Hi there,

here are 2 pages coming from 73s magazines.
1 is for SAE gross HPup to1973
in the other page you can see the SAE net hp for the 73 L82 and 454.

Using as reference the datas of 73s engine is possible to obtain the net hp of all the other pre 73 vettes.

1973 l82 sae gross= 320HP , sae net 250hp ( less 22%)
1973 454 sae gross= 370Hp , sae net 275hp (less 25%)

so applying these 22-25% , the power of the older 350 cid engines seems not so big anymore in respect to 74-82 Corvettes...
also , the increase of the CR from 9:1 to 11:1 on 350s , seems to give a power increase of not more than about 30-35hp net...
Great engines anyway...
Tomorrow I'll probably go to see a 1969 red 350/350 for sale. can't wait....

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Your argument doesn't hold water here. Try driving a pre smog Corvette, big or small block and you will understand what I mean. The older cars have tons more power than the mid 70s cars. Sae gross or net these cars were down on power. Remember, an L-88 had a reall power figure of around 500 horse.

 

Part of the reason for the dogginess of the mid-seventies ('75 on) was the cat. The first ones were very restrictive and also only one of them. Not to mention timing, cams, carb changes, etc to cope with the ever increasing smog regs of the time.

 

There is another reason that horsepower ratings dropped in 73. At the begining of 1972 Chevy changed the way they rated horspower in order to appease both the DOT and the insurance companies. Up until '72, they rated at the crank, in '71 an LS5 454 was rated at 365hp at the crank... about 290hp at the rear wheels... and it produced 395 ftlbs of torque. The exact same engine in '72 was rated at 270hp with no changes in compression. In 73, the LS4 was rated at 275hp, but still produced the same 395ftlbs at the rear wheels. By droping the compression, and changing the cam to work with the incoming unleaded fuel... it still produced almost 365hp at the crank.

Hope this helps with that pesky horsepower loss... this bothered me for years until I found an obscure note in the Corvette Black Book that set me straight.

Wedge
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From Mike Yager's Corvette Bible:
1970 LS-5 390/500
1971 LS-5 365/465 (dropped the CR for unleaded gas) [:'(]
1972 LS-5 270/390 (went to SAE net hp) []
1973 LS-4 275/380

 

My first clue was the console tag on my 73 454. It said 395ftlbs for torque... but no hp listing. So for years I'm thinkin... how do they fo that with no changes to the tranny. Then I found that statement in Antonicks Corvette Black Book that said the rating system had been changed from the crank to the rear wheels... the same place the other motor companies rated from. Bottom line... my 73 out of the box still gets outa its own way, almost as quick as my old LS6.
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I'll note your torque figure in my book. Not the first error I've found in Mike's book.

I got a console tag for a '71 for my L-82 that was close to my gross hp.

 

I'm searching on the net , but can't find the specs of the engine parts that differs from a 69 350/300 -350/350 and 70 LT1.
I mean the differences in terms of : cam , carb size, intake shape , heads...
which parts makes the difference of power among these engines?

 

Look for Alan Colvin's book Chevrolet by the Numbers. It is in 2 volumes, up to '69 and '70-75. It has the casting numbers for all parts,, broken down by year and application.
Hope this helps.
Wedge

I believe he also has one called Corvette by the Numbers also.
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How'd you reply? I can't get more than ten words thru.