From what i have learned on this forum and others, it looks like I will need to put a dish in my forged 103 pistons to get down to the right compression ratio for the SE255 cams. I have a 2008 Road King.
The pistons are 22942-00 SE forged flat tops, have 2cc worth of valve notches as shipped.
To get the quench tight, I figure I need about 6cc dish cut into the pistons. Is this going too far? The pistons are .280 thick, and if I take material off between the notches in an area of 2.3 x 2 it will take a cut of about .066 .
I figure that I will probably find the piston deck height at .005 to .008. So a .030 gasket should get me under .038 piston to head.
With the heads cleaned up in the chambers , I should have about 86cc.
The goal is to get decent quench, run on 91 octane anywhere, as we ride two up, loaded a fair amount.
On the subject of quench, just how close can it be set, and is it worth the trouble to get the last few thou in terms of octane requirements and torque increase? I have heard get it below .040, and some have talked about .030, although that sounds a bit tight.
Here are the numbers I figure on using;
.035 piston to head
8cc dish
86cc heads
9.37 static compression
yields 187.5 ccp at sealevel with SE255 cams
Is this about right, too conservative, or too agressive on compression?
Thanks, Greg

 

I think you have been reading too much.

The 07 & later TC96's have "negative deck height" - meaning the piston is actually "down in the hole". That is where you get that .005 ~ .008. Using your logic, that means quench = crushed gasket thickness + .005~.008 (say .030 + .008 = .038).

Any experienced engine builder will tell you that .030 is what you want to shoot for. I agree with that.

Sounds like you are worrying about hypotheticals or estimations. What you will ultimately want to do is mock assembly and take measurements.

There are several ways to work with "negative deck height". Once you know what it actually is, you can:
1) Get a gasket that gives you the desired .030", when the ACTUAL deck height is factored in.
2) Get pistons that are made "for the 07 & later bikes". The wrist pin hole is .008 lower.
3) Measure actual deck height and turn material off the base of the cylinder to lower the deck.

The simplest way is using the correct gasket. Cometic will sell you whatever size you request. It's just a phone call away.

Having said all that... the S/E stage II kit is a very basic upgrade. Get the right gasket & go.

If you put as much effort into getting the bike PROPERLY tuned after you build it, as you have thinking through this, you will be very happy.

 

I plan on a full mock up, but am trying to learn just what I will run into. I appreciate your response, but have more questions.
First off, I assume that the stock pistons will be down the hole.
Is the deck height on the forged pistons SE 22942 (arias 9826fh 22937.00 ) higher than a stock piston? How much?
If I am going to do this, it will be spot on or the best i can do within budget limits. but knowing I am going to incur extra machining will help me plan it out, as I don't have my own mill ,etc.
The amount of metal removal for the reverse dome looks to be a lot, as far as balance considerations go. My rough calc is it will change the piston weight by over 13 grams, and I am worried about affecting the balance. Are my numbers off?
I do plan on a dyno tune, to get the tune spot on. So if that allows me a bit more room on compression, great.

 

WTF, do the math! Any experienced engine builder will tell you that .030 is what you want to shoot for.

 

What Phil is saying, I think, is that hypothetical doesn't mean crap until you start really measuring things. None of your calculations matter without knowing the real measurements.

It shouldn't, but the variation between deck height can be a fair amount and then rod length variation etc. You are already planning on cutting pistons? Why? Measure....use the right gasket or mill the cylinder. Easier and doesn't affect your balance.

You are creating problems that don't exist.

You sound like you know what you are doing but let's get real, it's a 103 upgrade with mild cams.

 

All these questions are to help me see what I am probably going to find when I get it apart and start measuring, as well as to find out if I am considering something that has proven to be a bad idea. I don't want to create problems, but avoid them. I appreciate the input so far, for those that offered help. Can't say enough about how much I have learned on these boards. But the best rewards I have gotten are when , after taking in all I learned, I wind up with a piece of equipment that runs faster than it has a right to, for what is in it. When people ask," how'd you do that?" I always give credit to those I learned from. Nobody ever does it alone.
I

 

You are working with standard factory components, designed to bolt onto a 'normal' factory bike, not a race engine. If you were mixing parts from a variety of sources, or adapting parts not intended for your current project, your concerns would be very justified.

But the suggestions made already answer your question, to a very close degree. In other words you can get so close to what you are after, with the suggested parts, that getting closer is making a mountain of a molehill! You are not working with racer levels of tuning, just a mildly tuned touring motor.

Get it right as suggested and set up on a dyno and you will have a pretty fine motor. Then next year, when the disease gets back into your veins, you will have had a year to save up for a more serious tuning job!

You're on a slippery slope. You'll find the more you spend (effort and bucks) the more you will want to spend. Welcome aboard! Just round the corner there are 155 plus inch motors waiting....

Now please go fix that motor and let us know how it runs.....