http://www.tmanperformance.com/590.htm#helmolz

 

Please confirm the heads with a PN. Not familiar with "103 plus heads"; know a little about the 110+ heads but not a 103+ casting. If the heads are the 110+ castings, the chambers are 95cc and with flat top pistons, no decking and stock head gaskets, compression is going to be on the low side, even with the early intake close on the SE255 cams. The rest of the package looks good but the head/cam combination can be much improved, if the heads are 17071-08A. You would be better off with ported stock heads and a different set of cams. JMHO.

 

The heads are from a 03 SE103 kit, The front # 16965-03A & rear is 16971-03A these have a hemispherical combustion chamber just like the old shovels heads did. I can't find the paper work right now but they are set up to take a pretty high lift cam the way they came in the kit, Had to mill the rocker box and cover to clear the springs and the roller rockers. I think the plus just means that they already have the manual compression releases, That was a comment I overheard from the fella that did the clean up on them. Mirror polished the exhaust ports - polished the combustion chambers {they were powder coated} - and swirl finished the intake ports {not RUFF but not smooth ether. The reason I went with the 255's is I have a few friends running them and they love the low end pull that they have and still reasonable fuel mileage, {low to mid 40's loaded up} Just want more torque than the 88" had. What cams are you thinking of for a set up like this ???

 

If I'm correct you should have a domed piston with those heads. I could be wrong as they came out a few years ago. A good test would be to take a compression reading and see what cranking pressure is. Plus the cams are way wrong for the heads

 

The heads - pistons - Jugs - and CVO 253 cams were part of the SE 103 kit. The pistons are coated cast flat top, But the cams put the power a little higher up in the R's than I wanted, The compression for the kit as it came from Harley was listed @ 9 to 1 with the 253's. I figure with the 255's and the .030 head gaskets I should be a bit higher on compression, witch until I get it put back in the bike I can only crank it by hand and I don't know if cranking that slow would be any good for a compression check. This engine will not even see 4500 very often, Mainly touring on the highway and loaded up. running a DD6 trans also. Looking for low rpm power - What cams do you think would be a better option

 

See I could be wrong and was. The 255's came stock in the 110's so they do all right the best thing to do is go for it and try to see if you are happy with it. If so then just ride the bitch. There are some people that love the 255's. From a 88 to a 103 you will notice a huge change anyway. Good luck with it

 

Not second guessing you or your builder but the Stage IV 103" package included the 110+ heads and a 10.5:1 domed piston configured for the hemi chamber. Those chambers are huge at 98cc with huge intake and exhaust valves as well. That package also includes the SE260 cams, not the 255s. Your PNs have been updated; those head are what are now called the MVA heads; PN 16925/16934-08.

Those heads with flat top pistons and stock head gasket will produce a static compression of 8.8:1. With the 255 cams, corrected CR will be 8.5 and cranking compression about 170psi; the engine will be a turd. Things improve with a .030" head gasket with a static CR of 8.9, corrected at 8.7 and cranking CR at 177. The trick with those hemi chambers and domed pistons has always been getting the squish band set right. It's easy with flat tops and bathtub chambers but with a hemi chamber and domed pistons, it gets tricky and if not done right, detonation can become an issue. A good target for a dependable, well mannered street build is a corrected CR somewhere around 9.3 and craning compression between 180-190psi. Static will be what it will be; corrected and cranking ar the target and change with the intake close event of the selected cams.

JMHO but you would be better of with ported stock heads and flat top pistons. If you run the MVA heads, you should consider running the correct pistons for those heads. Once you get that sorted out, you can look at cams. When cam lifts exceed .600" valve train geometry is out of whack and gets noisy. The long duration and hi lift cams don't really start to work until you hti the higher rpm range and you are saying you rarely see 4500. A cam with .570"-.590" lift woud get the job done nicely and put much less strain on the valve train.

It's your build but, IMHO, the components are not a good match. Again, no disrespect to you or the builder, JMHO. I am telling you what I woud tell a friend that was considering building with that combination of parts.

 

I have seen the mva heads and my heads do not look like them in the combustion chamber at all, The mva chamber is not a true hemispherical shape and mine are. I'd place a picture if they were off the engine, This kit was not put together by some motor guy in a shop somewhere it is a true Harley SE kit From Harley and by Harley the only Things I did was to upgrade to a Forged crank instead of cast and did the true - balance & weld thing, the 255 cams, Roller rockers & forged rocker mounts, Hyd. Cam plate & oil pump Everything else is from the SE103 kit From Harley and the pistons that came with are flat top no raised face at all. The paper work with the kit states 9 to 1 compression. For grins I'll crank it by hand and see what the psi is, But I'm thinking it's gona be a little low turning so slow ? Oh and this is a stage 2 build with the 255's with the 253's its a stage 1 , Was told this from a HD dealer wrench and he showed me the catalog with that info.

 

103+ heads are a 98cc combustion chamber. those heads are ment to be run with a domed piston with the piston ment (p/n 22483-04) you get 10.5-1 but that p/n is obsolete.

those heads with no decking on a 255 cam will be at 9.01-1static with 8.74-1 corrected with that 255 cam 178.4 psi cranking compression.. the motor will be a complete turd... to put it to terms a old guy in a 3cyl geo metro would blow your wheels off


by the way i know i run the 103+ heads and pistons. if you want to run flat tops look at decking the heads down.... and them springs are good for 650 lift