|
|
Register To Post |
| Try2pas | Percentage of Loss from flyweel to rear tires | ||
|
Guru Newb
 
|
I have an '80 vette with a 4L70E 4 speed automatic trany. What percentage of flywheel or net horsepower will I loose when it is dynoed? I have heard 12%, 18%, 24% and 30%?
|
||
Posted on: 2010/8/19 3:07
|
|||
 Transfer
|
 
|
||
| Matatk | Re: Percentage of Loss from flyweel to rear tires | ||
|
Webmaster
 
|
The problem is there is no magic number that is the same for every car. Due to variances in drivetrains, efficiencies in transmissions, torque converters, etc....it changes based on the vehicle. One vehicle may have a more efficient drivetrain than another, thus lower the % of loss.
I've usually heard 15-20% for an automatic (some people say 18%), but I have no scientific evidence to support that, it's just what people say. Matthew |
||
Posted on: 2010/8/19 11:34
|
|||
|
_________________
2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
|||
|
Transfer
|
|
||
| Mekanic | Re: Percentage of Loss from flyweel to rear tires | ||
|
Registered Vendor
|
When i was doing injectors and had to convert RWHP to FWHP for calculating the correct size, I always used a 20% loss for automatic, and a 15% loss for manual.
It has never failed, is it exact.. no way, but it's pretty damn close for the correct parasitic loss numbers lol. |
||
Posted on: 2010/8/19 17:25
|
|||
|
_________________
~Rich Polo LT4 Yea tho I walk through the valley in the shadow of rice, I shall fear no turbo, for torque art with me. |
|||
|
Transfer
|
|
||
| 383tpimachine | Re: Percentage of Loss from flyweel to rear tires | ||
|
Master Guru
 
|
A 9in with a TH400 will eat ALOT more power than a T56 with a 7.5in 10 bolt. How much? Hard to say. Heavier the parts the most loss.
I use 20% as well |
||
Posted on: 2010/8/19 18:12
|
|||
|
_________________
1985 Atomic Orange 400YSIT56-Racecar build 1970 El Camino-Awaiting LSX |
|||
|
Transfer
|
|
||
| bogus | Re: Percentage of Loss from flyweel to rear tires | ||
|
Grand Imperial Pooh-Bah
 
|
A big question will be this: does your torque converter lock up?
If so, you are on to something. First off, the estimate is just that... but I have come to the conclusion that it isn't a constant. My reasoning: If an alternator draws 5hp at max load, why would that change on a 1000hp engine? Same goes with the automatic... Using the 20% rule, at 200hp, the A4 is sucking down 40hp... whereas the 1000hp engine is being robbed of 200hp. Again, I don't buy it. My GUESS is that the constant is about 40hp. That I beleive. 383tpimachine - The TH400 is a real pig... But the thing is, as far as I can figure it, the automatic is the real problem. A manual has no pumping losses... and I don't expect that there would be a measurable difference between a 9" vs 7.5". The ratio would have a much bigger impact on the result than the physical gear sizes. |
||
Posted on: 2010/8/19 18:44
|
|||
|
_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
|||
|
Transfer
|
|
||
| 383tpimachine | Re: Percentage of Loss from flyweel to rear tires | ||
|
Master Guru
|
Quote:
WIth teh rear end you are dealing with heavier parts. Inertia comes into play in this instance. More drag. 3.70 gears in both cases the 7.5 SHOULD make more power on the dyno. This is also assuming same axles rims etc and the only thing changing is the housing and 9 the bigger gear needed to fill the housing |
||
Posted on: 2010/8/19 19:02
|
|||
|
_________________
1985 Atomic Orange 400YSIT56-Racecar build 1970 El Camino-Awaiting LSX |
|||
|
Transfer
|
|
||
| WW7 | Re: Percentage of Loss from flyweel to rear tires | ||
|
Senior Guru
 
|
Here is a calculator to figure out the difference.WW
http://www.mk5cortinaestate.co.uk/calculator4.php |
||
Posted on: 2010/8/20 12:52
|
|||
|
Transfer
|
|
||
| 1Fast04Vert | Re: Percentage of Loss from flyweel to rear tires | ||
|
Elite Guru
 
