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OS 75AX on a MACS 1260 Pipe

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Old 10-24-2010, 05:38 PM
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SpinnerRow
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Default OS 75AX on a MACS 1260 Pipe

Stock muffler and an APC 13x6 Sport was 11,800 and with the pipe I was able to get it to 12,900. Stick a 1/2" piece back in and I can run a 13x8 at 12,000. Throttle response with the 13x6 is sick! This is going on a 6.5lb Rookie which has a 59" slightly swept wing. Should be a fun combo. I need to get a 12x8 APC and try that but I had a limited number of props with me today since I wasn't sure what this thing would like.

5% Ritch's Brew with 22% oil (11/11) and it is 86 degrees here in the Dallas area.

Is 12,900 decent RPM for this motor or does this thing like more RPMs? The size of the carb suggests this is a lower RPM torquer but I'm just guessing.
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Old 10-24-2010, 05:59 PM
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Default RE: OS 75AX on a MACS 1260 Pipe


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ORIGINAL: SpinnerRow

Stock muffler and an APC 13x6 Sport was 11,800 and with the pipe I was able to get it to 12,900. Stick a 1/2'' piece back in and I can run a 13x8 at 12,000. Throttle response with the 13x6 is sick! This is going on a 6.5lb Rookie which has a 59'' slightly swept wing. Should be a fun combo. I need to get a 12x8 APC and try that but I had a limited number of props with me today since I wasn't sure what this thing would like.

5% Ritch's Brew with 22% oil (11/11) and it is 86 degrees here in the Dallas area.

Is 12,900 decent RPM for this motor or does this thing like more RPMs? The size of the carb suggests this is a lower RPM torquer but I'm just guessing.

Those numbers look impressive. Do post your numbers on the APC 12x8 - for comparison, my Jett .90L with Jettstream muffler gets about 13K with the 12x8.

Here's a tip - for each of your runs for each prop/pipe length combo, use Pe Reivers' spreadsheet to calculate the horsepower you are getting. Plot those on a graph and you'll see where the sweet spot is rpm wise. We did this with an MVVS .77 and found that it was happiest piped to do between 10,500 and 12,000 rpm. Anywhere in this band, we could pipe the engine to get a little over 1.9 HP calculated.
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Old 10-26-2010, 06:11 AM
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Default RE: OS 75AX on a MACS 1260 Pipe

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ORIGINAL: Harry Lagman
Those numbers look impressive. Do post your numbers on the APC 12x8 - for comparison, my Jett .90L with Jettstream muffler gets about 13K with the 12x8.

Here's a tip - for each of your runs for each prop/pipe length combo, use Pe Reivers' spreadsheet to calculate the horsepower you are getting. Plot those on a graph and you'll see where the sweet spot is rpm wise. We did this with an MVVS .77 and found that it was happiest piped to do between 10,500 and 12,000 rpm. Anywhere in this band, we could pipe the engine to get a little over 1.9 HP calculated.
Weather was warmer and may more humid when I ran this test.

APC 12x8 and 12x7 got 12,600. Pipe is too long for these props. It would probably spin up a little more if I cut more off the header. Debating if I want to do that or not.
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Old 10-26-2010, 01:47 PM
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Default RE: OS 75AX on a MACS 1260 Pipe

Cut some more off the header. I'm in the 13,100 range on a 13x6. 12x8 is 12,700 and the 12x7 is about the same as the 13x6.

[link=http://www.youtube.com/watch?v=9U1e1LG2Fwg]Video of the 13x6 APC.[/link] Hard to be dissatisfied with this.
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Old 10-26-2010, 02:25 PM
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Default RE: OS 75AX on a MACS 1260 Pipe

Can a moderator move this to the Tachometer Forum? That's where I wanted this one to go in the first place.
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