Did we ever solve the RWHP to FWHP /or/ drivetrain loss conversion?

Pokageek · Aug 21, 2006

So is RWHP generally 80-85% of FWHP? or is it simply the 30HP rule? My car is putting out roughly 300RWHP (have to get it re-dyno'd after some changes). But it does NOT feel like 380HP (20% rule). It feels more like 330HP to be honest.

BlackVert · Aug 21, 2006

it is definately a percentage, not a static number. what is your combo anyway

300/.85 = 352

*edit*
http://www.superstang.com/horsepower.htm

final5-0 · Aug 21, 2006

You always wanna figure fw to rw

NOT

The other way around

Smaller number ... Smaller % kinda thing ... don't ya know

I only consider stick trans combos (more consistent) to be remotely close and usually use 15% for a ballpark value when I see a t5 is used.

Grady

Pokageek · Aug 21, 2006

BlackVert said:
it is definately a percentage, not a static number. what is your combo anyway

300/.85 = 352

*edit*
http://www.superstang.com/horsepower.htm

Great article, thanks. I updated my sig again.

Black95GTS · Aug 21, 2006

Adding more HP does not equate to proportional increase in drive train loss.

F=MA

For drive train loss to increase at the same percentage as horse power increases, acceleration would have to increase linearly, assuming the tranny doesn't change.

The faster you accelerate the drive train, the more power you need. The power needed increases faster then the drive train acceration.

if you add 135 fwhp you accelerate the drive train fast enough for roughly a 3 second drop in ets (300 rwhp at high 11s/low 12s).

If you add another 135 fwhp, you WILL NOT accelerate the drive train fast enough for another 3 second drop. At least, I've never seen a 485 fwhp car in the 9s.

Because drive train acceleration doesn't increase linearly with power, applying a flat percentage is bunk.

- Adam

final5-0 · Aug 21, 2006

Black95GTS said:
Adding more HP does not equate to proportional increase in drive train loss.

F=MA

For drive train loss to increase at the same percentage as horse power increases, acceleration would have to increase linearly, assuming the tranny doesn't change.

The faster you accelerate the drive train, the more power you need. The power needed increases faster then the drive train acceration.

if you add 135 fwhp you accelerate the drive train fast enough for roughly a 3 second drop in ets (300 rwhp at high 11s/low 12s).

If you add another 135 fwhp, you WILL NOT accelerate the drive train fast enough for another 3 second drop. At least, I've never seen a 485 fwhp car in the 9s.

Because drive train acceleration doesn't increase linearly with power, applying a flat percentage is bunk.

- Adam

I have to say I agree with your thinking

But for stick combos you see the most of on these boards in the 300 range give or take a little ..........

15% is usually not too far off the mark.

Again ... auto trans combos and high hp combos are gonna be farther from that little ballpark judgment method.

Grady

BlackVert · Aug 21, 2006

Black95GTS said:
Adding more HP does not equate to proportional increase in drive train loss.

F=MA

For drive train loss to increase at the same percentage as horse power increases, acceleration would have to increase linearly, assuming the tranny doesn't change.

The faster you accelerate the drive train, the more power you need. The power needed increases faster then the drive train acceration.

if you add 135 fwhp you accelerate the drive train fast enough for roughly a 3 second drop in ets (300 rwhp at high 11s/low 12s).

If you add another 135 fwhp, you WILL NOT accelerate the drive train fast enough for another 3 second drop. At least, I've never seen a 485 fwhp car in the 9s.

Because drive train acceleration doesn't increase linearly with power, applying a flat percentage is bunk.

- Adam

very true, more support that the the idea that there is a fixed hp loss through the drivetrain doesn't hold water. that is essentially what john's article says; the resistance through the drivetrain increases as more hp is applied to it.

perhaps a more accurate way to make a guess at fwhp could be to have a table that associates a certain percentage loss to apply depending on the rwhp figures. as the rwhp figure increases, the percentage lost also increases (probably exponentially), so that for every 100 hp you add at the fw, you end up getting less and less of that hp to the wheels.

sounds like the law of diminishing returns ...

for example, at 300 rwhp, the percentage lost 15%, so 300/0.85 = 352 fwhp, but at 400 rwhp, the percentage lost might be more like 25%, so the fwhp might be more like 400/0.75 = 533 ...

