almost_les
Zone Head
Posts: 590
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posted September 28, 2009 04:06 PM
lobe centers vs ptv clearance
can someone remind me the general rule of how much (roughly) ptv you gain/lose per degree of lobe center change. right now my exhaust is at 107 with .078" clearance and i want to know how many more degrees (roughly) i can go to get .065" PTV clearance. the motor isn't pulling as hard up high as i would like it to so i want to see how it will do playing with the exhaust cam. setup is: zx12r with stock pistons/cams/crank, ported head, and a thin head gasket for extra compression. intake lobe center also at 107, revving to 12.6k.
  
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KZScott
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posted September 28, 2009 05:04 PM
going with higher CL will increase clearance
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01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
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almost_les
Zone Head
Posts: 590
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posted September 28, 2009 06:51 PM
yeah, i remember about how bigger numbers give you bigger clearances, i just can't recall how much clearance you lose for each degree down you go.
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entropy
Moderator
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posted September 28, 2009 08:33 PM
with my set up i lose about .005" PTV for each degree lower on the CL's.
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KZScott
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posted September 29, 2009 04:43 AM
But you want higher numbers for more top end power right?
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01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
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tcchin
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posted September 29, 2009 06:29 AM
Or more overlap...
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WRECKSHOP
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posted September 29, 2009 07:21 AM
Come on GURU's...Chime In
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tcchin
Zone Head
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posted September 29, 2009 08:30 AM
Using Karl's numbers of .005"/degree, we have: .078"-.065"=.013" and .013"/.005=2.6 degrees. Of course, you would need to measure your real PTV, as this is just an estimate.
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almost_les
Zone Head
Posts: 590
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posted September 29, 2009 10:50 AM
yeah, more overlap. the goal is keeping full power at redline. around 11,500 im starating to lose hp. just to make sure i have the general theory down: bigger number on the intake means more retard it and is better for top end and smaller #'s for more mids and lows, and on the exhaust, bigger #'s means more advanced and less ovelap, while smaller #'s indicate retard and more overlap. right?  seems like im gonna be doing a lot of testing over the winter.
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dougmeyer
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posted September 29, 2009 12:01 PM
 Edited By: dougmeyer on 29 Sep 2009 20:03
It is not a constant rate. It varies with the piston's rate of movement per degree of rotation which is determined by stroke and rod length, and the lobe shape. You could plot it, or compute it, but you really have to measure it. There is essentially no other way.
You can certainly judge whether they will increase or decrease based on which way you move the cam, but how much per degree...... well you'll have to measure that or ya takes yer chances.
Also you might read this: http://www.muzzys.com/articles/lobe_centers.html
Doug
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Shane661
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posted September 29, 2009 12:08 PM
You are running to 12600 actual rpm, stock pistons and rods then?
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entropy
Moderator
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posted September 29, 2009 12:20 PM
quote:
It is not a constant rate. It varies with the piston's rate of movement per degree of rotation which is determined by stroke and rod length, and the lobe shape. You could plot it, or compute it, but you really have to measure it. There is essentially no other way.
You can certainly judge whether they will increase or decrease based on which way you move the cam, but how much per degree...... well you'll have to measure that or ya takes yer chances.
Also you might read this: http://www.muzzys.com/articles/lobe_centers.html
Doug
+1 to Doug.
The "about .005" " that i gave was in the area of CL = 106 to 102 for my set up.
AND
exh is different than intake,: I dis-remember which is which, but one is .0045/degree and the other is .0058" (ave over CL = 102-106)
AND
They are certainly different for different cam grinds.
I use those numbers to calculate how much to skim the head or sink the valves to get the CL's I want while keeping min PTV very close to int=.040, exh = .060.
BEWARE:
If you are playing with tight PTV, you must measure min PTV on all 16 valves, or use #1 as yr reference, but have yr head guy hold valve protrusion into the chamber +/- .001". This is not simple or cheap...
I have repeatedly seen the length of the valve keeper to sealing face vary up to .006"
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NOX
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posted September 29, 2009 02:07 PM
Wow, 12600,
I think my ecu was tripped to 12200.....
I know when I shift, it is DEEP in the red
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rgeorge
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posted September 29, 2009 04:48 PM
Edited By: rgeorge on 30 Sep 2009 00:48
I measured ptv for several cam positions during my motor build so I could get a feel for the usable range. Here is a table of my measurements from my engine build spreadsheet.
I built a double action ptv tool and set up two indicators at once to take the measurements. Sorry, didnt take any pics of the setup.
The JEs have a deep valve pockets and give plenty of clearance.
Duration is the same because for in and ex because stock intake cams are used on both sides.
On my next set of custom pistons I'll have less valve pocket on the intake side, and get more CR.
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almost_les
Zone Head
Posts: 590
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posted September 29, 2009 06:15 PM
thanks for the info guys. its starting to seem i'll be better off getting aftermarket pistons to get the cl's i want and still have safe clearances. i guess for now i'll just keep the numbers where they are at.
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KZScott
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posted September 29, 2009 06:26 PM
Flycut the pistons?
____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
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almost_les
Zone Head
Posts: 590
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posted September 29, 2009 06:39 PM
quote:
Flycut the pistons?
that might be a possibility. i think need to talk to sal about my options here.
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KZScott
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posted September 30, 2009 01:35 PM
that or sink the valves maybe. Karl has a little expirience there 
____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
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dougmeyer
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moderated
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posted September 30, 2009 01:59 PM
You don't want to be sinkin' the valves. Bad flow, spring installed height, and retainer/shim issues will ensue.
Also, when "customizing" your pistons by changing the depth of the valve pocket, be VERY wary of getting the floor of the inlet valve relief too close to the inside top edge of the top ring land.
D.
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almost_les
Zone Head
Posts: 590
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posted October 01, 2009 11:04 AM
talked to sal about possibly just flycutting the exhaust pockets. might go with that option... still need to to some tearing apart and measuring before i know for sure what will work out. does anyone know the stock head gasket thickness? i think i read somewhere that it is .023" but i would rather know for sure.
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Y2KZX12R
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CompetitionCNC.com
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posted October 02, 2009 10:48 AM
quote:
You don't want to be sinkin' the valves. Bad flow, spring installed height, and retainer/shim issues will ensue.
Also, when "customizing" your pistons by changing the depth of the valve pocket, be VERY wary of getting the floor of the inlet valve relief too close to the inside top edge of the top ring land.
D.
Good points Doug.
Its a battle to get over 15.5 to 1. Just ask Karl 
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