[marcfiebka]

There is obviously a difference between the two...people ask me "hey how much hp that thing have?" I tell them oh I got exhaust on it and stock is 260 so I'm thinking around 270? Apparently I'm way off! So what's the difference? When people say "with all bolt-ons you'll get 300 rwhp" does that mean HP is actually more like 350-400? I'm so confused! help!

[BWAL]

RWHP is less than crank hp, and rwhp is what you will actually see at the ground.. on mustangs there is about a 15% hp loss through the driveline from the crank to the rear wheels

[DrHolliday]

Depends what you call bolt ons You can get 300 rwhp with all bolt ons, some cams, and a good dyno tune. To get a rough estimate of engine HP divide rwhp by .8... soo 300 rwhp is about 375 engine HP

[00vabchgt]

the 260 HP rating is what the motor is rated at the flywheel. when on an engine dyno, you'll see about 260 HP. however, when it's in the car, the motor is also turning the accessories, like A/C, alternator, etc. on top of that there's a certain amount of driveline loss. this is because it takes power to turn all the stuff in the driveline, like the driveshaft, etc. the general rule of thumb is that your rear wheel HP will be about 15% less than the flywheel rating for a manual tranny. for auto its about 20%.

[bigbadwollfff04]

This is a dyno graph of a 2004 mustang gt 5 spd, shows you what at wheels will be with 260 at crank!!

http://www.performance-dyno.com/New%...ance-Dyno.html

go to graphs then click on page two and part way down you see 99-04, then you can get a comparison!!

[bransdaman78]

Originally Posted by BWAL09 RWHP is less than crank hp, and rwhp is what you will actually see at the ground.. on mustangs there is about a 15% hp loss through the driveline from the crank to the rear wheels

ive always been told 18% manual 20% auto

[ChrisJ]

I have always said 15% manual and 20% auto...Some more and some less...but its a nice round set of numbers...

[Timber]

When you explain parasitic driveline loss as a percentage of engine output it implies a relation where there is none. You take the engine out of the car, find some way to figure out how much hp it takes to turn the drivetrain. That's what it takes and it's unrelated to engine output. If you say it's 20% that implies the driveline would take more hp if the engine made more power.

[ckthecerealkiller]

Originally Posted by Timber When you explain parasitic driveline loss as a percentage of engine output it implies a relation where there is none. You take the engine out of the car, find some way to figure out how much hp it takes to turn the drivetrain. That's what it takes and it's unrelated to engine output. If you say it's 20% that implies the driveline would take more hp if the engine made more power.

Then you're implying it takes a specific number of horses to turn all of it.... Honestly there is NO exact science to getting numbers by doing math. The only way to do it is put it on a dyno.

Still it has shown that the most efficient way for a 5 speed mustang with stock drivetrain and all accessories is about 15% loss regardless of crank power.

You are right in saying that there is no actual relation to them but what we are saying is that it is the best way to ESTIMATE the hp numbers.

[Timber]

Originally Posted by ckthecerealkiller Originally Posted by Timber When you explain parasitic driveline loss as a percentage of engine output it implies a relation where there is none. You take the engine out of the car, find some way to figure out how much hp it takes to turn the drivetrain. That's what it takes and it's unrelated to engine output. If you say it's 20% that implies the driveline would take more hp if the engine made more power. Then you're implying it takes a specific number of horses to turn all of it.... Honestly there is NO exact science to getting numbers by doing math. The only way to do it is put it on a dyno. Still it has shown that the most efficient way for a 5 speed mustang with stock drivetrain and all accessories is about 15% loss regardless of crank power. You are right in saying that there is no actual relation to them but what we are saying is that it is the best way to ESTIMATE the hp numbers.

I'm not merely implying that the driveline takes a specific amount of hp to turn, I'm stating it as fact. And there is an exact way to figure it if you wanted to know - run the engine on an engine dyno then the car on the chassis dyno. The difference will be parasitic loss.

Still it has shown that the most efficient way for a 5 speed mustang with stock drivetrain and all accessories is about 15% loss regardless of crank power.

