This "fact" is new to me. Someone confirm please.

[BITeR]

From the looooong Supra vs. NSX forum, someone posted this "fact":

"The NSX has 275 HP that's transverse mounted, in a car
that weighs 3100 lbs. You loose about 25% power, from
a 90 degree directional change."

That can't be entierly true?

 

[Yellow Rose]

Originally posted by BITeR:
You loose about 25% power, from
a 90 degree directional change."

Absolutely not true. Ask any mechanical engineer. Or better yet, look at a dyno plot.

Mechanical power transmission is lost in each set of gears, CV joints, etc. If a car has X number of these items, then the overall power loss is Y horsepower - makes no difference if the engine is longitudinal or traverse.

 

[BITeR]

I agree. I just had to ask.
It should need one less gear, but that will probably only make 1 % difference at the most.

 

[nsxtasy]

The drivetrain loss in the NSX, as measured by the difference between power at the crank and at the wheels, is around 11 percent. That's extremely low for any car.

 

[MvM]

Although I don't know about the exact percentages, since every gear will make you loose more HP, turning the power direction 90 degrees with an extra differential should make you loose more HP.
I remember someone telling me that in the Ferrari 355/360 the difference between engine and wheel HP is about 75HP. I don't know if that's true but if so, my bet is that the extra gears needed to turn the direction must have something to do with it.

 

[nsxtasy]

Originally posted by MvM:
I remember someone telling me that in the Ferrari 355/360 the difference between engine and wheel HP is about 75HP.

The Ferraris usually also have a big discrepancy between engine HP in the marketing materials and engine HP measured at the crank...

 

[Yellow Rose]

This topic came up on The Tech List a couple of years ago. 1% power loss per gear mesh is a good number to use. I calculated the theoretical power loss in the NSX to be 12% and this takes into account the traverse engine configuration. For comparison I also calculated the power loss in a front engine American car with a driveshaft and rearwheel drive. I don't recall the exact number, but it was close to the NSX's 12%. Therefore, the engine configuration - traverse or longitudinal - has little to do with power loss. It is a function of how many gear sets and CV joints there are between the flywheel and tires.

[This message has been edited by AndyVecsey (edited 10 October 2002).]

 

[Yellow Rose]

Originally posted by MvM:
....turning the power direction 90 degrees with an extra differential should make you loose more HP.

Not in the case of the NSX - the engine's crankshaft is parallel to the drive axles. However, it is true in the case of a Ferrari where they are perpendicular.

 

[BITeR]

While we are at the topic, if we assume a 1% per gear to be a fair estimate, then powerloss is a fixed number unless there is a linear relationship between power and loss in each gear.
Example, 100 HP at crank - 12 % = 88 hp at the wheels.
The same car with 300 hp, should then have 288 hp at the wheels, but usually people subtract 12 %.

I know friction increases with power and speed, but is it really linear?

 

[Yellow Rose]

Originally posted by BITeR:
Example, 100 HP at crank - 12 % = 88 hp at the wheels. The same car with 300 hp, should then have 288 hp at the wheels, but usually people subtract 12 %.

I know friction increases with power and speed, but is it really linear?

Math error with the 300 HP engine example. The resulting HP at the pavement is 264 HP.

Friction between two rubbing materials is linear. However, aerodynamic friction is exponential.



[This message has been edited by AndyVecsey (edited 10 October 2002).]

 

[Larry Bastanza]

Andy,

quote:
--------------------------------------------------------------------------------
Originally posted by MvM:
....turning the power direction 90 degrees with an extra differential should make you loose more HP.
--------------------------------------------------------------------------------

If I understand what you are saying, then the 90 degree change will not really effect the power loss since it still is only 1 gearset meshing (No additional differential). Make sense?

Thanks,
LarryB

 

[BITeR]

No math error, the example was to show that if there was no added friction, the powerloss would be the same for a 300 hp and a 100 hp drivetrain. I just wanteed to know if friction was linear, whom I understand from you, is correct. Have to look that up in the books.

Things are clearer to me now anyways.
cheers)

 

[DutchBlackNsx]

I'm a bit of a lazzy bastard, but i remeber a thread a long time ago (or was it on NSXSC) where was stated that the 90 degrees gears where responsible for a bigger powerloss then the straight one we have on the NSX. I can't find the thread with the search, bummer...........Ken?


Mich

 

[nsxtasy]

Originally posted by DutchBlackNsx:
Ken?

 

[Zuerst]

BTW the 91~94 NSX have 270HP that weights around 3000lb. 95 and 96 have 270HP that weights around 3150(Targa), and the 97+ have 290HP on a 3150 plateform(Targa). Goes to show how much those people knows about the NSX.

Edit: I can't spell...

[This message has been edited by Zuerst (edited 10 October 2002).]

 

[ChopsJazz]

Originally posted by MvM:
I remember someone telling me that in the Ferrari 355/360 the difference between engine and wheel HP is about 75HP.

