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Discussion Starter · #1 ·
OK, so I am struggling to remember how to convert both RWD or 4WD numbers from WHP to BHP for comparing to factory horse power call-outs.

I vaguely remember it went something like this for 4WD pickups:


let's assume the 4WD dyno spits out 300(4whp)

300 x 1.3333 = 400bhp

let's assume the RWD dyno spits out 300(rwhp)

300 x 1.25 = 375bhp

But like I said, I vaguely remember. And I'm sure drive trains have changed since the 1970's and early 1980's.

Any helpful comments? Anyone with real live experience?
 

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It's different for every car. The biggest factor is the drivetrain loss, as in how efficiently the transmission, torque converter(for automatics), angle gear/transfer box, take the power from the flywheel and transfer it to the wheels. The more ressistance there is, less power you'll get at the wheels. There's no definite conversion because like I said, every car is different.
 

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Wheel horsepower output is dictated more by drivetrain loss as opposed to fwd, rwd, or awd. Typical drivetrain loss for manual transmissions range from about 12% to 18%, most automatic transmission equipped vehicles will see between 18% to 24%.

If you're vehicle is rated at 400bhp, and has an automatic drivetrain, you can expect to see around 320whp. If that same vehicle is equipped with a manual transmission, you would expect to see more along the lines of 335whp.

I am a dyno technician, and know these to be real world averages. Here is a link to my thread where I just dyno'd my t6 xc90.

http://forums.swedespeed.com/showthread.php?178539-Dyno-d-my-stock-04-xc90-T6
 

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OJS

I also am a bit confused on HP. All I can go with are the gains I see at each stage. But none of them started with what I would think was a 300HP baseline. If that is the case on a Mustang Dyno I lost 55 HP to the rear wheels ?
 

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Discussion Starter · #5 ·
Wheel horsepower output is dictated more by drivetrain loss as opposed to fwd, rwd, or awd. Typical drivetrain loss for manual transmissions range from about 12% to 18%, most automatic transmission equipped vehicles will see between 18% to 24%.

If you're vehicle is rated at 400bhp, and has an automatic drivetrain, you can expect to see around 320whp. If that same vehicle is equipped with a manual transmission, you would expect to see more along the lines of 335whp.

I am a dyno technician, and know these to be real world averages. Here is a link to my thread where I just dyno'd my t6 xc90.

http://forums.swedespeed.com/showthread.php?178539-Dyno-d-my-stock-04-xc90-T6
So what would your professional opinion be if a 4WD Mustang dyno reads my 07 R as 231whp @5600rpm and 288ft-lbs @2900rpm? What would you guess she's doing at the crank?
 

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OJS

I also am a bit confused on HP. All I can go with are the gains I see at each stage. But none of them started with what I would think was a 300HP baseline. If that is the case on a Mustang Dyno I lost 55 HP to the rear wheels ?
As I've heard, the Rs lose about 25% from the flywheel to the wheels. If you dynoed 245AWHP, then your engine makes about 306hp.
 

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Discussion Starter · #7 ·
OJS

I also am a bit confused on HP. All I can go with are the gains I see at each stage. But none of them started with what I would think was a 300HP baseline. If that is the case on a Mustang Dyno I lost 55 HP to the rear wheels ?
OUCH!!!
 

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Discussion Starter · #8 ·
As I've heard, the Rs lose about 25% from the flywheel to the wheels. If you dynoed 245AWHP, then your engine makes about 306hp.
The math seems, ...off. If I had 306 apples and I gave you 25%, I'd have 229.5 apples left.
 

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So what would your professional opinion be if a 4WD Mustang dyno reads my 07 R as 231whp @5600rpm and 288ft-lbs @2900rpm? What would you guess she's doing at the crank?
I've personally never operated a mustang dyno, we have an awd dyno dynamics, and a 2wd superflow. From what I hear, people say mustang dyno's read 'low', but low in comparison to what?? There is no industry standard for what dyno is 'real power'. Most people use dyno jet numbers as sort of the 'standard', however the only real reason for this is it's the most common dyno due to the fact that it's pretty much the cheapest on the market and therefore most people have more experience with dynojet numbers because the cost minded dyno shop probably has a dyno jet. Dynojet's are what are called 'inirtia only' dyno's. They do math based off of the acceleration of the rollers, vs. the acceleration of the engine speed (rpm). If you're not in a true 1:1 gear ratio, or your rpm input signal to the dyno is not accurate, it skews the data.

