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Old 05-19-2008, 03:31 PM
glen242 glen242 is offline
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I need intellegent input concerning HP ratings.

Many people say they have a 400-500 HP SBC. Displacement from 327 to 400 CI.

Where these HP numbers come from is usually not quoted, but very rarely, an engine dyno is cited, numbers usually supplied by whoever sold the engine.

A chassis dyno reading, and I know these numbers can be massaged, is usually never supplied by the car owner, so that a comparison can be made between engine and chassis dyno numbers. Rule of thumb was, I believe, 15-18% manual and 20% and up automatic drive train loss. Does this "rule of thumb" still hold true?

My prior 350, stock 180HP, according to GM, with a cam, new heads, 9.2CR, long tube 1 5/8" headers, ST10 transmission, and Performer intake, measured 217 RWHP on a Mustang dyno. Using the 20% loss figure I came up with 271 Engine HP. Not too bad, I thought. Was my math correct?

I guess what I am asking is "how do you know what your engine specs are if it has never been on a reputable engine or chassis dyno"? Some say 1/4 mile speed will tell you, but how about driver error during the run, wheel spin, etc.? Computer sims can be manipulated, by what is input, to give different results.

I see people stating they have 450-500 HP on engines that are less built than my present 383 and wonder where the numbers came from, as they are usually never stated. Are we turning into ricers where we take each alleged HP increase from each separate aftermarket part and add them together and then add the total of them to our factory HP?

Maybe I'm just an old fart, but I find it hard to believe that 1.3 HP/CI, in a 383, is easy to get on a NA STREET CAR.

I once told someone on a Corvette Forum that there were more 400+ HP SBC cars on the internet than on the street, and I stick by this statement.

You might want to consider this post just an old man/hotrodders vent.

Comments welcome.
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