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Porting and milling options for GPZ750? 15 Dec 2014 23:50 #656145

  • EdwidjR
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Just a thort.... sometimes its not about hp numbers but about the sensation.
Dynos give a bunch of numbers but don't always log the change felt at the throttle. A bit more compression often gives a crisper FEEL through the lower to mid rpms but little acctual hp gain.
long ago we stripped and balanced a new gsx750 motor. Match ported and minor rejetting to suit. Made for the smoothest crippest loveliest gsx motor all that rode thought it had been hot rodded. Made a couple of extra hp but FELT like a lot more......
just saying there is more to tuning than outright hp.
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Porting and milling options for GPZ750? 16 Dec 2014 06:06 #656150

  • ed spangler
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EdwidjR wrote: Just a thort.... sometimes its not about hp numbers but about the sensation.
Dynos give a bunch of numbers but don't always log the change felt at the throttle. A bit more compression often gives a crisper FEEL through the lower to mid rpms but little acctual hp gain.
long ago we stripped and balanced a new gsx750 motor. Match ported and minor rejetting to suit. Made for the smoothest crippest loveliest gsx motor all that rode thought it had been hot rodded. Made a couple of extra hp but FELT like a lot more......
just saying there is more to tuning than outright hp.


"Throttle Response" is better with Higher Compression, what do I mean? I have drag raced for more than 40+ years,while its true increased compression may not make huge Horsepower differences, when you launch a car with a 454 Chevy Big Block that has factory 8.5 compression vs an identical one that has 11.5 .CR...The "Throttle Response" and or "seat of the pants feeling" is quite different. I believe for lack of a better explanation the engine "responds" to increased throttle quicker Does that same apply to a motorcycle engine?? I think so.....just my opinion, only thing i have not heard anyone mention on this thread is whether milling head's and or block's affects Cam chain length? Valve train dynamics?? and does that in fact affect performance and reliability.?? Just my .02/ opinion and obviously all of us have one. 650ED your thoughts??
Have 1975 Kawasaki Z1-B & 2003 Harley Davidson Heritage Softail Classic
Had Hondas, Harleys and many ,many Z Series Kaws both Std. & LTD's

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Last edit: by ed spangler.

Porting and milling options for GPZ750? 16 Dec 2014 06:55 #656156

  • undiablo
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If you mill the head is 100% sure you will have to get your cam gears slotted to adjust timing.
Kawasaki KZ 750/4 LTD 1981
Kawasaki KLR 650 2011
Argentina - Buenos Aires

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Porting and milling options for GPZ750? 16 Dec 2014 07:17 #656159

  • SWest
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You can't go that far on the head.

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Porting and milling options for GPZ750? 16 Dec 2014 07:32 #656160

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ed spangler wrote:
"Throttle Response" is better with Higher Compression, what do I mean? I have drag raced for more than 40+ years,while its true increased compression may not make huge Horsepower differences, when you launch a car with a 454 Chevy Big Block that has factory 8.5 compression vs an identical one that has 11.5 .CR...The "Throttle Response" and or "seat of the pants feeling" is quite different. I believe for lack of a better explanation the engine "responds" to increased throttle quicker Does that same apply to a motorcycle engine?? I think so.....just my opinion, only thing i have not heard anyone mention on this thread is whether milling head's and or block's affects Cam chain length? Valve train dynamics?? and does that in fact affect performance and reliability.?? Just my .02/ opinion and obviously all of us have one. 650ED your thoughts??


I cannot speak from personal experience since my KZ650 is stock, but considering the bike in question is starting out with 9.5:1 compression I doubt one could bump the compression up as much as you did on the big block Chevy simply by milling the head without causing problems for a street bike. On the big block, going from 8.5 to 11.5 was a 35% increase in the compression ratio. A 35% CR increase on the GPZ750 would result in a 12.85:1 compression ratio; that's pretty high for a street KZ engine. In fact, there may not even be enough spare meat on the head or enough space between the valves and pistons to shave that much off, but I don't know if that is true. If you in fact did that, I suppose the chain tensioner would take up the slack in the cam chain, but I believe cam timing would need attention. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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Porting and milling options for GPZ750? 16 Dec 2014 08:06 #656171