Dyno dynamics, dynapacks, and I 'believe' mustang dyno's are load bearing dyno's. I know our dyno dynamics measure power actually from amount of force applied to the rollers, which is measured by strain gauges and is a way more accurate way to measure power/force/engergy than a simple mathematical equation.

With all of that being said, a dyno is a tool and no two dyno's are going to read the same, unless it's two identical dyno's calibrated at the same time to the same specs. The drivetrain percentage losses I posted are pretty much a generic rule of thumb that leave enough room to get a rough idea regardless of dyno being used or type of drivetrain.

If you're R is an auto, I would say it's probably pushing around 275bhp and 345 flywheel tq. If it's a manual, you're probably around 267bhp and around 340 flywheel tq. What is it rated from the factory, and what if any mods do you have done?
 

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Discussion Starter · #12 · (Edited)
I've personally never operated a mustang dyno, we have an awd dyno dynamics, and a 2wd superflow. From what I hear, people say mustang dyno's read 'low', but low in comparison to what?? There is no industry standard for what dyno is 'real power'. Most people use dyno jet numbers as sort of the 'standard', however the only real reason for this is it's the most common dyno due to the fact that it's pretty much the cheapest on the market and therefore most people have more experience with dynojet numbers because the cost minded dyno shop probably has a dyno jet. Dynojet's are what are called 'inirtia only' dyno's. They do math based off of the acceleration of the rollers, vs. the acceleration of the engine speed (rpm). If you're not in a true 1:1 gear ratio, or your rpm input signal to the dyno is not accurate, it skews the data.

Dyno dynamics, dynapacks, and I 'believe' mustang dyno's are load bearing dyno's. I know our dyno dynamics measure power actually from amount of force applied to the rollers, which is measured by strain gauges and is a way more accurate way to measure power/force/engergy than a simple mathematical equation.

With all of that being said, a dyno is a tool and no two dyno's are going to read the same, unless it's two identical dyno's calibrated at the same time to the same specs. The drivetrain percentage losses I posted are pretty much a generic rule of thumb that leave enough room to get a rough idea regardless of dyno being used or type of drivetrain.

If you're R is an auto, I would say it's probably pushing around 275bhp and 345 flywheel tq. If it's a manual, you're probably around 267bhp and around 340 flywheel tq. What is it rated from the factory, and what if any mods do you have done?
My 2007 S60R has the 6sp GearTronic tranny. Factory rates my R at 300hp. We did 7 dyno runs in 4th gear with intake temps between 70 degrees F and about 80 degrees F. (I believe 4th gear is 1.08 or close to that) at 71 degrees we recorded 231awhp and 288ft-lbs wheel torque. The lowest reading of 227hp and 279ft-lbs at was 78 degrees inlet temp.

This dyno set is my baseline before any mods and a day after a full end-to-end "vacation" service. My plan is to take it to the same dyno place run by the same guy at each major set of mods. So something like this:

1. Dyno for Baselne
2. Dyno after installing IC, Downpipe, Catback exhaust, Intake Manifold
3. Dyno after ECU upgrade.

maybe...
4. Dyno after Turbo upgrade.
 

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Well regardless of what the dyno actually records at the wheels, like I said, all dyno's are different and are merely a tool, the main thing you want to do is be sure to use the same dyno every time. If you got your baseline done on that particular dyno, in order to see real gains, you will need to continue to use the same dyno. You could put a cold air intake on and have the car redyno'd on a dynojet and it may say 260whp, but we all know you didn't really gain 30whp from an intake, just the difference in the dyno readings.

I baselined my xc90 and it was pretty much dead on with factory power ratings once drivetrain loss was factored in. I will be adding downpipe, exhaust, and tune very soon and will probably dyno after each individual install to see gains from each individual part, as well as total gains with all mods over stock.
 

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Discussion Starter · #14 · (Edited)
So given my details, you'd guess I'm pushing around 275bhp and 345 flywheel tq? So way below the factory rated 300bhp. OK, it is what it is.

That's interesting. I guess you've inadvertently myth-busted the 25% AWD drive train power loss that everyone keeps sighting. A 44bhp loss from 275bhp giving me my 231hp is only a 16% drive train loss.
 

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So given my details, you'd guess I'm pushing around 275bhp and 345 flywheel tq? So way below the factory rated 300bhp. OK, it is what it is.

