is there a formula to convert hp at the wheel to hp at the crank?

someone said it loose 20% by the time it down to the wheels meaning: rwhp + 20% = crank hp

also someone said take rwhp x 1.08= crank hp.

 

The more commonly accepted number on the boards for HP loss through the tranny is 17% to 18%.

The formula is super simple. Multiply RWHP by 1.18 to get crank HP. Or divide the advertised crank HP by 1.18 to get RWHP.


2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust

 

It depends on the comparison... If you take a G35 and put it on a dyno (which type doesn't matter) and that dyno tells you a stock G35C-6MT dyno's 280rwhp, and you know the stock G35 has 280 bhp then your "correction factor" is 1.0. You still have paracitic losses of ~18%, but the dyno is not properly calibrated to measure those losses. This is why correction factors can vary.

Hydrazine's recommendation of multiplying or dividing by 18% would not apply in this case. You have to do the math to know what the drive train losses are. By "doing the math" I mean take a stock g35 (same tranny type) and dyno it and figure out how much paracitic losses the dyno is calibrated to read. Basically you are dialing out the dyno error and if you get a correction factor of 1.22 you are seeing an exact 18% paracitic loss.

If you take off your tire and dyno on a dyna pack, you'll have less losses through the drivetrain so your "correction factor" (term used loosley) will be lower, and your output horsepower will be higher. Remember,

the SUM of the TORQUE = SUM of the INERTIA * Acceleration

There is no UNIVERSAL number for a "correction factor" that you can apply across the board. Hydrazine's answer to your question was represented in the CFDD where the stock 6MT's experienced an 18% paracitic loss through the drivetrain. The 5AT's experienced a 20% paracitic loss.

I hope this makes sense...

 

so roughly 18% loss for 6MT and 20% loss for 5AT?
everybody argee with this?

also another question.when car magazines list BHP,is that mean at the crank?.
and what exactly BHP stand for? i've heard:
-blow horse power
-brake horse power
-base horse power

 

I'd agree with Neffster that 18% drivetrain for MTs is correct (assuming that you're not adding rotational mass to the drivetrain; i.e. larger and/or heavier wheels, etc.). However, I'd disagree with 20% for the ATs though. 22-23% loss is more accurate from what I've seen on our NorCal dyno day.

That is also assuming that somewhere between the early 03's and now that they upgraded the ECU or such for more power. We had an early 03 AT Sedan that put out approx. 210 to the wheels, while my 04 AT Sedan put down 220 to the wheels even though we had almost identical mods (Pop-charger & Z tube [him] vs. K&N panel filter & Z tube [me]). And I also only had about 4-5k miles on my car at the time, so there is more room for break-in on mine.

There are always going to be other numerous factors that affect the numbers that people don't always consider (octane, tire pressure, sport wheels vs. standard wheels [I suspect the sports are heavier], sythetic oil vs dino oil vs the initial break-in oil, and on and on...). 18% and 23% are the most accurate for most purposes on the DynoJet. I personally to not like the DynoPack, because it takes the wheels' rotating mass out of the equation.

I'm not trying to start anything with anyone, in fact I agree with most of Neffster's observation about the findings with the various dyno days. I just disagree about the AT drivetrain losses given my research and observations.

 

4DrSkyline you might be right, however at the CFDD we observed exactly a 20% loss on the 5AT's. I'm sure it can vary from car to car, and 23% is only +/- 1.5% from the middle of the two numbers. What really matters is that you are satisfied with your vehicle! I for one am stoked to be driving such a nice car, that should be as fast as the new 2005's [img]/w3timages/icons/wink.gif[/img]!!!

 

Neffster,

Dyno correction factors and % transmission losses are mutually independant variables. Tinmans question "a formula to convert hp at the wheel to hp at the crank" pertains to losses between the wheel and the crank. Not to dyno factors.


2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust

 

Understood. I used the term "correction factor" when maybe I should have used the term "mathematical factor". I understand correction factors are used to determine what a given horsepower or torque would be at STP. Parasitic losses will, for the most part, be 18% on stock G35 6MT's and ~20% on stock G35 5AT's PERIOD.

If a dyno is not properly calibrated and reads high or low, the calculations that I did in the CFDD and the SoCal Dyno Day are the only way to determine bhp.

There is no way you can take the stock G35 6MT from the CFDD that dynoed 230rwhp and multiply or divide that number by .18 to get 280bhp. Also, there is no way that you can take the stock G35 6MT from the SoCal Dyno Day that dynoed 260rwhp and multiply or divide that number by .18 to get 280bhp. Those 2 stock cars dynoed over 30 rwhp apart, but are in no way that far off from each other. The only other factor could be the calibration (or lack there of) between the 2 different types of dynos. I simply used a “mathematical factor” (which I incorrectly called a correction factor) to determine ACTUAL crank horsepower as accurately as can be done so that the results of the 2 dynos could be compared.

