Standard bore, high compression pistons. KZ900

I found a low mileage bike that had not been started since 1985. The cylinders are perfect, everything in the engine looks like it is brand new. No carbon deposits anywhere in sight and absolutely no wear on anything. All I want to do is bring the compression up to the 10.25:1 mark from the lousy 8.5:1. Better fuel economy and a little extra power. I have been searching for a while and all I see is big bore kits.

Does anyone make such pistons? I have seen standard bore KZ1000 10.25:1 pistons but no 900 pistons. I know I could do a special order through Wiseco but that gets quite expensive.

Don't know of any...most aftermarket kits start at 1015. Not sure if Z1Enterprises sells any...thought they sold over-size pistons but can't find any. Probably easiest thing for what you want to do is find a used 1015 cylinder and switch to your motor with whatever size bore you want.

Crazyduck, for years I had your way of thinking, keep it standard minor changes only. Now after my modifications (which are still considered minor) I wonder why? have I been riding the standard Z1R for so long before my current changes. It is smoother, better economy, braking, handling and the power. Overall the difference changed my mind from selling it years ago. Today I still have ALL my standard engine and body parts but I'll never fit them back to the bike.
I've had many bikes since but the Z always stayed because of these mods........GO FOR IT

CrazyDuck wrote: I found a low mileage bike that had not been started since 1985. The cylinders are perfect, everything in the engine looks like it is brand new. No carbon deposits anywhere in sight and absolutely no wear on anything. All I want to do is bring the compression up to the 10.25:1 mark from the lousy 8.5:1. Better fuel economy and a little extra power. I have been searching for a while and all I see is big bore kits.

Does anyone make such pistons? I have seen standard bore KZ1000 10.25:1 pistons but no 900 pistons. I know I could do a special order through Wiseco but that gets quite expensive.

Raising compression from stock to 10.25:1 isn't going to buy you a heck of a lot for the cost of the pistons. It will make a difference. However on a dollar / hp ratio, it's a poor investment.

Without tearing things apart, the best initial investment you can make is good carburetors. Follow that up with or in combination with good drop in cams and you'll be better served in the dollar / hp ratio investment.

Unfortunately, there are no reasonably priced performance carburetors available anymore. Used smoothbores are a crapshoot. New ones cost a bunch. Going to CV carburetors can bring headaches you may not be ready for also.

So where does that leave you? Here's a realistic approach that should be relatively painless. Find some drop in cams for $150 or so. Bolt them in, adjust the valves, rejet your stock carburetors and ride it.....

Getting the KZ900 was the power upgrade that I wanted, my 40hp TX500 was a bit slow. I REALLY do not like low compression engines. If I have to go with a larger bore to bring the compression up, then I will. I am not going to bore out a perfect set of standard 900 cylinders though. The fuel economy and the low end torque is what I was going for. It won't be a huge power increase but I don't care.
The poor bike sat outside for 27 years after being low-sided which made it look really bad so I only paid $300 for it. The damn thing still had the original tires!

I want the bike to handle better in the twisty mountain roads. I have to get another swingarm to upgrade to the rear disc brake so that will probably go for a better swingarm while I am at it.

Don't know of anyone offering hi-comp 66 mm pistons. But here are 69.4 mm hi-comp pistons from www.americanclassix.com/streetfighter_conversions.html :

Here's the standard compression Pistons from Z1 that are in the Vendor's Section, and the American Classix 69.4's corrected clickable link.

CLICK

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> 900 Pistons

CLICK

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> American Classix 69.4 Pistons

Mill the head and redegree the cams