captras

Can anybody tell me what the horsepower rating at the flywheel is for a 75 L48 engine. I know the BHp is 165, but since GM changed the way they measure Hp in the 70's, I am trying to get an idea how it compares to late 6-'s early 70's 350 engines.

Thanks

Tom73

All factory HP ratings are at the fly wheel. The rating change was from GROSS HP to NET HP. Gross is the bare engine without any accessories, no emission, no water pump or alternator, no P/S pump, open air intake system, headers and an open exhaust. Power is rated at the fly wheel.

Net is with all standard equipment in place and working; emission, alternator and water pump, stock air intake assembly, stock exhaust manifolds with stock exhaust including mufflers, etc. Power is rated at the fly wheel.

tom...


[Modified by Tom73, 4:56 PM 5/24/2004]

captras

Well, actually, what I have read indicates you are not quite right as per this quote from a tech site on the internet that explains net vs gross:

"Net horsepower, by comparison, is a measurement taken at the driven wheels of a vehicle on what's called a dynamometer. This is done by placing the vehicle's driven wheels on a large roller and accelerating the wheels up to redline in first or second gear. The vehicle's ability to turn this roller is measured and calculated to come up with a figure that represents how much horsepower is actually available to move the vehicle around. Because a frictional loss between the engine and the driven wheels is unavoidable, wheel-driven horsepower will always be less than net horsepower."

So, my question is still unanswered...being...does anybody know the gross horsepower of a 75 L48.

Pete79L82

That statement is wrong. Tom73's description is correct. GM, nor any other manufacture to my knowledge, ever use a chssis dyno to rate HP. The ratings, regardless of net or gross, are always done on an engine dyno and measured at the flywheel.

So the "net" HP rating of your 75 L48 is 165HP at the flywheel.


[Modified by Pete79L82, 7:43 PM 5/24/2004]

captras

Well, regardless of who is wrong or right...I really wasnt looking to get into a debate of where it is measured....I just wanted to know if anybody knew the difference between the gross and the net....but...seems a simple question cant get a simple answer....Thanks anyway!

Pete79L82

There is no direct corallation between net and gross numbers. The closest you can do is guesstimate. If you look at the difference between base motors on a 71 (270HP gross) and 72 (200HP net) you can see that the net numbers are about 26% lower than the gross numbers. These motors were very close to the same. If you use the same corrilation on the 75 165HP net motor it would give you 223HP gross. Not an exact number but it may be close enough for what you want to do.

Hope this helped.

Pete


[Modified by Pete79L82, 7:55 PM 5/24/2004]

flynhi

From what I've read over the years, generally speaking, net on a car with an auto trans is about 20% less than gross. On a 4sp, net is about 18% less than gross.

Tom73

I have always heard that it was between 20 and 25% difference between net and gross. But it is a very inexact ratio. Will very highly by the types of engines (high performance vs sedan engines) and will have a higher percentage on the earlier engines than on the later engines (later are more efficient then the earlies).

tom...

page62

All of this said, it should be noted that one of the primary reasons for the '75 L48 having such low HP ratings is the highly restrictive catalytic converter. Remove or replace the cat...and voila! Instant HP increase. :yesnod:

captras

Yea, it gives me a ballpark...thanks!!! :hurray:

Tom73

Will,
Why would the transmission make any difference on Net and Gross since both HP ratings are at the flywheel?

tom...

wcsinx

:rolleyes: You got the simple & completely correct answer from Tom73. The article you quoted is referring to RWHP (rear wheel horsepower), and also as you were told there is no car manufacturer which provides this rating.

mandm1200

There are differences of opinions about gross versus net horsepower. Here is a link of one explanation and the one I feel is correct.

<http://www.edmunds.com/ownership/techcenter/articles/43845/article.html>
Gross horsepower is what the manufactures currently use and used for most of the time. There was a period of time when they used a net horsepower rating, which is totally different. Insurance companies didn't like the idea of 300+ horsepowered cars and charged higher rates for them. The car companies then started to use net horsepower figures in the 70's and it showed a significant drop. Joe Consumer likes to brag about hp and to make things equal across the board, manufactures now state gross horsepower. I am not convinced that running an alternator, emmisions, and air conditioning is going to eat up 75 horsepower or 26%. That 26% was due to checking the horsepower at the rear wheels. If you think about it, what is more important, hp at the flywheel or hp at the wheels?
Although Chevy used simlair engines there was a considerable drop in hp. Was it the catalytic converter or was it where they established the hp rating?

Mike

Tom73

Here is a link to a write up on Gross vs Net vs Wheel horsepower issue:
http://www-unix.oit.umass.edu/~tcroy...horsepower.htm

tom...

flood

I used the g-tech on my 75 L-48 4 speed. it came out to like 162hp.

Thats at the wheels I believe. All stock except rearend gears 3.70.

Also thats at 4500ft :cheers:

wcsinx

:iagree: I've always heard it explained the way this article does. I think a lot of people are confusing wheel and net hp.