Flywheel HP > Wheel HP??

[91CRXsiR]

so if a car has 200 HP at the flywheel like lets say.. the RS-X type S..

and at the wheels it only has about 170 HP.

that means 30 HP was loss through the drivetrain.

question is.. how to minimize that loss?.. better clutch? better oil?..

and will this greatly add to the "gains" of future mods?.

[Neurotoxic]

On the 240sx (or any other RWD for that matter), the driveshaft is often a source for performance losses. Having an aluminum or a CF one will reduce the loss (and actualy improve the car's response).

Other factors would be the clutch/flywheel and the differential. I'm probably missing a few more factors....

[Steeles]

clutch flywheel anything on the drivetrain. thats why its called drivetrain loss. figure 15% for FF 18% for FR and like 24% for AWD. I dunno how MR or RR stack up. my guess would be about like FF cars. in that 15% range. alll those are give and take numbers.

[91CRXsiR]

wow 24% for AWD?! .. no wonder the WRX rated 170 HP.. lost of 50 HP!..

so a carbon drive shaft huh? how much do those run? on gran turismo that thing cost a grip..

[Neurotoxic]

I don't have any precise price, but iirc a carbon driveshaft would be a couple of hundred $US.

They're a realy nice upgrade, but maybe for some more "extreme" applications. ie: I wouldn't even think of getting one without a race clutch/flywheel and some serious dyno results.

Otherwise, for a street setup, I'd say a custom-made aluminum DS would be cheaper and almost as efficient.

[91CRXsiR]

interesting... would a lighten flywheel help out w/ this?.

and why does a AWD take off 24 %??

[Jeff240sx]

Originally posted by 91CRXsiR
interesting... would a lighten flywheel help out w/ this?.

and why does a AWD take off 24 %??

Yes. Anything you do to the drivetrain will help, especially reducing rotational mass.
AWD loses so much because it has 4 wheels to turn, with a sophisticated power delivery system that uses 2 differentials, ect.
-Jeff

[Neurotoxic]

Originally posted by 91CRXsiR
interesting... would a lighten flywheel help out w/ this?.

and why does a AWD take off 24 %??

A lighten flywheel MIGHT help, depending on what you're looking for and what setup you have.

Since it's lighter, it starts rotating quicker. The downside is it also stops rotating quicker, because it has less inertia. The consequence will be a higher drop in RPM between each gear. A short-throw shifter might help though.

And the reason why there is so much power loss on an AWD is simply because there are more mechanical parts on the drivetrain, more places where the power of the engine has to be converted to a rotating movement (to spin your wheels). Instead of 2 wheels, there are 4 wheels on which you must apply power, and since nothing is perfect, the loss increases along with the number of involved components.

[AceInHole]

A lighten flywheel MIGHT help, depending on what you're looking for and what setup you have.

Since it's lighter, it starts rotating quicker. The downside is it also stops rotating quicker, because it has less inertia. The consequence will be a higher drop in RPM between each gear. A short-throw shifter might help though.

to clarify that, RPM's drop faster, and the short throw shifter would help by speeding up your shift from one gear to another (in case someone was thinking the shifter might help drivetrain losses).

it should also be noted that drivetrain loss percentage increases as power increases.

[lbcklik1486]

If u have an lsd, u might loose some extra horses too. I have seen sentra spec V's loose almost 25% because of the lsd.

[Jeff240sx]

Originally posted by lbcklik1486
If u have an lsd, u might loose some extra horses too. I have seen sentra spec V's loose almost 25% because of the lsd.

25% is entirely too high. 180bhp -40% for standard 15% loss for FWD and 25% for LSD = 108 hp at the wheels?? I really don't think that's correct. Even a 10% change from the LSD with standard losses will be 135hp at the wheels.
Too much loss.
-Jefff

[AceInHole]

I'm pretty sure he meant the entire drivetrain loss goes to 25% because of the LSD, not that the LSD adds an extra 25%.

Although... I've heard of numbers like 143whp for Spec-V's, so that'd be a bit under 20% total drivetrain loss.

[drift freaq]

I don't have any precise price, but iirc a carbon driveshaft would be a couple of hundred $US.

hahhaha, carbon fiber driveshafts are in the $800 range and above. Aluminum driveshafts are somewhere around $400-500 a one piece steel driveshaft would cost you $200-250 with replaceable u joints . Just going to the one piece driveshaft would help because you lose a lot of HP and torque through the center support bearing and extra u joints of the two piece driveshafts.
Also lightening your flywheel does help a lot in getting back some of the drivetrain HP loss. Ideally for a street engine though you do not want to go lower than 16lbs because after that you start losing bottom end torque.
I have seen this on street SR's and KA's . I ran a 16lb flywheel on my previous KA and basically it improved engine performance markedly. My engine was a low mileage KA and people used to trip on how quick the car was.
I have several socal240sx members that can back this up.

[d240t2]

Also lightening your flywheel does help a lot in getting back some of the drivetrain HP loss. Ideally for a street engine though you do not want to go lower than 16lbs because after that you start losing bottom end torque

Can you explain that point? I don't understand. Does the flywheel's mass create torque?

[transient]

An idea of pricing for a CF driveshaft, it's not pretty: http://www.titanmotorsports.com/acptdriveshaft.html

[nrcooled]

Enjuku now sells Aluminum drive shafts for $425. The Lightened flywheel in my SR has made a pretty remakable difference. I come on to boost faster and throttle response is insane. Just watch out for spinning tires

[Phlip]

Originally posted by d240t2
Can you explain that point? I don't understand. Does the flywheel's mass create torque?