If you want to compare the results of the 2 dyno days you need to determine a "mathematical factor" for each of the 2 dynos, and that is done by relating the stock 6MT dyno results on the dyna pack to Nissan’s claim of 280 bhp. This is what I did and apparently I didn't explain that well enough. Sorry for any confusion, but the mathematical approach in the SoCal thread is as correct as one can get by using simple mathematics alone.

 

Cool info, can someone post 4 things, what the Wheel hp and torque should be to have 260 hp?tq for the 6spd and auto sedan, and same for the coupe 6spd/auto to compare too!! My baseline reading were pretty good showing over 270 hp and torque at the crank on my dyno with just the injen intake.
My frist run was 237 hp and 244 tq and second run which i told every was from 3500k rpm to 5700k rpm and got 221 hp and 230 tq at the wheels and gave me a print out of that and i have no idea WHY!!


Martin
2003.5 BS G35
Nismo Aero/Sport Package
0-60 5.4 - 1/4 Mile 14.16 *GTech* and on 19's!!

 

If you were to go by Nissan's (read: Infiniti's) official numbers and factor a 18% drivetrain loss for MTs and a 20% drivetrain loss for ATs, then these would be the estimated numbers on a DynoJet:

Coupe (280hp; 270tq)
MT: 229.6 whp; 221.4 wtq
AT: 224.0 whp; 216.0 wtq

Sedan (260hp; 260tq)
MT: 213.2 whp; 213.2 wtq
AT: 208.0 whp; 208.0 wtq

The important thing to remember is if you're going for more horsepower and want to see the results of your modifications is to dyno your car all along the way. The "butt dyno" may be fine for feeling good about having just spent $1000 on an exhaust system, but the dynomometer will give you a better sense of any actual horsepower improvement. It's worth the money if you want true peace of mind, IMO. Once I get a coupe mid-pipe for my sedan, I'll be back at the same local shop dynoing again to see the results.

 

Oh wow, my print out baseline dyno with the Injen CAI i got 221 RWHP and 230 lb ft of torque!!


Martin
2003.5 BS G35
Nismo Aero/Sport Package
0-60 5.4 - 1/4 Mile 14.16 *GTech* and on 19's!!

 

My car dyno'd at 244.6 HP and 240 ft-lb torque today on a DynoJet 248C. This was at sea level and 65 degF.

Unless my calc's are wrong -- that gives me 298 HP at the crank.

Mods to date are -- K&N Filter, Z-tube intake, Stillen exhaust.



2003.5 Sedan 6MT, Brilliant Silver

 

This is assuming that the stock G35 coupe has exactly 280 HP. There is no way each and every one of the thousands of G35 coupes manufactured are at 280. Then throw in variations in gasoline, break in period, alignment on the dynojet, mileage of the car, time since last oil change, etc, and you end up with too many variables to obtain an exact drivetrain loss percentage. On top of that, we are assuming that the drivetrain loss remains at a fixed percentage whether or not the car makes 280 or 380 horsepower.

The usefullness of dyno days for me is to see how my car compares to other cars on that exact day. If I go back to the same dyno a week later, and get 5 HP less or 5 HP more, it doesn't mean anything, since this could be due to any of the confounding variables I listed above.

I think one way to try and estimate gains from mods is to take 2 cars to dyno everytime. The first car is kept stock, uses the same gasoline, to try and minimize fluctuations in dyno results (still not perfect though). The second car is the one you mod and dyno along the way. Everytime you dyno the second car, you dyno the first car on the same day on the same machine. Any variations in the dynos of the first car gives you a rough correction factor (assuming that it will give consistent HP ratings).

Rather than compare raw numbers, the other thing I like to do is to compare the shape of the dyno curves. I've dynoed my car three times now with various states of mods. Even if you move the curves to superimpose each other in the lower RPMs, you can see that above 4500K the car is much stronger in the top end now.



Edit: This graph is from my other post. See my thread about the polished plenum for a detailed explanation of the situations for each dyno.<P ID="edit"><FONT class="small"><EM>Edited by E_K on 09/25/04 08:57 PM.</EM></FONT></P>

 

E_K:
To what factors to you ascribe the little flat spot on your dyno readouts between 5000 and 5250 rpms?

Cpe 6MT/Aero/Prem/ATI/RT cats/Borla hdrs-catbcks/Nismo flywhl-cltch/TS-ECU/Tein flex EDFC/Stillen sways

 

I don't know. I see it on many G35/350z dynos, both modded and stock.

http://www.gurgen.com/clint/G35/2004...9_04_2004.html

Take a look at some of the dynos here, I'm not the only one. Maybe it's the A/F ratio, maybe that's when the intake valve timing is changed, but I'm open to any explanation.