Has anyone ever seen a legitimate figure (in %) for drivetrain loss on the G? I mean a situation where a motor has been dyno'd at the flywheel and then re-dyno'd at the wheels after install? The numbers I see thrown around in the forums indicate 20-25% loss which seems high, unless the factory numbers are inflated. I've built small block Chevy engines and even with an ugly 700R4 GM tranny and heavier gears, axles and wheels, the drivetrain loss is about 18-20% for an automatic and 15-18% for a stick.

If we don't have a solid basis for parasitic loss, camparing dyno numbers to gross engine output is useless and makes the factory claims excessive.

Thoughts? Thanks!

 

yeah this is a good Q. i keep reading about auto's that dyno between 210-220whp, which amounts to 25% drivetrain loss. excessively high, even on a auto RWD car i would think. usually #'s over 220 and people start b!tching about the type of dyno used and how it always reports higher #'s, etc. 6mt stock dynos up to the low 230s until ppl start complaining about the same BS. on my350z i keep reading about stock cars dynoing a lot higher (~10hp/10ftlb).

doesn't answer your question but i wonder what the figures are too...

 

In that case, multiply by 1.2 . . .

 

Nothing really to do with 5AT vs 6MT, just the 20% rule doesn't apply. There are a bunch of well modified NA cars on here that only pull around 250-255rwhp. Well, 250 x 1.2 = 300 gross hp. And these are rated at 298hp already, so all the mods get you 2hp only?

Also, if we agree that stock cars chassis dyno at 210-220, well 215 x 1.2 = 258 flywheel hp, a far cry from what Infiniti says (280 or 298).

Leaves us with three options (none too spectacular):
1. The G drivetrain suffers from a very high parasitic loss (>25%).
2. There isn't a good chassis dyno to be found.
or
3. The HP ratings given by Infiniti are highly inflated.

No flames please, I'm a huge G fan and a Nissan customer for years. Only trying to figure out the discrepencies.

 

I agree with your 3 options. I personally am leaning toward number 3. I have a hard time with 25% drivetrain loss but then again this is my first Nissan product, did the 300z have this amount of loss?

 

The bulk of the losses come from tire road interface 10-12%, then torque convertor 3-4% then differential 3%.

A better number is 22%

 

But...

"...if we agree that stock cars chassis dyno at 210-220, well 215 x 1.2 = 258 flywheel hp, a far cry from what Infiniti says (280 or 298)."

So 215 x 1.22 still only gives you 262. Perhaps a better question would be, was there a noticeable chassis dyno difference between the 03-04 cars and the 05's?

If a 298hp rated 6MT dyno's at 230rwhp, that's a huge 29.6% loss. I can't believe we are losing that much.

 

I am 100% sure that Nissan's numbers are inflated. I noticed that the 298hp is not the new "certified" HP figure. Most all import car manufacturers lowered their HP figures after the new certified numbers came out, while many domestic car numbers increased.

Now, as far as drivetrain loss %'s go, I'd be more inclined to believe that a MT, RWD car loses about 15% transmitting power to the wheels. However, I'm pretty certain that a flat percentage number being used to define drivetrain loss is a poor method of estimating this figure.

I would think that the drivetrain loss would be subject to diminishing returns. A stock G35 may have a 15% drivetrain loss, losing ~45 HP going to the wheels (assuming that the car had 300hp @ engine, legitimately). At the same time, to say that a 1000 HP G35 engine is going to lose 150 horsepower going to the wheels, through that same drivetrain seems a bit unrealistic.

This is all just my thoughts on the matter, but there will probably never be a definitive answer. Engine dynos are not readily available, and anyone that has one is not going to be running tests on the engine dyno, putting a car together, then comparing it to a WHP dyno like a dynojet, mustang, etc.

 

Drivetrain Parasitic Loss
In my opinion, I feel the "Parasitic loss factor is much less than most think.
My bet would be around 12 to 15% If all rules have stayed the same for HP factors for years, Its safe to say that this little 213 CI. Engine is putting out the power claimed by the factory. Growing up in the muscle car world and driving and drag racing many hi powered cars rated over 360 flywheel HP in the 3400 LB class and having a hard time breaking into 13s and over 100 mph quarter mile times(stock) makes me believe Nissan is very close to what they say. Out of the box the VQ is one very stout engine for its size. IM dying to have the time for the next few installs and get my G on a dyno. I know with the right setup its going to show some big numbers that are real world, with drivability. Its in Nissans favor to produce a car with small parasitic losses. There is no limit to perfection, its the journey!!

 

Whatever the driveline loss numbers are, the fact remains that the stock car puts out 210-220 whp on the street. This is incredibly weak compared to other cars quoted with similar crank numbers.

 

Where do you come up with the numbers? No way can a car with the torque the VQ has can run low 14s to high 13s with 3400 lbs. Something is pushing the car down the 1/4 mile and it has to be HP. I find it hard to believe that my car dyno'd 273 rwhp and 264 tq, and the dyno was off that much. I guess in time, I will need to back up my claims and bang out a mid 12s
with my ride. I know what I have, as of this writing and its not 225 HP.

 

Regardless of what some integrated single number giving you a rough approximation of average power is telling you, my numbers are coming directly from datalogged speed versus time runs on the street. The numbers are very repeatable and agree with raw Mustang dyno numbers in the same gear.

1) Log vehicle speed versus time (with Cipher).
2) Differentiate curve to get acceleration versus time.
3) Directly calculate force versus time using vehicle mass.
4) Convert to power versus time using vehicle speed.
5) Add in power lost to drag.

If you have any logs of your car doing an acceleration run on the street (say, a low rpm to redline run in 3rd), I can tell you what you're putting down on the street, if you're interested.

 

Best case senario would be to do a project to capture a large number of dyno numbers in stock form and then throw out the outliers (say top and bottom 10%) and then pull mean/avg information for the different models and years. I've run multiple dynos on the same vehicle in the past with swings of 20hp in results. Not an exact science unfortunately.

Maybe I'll get motivated enough to take that on someday.

HomieG35;
I agree with your math, but your 232whp stock is at the upper end of what I've seen captured. Hey, not knocking it, engines are not all the same and it sounds like yours is strong. Just saying that most numbers I see are less than that.