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 Post Posted: Mon Jan 16, 2012 9:32 pm 
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Yeah good Rick. Its not a contest is it if thats happening. I mean how can you judge different engines if whatever they have going on with the engines power curve affects the extent of the dyno error because the dyno is having problems.


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 Post Posted: Mon Jan 16, 2012 9:36 pm 
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Could the dip be an induction resonance issue, the runner length not optimum at that RPM?


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 Post Posted: Mon Jan 16, 2012 9:42 pm 
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I agree with that for the figures Rick posted but how come most or all of the engines did it? Surely there would have been variety, its just smells fishy to me.
The thing about the contest is the inaccuracy of the fuel lbs/hr. How bad is that! Their supposed to give you information to tune from and they give you that rubbish!.


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 Post Posted: Mon Jan 16, 2012 10:21 pm 
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I guess I should have guessed a type O. In the mag. they state best qualifying pull but they have our second best qualifying pull listed in the mag.

That pull in the mag. should have shown 546.5 for the SAM engine.

The fuel flow and BSFC numbers being in the weeds is a non issue to me, but they should have stated in the rules they won't be provided and not have them on the dyno sheets.
At the competition you get 18 minutes to make 3 Qualifying pulls, so really the engine should come to the competition ready to run with minimal tuning. They don't give AFR readings, that's up to the competitors to provide for them selves if they want them, and they should have said fuel flow too.

Some of those things are items we realised we should have had on the engine.
We should have had a crank case vacuum gauge on the engine at the competition. We saw a difference in crank case vacuum with/without mufflers when testing. That may have been different at the competition. Maybe it was positive and we should have undone the draft tubes at the competition.

Fuel flow. We should have tuned with a guage on the line to the carb and set it the same on our gauge at the competition regaurdless of what the gauge they provided said. It was interesting to change fuel pressure on the dyno, it made some difference.

And wind meter above the carb.

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Slow racing is better than no racing!

Randy


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 Post Posted: Mon Jan 16, 2012 10:41 pm 
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It is a tough contest to do correctly. There is some error in any dyno and repeatability < 0.5% is really hard and near impossible if considered over large weather changes. Small errors from each variable multiply and create large errors.

During the contest I saw several things that made things inaccurate while watching the others dyno their engines. I've dyno'd at 5 different places and the only one I didn't find something wrong in their setup, procedure or calibration was Patterson Racing Engines. I am not sure if they had everything that good or because it was my first time dynoing an engine and didn't know a lot about what was going on yet.

We'll see how many problems mine has when I get one. ](*,)

Rick


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 Post Posted: Mon Jan 16, 2012 11:24 pm 
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Its all good learning isnt it. Personally I dont take much regard for only doing engine dyno tuning compared to doing it in the car on a chassis dyno or on the track etc. I think its better to tune in a car as I can feel the engine and how its responding. Not all things can be measured. I would tune an engine on engine dynos and chassis dynos to prep it for the EMC. Ive had many experiences where I go to the engine dyno and then later on put it into the car and once its in the car on the rollers I can feel and hear whats not happy and I get it better. Its a very worthwhile exercise to do.
I think what Mark did for the carby challenge by tuning it in the car is a big part of succeeding with anything.


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