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Ok anybody know an accurate formula for working out Bhp?

S

Stumps

Diamond Member
Ok as the title states, I'm trying to calculate Brake(Flywheel) Horsepower from a rear wheel figure.
According to Ford Australia and the service manuals the figure for a ford falcon is 34.5hp (for an Auto) loss through the drivetrain.
now I would assume due to the lighter drivetrain weight of a manual transmission this figure would be lower.
I have 443.75hp at the wheels..using the 34.5hp figure that would give me 478.25hp at the fly wheel..does this sound accurate?
 
Loss through an automatic tranny is usually a percentage (or ratio) rather than a fixed number. A very efficient auto only loses about 15%. Most are around 20%.
 
thats what i thought but the service manaul lists a figure for automatics but not for manaul trans. any idea's
My driveline is as follows, Toploader 4spd with GTHO spec Twinplate clutch and a 3.5:1 9inch rear end.
the guy at the Speedshop who dynoed my car reckons I have better than 500hp but I think this is a bit high considering the relatively mild engine specs
 
google?

desktop dyno
?

If you have over 400 Rear wheel horsepower,I would not worry about
wahts at the crank. 😉

Take to the drag strip,and run the 1/4 mile>??

I doubt my Valiant will run less than 16.5,but hope to find out soon.

1964 Valiant,was 273 2 bll Factory,
now 318,dual exhaust, .430/.450 cam,
Edelbrock 1406 600cfm 4bbl.

I put #302 heads on,too,but did not know enough to upgrade the intake valves from 1.78,to the 1.88's that help a lot for upper end.

http://fox302.com/index.pl?s=vg&user=cavemanmoron&category=cavemanmoron&page=2
 
Like a previous poster said, there is no surefire way to tell because all trannies are different. If you have 440 at the wheels, It's likely you're near 500 at the motor.
 
Too many variables.

A good range for drivetrain loss is ~25 - 75HP.

I'm sure it goes higher and lower, though.

😉
 
I had a good chat with my mechanic and he is pretty sure that the ford figure is fairly accurate as it for the BW auto and diff combo for the falcon which is has a similar taxable horse power figure(the weight through the driveline is similar) to the toploader/9inch combo, so I have settled on 470-480bhp..which isn't bad at all for a worked 351 V8 🙂
 
Originally posted by: radioouman
Loss through an automatic tranny is usually a percentage (or ratio) rather than a fixed number. A very efficient auto only loses about 15%. Most are around 20%.
Click to expand...

Some claim it's actually both, a fixed loss plus a small percentage.

If I were to guess, this is probably especially true for high power engines. An engine making almost 500 HP at the crank, losing 20% through the tranny would mean 100 HP loss inside the tranny.
 
I doubt that i'm loosing any more than 50hp..the engine is just to mild to produce over 500hp..unless I add NOS and EFI😀
 
I got to do some testing today to determine some performance figures, according to the stop watch(jeez thats real accurate😛) 0-100km/h is under 4 seconds and 0-160km/h is under 7 seconds..pretty sweet, oh i wasn't driving cause i can't launch the beast to save myself, I'm just to savage with the clutch, but the speedshop guys who were timing it had trouble getting it to hook up as well so these figures are just a rough indication, I have no idea of how fast it goes, the speedo runs out at 240kmh and the tacho runs out at 7000 rpm..both of which I was able to surpase with relative ease in top gear, damn this thing accelerates real hard once it passes 3000rpm.
the speed shop guys reckon it would accellerate harder if I switched to a tricked up FMX or C4/C10 auto with a lower diff ratio...I reckon it's just fine for now😀
 
Originally posted by: Stumps
I got to do some testing today to determine some performance figures, according to the stop watch(jeez thats real accurate😛) 0-100km/h is under 4 seconds and 0-160km/h is under 7 seconds..pretty sweet, oh i wasn't driving cause i can't launch the beast to save myself, I'm just to savage with the clutch, but the speedshop guys who were timing it had trouble getting it to hook up as well so these figures are just a rough indication, I have no idea of how fast it goes, the speedo runs out at 240kmh and the tacho runs out at 7000 rpm..both of which I was able to surpase with relative ease in top gear, damn this thing accelerates real hard once it passes 3000rpm.
the speed shop guys reckon it would accellerate harder if I switched to a tricked up FMX or C4/C10 auto with a lower diff ratio...I reckon it's just fine for now😀
Click to expand...

hawt.

:beer:
 
The scored a dual 3 inch system today..sadly, which quietened it down a little but it still sounds plenty lumpy, the only real thing left to do is to get a paint job put on it and tidy up the interior.
all so far it owes me bout 20K which isnt bad at all, pity I'm still trying to explain all the reciepts to the missus🙁
 
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