|
Quote:
Interesting. According to that my mostly stock LT1, A4 has 341 hp at the crank. Not bad, explains why I can run dead even with a stock C5/LS1. |
||
Posted on: 2010/8/20 15:54
|
|||
|
_________________
2004 Vert. 475hp. Built by Vengeance Racing |
|||
|
Transfer
|
|
||
| c3corvette77 | Re: Percentage of Loss from flyweel to rear tires | ||
|
Guru Newb
|
i agree with bogus. been thinking about this myself, if it takes say 100 hp to overcome accy and driveline losses then no matter if you make 400 or 800, it's still eating 100 hp. wouldn't it be better to use a guess of X hp rather than X percent?
|
||
Posted on: 2010/8/28 3:05
|
|||
|
_________________
RIDE IT LIKE YOU STOLE IT! 
|
|||
|
Transfer
|
|
||
| flyboy | Re: Percentage of Loss from flyweel to rear tires | ||
|
Elite Guru
 
|
Quote:
Would a 100CHP engine then make 0 at the wheels? I think a % is better. |
||
Posted on: 2010/8/28 3:14
|
|||
|
Transfer
|
|
||
| Matatk | Re: Percentage of Loss from flyweel to rear tires | ||
|
Webmaster
|
Quote:
If you look at that formula posted above, it is not a simple percentage or simple hp number. If you use higher/lower hp #s, the ratio changes, assumingly based on what you are saying. Matthew |
||
Posted on: 2010/8/28 11:33
|
|||
|
_________________
2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
|||
|
Transfer
|
|
||
| c3corvette77 | Re: Percentage of Loss from flyweel to rear tires | ||
|
Guru Newb
|
Quote:
i went to that calculator. i did 400 and 480 hp at the crank with a manual trans and both came back with 68 hp less at the wheels. it's voodoo i tell ya..... |
||
Posted on: 2010/8/31 4:20
|
|||
|
Transfer
|
|
||
| Matatk | Re: Percentage of Loss from flyweel to rear tires | ||
|
Webmaster
|
Quote:
Lol...more of a coincidence than voodoo...  If you look at the percentage loss vs actual hp, that's the indicator. The numbers you quote are as follows:EG1: hp at crank 400/rwd/manual = 342/wheels = 14.5% loss EG2: hp at crank 480/rwd/manual = 412/wheels = 14.2% loss EG3: hp at crank 100/rwd/auto = 73/wheels = 27% loss EG4: hp at crank 350/rwd/auto = 281/wheels = 19.7% loss EG5: hp at crank 450/rwd/auto = 364/wheels = 19.1% loss I'm not saying the calculator is right/wrong, just that it appears to assume a certain baseline accessory loss in addition to drivetrain loss. As the hp increases, as a percentage it's more efficient. Matthew |
||
Posted on: 2010/8/31 12:06
|
|||
|
_________________
2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
|||
|
Transfer
|
|
||
| cuisinartvette | Re: Percentage of Loss from flyweel to rear tires | ||
|
Elite Guru
|
[QUOTE]and I don't expect that there would be a measurable difference between a 9" vs 7.5".[/QUOTE]
If youre referrring to a Ford 9"? Agreed, will suck more power than a typical rearend for sure agreed. Price to pay for strength though |
||
Posted on: 2010/9/1 1:07
|
|||
|
Transfer
|
|
||
| c3corvette77 | Re: Percentage of Loss from flyweel to rear tires | ||
|
Guru Newb
|
ok, so what we can glean from all this is that we just need to make way more horsepower.....lots more.....
|
||
Posted on: 2010/9/1 1:52
|
|||
|
_________________
RIDE IT LIKE YOU STOLE IT!
|
|||
|
Transfer
|
|
||
| Trae1976 | Re: Percentage of Loss from flyweel to rear tires | ||
|
2012 Memorial Day Car Show Winner!
 
|
Quote:
c3corvette77 wrote: Can't argue with that.  |
||
Posted on: 2010/9/1 13:31
|
|||
|
Transfer
|
|
||
You can view topic.
You cannot start a new topic.
You cannot reply to posts.
You cannot edit your posts.
You cannot delete your posts.
You cannot add new polls.
You cannot vote in polls.
You cannot attach files to posts.
You cannot post without approval.
|
|