Recommended Headwork for Slightly Overbored GPZ110

zed1015 wrote: 83/84 GPZ1100/Spectre etc bathtub style heads are actually higher comp ( smaller combustion chamber volume) than the earlier 'J' heads.

I was struggling with the connection to "DFI being used due to low compression".... :blink:

750 R1 wrote:

zed1015 wrote: 83/84 GPZ1100/Spectre etc bathtub style heads are actually higher comp ( smaller combustion chamber volume) than the earlier 'J' heads.

I was struggling with the connection to "DFI being used due to low compression".... :blink:

It Has NOTHING TO DO WITH COMPRESSION the reason was to improve operation at lower engine speeds.

If interested in reviewing my 84 bath tub top-end thread posted in 2015, see:
www.kzrider.com/forum/2-engine/596933-ca...-on-my-engine#658819

or zed1015's initial reply to that post which follows:

"Which engine do you want to fit it on.
One of the best heads to have for performance modding.
Bathtub/twin swirl head.
Same casting as GPZ Unitrack but probably shim over bucket instead of under.
Lower compression than earlier KZ9/1000 heads but slightly higher comp than the earlier twin shock GPZ and J heads.
Has steeper valve angle which allowed the larger valves to be used.
Be careful with piston to valve head clearances on assembly.
Depending on application you may need to fit different pistons or machine the valve pocket angle to avoid collision etc."

My question is, what effect does the unique combustion chamber (bath tub) shape have on the incoming air/fuel mix and outgoing exhaust gasses, compared with heads having the simple hemispheric shape?

The GPZ Bathtub head is of a twin swirl combustion chamber design which speeds up and increases combustion efficiency better than a plain hemisphere (simply search "Twin swirl" on google for more detailed info).
This equates to a fuller and faster burn which makes the most of the fuel available and decreases the amount of unburnt fuel lost on the exhaust phase.
Simply put. The twin swirl will produce more power than a plain hemi for the same amount of fuel.
This is why (as well as the bigger valves) the GPZ bathtub head is the one to have for performance gains.

Very interesting, so I should save my pennies once I have it running for a 1983 or 1984 GPZ1100 Head and cams? It will be a direct plug and play?

In the interim until I find that unicorn, does anyone know the max lift that I can get with stock valve springs if I decide to put in an aftermarket cam later on?

Edit; Added a word

DFIGPZ wrote:

750 R1 wrote:

zed1015 wrote: 83/84 GPZ1100/Spectre etc bathtub style heads are actually higher comp ( smaller combustion chamber volume) than the earlier 'J' heads.

I was struggling with the connection to "DFI being used due to low compression".... :blink:

It Has NOTHING TO DO WITH COMPRESSION the reason was to improve operation at lower engine speeds.

But thats exactly what you said....?

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 ?

Kawasaki was developing its injection systems on production bikes way before the bathtub heads {1980}, they were simply the first Japanese manufacturer to do so {in the race for better tech and emissions control}. I have an old mechanic friend thats been doing carb conversions on injected GPZ1100's for years, NO problems with low speed running, its a common conversion, Kawasaki's first few attempts at injection were quite primitive, it was introduced so Kawasaki could be ahead of the USA's tough emission regulations, improve operation right across the rev range, as well as better fuel economy............

In 1980, Kawasaki was the first motorcycle manufacturer to recognize that in the following years, bikes would have to meet even tougher compliance laws. Fuel-injection, rather than carburetion, on an engine would be one way to get a motorcycle through emission testing

Further reading for those interested (with pictures!):

kzrider.com/forum/2-engine/602288-kz-gpz...hings-to-know#723639

P.S. Whatever possessed me to do such a thing to my motor? :ohmy: 12,000 miles w/o issues, and it loves regular gas. :whistle:

diego092409 wrote: Very interesting, so I should save my pennies once I have it running for a 1983 or 1984 GPZ1100 Head and cams? It will be a direct plug and play?

In the interim until I find that unicorn, does anyone know the max lift that I can get with stock valve springs if I decide to put in an aftermarket cam later on?

