Real Power Numbers - WHP vs. BHP?

[Booky]

I was looking over the Hellcat power numbers the other day and something was not adding up - wheel horsepower (whp) vs. crank horsepower (bhp)

Stock (average) Hellcats dyno around 630 (whp).

If you take the 630 (average whp) x 1.12 (+12% A8 drivetrain loss) you get close to the 707 crank horsepower (bhp), which FCA advertised for the Hellcats.

But, according to FCA, it takes 70-80 hp just to turn the twin screw supercharger.
What happened to that 70-80 (bhp)?

If you were to add that 70-80 (bhp) to the existing drivetrain loss of 75 (bhp), shouldn't the real crank horsepower number be around 780 (bhp)?

The same can be said for the GT500's.
It appears the amount of (bhp) it takes to turn the supercharger is not factored into the final crank horsepower number?

What am I missing?


.

 

[Kiohtee]

Are you really so new to cars that you've never heard of underrating? This goes back to even LS1s, Terminators, etc. No telling how far back it actually really goes (before my time, 1992).

@Zemedici has said for a long time, even recently in another thread here, that Hellcats are underrated based on what he and his shop see them making on a dyno.

 

[Tacticalriflema]

They are measuring the HP at the crank with the supercharger on it, so that loss has been absorbed by the engine and it's still making X amount of HP at the crank.

If they have tested and verified the parasitic loss for that particular SC is say 75 HP, then the engine is making the crank HP plus that loss. However without the SC obviously it wouldn't be making that much HP.

One of the reasons exhaust driven turbochargers make more HP per lb of boost is significantly less parasitic HP loss among other factors.

 

[Tacticalriflema]

In response to the previous post, one of the Fiat Chrysler insiders has stated the Hellcats all make more than 707hp, at all areas of the country and elevations. 707 seemed like a catchy number to rate it vs. "735" .......to marketing at least.

 

[Booky]

Are you really so new to cars that you've never heard of underrating? This goes back to even LS1s, Terminators, etc. No telling how far back it actually really goes (before my time, 1992).

@Zemedici has said for a long time, even recently in another thread here, that Hellcats are underrated based on what he and his shop see them making on a dyno.

Yes, I am very new to supercharged cars.


I am well aware of underrated numbers on high performance factory cars.

But I have never heard anyone state that supercharged cars are extremely underrated compared to n/a cars due to the amount of bhp it takes to spin the supercharger.

 

[Booky]

They are measuring the HP at the crank with the supercharger on it, so that loss has been absorbed by the engine and it's still making X amount of HP at the crank.

If they have tested and verified the parasitic loss for that particular SC is say 75 HP, then the engine is making the crank HP plus that loss. However without the SC obviously it wouldn't be making that much HP.

One of the reasons exhaust driven turbochargers make more HP per lb of boost is significantly less parasitic HP loss among other factors.

Thank you for the explanation, I appreciate it.

 

[Kiohtee]

In response to the previous post, one of the Fiat Chrysler insiders has stated the Hellcats all make more than 707hp, at all areas of the country and elevations. 707 seemed like a catchy number to rate it vs. "735" .......to marketing at least.

But that's exactly my point. Plus, 707 is a high enough number to place them well above the competition and still have a performer, but also leave them room to underrate/more adequately rate another car for future use. They're a smart group over there at Dodge right now.

Yes, I am very new to supercharged cars.


I am well aware of underrated numbers on high performance factory cars.

But I have never heard anyone state that supercharged cars are extremely underrated compared to n/a cars due to the amount of bhp it takes to spin the supercharger.

It just so happens that most high performance factory cars are supercharged. I don't think they're mutually exclusive though. Look at LS1 cars for example.

 

[black92]

Yes, I am very new to supercharged cars.


I am well aware of underrated numbers on high performance factory cars.

But I have never heard anyone state that supercharged cars are extremely underrated compared to n/a cars due to the amount of bhp it takes to spin the supercharger.

What about the alternator, power steering pump, a/c pump, etc? Those all require power to run so the number could be even higher. I think a lot of people would laugh if they saw Dodge advertise the motor as, "This bad boy makes 782hp if you don't count the 75hp it takes the turn the blower! YeeHaw!" Heck, we can even reverse this and say motors that are turbocharged actually make lower hp because the turbo(s) provide free hp when boosted...

IMO, the end number the motor puts out at the crank or wheels when fully dressed is all that matters.

 

[Booky]

It just so happens that most high performance factory cars are supercharged.

I don't think they're mutually exclusive though. Look at LS1 cars for example.

