Estimating your Flywheel HP from a Dyno RWHP
#1
Cobra R Member
Thread Starter
Join Date: July 21, 2005
Posts: 1,538
Likes: 0
Received 0 Likes
on
0 Posts
Estimating your Flywheel HP from a Dyno RWHP
Ford tells us our cars are 300 hp at the flywheel. Most have dyno'd at 265 or so. So what is a good way to back figure our HP if we know the Dyno RWHP?
I have heard that 15% is a good estimate.
I have heard that 15% is a good estimate.
Last edited by traffic142; 10/30/09 at 07:25 PM.
#2
265/300=.8833333
If you wanna use 265 as a benchmark. Problem is every engine will yield different baseline hp numbers at the flywheel, auto transmissions will lose more power than a standard transmission, and of course different dynos will yield different rwhp numbers.
But for the sake of argument my car made 479 rwhp on the dyno. If you take my 479/.88333=542 hp at the crank.
Of course you could just multiply by 1.132 to get the number too.
And all this is just for arguments sake because there are so many variables.
If you wanna use 265 as a benchmark. Problem is every engine will yield different baseline hp numbers at the flywheel, auto transmissions will lose more power than a standard transmission, and of course different dynos will yield different rwhp numbers.
But for the sake of argument my car made 479 rwhp on the dyno. If you take my 479/.88333=542 hp at the crank.
Of course you could just multiply by 1.132 to get the number too.
And all this is just for arguments sake because there are so many variables.
#3
Cobra R Member
Thread Starter
Join Date: July 21, 2005
Posts: 1,538
Likes: 0
Received 0 Likes
on
0 Posts
I know most produced at dyno stock around 260 to 270 (some as low as 255 and as high as 275) depends on what day it was built, etc also. I know around 1972 Feds mandated net HP after all the accessories were added. Thanks
#7
GT Member
Join Date: September 17, 2009
Location: Woodbridge, Virginia
Posts: 157
Likes: 0
Received 0 Likes
on
0 Posts
Excuse my ignorance in this matter but where does the .80 and .85 figure come from? I just got home a few minutes ago from having my Automatic '05 GT Dynoed on a DynoJet. It yeilded 299.26 RWHP so at the .85 figure it would be 351.76 FHP or at .80 it comes to 373.75 FHP. I seriously doubt both of those figures for my car. I am not suggesting that either of you guys don't know what you are talking about but it just doesn't make sense to me.
#9
Tasca Super Boss 429 Member
Join Date: November 14, 2007
Location: Pacific NW USA
Posts: 3,652
Likes: 0
Received 8 Likes
on
6 Posts
That sounds right for a Dynojet dyno. A Mustang chassis dyno tends to read slightly lower and 15% for manuals and 20% for automatics is the generally accepted drivetrain losses for those. My car was dyno'd on a Mustang chassis dyno. The operator told me (as many others have told me) that cars typically dyno 5-10% more on a Dynojet vs a Mustang dyno.
#10
Tasca Super Boss 429 Member
Join Date: November 14, 2007
Location: Pacific NW USA
Posts: 3,652
Likes: 0
Received 8 Likes
on
6 Posts
Excuse my ignorance in this matter but where does the .80 and .85 figure come from? I just got home a few minutes ago from having my Automatic '05 GT Dynoed on a DynoJet. It yeilded 299.26 RWHP so at the .85 figure it would be 351.76 FHP or at .80 it comes to 373.75 FHP. I seriously doubt both of those figures for my car. I am not suggesting that either of you guys don't know what you are talking about but it just doesn't make sense to me.
IMHO, a Dynojet dyno (read my post above) reads higher RWHP due to the unrealistic way it measures power (Mustang dyno's are loaded with resistence to better emulate the real world). A 12% loss for manuals and 15% loss for automatics is probably as good a guess for a Dynojet as any (as 2k7gtcs pointed out above).
And if Ford rates an S197 GT Manual at 300 flywheel hp, and they put down 255 rwhp (on a Mustang dyno), that's a 15% drivetrain loss which supports the generally accepted figures. I've seen Mustang dyno sheets for stock GT automatics in the 240-245 rwhp range, which is right about at the 20% drivetrain loss bogey, too.
#11
Tasca Super Boss 429 Member
Join Date: November 14, 2007
Location: Pacific NW USA
Posts: 3,652
Likes: 0
Received 8 Likes
on
6 Posts
Older cars are much less efficient, by the way. I used to own a 1968 Pontiac GTO with a turbo 400 automatic transmission. Factory rated at 350 flywheel hp, and modified to around 425 flywheel hp (according to the shop that balanced, blueprinted, and built it for me), it only put down 283 rwhp - a 33% drivetrain loss.
#12
Team Mustang Source
That sounds right for a Dynojet dyno. A Mustang chassis dyno tends to read slightly lower and 15% for manuals and 20% for automatics is the generally accepted drivetrain losses for those. My car was dyno'd on a Mustang chassis dyno. The operator told me (as many others have told me) that cars typically dyno 5-10% more on a Dynojet vs a Mustang dyno.
Thread
Thread Starter
Forum
Replies
Last Post