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The deck height limits everything. Anything over 9.5/1 requires special fuel. For street applications Wiseco offers 9.25/1 pistons that can run on regular gas. I use premium but the gas today is far from when higher compression was the norm in the 70's. Nothing to be gained here.
Steve

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Porting and milling options for GPZ750? 16 Dec 2014 10:58 #656189

  • kawi810
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i run a 10.25 to 1 CR 810c kit in my gpz 750 with the head milled .i do not know what the real compression ratio is until i cc the chamber.i run dyna s with 34 degree's of total advance. i too have to run special gas but i usually find it at most gas stations its called supper unleaded LOL
original owner of a 1984 gpz 750
1985 turbo 750 stock, being restored.
1984 gpz 750 with 810 cc wiesco's megacycle cams(471-10) 34 mm flatslides v&h pipe ported head dyna ignition. bottom end, crank case from turbo 750 and sprockets.

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Porting and milling options for GPZ750? 16 Dec 2014 11:24 #656190

  • kawi810
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the real question is what would be the best head to build for the 810 cc kit motor?i have a choice of 84 gpz head -85 turbo 750 head or 81 kz 750 head .that would include mill deck to clean up surface , valve job , minor port clean up.i would like to send 1 out to larry cavanaugh but do not know which is the best to start with.
original owner of a 1984 gpz 750
1985 turbo 750 stock, being restored.
1984 gpz 750 with 810 cc wiesco's megacycle cams(471-10) 34 mm flatslides v&h pipe ported head dyna ignition. bottom end, crank case from turbo 750 and sprockets.

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Porting and milling options for GPZ750? 16 Dec 2014 14:31 #656201

  • Nessism
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kawi810 wrote: the real question is what would be the best head to build for the 810 cc kit motor?i have a choice of 84 gpz head -85 turbo 750 head or 81 kz 750 head .that would include mill deck to clean up surface , valve job , minor port clean up.i would like to send 1 out to larry cavanaugh but do not know which is the best to start with.


A late head with the "bathtub" shape would be the obvious choice I think. Not sure, but I think these heads do not have provision for a mechanical tach so that may be something to consider though.

Regarding milling the head to increase compression, again, as stated earlier, there is not enough deck surface to do this with a 750 head. The valve seats are already VERY close to the deck surface, so you can not take off more than a minor amount without hitting the valve seats. This is an interesting discussion and all, but you can't mill a 750 head to increase compression so the subject is mute.
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Last edit: by Nessism.

Porting and milling options for GPZ750? 16 Dec 2014 15:01 #656204

  • kawi810
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i am not to worried about milling the head just a clean up pass.more concerned about ports- how well they flow and chamber volume.which head would you choose to build? if you could choose any casting that bolted up to 750 block.i have all three options except a late 70's 650 head.which might be a choice for smaller cc chamber.this is my 84 gpz head see pic.what it comes down to is i want to send a head out for port work, valves,decking, which one ?
original owner of a 1984 gpz 750
1985 turbo 750 stock, being restored.
1984 gpz 750 with 810 cc wiesco's megacycle cams(471-10) 34 mm flatslides v&h pipe ported head dyna ignition. bottom end, crank case from turbo 750 and sprockets.

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Porting and milling options for GPZ750? 16 Dec 2014 15:07 #656205

  • kawi810
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gpz 750 head


Attachment 112.jpg not found



Attachment 137_2014-12-17.jpg not found

original owner of a 1984 gpz 750
1985 turbo 750 stock, being restored.
1984 gpz 750 with 810 cc wiesco's megacycle cams(471-10) 34 mm flatslides v&h pipe ported head dyna ignition. bottom end, crank case from turbo 750 and sprockets.
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Porting and milling options for GPZ750? 16 Dec 2014 15:14 #656206

  • taylee
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I want to have my head ceramic or powder coated. Is there a problem with having it baked at 500 degrees with the valves and guides left in it? I'd rather not disassemble everything if it's not going to harm it.
1985 GPZ750 (non-turbo)

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