That's interesting. I guess you've inadvertently myth-busted the 25% AWD drive train power loss that everyone keeps sighting. A 44bhp loss from 275bhp giving me my 231hp is only a 16% drive train loss.
44/231=.19 X 100 = 19% loss

Like what was said before, it varies from car to car. AWD systems are different, transmissions are different, etc. The generally accepted R drive train loss is 18%. Again, that just gives you a ballpark figure. So yes, 231whp is about 273bhp. 231 X 1.18 = 273. Since you have a GT though, it is probably closer to 20%, but the difference is small.

The 300hp claim from the factory is said to be optimistic, plus the car isn't brand new. Cars lose power as they age.
 

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Discussion Starter · #16 · (Edited)
44/231=.19 X 100 = 19% loss

Like what was said before, it varies from car to car. AWD systems are different, transmissions are different, etc. The generally accepted R drive train loss is 18%. Again, that just gives you a ballpark figure. So yes, 231whp is about 273bhp. 231 X 1.18 = 273. Since you have a GT though, it is probably closer to 20%, but the difference is small.

The 300hp claim from the factory is said to be optimistic, plus the car isn't brand new. Cars lose power as they age.
I know that there are variations from car to car including age and equipment options. I've had dozens of dyno's done back when. But I was both curious about the difference in efficiency in drive trains from my hotrod'ing era vs today, and also what the current accepted ballpark expected percentage loss was in converting whp to bhp was for our caRs.

So if those of you with experience say for R's it's about 18% for manual and 20% for auto then cool. That's what I'll use for ruff numbers.
 

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44/231=.19 X 100 = 19% loss

The generally accepted R drive train loss is 18%. Again, that just gives you a ballpark figure. So yes, 231whp is about 273bhp. 231 X 1.18 = 273. Since you have a GT though, it is probably closer to 20%, but the difference is small.
Your math is funny. When drive train loss is spoken of in terms of a percentage, it is a percentage of the crank or brake horsepower, not as a percentage of the wheel horsepower. If you assume that the R has a drive train loss of 18%, then an AWHP reading of 231 AWHP would equate to (231/(1-0.18)) = 282 BHP. In other words a loss of 51 BHP, which is 18% of 282 BHP.

Based on most of the AWD dyno runs that I've seen, I would ballpark drivetrain loss at 20% for MT and 22% for GT. In other words, assuming the 300 BHP stock rating is correct, you would expect a stock MT R to put out 240 AWHP and a stock GT R to put out 234 AWHP, which is remarkably close to ojs' result.
 

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Best way to tell how much HP you have is a set of 0-60 runs. Find a safe, flat road and get a couple of good accelerations in. Since your car is an 07 GT, it should be high 5s to 6 seconds. You can debate dyno numbers all you want. All that matters is the real world performance.
 

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I Dyno awd cars every day and would definitely not agree with a 25% drivetrain loss just based on awd system. I don't have much experience with dyno'ing volvo's so am unsure of typical know drivetrain losses between particular models. Most drivetrain loss is at the transmission, not the transfer case or from having multiple differentials. Also the only way to get accurate awd whp numbers is to ensure the Dyno you're using has the capability to be set up for the appropriate awd system on the car (front viscous, locked, center diff, electronic controlled distribution, etc.).
 

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OJS

I took the same approach that you are planning. I even use Accuweather Pro to make sure the temp is close to my baseline at 10am when we put the car on the dyno. I'm still not sure what type of BHP I have but I can tell better on the Dyno than real world driving. I thought for sure when the cams were in wrong the car had more top end.But now I can tell from 70+





Here is a short recap so far

The car started out with 241 best run with 235 low run


Step 1
EST Cold air intake
IPD HD coil packs
Snabb intake
Viva CBV
Stock Tune Stage 0 when I bought the car in December 2011
TME cat back exhaust
252 WHP


Step 2
IPD down pipe Ceramic coated
do88 Charged Air Pipe ceramic coated
RICA Stage II Tune
270 WHP


Step 3
Enem Cams with wrong install ( no oil rings)
225.5 WHP
Amazingly the still felt good, but that was the always optimistic wallet Dyno talking


Step 4
Sent ECU to ARD thinking it was just a tune
252.5 WHP

Step 5
Sent car to dealer for a crazy $$$ repair. They would not install the cams but would fix the oil ring problem. No more cam codes
Reinstalled an updated RICA stage II ( updated via website and a new FREE tune not cam specific)
286.4 WHP


Step 6
Sent ECU as well as A\F print out from Dyno run to ARD
ARD carbon Tune 304.8 WHP
 
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