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Cam timing question.

Old 12-24-2010, 09:11 AM
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Cam timing question.

Over the summer I have developed what I am almost positive is a leaking valve guide/seal. So while I'm in there fixing that I've decided to add a little to my mod list.


I've been seeing the mention of using exhaust cams in place of the intakes. Never actually heard of anyone doing it though. I may be the first! I got another set of exhaust cams of ebay a few weeks ago.


I would also like to play with the timing a little. I want to see how it responds with a little more overlap. Yes, I know I will lose some low range...it doesn't bother me.


This will be my first time doing this type of thing. So my question is how much should I change each cam? I realize that there is probably no exact answer but I was curious if anyone has an opinion on a good starting point. I've been looking at Mori and Yoshi specs to get an idea but I'm not sure how much their cam profiles influence where they set their lobe centers. My first thinking was about two degrees on each cam. Feel free to tell me that's wrong.



I also experimented with slotting the gears on the ones that came with the new/used exhaust cams. So I know that it can be done, by me, on the ones that are in the bike. The sprockets are hard! Filing has almost no effect. Carbide dremel bits do the trick. But I expect to consume a few when I do all eight slots later on.

Oh yeah... I'm also considering trying a DIY port and polish. I haven't entirely made up my mind yet, I''l wait until I get the heads off again and I can take another look.
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Old 12-24-2010, 10:14 AM
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Old 12-24-2010, 10:41 AM
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I've actually read that quite a few times. I was hoping for some insight that is a little more SuperHawk specific.
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Old 12-24-2010, 11:28 AM
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As far as the port and polish, just blend the bowls to the valve seat insert. I wouldnt touch it, as it is pretty dang good. You could work on the valve guide protrusion, but that is a significant risk for very little reward. This head can really flow. As for the overlap, you do need to realize that any change at the cam will be counted double in crankshaft degrees. You will be looking at changes less than 10 degrees crank, most likely. This means that 5 degrees of change at the camshaft, which really isnt that much altogether.

Other things that you can do, and others can weigh in here, is to lightly clean the combustion chambers (which have almost zero shrouding) and to remove excess weight (their are random pieces of metal in the chain passage on the head just hanging out and an extra boss on the head for "spare" CCT's).
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Old 12-24-2010, 11:53 AM
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commonly recommended if doing much of anything port wise is blending the bowls as mentioned, matching surfaces to intake/exhaust better and a 3 angle valve job as adding something. Mostly in the context of doing other mods to exhaust or higher comp pistons though.
For cam timing, you could look at the specs for the moriwaki or Yosh stage I cams and use that as some guide for where to set the stock cams if you are going to slot them and time them yourself. Its a reasonable starting point and the stage I cams don't really add much lift. The trick of 'swapping' is intake for exhaust cams and I believe it ends up working out to very close to about moriwaki timing using lobe center method on the stage I cams. You obviously change the power curve slightly and probably give somewhere to get more other places. I found when I did the stage I cams alone, there was virtually no change in power (measurable on the dyno at least), but when I added in everything else, including full exhaust that there was a noticeable increase - how much was due to what hard to measure - probably sum of the parts more then any one thing.
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Old 12-26-2010, 04:52 PM
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Found the leak!




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Old 04-26-2011, 09:16 AM
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Exhaust cams

I have an extra set of exhaust cams laying around. Is it worth swapping my factory intake cams out? I have a short block with je 11.5 .05 over that I was thinking of doing this too. Of corse I would polish, port match and 3 way. Is this going to be a seat in the pants difference?

Last edited by lukenukem47; 04-26-2011 at 09:19 AM.
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Old 04-26-2011, 10:47 AM
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What year is your bike and what year exhaust cams did you pick up??
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Old 04-26-2011, 11:22 AM
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The bike is a 02 the motor is 02 short, the heads and cams are 98 (both sets of exhaust cams). The ECM is 02 carbs are 98, air box is 98 k&n carbs are jetted not sure what jet number however

I'm taking apart 2 bikes to make one great one. Everything else I'm selling
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Old 04-26-2011, 04:57 PM
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My bike is a '98 with four '98 exhaust cams. Alone, I can't say say how much of a seat of the pants difference it will make. The lift is only marginally higher verses the intake cams. Same duration.

I degreed mine also. 101/106. Which I feel has made quite a bit of deffence. Lost a little of that tractor like grunt below 4k rpm but is much more alive in the upper ranges. I used to do most of my shifting around 7-8k. Now I'd say it's generally around 9. I also have HC JE pistons and a few other minor things (see signature.)

All of this together and the bike is a whole new animal. My dad has a bone stock VTR so I can ride them back to back. It's night and day.

Last edited by mboe794; 04-27-2011 at 04:53 PM.
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