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Old 12-07-2004, 09:04 AM
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Dyno Pulls and Blow by at high RPM

I recently went to a car show that had a Dyno at it. I took my car (http://home.earthlink.net/~noegoman1...%20Project.htm) and ran it on the dyno. When my car hit about 6000 rpm, a little black smoke came out the exhaust. I was alarmed at first. I thought a piston ring had cracked, or something worse. The car still runs great, with no burning of oil.
I watched several other cars on the dyno, and it seems that almost all cars start to burn oil or start creating smokey exhaust while at very high rpms.
Why is this? What is going on here? After thinking on this for a while, I came up with a theory that a high pressure in the crank case may be forcing a greater amount of oil into the cylinder. I would love to find out the actual cause of this. (and maybe possible fixes) -Ed

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Old 12-07-2004, 09:08 AM
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I think that High RPM/ High load there is not a lot of vacuum from the PCV to properly clear the crankcase and seal the rings?
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Old 12-07-2004, 10:06 AM
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I'm guessing the operator pulled a load on the dyno to prevent over over reving. This load deecreased the vacuum and opened the fuel enrichment circiut and the engine ran rich. Rich enough to bellow the black smoke.
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Old 12-07-2004, 10:39 AM
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A little black/brown smoke is a good thing when the engine is under load. It just means the engine is running a little rich, which is very important under load. AFR is much leaner under load. I would bet that johnsongrass hit the nail on the head.

BTW, what kind of numbers did the car make?

Chris
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Old 12-07-2004, 11:15 AM
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My dyno numbers

My car did not do very well on the dyno. I am currently investigating ways to correct any problems with it (and I am very much open to suggestions).

The car, with the holley systemax II on a 350 (.030) put up:

269.88 ft-lbs of torque

225.48 Horsepower

at the rear wheels.

The mixture started out very lean, at almost 16:1 ratio, but as the secondaries came in over a period of 500 rpm, the ratio richened to 14:1, then to 13.5:1 at the higher RPMs.

The dyno guys pointed out that it was knocking, so the timing was too far advanced.

What all can I do to get my number up to where they should be?
-Ed
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Old 12-07-2004, 12:57 PM
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The knocking is likely not from the timing, but from AFR. A gasoline engine should never run at 16:1...period. That is too lean even for cruising. 14:1 is way to lean for power. 13.5:1 is getting closer, but is still a little lean under full power in high RPM. You need to get the carb tuned properly. Likely just needs a bump in the jet size and possibly a lower value power valve.

If the timing is too far advance that will also cause you to loose power. This is because the engine is basically fighting itself due to the early ignition. Timing will likely need to be around 36 total advance. Some engines with better chamber heads will like a little less like 34 or even as low as 32.

Chris
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