gpz750 quench chamber heads on kz750 pistons

Thanks for the response turboguzzi, I apologize for not seeing it earlier. I just read through your build thread and it is pretty awesome. You confirmed allot of my thinking about this engine. Specifically about the porting I have already done among other things, that sectioned port mold was fantastic. That is just the sort of detailed information i was surprised I had been having such a hard time digging up.

Ok so I have a few questions for you if you are still interested in sharing. I hope you don't mind if I mix and match some stuff I've read from the build thread as well. I realize this was like 4 years ago so I understand if it's not all terribly fresh in your memory.

to get that you need to go down to 035-040 between the chamfered area on the head and the piston, not just at the nearest point but to have a relatively wide quench area of say 6-8 mm

I have decided to go with the 650 head and kz750 pistons. I haven't mocked it up yet because I was still pondering 810 pistons but my plan is to assemble without the base gasket and see where that puts the piston to deck height and see where i stand with piston to head clearance using the turbo mls headgasket. The 650 chamber is about 60 mm and the 750 piston is 66 so that gives me roughly 3 mm wide band all the way around if I can get the height right for quench. Now when you say 6-8 mm I take it this is like the radius measured width of the quench band and not the full diameter measure of which mine would be 6 mm?

Have you done specific back to back testing on these engines changing only the quench to see the differences in how it runs and ignition demands? I do believe in the results from your build but there are just so many changes being made at one time there it's hard to judge how much of the results to attribute to quench.

For anyone else reading this that has not read turboguzzi's build here is a refresher on the results I am referring to.

I'm down to only 28 degs full advance right now and the torque peak is still a very healthy 58 lb/ft, as good as a current GSXR750 with four valves and water cooling (just at lower revs, dang!) Stock GPZ750 was 41 lb/ft just to give you an idea, so you can get good torque with late timing too if you have the right turbulence inducing squish in there

BTW, the cruzing image 810 kit form ebay is pretty cheap....

Do you have any experience with these? I can't tell if you are serious about this or not. I am generally leery of things which seem to good to be true. I have decided to eventually boost the engine as my means to higher output vs displacement. This is what I have the most experience with and I've found a wealth of information on the turbo 750 engines of which allot caries over to the na 6/750s, especially if you want to boost them. I've already got a turbo crank setup in the 650 block with zr7 rods, all the oil clearances are perfect and the bigger flywheel and generator of the turbo will help with the additional electrical loads for the injection stuff later. I found the information about the zr7 oil pump and pressure relief valve from the 750turbo forum which I saw in your build thread you had also figured out independently years ago. I plan to break it in and get it running carbureted and naturally aspirated and move onto injection and boost later. My main concern with the 810 stuff isn't even the compression ratio with pistons available for the na wrist pin size (can't find used turbo rods yet) as i have tuned pump gas 9 - 10:1 compression ratio turbo setups in the past and also plan to use e85 for any higher detonation prone boost levels. My concern is the cylinder wall thickness at 69 mm boosted. I really wish there was an off the shelf stock bore forged piston around 8.5 - 9:1. The strength of the piston and strength of the cylinder wall and it's ability to dissipate heat (will also probably implement your yoshi vents) are more of a concern to me than 72 cc of displacement or a point of compression. Although I do appreciate that that 72 cc's carries with it another 3 mm of quench when mated to the 650 chamber,

On to the head,

so not much to do about the strong "S" line in 1 & 4?

my concern is that flow cant really stick to the outside wall (the right wall in cyl 4 for instance) so essentially the effective section gets chocked there and most of the flow conitnues to the pocket space left of the valve guide

The other thing i was considering was raising the floor a bit around points 4-5 for some venturi effect at the ssr.

GPZ head ports mostly cleaned in the bowl area. Prefered not to touch them until my flowbench is up and running

I apologize again for the mix n match quotes there, but did you get the flowbench running and did you ever attempt to address any of your thoughts on this matter?

I am also planning a simple flow bench but I did not wait for it to start making changes. I think I'm thinking what you were thinking but I think I'd like to actually put this thing into action before I draw any conclusions about the effectiveness of my port modifications.

Have you heard of a program called pipemax? I used this software to run some numbers on this engine and basically the ports are way too big stock. And that's on the 650 which is supposed to have the smallest ports. Then there's the effects of abrupt changes in cross sectional area which generally don't do great things for flow ala your S line. What is the unit of measure in that graph below the cross section? I am curious what the size difference is for the gpz ports.

Also what are your thoughts on dual plugging? Thinking about the benefits of dual plugs seems very related to the benefits of quench. More efficient combustion with less ignition advance which results as you have stated in a cooler running more reliable air cooled engine. Have you seen the latest version of the Chrysler design? This is the chamber for the hellcat engine.

no problem man, im used to people not bothering with info you leave them here but glad to see that you are back!

quite a lot of questions there, not sure i am going to answer them but will do the best i can. main issue is that i dont get is how this info is going to help you with a turbo build.... different game, crown shape is totaly diferent in those and port flow much less important.

if you look at what two stroke guys always with squish bands youll see that thye always went with quite wide bands, even more than 6-8mm, so all i can say is the more the better, i am not a pro engine builder with dozens of engines built, so dont have back to back numbers, but with a 12:1 CR and no piinging at all with the 98 octane gas we have here in italy i'd say the squish is doing its job. the engine also runs relatively cool ( for a race engine that is...)

muzzy did dual plugs in rainey's gpz750, but today only big twins with super large bores of more than 105 mm like ducati panigale, etc. bother with it. dont think it'll make a difference in a 70mm -ish bore. BTW what bore size that car's head?

i definetely going to use the cruizeimage 810 kit in a future street build, will let you know how it went, though it might take time till i have that motor running

trivia: unusually the zephyr 1100 is a twin plug head.

