Best bang for buck mods for 81 KZ550?

loudhvx wrote: I never noticed any difference between the gpz head and a kz head, but maybe there is some porting done (that was the rumor according to magazine articles, but I don't give that much weight considering how much else they get wrong). Obviously, since the gpz and kz use the same carbs, the inlet of the intake ports have to be the same. Maybe Kawasaki ported the heads on the bike that was lent out for reviews (the kz came out 1 year before the gpz, so magazines would have been able to inspect/compare the gpz test bike against a showroom kz).

The Zx 550 motor uses the same Kz550D (81 gpz) cases. The motor mounts are different on the Zx. It has more rubber mounting, but I think the motor is compatible to a Kz frame. Either way, the 82/83 motor bolts in. That's what I have in one of my 81's.

But I am also of the opinion you should keep the bike with the good motor in it. Once you change the motor, you will want the gpz brakes/wheels.

If your bike is running perfectly, I (like Nessism said) would leave it in tact. Just look for a hashed out project bike to play with. There are always plenty of bobbed/chopped incomplete bikes on craigslist for cheap. It would be great to see a chopped up Ltd become a decent gpz replica.

I have 3 bikes. One is a really nice kz650. I prefer not to perm mod that bike. My other bike is a 73 rd350. I have a lot done to that bike and it's on it's way out to have the motor all redone etc.

My 3 rd bike is this 81 kz550. It is a decent running bike and I rode it a few thousand miles last year as my primary bike. I have recently upgraded it to gpz forks and dual disk brakes up front. In the back it now has a gpz swing arm and rear disc brake wheel. I have a front fork brace for the bike also. Just ordered some exhaust from japan also. It's a good running bike but just wanted to give it a little extra. Not trying to make a superbike out of it. But if I could make another 5-10hp I would be plenty happy with it.

Does the 84-85 65hp motor bolt in?

54 rwhp on Cycle's dyno. Pretty good, considering the '82 GPz750 with factory ported and polished heads made 65 on the same dyno.

Your single biggest mod would be bore it out to 615, thereby bumping the compression up to 10.25:1, GPz cams, and a pipe.

There is a minor problem though - you can buy a used 1000 for the money you'll have in it, and the 1000 will make 79hp at the rear wheel stock.

GPzEric wrote: 54 rwhp on Cycle's dyno. Pretty good, considering the '82 GPz750 with factory ported and polished heads made 65 on the same dyno.

Your single biggest mod would be bore it out to 615, thereby bumping the compression up to 10.25:1, GPz cams, and a pipe.

There is a minor problem though - you can buy a used 1000 for the money you'll have in it, and the 1000 will make 79hp at the rear wheel stock.

I've already got more money into it than its worth. I don't really care about that as I like the bike. I just wanted to make what I have run the best or whats the best upgrade to get as much out of the bike as I can.

SO a 615 kit and gpz cams or finding an 84/85 65hp engine?

Sorry to ruin it for you, but the '84 / '85 didn't put out any more power than the '81, and actually were a little slower in the 1/4 mile.

Part of it was that the newer bikes had CV carbs, that didn't get going quite as fast, or that reshaped cam lobes cut low-end power in pursuit of top-end power.

If I can find my old magazines I might have the dyno tests on the '84.

What you're looking at are references to crankshaft power, which are always inflated compared to rear wheel (dyno) power.

GPzEric wrote: "Sorry to ruin it for you, but the '84 / '85 didn't put out any more power than the '81, and actually were a little slower in the 1/4 mile."

Not necessarily so. I believe you will find there were differences in the hp ratings and quarter mile times depending on which 1981 Kawasaki 550 model was being tested. For example, the 1981 KZ550 LTD had considerably less hp (50hp) than the 1981 GpZ 550 (58hp), and it would not be as quick as the GpZ model. So depending on which model the OP has the later engine may be a substantial upgrade. Ed

1981 KZ550-LTD
www.bikez.com/motorcycles/kawasaki_z_550_ltd_1981.php

1981 GpZ550
www.bikez.com/motorcycles/kawasaki_gpz_550_1981.php

Ape Racing lists a piston kit for the 82-on 550s.

The 84-85 Zx550A (gpz550) motor is going to put out more power than the 81 for sure. The 82/83 Kz550H (gpz550) did about the same or a little slower in the initial tests done by some magazines, but those were bikes that were tweaked and messed with by the testers. Later magazine tests had the 82 bike faster than the 81. The 82 bike may have weighed more as well.

The Zx550 should bolt in, but will need the opil cooler which, obviously is not a bolt-in if your frame is not made for it. It's an easy install, though.

So Zx550 motor or 615 kit? Why not both? The kit works on the Zx550 motor.

The guy to talk to is Corey Clough. He is on the Gpz550 forum most of the time, but he is a member here too. He spent 10+ years racing Zx550A's and has done the 615 kit to at least a few. He would probably also suggest Zephyr or Ninja carbs once all that is done if you are trying to maximize horsepower (and are willing to live with less streetability).

There is at least one GPz550 out there, with Moriwaki cams, 615kit, and bigger carbs on a homebuilt rack that is an honest 150mph motorcycle when the wind is right.

Thanks for the info fellas. Lots of good stuff here.

1) Decent 4-1 pipe and carb tuning if needed (small gain top end, lose a bit of bottom end compared to the 4-2)

2) Gpz cams, later zx550 were 280 degrees, 270 degrees for earlier models and IIRC 248 degrees for the z550.
(don't try to compare this duration against performance cam specs which have duration usually measured at 0.040" lift)

3) Gas flowed and ported head ZX with CV 30 or 32mm carbs- works great on these

4) Big bore kit


In that order, you won't get much power increase from a big bore kit over a tourque increase unless it can breathe better. These are very strong and tunable motors. The bottom end went on to the GPZ600 so good for 80 hp plus easy.

A zx motor and carbs would fit in but you may need to use a later ignition due to casting details on the ignition crank sensor mount area.

Tyrell Corp wrote: 1) Decent 4-1 pipe and carb tuning if needed (small gain top end, lose a bit of bottom end compared to the 4-2)

2) Gpz cams, later zx550 were 280 degrees, 270 degrees for earlier models and IIRC 248 degrees for the z550.
(don't try to compare this duration against performance cam specs which have duration usually measured at 0.040" lift)

3) Gas flowed and ported head ZX with CV 30 or 32mm carbs- works great on these

4) Big bore kit


In that order, you won't get much power increase from a big bore kit over a tourque increase unless it can breathe better. These are very strong and tunable motors. The bottom end went on to the GPZ600 so good for 80 hp plus easy.

A zx motor and carbs would fit in but you may need to use a later ignition due to casting details on the ignition crank sensor mount area.

I just ordered this exhaust. Hopefully its pretty good. Next step some tuning and GPZ cams.
Exhaust

Tyrell Corp wrote: A zx motor and carbs would fit in but you may need to use a later ignition due to casting details on the ignition crank sensor mount area.

I think you can go backward... older ignition into a newer motor. We put a mechanical advance 550 ignition into a Zx750 motor, so I assume it should go into a Zx550 motor.

I think the problem is fitting the newer ignition into an older motor. Though that seems odd now that I think of it since the Zx motor still uses a Kz550D crank case. Hmmm. May have to look into this. I have a Zx ignition and Kz motor around here somewhere.