I have been stuck in a world of carburetors ever since I started riding. About 5 years ago I decided to do a 124 for my FLTR and then in the mean time change it over to EFI. Well, I chose the path of least resistance and I reverted back to a carb. (I have everything needed for the EFI conversion). I also bought a 2016 Slim. This bike has a Stage I but that is about to change.
I am curious as to what parameters do you use when selecting a larger TB? I can't give any data as of right now on exhaust port entrance diameter or head flow data for the Slim as of yet.....
I want to learn and understand this more before I purchase as I have a feeling that I made this mistake for my FLTR and will probably repurchase some stuff.
Thanks. :scratch: :nix: :pop:
IMO, it's more about choke points & where you want the increase. If you have a high RPM big engine, a stock small TB will be the biggest restriction. If you have a huge TB and stock heads on a big engine, the heads are the choke point. If you have a big TB & well ported heads on a big engine, but V&H Big Shot Long pipes, the exhaust is the restriction.
High RPM power requires lots of air movement. Low RPM power requires velocity. Balance is the key- big slow ports on a small engine reduce velocity to the point of sluggishness, tiny ports on a big engine is like running a marathon while breathing through a straw.
Cubic inch and horsepower goal
So are you guys matching the manifold runner diameter to the port entrance diameter and crossing your fingers?
It seems to me that I would want a TB that flows close to same CFM as what the head flows (slightly more to speed up as it's entering the port)?
What do your heads flow?
Quote from: Ohio HD on January 01, 2022, 09:03:36 AMWhat do your heads flow?
I will get back to you on this as i have to find the flowchart. I will post a picture of it when I find it. It's over 300 at 600 lift IIRC.
I didn't remember correctly. Just under 300 cfm at 600 lift.