Rolling road rear wheel horsepower

[andyrob]

Took the coronet to John Sleath's on the way down to the nats for a quick check on the rolling road, Car ran fine air/fuel spot on, just a minor jet change, but 'only' made 533 bhp on rollers on street tyres, which didnt sound to good to me, but he said you get huge losses through auto boxes & a 900 hp engine he'd benched dyno'ed only made about 30 hp more than mine when in the car & on the rollers, he did say his rollers are 'realistic 'rather than 'optimistic'.
Car obviously makes good power as has run the times this weekend
Not sure on autos with high stall verters, but id expect a 10% -15% loss with a manual car
any views ??

[big block]

I was told up to 20-25% loss with and auto

[Jon Connolly]

Hard to know for sure but I weighed mine shortly after the dyno pull then put the figures for my 10.55 sec pass into a desktop calculator ( http://www.wallaceracing.com/Calculators.htm )

I had accurate figures for 1/4 E.T. + weight and that gave you the rear wheel hp.

Mine came out with an 8% drivetrain loss, which doesn`t sound much.

I would say with a margin of error 10- 15 % loss is more accurate.

[Dave-R]

I usually deduct 70hp from crank HP to get an idea of rear wheel power through a 727 and 8.74. Plus another 5hp for a Dana.

No idea how accurate that is but it usually gets me close.

[Anonymous]

Good subject this!

The higher the horsepower the greater the losses through an auto!!!
Even 600/700 horses will overload a fluid drive system.
Dyno's show true crank power output, once a convertor is bolted on you are on a downward slope of power losses.
The early dragster boys knew this and did lots of experimenting with different drive systems, and we ended up with Lenco's/Liberty's etc.

Gotta use a clutch if you wanna use all dem precious Horses!!!

Bacca loves Manuals!

[Rich]

Took the coronet to John Sleath's any views ??

Yep,,,,,,,,,,that Coronets the best car there for looks & go...Throw in the wanderlodge and we may be able to deal

[andyrob]

cheers rich,im flattered

[Dave999]

I too have heard 20-25% with an auto but thats BHP...
you do get torque benefits that might make up for that a bit with a torque converter/transmission which i'm sure is quite simple to understand once you look inside a torque converter I just never got round to bothering (i.e i don't have one)



Dave

[Jerry Smith]

Andy it's Marc, when we had the coronet on johns rollers it made 592.8 hp at the nats I thought you'd said it only made 10hp less now, wonder where 60hp has gone?

[andyrob]

marc, we found & looked @ your dyno graph, which yes your peak power was higher (not 593 ? though ?) but you were still fixing the problems with the car & you power curve was all over the place with nasty spikes on it & now it super smooth.
Ived have thought motor might have made more now its loosened up ??

[Jerry Smith]

If you check sleathy's website there's the video on there of our pull and it was definitely 592.8, but as you say not as clean a power curve as yours, not trying to pee on your chips Andy as your still running the same times as we did

[Cannonball]

we took hightowers challenger to johns it made from memory 333 hp
we then had his brother 4 wheel drive srt 8 jeep on the rollers it made a nats cock off 300hp 298.9 i think, and i think this engine is maybe advertised with 425 hp ???????????????

[big block]

So about 25% loss then

[Dave999]

provided that 425 is DIN or SAE not old style american run it with no alternator or fan and no air filter

type measurement.

YUP

also depends on the dyno
the dyno operator (and his skill) max rpm in 3rd will give different results to max rpm in 4th but third might spin the wheels on the rollers but 4th might overheat the engine but but but etc
the gear it was in
the tyres
how much air in the tyres
if you fill ya tyres with water you get better torque readings etc
the density of the air on the day
if it was humid
How the operator applies his correction factors for the environmental aspects he can't control. (many ways to do this mathematically and some ways come up with bigger coprrectioon factors)
whether there was an R in the month
if you had pork for ya tea
etc

hence a chassis dyno is better for gaugeing % improvment after a change provided you use the same dyno on a similar day with similar weather and have a bacon sandwich before you start.

for an all out power or torque rateing for a specifc motor
you'd need and engine dyno and take an average

if using a chassis dyno you'd need to visit a few more times and a few dynos and on different days and take an average.

and it helps if they are different types Brake/inertia type or the other type that i think spins a big paddle in some glue

chasis dyno gives you a clue as to how it will drive not how much, how big,
its best for where that peak power and torque is

hey i'm quiet good at spouting stuff i read on the internet aren't I


dave

[Dave999]

I know full well that cars that take part in the HorsePower heros dyno pulls at the aussie Summernats show
always seem to do much higher BHP rateings than they did when testing was taking place

what was 900 BHP suddenly is 999BHP on the day

it makes for a good show
but your win is by being the best 8 or the best 6 and the measurement is comparative so it doesn't matter.

King of the day is still the king even if the car he brought was useless for anything other than dyno work.

drive it home ahahahaha

Dave