81 and 84 GPZ1100 cylinder head comparisons

I was wonderin if anyone out there knew off hand what the main differences are between the 1981 cylinder head and the 1984 head. If any

Not compleitly sure, but i think the 84 GPZ head had a bigger combustion chamber ie: Bigger valves and such, im sure someone has more info into it than me. I do know that they can be milled to work with the kz bottom end, but it drops the compression 2 full points, so it goes from 8:1 to 6:1, perfect for running a turbo were you need lots a bost to make it scoot. I only know this because Plummen responded to one of my posts about putting the GPZ head on my 74 Z1 900.

the 81-82 has the hemi type combustion chamber like the older 900-1000 motors but has much bigger combustion chamber than the old kz motors.the 83-84 is a much better design but completely differant and wont work on the older motors without a great deal of money and parts changing including crank/rods and pistons

Be also aware that the 1981 GPz1100 head had the injectors mount directly into the head whereas the injectors were mounted on the throttle bodies starting in 1982. So, if you find a 1981 head, you have to deal with blocking off the injector ports if you run carbs or go with the later style injectors.

in order to run the late model gpz head you have to use j rods on the crank as they are .40" shorter [pin heights are different from kz to gpz pistons] and since the combustion chamber is larger you will have to get pistons made up to fit the gpz head or you won't have any compression.

timebomb33 wrote:

in order to run the late model gpz head you have to use j rods on the crank as they are .40" shorter [pin heights are different from kz to gpz pistons] and since the combustion chamber is larger you will have to get pistons made up to fit the gpz head or you won't have any compression.

slow down youre making my head spin here!:laugh: you can use the 81-82 gpz/81-90 something j head on the old motors depending on which path ya wanna follow.you can just run higher compression kz pistons knowing its going to drop around 2 full points depending on who you ask,or you can use j pistons on the stock kz rods with a spacer under the cylinder to make up for the kz rods.either way you need the cam chain adaptor to make it work.the 83-84 gpz also uses bigger wrist pins so its really cost prohibitive unless you have really deep pockets to make that one work,ive got some 83-84 kz/gpz 1100/1170 pistons someplace that i learned this on the hard way!:laugh:

Sorry I didnt explain clearly enough
Im running a 1981 GPZ motor in my ELR(my head has the injector ports in the head- I've already blocked them off and am running carbs).Motor runns great. Problem is , I have a small crack across one of the cam plug holes. I know of a nice 1984 GPZ 1100 head for sale and was wondering if I could just drop it on my 81 J motor .

totally differant animal,you need an81- j style head

Yea but an 1982 gpz head will work also,I know that much. And maybe 1000J heads will work too. Is the combustion chamber volume and valve sizes etc.simular on the 81 and 84 head ?

totally differant combustion chamber design im thinking the 81-82 gpz and the 81- j head are pretty much same thats why i lump them together.

barney wrote:

Sorry I didnt explain clearly enough
Im running a 1981 GPZ motor in my ELR(my head has the injector ports in the head- I've already blocked them off and am running carbs).Motor runns great. Problem is , I have a small crack across one of the cam plug holes. I know of a nice 1984 GPZ 1100 head for sale and was wondering if I could just drop it on my 81 J motor .

Why don't you ask Larry Cavan (user name)? Since he does this stuff for a living I'm inclined to think he knows what he's talking about.

Cavanaugh Racing Heads

www.flowbenchtech.com/porting/CRH/index.htm

The 83-84 head has what we call the "bath tub" combustion chamber. It also has larger valves.

Not too sure about volume differences, but the shape would mean aftermarket pistons for the early head, might have to be modified to clear the late chamber.

No connecting rods have to be changed.

Jay