After reading the great debate what is the true horsepower of my 300 horse 350? Did Chevy fudge all the numbers?
Thanks,
Mike

[brad6899]

hmm... this one is anybody's guess. Well, a new 350 crate motor with the same cam and 8.5:1 compression does 240hp through iron manifolds (265 with 1-5/8 headers). I am guessing with 10.0-10.25:1 compression add 15 hp to that number (maybe a little more). more importantly is how much did they fudge the toruqe (not to mention those numbers are generated on late 60's leaded gas)

[FrankP]

Didn't Chevrolet change from Net to Sae HP
ratings in like 72 or 73? Also what is the difference between the two and does either correlate to rear wheel HP at all?

[brad6899]

Yup, that too Think of it from the top down, lets say that the net is 10% high off the gross (300-10%=270) so 270 hp is the "net" on a hi compression engine. Then figure also their can be a lot of difference due to ignition tune, closed or open air filter, dual/single exhaust, size of the pipes (and design of the system) etc etc etc. I think the figure of 255 is probably pretty close. I think the torque figure on a 350/300 was 380lbft (lets assume that is 10% high) so probably around 345 lbft. OF course, at the rear wheel: take off 20% (guess) of both of those 255/345 = 205/275 at the rear wheel (which is still pretty decent for performance)

[Kyvox]

Before 1971, engines were rated at brake horsepower at the flywheel. in 1971 they switched to sae net horsepower, which is at the rear wheels with all accessories (air, ps, alt. etc.) running.

[Peter Constantine]

Kyvox-You're right about the change from gross to net HP,but I think the figure was still generated at the flywheel.Rear wheel numbers would be significantly lower.I could be wrong,but I think this is correct.

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HDZ/28

[travis]

Actually, net is with all accesories but is still at the flywheel. Net is also with the carb calibrated a couple of percent rich and the timing retarded a couple of degrees from factory specs so they get a more realistic number. Gross rated engines usually had a bit of supertune to them...optimized timing and jetting, no air cleaner, etc.

Here is the reason I'm asking,
chevy rated their mild 350 hydraulic lifter motor at 300 hp that same year. road and track stated 350 hp, sports car graphic claimed 370 plus,and car life was 400, just enough to spank a 468 maybe.
I dont know if this is correct has Chevrolet fudged all the numbers? I mean the 302 is a classic mirep now look this pops up.
Mike

I took the above quote off of the still a z 28 thread

[JohnZ]

Magazines (especially in those days) didn't have dynos, and they didn't rate engine power - the manufacturer did. All the magazines could do is talk about what it "felt" like, and those are Journalism majors talking, not engineers

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JohnZ
CRG
'69 Z28 Fathom Green

[KevinW]

I had my 350/300 rebuilt STOCK! flat tops, 041 heads, NOS 350/300 cam, 184 intake, not decked. Only deviation from stock was 1.94/1.60 valves, pocket porting and 2 valve relief pistons. CR should be 9.8-9.9 (instead of 10.25) with composite gaskets.
Per the machine shop guy and his piston books, he thinks it's 325 HP. I should know what the engine feels like this spring! Can't wait!

Kevin

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69' SS-350 Convert, M20, 3.55 posi. Totally Disassembled & in boxes (I'm working on it!)
69'(Hugger Orange -originally, Burgundy now) Z-21 Convert 327/PG, Driver

[This message has been edited by KevinW (edited 02-07-2002).]

[Sleepy-69]

I missed the 'big debate'.

I don't think the numbers were fudged. 300 ponies gross would mean about 250 at the rear wheels. One of the rags back in the day took a new 69 SS-350 4-speed with 3.55's and turned in high 14's on 14" 6 inch polys. Perhaps someone remembers specifics. But, that's at least 250 "net" hp.

And the 302, produced more than the advertised 290 hp. Some have stated from 325 to 340...this one was fudged in reverse to ensure insurance companies would keep writing policies on Z's.

My opinion.