Horsepower ratings mysterys

[B/STOCK]

At what place is the horsepower rated on the LS1. Some say at the crank some say rear wheels? Also where was the HP rated on the 68 models? Thanks, Michael

 

[Jim Shoemaker]

The LS1 is rated 345 HP at the flywheel

Jim

 

[Edmond]

If it's rated at 345 at the crank, then you'll get how much of that to the rear wheels?

 

[Jim Shoemaker]

An accepted practice is to substract about 15% for drivetrain loss; should make it 290+ at the rear wheels. Thought I read something on it that said stock was higher than that, but I can't recall where.

Jim

 

[B/STOCK]

If the LS1 is rated at the flywheel at 345 hp why does it have as good if not better times in the quarter than a 427-400hp. I realize the suspension and stock tires on the C5 are better but were talking a straight 1/4. Again, where was the hP measured on the 68s etc.

 

[Ken]

Keep in mind that parasitic drivetrain loss is much less in current model cars than it was in the "musclecar" era. In other words, technological advances have been able to get more power to the ground than in the past.

Jim is correct in that the general rule of thumb is about a 10-15 percent power loss for a given vehicle, those with automatic transmissions will usually have a greater loss in power to the wheels than the same vehicle would have with a manual.

_ken

 

[Edmond]

Is it safe to assume that the majority of cars regardless of whether they're American, European or Japanese print the crank HP?

Wider tires would be an advantage right? Because you have to grip the pavement to take off? A lower center of gravity would also help, along with better aerodynamics?

 

[Jim Shoemaker]

I believe that's the standard....if I put the 4.3L engine from my 4WD Blazer in my Cavalier, I think I'd get more RWHP......if I could get the Cavalier's nose off the ground and rear wheels on the ground.

Jim

 

[Edmond]

That probably won't be necessary

The Cavalier is FWD right?

 

[Jim Shoemaker]

Hard to drive with the nose in the asphalt though

Jim

 

[02 C-5]

Fast Red Vett : The new Ls1 has a broad torque band , 2500 to 5000 it pulls hard , and with a broad band of H.P. to help it go fast . A 69 427 corvette engine started at a low torque than raised through the rpms than reaching a peak than dropping off , H.P. did the same . The 427 torque was very strong , but the H.P. was good but started low than peaked at 6000 , plus the did not have the traction or suspension was not set up to hook up , I would take a 69 427 Corvette in a heart beat but it would be hard to run with a C-5
Thanks ,
Joe

 

[Scissors]

If the LS1 is rated at the flywheel at 345 hp why does it have as good if not better times in the quarter than a 427-400hp. I realize the suspension and stock tires on the C5 are better but were talking a straight 1/4. Again, where was the hP measured on the 68s etc.

Also remember that HP at the crank these days is SAE Net HP, in other words they take an engine, put on all of the accessories, and then measure the BHP (Brake Horse Power). Back in the 60's the HP numbers came from SAE Gross HP--just an engine, no accessories to drag it down (like the alternator and water pump). For the most part, engines measure before 1973 were SAE Gross and engines of '73 and after are SAE Net. Please note that SAE Net HP is about 20-25% lower than SAE Gross HP.

Example: Your 345 BHP LS1 would have been rated as a 431 BHP engine back in the 60's.

 

[Edmond]

Is it true that there is less parasitic loss in a 6 speed as compared to an auto?

 

[B/STOCK]

Thank you Scissors. I knew there was a year when the formula for measuring bhp was changed. I was looking for the year and the reason for the hp differences. 73 sounds correct and your explanation of the way the bhp was determined sounds correct. Many knowledgeable Vette owners I know often remarked that a LS1 is equal or stronger than a 400 hp 427 when measured at the rear wheels. They never could give me a reasonable explation. It's been driving me just a little nuts. Thanks all for the information.
This truly is a great site. My hats off to all of you. Thanks, Michael

 

[bjcarls]

Dyno test

I know this should not be on this forum but it might enlighten some. I have a Audi A4 AWD, and on the dyno it is
126 hp at all wheels and 170hp at the Crank: roughly 126*1.38 that is the loss that A4 owners will see (data provided by other source). I am guessing that the awd has much more waste than a Corvette. Take it for what you will.

 

[Scissors]

Is it true that there is less parasitic loss in a 6 speed as compared to an auto?

Correct. A manual transmission uses a clutch to physically connect the crank to the transmission's input shaft. 1 rotation of one=1 rotation of the other.

An automatic, on the other hand, uses a torque converter (basically a fan throwing fluid into another fan). In this case 1 rotation of the crank=less than 1 rotation of the transmission's input shaft. This is where the ~5% loss over a manual comes in to play.

Edit: Also remember that that automatic 'Vettes have a lower peak torque rating than the manual 'Vettes do. I believe, though I am not sure, that this is programmed into the computer. I do know that it's done because the automatic can't take as much torque as the manual can. It's quite a bit less beefy, though still tougher than your garden-variety grocery-getting transmission.

 

[Edmond]

So slower times for an automatic could be attributed to not only less RWHP than a 6 speed, but also to the fact that you have to wait for the computer to shift?

 

[Scissors]

So slower times for an automatic could be attributed to not only less RWHP than a 6 speed, but also to the fact that you have to wait for the computer to shift?

Well, that really depends on where your computer is programmed to shift at.

The automatic shifts more quickly than most people (though not all.) Whether or not it shifts at the correct RPM is another matter.

The automatic's shifting does, however, become a liability on a track because it's harder to keep your revs in the correct range, whereas you have six gears (like you'll ever use 6th in a race) on the manual to select from.

 

[vettepilot]

NET HP actually started in 1971. Example, the 300 HP 350 was reduced from the 1970 SAE Gross 300 HP to 1971 SAE NET 270 HP. That was not only the result of NET ratings, but also of lowered compression ratios. And of course the Catalytic Converters came into our life requiring no lead gas because the lead would cling to the catalyst and reduce the cat's. performance or ability to reduce emmissions.
Then from 1971 through 1973 the high compression engines were gradually phased out until eveything in 1973 was capable of running on lowered octane gasoline. This was across the board on all manufacturers if I remember correctly. From 1973 until the mid 80s HP ratings continued to fall. This was primarily because the emmission standards, and the fact that manufactureres were having a difficult time meeting those standards while preserving performance. As Engine Control modules computing power improved, so did the performance, and incidently fuel mileage. Today we drive cars with an enormous amount of computing power, and the result is having cars coming off the assembly line like the ZO6, 405 HP, 400 ft lbs of TQ, and still able to get 28 MPG on the HWY. That's impessive, and when you drive one of these monsters it's even more so.
Stan

In fact I'm so impressed with my ZO6 I couldn't even spell impressive correctly the first time.

 

[Stan A]

Drivetrain Losses

According to GM Tech department, the following is the breakdown on loss power from the flywheel to the rear wheels:

ZF6...........................15%
4+3..........................16%
700R.........................17%

Stan