gpz 550 cams in a kz550 or zr550?

Lou told me he put one of the ZX Cams I sent him years ago, in a head on a test stand, springs removed. and measured valve movement with a dial indicator and degree wheel. He told me if the lobe peak is a 12:00, the valve starts opening before 9:00 and closes after 3:00. This means I can’t measure the base circle with dial calipers. Makes sense to me.

I've been able to get very close to the factory advertised duration numbers. The factory does not advertise what lift they spec at. I had to back-calculate the factory lift spec. Then every cam I found complied with the advertised specs. I also measured duration at several other lift values to compare against aftermarket brands that are spec'd at different lift values. I spent a lot of time on it.

Just some added info. Cam lobe lift surface will have one side slightly larger, so the bucket will rotate around during operation.

Lou's cam information on his web page it chocked full of good actual testing information. Worth taking the time to read.
s3.amazonaws.com/gpzweb/CamsKZZXZR550500...KZZXZR550500400.html

Side Note:
Interesting to find out if both Megacycle and Web Cams follow the same duration ramp up before 9:00 and 3:00. I have degreed my Megacycle Cams several times, and can look for this information, but I have recorded measurements starting at 0.040" lift. When I rebuild my 615 bottom end, and reinstall the Megacycle 478-60 Cams, I will check the duration start point. The Megacycle Cams are welded, then ground off of that, so they don't use the same stock base circle.

Well zx cams are in (many thanks to Corey!!!). Bike is running well, though with a noticeable drop in low-end torque/acceleration. Hopefully that power is still somewhere but I can't crank up the rpms too high in the city to test. I'll do a little canyon carving tomorrow morning and report back.

Alright, I just spent few hours spanking my bike in the twisties and these are my impressions of the cam swap, along with some possible rationalizations given what little I know about anything.

Power is down across the whole rpm range, except possibly with the exception of very high rpms at or past the redline. Once, while passing a car at about 11K rpm (1K past the 10K redline) the bike felt like a rocket ship. Other than that it felt anemic. The butt dyno says it has about as much power as it did before rejetting and installing a performance exhaust (which bumped it up 6hp at the rear wheel). So I’m guessing it’s down about that much. I might do an actual dyno run to see the numbers and take a look at the torque/hp curves. Prior to the cam swap, I'd have a hard time keeping the front wheel down when taking off from a standstill if I spooled up the engine to about 4K rpm before takeoff. Now it just kind of leisurely takes off - not even close to lifting the front end. Before, in any gear when at 7K rpm or above, if I closed the throttle briefly then opened it up, the acceleration would push my head back. Nothing like that now.

mpg for the 84 mile ride was 36.5. That’s the lowest I’ve measured. It’s usually 40-45mpg. I wasn’t riding harder than usual. I think we lost some efficiency.

The engine is running smooooooth. That could be because of some minor maintenance I did along with the cam swap (e.g. carb sync, new carb caps, gapping spark plugs, that kind of thing). Or it could be because the bike is less torquey now so it’s not as bouncy an experience riding it. Also seems like there is less engine braking - so it’s smoother on acceleration and deceleration.

As I understand it, the only difference between the zx 550 cams and the “1st performance” grind cams that were in my zr550 is the duration. They have the same lift, and we installed the zx cams with the same lobe center as the stock zr550 cams (104 degrees for both intake and exhaust). Theoretically more duration could increase power by allowing more air and fuel in/out, but I’m thinking that by increasing the overlap we shifted the torque curve waaaay to the high end. We probably also lowered the compression to a degree that we lost more power than we gained by any increased scavenging due to the increased overlap. That loss of compression probably wasn’t as much of an issue with the gpz550, which had higher compression pistons to begin with. Also the gpz550 had the intake cam advanced 5 degrees (on the sprocket, 10 degrees on the crankshaft) relative to the exhaust cam (according to Lou's awesome camshaft webpage), which would have lowered overlap and maintained compression/torque. I thought I also read somewhere that the ’84 and above gpz550 also had a change in ignition timing, so there could be an additional variable at work.

Seems like there should be more power attainable here with the right settings. Think it’s worth trying to advance the intake cam? Would I need to worry about piston-to-valve clearance more at that point? Corey said the 104/104 timing worked better on his gpz550, but I wonder if that’s partly because of the compression differences in pistons and/or differences in ignition.

Operation Guinea Pig in full effect…

The 84/85 Gpz (Zx550A1/A2 and later) had an analog electronic advance system. I assume the Zr would have had the same or better. All of the Kz's were mechanical advance.

The mechanical advance is a compromise. It has more or less two settings... idle and full advance. The transition range of RPMs is small and happens before the power band takes effect. The compromise is that it is too far advanced at the intermediate RPMs, which can make the motor prone to knock, but then at the highest RPMs, it's not as advanced as it could be.

The Zx alleviates this compromise by reducing the initial increase in advance after idle and allowing the advance to slowly increase after that initial jump all the way to redline.

