AWHP vs HP (Question)

[Eclipse80]

Hi all . Thx in advance for helping me get some more knowledge on this. So, my 1995 Mitsubishi Eclipse GSX was recently Dyno’d at 384.9 AWHP. From what I read, that would roughly equate to 460 HP at the crank. A fellow enthusiast mentioned “Not good....lose 80hp Is the signal there are some problems into a trasmission......my GSX lose 30hp....”. After some research, I replied with what I thought was true but maybe I’m wrong or misunderstanding things: “
Actually, there’s no transmission problem here . The difference you’re seeing is just the normal drivetrain loss between horsepower at the crank (what manufacturers advertise) and horsepower at the wheels (what a dyno measures).
• HP (crank/flywheel) = engine’s rated output before the power goes through the drivetrain.
• AWHP (all-wheel horsepower) = what’s actually delivered to the wheels, after passing through the transmission, transfer case, diffs, and axles.

On AWD cars like the GSX, drivetrain loss is usually 20–25%, sometimes a bit more depending on setup. So if my car makes 384 AWHP, that lines up to roughly 460 HP at the crank.

Your GSX showing only a 30hp difference would be impossible on AWD — that would mean almost no drivetrain loss at all. So what you’re actually comparing is two different measurement points, not a mechanical problem.”

If you guys could help me out that would be great. Not necessarily for the post but really just for my understanding of everything. Thx again.

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[stealthee]

The fellow enthusiast is emphatically incorrect. He was either lied to by a dyno operator, or completely misunderstood something told to him.

DTL isn't some static number, but the general consensus is 15% on FWD, 18% on RWD, 20% on AWD.

Numbers also vary based on several factors like transmission type, tire size, rotational mass, etc.

 

[We're on Boost]

The guy who was talking about losing 30 hp was probably talking about the difference between corrected and un-corrected hp numbers. If he is also in El Paso (3,740 feet elevation) or around there, 30 hp could be about right for that difference. Your difference on that is about 384.9 minus 353.6 = 31.3 hp. Totally a different thing than drivetrain losses. You are correct about drivetrain losses and you are guessing your hp at the crank based on a rule of thumb that is in the right ballpark, it's not way off.

Here's a little problem that I don't know the answer to because I'm not an operator of Mustang dynos and I've never had my car on a Mustang dyno either.
I notice in your photo of the dyno screen that it says "Showing engine values" and it also says "Measure losses at end"
From the Mustang dyno operator's manual which I have a searchable pdf of, on page 134:

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So since yours says "Showing engine values", maybe it is already using its own internal method for taking power at the rollers and using that to estimate power at the engine. I don't know. Maybe that is actually hp at the crank that you are seeing there. Somebody in here would know. But what you should do is call your dyno guy, ask him if he still has the dyno files saved, and ask him to redisplay that page with the option "Showing Wheel Values" and see what the numbers are like that. You could ask him to explain it also but don' t just do that, get the revised screen shot too. The "explanation" and the numbers should add up to a correct understanding of it.
@1cleangsx in here posted a Mustang dyno screen shot in May 2023 and on his shot it says "Showing Wheel values" and it also says "Measure losses at end".

If you'd like to poke around in the Mustang operator's manual yourself, I'll post my copy of one here at the bottom. You'll notice that on page 135 there is a short explanation of "Measure losses at end". Also on page 26 you'll see why they put a W in front of CF for the correction factor. WCF means "Weather Correction Factor" and on page 331 they show a shot of the "Weather Station Parameters" screen which includes altitude. At high altitudes, your altitude is by far the predominant factor in this correction factor.

Oh heck the manual is 9MB which is too big to post here.
If you want it, I could post it in my google drive and make it available to "anybody with the link".

 

[We're on Boost]

Here's a link to the operator manual pdf download on an actual Mustang web page. This is the same manual dated 2017 that I referred to above. BTW the page numbers I gave are the numbers you see at the bottom of each page. They are different from the pdf sidebar page numbers you see in a pdf reader.
Mustang Dynamometer - Power Dyne PC - Operator Manual

 

[diambo4life]

I dyno'd my Galant on an AWD and a 2WD dyno (both Dynojet, same town but two different dynos, same week) and the difference was maybe 15-20whp.

 

[Car Cannibal]

Diablo can you post the top numbers of each so we can see the % drop, thanks.
Ex 600whp vs 585awhp

The above is a 2.5% difference which makes sense in loss between the drivetrains.

 

[diambo4life]

It was like 788whp and 768awhp or something like that. Dynojet SAE. It's been a few years....and that data is buried in my 10,000+ emails inbox. Michael Rizzotti (don't know his handle on here) had something similar with his 1G. Maybe 10-15whp difference on his car. This is going from my memory which is usually pretty good.

 

[Car Cannibal]

Yep 2.5%, pretty much the range many accept as the drivetrain loss for awd.

OP, auto vs manual trans also changes the numbers, converters are usually 3-15% slippage depending on what you got so that's the biggest unknown that requires log data to figure out to help.