I attended a dyno day where an F355 turned a 275 rwhp. My '91 NSX is at 271 rwhp. This seems about right when compared to F355s I've run with on the track (and street).

 

[Number9]

The chart below was from a 355 convertible that was tested during a Mountain View NSX club event. Not too shabby, rated by the manufacturer at 375 crank HP.

 

[Yellow Rose]

Originally posted by DutchBlackNsx:
I'm a bit of a lazzy bastard, but i remeber a thread a long time ago (or was it on NSXSC) where was stated that the 90 degrees gears where responsible for a bigger powerloss then the straight one we have on the NSX.

Mich - if you can find that thread, I'd like to debate it. If it is the same one I am thinking of, it was I that said the 90° orientation of the engine is not a contributing factor to NSX drivetrain losses.

At NSteXpo back in April, we had a dyno day. One of the cars stands out in my feeble memory as generating 243 RWHP. It was a stock 3.0L, which means that from the factory it produced 270 FWHP. This equates to a VERY respectable 10% drivetrain loss. In my mind, this is proof that the traverse engine configuration does not lead to parasitic HP loss. Not meaning to instigate flames, just stating fact.

 

[nsxtasy]

Originally posted by Number9:
The chart below was from a 355 convertible that was tested during a Mountain View NSX club event. Not too shabby, rated by the manufacturer at 375 crank HP.

Not great, though. Either the drivetrain losses are significantly higher (20 percent vs the NSX's 11 percent) or the power at the crank is less than claimed.

 

[effer]

Originally posted by BITeR:


You loose about 25% power, from
a 90 degree directional change."

That can't be entirely true?

Just close that "intelligent" debate in measuring hp at the wheels and comparing with power at the crank.

Make shure to compare same kind of power measurement at crank ( ex. SAE net with SAE net ) and also the same measurement procedure at wheels...

OTOH I am "LOL ing" a lot with that 90 degres argument on a car having its crankshaft PARALLEL to rotational axis of rear tires!!!

And maybe I am wrong but the NSX isn't a transverse gearbox layout like for example a Ferrari 348T !!!

In fact, the NSX layout seems to be fundamentally more efficient...

So what's the point?

If I am wrong tell me, I'm not perfect though...

 

[Number9]

Originally posted by nsxtasy:
Not great, though. Either the drivetrain losses are significantly higher (20 percent vs the NSX's 11 percent) or the power at the crank is less than claimed.

Good point that suggests a flaw with most of the present analysis of drivetrain losses - namely, we don't have good access to measured crank hp, just manufacturer specs which may be conservative or optimistic, hence we really don't know the actual loss.

Also, the loss function in this thread appears to be modeled as a % of crank HP, but in actuality, it could be that the drivetrain loss may be decomposed into components that are a function of HP output and RPM/gearing, respectively (which ignores aero - probably OK on a dyno). If the latter term dominates, then the percentage of crank HP model is wrong.

Anyway, would be nice if there any of you engineers who have worked in the auto biz and have better access to data/models could chime in.

 

[JoeSchmoe]

Originally posted by BITeR:
"You loose about 25% power, from
a 90 degree directional change."

IMHO, the 25% value is WAY too big. Most cars use a spiral bevel gear to do the 90 degree axis change. Spiral bevel gears are generally 95%-98% efficient and would not account for the huge discrepency.

I think there may be other issues here other than the 90 degree axis change. The high efficiency of the NSX gearbox may be due different gear tooth form, gear materials, gear clearances, bearing design/arramgements, lubrication, etc. These all contribute to the efficiency of a gearbox.


With regards to the 355 / 360 HP discrepency, perhaps Ferrari quoted numbers for their engines without exhaust/emmissions/accessories attached?

 

[JoeSchmoe]

Originally posted by effer:
And maybe I am wrong but the NSX isn't a transverse gearbox layout like for example a Ferrari 348T !!!

???

The NSX has a transverse mounted engine/gearbox.

The 348 had a longitudinally mounted engine/gearbox.

 

[JoeSchmoe]

OTOH, has anyone actually independently found the crank HP of the NSX engine (ie on a test stand and not calculated from the RWHP)? Maybe the engine actually puts out more than the claimed 270/290 HP and Honda lied about it the same way Mitsubishi under-rates the 3000GT to conform to the JDM 280HP cap?

 

[effer]

Originally posted by JoeSchmoe:
???

The NSX has a transverse mounted engine/gearbox.

The 348 had a longitudinally mounted engine/gearbox.

??? + ???

I think that the NSX is a transverse engine and longitudinal gearbox

the 348T is a longitudinal engine and transverse gearbox

gearbox layout is related to engine
( crankshaft ) not car's chassis.

Engine layout is related to chassis!!!

Can be confusing!

Don't want to flame about if there gonna be a new NSX but I just CAN'T imagine how Honda couldn't use the S2k 4 inline to create a 4L V8 producing 480 hp and even 580hp with its electrical assist device!!!

This way there would be no competition between S2K and new NSX. With 480-580 hp there will be also some regain of huge respect from competition!!!