Of interest to SF .61 owners
08-28-2007 | 01:36 PM
#1
Of interest to SF .61 owners
Hi all. I ordered an SK .70 muffler from Kangke Industrial; $17 plus s&h. That's about half the price of an OS #744B.
Anyway, it fits the O.S. SF .61 like it was made for it.
Its design appears to be very similar to the Tower .61/.75 muffler and I'm hoping that it will provide a similar boost in performance. It's every bit as loud as the Tower muffler, so I plan to take it to the field to run some props and get some tach readings, comparing it to the stock O.S. muffler. I'm hoping I will see an increase in performance. What do you think?
I also think it looks nice on the engine, kind of like an Ultra Thrust.
David
Anyway, it fits the O.S. SF .61 like it was made for it.
Its design appears to be very similar to the Tower .61/.75 muffler and I'm hoping that it will provide a similar boost in performance. It's every bit as loud as the Tower muffler, so I plan to take it to the field to run some props and get some tach readings, comparing it to the stock O.S. muffler. I'm hoping I will see an increase in performance. What do you think?
I also think it looks nice on the engine, kind of like an Ultra Thrust.
David
08-28-2007 | 01:43 PM
#2
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From: Blackfoot ,
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RE: Of interest to SF .61 owners
Thank you very much for this bit of information, I am anxious to hear about the test results , if this works out for the better I may change my pipe for this set up.
08-28-2007 | 06:07 PM
#4
RE: Of interest to SF .61 owners
Cyberwolf, I will definitely post some results. This could prove to be a real bargain hop-up.
FBD, the prop in the photos is a Zinger Pro 12x8. I'll also try a Zinger Pro 12x6 and an APC 11x10 (I don't have a 12x7 or 11x9). Other props I can try are APC 11x8, 11x11, 12x6 and 12x8. I agree that being a long stroke it should do well with the bigger props.
I have both an ABC and a ringed version of the SF. I just had a new ring installed and the top of the liner honed by Frank Bowman.
Here's a photo comparing the sizes of the SK and Tower mufflers. The SK is smaller in diameter, but about 3/4" longer.
David
FBD, the prop in the photos is a Zinger Pro 12x8. I'll also try a Zinger Pro 12x6 and an APC 11x10 (I don't have a 12x7 or 11x9). Other props I can try are APC 11x8, 11x11, 12x6 and 12x8. I agree that being a long stroke it should do well with the bigger props.
I have both an ABC and a ringed version of the SF. I just had a new ring installed and the top of the liner honed by Frank Bowman.
Here's a photo comparing the sizes of the SK and Tower mufflers. The SK is smaller in diameter, but about 3/4" longer.
David
08-29-2007 | 02:39 AM
#6
Senior Member
RE: Of interest to SF .61 owners
David,
Make sure to post the RPM you are seeing in the tachometer forum, compared with what you can remember for the original OS 744B muffler.
I believe it was said the Tower .61/.75 muffler is 'not as tuned' as the Tower/Hobbico .46 muffler.
That, however, did not get in the Tower .61's way of being tops on power, in the Dave Gierke MAN 05/03 engine shootout.
Make sure to post the RPM you are seeing in the tachometer forum, compared with what you can remember for the original OS 744B muffler.
I believe it was said the Tower .61/.75 muffler is 'not as tuned' as the Tower/Hobbico .46 muffler.
That, however, did not get in the Tower .61's way of being tops on power, in the Dave Gierke MAN 05/03 engine shootout.
09-20-2007 | 06:57 PM
#9
RE: Of interest to SF .61 owners
I had a chance to run my ringed SF .61 with the SK .70 muffler. I always forget to bring something to the field and this time it was the stock muffler for comparisons.
Since the bearings and the ring are brand new - less than two tanks having been run - I didn't lean it out to the absolute peak.
Power Master 10% with 3% extra castor added.
APC 12x6 - 11960
APC 12x8 - 11010
I think when the ring is fully seated it will improve some more, but I'm not really disappointed. These numbers are actually a couple hundred better than my Tower .61.
I still plan to tach the stock muffler and also run these same tests on my ABC version. I also want to test some "pattern" props an APC 11x10 and 11x11.
More to come.
David
I'm adding a screenshot of Pe's spreadsheet. Either prop is producing plenty of thrust for a 7 1/2lb UFO (this isn't a 3D plane). The calculated speeds are very different, though.
Since the bearings and the ring are brand new - less than two tanks having been run - I didn't lean it out to the absolute peak.
Power Master 10% with 3% extra castor added.
