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Lynn,
My last race bike a FZR 1000 used 4 43mm Kehin carbs. 165 rear wheel HP at 11,000 RPM. The intake tract was so short that you could probably reach in and touch the valve if you had long thin fingers. This bike would idle and with accel pumps even had excellent response. Even so I would have prefered the true demand system of FI if anything had been reasonably priced at the time. Jetting the carbs required a solid week of work. With FI we can tune around several types of problems. Different vacuum at various RPM caused by timing, reflected pulse in the intake tract, or whatever. Since we have both done a lot of tuning, I think you might agree with me that it is much EASIER to tune a system with too small a TB as opposed to an overly large one. The loss of reliable vacuum with a to-big TB can cause real headaches. This is especially true when somebody hasn't done this kind of work and doesn't even know how to "guess" what the problem is. I think the biggest frustration for the amature tuner is to big a carb or throttle body. My $0.02 worth.
Bill Jepson
So the bigger the TB the less it should affect the tuned length, and conversly the smaller the TB the more it should affect the tuned length.
For a reference the difference between carbed and injected engines with a restrictor in the injected system the same size as the choke in the carbed engine as 5 to 8 HP. This is mostly the loss of the booster venturi in the center of the hole.
The improvement in a carbed engine between 36MM and 38MM chokes is about 5 HP. Per Daryl Drummond. Race engine builder.
Is this fun to think about or what?
Lynn E.Hanover
----- Original Message -----
Sent: Tuesday, May 01, 2007 12:27 PM
Subject: [FlyRotary] Re: Throttle body size/ other "Paul" issues
Interesting Lynn,
For the comparison that is 2,035 square mm inlet area. Assuming the bigger 13B could use 1/3 More inlet area the total would be 2,646 square mm. The inlet area of the 65 mm throttle body is 3,318 square mm. Seems like a 65 mm TB would be more than up to the task. A 60 mm TB is 2,827 square mm for reference. Plenty big Buly
Bill Jepson
-----Original Message-----
From: lehanover@aol.com
To: flyrotary@lancaironline.net
Sent: Tue, 1 May 2007 9:08 AM
Subject: [FlyRotary] Re: Throttle body size/ other "Paul" issues
Two 36MM chokes is enough for 244.8 HP at 9,400 RPM, and About 176 HP at 7,000 RPM. I am in California and the dyno sheet is in Hebron Ohio. But I can quote it when I get back if it would help anyone.
Lynn E. Hanover
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