Anyone here used the cruizin image kit? people are sceptical as they are cheap, but I guess kawasaki are buying pistons in for a fraction of that .

how this info is going to help you with a turbo build.... different game, crown shape is totaly diferent in those and port flow much less important.

Well I beg to differ, I think the port flow is actually more important in a turbo engine. I know forced induction will make power despite crappy head flow but I am learning more and more that the best na engines, head wise, make the best turbo engines. If anything I think the quality of the port work is multiplied in a turbo engine.

I realize the piston crown is very different with lower compression hemi pistons but the quench area still has the same affect whether the cylinder pressures are high from static compression or high dynamic compression with boost.

with a 12:1 CR and no piinging at all with the 98 octane gas we have here in italy i'd say the squish is doing its job. the engine also runs relatively cool

The objective is still more efficient combustion resulting in cooler running and increased detonation suppression, all good things for a turbo engine.

muzzy did dual plugs in rainey's gpz750, but today only big twins with super large bores of more than 105 mm like ducati panigale, etc. bother with it. dont think it'll make a difference in a 70mm -ish bore. BTW what bore size that car's head?

I can see how it would be less useful on smaller bores and probably even less so on flat top pistons. However, I have read about dual plug kz1000s requiring timing changes though which is a 70mm bore.

Ignition Timing:
Kaw KZ 900 / 1000 / GPZ
Single plug head - 38 degrees
Dual plug Head - 32 - 34 degrees

From www.aperaceparts.com/cope.html

I don't know all the details about this information but if it's accurate 4-6 degrees is a pretty significant change.

if you look at what two stroke guys always with squish bands youll see that thye always went with quite wide bands, even more than 6-8mm, so all i can say is the more the better

It's funny you mention that as I did actually begin researching that specifically just after i finished my last post here. The 2 stroke chamber design has no valves to contend with in its design so the chamber shape and spark plug placement are dictated entirely by combustion efficiency without much compromise. In my quick research I found the consensus seems to be 50% of the bore area for quench.



From www.ozebook.com/compendium/t500_files/morgan/head.htm

Besides even if none of your work did apply to my build I still find it fascinating and I love to learn about more advanced engine modifications whenever I have an opportunity too. I loved reading your build thread and the results were very impressive. It really gave me allot to think about and learn from.

So did you ever get around to messing with the flowbench or porting?

the way i see it , 38 degs one plug is REALLY bad, due to no squish turbulence, i.e. no help in accelerating the flame front.

32 - 34, same no squish problem, but slightly better timing due to flame front having to do only half the distance

i got best power at 28 degs with a 69mm bore/single plug ! that's what i call significantly faster should tel you something about the importance of REALLY good squish,

during my gpz racer 5 year career, never felt power was the a problem, I often could draft much more modern 16 valve 750 air-oil gsxrs

weight and wheelbase where the main limits to lap times of my bike, so never got around to doing port and flow development

just checked the hellcat bore, more than a 100mm, no wonder they went dual plugs.... told ya

T/G I've got ? about the best power at 28 degs I'll ask in my race thread
so not to hijack here.

Man I could have sworn I put the hellcat bore at roughly 104mm in my last post, sorry about that. You answer a bunch of my questions and then ask me one and I didn't answer you.

I'm not disputing your assessment at all, from what I've found so far your work and explanation of quench in these engines is far better than anything else I've come across.

I understand about the power thing, like I said your level of competitiveness, your results with this engine work speak for themselves and again I thank you for sharing the information. I am taking your advise seriously and i will try to maximize quench in my engine build.

Would you mind sharing your thoughts maybe on what you would have looked to work on in the ports if you had proceeded with that?

zukdave , it's not a thread jack at all really, I suspect turboguzzis explanation about the 28 degrees will revolve around his quench modifications which is basically the main discussion point of this thread. Have you read his build thread already? He has explained allot of the engine work he did already there.

another reason i didnt touch the ports in the gpz is that with their VERY long, s-shape they have, specially in the outboard cyls, i felt like i wouldnt be able to do much with my porting tool, access is real hard.

if was to tackle tpday the ports in a 750 jead, i would do what memeber injected did in his racer: cut off most of the port and attach new straights stubs without the S-curve.

cutting off the port would give you proper acces to the important areas to work on and straight stubs much better flow. carb spacing would totally change of course, not a problem if you fit CR's

in my CB500/4, this is exactly what i did, was getting 62 rwhp form 500 c.c. compare to the twisitng ports of the 750 and youll see what i mean