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Discussion Starter · #1 ·
Whats up fellas. Allright here is my question. I was thinking about ordering the high comp. piston from Alba. It is suposed to bring the compression up to 12 - 1. What does every body think about this. Will there be a noticable gain, and will I have to run race gas or anything like that.
 

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Do a search for threads about changing your head gasket to that of the DRZ dirtbike. It may be cheaper with nearly the same results.
 

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$12 jug/head gasket or $136 piston....

Being that you change out the gasket anyway to install the piston this is a no brainer... Same compression result, unless you want to run 106 or 110 racing fuel and customize the valve to piston clearance you can do both and will benefit with more power.
 

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Ahhhhhhhhhhh, the smell of 110. Has a calming effect on the soul.

You will notice a nice improvement Kawazuki78
 

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Above 11:1 must run higher octane than pump gas 93. 11:1 compression
still able to run 93, but not below. Using below 93 on 11:1 can cause
the fuel to ignite to early. From 9:1 to 11:1 compression is ~3% gain
in HP for every 1:1 increase, so from 9:1 to 10:1 would be ~3% gain in
hp, and so on..... This 3% gain is in addition to displacement gain
on piston size increase. In other words seperate from boring. But
keep in mind that above 11:1 you'll only get ~1.5% gain, so the
advantages above 11:1 are minimal.
 

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I saw a 13:1 blow a head gasket. I may change the cams and leave the piston stock.
 

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Mattltz400 the z has 11.3 to 1 and runs fine on 93. the DRZ has 12.2 to 1 and runs fine on 93. Your theory has more holes than swiss cheese. If 12 to 1 is as high as you want to go and you are refering to a standard bore size then I would say the same as the others, go with a DRZ base gasket and that will put you around 12:1.[/quote]
 

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Thats odd cause I run my Z on regular gas which is what 87 and have no side effects. Now if i decide to add in the Intake cam then I will start runnin 93 but until then i will stick with 87
 
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You can’t go just by the compression ratio the shape of the combustion chamber and what’s called the squish area/band have allot to do with figuring out what octane you will need to run.
 

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Hey guys...I'm at 13.5:1 and no problems. I run VP C12 (108) but still as reliable as stock.
 

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Hey Treystoys have you done any dyno runs on your z or do you have a rough guess on your horsepower.I think I am going to go with the lrd 440 kit.I think that kit has the highest compression out of all the kits I seen.I have always been happy with lrd.
 

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I'm now running the 470 big bore from Thumper. The base gasket that they sell is Cometic and is .010 thick,, this along with shaving .013 off the the top of the cylinder put my deck height at .010 +/- .002 After reassymbly I pulled a compression check and it was 220psi. Not bad. Naturally the more compression you have the more torque you'll create. But of course there is a limit. If your stock now,, go with that piston you want or the one from GT Thunder. He has a Badass piston for the stock bore and deck height has already been figured in to the desighn so you dont have to shave anything. I assume he has it set up to run the thin base gasket though.
 

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Discussion Starter · #13 ·
Thanks, still have not decided but will be ordering the parts this week.
 

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Zman...no dyno tests yet. I did find a shop locally that has a dyno. I may take it there, but I want to wait till I have all my gadgets installed. I'm installing my heavy duty valve springs today, then I'll be waiting for the dyna ignition to come out and later on the 40mm fcr carb.

I hate to be over optimistic, so I'm guessing in the high 40hp range as I sit now. The reason I say that is cause speed wise in a drag race my bike will run with a Banshee that has a set of good pipes, filters, and jetted properly...they put out 45-50 hp like that, so I figure I'm in that ballpark. I'm very happy with the bike like it is, I just want the extra 1000 or so rpms out of the cdi, and I'm pretty sure the larger carb will be a must when I'm spinning 10,000+ rpms.

By the way, the only difference between the LRD 12:1 440 kit and their 13.5:1 kit in a thinner gasket used on the later. They use Cometic gaskets as well. My piston is a JE.
 

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Matt is rite but hes thinking more 400ex or air cooled engines. The Z is liquid cooled so u can run a hi comp ratio. I think the max ratio is something like 12.5:1 w/out race gas. Not sure about that but its close.


Later
 
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