Hi, I have a Dyna 2006 with 15.000 miles on it. Bike has S&S AC and SEII mufflers.

Last winter I installed an Andrews 21h cam, together with the Feuling oe+ cam plate and oil pump, S&S lifters and S&S adjustable pushrods. After autotuned it with PowerVision, bike runs quite well and much better than before. Everything is better; no sumping, higher oil pressure (never goes below 10 psi), better torque etc.

This winter I want to dedicate to installing a big bore kit. (To achieve better torque.) Wether I will buy new stuff or let someone drill the cylinders, I dont know yet. (Maybe I will have the heads ported as well.)

The stock compression is 1:8.9. Andrews recommends not increasing the compression to more than 1:9.7 with the 26h.

Now to my questions: Is there a big bore kit which put the compression at 1:9.5 or so? Also; does porting the heads increase compression? If someone, for exampel, drills the cylinders and port the heads, how do I now what compression I will get?

I know there are high compression pistons, but I guess I only need ordinary pistons. Also wonder about behive springs and other things to add.

I do not know so much about this, as the reader of this post might already have guessed. But I think I have pictured out what I want, and now I hope I will get some good tips and advice.

Sharing your knowledge and advice here is much appreciated.

Drive safe and Best Regards
Oak Mountain Rider
(Sweden)

 

I debated to reply to your post for a variety of reasons; main one being, it is such an open ended post, it is very hard to answer but I decided to take a shot.

First, I would suggest that you do a bit of reading just to get a basic understanding of compression. You should become familiar with the different levels (maybe a better word) of compression; static, corrected and cold cranking pressure (CCP). You will learn that static compression is simply the ratio of the cylinder head chamber volume and the cylinder volume; it is just a number and when building one of these motors, actually doesn't mean much. What is important are corrected compression and CCP; compression under operating conditions which introduces another variable, the timing of the close of the intake valve. The timing of the close of the intake valve after bottom dead center (ABDC) is a function of cam selection and the earlier or later after ABDC the intake valve closes changes the volume of the cylinder as the piston travels up/down in the cylinder. This is why many builders will suggest selecting a cam based on the owner's riding style, i.e., torque vs horsepower and build the motor around the cam. Maybe a little in the weeds for you but do some reading and this will make sense.

The two primary ways compression is set are using domed pistons and/or deckng the cylinder heads; both reduce chamber volume. So, if you plan to run the Andrews 26 cam which has an intake valve close of 36* ABDC, you build around that. So, that answers the question about big bore kits that will set compression at a desired level. The dome volume of the piston in the kit will be the factor that influences compression.

Beehive springs have nothing to do with compression and your 2006 cylinder heads have beehive springs capable of accomodating higher lift cams.

Porting heads does not increase compression unless the heads are "decked", i.e., material is removed from the head surface therein reducing chamber volume.

I have attached a link to a compression calculator which a lot of forum members use when planning to build up a motor. I know that you probably don't know enough about what I have just posted to make sense of the calculator but once you do some reading and start to understand compression, it will make sense and you can ask better questions. You can bore your cylinders to 3.875" for a 95" displacement; 3.938" for a 98" displacement or you can install an HD or S&S big bore kit for 95", 98" or 100"; those are your big bore choices without splitting the cases and that's another can of worms which I don't think you want to open.
http://www.bigboyzheadporting.com/TwinCamComp.htm

I can tell you that it is generally accpeted that it is better to bore your cylinders to fit new pistons is better than a kit. Having said that if you don't have a machine shop that is experienced with boring Harley cylinders, a kit from S&S might be a better way to go.

Do you have access to a dyno tuner? If not, that will affect how aggressive you might go with compression. Higher compression motors are more sensitive to tuning that motors with moderated compression.

I could go on and on trying to explain and even develop a build plan around the 26 cams but it would be waste fo time and there would be 10 othre forum members that would disagree with whatever plan I proposed; there are so many variables in play.

You basically have two choices. You can better educate your self about compression and motor building so you can come up with a basic build plan that could be tweaked here or you can just start a new thread asking for build plans around the 26 cams.

Do you have access to quality fuel; 91 octane or better? Also a factor to consider when dealing with compression.

Anyway, that's as far as I dare go. See what you can do with it.

 

I have Andrews 26h, not 21h, which accidentally wrote at the beginning of the post. Sorry for that.

 

Thank you so much Sir. Now I understand how little I understand about this. I think I will have to do some extra reading, as you recommend. And then I may return to what you have written here, hopefully understanding it in a better light. And hopefully I will also understand the hole thing so much that I later in this thread will present an idea of a rebuild.

