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Old 07-18-2003, 12:27 PM   #1
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Default How much horsepower does a stock Z28 have?

Hi, I was curious what a stock Z28 has for horsepower, not to the ground though, I know when you read about them they say 305 or whatever but has anyone heard of any test done that show more for a stock engine? Thanks.
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Old 07-18-2003, 12:40 PM   #2
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Default Re: How much horsepower does a stock Z28 have?

I've never read anything about that, but I would imagine (given the car was a copmletely stock M6) it would be around 360-370 bhp (conservitively speaking).

Anyone else have any hard proof info to add?
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Old 07-18-2003, 12:59 PM   #3
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Default Re: How much horsepower does a stock Z28 have?

uhhh... they are rated at 305hp from the factory, common knowledge. Also common knowledge is that they are grossly under rated and will normally dyno ~300hp-310hp (auto) and ~310hp-315hp (manual) stock.
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Old 07-18-2003, 01:04 PM   #4
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Default Re: How much horsepower does a stock Z28 have?

ohh? okey, hmm I am curious do you know why GM rates the cars so low then? like in the magazines you always see around the 305 range, but the reason I brought it up is I had a few people in the past ride in my car, and they have owned some fairly high hp rated cars back in the day, seem to think the Z28s have more than 305 just by them driving in the car, so that's kind of what made me ask, thanks for the info.
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Old 07-18-2003, 01:06 PM   #5
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Default Re: How much horsepower does a stock Z28 have?

ok now i am confused, the factory hp, is that to the ground? like when you read 305 are they saying that dynod that much? or just saying total hp is 305?
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Old 07-18-2003, 01:10 PM   #6
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Default Re: How much horsepower does a stock Z28 have?

The factory rated horsepower is supposedly flywheel horsepower. However in the case of the F-Body's that are rated 305hp, they are under rated by approximately 50hp. They in fact should be rated around 360hp-370hp like MOBE said. The rear wheel horsepower these cars put out is what I quoted above.
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Old 07-18-2003, 01:12 PM   #7
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Default Re: How much horsepower does a stock Z28 have?

oh wow!! geez so they really do under rate these cars, that's interesting, thanks for the info, I never relaized they were rated like that, thanks.
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Old 07-18-2003, 01:13 PM   #8
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Default Re: How much horsepower does a stock Z28 have?

Quote:
ok now i am confused, the factory hp, is that to the ground? like when you read 305 are they saying that dynod that much? or just saying total hp is 305?
Factory hp ratings are supposed to represent bhp (brake horsepower), i.e. power at the flywheel with the engine in the same configuration as it would be in the car (exhaust, cats, accessories, etc).
In my experience, GM's factory ratings are pretty accurate - unless you're encroaching on Corvette territory
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Old 07-18-2003, 01:42 PM   #9
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Default Re: How much horsepower does a stock Z28 have?

Pardon me!

I inturpreted the question incorrectly. I guess?
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Old 07-18-2003, 01:44 PM   #10
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Default Re: How much horsepower does a stock Z28 have?

oh no actually you answered what I was looking for too, I was just getting confused with the base hp rating, thanks.
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Old 07-18-2003, 01:50 PM   #11
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Default Re: How much horsepower does a stock Z28 have?

White2000Z28, I think what these people who rode in your car meant was that they had hot rods or muscle cars back in the 60's and 70's. Back then cars were rated differently. In '71 or '72 (someone correct me if I'm wrong) the Society of Automotive Engineers mandated that horsepower be rated in net terms, meaning that exhaust, drivetrain, etc. be attached when making the measurement. And of course we all know that all these things reduce horsepower (as opposed to measuring simply how much HP the engine alone puts out). So, a '69 Ram Air IV GTO, which I believe was rated at about 360-370 horsepower, would probably be more like 290-300 by today's standards. I hope this answers your question. Anybody else feel free to add more if I'm not correct here.
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Old 07-18-2003, 02:11 PM   #12
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Default Re: How much horsepower does a stock Z28 have?

hmm I see, yeah that makes a lot of sense, yeah because I get a lot of people when I first got my car they would ride in it, and it would seem as fast as there old muscle car to them, and they had a lot more hp in there car, so maybe that's the thing, just like you said.
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Old 07-18-2003, 02:20 PM   #13
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Default Re: How much horsepower does a stock Z28 have?

And actually, if you look up old quarter mile times from the old muscle cars, a lot of them weren't all that quick (especially considering how much HP they supposedly made). The old GTO Ram Air III's and IV's had great HP ratings but they only ran high 13's to low 14's, so the belief that cars were so much faster back then is really a misconception. Right now, engines are much more efficient and making much more horsepower than they ever have.
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Old 07-18-2003, 02:23 PM   #14
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Default Re: How much horsepower does a stock Z28 have?

yeah you are right, I have read 1/4 times on older muscle cars and noticed that same thing you said.
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Old 07-18-2003, 02:45 PM   #15
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Default Re: How much horsepower does a stock Z28 have?

The 69 RAIV motor was under rated! The reason they ran high 13's was the 60's type of tires. During testing they would spin both tires the entire 1/4 mile.

If you added Slicks, bone stock, it would run mid/ high 12's... With headers and exhaust they were in the high 11's.

But the way the Factory rated them changed in 71/72.
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Old 07-18-2003, 03:13 PM   #16
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Default Re: How much horsepower does a stock Z28 have?

I disagree. The old stuff was not that fast.

Put a big slick, open headers, and tune the car for 100 octane and they would run just as good with a much smaller engine.

Heck a lot of old musclecars run in the 14's and run 14 second mph.

Our cars do 300rwhp easily, and that's more like a 350hp motor not a 305hp motor as rated by GM.
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Old 07-18-2003, 04:03 PM   #17
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Default Re: How much horsepower does a stock Z28 have?

It had alot to do with the old school 7" wide, hard as rock, non-gripping tires offered in the late 60's early 70's. With the tire technology now, I think the quoted times of old muscle cars would be much quicker.
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Old 07-18-2003, 04:09 PM   #18
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Default Re: How much horsepower does a stock Z28 have?

Do one thing, Install a 7" rim on your car along with a E-70 bias ply tire and see how well it runs...

Plus the GTO's and Chevelles were as aerodynamic as a brick...

Truth is, Some motors were over rated, some were under rated. I chose to chime in because someone picked the Ram Air IV motor as an example. That motor was a HORSE.

I saw them when they were new, and I've owned over a Dozen F- body's from a 71 TA to a 99 Z.

I'm not taking anything away from the new cars, FI, Computers, Chamber design, ect has made them very fast and reliable.
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Old 07-18-2003, 04:28 PM   #19
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Default Re: How much horsepower does a stock Z28 have?

Look at the mph they ran. They did not make as much power, and the cars were tanks. Look at how few of those cars went over 100mph in the quarter stock. The trap speed would not be adversely affected by the lack of traction.

Sure my buddy's 69 Camaro SS went 11's with open headers and 4.88 gears but that was not stock and I don't recall how much he advanced the timing. That was not with the stock intake and carb either.
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Old 07-18-2003, 04:35 PM   #20
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Default Re: How much horsepower does a stock Z28 have?

Ahhh... But the oldies are so bad *** looking tho.

One of the coolest things I ever saw at the track was a '68 Camaro run a 7.2 @ 189. Now thats movin!

Of course tho, it looked like a nuclear power plant was growing out of the hood, and he was spraying a 300 shot, I believe.
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Old 07-18-2003, 04:35 PM
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