Thank you! This was the kind of information I was looking for. You state that OEM pistons typically do not have the valve reliefs cut out enough, without doing a big bore is there a good recommended piston to use that would have good relief cutouts? I wouldn't be against having the cylinders bored slightly, as they probably could use a good cross hatching anyway.

 

If you are considering boring, might as well bore to 95"/98" since boring and piston cost will be the same as boring .020" OS. If I have calculated correctly, you chambers should be about 77cc now with the .054" cut and boring to 98" pushes corrected CR and CCP a bit high for the SE203 cams, at least for me. You just need to verify chamber volume and do the math and keep corrected CR and CCP manageable.

If boring to 95", SE cast flat tops; no worries about crank balance.

If boring to 98", CP/Carillo would be my choice; the Bullet series. I would also order the heavy wall pin to match the weight to the OEM piston to maintain the factory crank balance factor. IIRC, the pin that comes with the piston is about 45 grams lighter than the heavy wall pin which makes the standard CP piston/rings/locks/pin weight about that much lighter than the OEM piston assembly; or less than 10% lighter than the OEM piston assembly. I have been told by someone who knows that a variance of less than 10% should not affect crank balance so even with the standard pin, crank balance is probably not an issue.

The only reason I mention this is that I learned this lesson the hard way; the story of my life. I have posted this information in the past. Several years ago, I replaced a set of JE 4.125" pistons with a set of MTC 4.125" pistons on a crank assembly that had been balanced to the weight of the JE piston assembly. The swap changed a smooth running motor to one with a nasty vibration between 2800-3200 rpms up and down the rpm ranges; the bike was unrideable. After some head scratching and discussions with the crank builder, we figured that the MTC pistons must be lighter, or heavier, than the JE pistons enough to affect the crank balance factor. After tearing the top end down and weighing both piston assemblies, I found that the MTC assembly was nearly 20% lighter than the JE piston assembly. Bored .010" over and replace the MTC pistons with a set of .010" OS JE pistons; problem solved. It was in the course of these discussions with the crank builder that the "less than 10%" variance discussion came up. So, now, when replacing pistons I weigh everything to get the weight of the replacement assembly as close to the weight of the replaced assembly as possible. Some on this forum might think "overkill" and it may be but that's how I do it; you can do what you want with the information.

I have to say, now that you are on this path with possibly more displacement and ported heads, why not consider upgrading that cam chest with a better set of cams, CYCO tensioners and new inner/outer cam bearings? You will also need fuel management and a proper tune. You are about to go down the rabbit hole.

 

Again, thanks for the great responses. I am a bit worried about going with a big bore setup as I have heard from many that the reliability drops significantly - that doesn't mean they didnt just slap a kit in there and not do everything properly. I put on a decent amount of miles a year and would like to keep reliability. If big boring, I would stay at the 95" mark, if everything is calculated properly, do you imagine reliability will be maintained?

As for the cams, I have been considering going with a better set. They were installed before I got the bike along with what you mentioned - inner/outer bearings replaced and CYCO tensioners installed. So I would really just need to replace the cams.

If I went with a 95" bore, SE cast flat tops, kept the SE-203 cams, and used my buddies heads - .054 shaved, ported, and big valves/springs - What else will I need to consider moving forward? Fuel management won't be needed as it is carbed and carb tuning won't be an issue.

 

FYI - I had a feeling I would be going down the rabbit hole when I started this tread

 

No worries on reliability; keep CCP in the 190-195psi range and keep up with regular maintenance and put reliability out of your head as it is not an issue.

As has been suggested, it would be wise to have the heads broken down, cleaned up and guide seals replaced.

You will probably get suggestions to toss the OEM cam plate and replace it with one of the SE billet upgrade kits with hydraulic tensioners, roller chains and higher capacity oil pump. If you have the $$ laying around, why not; however, you don't NEED it. I ran a strong 95" in an '05 softail with the OEM cam plate/pump and geared cams for years with no issues; your call. As part of the machine work, I would have manual compression releases installed in the ported heads; cheap and will extend starter and battery life. I would also measure deck height and consider trimming the cylinders to 0.00" deck height depending on actual and how the math works out when calculating compression. You will need to know deck height to do the compression math.

Fuel management is just part of the tuning process, you should replace the OEM ignition module with a programmable piece like the Daytona TwinTec TC88. The OEM ignition module is not programmable and the factory timing settings will not be right for the new motor configuration.

Lots of good cams available if you decide to replace the SE203s but you are working with a fixed data point which is the chamber volume and you will have to make the cam selection based on the math. Two that come to mind to look at are the S&S570 and the Andrews 57, cams with an intake close in the 36*-40* range. You should also verify the lift that the springs in the ported heads can accommodate; they are probably OK for the cam mentioned but don't guess, measure.

 

One of point to remind you of is that the SE pistons will likely need the valve pocket cut with a bidder valved milled head.

 

If you get creative you can check the combustion chamber volume at home to get a ideal. How accruate is how creative you get. Realky not hard. Just ask Google how.

. Whats your reason of fear with big bore kits ? Considering they were done by a reputable shop.. .prodrag,hillside etc?



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Really no fear now after talking to you guys. I have just heard stories from guys about the big bore kits, but mind you they most likely just slapped it together and didnt take the time to calculate and dial in the compression ratio and everything.

 

If the valves reliefs need to be opened some to accommodate the head, this can be done with a Dremel at home, right? Is there a set of pistons that have deeper reliefs that wont require messing around with that?

 

I'll try and avoid the cam plates, cam upgrades, and oil pump upgrade. I'll look into the rest of what you suggested. Prior to making any purchases, outside of the heads, I will get everything calculated and a plan of action written up. Once I have all of that figured out I will let you guys know so that I can ensure I am all set and not shooting myself in the foot somewhere.

Thanks again for all the help guys!