Billet Intake Mods

Discussion in 'Performance Mods' started by Dave C, Feb 9, 2011.

  1. Dave C

    Dave C Member

    I read about people having these break on them. I got the standard size pipe and knew what the problem people were having with them was. The part is only semi-finished. The sharp edges and machineing marks are all over the piece. Engine builders call these "Stress Risers". If you've heard of Polishing connecting rod that is why they're polished. I tried adding a photo of a Childs & Albert aluminum con rod. As you can see it's polished on all surfaces except the machined ones and it blends them in anyway.

    I used 220 grit wet/dry sand paper to knock down the edges and work over the inside transition from a straight pipe going to the port to the expansion section of the pipe. If you feel up inside the transition it will feel rough. Sand it smooth with a roll of sandpaper wrapped around your little finger, 1 layer is enough. You're finished with the piece when you can no longer see or feel any machine marks or sharp edges anywhere.

    I then got the larger one made for the CNS carb. Mods were definatly in order. Physically larger than the smaller one ment for stock carbs. Oddest thing, though. The passage inside is the same size as the smaller pipe with a really thick wall. They had to reduce the size of the head of the cap screw to get them to fit. Plus on the leading end theres a ring that sticks out, I guess to fit into the carb for a tight fit. On my bike I had to remote mount the carb. It's on a piece of clear plastic tubing. I had to adapt a Briggs intake by doing lots of machine work to make it fit. I hated the ring on the pipe, aerodynamicaly it's called a "frustrum" as in frustrated. The air hits that obstruction and flow drops off dramatically. The ring had to go. I have a set of large drills bits I got years ago at Harbor Freight that run from 1/2 inch up to 1 Inch in 1/32ths. I used the 11/32ths and bored the hole out taking the ring away. The bit slightly enlarged the port outlet, easily blended with sandpaper. Because this is intended to be used with a tubing adapter the flat end wouldn't do. Now that the ring was gone I used a very large drill bit to chamfer the inlet side of the carb. Useing the sand paper I sanded until I had a nice radius. It looks like an early gokart velocity stack. Sand the transition and remove machine marks and your good to go.:cool2:

    Attached Files:

  2. jaguar

    jaguar Well-Known Member

    Why did you put a picture of a connecting rod instead of a billet intake?
  3. Dave C

    Dave C Member

    I was illistrating how an aluminum part should be finished and I could think of no better part than a Childs & Albert connecting rod to demonstrate. You can see the billet part at Pirate Cycle's site. It's very unfinished. There should be no sharp edges and the C&A rod well shows that attention to detail. If they DIDN't do the smoothing and blending they wouldn't be the largest manufacturer of aluminum raceing rods.
  4. jaguar

    jaguar Well-Known Member

    What a great idea: an aluminum connecting rod! That would solve most of the crank balancing problem.
    I don't see, even with sharp external edges how the billet intake can break. I'll bet it happens because one bolt comes loose and stresses the other side. I have have one and love it.
  5. Dave C

    Dave C Member

    The sharp edges are called "stress risers" and do exactally what it says; gives a place for a crack to start. You'd think that more material is better but that's not true. I've read Hot Rod and Circle Track magazines for years and I can remember an artical where they used ultrasound, a liqued, and semi finished and finished parts. What they were showing was the difference in the waves coming off the parts under ultrasonic vibration. The rough parts had spiky waves coming off and the smoothed parts had a nice, even rounded wave coming off the part. The up-shot is the places where the rough waves came off the parts were prone to cracking and after polishing the chance of breakage was greatly lessened by making the parts nice smooth and shiny :)