Think about what you just said. 15% loss regardless of crank power. So if the car had a 150 hp 4 cyl parasitic loss would be 22.5 hp. And since you say it has been shown 15% is the rule regardless of crank power the 150 hp 4 cyl is being replaced with a 300 hp 8 cyl. Now we're up to 45 hp of parasitic driveline loss with only an engine swap. What about a 500 hp engine? 75 hp to turn the driveline? Of course not.

I'm not jumping your shit or trying to make you look stupid and I certainly am not trying to piss anyone off. Just pointing out it doesn't work that way.

[02steedagt]

timber.... what your saying makes sense. perhaps it's not actually a linear relationship.??

[ChrisJ]

Their are really too many aspects to put into play for this...

I just do 15% on manual 20% on auto becuase that way when you get a bigger number you are happier...Its a rule of thumb I use...it is not perfect by any means of the word...

But what you ahve to add in there as well is there is alot more rotating mass there when you throw the V8 in...Also the transmissions are normally bigger...It could be any number it is really up to each person's own self...

And I definately see what you are saying Timber and I do see how you are thinking and do believe you are partially right and others are partially right as well...

[mjkids]

a stock gt is maybe 225 to 230 to the rwhp, the max the engine can handle is 375 to 400 hp if you want it to last. simple bolt ons will put you around 250 to 280 tops . a good bolt on and the best bolt on is a s.c. that will put you in around 350 to 400

[ChrisJ]

Originally Posted by mjkids a stock gt is maybe 225 to 230 to the rwhp, the max the engine can handle is 375 to 400 hp if you want it to last. simple bolt ons will put you around 250 to 280 tops . a good bolt on and the best bolt on is a s.c. that will put you in around 350 to 400

You can get to 315 (+/- 10) from bolt-ons...Timber and quite a few others have done it...

[mjkids]

maybe with cams & heads

[ChrisJ]

Yeah I count those as bolt-ons...Should have mentioned that...

[acmillr]

Originally Posted by Timber When you explain parasitic driveline loss as a percentage of engine output it implies a relation where there is none. You take the engine out of the car, find some way to figure out how much hp it takes to turn the drivetrain. That's what it takes and it's unrelated to engine output. If you say it's 20% that implies the driveline would take more hp if the engine made more power.

Actually (and I hate to call you out, but it was bound to happen), as you make more HP, you will lose more HP through the driveline. There is a linear relationship. It may not be exact, but that is how it works. If you lose 30-45 HP on a 260 HP motor through the drivetrain, you will lose probably 50 -80 with a 350+ HP motor.

"How do you know this Adam?", you may ask.

I reply to you, I am awesome, that's how.............

[02steedagt]

Originally Posted by acmillr I am awesome, that's how.............

and I believe you.

[Timber]

Originally Posted by acmillr Originally Posted by Timber When you explain parasitic driveline loss as a percentage of engine output it implies a relation where there is none. You take the engine out of the car, find some way to figure out how much hp it takes to turn the drivetrain. That's what it takes and it's unrelated to engine output. If you say it's 20% that implies the driveline would take more hp if the engine made more power. Actually (and I hate to call you out, but it was bound to happen), as you make more HP, you will lose more HP through the driveline. There is a linear relationship. It may not be exact, but that is how it works. If you lose 30-45 HP on a 260 HP motor through the drivetrain, you will lose probably 50 -80 with a 350+ HP motor. "How do you know this Adam?", you may ask. I reply to you, I am awesome, that's how.............

I don't mind being called out, it's a personal observation and I'm not an automotive engineer. I've heard the percentage rule all my life. I can see where frictional losses would increase the harder a driveline is pushed but not enough to remain a linear relationship. For instance, the more hp put to the input shaft of the tranny, the more force there will be on the gear contact patches in the tranny and rear end. But oil also has a shear strength.

I can accept being wrong, but I need something more technical than you are awesome.



So school me.



School me. Explain.

[Timber]

Originally Posted by 02steedagt Originally Posted by acmillr I am awesome, that's how............. and I believe you.

If he offers you Kool-Aid, politely refuse...