Proper dyno run + typo in manuals?
11-21-2003, 01:26 AM
#1
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Proper dyno run + TQ typo in manuals?
'81 4.5L US Auto 130K miles
Open airbox, 3" exhaust, PCV via exhaust
No cat, A/C, air pump, or engine driven fan
Chevron 89 octane, fuel pressure @ 3 bar/43 PSI
Stock ignition, paper air filter, stock exhaust manifolds
Dynojet SAE figures with 20% added for the automatic transmission.
No cam advance, 23 degrees ignition: HP 234@5400, TQ 262@3900
3 degrees cam, 29 degrees ignition: HP 228@4900, TQ 267@3500
Factory specifications (see below): HP 220@5500, TQ 256@4000
Top speed on rollers: 156 MPH @ 6200 RPM
*Original Run*
Open airbox, 3" exhaust, PCV via exhaust
No cat, A/C, air pump, or engine driven fan
Chevron 89 octane, fuel pressure @ 3 bar/43 PSI
Stock ignition, paper air filter, stock exhaust manifolds
Dynojet SAE figures with 20% added for the automatic transmission.
No cam advance, 23 degrees ignition: HP 234@5400, TQ 262@3900
3 degrees cam, 29 degrees ignition: HP 228@4900, TQ 267@3500
Factory specifications (see below): HP 220@5500, TQ 256@4000
Top speed on rollers: 156 MPH @ 6200 RPM
*Original Run*
Last edited by PorKen; 03-03-2004 at 12:07 AM.
11-21-2003, 03:33 PM
#2
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Typo or conspiracy?
In the glovebox manual, the workshop manual, car reviews such as R&T, (and on 928 Specs site), the torque for '80-'82 US engines is listed at 265 ft/lbs.
In the manuals the metric value is 348 NM (newton/meters), which at a conversion of .7376 is 256 ft/lbs!
There's a chart in the back of the glovebox manual which has the HP/TQ curves and you can clearly see the torque peak is under 260.
In the manuals the metric value is 348 NM (newton/meters), which at a conversion of .7376 is 256 ft/lbs!
There's a chart in the back of the glovebox manual which has the HP/TQ curves and you can clearly see the torque peak is under 260.
Last edited by PorKen; 12-14-2003 at 06:42 PM.
11-21-2003, 09:15 PM
#3
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Graphs
The initial bump in torque is from torque converter multiplication.
0 degrees cam advance
3 degrees cam advance
By RPM:
By MPH:
0 degrees cam advance
3 degrees cam advance
By RPM:
By MPH:
12-14-2003, 05:35 PM
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12-14-2003, 07:24 PM
#6
Nordschleife Master
I wouldn't worry about making direct comparisons to the handbooks. Those numbers are based on a engine dyno, not a chassis dyno. And there will be variations between engines.
The 20% factor is a ballpark estimate. Applying that to dynojet numbers doesn't give you what the engine is doing.
Another issue is that a dynojet is not measuring torque at all. It is measuring power applied to the rollers and engine RPM. It then back-calculates what the torque would be based on the power and RPM.
Since you car is an automatic, the torque convertor will amplify torque from the engine at the expense of RPMs on the output. If it's showing torque as higher than you expect, that's probably it.
Nowhere in the calculations does the Dynojet try to figure out the actual torque on the drive wheels which would lead to the engine torque. It can determine the torque applied to the drums, but that is a different number. It would actually be the same if the drums and tires had the same diameter.
The 20% factor is a ballpark estimate. Applying that to dynojet numbers doesn't give you what the engine is doing.
Another issue is that a dynojet is not measuring torque at all. It is measuring power applied to the rollers and engine RPM. It then back-calculates what the torque would be based on the power and RPM.
Since you car is an automatic, the torque convertor will amplify torque from the engine at the expense of RPMs on the output. If it's showing torque as higher than you expect, that's probably it.
Nowhere in the calculations does the Dynojet try to figure out the actual torque on the drive wheels which would lead to the engine torque. It can determine the torque applied to the drums, but that is a different number. It would actually be the same if the drums and tires had the same diameter.
12-14-2003, 08:53 PM
#7
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GlenL - I wasn't concerned too much with the comparison, just pointing out the mistake in the literature.
