markKlein

As most of you know (and some of you remember), in 72 they changed from "gross" HP ratings to "net" ratings they use today. I know I have a rule of thumb I use to try and compare numbers from the "good old days" to current ratings, I was just wondering what everyone else uses.

(I know there are tons of variables, but as a general guideline, what do you use?)

dukeallen

I remember being told to knock off 20 percent. YMMV.

c4cruiser

A Google search on "gross versus net horsepower" turned up this

93Rubie

These numbers are from a chart on page 183 from Dave McLellan's book Corvette From the Inside

1970 LT1 370HP gross, 325 HP Net

1992 LT1 300HP Net

Dave states in his book it was called LT1 in 92 because it was the first small block to exceed the legendary engine of 70 in performance.

As we all know a 1970 LT1 Corvette is a sought after and held as a highwater mark of Small Block development.

Food for thought...

bb62

No, the change happened in 1971 where GM published BOTH gross and net ratings. For the Corvette, the following ratings were:

LS6 - 425HP Gross, 325HP Net
LS5 - 365HP Gross, 270HP Net
LT1 - 330HP Gross, 275HP Net
L48 - 270HP Gross, 210HP Net

What is interesting to me is that performance of the 325HP net rating for the LS6 and the 330HP of the C4 LT4 is almost identical - there must be something objective about the Net numbers.

not08crmanymore

Wait,according to this,the 70 beats the LT1 by 25 net HP.

James93LT1

http://www.s-series.org/htm/tech/GMP...ts/014-019.pdf
LT4 375hp Gross
LT4 330hp Net
LT4 300RWHP average on Dynojet

93Rubie

Yes, but that is not the WHOLE picture. My 93 will walk all over a stock to stock comparison of a 70 to my 93, in a straight line and other wise. I said, "performance" not HP. HP is not everything, weight, gearing, tires, DRIVER, etc...are huge factors. Hope this clarifies my statement.

Gross numbers are with no engine accessories, like water pumps, alternators, etc...open exhuast systems, etc....VERY unrealistic.

Net Numbers are with engine accessories and full exhaust, etc...VERY realistic.

Older Gross Numbers are a joke, engine might make that HP but it NEVER will when installed in a actual car.

Today's numbers are in a era of VERY strict emissions and fuel economy requirements which make them all the more amazing, then again not really all things considered.

mashinter

Dave's book on page 71 has: " 370 ghp equalled no more than 300 nhp."

Also on page 71: "the '92 LT1 outperformed the original LT1 both on the dyno and in the car. A heavier car rated at 300 nhp would beat a lighter car rated at 370 ghp."

I think the chart is wrong.

Paul Workman

Peak or gross hp is a trap.

Something MOST focus on to the exclusion of everything else (besides 1/4 mile results) is the peak HP. Power under the curve means a lot more than HP at a single rpm value. My wife's little L46 with it's mild cam and headers is crowding 400 FWHP. But, my 300 net 95 LT1/M6 would eat that C3 of hers - 4:10 rear and all, any way you wanted to test them.

Same is true for most 2-valve V8s vs. the LT5s. The looooooong, relatively flat torque curve allows the characteristics of the LT5 to compete with other 2-valve, pushrod) engines with as much as a 25 HP "advantage".

A couple years ago I was driving Ami's 69 C3 vert with the L46 w/ the cam, etc and 4:10 rear & M4. =Jeff= was following me in his "lowly" stock 375 HP LT5/ZR-1.

The country blacktop was clear for a good half mile, and so I dropped the hammer and rowed through the gears, letting the little SBC pound it's heart out in all 4 gears before I looked up into the rear view mirror.

I expected to see =Jeff= back there, maybe 4-5 car lengths, but catching up. SHEEEIIIIITTTT!!!! You would have thought I must have had a tow rope attached to his car, cuz he was right there on my bumper - big "chit-eatin' grin and all!!

HP claims are fun to talk about. But, trap numbers talk, and HP walks. Most of the HP claims amount to just so much dick measuring. That extends to dyno numbers too, except for relative measurments as part of a tuning session.

P.

bb62

Paul,

Except that 93Rubie is wrong. The 1970 LT-1 is a potent machine that has better torque under the curve than the latter C4 based LT1. See the following for a discussion and comparative torque curves for the 70 compared with a 96 LT1:

http://www.vetteweb.com/tech/vemp_10...e/viewall.html

The 70 even weighs a little less than the 93. For straight away acceleration, there is not much that the 93 would have over a 70 for this engine. Comparing contemporary tests would not be fair as the old 70s were using bias ply tires are the time. Both cars are mid 5 sec 0-60 and high 13 sec 1/4 mile cars.

James93LT1

Neat article, but to be fair, I think they should have used a electric water pump on both engines.

93Rubie

Indeed you are correct, I checked that page. I have noticed some minor hicups in the book but otherwise great read.

93Rubie

Not sure on the weight but the books I have state a 70 LT-1 is a little heavier C&D has a Jun 71 LT-1 listed at 3370 which is slightly heavier than a 93.

That is a interesting article but they sum it up saying they share a LOT in common in power output.

As far as 70 vs. 90's LT1 performance in a straight line, Dave McLellan states on page 71 of his book, "When we introduced the new LT1 in 1992, we gave it its historically important designation only because it OUTPERFORMED the original LT1, both on the dynomometer and in the car. A heavier car rated at 300nhp would beat a lighter car rated at 370ghp. " So maybe the 70 is lighter, IDK???

So no offense but who am I going to believe you or Dave McLellan?

FYI, I run mid 13's. (13.48 Personal Best) and typically trap 105ish. I've ran as fast as 108.83. I bet I can run low 13's pending better 60 foots, I'm working on that.

It would be interesting to run a couple bone stockers (with equal tires) I bet it would be close.

Regardless, BOTH engines are legends in their own right. I think the 70 with its solid lifters and radical cam has more character but the newer LT1 gets the job done and kept the car very competitive in the 90's. It also paved the way towards the LSX series of V8's.

GREGGPENN

I dunno. (In your best wiseguy voice say...) Hey...whaddya godda do to sell some new detroit around here, uh?

Seriously, I'm still not sure enough has been qualified on the OP without going into emano-emano comparisons?

What about drivetrain losses in auto's vs stick's? Are you trying to compare the engines or the cars?

93Rubie

I think the OP gets the whole gross versus net thing by now, at least I hope so. It has been well defined at this point.

I think Dave was comparing the engines and the cars, so both.

We don't have to worry about stick versus auto the 70 LT-1's where all stick only as far as I know.

I do not disagree with bb62's assessment of torque curves of the LT1's. I do think a typical 90's LT1 would be faster, but like I said a race between a 90's and a 70 would be close with equal tires. Just pointing to what Dave M. said, he is probably smarter than us all on Corvettes so...

gunnerjuju

Wow very informative tread. Thank you all

markKlein

I know the difference, I was just trying to see what gross numbers others used to try and compare. i know there are tons of factors (what about deliberaely underreporting HP in the sixties?), but for high level comparison I will continue to subtract 20-25%, or add 25-33%.

Thanks everyone for your input.