Help with dyno problems

[scorch70]

Hey Guys, I went to my local dyno shop Friday, to find out if I had gotten any gains from installing my midpipe. Anyway, I did about 10 runs, but we could never get accurate numbers. The dyno was having trouble getting correct RPMs. When I would start a run, the RPMs graph on the monitor would read correctly. However, about 4 grand, it would start bouncing around all over the place (the in car RPM gauge looked normal).

I got readings from 113whp/130tq to 114whp/205 tq. We even tried an optical reader, which measures the speed of your belt turning and calculates RPM, and that didnt work either.

I have been to this same dyno the previous two times, and no problems. Can you guys help me out? I know that you are supposed to clamp a wire coming off the spark plugs to read the RPM, but any idea what color the wire is? Does it matter which spark plug?

This is very frustrating. Now I am looking to have to travel 200 miles to dyno if I cant figure this out. The operator said he had never had trouble like this before.


Thanks
p.s. Its a dynojet dyno.

 

[Gen1GT]

Hmm, doesn't sound like the dynojet operator is very experienced. On a Dynojet, you can plot the horsepower curve over speed, rather than RPM. It's actually more accurate. You should be able to go back to the shop and have him load up the file, and show the scale in speed rather than RPM. Like this.

 

[scorch70]

Hmm, doesn't sound like the dynojet operator is very experienced. On a Dynojet, you can plot the horsepower curve over speed, rather than RPM. It's actually more accurate. You should be able to go back to the shop and have him load up the file, and show the scale in speed rather than RPM. Like this.

Thanks for the reply Josh. He may have tried this, but I dont know for sure. How does the dynojet determine speed? Just by how fast the drum is turning? So no other sensors are needed (the wire clip)?

I honestly prefer the RPM scale (I like to know where in the RPM band the engine is doing what), but if mph will work I would use that.

Any one else have any ideas in case this doesnt work?

Thanks

 

[Gen1GT]

force=massacceleration

The roller is a known mass and diameter, and by how quickly the car accelerates the roller, the computer calculates power and torque A dynojet doesn't even need an RPM pickup to give it's figures. It's just a valuable tuning tool. I've done a couple runs where we had a bad pick-up and weren't able to use the RPM chart.

It doesn't really say why you had issues with yours though. We just made sure all the connections were good, and the pick-up was over the ignition wires properly and it all worked well again the next run.....

 

[scorch70]

force=massacceleration

The roller is a known mass and diameter, and by how quickly the car accelerates the roller, the computer calculates power and torque A dynojet doesn't even need an RPM pickup to give it's figures. It's just a valuable tuning tool. I've done a couple runs where we had a bad pick-up and weren't able to use the RPM chart.

It doesn't really say why you had issues with yours though. We just made sure all the connections were good, and the pick-up was over the ignition wires properly and it all worked well again the next run.....

I did about 10 runs, and none of them were reliable. I will email the dyno guy and see if we can try again in a couple of weeks without the rpm monitor.

Thanks for the help Josh

 

[twilightprotege]

the only problem i have with the speed vs rpm (my dyno's are all speed not rpm) is that when i changed from the stock 195/50/16 tyres to the current 205/45/16, speed dropped. so instead of going to 124kph in 3rd i was only going to 118kph. also, that speed is not what i see in the car. in 3rd my car can get to about 135kph

 

[viVid]

Sounds like a loose or bad lead? I wouldn't know, I have yet to dyno my car...