Dunatic12 Posted December 16, 2019 Report Share Posted December 16, 2019 I have a fresh build on an '06. first bore on cylinders with new weisco pistons and rings. Mild port by McDermott (formerly trinity). T5's, VF3 reeds, stock carbs, stock airbox (no lid) and cool head (currently 19cc domes), 150psi on both sides at 1430 elevation. No timing advance yet. I don't really understand the correlation of compression and race gas (VP 110) and the impact of the current compression. I have heard conflicting info on compression and the need to run race gas as well as compression and losing horsepower at a certain point. Many years ago I was running everything above only change was a stock head that was milled. I ran pump gas and all was fine. Now I have this cool head and can't figure out what domes I should be running for optimal compression and horsepower. Quote Link to comment Share on other sites More sharing options...
Pinkylee Posted December 16, 2019 Report Share Posted December 16, 2019 I have a basically the exact same set up. Just had my cylinders ported by Jeff at F.A.S.T. Will also be running 19cc domes. Jeff told me that I should be around 160 compression and running 93 octane is fine. That is actually what I told him I wanted to run. Before He started my port work. Quote Link to comment Share on other sites More sharing options...
Ayesully810 Posted December 16, 2019 Report Share Posted December 16, 2019 (edited) there is debate on this as far as i can see but for the most part most builders that you talk to will tell you around 160 you wanna run 100 octane (or half 110 half 93) and any compression above that race fuel. I ran 93 on my old 4 mil stock cylinder setup at 160 psi with no detonation issues, but the first time i took it to the dunes I was backing plugs out all day, higher octane would have helped in that case ( or less timing), terrain can play a role. Edited December 16, 2019 by Ayesully810 Quote Link to comment Share on other sites More sharing options...
SKEETER Posted December 16, 2019 Report Share Posted December 16, 2019 15cc and +11 on timing is ideal Quote Link to comment Share on other sites More sharing options...
gusto Posted December 17, 2019 Report Share Posted December 17, 2019 7 hours ago, Dunatic12 said: I have a fresh build on an '06. first bore on cylinders with new weisco pistons and rings. Mild port by McDermott (formerly trinity). T5's, VF3 reeds, stock carbs, stock airbox (no lid) and cool head (currently 19cc domes), 150psi on both sides at 1430 elevation. No timing advance yet. I don't really understand the correlation of compression and race gas (VP 110) and the impact of the current compression. I have heard conflicting info on compression and the need to run race gas as well as compression and losing horsepower at a certain point. Many years ago I was running everything above only change was a stock head that was milled. I ran pump gas and all was fine. Now I have this cool head and can't figure out what domes I should be running for optimal compression and horsepower. I think your original set up with the milled head would be less compression than your current set up with 19cc domes. i ran 20cc domes on my 4 mil and 93 octane was on the edge. I’d order a different set of domes Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted December 19, 2019 Report Share Posted December 19, 2019 Go 21’s if you wanna be on pump fuel. 19cc’s are typically showing much more compression then that. I’d suspect that there is some pretty thick gaskets in that set up or the gauge is a bit off. Potted motors can read much lower when comp testing, but it sounded like your’s is kind of mild. What was squish on the motor? Quote Link to comment Share on other sites More sharing options...
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