stunthanger.com
Engine basics => Engine set up tips => Topic started by: Dennis Toth on April 24, 2019, 05:44:21 PM
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Guys,
I found my Ringmaster needing a bit more power to get through the OTS vertical 8's in the wind. The ship has a OS Max 25, with a 0.25" venturi and ST NVA. Had been running a 9x6 APC and 7% nitro, 26% oil fuel. If we go a bit lean (from a very rich 2 cycle to a kinda rich 2 cycle) the ship picks up a just a bit of speed and will do OK. Looking at the set-ups for the FP20/25 they have venturi's of around 0.265", for the old MAX this is a bit outside the range of rpm needed for good pumping but maybe a 0.257" would work and still have a good neeedle. Seems the 0.25" might be a bit small with the ST NVA, but I get very consistent needle settings. I would like to see if I can get to a 9 3/4 -10" diameter 5"ish pitch prop (narrow blade) to get a little more pull through the top without stressing the engine to much.
Question is can going up to say 10 -15% nitro with the current set-up give the power boost that you would get if I went to a larger venturi say 0.257"?
Best, DennisT
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Guys,
I found my Ringmaster needing a bit more power to get through the OTS vertical 8's in the wind. The ship has a OS Max 25, with a 0.25" venturi and ST NVA. Had been running a 9x6 APC and 7% nitro, 26% oil fuel. If we go a bit lean (from a very rich 2 cycle to a kinda rich 2 cycle) the ship picks up a just a bit of speed and will do OK. Looking at the set-ups for the FP20/25 they have venturi's of around 0.265", for the old MAX this is a bit outside the range of rpm needed for good pumping but maybe a 0.257" would work and still have a good neeedle. Seems the 0.25" might be a bit small with the ST NVA, but I get very consistent needle settings. I would like to see if I can get to a 9 3/4 -10" diameter 5"ish pitch prop (narrow blade) to get a little more pull through the top without stressing the engine to much.
Question is can going up to say 10 -15% nitro with the current set-up give the power boost that you would get if I went to a larger venturi say 0.257"?
This is a 25-S (baffle piston)?
Brett
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Yes, is it the older .25S? If so, you are choking it down with the ST NVA. If you have a slightly larger venturi, try that first. Or find an original OS NVA, but you probably drilled everything out to to accommodate the ST unit. A foot or so shorter lines might help. But I think you'll find that older .25 won't pull much prop, and no sense comparing to to an FP-20 or .25. These are way different animals. The easiest ti try would be 10% nitro and/or shorter lines.
Type at you later,
Dan McEntee
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The venturi needs to be opened first try drilling it out to .275, That is more in the range when using a .157 diameter spray bar
Randy