My 107 had head work, woods triple 888 cams, exhaust, airfilter, pushrods, and lifters. The compression is 10:2 and my Woods 888 cams are better suited for 10:8 and higher compression. At the moment I dont want to spend extra money on new pistons and cylinders with 10:8 compression. Can I bump the compression to 10:5 and if so what would be the best bet?

 

Have you considered off setting the cam 4 degrees? What are you hoping to gain / improve upon with the increase in compression?

 

get pistons & do it right.im wondering why a guy would pick a cam set,then not want to set compression where the cam set requires it to be (???)

 

Moving from 10.2, 10.5 would equate to just about .018" removed from the cylinder head surface.
Scott

 

Gotta ask some questions. How do you know static CR is 10.2? IMHO, you should be looking at corrected CR and CCP. Plugged some numbers into the BB compression calculator and get 10.2 static, 9.3 corrected and 191 CP for 107", stock (.045") head gasket, flat top pistons with -1.5cc dome, 85cc chambers, 43* intake close for the 888 cams and 0.00" deck. Since I know nothing about the 888 cam set, I can't say that is good or bad but as far as numbers go, a little on the low side but not terrible. Pushing to 10.8 static gets 9.8 corrected CR and 207psi which, for me, would work much better assuming compression releases are installed and a good tuner was available.

It would not be difficult to push to hit 9.8 corrected/207 CCP. What head gasket? If .045", a .030" head gasket will get you to 9.5 corrected/198 CCP. Add 4* advance key gets 9.7 corrected CR/203 CCP. Shave .010" off the heads and you hit the 9.8 corrected/207 CCP but static CR is only about 10.6. Doesn't have to be 10.8 to deliver the dynamic compression increase that seems to be required for the 888 cams.

If using a .030" head gasket, 107", stock (.045"), flat top pistons with -1.5cc dome, 85cc chambers and 0.00" deck, static should be 10.45, corrected CR at 9.5 and CCP at 205. Advance the cams 4* pushes corrected CR to 9.7 and CCP to 205psi.

I don't see a problem to get the compression increase, or very close to the target for the 888 cams assuming the above assumptions are accurate. Instead of using 10.2 static as a baseline, run a compression test and use CCP as that baseline. Couple of ways to get there at a low cost. Of course, you could leave all as is and 86 the 888 cams for another cam set with an earlier intake close that will deliver the desired corrected CR and CCP. JMHO.

 

The pistons and cylinders were from Revperf. They offer the 10:2 compression. I emailed them to ask what the cylinder head combustion chamber volume was on the heads they did for me. I havent received a response yet

 

Yes a lot of measurements need to be taken first so you know which way to tackle the issue. Head cc’s, how far pistons are down the hole, piston dish or dome and cams being used. If possible I would be shaving the heads to reach desired comp. of course though you need to make sure you still have adequate valve clearances

 

To make a long story short. I didnt the motor. I had my 103 SG built into a 117 a few months after getting from a 96 to a 103. The 888 cams were removed and put into the Dyna and I showed the guy who built it the specs (certified harley master tech by the way and I guess that didnt matter). I showed him the revperf head spec and showed him the 107 revperf 107 big bore kit at 10:2. He said ok Ill built it. That was that. And i never understood why my buddies 2016 Low Rider S with just an upgraded airfilter and exhaust would run away in 3rd gear. Did my research and found out the 888 cams were best suited for 10:8 and higher compression.

I was told if I change pistons to higher compression I may get piston slop. Thats why I asked if I could bump up compression with different gasket. So my 4 options are
1) Get new pistons
2) New gaskets
3) Get a set of Fuel moto 10:8 compression pistons and cylinders
4) Just get woods 777 cams which might be the route I will go

 

Or as Scott said, mill your heads down the required amount to raise the compression to where you want/need it.
If you can do this without causing other problems this would by far be the easiest and cheapest as you wouldn’t be buying any other parts

I took 0.035” off mine to lower the chamber cc from 87cc to 82 cc so it’s 0.007 off for 1cc.
do the calculations in the BB calculator to see how much you need to take off

 

milling the heads would be the easiest way.i am wondering why would going to higher compression result in piston slap? not true at all.that said,im not a big fan of the nikasil cylinders anyway,id look for a 107" using OEM cast iron lined cylinders