I have a few questions I can't find the answer to anywhere. I have a SE 95" piston and cylinder kit (10.25/10.5:1) P/N 22661-99A. I don't see how they can list a compression ratio and not know the combustion chamber size. I have my engine torn down and my heads back fro the porter but, I don't want to put it back together until I know where they get their compression rating. Head gasket and chamber size has a large effect on compression. Are they assuming all Harley TC heads have the same size chamber? I have been building car engines for a long time and all pistons come witha range based on different combustion chamber sizes. I can pull that info up in a matter of minutes for a Chevy engine but, for some reason it is no where to be found for a Harley (or at least I don't know ehere to look). What I need to know is what cobustion chamber size they are using to rate these pistons. I can figure my head gasket thickness from there and figure out if I need to shave the heads any to get to where I want to be. Any help would be apreciated or direction to where I can find the info would be great.

 

These are the SE high comp.cast for the original stock heads. Stock cylinder head volume is approx. 83cc. With stock untouched heads this should work out to 10.25:1 using .052 head gasket is how I believe HD figures it. Of course any change porter did will affect this and keep in mind it is only ball park #.Piston deck in cylinder, ectwill change slightly.If you are interested in a compression calculator I can direct you to one.

 

Thanks for the info. Yes I am interested in the compression calculator. I cc'd my heads today and I am at 86.9 front and 85.5 front head. I will check my deck height tomorrow and go from there. I need to be at 10.5:1 to match the rest of my combination.

 

I tryed to attach the calculator in my 1st post but could'nt as it has to be opened inworks spreadsheet. Email me at ELDOCOWBOY@YAHOO.COM and I will tell you how to get to it. This site may haveone but I haven't seen it. My SE heads should be 76cc as advertised but most work out at 77 or more cc's (heavy on the more) HD tends to underestimate there cc's. Probably as a safty net of sorts to make sure they do not have to much compression for performance builds as better to have alittle less comp. than desired than to much. IMO

 

Stock heads are normally in the high 80's for chamber cc's.............and vary greatly in sets.

The only way to ever know is to have your heads cc'ed, and then milled to equal them out and get the desired CR.

Steve

 

Steve,
I did cc my heads yesterday and they did vary, as I expected. front head 86.9cc and rear head 85.5. At this point I just need to install my jugs and measure deck height, I will then know how much to mill and what head gasket I need. I have been building car engines for a long time so none of that stuff is new to me. What bugs me is the piston set doesn't say it is 10.25:1 with XXcc chambers. Since they have a mild pop up on them which the size isn't listed, I guess I will have to build a fixture to cc the pistons too, with flat tops or dish pistons it's easy to cc them and no cylinder or fixture is needed. I guess what I'm saying is there is a lack of information about the pistons in this kit which is not something I am used to. I will try to call a few dealers and see if they can offer any info on the pistons.

 

Try giving Bean a call at Big Boyz Cycles, he will be able to give you a real answer......not some dealer BS answer.

With flatops, my chambers are at 82cc and I'm using a .030 cometic for a CR of 9.6-1.

I hear what you're saying..........they sell a 10.25-1 piston, but they don't say with what chamber size.

Steve

 

You also might try to do what I do with my car engines. Do a trail assembly. Put the piston to TDC. Measure the amount to trans fluid you can put in the spark plug hole. That is your TDC volume and allows for head gasket and piston dome. Add to that amount the volume of the cylinder andthat is your BDC volume. Divide one into the other and you have the CR.

 

Here is what I have found out so far. Harley doesn't provide any info about the pistons. Local dealers don't know any more about them than I do or have already found out. At this point I am going to use clay to take an impression of the pistons and figure out the dome volume so I can proceed and be sure my compression is exactly where I want it. There is no possible way to know your true compression ratio if they don't provide numbers to work with. Most people don't care to measure and be as critical as I am but, I'm just that way.

The dealer told me that with stock heads and head gasket with this S/E kit I would be at 10.25:1 but, without knowing what cc heads they are using as the standard that information is ballpark at best. Flat tops would have been so much easier.

I do have an e-mail out to Bean at Big Boyz Cycles, I tried calling but, the phone was busy everytime I tried. I'm sure he is busy.

Buckndol,
Your tranny fluid method would work but, is a bit messy. Thanks for the idea, I may be able to use that in the future.

Thanks for the help guys.

 

Well I took an impression of the piston tops (sing modeling clay) and cc'd the impressions. The net (minus the valve reliefs)dome on these pistons are 18cc. Just thought I would post the info just in case another person needs it. This will save them a lot of time and effort. Why HD doesn't measure or post the info is beyond me. Aslo according to the info I could find milling .020 of the twin cam heads increases compression by .4 Hope this info is helpful to some of you.