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General question about Dyno testing results

792 Views 12 Replies 9 Participants Last post by  tmendham
I had my car dyno'd last week as part of a final tune up. I know that I now have the REAL horsepower and torque figures for my car. Obviously, they are very different than the advertised numbers for my engine at the flywheel.

My question is this; on new cars, are the advertised HP / torque figures for the flywheel or rear-wheel?

In the interest of full disclosure, the Ford 302/5L long block (6007-XB3) is advertised at 345 hp. My results: 246.3 hp at about 5,500rpm and 274.1 ft-lbs at about 3,750rpm.

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Thanks for posting those real world numbers. Some one with a new mustang with the stock motor needs to post theirs as well.
Also somebody with a box stock K car. There is so much mythology connected to horsepower numbers. We here at the VMF could set the world straight.
Advertised numbers are most always at the flywheel because they are a larger number. Rule of thumb is 20% less at the rear wheels.
Rear wheel with accessories. The ~30% difference that you see with your engine is very typical.
Factory horsepower tests are conducted with JUST the engine - No rear wheels. This is something like a starter bench test at Kragen. The starter on the bench machine can spin and create a voltage almost 2 times higher than a starter in a car - Why? Simple. Because as you know, the starter interacts with the flywheel of the transmission, creating friction and putting resistance onto the starter drive.

My girlfriend's bone stock 2000 Mustang GT puts out 218 horsepower @ 5,300 RPM and 255 lb-ft of torque at 4000 RPM - Stock advertised for this car is 260 horsepower at 5250 RPM and 302 lb-ft of torque at 4000 RPM. I see a problem with this!

Kinda makes you feel like your V8 is rather anemic eh? Shoot, my "six banger" puts out 132 rear wheel horsepower - th 3.8 liter V-6 spins to produce 156... Too bad my 6 cylinder motor is housed in a shell that has a curb weight that's 400 pounds heavier. /forums/images/icons/smile.gif
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"Kinda makes you feel like your V8 is rather anemic eh?"

No... not really. I'm going to be buying a lot of tires this summer trying to get used to this car! It is pretty fast /forums/images/icons/cool.gif.
My first thought was...29% loss - must be an automatic tranny. Then I looked at your byline and read T5. So now, I don't understand the results. Do you have PS, AC??? Where did that 5 - 10% go?
The 345 quote from Ford is with "...Ford Racing induction kit, headers, and a 65mm throttle body not included." I went basic with an Edelbrock carburetor and manifold. P/S yes, but no A/C. Frankly I was expecting 275 or so, but I'm still happy with the results.
I think you would pick up some HP with a Holley 650dp, made a night and day difference on my engine.
Did they do any timing changes while on the dyno? Did they chart the air/fuel and make adjustments
to the jets. We picked up 40 rear wheels hp with jet and timing changes.
Gross horsepower figures from back in the day are what alot of us relate to. In 1972 or so the factory hp numbers changed to net hp.

Gross or flywheel hp numbers were taken from a seasoned and well tuned engine on a stand. The only thing being driven were the oil pump and fuel pump. No fan, water pump, alt, ps, ac etc. No air cleaner or exhaust manifolds.

Net horsepower, like the numbers advertised today, is supposedly taken with an engine in a vehicle with all accessories hooked up. I have heard that the number is at the flywheel. But I have also heard the number is at the back end of the tranny.

Anyway, IMHO those are very good RW numbers. I wouldn't be setoff by naysayers if I were you. I also appreciate you sharing the info. Along with the other post above regarding the late model GT.

In our search for the "Holy Grail" of performance, we must use what tools we have to judge the output of our engines. Some will discount both chassis and engine dynos as being inaccurate gauges for hp/trq output. Saying that different dynos, software, operators, weather, stars or whatever, make the readings too varied. So what are we to do? Use three different dyno machines in three hours on the same day and then average them out? All we can do, is use the best that is available to us and go from there.

To others, only a time slip will do. But in order to get the hp/trq numbers we seek, we still must add et/trap speed to some other formula to try and quantify power. And believe me, quantifying horsepower is what it is all about. Just do a search for "horsepower" and see how many posts turn up. Never mind that on the street torque is more important.

So, congratulations on your numbers. How about a "huffer" on top of that crate motor? Could give you another 100+ hp you know!!!*G*
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Companies that advertise dyno numbers are notorious liars.

Regarding your own rear wheel dyno numbers It gets even worse. Your car is sitting still and the front wheels aren't rolling. Add wind resistance at speed and the rolling resistance of the front wheels and your numbers will go down even more.

I always prefer the 1/4 mile dyno.
I just asked a simple little question!! I am happy with what I've got /forums/images/icons/smile.gif. When I get around to doing my formal introduction to the forum, you guys will understand why I just said that. I've been a car nut most of my life and I just never knew what was being advertised by manufacturers.

In response to Billgear and others, the carb was tuned and jetted before the final run (what I posted). In fact, the speed shop owner said himself, "You get some new heads and a hotter cam, and I could get 50 more HP." Thanks to everyone!

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