Dynos vs finals drives, weight loss, etc.

[mike_ekim1024]

I believe I've ready some dynos can factor in acceleration, but does that include changing final drives, lightening the car, etc.? I feel if many of us are staying N/A that it's important to measure these factors also.

What about other measurements.. 0 - 60, 5 - 60, etc. on a dyno? Or per gear measurements.. slicing 0 - 1XX mpg logs into specific gears?

Mike

[mike_ekim1024]

No? If you take out 300lbs, will it show +whp on some dynos? Or some other measurement?

[andrew5826]

Originally Posted by mike_ekim1024

No? If you take out 300lbs, will it show +whp on some dynos? Or some other measurement?

i dont think weight loss of the car will show on the dyno. only when you are putting that power to the ground and accelerating

[troek]

i think bang for your buck the final drive will gain you the most in terms of acceleration, but alot of people might not be willing to deal with the higher rpms on the highway.

[wparsons]

If you take a bunch of rotating mass out of the driveline you might see 1 or 2 hp show up, but you'll feel it A LOT more when you're accelerating.

[arghx7]

I've never seen anything more than hearsay on the "real world" answer to these questions. What I'm saying is, there could easily be a difference between what "should" be going on and what happens in the real world. What I can say is this:

Any dyno, set up and maintained correctly, should not be affected by something that doesn't change wheel torque. BUT if I had to name a type of dyno that would be most susceptible to changes in tire size, weight, etc, it would be your typical low-end Dynojet inertia dyno that can't do any loading. This is because an inertia dyno doesn't directly measure torque. It measures how fast the rollers accelerate, to calculate the power, and then back calculates torque if it has an accurate engine speed signal.

[mrk1]

When I think of people who appreciate mods like a carbon driveshaft for example. They are not usually the type who are fixated on a dyno number. Lightweight is more of a driver mod. Ive always had the hardest time selling customers on final drives if they haven't experienced them. It is a considerable amount of money that doesn't really come with that tangible HP gain. Once I installed a diff for free in a friends car to prove a point, he then gladly paid after a test drive.

[Dustin]

Originally Posted by mrk1

When I think of people who appreciate mods like a carbon driveshaft for example. They are not usually the type who are fixated on a dyno number. Lightweight is more of a driver mod. Ive always had the hardest time selling customers on final drives if they haven't experienced them. It is a considerable amount of money that doesn't really come with that tangible HP gain. Once I installed a diff for free in a friends car to prove a point, he then gladly paid after a test drive.

My brother told me the same thing. I was hesitant at first, but one thing I know is he wouldn't steer me in the wrong direction. That's why changing the final drive and going with a more aggressive differential are the first major modifications I'm doing. Hopefully I'll be finished with it soon.

[jamesm]

changing the final drive isn't some sort of unicorn mod though. it doesn't actually make you accelerate faster depending on how far you plan on accelerating, since you have to shift earlier with the shorter gearing. depending on where and how you drive, it could serve you well to go the other way and 'accelerate slower'.

[mike_ekim1024]

Originally Posted by mrk1

When I think of people who appreciate mods like a carbon driveshaft for example. They are not usually the type who are fixated on a dyno number. Lightweight is more of a driver mod. Ive always had the hardest time selling customers on final drives if they haven't experienced them. It is a considerable amount of money that doesn't really come with that tangible HP gain. Once I installed a diff for free in a friends car to prove a point, he then gladly paid after a test drive.

A lighter driveshaft will give you a different power-to-weight ratio, so that's somewhat measurable. But I agree, it's just some number - you don't know how it feels until you really drive it. Looking at this wiki page, they describe many of the factors related to handling, but it's not the complete picture:

[ame="http://en.wikipedia.org/wiki/Automobile_handling"]Automobile handling - Wikipedia, the free encyclopedia[/ame]


What else could be added to this this list? I'm not asking just for myself, but for the thread and to keep building up information.

HP / Torque       Displacement, forced induction, N2O, water injection
Rotational Mass   Lightweight pulleys, cf driveshaft, clutch, brakes
Sprung weight     Interior, battery, fluids, seats, etc., etc.
Unsprung weight   Wheels, suspension, brakes, rotors, axles
Traction          Wheels, alignment, suspension, chassis, track and wheelbase
Gearing           Clutch, transmission, final drive, wheels
Weight distrib.   Suspension, engine placement, driver weight/placement
Aerodynamics      Front lip, wing, underpanels, rear diffuser, cannards

Some related pages:

http://www.pistonheads.com/gassing/topic.asp?t=858223
http://www.w8ji.com/rotating_mass_acceleration.htm

[MAPerformance]

Originally Posted by jamesm

changing the final drive isn't some sort of unicorn mod though. it doesn't actually make you accelerate faster depending on how far you plan on accelerating, since you have to shift earlier with the shorter gearing. depending on where and how you drive, it could serve you well to go the other way and 'accelerate slower'.

Agreed. I had 4.77 gears in my S2000 a few years back. Granted, it did make it peppier at lower speeds and helped with acceleration from a dead stop, but on the highway, a stock geared S2k could keep up and sometimes pulled away because of the torque advantage.

[wparsons]

Originally Posted by MAPerformance

Agreed. I had 4.77 gears in my S2000 a few years back. Granted, it did make it peppier at lower speeds and helped with acceleration from a dead stop, but on the highway, a stock geared S2k could keep up and sometimes pulled away because of the torque advantage.

What torque advantage? A taller final drive puts less torque to the wheels than a shorter one, so if anything you would've had the torque advantage. Ignoring having to shift earlier, a shorter FD will accelerate faster every time.

[MAPerformance]

Originally Posted by wparsons

What torque advantage? A taller final drive puts less torque to the wheels than a shorter one, so if anything you would've had the torque advantage. Ignoring having to shift earlier, a shorter FD will accelerate faster every time.

Correct, but on that specific car, or at least with my personal experience, it was quicker to 80mph. After that, it hit a wall. Stock gear S2k's could pull past me, especially after 100mph. But yes, below that, I could pull ahead, with the biggest advantage being in 2nd and 3rd gear.

[chrisl]

Originally Posted by wparsons

What torque advantage? A taller final drive puts less torque to the wheels than a shorter one, so if anything you would've had the torque advantage. Ignoring having to shift earlier, a shorter FD will accelerate faster every time.

Only in first gear, assuming both cars are running it all the way up to redline. Yes, on the highway, with both cars in 5th (for example), the one with the shorter FD will accelerate faster. If both cars are going for maximum acceleration though, the one with the shorter final drive might be in 4th, while the stock geared one might be in 3rd. This pretty much negates the advantage at higher speeds.