Why is the L-72 rated higher than the LS-5? - Team Camaro Tech
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post #1 of 12 (permalink) Old Apr 13th, 01, 02:04 PM Thread Starter
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Ron
 
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I was wondering why the L72 427 (390 hp) is rated higher than the LS-5 454 (365? hp).
I think they both have the smaller intake valves 2.06. I would think is they are that similer the more cubic inches would be rated higher.
I'm wondering because i'm buying a 427 and i'm curious if there is an advantage to the 427 over the 454.
Thanks.
Ron

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post #2 of 12 (permalink) Old Apr 13th, 01, 03:20 PM
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The L72 is a 425hp engine 11to1 compression solid lifter cam big valve heads 780 holley. The LS5 is 10to1 oval port heads Qjet hydraulic cam.

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post #3 of 12 (permalink) Old Apr 13th, 01, 03:24 PM Thread Starter
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OK, my mistake. Which one is the 390 hp 427?
Ron
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post #4 of 12 (permalink) Old Apr 13th, 01, 04:54 PM
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The real difference is that GM was into somewhat exaggerated HP numbers in the mid 60s and by the 70s they started to tell the truth.

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post #5 of 12 (permalink) Old Apr 13th, 01, 05:18 PM
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Not in this case. MCR recently featured a dyno test on an L72. Had just over 425hp with exhaust manifolds.
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post #6 of 12 (permalink) Old Apr 13th, 01, 05:46 PM
 
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William is correct! That was my motor they dyno'd. I actually thought we would get more out of it. Hope you enjoyed the article.

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post #7 of 12 (permalink) Old Apr 13th, 01, 05:50 PM
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oger,

Actually it was quite the opposite. GM figures have been proven to be conservative. They did this primarily to appease the insurance companies. They went from GROSS HP ratings to NET HP ratings primarily for the same reason.

As a matter of fact a LS1 powered Z-28 will actually dyno out at around 305 horsepower AT THE REAR WHEELS. This is roughly 380HP at the MOTOR and GM tells you it's rated 320HP.
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post #8 of 12 (permalink) Old Apr 13th, 01, 06:12 PM
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You asked about the 390HP not the 425HP I oun a 425HP vette and it is a whole bunch faster than a 390HP. car far more than 35HP would cause.

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post #9 of 12 (permalink) Old Apr 13th, 01, 06:46 PM
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Hey PETE, that was a great article in MCR! Really showed how tuning has an affect on an old motor. I wonder how much horsepower is hiding in mine?

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post #10 of 12 (permalink) Old Apr 13th, 01, 11:52 PM
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Chris the one thing those motors like is an equal lenght 4tube header. Not a sort of header but a true equal length. There is something wierd about HP BB chevs and the performance increases that headers bring. I haven't seen any other motor react as much to them.

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post #11 of 12 (permalink) Old Apr 14th, 01, 05:48 AM
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Chevy played games with hp ratings. The 65 Corvettte L78 396 was rated at 425hp. In 66 the Corvette L72 427 was released first as 450hp then changed to 425hp with no changes to the engine. The L88 was rated at 430hp. Chevy didn't make up the numbers but did use different RPMs on the dyno to get numbers that they wanted to publish.
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post #12 of 12 (permalink) Old Apr 14th, 01, 06:23 AM
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Hey Pete,

Great article! Congrats on getting into the magazine!
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