Cam Timing

Q. a question for you, ken… in a post to this thread on aug. 4th (about cam timing) you wrote, “The stock numbers are 107,104. The best Hp numbers found on a dyno are 103,107”. are these numbers for the ’91-’95 motor, or for the ’96-’00? i am assuming that these numbers are int,exh @ 1mm of lift.

A. Those numbers are indeed taken at 1mm of lift, for intake and exhaust. Stock #s are 107 intake, 104 exhaust. I measure at 1mm of lift LESS valve lash. Or in other words if valve clearance on valve being checked was say .010, I actually check at a lift of .030. This is easier than re-shimming the valve to 0 clearance and always works out the same. The posting were I said 103,107 was a typo, it should have read 104,107.

If you calculate off the stock numbers provided by the shop manual, you get 105,105, which is why I guess Muzzy recommends those.

I once found a mathematical calculation where the length of the con rod and the stroke dimension were used to find the theoretically perfect lobe center for the intake cam. Those numbers for the 7 inputted works out to 103 for a 91-95, Zx7 and for the 96-00 motor also. Interestingly enough the Kawasaki RACE KIT catalogue recommends 103 +/- 1 for intake and 105 +/-2 for exhaust

The smaller # on the intake means the valve begins to open sooner starting cylinder filling. There was a interesting post a few days ago about compression versus cam timing/Duration.

I usually time cams by engine compression searching for the figures that give me the highest cranking compression. This however is a lot of hard work.

On the 91-95, and 96-00 motors, I have found the highest cranking compression at 104intake, 107 exhaust. Man, im giving away all my secrets to this club!!

I do not have all the exact open and close #s with me today but will post them for you ,For both the stock cams and the KIT cams.

In my 937R I run a replica version of the Kawasaki kit cams, which have more lift and duration than stock. I will post those numbers for everyone Monday as I do not have them with me today.

Also keep in mine the numbers in the shop manual are BOGUS as they are the exact .001 inch of lift open to the .001 inch of lift closing. A valve has to be at least 1mm open in order to flow any appreciable amount of air!!. That’s why the duration seems so long when it really isn’t. They are including all the movement of the ramps on both sides of the lobe. This does nothing for us, so why calculate it. BOGUS #s. I have measured many ZX7s STOCK cam timing have found them to be very consistent and the same.

For 89-90 motors, 102 intake, 104exhaust gives the highest cranking compression.

Ken Waters

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Cam timing is one of those things that everybody does differently. I have no answer as to how they got the figures that they reported to you. Problem is, a lot of people are very secretive about stuff and the truth is they don’t always tell you what is really what. People who are very good at timing cams and cutting valve seats have to be the worst, and that’s unfortunate. The 104,107 are top end numbers that do sacrifice some midrange, as far as the curve goes.

Your 97,102 could very well measure out at something totally different, if I check it and vice versa.

What you really need to know is open and closing numbers. Did they give you those???

I will post those numbers Monday for stock and for Kit cams, and my own personal #s. It will be Monday morning 6:30am EST, before I will be back on the Web. Look for this info after then.

Sig, My 937R was producing 138 hp with the 105,105 Muzzy numbers. Changing to 104,107 brought power up to 142 with no other changes.

Keep in mind, my engine is built to the max! I have put 13,000 miles on it in this current state of tune with no reliability problems so far.

BUT HEY, everybody get this. I posted elsewhere on this site about running this past Sunday at Atlanta Motor Speedway. I really ran the bike hard there, coming off NASCAR turn two apron down the back straightaway. SOOOOOOOO when I got home I decided to check valve adjustment. Guess what I found??? A piece of the cam chain GUIDE, that fits in the top of the valve cover had broken all into pieces. That’s the rubber piece that snaps into the valve cover.

So I dropped my oil pan and found chunks of it in there along with the oil pump pickup screen almost clogged. Talking about dodging a bullet!! I have never seen or heard of this piece doing that. Good cheap insurance to replace this at the next valve adjustment.

I could only imagine my engine blowing from oil starvation down AMSs long back straightaway.

Ken Waters

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Jay, NO, I do not find Top Dead center by sticking a dial indicator through a spark plug hole. I use what’s known as a positive top dead center stop threaded into the sparkplug hole. Like a extra long spark plug that the piston hits as you turn the crank by hand. With the degree wheel installed you split the difference and that’s true TDC. There is no more accurate way of doing this since the piston tends to dwell at TDC a few degrees. This is the way NASCAR engine builders do it. I know this to be fact as my Father was one.

Josh, as far as checking it at .050″ of lift, that’s industry standard for cars, where the industry standard for motorcycles is 1mm or .040. If you order a megacycle catalogue you will see all of their cams listed as 1mm of lift. It really doesn’t matter. I could check MY cams at both 1mm and or .050″ and will come up with the exact same lobe centers, but different degrees of duration.

That’s what makes it difficult to compare one cam to another.

Kawasaki lists it cams in the official shop manual at .000″ of lift giving very optimistic duration numbers that are meaningless!!!

Stock ZX7 cams measured at 1mm of lift work out to opens at 14degrees before top dead center, closes at 48 degrees after bottom dead center. If we do the math 14+48+180 divided by 2 -the smallest # 14 equals a lobe center of 107. I have found this to be so on every ZX7 I’ve checked. How many have I checked? ALOT!

The exhaust measured at 1mm of lift works out to opens at 40 degrees before bottom dead center and closes at 12 degrees after top dead center.

The math 40+12+180 equals a duration of 232 degrees. 232 divided by 2 and subtract the smallest #(12) equals a lobe center of 104. The number Ive seen on every stock ZX7.

That’s why Muzzy recommends 105/105 for all Zxs 91-95 and 96-00, if you go by the numbers in the KAW shop manual you come up with 105/105.

I run Race kit cams which has more lift and duration. The current specs in my engine today are

Intake opens 21/closes49, this gives a duration of 250degrees, exactly 8 degrees more duration, not much but has .021″ more lift.

Exhaust opens49/closes15 for a duration of 244 degrees a increase of 12 degrees but also a increase in lift of .010.

The lobe displacement numbers work out to 104 intake, 107 exhaust. Right were I like them . I see no way possible for Jays cams to be at 97/102.

In 1992 I was helping out a racer I just met who had already previously taken his engine to pro road racer Mike Harth to build. He was building a replica of the engine he used to beat Scott Russel at Daytona that year in the 50 mile supersport race. Actually Scott ran out of gas on the last lap while Mike was running second. It was later determined that Mikes bike had a steel gas tank instead of aluminium and apparently steel is thinner and could hold a few drops more gas.

Anyway, when I went to pick up the motor I asked him what the cam timing was and his response was “THATS A PROFESSIONAL SECRET”!At that time the only way to do it was to press off the old gear an repress it back on. There were no hub kits on the market then. I later discovered the timing was stock at 107/104. The point is, who can you believe??? Maybe factory didn’t want to tell Jay the truth for the same reasons. HE HE they say, we will just tell him 97/102 and screw everyone he tells. I’m not dissing factory, its just those numbers taken at 1mm of lift, cant work!!! How about my honesty??? Well how far off are my numbers of 104/107 from Muzzys 105/105. Probably not that much.

Ken Waters

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