Raising compression from 10:2 to 10:5 question
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Road Master
Joined: Jul 2010
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From: Long Island
Raising compression from 10:2 to 10:5 question
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?
Road Warrior
Joined: Oct 2013
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From: Seabrook, NH
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?
HDF Community Team
Joined: Jun 2006
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From: san antonio
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?
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.
Last edited by djl; Jun 4, 2019 at 09:50 AM.
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Road Master
Joined: Jul 2010
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From: Long Island
compression
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.
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.
Road Warrior
Joined: Aug 2007
Posts: 1,392
Likes: 43
From: South Australia
Yes a lot of measurements need to be taken first so you know which way to tackle the issue. Head ccs, 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
Last edited by Tat2u; Jun 4, 2019 at 11:54 PM.
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Road Master
Joined: Jul 2010
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From: Long Island
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
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Road Warrior
Joined: Aug 2007
Posts: 1,392
Likes: 43
From: South Australia
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 wouldnt be buying any other parts
I took 0.035 off mine to lower the chamber cc from 87cc to 82 cc so its 0.007 off for 1cc.
do the calculations in the BB calculator to see how much you need to take off
If you can do this without causing other problems this would by far be the easiest and cheapest as you wouldnt be buying any other parts
I took 0.035 off mine to lower the chamber cc from 87cc to 82 cc so its 0.007 off for 1cc.
do the calculations in the BB calculator to see how much you need to take off
Last edited by Tat2u; Jun 5, 2019 at 04:16 AM.
Banned
Joined: Sep 2009
Posts: 3,569
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From: deland,florida
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