Multiply or Divide?
Thread Starter
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Multiply or Divide?
I know this kind of a retarded question but I am curious do you multiply or divide to convert RWHP into FWHP. I would think that if there is 16% drive train loss (just a guess BTW) that the answer would be dividing but am not sure. For instance if my car made 414 RWHP you would say that it is 84% of the FWHP so 414/.84=492.86 –vs - 414x1.16=480.24
Racer
Joined: Jul 2004
Posts: 434
Likes: 0
From: Santa Barbara Minnesota
Whats FWHP?
Originally Posted by FD2BLK
I know this kind of a retarded question but I am curious do you multiply or divide to convert RWHP into FWHP. I would think that if there is 16% drive train loss (just a guess BTW) that the answer would be dividing but am not sure. For instance if my car made 414 RWHP you would say that it is 84% of the FWHP so 414/.84=492.86 –vs - 414x1.16=480.24
414 X .84% = 347 CHP. HP at the crank.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Yes you divide by 0.84. The reason is that the original 16% number was referenced to the FWHP.
Multiplying by 1.16 would mean that you have 16% more FWHP than RWHP, which is not the same as having 16% less RWHP than FWHP.
Multiplying by 1.16 would mean that you have 16% more FWHP than RWHP, which is not the same as having 16% less RWHP than FWHP.
Racer
Joined: Jul 2004
Posts: 434
Likes: 0
From: Santa Barbara Minnesota
Whats FWHP?
Originally Posted by FD2BLK
I know this kind of a retarded question but I am curious do you multiply or divide to convert RWHP into FWHP. I would think that if there is 16% drive train loss (just a guess BTW) that the answer would be dividing but am not sure. For instance if my car made 414 RWHP you would say that it is 84% of the FWHP so 414/.84=492.86 –vs - 414x1.16=480.24
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Ok, assuming 16% DT loss, RWHP must be 16% lower than CHP, or
RWHP = CHP - CHP * .16 = CHP * (1-.16 ) = CHP * .84
so,
CHP = RWHP / .84
In your example you have 414RWHP, so you would have:
493CWHP = 414RWHP / .84
RWHP = CHP - CHP * .16 = CHP * (1-.16 ) = CHP * .84
so,
CHP = RWHP / .84
In your example you have 414RWHP, so you would have:
493CWHP = 414RWHP / .84
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Originally Posted by steve9899
Wait a minute. Your profile says you're an electrical engineer...
Yeah so, I'm to be a mechanical engineer and I just got finished with my statics homework. It SHOULD have taken and hour to do it LAST night. I just finished it today. It literally kicked my *** and it was nobody's fault but my own!
We all have our moments.
Racer
Joined: Jul 2004
Posts: 434
Likes: 0
From: Santa Barbara Minnesota
Originally Posted by Nathan Plemons
Yeah so, I'm to be a mechanical engineer and I just got finished with my statics homework. It SHOULD have taken and hour to do it LAST night. I just finished it today. It literally kicked my *** and it was nobody's fault but my own!
We all have our moments.
We all have our moments.
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Thread Starter
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
I just wasn't sure if the reference was actually stating that there was 16% drive train loss (Roughly) or if they where calculating for drive train loss by multiplying by 1.16. I have seen it posted both ways and never seen an actual formulation or dyno results either way. I planed on building a 500 HP motor when I started and feel there is a little left in tuning so I was hoping for the / rather then the *. My car had a miss the day we tuned and it made for a long day so I think with another day of dyno tuning it could make 420 RWHP and close to 420 RWTQ. Thanks for all the input
Melting Slicks
Joined: May 2004
Posts: 2,286
Likes: 2
From: Stamping Ground KY
Err, 16% drivetrain loss means that if you have 100 CHP you'd have 84 RWHP.
So to go from RWHP to CHP you have to multiply RWHP by 1/(1-16%) [or whatever percent your drivetrain loss is] which is about 1.19 in this case.
so 84 RWHP * 1.19 = 100 CHP
and in your case:
414 * 1.19 = ~493 CHP
65Z01 gets the prize.
So to go from RWHP to CHP you have to multiply RWHP by 1/(1-16%) [or whatever percent your drivetrain loss is] which is about 1.19 in this case.
so 84 RWHP * 1.19 = 100 CHP
and in your case:
414 * 1.19 = ~493 CHP
65Z01 gets the prize.
Team Owner
Joined: Sep 2002
Posts: 22,209
Likes: 12
From: OBAMA IS HITLER
this might sound really stupid, but would the formulas apply whether your talking 100chp or 10,000chp as the basis?
ex: assuming 16% total loss: 100chp * .84 = 84rwhp
1000chp * .84 = 840rwhp (is it really THAT much of a loss?)
just seems to me there's some additional factoring of some kind (ie, not a linear equation) that comes into play as the chp goes up. maybe i'm just confused like i normally am
ex: assuming 16% total loss: 100chp * .84 = 84rwhp
1000chp * .84 = 840rwhp (is it really THAT much of a loss?)
just seems to me there's some additional factoring of some kind (ie, not a linear equation) that comes into play as the chp goes up. maybe i'm just confused like i normally am
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Originally Posted by bradvette
this might sound really stupid, but would the formulas apply whether your talking 100chp or 10,000chp as the basis?
ex: assuming 16% total loss: 100chp * .84 = 84rwhp
1000chp * .84 = 840rwhp (is it really THAT much of a loss?)
just seems to me there's some additional factoring of some kind (ie, not a linear equation) that comes into play as the chp goes up. maybe i'm just confused like i normally am
ex: assuming 16% total loss: 100chp * .84 = 84rwhp
1000chp * .84 = 840rwhp (is it really THAT much of a loss?)
just seems to me there's some additional factoring of some kind (ie, not a linear equation) that comes into play as the chp goes up. maybe i'm just confused like i normally am
Melting Slicks
Joined: May 2004
Posts: 2,286
Likes: 2
From: Stamping Ground KY
finding a dyno wasn't so hard, and once you get the numbers you have a stronger basis for figuring out your acceleration and top speed (there's still some handwaveing, but less so).
Finding your top speed in real life is more difficult (and generally not legal), so I'll live with my educated guess and maybe someday I'll get to test it out...
Finding your top speed in real life is more difficult (and generally not legal), so I'll live with my educated guess and maybe someday I'll get to test it out...
Melting Slicks
Joined: Apr 2003
Posts: 2,150
Likes: 6
From: NS
Originally Posted by steve9899
Yes you divide by 0.84. The reason is that the original 16% number was referenced to the FWHP.
Multiplying by 1.16 would mean that you have 16% more FWHP than RWHP, which is not the same as having 16% less RWHP than FWHP.
Multiplying by 1.16 would mean that you have 16% more FWHP than RWHP, which is not the same as having 16% less RWHP than FWHP.
Good explanation.