zrxdean
Needs a job
Posts: 2225
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posted June 08, 2007 07:51 AM
Race exhaust cam smaller than stock... 'splain it to me.
I'm a little clueless about the kit exhaust cam. Can anyone shed some light on this?
Dean
  
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zrxdean
Needs a job
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posted June 08, 2007 07:52 AM
Something a little more detailed than "bigger isn't always better" please.
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rgeorge
Expert Class
Posts: 220
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posted June 08, 2007 09:52 AM
I don't know anything about those cams but I can take a guess.
"Race" cams have a much more aggressive lobe profile than stock cams.
With an OEM cam the valve opens slowly to its maximum lift and then closes slowly. Because of the mild profile the valve train has a long life with low maintenance and is very reliable.
A "Race" cam pushes the valve open quicker and holds it open for a long time before closing quickly.
Just think - Area under the lobe profile curve
Just tor shits and grins, if you were to look at the duration at 3mm lift ( when things are really flowing) instead of 1mm, I would bet that the "race cam" would suddenly look much bigger than the stock cam.
PM Doug Meyer. He has LOTS of experience with Kawasaki camshafts.
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dubious
Needs a life
Needs more time to ride!
Posts: 8442
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posted June 08, 2007 10:06 AM
+1,
that and with the intake being longer duration and lift, you would likely have too much blow down with the stock exhaust cam duration.
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zrxdean
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posted June 08, 2007 10:20 AM
It could be a steeper ramp, but it would have to be a lot more aggressive to compensate for the .5mm less lift and 12 deg less duration. I guess we need more info.
I've never seen an aftermarket exhaust cam with smaller lift and shorter duration, has anyone else?
Dean
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dubious
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posted June 08, 2007 10:28 AM
to prevent blowdown, and the cams are inetended for use with high compression head gasket, =less comb. chamber volume, equals increase blowdown of the intake charge.
The larger intake cam dumps more charge in, free flow exh. and less comb chamber volume with too much valve overlap woul likely dump raw unburned fuel / air into the exhaust.
When it burns in the pipe, you lose HP, need to keep the charge in the cylinder during the burn...
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zrxdean
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posted June 08, 2007 10:47 AM
I understand, but couldn't this be better controlled with cam timing? Maybe I'm missing something.
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rgeorge
Expert Class
Posts: 220
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posted June 08, 2007 01:51 PM
Keep in mind that the stock cams are designed with the stock (somewhat restrictive) exhaust and the race cam is for use with free flowing exhaust.
But I don't understand why they use less lift
Rather than just making guesses as to what is happening with the cam timings, I will show you some good reading material that will help you guess for yourself.
Go to
http://www.wighat.com/fcr3/camtruth.htm
and skip down to these sections:
Exhaust Outflow Interaction
Mixing and Matching Components
This page is very dense with information. Ive read it several times and probably haven't picked up half of the info yet
The engine theory page and his valve timing chart are also very informative.
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zrxdean
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posted June 09, 2007 06:31 AM
 Edited By: zrxdean on 9 Jun 2007 07:58
Interesting reading from Buddy Rawls, thanks for the link. I read it through, some sections twice. I confess that I'm not any clearer on the smaller exhaust cam, as opposed to using lobe centers to manage cylinder pressure.
Maybe I will call Webcam and see if they can shed any light on it.
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zrxdean
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posted June 09, 2007 06:58 AM
I sent Buddy Rawls an email about this, maybe he can help me understand.
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zrxdean
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posted June 09, 2007 10:52 AM
Here's Buddy Rawls' fast response;
Dean, correctly derived valve events are functions of the intake and exhaust flow relationships (restrictions essentially) and the pumping volume of the cylinder. Situations in which the exhaust has a very high flow relationship, compared to the intake, can easily have less exhaust valve activity than the intake.
the way it really works is like this: for a given cylinder displacement, over a given rpm band, the intake and exhaust port flow parameters (seen as a restriction to the cylinder) will dictate the intake and exhaust openings and closings and ramp rates, with respect to the piston position (or crank rotation).
the finished valve events and ramp rates will translate into lobe durations and intake and exhaust centerlines. These durations and lifts and lobe separations (if single cam) are used for manufacturing and identifying the cam. looking at cam specs without knowing the flow relationships is futile. You cant say this cam is good and that cam is not, without knowing the engine parameters.
I was working with a guy on a toyota 20R/22RE 4x4 once. the cam grinder I was using did not have a lot of choices for the lobes that work on that core. So, I went to after market 4x4 shops to see what was available. what I saw was most everyone was offering the same cams, or rather very similar looking cams. The cams were the basic 10-12 degree intake/exhaust split with a lobe separation angle around 112. categorically, they looked just like everybody's small block chevy cams that the aftermarket had been peddling for years. They even went into detail to explain how thoroughly tested the profiles were. i called and talked to several of the places, asking questions about exhaust system diameters, and intake flow and yada-yada, and they could not tell me anything. So i started playing devils advocate, asking about one set-up, then another. It got to where they would pawn the questions out of their league and say, the cams were spec'd by another company, and they just sold them.
