wrongway
Pro
Posts: 1078
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posted April 22, 2011 07:52 PM
I know 46's help a stock motor ... I dont know if 47's make more power with a stock intake runner. Maybe Jim knows.....
I can get you a set of each if you want to try both.
Roy
  
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Shane661
Needs a life
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posted April 23, 2011 04:07 AM
quote:
So on a Stock motor with a supersport head.Should you do the 47mm or 48mm TB's?
No need for 48's on a stock motor. 47mm is more than adequate. Look at the kind of power they make on big cc Busa's with stock 46's...
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Y2KZX12R
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posted April 23, 2011 04:46 AM
The 47's are good for all applications. The 48's would only really benefit a 2x5 or a 3x5 motor. In short, these throttle bodies work best with a port designed to match.
All of this is about taper not CFM flow. A 1570cc zx14 at 12000 rpm uses about 1/4 of the flow potential of the four 47mm bores. in other words the engine is consuming lets say (i don't have the numbers here in front of me know) 300 CFM. Well these 47mm throttle bodies flow over 1200 cfm.
When you have large amounts of taper in a port like these bike heads, the pressure gradient in the port is large. So the pressure at the MCSA is much lower than the pressure at the lip of the bell-mouth. This rapid gradient helps use the 14+ psi of ambient air pressure to push air into the engine. If you have a partial vacuum or lower pressure gradient right to the bell mouth the engine wont make the high rpm power.
Generally the shorter the port and the more total taper the better the port is for high rpm. But is makes the port really bad for low and mid-range power.
This is why porting one of these heads for flow on a flow bench doesn't work. Yes you can keep enlarging the port and flow more and more air but the velocity goes down as does the power.
Theres a lot of math that goes into one of our CNC ports. There all designed in the computer in a 3D model so we can control every aspect of the port. There are 5 critical math calculations that go into the design of a port and all 5 have to be right. Changing a ports MCSA from 1.62 sq in to 1.72 sq in (about .010" of material removal) has a dramatic effect on power. Port MCSA must be matched to the engine size as close as possible.
Bigger isn't always better.
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Y2KZX12R
CompetitionCNC.com
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wrongway
Pro
Posts: 1078
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posted April 23, 2011 07:44 AM
Good write up Jim. One thing I did notice is that the taper on the stock throttle bodies are completely removed when they are bored out to 48mm. there is still a fair amount of taper left with the 46 mm bores.
Do you think that the throttle body not having any taper ( with the 48 mm) have a negative affect?
Also , I am assuming that the fuel map need to be increased by the same amount as the increase in air flow , wether the increase is from throttle bodies or porting, at least on the high rpm side. Would that be a good way to get a baseline map?
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smokinZX14
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posted April 23, 2011 12:40 PM
Good info Jim , Thanks ..
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Smokin Performance Cycles..
Tampa Bay , FL .. Brocks Performance Dealer ..
Gen 2 ZX14R Best ET 8.43 , Best MPH 164.95
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BlackMagic14
Needs a job
Posts: 2058
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posted April 23, 2011 02:13 PM
So do the 47mm TB's with a SS head reduce power in Low RPM's
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Swiftkart
Expert Class
Posts: 349
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posted April 24, 2011 01:30 PM
quote:
So do the 47mm TB's with a SS head reduce power in Low RPM's
No, they make more power all the way across the powerband, which surprised me, I thought for sure the 44's would be better down low, but they weren't on SS head.
.
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2006 ZX14, Brock CT-Meg, PC, ignition module, E85, 214 lbs suited, 8.96@152.32 1.46 60'
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Y2KZX12R
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posted April 24, 2011 04:12 PM
 Edited By: Y2KZX12R on 25 Apr 2011 00:17
quote:
So do the 47mm TB's with a SS head reduce power in Low RPM's
quote:
No, they make more power all the way across the powerband, which surprised me, I thought for sure the 44's would be better down low, but they weren't on SS head.
There is no power reduction from the 47mm throttle bodies at any rpm with a stock head or ss head.
Roy, yea the 47's are almost straight threw. The fuel you need to add is just for the extra 6-8 or so hp, not the difference in airflow. Its not much.
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Y2KZX12R
CompetitionCNC.com
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