gpz 550 cams in a kz550 or zr550?

Zaddict wrote:

I found photos are not always the best way to compare plugs without a reference plug to compare to in the photo. A dark photo makes plugs look richer, and vice versa. But the plugs in that photo look pretty good to me, compared to what i get out of my gpz's. One looks to have a noticeably darker ground electrode, but other than that, the other three look pretty good.

Yeah, I think those plugs look OK but I can tell you they're darker than I've ever seen them.

Corey, you're correct, everything seems to be running fine now. Just went for another test ride and all seems normal. My impression is as before, a little down on the low-end from the zr550 cams, a little higher on the high-end (to the point where I surprised myself a few times today, as in "oh shit, better put on the brakes quick!"

I was extra careful buttoning everything up yesterday. No problems with idle so far. No explosions while starting.
The bike starts fine hot and cold, and pulls well across the rpm range.
I'll try leaving the petcock on PRI. I just rebuilt the carbs a few months ago, with new float needles and gaskets. Would be surprised if that was an issue.
Engine oil smells normal.
No fuel or oil in the airbox.
Nothing restricting the air filter/box.

mpg for today's 85 mile ride was 35.8.

There's an inefficiency somewhere. I'm guessing the bike is running rich. I'm scheduled for a dyno run Tuesday, if my job schedule allows. Will report back.

I'd put a set of NEW plugs in it and to plug chop. Ride it on the old plugs to a place you can do
WFO blast put the new one's in bust it's ass WFO pull the clutch shut it off stop swap plugs and
ride bach home and look at the plugs.

I'm reading about cam duration and compression. Interesting stuff.

"The most common issues associated with a long-duration cam on the street are a very rich fuel mixture, mild to outright annoying hesitation under light acceleration, an extreme bog under hard acceleration, extremely poor fuel mileage, fouled spark plugs and in general very poor throttle response.

One of the biggest problems with big camshafts is when the cam is added to an engine with insufficient compression. In most cam catalogs, the larger camshaft descriptions include a compression ratio recommendation. For example, COMP’s Xtreme Energy hydraulic flat tappet XE294H cam with 250/256 degrees of duration at 0.050 and 0.588/0.593 inch lift and a 110-degrees lobe separation angle (LSA), recommends no less than 10.5:1 compression when using this cam. This recommendation is often ignored when selecting this cam but it actually is there for a very good reason. As intake duration increases, the intake closing point occurs much later. If you think about it, the engine cannot begin to compress the intake charge until the intake valve is closed. So the engine’s effective compression will be much lower than its static compression ratio because the intake valve closes later. This results in reduced cylinder pressure—especially at low engine speeds. That’s why after a big cam is installed in your engine, it seems like the engine feels sluggish at lower engine speeds.

Proof of this is to perform a cranking compression test before and after the cam swap. What you will find is that the big new cam has reduced the cranking pressure by perhaps 10-psi. The engine has not lost ring seal – the later closing intake valve prevents the engine from creating cylinder pressure until the intake valve closes. The best way to maintain a cranking compression of around 180 to 190-psi with a long-duration cam is to increase the static compression ratio. "

They go on to recommend advancing the ignition as workaround.

Very curious to see what the dyno/gas data look like.

My weekend cam degree test is on hold due to lack of valve cover gaskets. Arrrgh! I always have spare VCG's in my parts bin, but last time must have grabbed the last one.

Sounds like you have checked everything, and the exhaust sniff test at the dyno should tell the story. When you get it on the dyno, and if you will get a recommended change, before you buy any new main jets, I have a bunch of the Factory Pro variety. So you are leaving everything as it is for this dyno to find out what's happening, right? Remember, if you opt to change to pod filters in the future, I still have that good used set with your name on them.

Looking at your pics it seems the timing marks are lining up with the cams in that position - though difficult to tell from that viewpoint exactly, Your chain is not meshed tight on the cam sprockets, Any slack in the chain and your cam and crank alignment marks become meaningless. (If you miss the lines then just turn it over twice to get back again, never reverse it.)

I would check the marks again with the tensioner in place and turn it over a few times to get the slack behind the cams and taken up by the tensioner. It is easy to be one pin or tooth out and they do run ok. If the head has been skimmed before your EX mark may be noticeably below the gasket face line datum.


Adam documented some of his ZR615 development on the gpz550 forum and he had his own zephyr site. I though it odd to run just one of a pair of megacycle cams, and without any actual tested lobe centre numbers I was openly sceptical about it. He had a theory about cylinder head port differences making some gpz cam tuning specs not applicable to his ZR.

I always found it really odd the 92 degree IN cam setting, no other performance cam is spec anything like that...or even the earlier gpz and kz cams. My rpm power cam settings was 108 /112 . It is a pro TTS uk gas flowed zx head.

You may also/and have a flat spot somewhere in your fueling not apparent from a WOT plug chop. Maybe experiment with needle position anti- tamper can be shimmed with tiny washers, pilot airscrews can be accessed under rubber bungs IIRC.
I did quite a lot of trial and error on the main jetting, needle and position and pilot airscrews to get it good. (4-1 / pods ) . Even the factory fueling is quite different between the various similar 550 variants- all running on the same carbs, pipes and airbox.

