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Throttle Body Selection

Started by WhipLash96, January 01, 2022, 06:58:15 AM

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WhipLash96

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:
Thanks,
Whip

rigidthumper

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.
Ignorance is bliss, and accuracy expensive. How much of either can you afford?

harpwrench


WhipLash96

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)?
Thanks,
Whip

Ohio HD


WhipLash96

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.
Thanks,
Whip

WhipLash96

I didn't remember correctly. Just under 300 cfm at 600 lift.
Thanks,
Whip