Edit; Added a word

Be careful changing the cams later to a higher lift without cleaning the valve stems.
A lot of the seals die because the valve stem gums up to a lower lift, then when a higher lift cam is added the seal goes on the gummed area causing the seals to fail.

daveo did some nice work on this subject.
My block seeps just a little oil that I notice after I park it hot and leave it sitting a few days, probably because one of the gaskets around the block spacer didn't seal perfect, but for the HP I got from the '84 head I don't mind wiping up a quarter-sized spot of oil.
Mine makes so much power the clutch started slipping the first time I hit it to 7000 rpms - so we rebuilt it with stock Kawi clutch plates, and stiffer springs.

diego092409 wrote: Very interesting, so I should save my pennies once I have it running for a 1983 or 1984 GPZ1100 Head and cams? It will be a direct plug and play?

In the interim until I find that unicorn, does anyone know the max lift that I can get with stock valve springs if I decide to put in an aftermarket cam later on?

Edit; Added a word

Like I said before save our pennies and have stock head ported , VJ etc you will be farther ahead Common Sense I have put hundreds of KZ / GPZ engines together leave the 83 /84 heads for the drag racers and top end power . can you use the 83 /84 head yes but valve angles are not the same these people who say yea they put carbs on 83 /84 1100 W/O issue are BS a lot of tuning involved or the use of aftermarket carbs look at all the post on this site about pods not working these same members that tell this BS cannot even get carbs with pods on stock machines tuned never the less one that has a head with low velocity at low rpms , also these same people were the first to scrap the factory DFI on the 83/84 1100s because they did not have a clue on how to make it work , these same people want to trap you into doing this. the better way would be do the stock head to 84 cfm vs the 83 /84 also 84 cfm and the one with ported head will have better street manners. Take it for what its worth or just get a 83 /84 head port it to 120cfm and let me know how it does on the street .

DFIGPZ wrote:

diego092409 wrote: Very interesting, so I should save my pennies once I have it running for a 1983 or 1984 GPZ1100 Head and cams? It will be a direct plug and play?

In the interim until I find that unicorn, does anyone know the max lift that I can get with stock valve springs if I decide to put in an aftermarket cam later on?

Edit; Added a word

Like I said before save our pennies and have stock head ported , VJ etc you will be farther ahead Common Sense I have put hundreds of KZ / GPZ engines together leave the 83 /84 heads for the drag racers and top end power . can you use the 83 /84 head yes but valve angles are not the same these people who say yea they put carbs on 83 /84 1100 W/O issue are BS a lot of tuning involved or the use of aftermarket carbs look at all the post on this site about pods not working these same members that tell this BS cannot even get carbs with pods on stock machines tuned never the less one that has a head with low velocity at low rpms , also these same people were the first to scrap the factory DFI on the 83/84 1100s because they did not have a clue on how to make it work , these same people want to trap you into doing this. the better way would be do the stock head to 84 cfm vs the 83 /84 also 84 cfm and the one with ported head will have better street manners. Take it for what its worth or just get a 83 /84 head port it to 120cfm and let me know how it does on the street .

You make a lot of assumptions there mate, most, if not all are wrong, it reads like a conspiracy theory !!! As for your carb conversion theories, hahahaha.... Just wow.... :blink:

This has turned out to be quite a topic!

First - If I ever rebuild my 1100B2 again I'll spend the big bucks, and use the '84 Connecting rods and '84 Wiseco pistons, so I won't have to have the block spacer. Because if you run the '82 Wiseco pistons with the bathtub head, the high compression piston will rub the head.

daveo did some kick-ass work with his setup getting the clearances right.

Second, the '83-'84 Cams are a nice improvement, and are really nice with the added displacement / compression of a big bore kit. (Even though Larry Cavanaugh calls these 'baby grinds')

Third - the '83-'84 heads are superior to the KZ1000J head in just about every way. They have the 1mm bigger intake valves, and the .5 bigger exhaust valves, and the valves recessed /re-angled for clearance. Try doing that to your J head.

Lastly - I've seen a couple of carbed GPz's - and neither one of them rev as quickly or cleanly as my mostly-stock DFI with resistor-mod.
Plus, who wants to butcher up a nice stock tank?