musicman2

What's the-- FORMULA-- for this question ?? If you have 460 rwhp--what's the Crank HP--the engine HP ??? THANKS !!

Katech_Zach

Depending on the dyno and vehicle, 8-20%.

taken19

If its a manual, probably 510-525 crank Hp. The actual number depends on type on fluids, gears, and Manu otee variables. Glass Slipper posted a while back the actual science used to determine crank Hp and it's pretty complicated. Some people use a flat 12-15% for manual and 15-18% for auto and some use a flat Hp loss between crank and wheel (in the neighborhood of 55-65 Hp). In actuality, it's something in between the two.

Run a search for posts by Glass Slipper for a detailed explanation.

FloydSummerOf68

If you have 460rwhp you're likely around 520 crank.

I don't believe the % stays constant.

The safest, conservative estimate is likely to just add the amount you generally lose when dynoing stock, so ~60 rwhp. That's what I always do.

musicman2

It's a DYNO-JET--- What's the % difference between a 6 speed-Automatic--&--Stick shift

eboggs_jkvl

If you have 460 RWHP and an auto you have a Crank HP toward the lower % in post #2. The auto loses more power than the Manual so you need more crank power for your number. Conversely, 460 RWHP will equate to a number more toward the higher % in post #2. The manual can transfer more power from the crank to the Rear wheels. (I hope I got that right, I might have gotten confused! )

So, for example, you have 400 crank
M6 and you might get 345 at the RWHP
A6 and you might get 325 at the RWHP.

There isn't a hard cold set in stone formula that you can plug in and get an absolute HP figure. Sorry, too many variables for me to gather. You have to put the darn thing on the dyno to get an actual answer.

Elmer

eboggs_jkvl

The A6 will give less rwhp than the M6.


Again, there is no hard formula that you can use.

HOXXOH

This begs the question: Why does it matter?

Unless it's simply for bragging rights, in which case just pick a number you like.

Just spinning a drum on a dyno means nothing if you can't put it on the ground.

A timeslip is a more accurate method to relate the amount of work being done.

Katech_Zach

My wide ranging response was a bit tongue-in-cheek, albeit true based on my personal experiences. There are a multitude of variables and methods that contribute to the outcome and there is no one right answer or formula. On our dyno we see about 15% with a manual and 20% with automatics for most GM vehicles. Other vehicles can have less drivetrain loss.

musicman2

THANKS !!---THANKS !!---for ALL the answers--this will be saved in my library---exactly what i was looking for--great bunch of guys with all the answers your looking for !!!-------John

Shifter6

People commonly believe the difference between crank hp and wheel hp is a set percentage, usually people say 15%. My dyno experience has led me to believe any given drive train requires a fixed amout of hp to drive and the number is the same regardless of engine output.

I would say the typical T56 C6 drivetrain takes around 60hp to drive.

I had a T-5, 8.8 inch ford rear drivetrain take 45hp to drive (verified by dyno). This was with fresh synthetic fluids and a new aluminum driveshaft.

JoesC5

From published dyno runs, it seems the C6 has close to the following percentages.

manual transmission..... 10 to 12%
Auto transmission........ 15 to 17%

Part of the problem is that the various car's don't have different driveline losses, but the cars are measured on different dyno's under different conditions. Hard to compare a C6 run on Tiny Tim's Dynojet in Miami in May to a C6 run on Bubba Bob's Mustang in Minot in January to a C6 run on Ball Bustin' Brand X in Phoenix in August.

TMyers

The other thing to remember is the A6 does not have a true 1-1 ratio so that throws the numbers off as well.

KWC6

perfect answer...

vrybad

That is how I have always looked at it.
Keeps it simple without leading to over-inflated estimates.

I'd have to disagree, unless you are trying to determine the amount of work done over 1/4 of a mile.
Too many variables, a great one being traction, to skew results unfavorably.
On the dyno, you can minimize traction issues from launching and measure force over time and it can be compared against other setups, although I do agree that it shouldn't be taken TOO seriously.

glass slipper

I've never heard of this...how does not having a true 1:1 ratio in the A6 throw the numbers off??? I'm even more worried about what a false 1:1 ratio does to the numbers.

Turbo6TA

From what I have seen, an LS3 (factory rated at 436 HP) with the A6 transmission will make about 370 rwhp on a DynoJet.

That's 66 HP less than the rated 436 HP ... or a total loss of 15%



If you use the 15% loss number for an A6 car, 460 rwhp would give the car a factory rated HP of about 540 HP

TMyers

HP is determined by torque, HP=TQxRPM/5252. The A6 if I remember correctly 1.15:1 ratio in 4th gear. This will provide a higher torque rating than a true 1:1 ratio. If you are trying to find crank HP this has to be taken into account.

Turbo6TA

Good point. The M6 cars are in fact 1.00-1 in 4th, but the A6 cars are 1.15-1

However, if you look at the Final Overall Drive Ratios (takes into account the axle ratio too) of the various cars while in 4th gear, the numbers for the A6 cars are a higher (steeper) overall ratio than the M6 cars ... IE: 3.14 for an GS/A6 vs a 3.42 for an M6 car.



.

glass slipper

You are so confused. First, what is a "true 1:1 ratio"? That implies there's a "false 1:1 ratio".
You're trying to take what applies to manual transmissions and apply it to automatic transmissions because you don't know what makes 4th gear (the 1:1 ratio) the best gear to dyno a manual transmission Corvette in. There are no gears for 4th gear...the input and output shafts are locked together and you avoid the gear losses associated with the other 5 gears which amounts to 2-3% or 10-15 HP on a Z06/LS7. Less HP loss is the main advantage for the M6. In addition, 1st-3rd will have higher inertia losses on a pure inertia chassis dyno while 5th & 6th will exceed the speed rating of a lot of chassis dynos. For the A6, 1st-6th gear all have power flowing through gearsets meaning there are no gears with zero geartooth HP loss. It does not mean HP can't be measured just as accurately in the A6 in 4th gear as the M6 in 4th gear...nothing has to be taken into account.
A chassis dyno measures engine HP via the wheels because it's easier than pulling the engine and setting it up on an engine stand. It's referred to as RWHP because it is impossible to correlate chassis HP numbers to crank HP numbers. And contrary to what you think, the Dynojet (as well as others) measures HP first THEN calculates torque so the actual torque at the rear wheels has no affect on the engine HP/Torque as measured by the rear wheels. The Dynojet only has an RPM pick-up so it can make the HP to Torque calculation during the run.
The idea of gears affecting HP is also contrary to the 1st Law of Thermodynamics which says energy/power can not be created or destroyed. In short, you can neither multiply or divide HP with gears...of course you can multiply the hell out of torque but that's a force, not energy/power. Gears have no affect on engine HP at the wheels by virtue of the gear ratio only. There are side effects from different gear ratios but the result depends on the type of dyno...a pure absorption dyno will show an increase in RWHP while a pure inertia dyno will show a decrease in RWHP.