Technical > Spud Miller's Cave

Time for some changes

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masracingtd1167:
If I am going to make this change over to small percentage work I need to make some changes to my motor ! I am replacing my pistons so I might as well get the right parts ! I had 14.5 compression and my plan is to run about 30 percent so I am thinking about 12.5 ? I used .043 top and second rings with a total seal gapless top ring ! I also had gas ported pistons ! Bad idea ? Never had a bad plug reading but I did lift a ring land on one piston ! i put athicker head gasket on it and I think that may have led to the ring land lifting  my total deck was .072 ! I will go back to the .041 gasket !I am crossing the finish line at 9600 rpm so I think a gear change will help too ! Any help or thoughts would be greatly appreciated ! Thanks Bill

Curly1:
I do not know much about this but on one of my motors it had 13.5 compression and I believe it would work on 20%. On my 14.6 compression motor I was having trouble at 4 or 5%. Now those motors were not exactly the same and cam, temperature, timing and other stuff comes into play but it did prove to me that if you are going to run any Nitro drop the compression some.  Now you need some compression to make your cam work so I do not know how much is too much. Also get good hygrometers to measure it exactly as even 1% makes a difference. 

Spud Miller:

--- Quote from: masracingtd1167 on December 01, 2018, 08:20:56 AM ---If I am going to make this change over to small percentage work I need to make some changes to my motor ! I am replacing my pistons so I might as well get the right parts ! I had 14.5 compression and my plan is to run about 30 percent so I am thinking about 12.5 ? I used .043 top and second rings with a total seal gapless top ring ! I also had gas ported pistons ! Bad idea ? Never had a bad plug reading but I did lift a ring land on one piston ! i put athicker head gasket on it and I think that may have led to the ring land lifting  my total deck was .072 ! I will go back to the .041 gasket !I am crossing the finish line at 9600 rpm so I think a gear change will help too ! Any help or thoughts would be greatly appreciated ! Thanks Bill

--- End quote ---

Yes, I think 12.5 should be ok for 30%. I like the gear change idea too...no need to spin it so tight if you can make the power down low.

 Spud

masracingtd1167:
Thank you for the reply's Spud and Curly ! I don't want to drop the compression two low like Curly said and make a turd out of it ! What are your thoughts on what to use for a ring Package ? I was using a total seal gapless top ring and a napier second ring both .043 and the gas ports which I think was a bad thing for Nitro !

Spud Miller:

 I don't have any experience with gas ports, but I don't think they're a good thing for use with nitro.  I've heard that running a gapless top ring isn't good with that either. Something about fuel getting trapped between the rings and causing flutter. That's probably at high percentages and volumes however.

 At 30%, I think most of the rules for methanol still apply but I would call and talk to the ring experts.

 Spud

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