[73XR-7owner]

ok, so it's a non-motorhead (translation: bonehead) question, but will somebody please tell me how horsepower is measured? i don't mean by ford or GM, but when the guy who had my car put the new engine in, how did he know what the hp was???

 

[68XR7]

Prior to 1972 it was measured at the flywheel with nothing else attached. This was the "gross" hp rating. 1972 and up is measured at the rear wheels with all accessories attached. This is the "net" hp rating.

 

[modifiedmark]

It has to be put on a dyno. There are two kinds, a engine dyno and a chassis dyno. The engine has to be physically bolted to a engine dyno and therefore it has to be done out of the vehicle. The chassis dyno works by tying the car down with its drive wheels on a set of rollers, and it will mesure hp at the back wheels.
Either setup is not exactly cheap and they are time consuming enough that the avarage Joe will not bother with it.
I would bet that your cars previous owner didnt bother with it either and his quotes to you on hp were just a guess. Alot of people try to tell you what there hp is but unless they actually had it dynoed they dont know and are useally just ending up telling a big fish story.
There is a computer program out there called desktop dyno and some people think its accurate. I dont have any experiance with it but I belive there are too many variables involved for it to be completely accurate unless you know everything involved with the engine, down to head port flows, exact compression ratios etc, so it would be just a round about figure for most people. mm

 

[73XR-7owner]

thanks, mark, that's the answer i was looking for...

yours is helpful, too, 68, but i was asking about it literally.

so in reality, there aren't many out there (and probably on here) who REALLY know what their actual horsepower is. most people just start with whatever ford tells them the 351C or W or CJ or whatever, 2V or 4V puts out, then they add for the mods they make based on, what, gut feeling?

not very freaking scientific is it?

 

[ChadInman]

Yeah sadly this is mostly true. It can be pretty expensive to dyno a car so it's not like you can do it with every mod unless your name is "Bill Gates". most of the people who fib about hp are import drivers, as we all know, you can not make an import fast. - Chad

 

[73XR-7owner]

ok, so where does the HP guess come from?

is there a book or a website that says, add this to your engine and get X horsepower? maybe it says on the side of the box...

my reason for asking about this is that i was told i have 325 horsepower. whether that is true or not is irrelevant to whatever horsepower i actually have, but it would be nice to know approximately what the real number is. how would i go about figuring it? where do i get the information?

 

[Logan]

Getting dyno'd isn't as expensive as you think. Find a local speed shop and go for it. Most shops offer 3 pulls for around $50-60... I've never paid more than $60 and you get handy dyno sheets like these...


This is from my Lightning...

 

[modifiedmark]

Logan, your right that is pretty reasonalble. I never really checked it out but offhand I never have heard of a shop around here haveing a chassis dyno. I'm sure that there around if I checked into it as I'm only 60 miles from Chicago. I dont think you could get any of the "elite" from Chicago to do it for that price though.mm

 

[73XR-7owner]

that is pretty cool, Logan....

and of course it begs another question. Wouldn't the gas you used that day and maybe even the weather (especially barometric pressure) affect the performance? Okay, so maybe I'm getting waaaay too technical here, and maybe I'm the only one who's even remotely interested, but it seems to me that any measurement of horsepower depends on so many factors that it would only be good for that particular moment.

For example, I believe it was you, Logan, who told someone (Chad?) that the way to improve horsepower was to increase in-flow and out-flow of air. If I am not mistaken, then wouldn't that mean that the horsepower rating at sea level would be greater than it would be at 2500 or 5000 feet of elevation?

 

[ChadInman]

Generally that's true another thing to look at is when you have ram air induction- that won't show up on the dyno even though it will on the quarter mile Car's always run slower in colorado than california. As far as the cost of a Dyno goes... I've never seen a place that charged less then $100 around here in the bay area in California everything cost money, and everything is against the law. Where I live you get tickets for having flowmaster mufflers!!! Also Logan wasn't telling me that, he was saying it to the guy who was lookin to soup up his 351C and I agreed- Chad

 

[Cougrrcj]

Hosepower ratings

OK, there are equations you can use that take your car's real world performance and they figure out what kind of horsepower you're putting out. This equation, of course, assumes that your car is optimized to putting its best performance in the test. Still, it is a pretty good guesstimate.

