Chassis Dyno experiences

[Florida Fiesta]

Well here's some more info..
The dyno was a DynoJet.. I don't know the model.
the carb is a weber 32/36 dgv with f6 emulsions on both sides.
First run we saw AFR around 14 after 3,500 rpm. the guy said to open the fuel jet. We did it by 10-15 increments a couple of times until we used the largest fuel jet I own. then did a run with a lower air jet, but the afr/bhp/torque all stayed about the same.
I'll have to open it up a check, but I think we ended up with 205 fuel and 165 air in the secondary.
then we moved the timing a couple of times - retared 2 degrees from where we started seemed to be the sweet spot.
Again, seems like great info if I'm drag racing my Fiesta (watch out all you SMART cars!), but I'm sceptical of what will happen halfway down the back straight with what I think are huge fuel jets - seems like it would bog down.

[joeg]

It won't bog...just run out of steam!

I figure the 205 is a bit large.

Unfortunately, when you run out of jets to test, it becomes a bit of a wasted effort.

Beg or buy more of a jet collection around what you have presently.

[mossaidis]

AFR will vary based on where you are taking the sample from. ratio can change just be moving your sampling location by a few feet.

[C. Ludwig]

AFR will vary based on where you are taking the sample from. ratio can change just be moving your sampling location by a few feet.

It certainly shouldn't. If it does you have issues. Assuming all cylinders are running at the same AFR (they never do) you should be able to measure the same AFR at the exhaust port as you do at the collector or at the tail pipe. If you aren't then you most likely have an exhaust leak at some point in the stream.

Ignoring how real world airflow at speed on the track might affect the engine there should be minimal difference between the tune you see on the dyno and what you see on the track. Tuning is what dynos are used for... If they didn't provide repeatable results no one would use them. One of the most basic rules of tuning is to give the engine what it wants which means sometimes you have to step outside of the box to optimize a tune. Now that may mean that something is wrong with the engine package and you're compensating for it. But the dyno and test equipment, when properly calibrated and used, does not lie.

[billf]

Just be aware that the "Power Valve" of the Weber carbs is what you see at the bottom of the float bowl. That is a valve that allows passage of fuel downward when the vacuum signal is lost (acceleration, full throttle), then horizontally toward the emulsion tubes. It is in this passage (horizontal) where the actual fixed high speed jet is put. It is only accessable by removing the lead soft plug in the front of the carb...that is when you will see it. It is about half way down the passage. the jet is what meters the amount of fuel.

Increasing the size of the valve will not increase the amount of fuel entering the power jet.

Thought I'd pass that on.

Good racing.

Bill