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bob27s -> RE: Magnum R and Jett (8/19/2005 4:01:13 PM)
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Hi Mike....
thanks for writing.
So you are doing a rear exhaust magnum conversion huh? Fun !
All of the sport jett engines throttle great. None of that on/off sorta stuff. :) However, the more critical you tune the engines for speed, you sometimes end up with a very sharp pipe-step that makes the midrange a pain in the buns. Most of the time we do not recommend tuning like that.
The West .50 is a real nice engine. Lots of power. My experince on the Magnum has been that the Jett SJ-50 with the SS muffler (higher rpm tune) installed is about the same performance as the Weston .50 with its full pipe. Prop selection is different... you have to match the prop to the SS muffler. APC 9x7, 8.75x8, 8.8x8.5 or 8.5x7.25 props are ideal. On the .50V engine, you run a tiny 8" prop and cut the pipe shorter.
As for recommendations --- depends on your end goal a bit. I assume this is - fast -
Yes, a FIRE - 50 would be great. Cast case or BSE - your choice - You just have to decide if you want a quiet pipe or a nitro pipe.
Engine is well behaved, and can be tuned for what ever prop you want to run.
Id suggest setting it up like a "Whiplash/Diamond Dust" engine, tuned for 18K "plus". Prop accordingly (dub will recommend props).
Image attached here is Zach Dempsey's Shrike. FIRE-50, Riser header with nitro pipe. Turns 8.8x8.75 at 19100 RPM peak, ground.
Would it be possible for you to utilize the standard 15deg angled exhaust ? This is a straight pipe setup, pipe angles up from the engine about 15 deg.
[image]http://www.jettengineering.com/engines/fire40.jpg[/image]
Or do you really need a riser header ? The stock o-ring exhaust is nice because you can purchase a tuned, fully welded pipe setup - no leaks, and its more compact. The riser header requires a coupler.
The extreme option here.....
One of Dubs new FIRE-60LX engines. High timed sleeve, improved sub-port induction, typically turns a full blade APC 10x6 over 18,000 rpm. Thats monster power from a "40". Figure on turning a 8.8x9.25 about 19K peak, ground. This setup runs great, still idles and transitions. Just take the time to break it in properly, learn to set the needle in that process. Always set it 600-700 rpm off of peak at launch, and it will last a good long time.
I hope this is helpful.
Bob
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