GPZ 750 Engine Number

[Royalratch]

Can anyone tell me more about this - year and model etc?


KZ750EE140231

[doebag]

1984

Either Z750-L4 or ZX750-A2,

[Royalratch]

But its a GPZ right?

Wikipedia (don't laugh) says the last version of air-cooled GPZ motors (1983) were producing 92bhp @ 9000rpm - seems a lot.

[sanderz]

Not sure if this is of any help but it gives the spec of each bike listed.

http://www.motorcyclespecs.co.za/bikes/Kawasaki.htm

[doebag]

Kawasaki quote 86 at 9,500 RPM for the GPz750A, and 80 at 9,500 for the Z750L.

Both bikes engines run in the same number sequence, the difference in power seems to be down to camshaft timing. Japanese spec. GPz seems to have same power as UK Z750L

So unless you can identify the camshafts, it could be either, but only 6HP difference.

[Mark Stratton]

I'm pretty sure that if you use GT750 cams in a Z/Gpz engine you will increase power by about 6-9bhp. Apparently the GT cams were a much higher lift than the Z/Gpz and thus increased power.

[Royalratch]

I thought GPZ cams were the hottest of that engine type - and certainly more so than regular Z cams?

[Mark Stratton]

Royalratch

I had a Z750L4 and the mechanic at the local Kawasaki dealer told me that if I wanted any extra horsepower the easiest way was to use a GT750 head although just swapping the cams was sufficient.

Could be a load of b****cks but at the time he seemed genuine about it and coming from a dealer I would have thought they knew what they were talking about either that or he had some that he thought he might be able to sell to me to get them off of his hands

[Royalratch]

As fars as I know, the GPZ head is best, with highest lift cams of all the small fours and larger valves. There was also talk of slight porting but that was just banter - the previous 2 tweaks are fact.

It's hard enough getting sellers to confirm a head is a genuine GPZ head let alone a GT variant?

I just want the best possible start point for my 810cc conversion - and the head will be thoroughly sorted anyway so for me it's the cams I'm after mainly and the valve gear.

[kev edwards]

I know the gt 750 cams are the same as the zephyr 750 cams, i have measured and compared them side by side, i have a Gt head in the garage without cams and shims if anyone want's to buy it.

[Mark Stratton]

As I said Royalratch I could have been fed a load of bo***cks by someone desperate to get rid of some.

I think it was something like the much later ZR7 was it not that utilised the GPz 750 engine of old or at least parts of it. It looked very very similar.

I'm sure there will be someone out there who knows.

[Crofty]

To accurately check the head for being GPZ, you would need to measure the combustion chamber volume.
The Z650 has a combustion chamber volume of 23.7 cc. The 82 GPz750 has a combustion chamber volume of 24.9 cc. The 83-85 GPz750 have chamber volumes of 25.9 cc . The Z750 H 24.8cc and Z750 L 25.3 cc

It is also possible to look at the inlet throats, they were 'tickled' at the factory to give a slight benefit in gas flow.
The cams I have are stamped R2, that jb sold me, not sure what others may be stamped.
Are the GPz badges still on the covers?, not an accurate guarantee but a pointer in the right direction.
Sump should have oil cooler take offs.
Not sure about inlet valve size, might be 1mm bigger
Crofty

[steve.w]

1984

Either Z750-L4 or ZX750-A2,

didnt the l4 have the clutch mechanism on the sproket casing

[Royalratch]

Cheers Crofty. The one you put me onto looks great and the covers are there - Steve is kindly popping the rocker cover off to check the cams and valve gear.

I'm more just trying to fully understand the differences...

[big green bus]

The GT 750 had a bit more power the the first Gpz750R1, but the ZX750A series had the highest lift cams, all the earlystock racers used to fit the uni-trac cams (even into the zephyr engines). Just as a matter of interest Kent still do a race profile cam for the 750 as do Yoshimura, these bikes do run very well with RS34's flatslides or GSXR750 29 mikuni's (with the float heights altered) but the biggest improvement to these engines is the Wiseco 810 kit, the change is amazing.
The Zephyr is the same engine, but was designed as a cruiser not as a front line sports bike as the uni-trac was in the 80's, so has the milder cams in maybe even lower compression (not a 100% on the comp)