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Old 04-23-2008, 02:32 PM
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bob27s
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Default RE: 140+ mph H9 Sundowner 50 Arf

I'd not recommend trying the pump. They rarely work on the Jett engines, and they are very difficult to work with on tuned exhaust systems.

About 20% of the power the engine develops comes from the jett-stream muffler. A straight or open exhaust would drop performance. Plus it needs the balance of backpressure from the exhaust system.

You could use a full size pipe - that can help it perform a bit better, and Ive seen some photos around here of decent pipe/header installs on the sundowner.

The 90LX configured for the GP Toni has the longest extention kit we recommend for the engine. That setup turns a 12x6 up around 14,000 rpm, and an 11x8 a little bit higher than that on ground peak. Runs about 800-1000 rpm lower rpm than without the extensions. Add more extentions than that and you either have to work with props to find a sweetspot where the muffler stages properly... or consider the regular lower timed 90L engine.