Well, advancing the intake to the Zx timing would make the intake valve close sooner, restoring compression at lower RPMs. Maybe that is needed more-so with the lower compression of the Zr motor than on the Zx.

It looks like you have two Zr sprockets right now. If you can sweet-talk Corey out of a Z4/IN sprocket, I would try that on the intake just to see what happens.

loudhvx wrote: Well, advancing the intake to the Zx timing would make the intake valve close sooner, restoring compression at lower RPMs. Maybe that is needed more-so with the lower compression of the Zr motor than on the Zx.

It looks like you have two Zr sprockets right now. If you can sweet-talk Corey out of a Z4/IN sprocket, I would try that on the intake just to see what happens.

But then that would increase the overlap by a corresponding amount, correct? Though from what I've read the intake closing timing is the single most important cam setting. Maybe worth a shot. As it so happens Corey was kind enough to give me the ZX sprockets along with the cams, so I just need to find time for the swap.

It looks like you have two Zr sprockets right now. If you can sweet-talk Corey out of a Z4/IN sprocket, I would try that on the intake just to see what happens.



Head....Bang....Table getting somewhere now. I assumed 'thought' you were timing ZX gpz cams per ZX gpz settings.

Zaddict: find those lobe centres, it will clear up a lot of unknowns. Also feed your addiction with slotted cams and dial-in where you want your power....red line rpm or more midrange for street... I predict you have too much overlap and/or too far advanced advanced..hence the strong rpm power.

The late ZX GPz cams...550 750 1100 were all longer duration for rpm power at the cost of bottom end grunt. My GPz powered Lawson 1000R was a pussycat...until you stepped on it's tail and at about 6krpm and fully on main jets it sounded like heavy metal as it wanted to rip my arms out of their sockets and everything around me started moving backwards - it was a true Jekyll and Mr Hyde. Experienced muscle bike riders will will be laughing at this English eccentric here being scared of a ligthly tuned gpz11 mill...just how it felt to me.

Stick with it, any modification always involves a certain extent of shakedown fine tuning; these 550's are amazing...had about 10 over the years. When you get it right you will know it.

Around 25 years ago, as a novice but with big ideas I had a project with the motor in and out about 5 times and months of tweaking...then years of fine tuning and other bits wanted to change or needed finishing.

Getting a bit better at it nowadays, but even a top pro could spend a lot of hours setting cams. ignition and carbs nearly right.

Zaddict wrote:

loudhvx wrote: Well, advancing the intake to the Zx timing would make the intake valve close sooner, restoring compression at lower RPMs. Maybe that is needed more-so with the lower compression of the Zr motor than on the Zx.

It looks like you have two Zr sprockets right now. If you can sweet-talk Corey out of a Z4/IN sprocket, I would try that on the intake just to see what happens.

But then that would increase the overlap by a corresponding amount, correct? Though from what I've read the intake closing timing is the single most important cam setting. Maybe worth a shot. As it so happens Corey was kind enough to give me the ZX sprockets along with the cams, so I just need to find time for the swap.

*EDIT*
Zaddict- You are correct, by putting in the ZX intake sprocket it will advance the valve opening. (Opening the intake valve 10° sooner.) Increasing the the valve overlap and making your low end dynamic compression (and thusly your low end power) even worse.

Your current setup


With ZX sprockets


10° more valve overlap using the ZX intake cam. ( Not forgetting the ZR and ZX exhaust sprockets are identical.)

*EDIT*
There is also the worry that the Intake valve opening sooner means it will increase the likelihood that the piston could kiss the Intake valve at [strike]high RPM's.[/strike] any rpm. ( Valve opening is not affected by high rpm valve float like valve closing. My bad!)
Yes....The zr550 piston is lower compression, BUT the deck heights are identical and the ZX550 piston has deeper valve pockets. It has deeper valve pockets because Kawasaki must have realized that the longer duration cams must have increased the likelihood of valve-to-piston-interference.
In 1982-83 the gpz550 pistons got 10:1 compression. But the 1984-86 zx550's got their own specific 10:1 pistons once they redesigned the cams. I don't believe that was just coincidence.
There is a very good possibility that I am wrong, and until we scientifically solve/prove this unknown, I don't want Zaddict to find the out the hard way that [strike]at 11,000 RPM's[/strike] he is going to need all new pistons and valves.

There is also the worry of valves colliding with each other. They definitely cross each others paths during normal operation, but I don't know how close they get to each other. If the ZR valves are bigger than Zx valves, I would look closely at that, but I'm not sure how you would do that though.

I think I might have a gpz head with cams installed. If I do, and I get some time, possibly after Christmas, I can try to see how close they are on a two-groove grind. That might give us some idea if it really is a concern. Luckily, valves open pretty slowly so maybe it's not a problem.

Looks like the stars are aligning for a dyno run tomorrow. Stay tuned. (No pun intended).