aluminum drive shaft - anyone?

[churchx]

Depends. Same as removing that weight from anywhere IF you look at moving at constant speed ONLY. NOT the same, if you count how quickly you get to that speed i.e. acceleration. Not by much, probably not too noticeable by "butt dyno" if this upgrade is only one done, but summing up all the possible rotational weight lightening (pulleys, LWFW, brakes, wheels) it will improve acceleration more then removing same weight from elsewhere both felt by driver and by clock on timed racing, wherever acceleration matters. Engine has to spend some work to get those spinning parts .. well, spinning. Less the mass it needs to spin up - less energy spent on that. After spinning parts are spun up, they have their kinetic momentum, and if not changing speed anymore, engine doesn't spend extra. But during time of spinup you need some energy.

[stugray]

Originally Posted by churchx

Depends. Same as removing that weight from anywhere IF you look at moving at constant speed ONLY. NOT the same, if you count how quickly you get to that speed i.e. acceleration. Not by much, probably not too noticeable by "butt dyno" if this upgrade is only one done, but summing up all the possible rotational weight lightening (pulleys, LWFW, brakes, wheels) it will improve acceleration more then removing same weight from elsewhere both felt by driver and by clock on timed racing, wherever acceleration matters. Engine has to spend some work to get those spinning parts .. well, spinning. Less the mass it needs to spin up - less energy spent on that. After spinning parts are spun up, they have their kinetic momentum, and if not changing speed anymore, engine doesn't spend extra. But during time of spinup you need some energy.

Agreed that reducing rotating mass will help with acceleration.
The original arguement was is it "noticeable".

Then the arguement keeps coming up where people state "Installing a lightweight driveshaft will give you more horsepower".
I now ALSO call BS on how reducing rotating mass can help to increase measured horsepower.

Again, IF horsepower can be measured at constant RPM, then the rotational mass plays NO PART in the measurement since the heavier components only hurt you when the system is accelerating.

So can you see a difference in a dyno RUN with lighter components? - Yes.
Can you see improved HP numbers at a specific RPM - NO.

[stugray]

[jvincent]

Originally Posted by stugray

Again, IF horsepower can be measured at constant RPM, then the rotational mass plays NO PART in the measurement since the heavier components only hurt you when the system is accelerating.

So can you see a difference in a dyno RUN with lighter components? - Yes.
Can you see improved HP numbers at a specific RPM - NO.

@stugray, take your Physics textbook and go home!

[cdrazic93]

Originally Posted by jvincent

@stugray, take your Physics textbook and go home!

Lol that was me who quoted my textbook.

[Jaden]

Originally Posted by CSG Mike

@stugray

I wonder how much drivetrain loss is mitigated by eliminating the extra joint in the stock driveshaft... I'll need to try mounting a gopro somewhere that can see how much flex there is under the car.

Also, the harmonic resonance of the whole car is changed; I've always wondered if the stock driveshaft was for cost purposes or NVH purposes. This is something beyond the scope of my knowledge and anecdotal evidence...

Back on page three or four there was a guy who dyno'd his v6 mustang before and after switching to a one piece alum ds. He gained 8hp 8tq...

My guess would be just about all of that was from eliminating the two piece ds and the losses that extra join create.

Jaden

[stugray]

Originally Posted by Jaden

Back on page three or four there was a guy who dyno'd his v6 mustang before and after switching to a one piece alum ds. He gained 8hp 8tq...

My guess would be just about all of that was from eliminating the two piece ds and the losses that extra join create.

Jaden

Or maybe the fact that separate dyno runs on a car (same day) back to back can vary by +/- 5hp.

Just guessing that the before & after runs were not just 10 minutes between runs and all else being the same
AND.... was the person running the dyno the same person who SOLD the driveshaft?
I can absolutely guarantee that IF a dyno operator wanted to show a 8hp difference he could do it with no effort.

[Poodles]

I really was hoping this thread would finally die out...

Looks like I was wrong and people still don't understand why the factory used a two-piece.

[GT86_PRAGUE]

Originally Posted by Poodles

I really was hoping this thread would finally die out...

Looks like I was wrong and people still don't understand why the factory used a two-piece.

Why?

[stugray]

Originally Posted by Poodles

I really was hoping this thread would finally die out...

Looks like I was wrong and people still don't understand why the factory used a two-piece.

Well we can change the topic slightly to:
"How does a dyno REALLY work?"

Would you get a different dyno result if you stopped at each 100 RPM increment from 1000 to 7500 and performed the "brake-horsepower" measurement?
If you plotted each discrete RPM versus HP (Torque * RPM) data point, would it look exactly like a "dyno-pull" plot?
Or does the "dyno-pull" dataset look different from the "brake-horsepower versus RPM" plot?

I suspect that the two plots would be very close.

[nunonuna]

Dyno comparison before & after install of aluminum LWDS + LW Pulley + grimspeed intake.

I would say no gain shows since the gain(after LWDS with 2 other mods) in the graph is minimum and each runs were done on different days.
My buttdyno claims no difference. Oh actually there is a difference which is NVH. I even tried to rotate it to find a better balanced spot, but no luck. It really drives me crazy on highway because back mirror image blurs due to this vibration.

[Poodles]

Originally Posted by GT86_PRAGUE

Why?

Critical speeds.

Originally Posted by stugray

Well we can change the topic slightly to:
"How does a dyno REALLY work?"

Would you get a different dyno result if you stopped at each 100 RPM increment from 1000 to 7500 and performed the "brake-horsepower" measurement?
If you plotted each discrete RPM versus HP (Torque * RPM) data point, would it look exactly like a "dyno-pull" plot?
Or does the "dyno-pull" dataset look different from the "brake-horsepower versus RPM" plot?

I suspect that the two plots would be very close.

Yep, depending on the dyno, any reduction in rotating mass could show more power because of how the dyno operates. Of course this is how we get those nice dyno sheets we all like to see, but it's not really accurate.

Main things that dynos are good for (and things to remember):
- They're not dead accurate. Small variences are seen in back to back pulls, so why the hell do you believe the crap about gaining a couple HP? This is within the margin of error of the dyno.
- They're best used to compare changes to your car. Considering the stacked tolerances (car, weather, location, dyno...) comparing to another car is a fool's errand.
- They're great for tuning as they can induce stead state loads and can be used to diagnose. A tiny blip on a log from on the street can essentially be caused for any amount of time needed to figure out what's going on. This is why tuners use them, plus you don't have to break all sorts of traffic laws to get the data needed.
- Making your e-peen bigger because you wanted a hero dyno graph (cause let's be real, people actually do this...)

[Turdinator]

Question to those in the know, where does error come from? Is it the dyno itself or the car and how it is attached to the dyno? I would have thought the dyno's that spin up a known mass would have fairly repeatable results?

[GT86_PRAGUE]

Originally Posted by Poodles

Critical speeds.

In what speed will DSS CF MT going to brake?