upgrading to a j model head

OK... so here is a couple of questiosn for those in the know...

- Why change up the head to a Jmodel... seems that there is no benefit. Possibly bigger valve? but with the compression issue, seems like that is a not cutting it. What am I missing?

- If I swapped to a Jmodel head... and used a 1075kit 10.25:1, then the end result being an 8.25:1 compression, the bike will lack power and be as boring as stock if not more so... Any input here?

mark1122 wrote:

why not fix the original head?

ended up being a little cheaper... I was assured that the bike would run. Maybe I was taken for a ride...

Switching to a J head is a lot cheaper than having the head prorted. The J head has bigger valves and flows a lot better. Adding a 1075 kit would give you more displacement. "No replacement for displacement". If you want you could go with the 12.5/1 1075 kit. That would wake it up but you might have to run a higher grade of gas. $$$$ And depending on what carbs you have you might also need an upgrade. More $$$$$ Speed aint cheap.

well, to be fair, I'm not going for a ton of speed... I just want the bike to run and run well. I have mikuni bs34 on the bike now.

The cheapest solution is to buy a 1015 head and sell your J head, I think the J head sells for more $$ than the 1015 head so you might make money doing it that way.

so thanks to the kzrider classifieds, I have purchased a new head for my KZ1000 police bike. It's off a j model and includes the necessary cam conversion tower and ended up being less than I expected to pay to get new valves. The guy I bought it from said that from there all I would need is a new valve cover gasket, cam plugs and valve reed covers.

Was the seller a member that has posted here, or just someone who joined just to advertise the head?

I posted a classified looking for a new head. He contacted me from reading my "wanted" post.
I spent 350 for the head, cam conversion tower and shipping. My bill at APE is going to be about 200 before shipping unless the valves do need to be replaced. Maybe I should just sell the thing and get my valves done. It DOES seem like it would be easier all around.

What do you think????

Bicycle Lee wrote:

I posted a classified looking for a new head. He contacted me from reading my "wanted" post.
I spent 350 for the head, cam conversion tower and shipping. My bill at APE is going to be about 200 before shipping unless the valves do need to be replaced. Maybe I should just sell the thing and get my valves done. It DOES seem like it would be easier all around.

What do you think????

I think that's exactly what you should do, unless you are looking for serious power, in which case I'd send your original head to Larry Cavanaugh and ask him to make it fast and streetable

who is this Larry Cavanaugh?? Where do I find him. I found a good deal on new pistons, rings etc...
more than I wanted to spend, but maybe I can make the purchase just this once...

donthekawguy wrote:

Switching to a J head is a lot cheaper than having the head prorted. The J head has bigger valves and flows a lot better. Adding a 1075 kit would give you more displacement. "No replacement for displacement". If you want you could go with the 12.5/1 1075 kit. That would wake it up but you might have to run a higher grade of gas. $$$$ And depending on what carbs you have you might also need an upgrade. More $$$$$ Speed aint cheap.

Not exactly like that. www.flowbenchtech.com/porting/CRH/kz-data.htm

For starters, the J head has bigger valves and bigger ports. It was designed for CV type carbs to be used when Kaw updated the old KZ motor. Unfortunately, even with 1mm larger valves the J head doesn't flow drastic amounts of air over the stock KZ head.

You're wasting your time putting a J head on the bike if you don't use the correct pistons to go with it. There is no free lunch.

Stock Cylinder Head Flow Data @.500" Lift - 10" Water
KZ 900 - 68 CFM
1000 - 68 CFM
J 998 - 70 CFM
83-85 GPz11 - 83 CFM

so now I guess my question is:

with the j head, bored cylinders and new 10.25:1 pistons, would this be complete? Are there any other parts or upgrades that would be necessary for this rebuild? Assuming everything else on the bike works fine...
If it's going to require more parts I think I will just get my valves replaced....

So I guess the guy who sold it to me really DID just want to make a sale and took advantage of my lack of knowledge... fool me once....

so after much deliberation, I have decided to just sell the j head once I get it back from APE and fix the valves on my old KZ head. I probably won't be able to get as much for it as I've spent on it, but I am hoping to get at least enough to do my valves.
Any takers? :laugh: