have a few questions to shoot at you fine folks. first off i set out early this winter to get some ponies in my stage 1 fatboy..well thats exactly what i achieved..but was it enough? probably never will be. anyway heres what i did. started out as an 88" stock internal motor with 35k on it. only additions were super trapp mean mothers II staggered drag pipes and a K&N high flow filter, and of course a harley dyno tune injected into the bowls of the stock ECM. the bike ran great and had no issues, but i needed more and i really wanted to eliminate the stress of thinking about those pompous little orange chain tensioners that my cam chains were gliding across and possibly eating away. so i dug into the beast and heres what i did.

HEADS: ported-polished, new valve guides, stem seals, beehive springs good for .600 lift, valves 1.90 intake 1.63 exhaust .040 milled off for compression along with a .30 mls gasket set(ill come back to this in a minute). end result they bench flow 150 cfm @ 10"

CAMS: SS cycle .583 gear drive kit w/out the auto decompressing mechanism kit #330-0107 (my crank run-out was fine)
Intake Opening (degrees): 08
Intake Closing (degrees): 15
Exhaust Opening (degrees): 60
Exhaust Closing (degrees): 22
Intake Duration (degrees): 204
Exhaust Duration (degrees): 262
Valve Lift (in): .583

fuel moto adjustables (a.k.a. smith brothers)

ALL new primary(bearing, sprocket, chain, tensioner), alto k2 kevlar clutch heavy spring, power commander V

clearanced cam cover and rocker box covers.

left the bottom end alone. stock 88" cylinders and pistons. my head guy said i should be able to reach 9.5:1 compression with the milled heads and the MLS gasket. which is where the .583 likes to run.

anyway

now heres where it gets technical. i wrenched it all back together fired it up with a good tune from the fellas at fuel moto and the bike runs strong..but it seems like i could do better..and heres where my questions come into play.

i pressure tested each cylinder and im only gettin 150psi dead nuts even from both cylinders..so now im debating on doing a big bore. like i said the bike runs great but im thinking that the cams right now are not even clost to 9.5:1 compression and i could have a lot of untapped power by having a smaller displacement and lower compression. will the big bore help me? or am i missing something with my compression here? it seems that 150psi puts be somewhere around 8.0:1?? how is that even possible? if i bore this baby up to a 98" with 10.0:1 i feel like id be much better off? also debating on roller rockers?

 

Something's wrong for sure. By my calculations you should see 185-190 CCP. Did you hold that throttle wide open? Is your battery fully charged? Can you trust your tester gauge? Run the test again with a fully charged battery, holding throttle wide open and use a different tester.

 

I will get a different gauge tomorrow and re-test

 

Even if I was at 185..according to bigboyz calculator that puts me around 9.0:1...if I bump it up to 10 with more displacement it seems like I'd gain some pretty noticeable torque? Especially if I add a thunderheader? I just want to use these cams to their full potential. ss cycle says 9.5:1-10.0:1 . Seems like I'd want to get in that range. Just wondering if the gains would be worth the $ and noticeable.

 

Easy Start cams?

 

Nope non easy start.

 

No pony in this race, but what exactly is the volume of the combustion chamber?

 

Heads are 83cc, deck height .006, stock pistons are what? -1.5cc?

 

Does that get us anywhere? Ha

 

Bore to 95/98 will do it. But still doesn't explain the low compression; need to figure that out first.