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United States, TX
Joined Nov 2019
2,354 Posts
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Discussion
Header length / canister Performance Question
Stupid Question Here -
If one were to use a slightly longer Teflon coupler on one header to match up canister exhaust outlets, (basically making up for the cylinder stagger) is that a deal-killer in terms of performance? I realize that ideally, they need to be the same length for back pressure / balance. But my guess is, it would never be realized in either actual engine performance or longevity. But asking those with more real world knowledge than me. Thank you. JAM |
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United States, TX
Joined Nov 2019
2,354 Posts
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Hey Rsnow - thank you for the response.
The cylinder stagger on the DA-100 I’m working with is 18mm (slightly less than 3/4”). So that’s all we’re talking here. In other words, 18mm is all it would take to get the exhaust stinger outlets lined up where I need them. The previous owner of this engine / canisters just put that 18mm gap in the Teflon coupler on the short side and by all appearances, it did okay. He also did not have any issues operating the engine this way. I just bought some header extensions from DA for my DA-170 but I added equal amounts to both headers on that install. I’m like you, I think I’d rather extend the header and keep the gap around 3-6mm as DA recommends. While I am generally very particular about things like this, keeping things balanced, etc, I really need to use the extra 18mm to get the exhaust outlets lined up. And as I said before, I am really skeptical I’m going to notice anything on the engine performance/longevity side but thought I’d ask. Pic attached of exactly what I’m doing here. As you can see, one cylinder works out absolutely perfect. The other will need 18mm extension. Being able to extend 18mm is the difference between being able to use these front dump canisters or having to buy a new set of rear dumps. If I have to, I have to. But if I can use these, all the better. Thanks again! JAM |
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springdale, pa usa
Joined Aug 2006
978 Posts
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Years ago I purchase a ZDZ RV80, JMB pipe and Cannister at the Toledo show from RC Showcase. I had asked if I can cut the the pipe and the man stated the length was 1/4 wave tuned and suggested that I not cut the pipe. Following his recommendation I build the the plane to fit. Still have it today and all I can say is it sounds great. With all that being said your pipes appear to be much longer than what I have possibly by a factor of 2. Don't know if it is BS or not, just know it worked.
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United States, TX
Joined Nov 2019
2,354 Posts
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Quote:
Yeah, that’s a whole other topic as well. These headers are basically the same length at the ones I purchased for my DA-170. They are also the ones DA recommends on their website for a DA-100. Personally, I don’t see how those two engines could possibly have anywhere near the same header length. But I would “hope” if this is what DA recommends, they have the testing to back it up. I don’t really have the time to test it for myself. |
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Slight OT but those headers appear to extremely long in general and in relation to the canisters. My experience with cans is the longer the header length the worse the mid-range response is. If you plan on just carving up the sky at a good clip then probably fine, but anything requiring precise mid-range throttle control is likely going to be a challenge. I also don't think offsetting the stagger to match the stingers is going to be ideal. If set on the idea I would try to run it up on the bench and test a few configs. 3/4" can be a significant difference depending on the combo; especially if you're in the sweet spot.
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Unless looks are deceiving they do appear long. Generally I have run on 100 to 120 twins about 11 to 11.5 inch and been pleased. You're probably around 13 to 14 on your 170 twin.
Also dependent on volume and length of the cannister. Do try to keep the header length very close to same for each cylinder. No harm in calling DA and asking what they recommend for their 100 |
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United States, TX
Joined Nov 2019
2,354 Posts
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Thanks for the replies.
These headers are 12.5” just purchased from DA. Just got off the phone with Vernie and he said they do not recommend cutting them. He assured me that the length they sell for each engine is correct. FWIW - the ones I purchased for my DA-170 were also 12.5”. Only difference was they had round vs. square ports, obviously. I bought extensions and made them 14” based on testing by Reza. Vernie also said not to stagger the length, so there’s that. |
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United States, TX
Joined Nov 2019
2,354 Posts
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Quote:
I’m to the point (where I usually get), where I’m just going to build a stand and do the testing myself. The build I’m doing for this engine is a ways from being complete, so really I do have the time. I have these new headers and I have the stock exhaust so I can test both. I really need to stagger one canister to align exhaust tips if possible and I just want to see for myself how that affects the performance. I haven’t seen where anyone has done the same and posted their results which is really what I was looking for. I do realize that ideally they need to be the same length but was more curious how damaging it was to the performance if they were not. I have little doubt the previous owner had the canister exits aligned. There is a carbon witness gap of about 7/8” in one Teflon coupler and an 1/8” carbon gap in the other and the headers are the exact same length. He said it ran like a top. I’ve seen a video and I sure couldn’t discern anything negative from it. I will compare CHTs, and RPMs and see what I come up with. Thanks for the post. |
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The only way to determine engine power / effects is on a dyno
A simple eddy-current disc design works great I designed & and used one back in the eighties to test the effects of high nitro volumes Vs methanol & propylene-oxide Much time and expense paid off - held 2 individual state champion titles , NSW & QLD |
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Hammond, Indiana
Joined Jan 2006
498 Posts
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All canisters are not the same. For example, JMB canisters are not tuned and give the best performance with the shortest header possible. Who made your canister? I would follow the manufacturer’s recommendation for header length.
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United States, TX
Joined Nov 2019
2,354 Posts
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I’ve been trying to find that out. I have another thread asking for any ideas. PO says he thinks they’re KS but there’s no knurling on the canister inlet and other places so I don’t believe they are.
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I've got the similar question re DLE130 with MTW TD80K here:
https://www.flyinggiants.com/forums/...d.php?t=309861 I'm mounting this combo in my 1/3 Scale Extra 300 2,7m wingspan plane. Classic aerobatics, scale, no 3D aspirations. Will be using the Falcon 2blade 28-12 to start, may change it to a more scale 3blade later. MTW couldn't give me a recommended header length for this engine. |
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