Subject: Re: Nice head comparo here by BeachBum on 2008/12/22 16:55:46
Quote:
bogus wrote: I come back to my comment that dyno's are junk.
I hate chassis dyno's. Unless you are using to baseline and consistantly use the same unit, you are asking for skewed numbers. Even then, it depends entirely on maintenance to the unit and weather conditions.
I do trust engine dyno's a little more, but they must be kept cool to work at their best. Again, calibration is key.
I harken back to my RC car racing days. I had a dyno for those little electric motors we used. With that, I would test the motor three times to let temperature equalize things. We would use the the last test and just accept it, due to the heat issues. Even then, these tests were simply a gauge... and the same motor tested on two of the same dyno's would give different numbers.
I agree with what you say above about chassis dyno's..... particuarily if you have an automatic with a loose converter, they simply are not accurate, even the same one from pull to pull, the output is effected by the rpm you began the pull at and how quickly you went into the pedal. I've had multiple pulls on the same dyno on the same day, with the engine at the same temp for each pull and seen differences in torque of literally 80 ftlbs and peak HP of 30....
I doubt if I even have my new set-up chassis dynoed.... I'll use the timeslip instead, which is more fun than a chassis dyno anyway, and its cheaper too.
If you have a lock-up converter, you can lock it up and get better more accurate results, but, you do need to typically be a little higher in the rpm range before you lock it up considering even with multiple clutch disks, they do not like to be locked up at wot early in the power band.
The below is what Precision Industries says about chassis dynos.