APC 12x6 - 11960
APC 12x8 - 11010
I think when the ring is fully seated it will improve some more, but I'm not really disappointed. These numbers are actually a couple hundred better than my Tower .61.
I still plan to tach the stock muffler and also run these same tests on my ABC version. I also want to test some "pattern" props an APC 11x10 and 11x11.
More to come.
David
I'm adding a screenshot of Pe's spreadsheet. Either prop is producing plenty of thrust for a 7 1/2lb UFO (this isn't a 3D plane). The calculated speeds are very different, though.
09-21-2007 | 11:13 AM
#10
RE: Of interest to SF .61 owners
Ok, lots more data on the SK .70 muffler. The weather was cool and very damp, actually foggy at the field. This probably has some impact, I guess.
Today I ran my ABC(N) SF .61 with both the SK and the stock mufflers. The SK is a dud. Not at all what I was hoping for. Also, my ringed version is stronger than the ABC. I wasn't expecting that, either.
Here's what I recorded.
Power master 10% with extra castor added.
SK .70 muffler:
APC 11x11 - 9400
APC 11x10 - 10960
APC 12x6 - 11710
APC 12x8 - 10630
Stock muffler:
APC 11x11 - 9730
APC 11x10 - 10720
APC 12x6 - 12130
APC 12x8 - 10750
You can see that the stock muffler actually has a slight edge. Believe it or not, it is noticeably quieter, too (but still pretty loud).
The good news is that the SK is about half the cost of an OS #744B, so, if you need a replacement it's an option.
I still want to run more tests on the ringed engine, but I had to leave the field.
David
Today I ran my ABC(N) SF .61 with both the SK and the stock mufflers. The SK is a dud. Not at all what I was hoping for. Also, my ringed version is stronger than the ABC. I wasn't expecting that, either.
Here's what I recorded.
Power master 10% with extra castor added.
SK .70 muffler:
APC 11x11 - 9400
APC 11x10 - 10960
APC 12x6 - 11710
APC 12x8 - 10630
Stock muffler:
APC 11x11 - 9730
APC 11x10 - 10720
APC 12x6 - 12130
APC 12x8 - 10750
You can see that the stock muffler actually has a slight edge. Believe it or not, it is noticeably quieter, too (but still pretty loud).
The good news is that the SK is about half the cost of an OS #744B, so, if you need a replacement it's an option.
I still want to run more tests on the ringed engine, but I had to leave the field.
David
09-21-2007 | 03:35 PM
#11
Senior Member
My Feedback: (14)
RE: Of interest to SF .61 owners
ORIGINAL: rainedave
Ok, lots more data on the SK .70 muffler. The weather was cool and very damp, actually foggy at the field. This probably has some impact, I guess.
Today I ran my ABC(N) SF .61 with both the SK and the stock mufflers. The SK is a dud. Not at all what I was hoping for. Also, my ringed version is stronger than the ABC. I wasn't expecting that, either.
Here's what I recorded.
Power master 10% with extra castor added.
SK .70 muffler:
APC 11x11 - 9400
APC 11x10 - 10960
APC 12x6 - 11710
APC 12x8 - 10630
Stock muffler:
APC 11x11 - 9730
APC 11x10 - 10720
APC 12x6 - 12130
APC 12x8 - 10750
You can see that the stock muffler actually has a slight edge. Believe it or not, it is noticeably quieter, too (but still pretty loud).
The good news is that the SK is about half the cost of an OS #744B, so, if you need a replacement it's an option.
I still want to run more tests on the ringed engine, but I had to leave the field.
David
Ok, lots more data on the SK .70 muffler. The weather was cool and very damp, actually foggy at the field. This probably has some impact, I guess.
Today I ran my ABC(N) SF .61 with both the SK and the stock mufflers. The SK is a dud. Not at all what I was hoping for. Also, my ringed version is stronger than the ABC. I wasn't expecting that, either.
Here's what I recorded.
Power master 10% with extra castor added.
SK .70 muffler:
APC 11x11 - 9400
APC 11x10 - 10960
APC 12x6 - 11710
APC 12x8 - 10630
Stock muffler:
APC 11x11 - 9730
APC 11x10 - 10720
APC 12x6 - 12130
APC 12x8 - 10750
You can see that the stock muffler actually has a slight edge. Believe it or not, it is noticeably quieter, too (but still pretty loud).
The good news is that the SK is about half the cost of an OS #744B, so, if you need a replacement it's an option.
I still want to run more tests on the ringed engine, but I had to leave the field.
David
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Mufflers, like engines, work best when following the old addage, "There's no replacement for displacement". <G>
Ed Cregger