But before that, perhaps you, (or someone else here), knows which one of the three types of compression (static, corrected or CCP) is used by Harley in their specifications (1:8.9) and also which type of these compressions Andrews might have been meant as a limit for the 26h (1:9.7).

As for tuners, I so far have been relying on Autotune. I think tuners are a bit far away from here, but I may visit one after the big bore is installed, especially if Autotune will appear insufficient.

I think I will have someone to drill my cylinders. There are very reputable machine shops here.

As for oktan, here in Sweden we have 95 oktan with 10% etanol and at the bigger petrolstations we have 98 oktan with 5% etanol. (I usually fill the latter.)

Again, thank you for your profound answer.

Best Regards
Oak Mountain Rider

P. S.
I apologize if my grammar sometimes is faulty in this conversation.

 

95" big bore and andrews 26 cams is/was a popular upgrade for 88cu twin cams
2006 heads will work fine as is with andrews 26 cams. 06 and later heads should flow better than earlier ones.
Whether you go with a cylinder and piston kit or bore your existing cylinders might depend on the experience of your motorcycle machine shop with harley cylinders. Some harley specific tooling is required.
Just looking at numbers, S&S 97" kit would work well with that cam and your heads but I personally have never used that kit.
Advertised compression ratios for kits are for static compression ratios and are not necessarily what you're going to get. Lots of variables like combustion chamber volume, head gasket thickness, ect., ect.

Europe and the US rate fuel octane a little differently. Your 98 octane is roughly equal to US 92. Anyways yes use the premium when possible

 

[QUOTE=OakMountainRider;20831950]But before that, perhaps you, (or someone else here), knows which one of the three types of compression (static, corrected or CCP) is used by Harley in their specifications (1:8.9) and also which type of these compressions Andrews might have been meant as a limit for the 26h (1:9.7).

Harley, as well as other manufacturers and aftermarket vendors all refer to static compression since corrected compression and CCP depend on other variables but static compression is simply the mathematical results of comparing cylinder volume to head chamber volume. As I said in my previous post, static compression is just a number. Static compression can be 9:1 but corrected compression and CCP will increase/decrease depending on other variables. Play with the calculator you now have access to and select a displacement at the top, i.e., 88", 95", etc., doesn't matter which one. Leave all the other inputs as the standard values but then go down to Corrected Compression and select a cam. The close of the intake valve will show up in the window for the selected cam; note the corrected compression and CCP. Then, select another cam with a different intake close and note two things, static compression does not change but corrected compression and CCP do. Next leave the standard values as the are but change the cylinder head volume and note that all three compression values change. Now try the same thing with piston dome volume changes and note that all three compression values change. So, you can see by manipulating the variables you can come up with a suitable build configuration as well as the work and parts required to build.

As for tuners, I so far have been relying on Autotune. I think tuners are a bit far away from here, but I may visit one after the big bore is installed, especially if Autotune will appear insufficient.

In this case your compression goal should probably moderate; corrected compression at about 9.6 andd CCP 185-190psi.

I think I will have someone to drill my cylinders. There are very reputable machine shops here.

As I and tdrglide have pointed out, you need to make sure that the machine shop has experience with boring and fiitting pistons for Harley Davidson. As tdrglide has pointed out, specific tooling/equipment for Harley Davidson cylinders is required.

As for oktan, here in Sweden we have 95 oktan with 10% etanol and at the bigger petrolstations we have 98 oktan with 5% etanol. (I usually fill the latter.)
Just always used the premium grade and no worries on you grammar; better than some of my friends.:icon_doh"

 

[QUOTE=djl;20832511]Thanks for your answer. Yep, I am playing with the BigBoyz calculator now and having fun :-) Seems like I can go for:

Cylinders: 95ci
Head gasket: 0.045
Pistons: 10.25:1 SE Cast 95 10.5-11(10.5 filled in the calculator)
Cam: Andrews 26

And then end up with a corrected compression of 9.64:1

Compared to the present corrected compression of 8.13:1, which I seem to have now (with all stock except for the Andrews 26), 9.64:1 appears amazing! And together with the extra 7ci, the bike should really come alive, I think.

 

Hello tdrglide,


Thanks a lot for your answer. I am just getting in to this subject to get knowledge about it and to understand it better. By every answer I get here I learn more. So thanks again.

Best Regards
Oak Mountain Rider

 

Whatever you do, if you go much over 190 psi CCP, you will most likely want to add manual compression releases to your heads, or you will start chewing up starter clutches and ring gears

 

Thanks, yes I will consider that, as I do not have S&S easy start cams.