Quote:
Originally Posted by Daox
That is a bit larger than I'd go. How much horsepower does this engine put out? What are the normal cruising rpms? What rpm range are you targeting to increase torque?
From the literature I have, a 1.5" primary is good for 26-38 hp per cylinder. 1.25" would be plenty (17-22 hp per cylinder) with a 1.5" collector outlet (which emphasizes low rpm torque).
Edit: I just checked the outlets on my 82 CM400, and outlets on the mufflers are only around 5/8" and that engine puts out roughly 43hp.
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Yeah, that's the muffler outlet, though. The primary pipes are 1.5" off the head.
The OEM exhaust on my CM185T has 1.5" primaries leading in to 1" mufflers with expansion chambers in them. I just figured on staying with the 1.5 primaries because I already have them.. ya know, using what's there. I can just re-bend the pipes to the shape I need, after I heat them up.
If I go with smaller primaries, I have reversion issues, because the holes in the head are 1.5" as well. It's a 180cc engine, according to the jug casting.
I'm trying to get more torque in the 2000-4000 range, the engine's HP is like 15@9500... I wish I had a dyno graph of it, but I don't. It's got a relatively high RPM at 55-60MPH, but I can't tell exactly what it is b/c of the lack of a tach thus far, not to mention that it's non-operational at the moment.
I just figured since I had to redo the exhaust anyway, I might as well do it something closer to optimal.