horsepower question?????????
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Intermediate
Joined: Jun 2005
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horsepower question?????????
i have a 1969 L36 convertible 427/390 horsepower (a/c delete, power steering delete). is this a gross or net h.p. rating? some people say the horsepower on these cars were seriously under rated, why is this? Anyone know what a realistic horsepower # would be? has anyone dyno'd?
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Joined: Sep 2005
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From: Farragut,TN
Falken, the horse power rating was gross at the flywheel with out accesroies hooked up. but with that being said most of the high output engines were mostly underrated thanks to the feds and insurance cos.
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From: NM
In '69 there were Gross rated. The Net rating did not come along till '72.
Under-rated??? Don't forget, the 427/390 was the base big block. In '69 you had three other 427s that were rated higher. If they were going to under-rate one it would be one of the high power ones. I would guess that in Net HP terms you are looking at low 300's.
tom...
Under-rated??? Don't forget, the 427/390 was the base big block. In '69 you had three other 427s that were rated higher. If they were going to under-rate one it would be one of the high power ones. I would guess that in Net HP terms you are looking at low 300's.
tom...
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Originally Posted by Tom73
In '69 there were Gross rated. The Net rating did not come along till '72.
Under-rated??? Don't forget, the 427/390 was the base big block. In '69 you had three other 427s that were rated higher. If they were going to under-rate one it would be one of the high power ones. I would guess that in Net HP terms you are looking at low 300's.
tom...
Under-rated??? Don't forget, the 427/390 was the base big block. In '69 you had three other 427s that were rated higher. If they were going to under-rate one it would be one of the high power ones. I would guess that in Net HP terms you are looking at low 300's.
tom...
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Joined: Mar 2001
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From: Living in the Hartland
Techically GM never understated the hp, they just 'choose' to use the output reading at a rpm lower than the eng's max hp rpm, the hp they state I believe is accurate at the rpm stated but is not the eng's max hp
Team Owner
Joined: Jul 1999
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From: Huntersville NC
I have a 68 L-36. I don't think GM played any games with this engine. The 390 gross hp was probably accurate. That is the equivalent of around 300 net hp (today's ratings for an engine in a new car) so it would be similar to the LT1 vettes of 92 - 96, but produces more torque.
I would guess a factory fresh L-36 would produce around 270 rwhp on a dyno. With headers and exhaust and some carb and distributor (timing) tuning I got up to 300 rwhp.
I would guess a factory fresh L-36 would produce around 270 rwhp on a dyno. With headers and exhaust and some carb and distributor (timing) tuning I got up to 300 rwhp.
Instructor
Joined: Apr 2006
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From: Wallaceburg Ontario
I've always been told that the difference between gross and net horsepower is about 20%. If that was totally accurate, you'd be lookin' at 312 net horsepower at the flywheel. Net flywheel to rwhp probably depends largely on your transmission (automatics use up more, I think), rear end, tires, etc.
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From: Orange County Ca
I have had my 69 427/390 mostly stock on the dyno. PRNDL is right on the money. Rear wheel ratings of 360 tq and 270 hp. I then switched to Hooker headers and side pipes. I believe I picked up noticable hp. Anyway, it really sounds cool.
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From: Va. Beach Va.
Originally Posted by glenkov48
I have had my 69 427/390 mostly stock on the dyno. PRNDL is right on the money. Rear wheel ratings of 360 tq and 270 hp. I then switched to Hooker headers and side pipes. I believe I picked up noticable hp. Anyway, it really sounds cool.
http://www-unix.oit.umass.edu/~tcroy/horsepower.htm