Woods 50.5 vs 48 mm mic

[dynajohn]

I am currently running a Woods 50.5 cv on my 117 C.I. twin cam. This motor is making excellent numbers at 147 HP and 144.5 TQ. I would like to try the mic 48 hoping to improve the peak a little. I am currently running a T-Man performance modified S&S G manifold with the Woods carb and I would run the same manifold configured for the mic 48 with a raceback. What do you think? :)

[Mike]

The carb that is on the bike is going to be tough to beat. Having said that, we know from flow bench work and experiance that a Mikuni compares to CV style carbs as if it were 4mm larger. I.E., a 45 Mikuni flows nearly the same air as a 50 CV and a 40 Mik sim. to 44CV. In theory the 48 should produce higher peak numbers than the WA 50.5. We would normally recommend the Mik 48 as part of a package such as yours. We have found that 150-155hp seems to be a peak for these carbs, so in cases where a motor has a higher potential, we have to look elsewhere. Now we get into stuff that is not user friendly for street applications. This all assumes the rest of the package will support higher numbers (pipe, heads, cam, etc.). The air cleaner will have to be something similar to the WA unit on your 50.5 (assuming your running his air package). Zippers has some new ones similar to the H-D 51 CV. I like the inward tapper as opposed to the opposite, it just seems the air flow is less obstructed as it's gathered at the mouth of the carb and is already headed in the right direction. If you decide to make the change, let me know how it works!
Regards, Mike

[dynajohn]

By preferring an inward taper on the air cleaner are you referring to the big Woods type K&N filter that is larger on the outside (came with my 50.5 from Bobby) and tapers to a smaller size at the carb or the filter that came with the 51mm kit from Harley that tapers to a smaller diameter on the outside? The Woods filter flows great but interferes with my right leg. When dyno tuning this engine combination there was only about a 1 HP drop with the Woods filter in place (insignificant and within the normal deviation between runs in my opinion). We didn't test with the smaller filter that came with the stock 51mm carb so I don't know if it would have flowed as well. Have you experimented yourself or heard of anyone modifying the 48 mic on the inlet side (not boring out the carb) to get higher flow? I have talked to one tuner that says he modified the 48 mic inlet by changing the taper into the carb venturi and consistently picked up HP and TQ? :)

[Mike]

I prefer the taper get smaller away from the carb, as the SE 51 does. The Wood and others taper toward the carb. The air has to make a longer/sharper bend to enter the mouth of the carb with those that taper towards the carb. Intuitively this does not seem as good as the straighter path from those that taper away from the carb. Dyno testing seems to bear this out, but both flow enough it is a small difference (we've seen similar hp drops when the elements are removed vs. installed). The inlet modifications are done by both T-man and Walter's Technologies and does make a significant difference with a well optomized package. Some air cleaner adapters affectively undo this mod. T-man has a very good complete package that uses the S&S manifold you mentioned earlier (but he uses the Wood stlye a/c, unless we ask for SE 51 style). I'll see him in two weeks at Cincinnati and will talk to him about this (Zippers also).
Regards, Mike

[dynajohn]

Thanks Mike. It is Tom Reiser I was referring to. He built the original 117 motor I was referring to and has my 03 Dyna at his shop now for further modifications. He is working on an interesting plenum manifold setup for my bike, ask him about it at Cincinnati. The T-Man 48 mic you referred to will be a fallback setup if the plenum setup doesn't prove to be fully streetable. Wish I could be at Cincinnati like last year but I wont make it this year. Very nice web site.

[Mike]

Thanks for the compliment on our web site, it's only going to get better! With any luck TR and I can have dinner one night in Cincity(we tried last year but didn't work out).
Mike

[sean fxd]

<<In theory the 48 should produce higher peak numbers than the WA 50.5. We would normally recommend the Mik 48 as part of a package such as yours. We have found that 150-155hp seems to be a peak for these carbs>>

This would only be in a case where the flow requirements of the engine exceeded the capcity of the WA 50.5 correct? Or are you saying that the 48 will always produce higher peak numbers. Thank you...very nice forum here.

[Mike]

Yes, if the flow capacity of the heads/exhaust/cam combo is greater than that of the carb. The real limit is the HP potential of the motor combo. The CV will be a more turbulant carb vs. the Mikuni and therfore flow less air, size for size. The carbs ability to gather air at it's entrance also plays a part.
Mike