Recommended Headwork for Slightly Overbored GPZ110

diego092409 wrote: My goal is a solid reliable running bike that is moderately quick, not going out to hustle sport bikes, just a nice sounding streetable cruiser, potentially teaching motorcycle safety classes with it.

Can somebody clearly demonstrate that a ported head will be better than a stock GPz head for achieving the op's goal?

TexasKZ wrote:

diego092409 wrote: My goal is a solid reliable running bike that is moderately quick, not going out to hustle sport bikes, just a nice sounding streetable cruiser, potentially teaching motorcycle safety classes with it.

Can somebody clearly demonstrate that a ported head will be better than a stock GPz head for achieving the op's goal?

Surely you're not suggesting a ported head won't increase power..? A ported head, even a cleaned up head {ports of course}, will make more power, as will a number of other mods. Its just my experience that there's usually more power locked up in the stock heads of these old bikes than any other single modification.....

But if you start with the best factory head then do the port work :ohmy:

Of course a properly ported head will make more power, especially near the top of the rpm range, but I really don't think that is what the op wants. Please look at the quote.

750 R1 wrote:

TexasKZ wrote:

diego092409 wrote: My goal is a solid reliable running bike that is moderately quick, not going out to hustle sport bikes, just a nice sounding streetable cruiser, potentially teaching motorcycle safety classes with it.

Can somebody clearly demonstrate that a ported head will be better than a stock GPz head for achieving the op's goal?

Surely you're not suggesting a ported head won't increase power..? A ported head, even a cleaned up head {ports of course}, will make more power, as will a number of other mods. Its just my experience that there's usually more power locked up in the stock heads of these old bikes than any other single modification.....

Moderators----

How did my reply to the 1981 750E thread end up here?

TexasKZ wrote: Moderators----

How did my reply to the 1981 750E thread end up here?

Moved it. Took me a few tries , but moved it :whistle:

Dave

TexasKZ wrote: Of course a properly ported head will make more power, especially near the top of the rpm range, but I really don't think that is what the op wants. Please look at the quote.

750 R1 wrote:

TexasKZ wrote:

diego092409 wrote: My goal is a solid reliable running bike that is moderately quick, not going out to hustle sport bikes, just a nice sounding streetable cruiser, potentially teaching motorcycle safety classes with it.

Can somebody clearly demonstrate that a ported head will be better than a stock GPz head for achieving the op's goal?

Surely you're not suggesting a ported head won't increase power..? A ported head, even a cleaned up head {ports of course}, will make more power, as will a number of other mods. Its just my experience that there's usually more power locked up in the stock heads of these old bikes than any other single modification.....

Please look at the tongue sticking out smiley Texas {having some fun}, also look at the thread title {serious :laugh: } .... If the headwork isn't too extreme there will be improvements right across the rev range, just use the smaller stock valves and don't go huge on the cam........

Interesting especially the link to the Bathtub head. As some of you might remember I just put together my Frankinbike (GPZ1100B with all my spare bits).
I had no intention of making a rocketship but ended up with one. The porting without doubt was one of the reasons and the other was the 83 GPZ1100A cams. I was amazed at the low/ top end power it puts out when ALL else is stock (I had a J model head, pistons STD, Valves STD etc). It might not compare to some big bore bikes but it won't be embarrassed either.
I must add the bike weights 215kg wet (half tank of fuel).
So my recommendation, porting at least and decent cams for street use (not racing cams) BUT don't forget change the valve springs if they are old.
Also don't forget more power means a wilder ride unless other running mods are made (frame etc)

Bozo wrote: Interesting especially the link to the Bathtub head. As some of you might remember I just put together my Frankinbike (GPZ1100B with all my spare bits).
I had no intention of making a rocketship but ended up with one. The porting without doubt was one of the reasons and the other was the 83 GPZ1100A cams. I was amazed at the low/ top end power it puts out when ALL else is stock (I had a J model head, pistons STD, Valves STD etc). It might not compare to some big bore bikes but it won't be embarrassed either.
I must add the bike weights 215kg wet (half tank of fuel).
So my recommendation, porting at least and decent cams for street use (not racing cams) BUT don't forget change the valve springs if they are old.
Also don't forget more power means a wilder ride unless other running mods are made (frame etc)

Thought I was reading about my own engine for a moment. :whistle: The exception being the ZN 1100 (bath tub) head, on which the valves were left stock too.
The head did have minimal factory porting originally done by Kawasaki, limited to the intake runners directly above the valves. I wonder what a quality minimal porting job on the head would do for the engine performance, or if it would even be worth having done for a street bike.
What would be the going-rate for a porting job on a J or GPz bath tub head, retaining the stock valves as well?

Daveo, I ported my GPZ head myself, I concentrated on the flow not so much making the port wider, I did not make them mirror shine, I purposely left them slightly rough. The valve seats were ported to the seat and both Intake and exhaust outputs were matched to what ever was bolted to them.
I run 36mm CV's from the ZRX (minor mods required), the response is incredible (its the pumpers). Some say these are too big but I dare anyone after riding this bike to criticize them (low and topend).
The cams haven't been dialed in and the way its going now, that can wait. At present I'm doing final touches to get good fuel economy without loosing power.
I have a fairly beat up 83 head in my shed and after reading this I have decided to remove the spiders and try to clean it up for the future

Edit: I stated a GPZ head porting I meant a Z1000J head which is fitted to Frankibike

Porting the stock 'J' Model head is a better option than the 83/84 Head Lower Compression, Low port Velocity Why do you think 83 / 84 GPZ 1100 Had DFI ? poor low speed response Stock 83 /84 head flows approx 84-86 cfm porting a 'J" head to those numbers by a Competent Porter ! to the same numbers way better for carbed street engine .

83/84 GPZ1100/Spectre etc bathtub style heads are actually higher comp ( smaller combustion chamber volume) than the earlier 'J' heads.