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Rototest hub dyno question

Posted: Mon Sep 09, 2013 2:03 pm
by saresks
In case if anyone knows inner workings of Swedish made Rototest VPA:

I dynoed my fresh built Olds 403 in Olds Cutlass G-body. At first reference pull driveshaft broke at 5500, but that's another story.

First, dyno operator didn't measure true engine rpm, just calculated value based on rear end ratio and wheel rpm. So 9.5" 3000+ converter slippage wasn't taken into account, which does affect hp readings somewhat.

Car specs:
408 cid, 11:1 comp, 224/234 flat tappet cam, Edel RPM intake, 750+ CFM carb
9.5" 3000+ stall converter, TH200-4R trans.
3.55:1 rear end

Pull mode: sweep 225 (acceleration 225rpm/sec)

Dyno guy was able to open the throttle at 3600, to prevent kickdown to 2nd gear. From 3600 to 4850 on top of the monitor screen next to the car there was an message "Maximum torque (RF)" and during that range rpm's climbed at much faster rate, about 650 rpm/sec. Just after max torque message went off, peak tq was recorded (452 Nm). Guessing 5% converter slip, that was at 5124 rpm.

Now, there is no way this spec engine would peak tq so high, but rather around 4000-4300 rpm. This leads me to suspect the Tq readings at 3600-4850 rpm. Also considering climb rate 650 rpm/sec, that will eat torque to speed up rotating mass.
It seemed for some reason dyno system overloaded and wasn't able to brake engine for steady climb rate. So, what happened and are the readings worth nothing? This is not a torque monster, but just a healthy, emission level restricted (Europe/Finland policy) olds sb.

Ah, either dyno guy or Rototest company didn't help much or nothing.