 

[Kiohtee]

What about the alternator, power steering pump, a/c pump, etc? Those all require power to run so the number could be even higher. I think a lot of people would laugh if they saw Dodge advertise the motor as, "This bad boy makes 782hp if you don't count the 75hp it takes the turn the blower! YeeHaw!" Heck, we can even reverse this and say motors that are turbocharged actually make lower hp because the turbo(s) provide free hp when boosted...

IMO, the end number the motor puts out at the crank or wheels when fully dressed is all that matters.

The point of this thread is that the rear wheel horsepower numbers sometimes don't match the crank/brake horsepower numbers manufacturers use to advertise their cars (usually for the better, but sometimes worse).

Also, most cars have electric power steering now. Haha

 

[Kiohtee]

Care to prove me wrong? Not using utterly expensive, usually unattainable exotic cars? You seem really triggered that I'm giving my opinion on this matter. I'll start by helping prove my point of view;

Terminators, GT500s, '04-06 GTs, ZL1s, C7 Z06s, Hellcats, CTS-Vs, F-Types and who knows how many more.

 

[black92]

The point of this thread is that the rear wheel horsepower numbers sometimes don't match the crank/brake horsepower numbers manufacturers use to advertise their cars (usually for the better, but sometimes worse).

Also, most cars have electric power steering now. Haha

Hey, quit being nitpicky! lol

To your point about being for the better, the '17 Civic Type R is also severely underrated.

 

[Nate14120]

I just want to point out the math is wrong. Figuring drivetrain loss you would divide 630 by 0.88. Multiplying 630 by 1.12 is not the same.

People do it wrong for e85 estimates all the time when estimating how much e85 a pump rated for gas will support.

 

[SVT-BansheeMan]

A time slip matters, not a tuning tool.

 

[Booky]

Care to prove me wrong? Not using utterly expensive, usually unattainable exotic cars? You seem really triggered that I'm giving my opinion on this matter. I'll start by helping prove my point of view;

Terminators, GT500s, '04-06 GTs, ZL1s, C7 Z06s, Hellcats, CTS-Vs, F-Types and who knows how many more.

Just for an example, Compare the amount of GT500's, ZL1's and Hellcats produced to the number of N/A V8 Mustangs, Camaros and Challengers that are produced every year.

Now tell me again how Most high performance factory cars are supercharged?

 

[Kiohtee]

Just for an example, Compare the amount of GT500's, ZL1's and Hellcats produced to the number of N/A V8 Mustangs, Camaros and Challengers that are produced every year.

Now tell me again how Most high performance factory cars are supercharged?

I wasn't aware that those were considered high performance factory cars honestly. At least not by the majority of performance enthusiasts. I guess everyone's definition of that is as open as "what is stock" and "what is a bolt-on."

 

[Booky]

I wasn't aware that those were considered high performance factory cars honestly. At least not by the majority of performance enthusiasts. I guess everyone's definition of that is as open as "what is stock" and "what is a bolt-on."

I am pretty sure the 5.0, SS and 392 owners and enthusiasts consider those cars high performance.

Edit: Removed smart-ass comment.

 

[Black02GT]

Are we really still having the "factory freak" and "under-rated" argument in 2017.

These modern ratings are SAE Net Horsepower which is rated at the crank with all the accessories, emissions, exhaust, intake, etc attached. It has to be done in ISO certified facilities, with certified third party witnesses blah blah. I would trust they are more accurate than a shop dyno which has a lot of adjustable variables. Not to mention performance shops have a stake in their dynos being a little "happy".

My car (03 cobra engine) with a a mid-pipe, catback, steeda filter and 3.0 pulley dynoed 480 at Mustang Magic back in the day (don't use them anymore). I don't believe for a second it was actually making that much power. Dynos are really only to tell what gains you're making from a base pull on the SAME DYNO as you're making adjustments.

Think about it from the manufacturer stand point, why would you advertise less? If it makes 747 and you wanted to advertise 707 why wouldn't you just lower the boost or timing and have less wear and therefore less broken parts that are being warranted out?

 

[Kiohtee]

I am pretty sure the 5.0, SS and 392 owners and enthusiasts consider those cars high performance.

Edit: Removed smart-ass comment.

Maybe so. I don't personally. I have always defaulted to the bread and butter portion of a offering when hearing "high performance." Either way, that's not what this conversation is even about. As for the removed comment, debate maturely without making it personal or being an ass. Stop letting your feelings and inability to post a meme interfere with your ability to conversate.

 

[Booky]

As for the removed comment, debate maturely without making it personal or being an ass. Stop letting your feelings and inability to post a meme interfere with your ability to conversate.

What part of the "removed smart-ass comment" did you not understand.

I posted something, then felt it may be taken the wrong way, so I edited my post and removed it.

Understand?