Dear Ralph: I have a 1997 Arctic Cat ZR 440 that I am trying to get the clutches set up on. I have just...

Dear Ralph:
I have a 1997 Arctic Cat ZR 440 that I am trying to get the clutches set up on. I have just recently installed V-Force reeds and Black Magic twin pipes. My question is, Black Magic says engine should run at 9200 RPMs peak, and to me that seems a little high. I have already seen my friend lose a motor due to overreving. I’m currently running about 8600 RPM with notched 47.5g weights and a 54/48 helix with red secondary spring in first hole, sled pulls 8600 RPM out of the hole, but falls to 8400-8500 RPM with top end speed at about 100 mph. What do you suggest I do? Thanks and keep up the good work.

For you to question if 9200 RPM is the correct RPM to run at is one thing, questioning it from a reliability / durability stand point is a totally different issue. Each and every exhaust system is designed to produce maximum power in a very specific RPM range. If Black Magic told you that pipe set on your engine was designed to operate at 9200 RPM, then I would trust their expertise and experience. If you want to get the best performance out of your sled, clutch it to spin at the RPM specified by the pipe manufacturer unless you have proven that it works better at a different RPM. Start with the recommended clutching specs for your temperature and elevation from Black Magic, and perform the fine tuning adjustments from there. If you’re really that worried about engine durability, you can always put the stock exhaust back on.
If your sled was in my shop I’d hook it up to our DynoJet track dyno and we’d find out what engine RPM puts the most power to the ground. I’ll bet it’d be in the 9000-9200 RPM area.

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