I did not have access to a flow bench, so i measured cross-sections and port volumes to calculate the max flow potential. what I determined was the exhaust to intake ratio was nearly 1:1. I ran the numbers on the valve events and the numbers did not look ANYTHING like what the 4x4 places were selling. I finally found reference to one build shop that was doing some open wheel racing classes for road racing, using the toyota motors. And guess what? the specs he had listed were very similar to the trends I had calculated. so I contacted them. turns out they were an R&D shop for the real "Toyota" guys over in the states. Not only were they doing the open wheel race cars, but also lots of 4x4 stuff, as well as working on the new toyota V8 (at the time). I talked to them about what the calcs were showing, and struck up a good relationship with the main engine guy. etc etc etc.
Anyway, what I was trying to show is that things are not always as they seem. Just because something looks out of the ordinary or different from conventional thought does not mean squat. there is no requirment at all for a cam to look like this or look like that. the cam is what it is.
In buying in the aftermarket, off the shelf, you are limited to whats out there. there is nothing wrong with whats out there. But blindly grabbing and buying is not the way to do it. For instance, I can calculate valve events, and select an OTS cam that will work quite well. But the cam was not blindly chosen. the end effect is that the cam is an awesome cam. truth is, the cam is just a hunk of metal. the leg work is in knowing what you need. This is where the average enthusiast can go wrong.
If the factory is offering the performance cams then I would have to assume they have been very well thought out. WHAT YOU HAVE TO DO is talk to them to determine if your entire motor set-up was close enough to their test engine to make the cams a valid bolt-in for you. If you have added headers, they may be different diameters or configuration than what they used, or the rpm you want may be different, etc etc. It will be virtually impossible to talk to the Kawasaki engineers, but you might can find some heavy shops that do a lot of the work for Kawasaki that can give you some answers. You dont want Bolt-on Barneys, you need people that really understand whats happening.
Buddy
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supra5677
Pro
Posts: 1279
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posted June 09, 2007 08:27 PM
I agree the closing ramps on the exhaust are probably way more aggressive.. So many other factors to consider as well. I'm sure kawi took all factors into account..
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supra5677
Pro
Posts: 1279
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posted June 09, 2007 08:35 PM
Is the advertise duration total duration or duration at .050.. Duration at .040 or .050 is what counts.. My webcam intake on my zx12r has more lift, more duration at .050 but less total duration... Find out what the duration at .050 is compared to the stock exhaust cam.. Learned that from DougM
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krexken
Zone Head
Posts: 732
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posted June 11, 2007 11:12 AM
Great info, Dean, not that I understand it entirely. The 10 I may get to work on was only gonna get an intake cam. Not sure why.
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zrxdean
Needs a job
Posts: 2225
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posted June 11, 2007 12:57 PM
This may be why, there's a few posts on another board about the exhaust cam being smaller, costing horsepower. No one knows why.
Supra the KHI numbers above are total duration, for both stock and kit cams.
Just installed a race intake cam with stock exhaust, 108in/104ex, .028" squish (.5mm gasket), Wiseco stock bore pistons. Hopefully have it ready to dyno this weekend.
Good luck with your build Ken.
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supra5677
Pro
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posted June 12, 2007 07:26 AM
ok Nice combination. Did you extend the rev limiter or leave it stock?
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zrxdean
Needs a job
Posts: 2225
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posted June 12, 2007 11:02 AM
Thanks. Stock limiter, the ECU extension trick doesn't work on the ZX10 Im told. I'm not gonna shell for the DJ timing box just yet.
I PM'd Doug Meyer about the cam, I'll post what he says.
Dean
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supra5677
Pro
Posts: 1279
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posted June 14, 2007 07:03 AM
Nikko G pack extends the revlimiter..
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zrxdean
Needs a job
Posts: 2225
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posted June 14, 2007 07:54 AM
Thanks, I'll look into it. If it carries torque later with the hot intake cam I may need it. Have you used one?
I heard back from Doug, he's not sure about the kit exhaust cam and is gonna see what he can find out.
Dean
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technic
Parking Attendant
Posts: 11
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posted June 14, 2007 10:45 PM
I used the kit intake cam, kit exhaust cam with kit springs, degreed to 107/104 thin head gasket, standard exhaust with cat removed and mufflers rebaffled and pc mapped with 173.31hp and 80.41 torque id like to run an akrapovic but its all $
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zrxdean
Needs a job
Posts: 2225
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posted June 15, 2007 08:05 AM
Interesting. Do you have the before numbers? I'll give you a 12-pack to make a pull, swap out the kit exhaust cam for the OEM cam and make another pull...
Dean
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technic
Parking Attendant
Posts: 11
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posted June 22, 2007 01:52 AM
Yeah.. nah id rather b riding than pulling 
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