With a straight tuned pipe (gotta wait on some easing up of the cash flow for the Irwin pipe) how long should my header pipe be? K&B .67 O/B going to be mostly sport running with bursts of full speed not racing. Stock carb, stock flywheel, 12" tuned pipe 2" expansion, Prather Lap Cat III, Prather 240 stock prop, 20% O'Donnell fuel
Header length
- Thread starter Atious
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Trial an air I think i,m sure a expert wiil fill you in. Whats up with the 20% fuel I think 40% is the way to go to get some more heat in the motor ,like i said I,m sure someone will give you all the info you need ,I allways run 40% in my .67 outboards i just hooked up a erwin pipe on mine so i can't wait for warm weather. 
hay atious i do no one thing for sure my lap cat shoots a sweet roostertail with my .67 , i just wonder if the roost will shoot off your straight pipe and ruin the cool factor ???My htb boats are great but but no cool roostertail :'(If i new how to put vidio on this site i would let you see some cool toledo pond action.Just remeber with the right set up a 7.5 will go just as fast I but a 7.5 on my lap cat lll with a erwin pipe an ran 48 mph with out even doing nothing but bolting it on.Only reason im telling you this is it gets better fuel economy than a .67 40% fuel is 22 bucks a gallon at my local hobby store. were are you from anyway. nice chatting with you.
I'm in Maine. The closest decent hobby shop has 40% obscure name nitro for 47 a gallon. No way would I pay that. The 20% is what tower had for O'Donnell. I placed a large order with them so I had them throw it in as well for my cars. I figure it oughta be good enough to start out with. My engine isnt as "like new" as it was advertised on Ebay. I'll likely get some 40% after buying a rebuild kit for it.
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Hey Atious,
With K & B parts so hard to get I'd stick w/the 20% nitro like your using now. Parts tend to break less w/lower nitro.
It is possible that w/a straight pipe that the rooster tail will cool the pipe causing the motor to die but not likely if your going fast!
As for the header I think mine used to be 3 inches.
With K & B parts so hard to get I'd stick w/the 20% nitro like your using now. Parts tend to break less w/lower nitro.
It is possible that w/a straight pipe that the rooster tail will cool the pipe causing the motor to die but not likely if your going fast!
As for the header I think mine used to be 3 inches.
Thanks for the reply. The strain on the engine, plus the fact that the engine is used, is why I will use 20% for now. Perhaps if I can locate a couple piston and sleeve sets I'll go up some on the %.
I have several machines for fabbing various things so made a header pipe similar to those I've seen on sites linked here. My experience with nitro boats is virtually nil, so I'm kinda looking for the longest to begin with. I can shorten as I go but adding sucks.
I have several machines for fabbing various things so made a header pipe similar to those I've seen on sites linked here. My experience with nitro boats is virtually nil, so I'm kinda looking for the longest to begin with. I can shorten as I go but adding sucks.
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