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Crank vs Real Numbers

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67 Marlin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 67 Marlin Quote  Post ReplyReply Direct Link To This Post Posted: Apr/15/2018 at 2:10am
My 1967 TSM mentions "taxable horsepower." For the 343 with 280 hp, it says 57 taxable. When I saw that, I figured it meant 223 hp at the wheels.

Sounds like an appropriate term if they're using it to go from crank to wheels, but I don't know if that's exactly what it meant, or if so, how precise the "tax rate" was. If this is an appropriate tax rate, can I use the 390 intake that was in the trunk when I bought it as a tax deduction Big smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rogue_66 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/16/2018 at 1:51am
Originally posted by Ken_Parkman Ken_Parkman wrote:

BTW another difference on a chassis dyno is rate of acceleration. The faster the acceleration, the less accurate as the cars change in rotational inertia absorbs power. A pull in a lower gear, or a higher number rear axle or heavier tire makes a lower power reading.


I've never run the car on the strip as we built it to drive across country to shows & such. My wife & I drove it from Denver to Kenosha & back in 2014 without incident or breakdown. 18 MPG with the AC running the whole way. Yes on altitude Ken...& thanks everyone for sharing info...the dyno run was at 5280 ft. The main purpose of the dyno run was for tuning purposes as I was wanting to know how close the car was jetted for this altitude. We'll be moving to sea level within the next 4 months & I thought it might be a good way to get an accurate AFR under load as a baseline.

Per the video I shot, it took 3 seconds on the first run to accelerate from 2000 to 5000 RPM & 4 seconds on the second run to accelerate from 2000 to 5200 RPM. The drivetrain is as follows...T5Z World Class tranny with 2.95 first gear & 37% overdrive 5th gear mated to 354 AMC Twin Grip rear end gears. Torque links & stock 1972 Gremlin diameter tires...10.5" in width. The runs were done with the transmission in third gear. On the highway at 2200 RPM in 5th the car cruises @ 75MPH. IIRC fourth gear in that tranny is a 1 to 1 ratio. Could it be possible the operator entered the wrong parameters not knowing it was a five speed? BTY...I can't imagine the car weighs more than 2800 lbs full of gas with me in it but haven't verified that yet.

Here's the printout for the second run mentioned above if it helps get to the bottom of this mystery.

   
Cheers & Thanks,
Dean

 

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motorhead_1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote motorhead_1 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/16/2018 at 5:24am
the type of dyno will make a difference. dynojet will read the highest IIRC.
mustang ~12% lower
then there's the heartbreaker dyno, the dyno dynamics reading lower yet. 

69 SC/Rambler tribute with 401/th400, 68 Rebel SST, 67 Rebel
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken_Parkman Quote  Post ReplyReply Direct Link To This Post Posted: Apr/16/2018 at 8:41pm
Never been on a mustang, but have heard they give a lower number. Wonder what the reason is if true. Power is a basic engineering definition, so it should not be hard but it is.

Also sorta humbling sometimes.

Not knowing how the mustang calculates a dynojet would give a lower number in 3rd gear so that is some of your story. You should make the pull in 4th. The concern with OD is wheel speed, and in 5th at 5200 rpm would be a whole lot. Tires do come apart on chassis dynos (been there done that - not good) so you don't want to be too far outside the tire speed rating.

Use it for tuning, then go to the track and you really know.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote motorhead_1 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/17/2018 at 4:08am
forgot about the dyna-pack hub mounted dyno, no need to worry about blowing up tires. takes the weight of the wheel and tire out of the equation, so will read slightly higher. 

all different dynos aside, they are just a tool to aid in tuning. for accurate before and after shots use the same dyno, same operator etc. unless you are bench racing and want to brag about 5 more hp than the next guy. 

tune the engine on the dyno and the chassis at the track...
69 SC/Rambler tribute with 401/th400, 68 Rebel SST, 67 Rebel
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