My race 74 Camaro with its 'baby' big block (396) ran a [email protected] quarter mile pass. It weighed 3700# with me in it. The equations can be based on elapsed time for the run, or top mph. One method said I had 425 HP, and the other figured out to 460 HP. I average the two and say 440 HP to the rear wheels.

Beta Cat ran [email protected] At 3850# with me in it, that figures out to between 290 and 340 HP Considering a 'stock' 73 351C-4V was rated at 225 net HP and a earlier 351C-4V was rated at 300 gross HP, I kinda wonder how accurate that is.

Then again, the car manufacturers were playing games with the HP figures for a number of reasons. One was the Insurance industry. The higher the HP rating, the higher your insurance rates. The other reason for the games was for drag racing classification. The higher the HP rating, the more difficult (Faster) classes you had to race against. A good example of the under-rating was the 428-CJ. 335 gross HP? HA! Even the drag racing sanctioning bodies put it much closer to 400HP.

I guess it all boils down to which way you really wanna go with this. You can guesstimate without any real clue, you can get sorta close by taking your car to the track and wailing on it, or you can spend the $$ and have it run on a chassis dynomometer. The choice is yours.

 

[ChadInman]

...or just keep your car stock that way you never have to worry about it... -Chad

Of course I'm joking!

 

[73XR-7owner]

and a funny joke it is!

(hey, where'd these new smilies come from?)

cj, what you say and chad's joke, too, points out one other problem the car manufacturers had. the buyers wanted high horsepower. :eek2: that came in conflict with the insurance companies and the drag racing folks. :1poke: i wonder what would have happened if the arabs hadn't cut off the oil? :finger:

(Logan has been shopping it seems....)

:wave:

 

[texrep]

besides bragging rights .....does it really matter? As long as it runs good and starts all the time and makes you happy when you romp on it.... it's just a thing to brag on at the car show IMHO

Don
:1poke: :aug2: :dogpile: these are so kool !!!!

 

[edsel]

wow this really opened a bag of cats(ha ha).to see a chart of 1/4 and 1/8th mile times to calculate hp(accurate? who knows) go to www.farmingtondragway.com then click on links,then enter csp racing(mopar guys) and there are the specs.hope this helps

 

[73XR-7owner]

i wonder how much server space these new smilies take up?

I guess it really isn't important beyond bragging rights, tex, but then again what good are bragging rights if there is no accuracy? Back in high school physics class uke: there were mathmatical fomulas ("fomulae" for Logan - hehehe) for calculating horsepower, but I don't remember if they applied to internal combustion engines.

I'll check out those drag stats later, edsel. Right now I'm out of cigarettes, so I must make haste to town and work.

Now if I just had more horsepower in the PT, I'd get to the store that much quicker....

:wave:

 

[73XR-7owner]

hey, Logan...

puke guy doesn't work. i hate it when that happens....

 

[Steve Eitzen]

Windsor Dyno Test

John Benoit just did a dyno test on the most recent rebuild of my '69 Windsor. Engine mods include:

Punched out to 362 cubes
Ford Motorsport cam
Holley 600 cfm carb
Edelbrock Performer manifold
Pertronix Ignition
Forged pistons
Chrome-moly rings
Balanced crank

The bottom line was 207 [email protected],200 RPM (280 ft/lbs of torque @ 3,400 RPM) at the rear wheels. Using the usual rule of thumb, that means the gross horsepower rating ought to be 320-350.

Now we go out trolling for Camaros.

Keep on Cattin'!

Steve

 

[73XR-7owner]

Steve...

:wave: Hi.

Which weighed more, the 69 Cougar or 69 Camaro. I figure you'd know...

 

[73XR-7owner]

blame it on my old memory, Logan...

You probably wonder what the hell I'm talking about up there ("fomulae" for Logan - hehehe). That's because I should have written "Steve."