Unreal

How hard is it to pick up 10lbs? Now a guy that can lift 100lbs or 1000lbs, does that change it? It isn't 10% of the persons strength. It takes say ~10hp to turn the gears in the rear end, 10hp to turn a drive shaft. Going from 400hp to 800hp doesn't make those numbers all the sudden double.

A modern LS 6 speed drive train takes ~40hp to spin, and auto ~60ish. There is a certain percentage that changes with power, and stall slip/etc that can calculate in, but saying 10/15/20% is nothing more than old men trying to make them feel good about numbers and not close to reality.

Dave502

I understand that,.....What are the losses?.....All I'm trying to find out is what should a Dynojet and Mustang Dynos (which will be different)...be reading on a C6 GS RWHP with a 6 speed and an automatic .GM says the motor is putting out 430 hp......We are beating around the bush myself included....Give me an answer,and I'll confront some of these guys that have dynos....And they don't know the answer either 😊....Help me out,or have all the Gurus left the building.....
Thanks

erick_e

There is no certified standard to measure parasitic drivetrain loss which is why you are getting different answers. Additionally, take into consideration that most dyno RWHP numbers have to be converted to an SAE standard number to adjust for temperature and barometric conditions.

CTD

Exactly

Unreal

Weather, tire pressure, tires used, gas used, wheels on the car, age of spark plugs, carbon build up, engine temp, transmission temp, etc etc etc etc etc.

Dan_the_C5_Man

I am going to throw the OP a bone here..

Although everyone that has posted "you can't put a specific percentage on drive train loss" and the quagmire of comparing one dyno result to another (and they are all right), to give you some information to work with..

1. All North American manufacturers state their HP ratings as CRANK HP, never RWHP, for obvious reasons (crank HP will always be higher of course, and higher is always better in the marketing department). Some European manufacturers don't play that "game" - if it says "505 HP" on the fender, that means 505 to the wheels

2. JUST to give you SOMETHING to work with here - ***-U-MEing GM is truthful about the 505 LS7 rating, on a local, consistent Dynojet brand inertia dyno, stock cars put down approximately 460 RWHP. Some quick and dirty math reveals a 9% drive train loss.

MY car, on this same dyno, put down 473 HP, bone stock. Now, does this mean my car is "special" because magically it only has 7% drive train loss as opposed to another stock Z? Or is it that my engine is making MORE than 505 HP at the crank? Hint - it's the second one..

So, you can see the complexities of using a generic percentage for estimating crank HP. As the power level goes up, the less true a fixed percentage becomes.

My advice - pick the 10% loss for a manual trans (assuming a similar power level to a stock Z) and guesstimate away, but always know and understand the numbers for crank HP you come up with are just that - a somewhat educated guess, but a guess non-the-less - good for bench racing and "mine is bigger than yours" discussions, but that's about it.

548chevelle

example- lets say a particular drivetrain loses 50 hp. if a 400 hp engine is hooked to it thats a 12% loss. if a 650 hp engine is hooked to it thats an 8% loss.

olddragger

Parasitic loss and engine crank hp are not directly proportional. They are separate findings.
Reduce parasitic loss ( one thing I believe that is not addressed enough) and more hp will be available to turn the wheels. Most people just increase the power output of the engine.

Bigjsn250

The problem starts when people assign a percentage to drivetrain loss. Your example shows this to be confusing. Drivetrain loss does not change unless you do something to change it. Adding hp/tq does not change the loss. If its 50 hp with a 400hp engine it's still 50hp with a 500hp engine.

What we should be saying is a c6 corvette sees a 50-60 hp loss with an auto and 40-50 with the m6.

OP most people with z's are seeing 460ish stock. Ls3 guys 370-380 auto, 380-390 6m. Ls2 330 auto 340-50m6.

Best thing you can do is run the car and get a trap speed, average of a bunch is even better. Whatever tuning or mods you do compare to that trap speed.

Dave502

Talked to a GM tech last week and he said the hp given by GM is rwhp with an auto transmission (what he was told in the classes) ...which to me means a Dynojet should be reading real close to 430 rwhp on a baseline Dyno run on a C6 Corvette with stock LS3 and a Mustang Dyno 10 % + or - less.......What you see is a lot different.....The only thing a Dyno does is tell you that your car has hp.....actual hp...NO!!!

Dan_the_C5_Man

Everyone knows GM publishes crankshaft HP, not RWHP.

You might want to question any other information your GM tech buddy provides to you.

Bigjsn250

Totally incorrect, but believe what you want.

schpenxel

GM Tech is an idiot. This info is very wrong.

Dave502

I'm not trying to be an ***.....what is your answer??....what should a Dynojet be reading for a baseline rwhp on a stock c6 LS3 Which GM says is 430 hp......there have been hundreds dynoed and it seems to me the numbers should be pretty close with variations in outside temps,etc.....This isn't a trick question..The tech I talked to is a lead mechanic for nine years here at a dealership.....I thought he knew what he was talking about.....Ill let him know that he doesn't have a clue of the hp.

schpenxel

370-375 RWHP'ish, LS3

https://www.corvetteforum.com/forums...post1580531197

Unreal

He is a complete idiot.

Go look at stock ls3 graphs. 350-375 is about normal, depending on conditions. Since dynoing at a shop isn't' controlled, something as simple as the car being warm, or a warm day will easily have 20+hp swings.

Dealership techs are not trained on dynos. All cars are rated SAE at the crank, per the standard.

LSX228R

I've seen a lot in the 370-385 range. I have also seen a few Mustang dyno's read the same as a dyno jet.

Unreal

Yep, mustang dynos don't always read lower. It depends on the setup and load the operator enters.