Calculating torque

[efnfast]

Soooo, the dyno showed 451 RWHP, 15% drive train loss, calculates to 530 CSHP. Now, dyno shows 403 lb/ft of torque. Also 15% loss? That calculates to 474 RWTQ.
'zit work that way? - Steve

[lfalzarano]

Approximately, yes.


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[jss06c6]

Originally Posted by efnfast

Soooo, the dyno showed 451 RWHP, 15% drive train loss, calculates to 530 CSHP. Now, dyno shows 403 lb/ft of torque. Also 15% loss? That calculates to 474 RWTQ.
'zit work that way? - Steve

Nice numbers! Did you re-cam the engine? You're 90 HP over my '91 which has full SW headers and exhaust and tune..

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[efnfast]

Originally Posted by jss06c6

Nice numbers! Did you re-cam the engine? You're 90 HP over my '91 which has full SW headers and exhaust and tune..

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Full porting
4 reground cams
15# flywheel
3.73 gears
Custom tune
Done on a Land and Sea, and I got to tour the factory where the dyno was made.

[jss06c6]

Got it.. going to Port mine this fall and re-tune. Hoping to get to 380 - 390 at the wheels. Pulled my Fidanza and went back in with original Dual Mass setup..

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[efnfast]

I also did light weight pulleys, so I really lightened up the rotating mass, plus I went with a performance clutch. No rotating mass and a grabby clutch....

[Paul Workman]

I agree w/ lfalzarano. i.e., "approximately" is right on.

Steve: The formula HP = (TxRPM)/5252 is not in question, but depending on who's correction factor one uses depends on the vehicle. the 0.85 correction factor (CF) is generally accepted to be "accurate" for our cars w/ the ZF trans, but if you compare numbers measured at the wheels to values (supposedly measured) at the crank, it quickly becomes obvious that the CF can very: i.e., there is no concrete or universal CF.

Then there's other corrections dialed in, e.g., air temp, altitude, etc. A quote from one of the car rags years ago: "Within reason, tell me what you want the dyno results to be, and I'll dial up conditions that will give you the results you want to see!"

Want more? Enter the Mustang dyno - designed to consider wind resistance as speed increases, which is deducted from the HP/Torque output display. And, the Mustang too considers temperature and barometric conditions at the time of the test.

Dynojet (inertia type) vs. Mustang: The "Jet" provides relative (before and after) raw data, whereas the Mustang provides massaged data better suited perhaps for predicting actual acceleration/max speed. And as always, "Garbage in = garbage out!" The less the raw (measurement) data is manipulated, the more accurate. Because differences in machines' calibration, i.e., which standard (SAE #xxxx, etc) is incorporated, plus atmospheric conditions entered at the time of the test, results between two machines or machine operators can vary significantly.

So, what to do??? For one, choose whatever machine/operator combination you trust for your application, and limit all your data collection to that combination! And, for another, I focus more on the rear wheel data and relative results/actual track results, and refer to the calculated "at the crank" measurements more for "bragging rights".

[lfalzarano]

Bragging rights are earned at the finish line. Measurement only indicate the relative improvement due to a engine modification. Paul is on spot for all the variables that enter into the estimate.


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[efnfast]

Paul, that all makes sense.
My dyno guy uses an SAE correction factor for local weather conditions.
On top of all that, they can program in a cheat factor on the machine and make it say pretty much whatever they want. I.E., they can add or subtract some percentage in the programming that we the end user never sees.

[Paul Workman]

There used to be a shop outta Kalifornia that advertised on the C.F. forum that posted "stock" (read: reader beware!) Dyno results for over 100 LT4s. The data showed the apex of the bell curve to be (IIRC) 350ish - which flies in the face of the 330hp factory rating. Interesting.

Want another? The factory stats for the famous 427ci L88 listing was 430 HP the same year the L79 427 was listed at 435 HP. Why would anyone want to pay PRIMIUM $ for a roudy, solid lifter cammed, 12.5;1 compression, 101 octane motor that made less HP than a very streetable L79? Obviously, most customers didn't - as build orders for the L88 Vettes never reached the 100 mark.

Fact: it's another example of numbers gamesmanship designed to throw off the general public, to encourage or discourage (skew) sales to suit a particular purpose. And, the C5 with the 348 Hp LS-1 was about to be debuted. Corvette was once again "on the ropes". So, did GM go shopping for some performance numbers they would feel comfortable publishing for the out-going C4, enough to give sales for the beleaguered C4 (Corvette) a much needed shot in the arm, and yet not so much as to take too much away from the new model? GM has done it in rhe past (the L88 vs. L79) for lesser reasons, would they/did they do it again to the LT4 C4? Time slips talk and B.S.
(dyno #'s) walk.

Just give me the rwhp/torque #s and call it good!