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A couple weeks ago we took 11 cars from the Rocky Mountain chapter to a dyno shop in Denver. I took my '66 327/350 hp and made 3 runs. All 3 runs had similar results, hp was 188 at the rear wheels and torque was 247. My car runs strong and I believe the numbers were adjusted for our high altitude, but there were no other cars similar to mine to compare with. My question is; what should I expect the numbers to higher?
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Re: '66 Horsepower Question
When you dyno test there are two sets of number you must understand.
The first is "observed data". This is the amount of torque/power actually recorded on the dyno, which is affected by weather conditions and altitude.
The second is "corrected data". This is the torque/power derived after applying a "correction factor" to "correct" the observed torque/power to some set of "standard condtions". One common set of standard conditions is "standard sea level conditions", which are 29.92" Hg. 59 deg. R, and usually "dry air or zero humidity.
Most dyno operators who use Dynojet Dynamometers use "SAE standard condtions", which is about 29.3" 85 deg. F. dry air.
If you are at significant altitude the correction factor may be significant - on the order of 20 percent. Your dyno sheet should have the actual recorded temperature, air pressure, and humiditiy at the time you did the run, and from this, any "correction factor" can be computed.
So are the numbers you quoted "observed" or "corrected", and if corrected, what "standard condtions" were used for the corrected data? There should be something on your printout to give you a hint. If you can't figure it out, talk to the dyno operator. He should have explained it to you the day you did your run. Not knowing the context of the data makes it essentially worthless.
When you quote peak torque and power, you should also give the respective engine speeds for each.
Duke -
Re: '66 Horsepower Question
Mark when you find out the corrected data for your runs will you post them? Interested in what a 327/350 has at the rear wheels. ThanksComment
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Re: 59 deg. R
That's downright chilly !!
GeezerComment
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Re: 59 deg. R
Typo! Of course I meant degrees Fahrenheit, not Rankine.
For those of you not familiar with "degrees R", it is a scale that starts at absolute zero using increments equal to the Fahrenheit scale, so zero F is 460R.
The equivalent for the Celsius scale is the Kelvin scale, and zero celsius (32F) corresponds to 273K.
DukeComment
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Re: '66 Horsepower Question
Duke, I appreciate your response and I've sent an e-mail to the dyno shop with your questions attached. I'll post their response when I get a reply.Comment
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Re: '66 Horsepower Question
I'll be interested in hearing the answers. Back in '63 S&S Research, the outfit that preped Alan Green's AP SWC driven by Jerry Grant, told me that a good '63 FI engine made about 250 RWHP. This was probably corrected to standard sea level conditions, and current "standard SAE condtions" would probably be about 3 percent less. Back then SCCA engines were basically showroom stock except for open exhaust, but headers were not allowed, nor was head porting.
I expect that a good L-79 would make about 220-230 RWHP corrected to standard SAE conditons. With some head massaging and an LT-1 cam a good 327 might make about 275 HP with open exhaust or a set of very low restriction mufflers.
Compare this to a modern LS1 at about 300 RWHP and a LS6 at about 350.
DukeComment
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Re: '66 Horsepower Question
Here is a comment from the "partially informed".
It has always been my understanding that GM measured gross horsepower in their cars up until the 1972 model year. I has therefore assumed that this gross horsepower was that hp/torque that was deliverd, not at the rear wheels of a real car with real friction and accessories, but either on a test stand or in a lab setting. Have I been under the wrong assumption for all of these years?
One of the thoughts that reinforced this idea was that the hp took a steep dive in 1972, not just due to lowered compression ratio, but do to a net hp, as delivered with most, if not all, of the driveline friction and power robbing accessories. That is one of the reasons why the Z06 is so impresseive - 405 hp at the real wheels.
So, am I misinformed?
GaryComment
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Re: '66 Horsepower Question
SAE gross horsepower was measured with no engine accessories and a laboratory exhaust system with no mufflers and a suction pump. Fuel and spark timing were adjusted to optimum, which did not necessarily represent the production calibration, and observed data was corrected to standard sea level conditons.
SAE net horsepower is measured "as installed" in the vehicle with production calibration, accessories, and the vehicle exhaust system and observed data is corrected to SAE standard condtions.
Rear wheel horsepower subtracts drivetrain and tire loss from net flywheel power. As a rough (sometimes very rough) rule of thumb, SAE net power is 80 percent of gross, and RWHP is 85 percent of net.
Apply these to a 350 HP L-79- (.80)(.85)350 - and you are left with 238 HP at the rear wheels assuming the 350 gross was reasonalbly honest.
DukeComment
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