Dear Wady,

I recently purchased a dual stage Compucar set-up with two nozzles per runner. One of the local Pro Mod guys has told me that once you run both stages you have to change all the jetting for each cylinder.

Compucar tells me you shouldn't have to stagger the jets and that you tune each system separate and then run them both.

The local Pro Mod guy says on one stage the jetting can be square, but no way with both.

Is this true? Shouldn't you be able to run square getting as long as the tune is not on the edge?

Stephen

Stephen,

Do yourself a BIG favor and listen to the Pro Mod racers advice! Stagger jetting is very important in multiple stage nitrous systems if you don't want to make ashtrays out of race pistons! What will happen if you do not adjust jetting per runner will be that you will overload some of the runners with nitrous and not enough fuel and BINGO..... damaged engine.

If you were to stand in front of your engine and rotate the cam and watch the valvetrain sequence you will see exactly what cylinders need to be jetted differently than others. The cylinders that see valve opening right next to each other will get the overload of nitrous. Because nitrous is a light vapor and hangs around in the manifold versus the heavier fuel that drips down into the head port, the nitrous will then go to the next runner that starts to flow, and that is when the trouble starts.

Try to jet each cylinder as if was a separate engine in the block and jet it till it's happy. Spark plug readings are the best way to read the results of the tune up so read them CAREFULLY!

As far as square jetting, yes, you can do it that way in two stages providing, as you say, the tune up is NOT on the RAGGED EDGE! But you will not get the maximum performance that is available from a two-stage system as it will probably be way rich on the Fuel side.

I don't have exact tune up jetting numbers but I do know that the Pro Mod guys do run multiple stages and they are stagger jetted all over the tune up map and get great results.

Hope I have helped you with this and thanks for writing.

Wady Hamam

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