Regarding the cams: Is it possible it needs to rejet for the different breathing?
I would have liked to see a wideband result before and after the cam swap.
I would live with it a little while and see if the plugs change color.
Maybe it's too rich in the midrange (less breathing there) and too lean in the upper range?
The off-idle throttle position, like 1/16 to 1/8 is where you get your light cruising MPG. It's probably where the duration overlap would have the most detrimental effect too, so would need the most corrective jetting (pilot jetting or needle position). When I was doing wideband testing, I found all of the cruising up to nearly 80 mph was done with less than 1/4 throttle on the TK22 carbs. Usually 60mph was 1/8 or less throttle. I imagine it can't be that different on the ZR.

It's hard to argue against Corey's racing results, but he did tuning on a Dyno to dial in the jetting.

You have detailed and deduced a lot of what I would have from your description.

Seeing as I have the same bike with the exact same carbs, jet kit, ignition curve with the same cams...I believe you have correctly deduced that the loss in dynamic compression combined with the 9.5:1 pistons has lost torque moved the usable power to far up the power band.
I was very concerned about the ignition timing differences between the two bikes but it seems that more "vintage" timing curves are around 41° and the more modern curves are in the mid 30's. (That may be due to better availability of quality fuels found around the globe today, so less broad curves are used.) I even modified my ignition rotor to advance the curve 5 degrees, but it made zero difference that my butt-dyno could tell.

zr550 timing curve


zx550 timing curve


The only differences with mine is that I used the stock 94/104 degree cam timing and the zx550 pistons. It pulls strong up until 6K and then it hits hard and dosen't stop even into the redline. ( Normally I don't like to even get close to the redline, but if I give it the beans, it is easy to do as it won't stop pulling. So one eye has to always be on the tach.)

Food for thought on a really great thread.

I wonder if we should try to find someone using the Zx cams in a standard Kz, and see what their experience was with Zx cams and 9.5 comp.

loudhvx wrote: I wonder if we should try to find someone using the Zx cams in a standard Kz, and see what their experisnce was with Sx cams and 9.5 comp.

Tyrell Corp mentioned earlier that he'd put zx cams in a "z550", which I think is the same as a kz550, though he had them set at 108 /113.

loudhvx wrote:
Regarding the cams: Is it possible it needs to rejet for the different breathing?
I would have liked to see a wideband result before and after the cam swap.
I would live with it a little while and see if the plugs change color.
Maybe it's too rich in the midrange (less breathing there) and too lean in the upper range?
The off-idle throttle position, like 1/16 to 1/8 is where you get your light cruising MPG. It's probably where the duration overlap would have the most detrimental effect too, so would need the most corrective jetting (pilot jetting or needle position). When I was doing wideband testing, I found all of the cruising up to nearly 80 mph was done with less than 1/4 throttle on the TK22 carbs. Usually 60mph was 1/8 or less throttle. I imagine it can't be that different on the ZR.

It's hard to argue against Corey's racing results, but he did tuning on a Dyno to dial in the jetting.

I'm leaning toward doing a dyno run so we can have a better idea what's going on. I have recent dyno results from before the cam change that we could use for comparison purposes. I'd be surprised if jetting is an issue given that DaftRusty has the same jetting on his zr550 with no probs (though he does have the zx550 pistons and the stock zx 94/104 timing).

Your cam timing is out, one or both cams. Too much overlap or too far advanced I would guess. Does it seem to crank faster on the starter button?

I would try to establish exactly where your cam timing is now, rather what you think it is. IIRC The pin count for the camchain is 43/44 to the alignment line on the cam sprocket face. Check this with FSM.

Find TDC with a stop-not the timing rotor, attach a timing degree wheel to crank nose and pointer to the crankcase m6 cover hole. See where the cam opens and closes and find your midpoint - on both. This gives your lobe centres.

Generally 105 to 110 degrees, higher number for rpm power, lower for midrange. Slotted sprockets can be used to adjust timing, or you may just be one tooth out (so too much overlap). Also easy to use the wrong mount holes - each sprocket has six holes , two are used for each different timing. (So just one part covers three different cam timing settings for both cams)

Skimmed heads, worn camchains, manufacturing tolerances and wear all affects this factory timing, but I suspect your cam timing out a bit.



... So I went to plan B and used stock zx550 pistons. It took me three different sets from different engines to find four pistons that didn't have detonation pitting, chipped ring lands or ovaled wrist pin bores.
Interesting, just the same failure mode of mine.

Alright, I have another theory. It's two parts and if it's true it would explain all the symptoms of lackluster performance I noticed during this morning's ride:
1) I'm an idiot
2) My clutch was slipping
I just adjusted the clutch cable and went for a short ride and was once again getting that herky-jerky/torquey feeling on acceleration that I know and love. Could be all good - let me test a little more before we put too much more thought into this.