gpz 550 cams in a kz550 or zr550?

has anybody done this swap? I have a line on a set of '84 gpz cams (generous offer from Corey Clough). Wondering how my zr550 might like them. From what I understand (from Loudvx's cams web page), the zr550 already has the same cams as the early gpz's, the "first performance grind". So it's a matter of how different the '84 cams were from prior ones. The '84 gpz 550 did have ridiculous hp numbers (68 hp claimed), but not sure how that would translate to a zr550 and if that would be at expense of low-end torque.

I did the 84–86 gpz550 (zx550a1) cam and piston swap in my zr550.
The cams bolt right in with just readjusting the valve lash to match the “new” cams. The base circles are the same, so no valve trimming is required.
But....the kz/zr550 has 9.5:1 compression ratio and the zx550 has 10:1.
(The kz550’s and zr550 use the exact same piston. )
This can be seen by the slightly raised dome on the zx550 pistons.
The zx550 on the left and zr550 on the right.



This .5 bump in compression combined with the higher lift and duration cams is what gives the zx550 roughly 15 more horsepower and 5lbs more torque.

But.... zx550 pistons have an intake valve pocket that is roughly ~1.25mm deeper than the zr550. (I neglected to measure the exhaust pocket.). So it may not be safe to put in the zx550 cams in the Zephyr without also changing the pistons as well. There is a possibility of the valves smacking the pistons at high revs.
That is what I did on mine as I was afraid of the valves colliding with pistons due to the increased lift, plus I wanted the extra little bump in compression.
It was worth all the effort and it pulls all the way into the redline. Definitly worth it if you need to take apart the top end to do a valve job.


EDIT: The 81-83 gpz550 also has 10:1 compression, but the pistons only share a part number for those 3 years. Which means that in 84 they redesigned the pistons with deeper valve pockets for the corresponding higher lift cams. So beware of buying gpz pistons that are not specifically advertised as being from a 84-86 zx550.

Hope this helps.

awesome info, thanks Rusty.

You're not selling your 550 are you? I saw a Rusty on the Zephyr Owners FB page who was selling a black zr550. Didn't have pods though, and I'd be surprised if you sold yours after all the love/work you put into it...

That would be me on Facebook.
I barely rode my Zephyr a 100 miles this year and paid for insurance the whole time it sat.
Next spring I will see if I still want to sell it along with all my spares and gpz550 parts I have amassed. I keep thinking of all the neat tools/welder I could buy with the proceeds.

I have since switched back to the stock air box and used the pods on my Kz750 so it has a Factory Pro stage 1 jet kit right now.

Do it, I had a z550 motor and swapped a gas flowed head and zx550 cams and it was a lot of fun - I threw the motor together just for a summer but it lasted years and 3500 miles before I screwed a piston on a (to destruction) spark advance experiment.

Pod filters and a 4-1 (when set up right) works good. Interestingly the lower compression flat top kz pistons worked just great with the skimmed head. I dialed in the cams 108 /113 odd setting but it loved it. One could screech it well past the redline, it was such a blast, ths was an rpm tune but also had nice midrange power.. also it ran so smooth. CR isn't everything imo.

Nothing screams or revs like an 8 valve 550 on the redline, true heavy metal soundtrack - like a Hornet on Crack.

One factor to consider is wether your valve pockets are deep enough, and if your head has already been skimmed. There are generous clearances there anyway. There are ways of checking this -nosey through the /my history here if you like.

Nice of Corey to look after you on those cams - quite sought after now. Recently he gave me some wiseco circlips and nos valve keepers what a Star .

Daftrusty wrote: That would be me on Facebook.
I barely rode my Zephyr a 100 miles this year and paid for insurance the whole time it sat.
Next spring I will see if I still want to sell it along with all my spares and gpz550 parts I have amassed. I keep thinking of all the neat tools/welder I could buy with the proceeds.

I have since switched back to the stock air box and used the pods on my Kz750 so it has a Factory Pro stage 1 jet kit right now.

Got it. Saw your similar note on the FB page. So I take it you're enjoying the 750 more than the 550? I've thought about getting a bigger bike, but I love the look and lightness of the 550, so if I can get enough power out of it I'd rather do that.

I may have to buy your 550 when the time comes, or convince my brother in Indiana to do so.

The discussion below does not really affect the Zr550, but I thought I'd post it for anyone interested, or on the odd chance someone can actually confirm the swap. As Tyrell mentioned, it definitely works with the 9.5:1 motors (-1121 pistons).

