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Old 07-02-2013, 10:45 AM   #1
snowwolfe
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Default Question about earlier HP ratings

I have always been confused about how the HP ratings were different in the older days and why most of the big block cars of the mid to late 60's such as the C2 did not run as fast as the modern C6's. Thought I would ask the question here since you guys know your stuff.

I'll toss out an example. A 67 427/435 hp. If this motor was ran on the dyno today how would it rate? A 436 hp C6 would put down about 390 rwhp.

Not trying to start a debate as my all time favorite car is a 67. Just trying to understand why these older jems did not run as fast as todays cars.
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Old 07-02-2013, 10:53 AM   #2
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Old rating pre 71 was gross new is net. Anther reason old cars seem slow is becouse of the tires of the day
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Old 07-02-2013, 11:14 AM   #3
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What would a old gross rating of 435 equal in todays world?
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Old 07-02-2013, 11:31 AM   #4
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It isn't just the peak HP, but rather the greater average Tq and HP across teh RPM band that makes todays cars faster.

I would suggest that a factory stock 435/427 would put down about 350-370 Tq/350-370 HP to the rear wheels, Headers, ported heads, modified exhaust and a better intake would increase those numbers by 30 or so


A few years ago, I built a 427 small block, with modern heads that breath, and a modern cam, and even at 9.3:1 CR, it puts down more average HP than an old L88 ever did, even though the L88 would have a peak Tq and HP that is 15-26% higher higher than my motor, because my Tq curve is almost totally flat, where as teh L88 is very peaky, without much bottom end.

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Old 07-02-2013, 11:41 AM   #5
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There's no set conversion factor, plus the fact that advertised HP may or may not have been what the engine actually developed. Some ratings were deliberately toned down to get the insurance crowd off their back amongst other reasons.

As a wild guess:

Assuming the 435 HP claimed was legit peak HP. To convert from gross HP to net HP, let's deduct 25%. This percentage seems accurate because that's the difference shown in GM numbers in 1971 when both gross and net were advertised.

Net HP: 326.

You're asking about RWHP, as measured on a dyno. Again, there's no fixed conversion ratio from Net HP to RWHP. Let's say 20% loss for a Muncie four speed

RWHP: 261.
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Old 07-02-2013, 01:07 PM   #6
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cool thread
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Old 07-02-2013, 02:00 PM   #7
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My lightly modified L79 put down 292 RWHP, and 302 RWTq.

Lightly modified: Bow Tie heads, headers, and aftermarket intake and Holley 650 DP with L46 350/350 Hyd cam The factory CE shortblock had about 40K miles on it at that time. I would think an extra 100 CI, even unmodified, would beat that, by some amount.

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Old 07-02-2013, 02:12 PM   #8
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Quote:
Originally Posted by AZDoug View Post
It isn't just the peak HP, but rather the greater average Tq and HP across teh RPM band that makes todays cars faster.

I would suggest that a factory stock 435/427 would put down about 350-370 Tq/350-370 HP to the rear wheels, Headers, ported heads, modified exhaust and a better intake would increase those numbers by 30 or so


A few years ago, I built a 427 small block, with modern heads that breath, and a modern cam, and even at 9.3:1 CR, it puts down more average HP than an old L88 ever did, even though the L88 would have a peak Tq and HP that is 15-26% higher higher than my motor, because my Tq curve is almost totally flat, where as teh L88 is very peaky, without much bottom end.

Doug
And how many $ per hp with that small block 427 ?
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Old 07-02-2013, 02:36 PM   #9
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Quote:
Originally Posted by 63split63 View Post
And how many $ per hp with that small block 427 ?
My 427 SB cost about $12 per hp.
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Old 07-02-2013, 03:01 PM   #10
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Quote:
Originally Posted by 63split63 View Post
And how many $ per hp with that small block 427 ?
A bunch. Most of the money was in the Dart block, Dart Pro1 CNC heads Callies crank and custom EFI. The rest just sort of added on from there. But, the motor will run past 7000 RPM, even though it is pointless since power starts falling off quite a bit sooner than that.

No biggie, its only money.

Doug

Last edited by AZDoug; 07-02-2013 at 03:04 PM.
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Old 07-02-2013, 04:47 PM   #11
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I did a couple of dyno pulls on my stock 427 L72 two years ago for a real tune up and to set the AFR:s across the RPM band and ended up with 291hp/ 331tq at the wheels in stock config.

I did a few more pulls last month but this time with a few mods added and gained +14hp/16tq to 305hp/ 347tq at the wheels.
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