I don't think it causes you to LOSE the torque the engine creates, it kinda changes where it is in the power band, you know? It's like the fact that I had never driven a car with a lightened flywheel before saturday in brandon's car, and you saw how I stalled that bitch twice before I got used to it? The torque wasn't to be had at as low an RPM as I was used to in my bone stock KA...

[AceInHole]

It isn't that the flywheel creates torque.... but its rotational inertia might do something like help it "retain" torque, since the momentum of the flywheel is adding a force to the drivetrain while the drivetrain attempts to deccelerate the flywheel. The only time this would happen is when accelerating from a stop, though.

[d240t2]

It isn't that the torque isn't there...it is that the inertia isn't there.

Like, if you had a 50lb flywheel, you could just drop the clutch, and it wouldn't kill the engine. The flywheel would store enough energy that it could transfer that to the driveshaft and wheels without dropping the speed enough to kill the engine. With the light flywheel...you just don't have as much momentum...so you have to be more finicky about letting the clutch out and giving it gas.

Dennis

[AceInHole]

Originally posted by d240t2
It isn't that the torque isn't there...it is that the inertia isn't there.

Like, if you had a 50lb flywheel, you could just drop the clutch, and it wouldn't kill the engine. The flywheel would store enough energy that it could transfer that to the driveshaft and wheels without dropping the speed enough to kill the engine. With the light flywheel...you just don't have as much momentum...so you have to be more finicky about letting the clutch out and giving it gas.

Dennis

Hmmm.... i read this thinking you were correcting my statement

[Dream240]

Whoa, there's...just...too many terms....must rest....uhhh...
Okay, to be put in lamens terms, lightened flywheels will make you rev faster and help you reach your mid-range power quicker. Which is what you want. When you combine the lightened drivetrain parts with your exhaust, intake, etc., you will get a fast revving car that has good mid-to-high end power like V-TEC engines. And you will enjoy the speedy, sporty feel the car will give you.

[mrdirty]

Lightened flywheel:
Advantage:
-quicker ramp up
-quicker ramp down
-quicker shifts (downshift: rev drops quicker due to higher relative friction = quicker shift)

Disadvantage:
-engine runs "rougher", higher rotating mass smooths out power
delivery.
-lower durability
-clutch ingagement needs to be more precise.
-rougher power curve (per cycle) = higher accelerations of piston
= higher loads on pins.

[AceInHole]

should also note that it increases your chances of stalling while revving down from high rpms. some turbo cars have trouble not stalling from those situations with a normal flywheel.

[HaLo]

Originally posted by AceInHole
should also note that it increases your chances of stalling while revving down from high rpms. some turbo cars have trouble not stalling from those situations with a normal flywheel.

I did notice my car was stalling everytime I depressed the clutch and let it go to 0 rpm... I thought my blow-off valve wasn't adjusted correctly.

[AceInHole]

Originally posted by HaLo
I did notice my car was stalling everytime I depressed the clutch and let it go to 0 rpm... I thought my blow-off valve wasn't adjusted correctly.

it could be a combination of both the BOV and flywheel. In reality the engine shouldn't dip so low giong off throttle

[misnomer]

I just wanted to summarize and clarify a bit (for the non-physics inclined peoples). . .


Basically, it takes torque to make things rotate. The heavier the thing or the wider the thing's radius, the more torque it's going to use. Hence lightened flywheels, lightened driveshafts and whatnot can improve performance simply by reducing the amount of power lost to making these components rotate. Rear drive car's lose more than front drive cars because you have more components, hence more mass, between the motor and the wheels. Limited slip differentials (viscous, in the case of the 240sx and Sentra), tend to add more mass to this, and increase the loss.

All wheel drive cars are the worst simply because instead of two wheels to get driveshafts to, you have four wheels. More space to cover, more mass needed in the driveshafts, more torque needed to spin them, less torque available to the wheels. Same with the differential, keep in mind most AWD cars have not one or even two, but three differentials (one for the front wheels, one for the rear wheels, and one between the front and rear wheels), each with their own gobs of mass to spin.

Basically, parasitic drivetrain loss can be reduced a bit, but beyond the flywheel and driveshaft, there isn't much else you can do.

[mrdirty]

Misnomer:
You're not "losing" any power unless you ramp up the engine, drop the clutch and let it drop; otherwise the power you invested into spinning up the rotating assembly is reclaimed as u come off the gas. It's true that there is a higher energy loss on the downshift because of this added mass though (probably what u meant) from clutch friction (another reason to rev match).

You sound like u already know this, just want to make sure no-one confuses this w/ an actual "loss" such as friction.

[HaLo]

Originally posted by AceInHole
it could be a combination of both the BOV and flywheel. In reality the engine shouldn't dip so low giong off throttle

that's what I originally thought.... I guess that's one of the first things I need to adjust when I get my car out of storage.

[Dream240]

Originally posted by mrdirty
Misnomer:
You're not "losing" any power unless you ramp up the engine, drop the clutch and let it drop; otherwise the power you invested into spinning up the rotating assembly is reclaimed as u come off the gas. It's true that there is a higher energy loss on the downshift because of this added mass though (probably what u meant) from clutch friction (another reason to rev match).

You sound like u already know this, just want to make sure no-one confuses this w/ an actual "loss" such as friction.

Uhhh....yeah....what he said.
Hey misnomer was trying to sum it up (like I did but better) for people that just want a straight answer without all the long sentences. And most of the guys in the forum are new to a car's mechanicals. You're keepng their heads ringin'! I get what you're saying but, i'm sure the original starter didn't need all the terminology. But you're still correct with the deduction on energy loss.

[misnomer]

You're absolutely right, I'm just trying not to beat people up with physics terms :-)