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Originally Posted by hjennings
Net vs Gross horsepower. They used to measure the HP without the accessories, now they measure them with (that started that in '71 or '72 I believe).
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The difference between measurement at the engine output, and output to the wheels is what it was explained as to me. Sounds pretty similar though, previous was output of just the motor, current is output of motor and everything else. '71-'72 sounds about right as well. *Somewhere* in my stuff I actually have a report and charts that I did back in college (in early 80s) on just this subject, the change in HP rating.
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Some of the specs are hard to find on these old engines. I've found some data on the heads that says the flow about the same as a 350 from that era. That sounds OK, except those flow numbers are total, and the V8 is split between 8 cylinders while our engines are only feeding 6 (so less flow per cylinder).
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Okay, I guess I don't understand flow...
Flow of "X" divided by 8 cylinders will be less than the same flow divided by 6 cylinders. Flow of 48 divided by 8 would be 6 per cylinder while the same 48 divided by 6 would be 8 per cylinder.
The other way to look at it is that if the flow is the same as a v8, they might mean the flow per cylinder is comparable.
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I said above I'd probably go with a 305E engine. My thinking there is it probably has the most flow per cubic inch of any of the GMC V6 engines. If somebody can confirm or deny this please let me know. I'm sure it'd be between a 305E and a 351E (Magnum heads). The 351 may be the one to use. Not sure until I find the flow numbers.
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305 E isn't magnum. a 305 is a 305 is a 305, essentially.
351E or M is the magnum vs. 351C.
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500hp is a complete wild *** guess. I hate evening saying that, as we have built several engines and can usually tell a customer what a certain combo will make and the dyno is always really close. With a buildup of a turbo GMC V6, it's never been done. So who knows. A big part of it is how much boost and how many RPMs the block/crank/rods can take. I'm guessing that these engines are very strong (as far as how much HP they can take.... they've never been tested at any sort of limits). So who knows, might be able to handle some insane boost levels.
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Since you have in a previous posting mentioned changing the weight of the internal components, previous experiences may not apply... but stock these engines do not take high RPM well. Being so solid and heavy they seem to come apart if the revolutions are taken too high. Got mine stuck, tried to power out, and spun/destroyed bearings (ultimately threw a rod, but that was my fault for using it before fixing it, but indicates damage was done due to the high revolutions).