Black95GTS · Aug 21, 2006

final5-0 said:
I have to say I agree with your thinking

But for stick combos you see the most of on these boards in the 300 range give or take a little ..........

15% is usually not too far off the mark.

Again ... auto trans combos and high hp combos are gonna be farther from that little ballpark judgment method.

Grady

I concur.

I just wanted to make sure nobody built a 1000HP motor and expected a 150HP loss through the drive train! "Keyboard engineering" needs to be thoroughly vetted.

Don't quote me on this, but I believe it was Joe Sherman (THE Joe Sherman) just claims 22HP lost through a T5 and he leaves it at that. Joe Sherman knows Mustangs!

Adam

bimmertech · Aug 21, 2006

i have debated this very topic in detail and i will always support the 30hp loss--not percentage.

final5-0 · Aug 21, 2006

bimmertech said:
i have debated this very topic in detail and i will always support the 30hp loss--not percentage.

Ben

Are you saying a 330 fw combo puts 300 to the wheels

Grady

bimmertech · Aug 21, 2006

final5-0 said:
Ben

Are you saying a 330 fw combo puts 300 to the wheels

Grady

yes sir--on a dynojet

trickflow used to advertise the top end kit as 330-350hp and most guys will see 30hp less on a dynojet.

C6 ZO6 is rated at 505hp and routinely puts out 470-475rwhp on a dynojet.

smaller hp engines i have routinely seen make 30hp less than factory advertised ratings--which would be greater than 15%.

i recently attended a baseline dynojet chassis dyno pull of a 89 M3 with a built 2.5 that made 219 on an engine dyno then turned around and made 185rwhp.

for me people can talk about mass and force and resistance and all that stuff i don't care about, what it boils down to me is i see too much evidence that supports my(and few others) theory.

i'm not saying i am 100% right, but its what i believe.

SWYZ721 · Aug 21, 2006

bimmertech said:
for me people can talk about mass and force and resistance and all that stuff i don't care about, what it boils down to me is i see too much evidence that supports my(and few others) theory.

Yes, you are using empirical evidence which is all well and good, but using the same logic I don't know if China exists because I've never SEEN it. I do know that Thailand exists because I have SEEN it many times.

The more horsepower you have, the more the drivetrain loss will be (percentage-wise), that's plain and simple.

The fact the more power is produced, more heat is created, and power is transferred less efficiently.

Black95GTS · Aug 22, 2006

SWYZ721 said:
Yes, you are using empirical evidence which is all well and good, but using the same logic I don't know if China exists because I've never SEEN it.

Facts are facts. I'll argue Newtonian physics with you all day but if the guy who works on engines for a living notices a consistent trend, I'm not going to ignore it.

Adam

final5-0 · Aug 22, 2006

Black95GTS said:
Facts are facts. I'll argue Newtonian physics with you all day but if the guy who works on engines for a living notices a consistent trend, I'm not going to ignore it.

Adam

Again Adam

I think along the same lines as you

A thing or two to consider as well ...............

Experience/hard data has way more credibility with me than other things
however
I do always TRY to keep an open mind

The Fox tb conversion is one of those things I keep an open mind about
but for the time being .......
I don't see it as a na combo performance gain benefit

anyway ......................

IMHO ... sae dynojet hp/tq curves are a valid way to compare the combos you find on these boards.

Some say on the dyno ... take it to the track

I can definitely call on 1/4 mile comparisons due to the driver.

My intent is not to poo poo 1/4 mile testing or anything like that
but ... for me
1/4 mile track is one of those experience things (and lots of it) talked about above.

Bottom Line is whether dyno or 1/4 mile results .............

Both have their place as effective tools to compare combos.

100% accuracy is not always a necessity ...... to compare that is
simply because if you have enough data ... over time ... the trends seen from that data cannot be denied

Grady

Did we ever solve the RWHP to FWHP /or/ drivetrain loss conversion?

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