enthusiast
Joined: Sep 2004
Posts: 564
Likes: 0
From: Omaha, NE
We are discussing the best tuning proceedures, however, less important, on some combos 5th or even 6th can produce more measured RWHP. A higher trans gear reduces the engine/drivetrain inertia losses due to their lessor rate of acceleration which sometimes offsets the slight loss in a transmission's efficiancy. But if the rear gear and transmission gear combo generates too high of a testing MPH, the additional tires, gears and bearing frictional losses negate the lessor rate of acceleration gains. So peak HP/TQ measurement gear selection vary, often unpredictably.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
TECH Addict
Joined: Jul 2005
Posts: 2,153
Likes: 3
Originally Posted by kbracing96
Peak numbers won't be as high as you would have more drive train loss, as you are not running 1:1 though the trans in 5th gear causing more friction with gears turning at different speeds..
Originally Posted by engineermike
We found the opposite to be true. Dyno'd my last car in 1st, 2nd, then Drive. The power and torque numbers were progressvely higher. The way it works is the drivetrain weight absorbs less power when it rev's slower in the higher gears.
TECH Addict
Joined: Jul 2005
Posts: 2,153
Likes: 3
Originally Posted by kbracing96
1, you are loading the turbo more in D and 2, there is less drive train loss being in D as all the gears in the trans a spinning a the same speed.
2. Efficiency of a gearset has little to do with ratio, be it reducing or increasing.
When you use an inertial dyno, a certain amount of power is put into accelerating the crankshaft, damper, converter, transmission gears, driveshaft, and wheels. The slower all of these accelerate, the more power can be put into accelerating the drum. So, with higher gears, the rwhp reading will only go up to a point of diminishing returns.
With my old combo, the numbers were:
1st: 260 rwhp
2nd: 315 rwhp
3rd: 335 rwhp
I'm sure if I had dyno'd it in OD, it would've been somewhere around 340 rwhp.