th400 eating power
05-22-2007, 11:36 AM
#4
last year 2nd full run was 10.8 @ 123, car made 440 rw thru a th400, suspension not working at all.
dyno power #'s mean nothing when there's an unlocked auto in the picture, track times will tell ya what it's really making with the mph/weight calculation.
dyno power #'s mean nothing when there's an unlocked auto in the picture, track times will tell ya what it's really making with the mph/weight calculation.
05-22-2007, 03:52 PM
#5
Dyno jets are completely accurate within +/- 1% if SAE Corrected. They tell you how much power you are putting to the ground. An auto with a big stall eats up a lot of power so it is hard to say how much power you are making at the engine. Usually 20% loss for autos and 15% loss for manuals. Give or take a few percentage points.
But yes, dyno jets are accurate.
10.85 with 403 rwhp here. 10.81 with 410 rwhp seems about right to me.
But yes, dyno jets are accurate.
10.85 with 403 rwhp here. 10.81 with 410 rwhp seems about right to me.
05-23-2007, 08:28 PM
#6
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TH400's with large stalls are going to absorb power. What the dyno reads is accurate, no matter what dyno you're using. Now with our dyno, the TH400 with a large stall is going to show that not that much power got to the tires. It's not going to tell you how much power is at the fly wheel by using the simple 15% drivetrain loss for manual, and 19% for automatic calculation. If you only make 400rwhp through a TH400, you're going to blow the doors off a M6 that made 400rwhp.
For instance, yesterday we had a 383 LT1 on our Mustang MD-1100SE dyno. Inductive pick ups on LT1's are a pain in the **** to get working, so we went off roll speed to get and RPM reference. With the dyno reading 6000rpm, the scan data from the pull showed that 6500rpm was reached. 6000/6500rpm is 92%. You can assume that the converter is then 92% efficient, or has an 8% slip factor, however you want to look at it. Now add that extra 8% loss to the already 19% being asborbed by the rest of the drivetrain, and you're closer to 27%. I'd say realistic it's closer to 30% with a 12 bolt or 9" and large gear.
The only things dyno's should be used for is for correcting AFR, not as a benchmark for how fast a car is, and weather or not any changes made, via tune or change of parts, made more or less power. Now where a DynoJet may not be accurate, is to whether or not it is able to produce the same conditions or similar conditions as your car will see at the track. That's where loaded dyno's, such as Mustang Dyno's have DynoJet's beat for the most part.
Not to mention different dyno's arrive at their power results differently. DynoJets do calculations based on the acceleration in rpms (of the roller) over time. If you're able to increase from 4000rpm to 5000rpm in 1.2sec, then you're making more power than a vehicle that goes from 4000rpm to 5000rpm in 2 seconds. Mustang dyno's actually measure the force applied to the dyno with load sensor to measure torque. Then using the RPM as a reference, is able to calculate horsepower.
Irregardless, if you make 450rwhp horsepower on a dyno, and you have the sheet to show it to people, then you made 450rwhp. No body's going to question it. In that regards, all dyno's are accurate. Now the question is whether or not the dyno reading is realistic.
For instance, yesterday we had a 383 LT1 on our Mustang MD-1100SE dyno. Inductive pick ups on LT1's are a pain in the **** to get working, so we went off roll speed to get and RPM reference. With the dyno reading 6000rpm, the scan data from the pull showed that 6500rpm was reached. 6000/6500rpm is 92%. You can assume that the converter is then 92% efficient, or has an 8% slip factor, however you want to look at it. Now add that extra 8% loss to the already 19% being asborbed by the rest of the drivetrain, and you're closer to 27%. I'd say realistic it's closer to 30% with a 12 bolt or 9" and large gear.
The only things dyno's should be used for is for correcting AFR, not as a benchmark for how fast a car is, and weather or not any changes made, via tune or change of parts, made more or less power. Now where a DynoJet may not be accurate, is to whether or not it is able to produce the same conditions or similar conditions as your car will see at the track. That's where loaded dyno's, such as Mustang Dyno's have DynoJet's beat for the most part.
Not to mention different dyno's arrive at their power results differently. DynoJets do calculations based on the acceleration in rpms (of the roller) over time. If you're able to increase from 4000rpm to 5000rpm in 1.2sec, then you're making more power than a vehicle that goes from 4000rpm to 5000rpm in 2 seconds. Mustang dyno's actually measure the force applied to the dyno with load sensor to measure torque. Then using the RPM as a reference, is able to calculate horsepower.
Irregardless, if you make 450rwhp horsepower on a dyno, and you have the sheet to show it to people, then you made 450rwhp. No body's going to question it. In that regards, all dyno's are accurate. Now the question is whether or not the dyno reading is realistic.
