trying to save a bit of work. I don't want to assemble the motor with clay in piston to see it I have enough clearance for the valves if I can help it. 2009 ultra 103 with 255 cams, had flat top pistons with stock heads and stock push rods no problem, Now I am adding mva heads 16925-08 and 10.5:1 pistons 22137-08b and adjustable push rods. 18404-08. Noticed that the valve springs are bigger ,hope they clear my rocker boxes. lift numbers 255 seem lower than other cams .556int .556ex compared to
258 cam .569int .569ex and 260cam .609int .609ex 263cam .637int .637ex 266ecam .658int .658ex hope I'm looking at right lift tables
anyone have these heads and pistons with similar cams, and know if clearance will be ok

 

IMO, with your build I would mock it up and get an actual VtoP clearance and not go with a general concenses. The valve springs being larger shouldnt make that much difference in size, I would assume the installed height is close to HD.

 

The SE255 cams should NOT be used with high compression pistons, you are asking for trouble. The CCP on these cams is high to begin with and by adding the HC pistons you are making it even higher.

 

Just wanted to add this from the SE race book:

SE-255 CAM KIT
The ultimate in torque cams, this cam offers substantial
increased in low end torque for engines up to 110 cubic
inches with compression ratios up to 10 to 1. The low end
torque increases are great for heavy bikes or for the person
who routinely shifts below 4500 rpm and wants the power
available to pass without downshifting. The cam still makes
peak power above 5000 rpm so people with lighter bikes will
enjoy the torque increases without feeling like the bike runs
out of air at higher engines speeds. These cams are used in
the ’07 and later street legal 1690 Stage II kits and the 110
Stage Kits. Compression releases may be required depending
on displacement and compression ratio. For race application
only.
25638-07 $299.95
Fits ’06-later Dyna, and ’07-later Softail and
Touring models.

 

if i leave the stock pistons in with these heads I will drop drop existing 10:1 to 8.7 and the cost of the heads will be useless with compression that low. the 10:5 was the closest piston to stay at the 10 to 1 range. If it becomes a problem I can easily change the cams now that I have adjustable push rods. I'll see what the dyno turns up and go from there. The stage 4 kit comes with this head piston config with 260 cams with a lift of .609 I realise the compression is .4 over what the book says, the duration and overlap is why the 255 gulps in so much air. Its alot easier to change cams than taking the heads off again and pistons and intake, rocker boxes.
I am more worried about clearances , just don't want to have to put it all together with clay just to find out that some one may know what configurations wont clear.
Anyway I'm off the pick the mechanics brains at harley dealer to see if he has done builds with these heads and pistons, sure bet he has.

 

Harley advertises the 255 cams as being good to 10:1, but most builders will tell you to keep the static cr under 9.7. Talking to the mechanic at your dealership is a very good idea.

 

looks like new gaskets in kit I bought are .055 thick. old one I took out is squashed to .047. so if I use the ones I got and not the .030 gaskets I keep seeing listed in here I should drop compression a bit and gain some added valve clearance too.

 

It's not just the compression that's wrong, it's the shape of the pistons and combustion chambers.

As you probably know, the hemispherical shape of the mva and htcc combustion chambers are completely different than the bathtub chambers in the stock twin cam motors. The mva heads you bought are excellent pieces, but you have to use domed pistons that are designed to work with them. The squish areas in these heads come from the shape of the piston domes. Even if you milled the heads down to 85cc, the shape of the combustion chamber would still be all wrong.

I found this picture on the forum. The piston on the left has the dished dome designed for the type of heads you have. The squish area is created by the shape of the sides of the dome. You need to squish the gasses together towards the ignition source. On the bathtub heads, the squish zone is created alongside the bathtub shape of the combustion chamber, which is smaller in area than the top of the piston.



Putting together a build using SE parts works really well, as long as you have the matching parts. Pistons, heads, pushrods, and cams all have to be matching. The moco has spent a lot of R&D money to get these combinations right, it's when we start mixing and mis-matching parts that we run into trouble. I know you've matched your pistons to the heads, but the cams also need to be right in order for everything to work as well as possible.

 

I know you're not looking for a primer on pistons and heads, that last post was partly for some other guys who are wondering why we don't use some of the SE heads more often on these performance builds.

As far as your piston to valve clearance, that's not going to be your problem.

 

the 22137-08b pistons are out the head piston chart in catalog, they go with the mva heads. I could have gotten 11:1 pistons but didnt due to my cam selection. So everything should be a matched set. page 49 2011 se catalog under 103 ci section.. they dont even give a listing for mva with the flat tops. listing after it is the forged flat top is 9:1. still too low for mva heads.

thanks boo