1075 Kits: What's the difference b/w compression ratios?

I am thinking about putting a 1075 kit on my B2. In looking at the APE site, they show kits available with compression ratios of 8.5:1, 10.25:1, and 12:1.

What is the difference in terms of street use? I assume that 8.5 is the "mildest" and 12:1 is more for racing? But if I went with a 10.25:1, what should I expect? Do I need to change to HD studs? Different cams? Premium Gas? Other considerations?

Thanks.

Post edited by: Skyman, at: 2007/10/29 12:09

8.5:1 is for turbo use.

10.25:1 is for street use and needs Premium gas.

12:1 is for racing and requires racing gas.

Thanks, Steell!

With the 10.25:1 kit, are heavy duty studs needed? Can I still use my stock cams?

Thanks.

Well, the studs aren't too expensive, so I'd use them whether required or not, and cams (such as the APE 410) would give you a nice power boost (I'd get the springs also), but they are not "required".

Sure gets expensive, don't it

steell wrote:

Sure gets expensive, don't it

Yeah, if I do this, I'll probably take it one step at a time. Maybe include the studs. Cams and springs can wait.

For a cheap cam upgrade, look for some 83-84 GPz1100 cams. APE sells the sprockets you need to bolt them in the early 1000's.

Keep in mind that stock compression is 8.7:1 I think. What Steve E. is calling "turbo application" is more like OEM application. The nice thing is that regular gas is cheaper than hi-test which I think you will need with the 10:25:1 compression. You may need to retard your ignition advance to keep from pinging. I think if I were going to buy this stuff, I would save my pennies and get the APE 1075 kit which includes the cams, springs (I think?) and the oversized pistons. I would ask them about ignition issues related to the upgrade and what they recommend. I would also take the new pistons AND my block to a good bike machine shop because the shop MUST use the pistons to calculate how much to bore the cylinder bores. I would also consider new cam chain bits and getting the cylinder head done with new guides... In fact I have been considering what I would do if I had some money myself hehe I will probably be starting a new bike project in the near future. When considering the machine work, APE is not cheap and you have to pay for shipping heavy parts but they likely know what they are doing. I have seen quite a few situations where folks used local machine shops that specialize in car engine work and the results were not good... I would seriously look for a good MOTORCYCLE machine shop or use APE.

Regarding what George said about using a motorcycle specific machine shop, keep in mind that APE has a brand new facility with brand new state of the art machines.

I have the capability to bore cylinders, and I have a friend that owns and operates a motorcycle specific machine shop. My friend bores and hones my 750 twin cylinders (he's much better than I am and has better equipment), but since I am going for ultimate performance from my 750E project, I'm sending the block and cylinders to APE (and possibly the cylinder head, APE has a brand new Serdi).

If I had to choose between using a local automotive machine shop or sending the stuff to APE, I'd send it to APE.

I bought my Wiseco 615 kit from APE, and they did all of the necessary machine work. Sent them two complete heads, and two barrels to choose the best from, and to use for parts. They sent me back the unused parts. You will need them to match the pistons to your cylinders. They can also get the piston kit for you. I am very satisfied with the work they do, and highly recommend them. APE Jay checks in here often, and answers all questions. That's another good thing.

Skyman wrote:

I am thinking about putting a 1075 kit on my B2. In looking at the APE site, they show kits available with compression ratios of 8.5:1, 10.25:1, and 12:1.

What is the difference in terms of street use? I assume that 8.5 is the "mildest" and 12:1 is more for racing? But if I went with a 10.25:1, what should I expect? Do I need to change to HD studs? Different cams? Premium Gas? Other considerations?

Thanks.<br><br>Post edited by: Skyman, at: 2007/10/29 12:09

My 2 cents on this....

Performance cost money....so...it's not what you spend but what you buy that makes all the difference.




There's really only 1 logical choice for the N/A street motors and that's the 10:25:1 compression ratio. If you're not going to put any compression to it, then I wouldnt' bother with a big bore kit..look into 1st over OEM pistons instead.

Jeff at Z1 has a great price on the 1075 Wiseco kits. I'd spend an extra few bucks and get an OEM KZ1000 cylinder base gasket, even though a cometic gasket comes with the kit. The cometic head gasket is fine.

Web, Megacycle and Cam Motion all have nice drop in cams that when combined with the big bore kit will really wake up a tired KZ. If you want your eyes fully opened at a reasonable cost...get some head work done and stay with stock valves. You can get by with the stock KZ1000 crankshaft if it's still in good working condition.

Larry, why the comment regarding the Cometic base gasket? I buy OEM head gaskets as I have never been overly fond of some of the aftermarket head gaskets that come in kits but have not heard of a problem with base gaskets... they are just heavy gauge paper I think. Have you had negative experience with Cometic base gaskets? I have found their stuff really good in the past but seldom buy it as I am a K&L dealer and generally buy Versah gaskets which are decent.

As far as compression... It looks like an owner's goals should determine the compression of the piston kit. For those who are not all that interested in hot-rodding and are looking for reliability and economy, the 8.5:1 compression makes sense. I would never try and hot-rod one of my KZs because I already own a modern bike that is far faster than a most vintage street KZs. In order to make a KZ as fast as the modern bike, I would have to go a lot farther with mods than the street cams and mild displacement and compression bump.