With many discussions on the Gpz550 forum, the one combination we have not confirmed was the Zx550A (3-groove marks) camshafts as a drop-in swap on a Kz550 D or H (81-83 gpz550) motor (-1127 pistons). Those motors, as mentioned, also have 10:1 compression, but the valve pockets are not as deep, and likely the dome is lower compared to the Zx550A (-1166 pistons).

But there is another factor involved, and that is the timing. The Zx550A has the intake camshaft advanced through the use of different holes on the intake sprocket. The sprocket is the same casting as all other Kz550 sprockets, but it has two extra holes drilled in what would otherwise be blank panels on the sprocket wall. One of the extra holes eliminates the Kz550 intake timing mark, you can probably get a decent estimate of where the mark would be.

So then the question becomes... does the piston need larger pockets because the cam duration is longer (maximum lobe lift is about the same or even a hair lower), or are the pockets larger to accommodate the change in timing?

Another question is, are both pockets indeed deeper? The intake likely is, but is the exhaust? Since there is a higher dome to make up volume lost in the intake pocket, does it just make the exhaust pocket look deeper, or is it actually deeper (than a Kz550 D/H gpz piston)? The Zx guys seem to stick with Zx motors and the Kz guys seem to stick with Kz motors, so no one has really done a very precise, side-by-side comparison, that I know of.

If the pockets are bigger due to the timing change, then it may be safe to use Zx550-Gpz cams in a KZ550-Gpz motor, as long as you use the standard Kz timing, which, if I recall, is what Corey recommends anyway... that is, using Zx550 cams but use Kz550 valve timing. I'd like him to confirm that, though.

I'm only enjoying my 750 more right now because I have spent so much time building it and trying to break it in and work out the bugs.
They are totally different bikes. Compared to the the 750 the 550 feels so light. Almost like bicycle light. It is so nimble and easy to fling around. Not that the 750 feels like lumbering beast that is hard handle, (quite the opposite) it just obvious how much heavier it compared to the 550 when trying to fling it around or do tight u-turns in the driveway.
The 550 also just wants to rev. When giving the 550 the beans, it just takes off and effortlessly screams all the way into the redline with no sign of stopping. ( I love this about the 550's ) The 750 just has grunt that shoves you forward and rises in rpm's until it eventually runs out of steam. ( I also love the grunt of torque)
If I was a wealthier man, I would happily keep both as I love them both.

I have zero regrets doing the zx550 cams and pistons.
But if I was to do it agin, I would do the 615 upgrade. I wanted to do it initially, but I couldn't swing the price of the 615 Wiseco pistons and the cost of machine work. 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. I spent more on used pistons than what the cruzinimage 615 pistons are new. Hell, new OEM head gasket and rings for all four pistons cost more than the cruzinimage kit. (But the cruzinimage 615 kit is only listed for 81-83 gpz550, so it is unknown if they have valve pockets that are deep enough for the zx550 cams?!?!?)
If you ever decide to freshen up your top end with the zx cams and have the financial wherewithal, do the Wiseco pistons. If not, put in zx550 ones as they will still give you more pep in your step.

Food for thought.

This information should be noted about GPz and KZ Cam Timing:

1)Factory ZX Lobe center timing
EX uses the round holes - 104 deg
IN uses the Square holes - 94 deg

2) Factory KZ/early GpZ
This is what I'm using with my ZX cams and what I suggested
EX uses the round holes - 104 deg
IN uses the hex holes - 104 deg

The plan for Mark is to install the intake and exhaust on his current ZR Gears, so he can retain the timing marks. This will change the intake lobe center to 104*, better than the stock ZX550 94* Lobe Center, and leave the exhaust timing as it is. I am using this 104* timing now with my 550 engine, and it made a noticeable difference. See attachments.

Thanks for confirming Corey. 104/104 is the normal Kz timing. I wonder why kaw made the zx 94/104. More torque at lower rpm?

I have no idea why that intake timing was given to the A Model, but this intake cam change works better. Gary Bishop actually turned me on to that, and I like it.

As for the ZX Cams in the D and H Model Engines, there should be ample piston to valve clearance. I don't think the added lift or duration is that much of a difference. Mark (Zaddict) and I will find this out when we do the cam swap.

***Pictures courtesy of Gary Bishop.***

The Zx cams I measured have the same lift as the D and H cams, but the duration is longer. Is Mark getting higher compression pistons? The D and H are 10:1 while the Zr is 9.5:1.