Loss of power with exhaust extension
07-17-2006, 10:47 AM
#1
Loss of power with exhaust extension
I mentioned this before, but I will do it again since I just had to "modify" an extension.
Check the opening inside the extension with the exhaust port on the engine. The OS extensions for a 46 need to have about 1/8" trimmed from the inside of EACH end, plus about 1/32 from each side to match the exhaust port opening on the engine. The Dubro extensions for a 46 are USUALLY pretty close to the exhaust port size.
I found the easiest way to trim them back is to use a dremel with a 1/8" rotorary cutter and finish them up with a small triangular file. Takes about 20 minutes to do. Make sure you hold the extension with a pair of needle nose pliers while using the dremel - the extension gets hot REAL fast.
Check the opening inside the extension with the exhaust port on the engine. The OS extensions for a 46 need to have about 1/8" trimmed from the inside of EACH end, plus about 1/32 from each side to match the exhaust port opening on the engine. The Dubro extensions for a 46 are USUALLY pretty close to the exhaust port size.
I found the easiest way to trim them back is to use a dremel with a 1/8" rotorary cutter and finish them up with a small triangular file. Takes about 20 minutes to do. Make sure you hold the extension with a pair of needle nose pliers while using the dremel - the extension gets hot REAL fast.
07-17-2006, 04:16 PM
#2
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RE: Loss of power with exhaust extension
I asked Dub Jett if having the header port match the exhaust port made any difference and he said "not really" and that the reason some motors have such big exhaust ports is for weight and money savings.
You'd have to have quite a difference in sizes before it would effect the performance.
You'd have to have quite a difference in sizes before it would effect the performance.
07-18-2006, 07:33 AM
#4
Senior Member
RE: Loss of power with exhaust extension
Anything protruding into the exhaust flow is going to have some effect. And if the projection is a square ledge, you can bet part of the effect is going to be turbulence. And turbulence is bad.
It's standard practice to reduce any projecting edges to improve flow. But the best way to deal with an edge that is squarely blocking the flow is to remove it.
Another thing a flat surface facing the exhaust flow will do, is act like tuned pipes act. It will reflect flow pulses directly back upstream.
So I'd vote to remove any square projections.
It's standard practice to reduce any projecting edges to improve flow. But the best way to deal with an edge that is squarely blocking the flow is to remove it.
Another thing a flat surface facing the exhaust flow will do, is act like tuned pipes act. It will reflect flow pulses directly back upstream.
So I'd vote to remove any square projections.
07-18-2006, 07:42 AM
#5
Senior Member
RE: Loss of power with exhaust extension
By the way, I gotta jump the thread off topic just slightly............ (not a new thing for me 
is it)
You really need to always lock down your workpiece when using a Dremel. The workpiece needs to be held by something else, like a vice. And it needs to be held securely.
When you're using a Dremel, you need to have both hands available to keep the Dremel tool under control. Truth is, you don't really want to be trying to control the workpiece with one hand and the Dremel with the other. When your brain shifts over to figuring out how to move the workpiece, it's not doing a 100% job with the hand holding the Dremel, and vice versa. And what can happen?
You let the workpiece slip and the Dremel throws it, or you lose grip on the Dremel and it digs in. Best thing that might happen is the cut gets a bit ugly. But what might happen also is you drop the Dremel. And it's bit is turning what? 20,000 rpm and is nasty little teeth that're SHARP as razor blades. Best thing that might then happen is that something hits the floor and isn't ruined too badly. But what if the Dremel lands on your foot? Or your leg? Or YOU WERE SITTING DOWN AND IT LANDS IN YOUR LAP..........
Nah..... Don't be trying to hold your work with your hand OR pliers. You got too much to lose.
is it)You really need to always lock down your workpiece when using a Dremel. The workpiece needs to be held by something else, like a vice. And it needs to be held securely.
When you're using a Dremel, you need to have both hands available to keep the Dremel tool under control. Truth is, you don't really want to be trying to control the workpiece with one hand and the Dremel with the other. When your brain shifts over to figuring out how to move the workpiece, it's not doing a 100% job with the hand holding the Dremel, and vice versa. And what can happen?
You let the workpiece slip and the Dremel throws it, or you lose grip on the Dremel and it digs in. Best thing that might happen is the cut gets a bit ugly. But what might happen also is you drop the Dremel. And it's bit is turning what? 20,000 rpm and is nasty little teeth that're SHARP as razor blades. Best thing that might then happen is that something hits the floor and isn't ruined too badly. But what if the Dremel lands on your foot? Or your leg? Or YOU WERE SITTING DOWN AND IT LANDS IN YOUR LAP..........
Nah..... Don't be trying to hold your work with your hand OR pliers. You got too much to lose.
07-18-2006, 08:07 AM
#6
Senior Member
RE: Loss of power with exhaust extension
I'm not sure what OS 46 is being mentioned here or which OS extensions but............
I've got a couple of different OS in 40, 45, and 46 size. The Du-Bro Muffler Extension for .40 to .46 (Cat#699) I've got actually is slightly larger inside than the exhausts of all those engines that it's bolts fit.
What I found with my OS46AX, was that the P-Box Muffler (E-3010) that comes with the engine has an opening that is about a 32nd narrower than the Du-Bro extension. Since that might introduce a disrupting backflow pulse (and would cause turbulence for sure), I used a flat file and cut the corners there. I just put a 45-50 degree angle into the muffler with the file.
I've got a couple of different OS in 40, 45, and 46 size. The Du-Bro Muffler Extension for .40 to .46 (Cat#699) I've got actually is slightly larger inside than the exhausts of all those engines that it's bolts fit.
What I found with my OS46AX, was that the P-Box Muffler (E-3010) that comes with the engine has an opening that is about a 32nd narrower than the Du-Bro extension. Since that might introduce a disrupting backflow pulse (and would cause turbulence for sure), I used a flat file and cut the corners there. I just put a 45-50 degree angle into the muffler with the file.
07-18-2006, 03:22 PM
#7
RE: Loss of power with exhaust extension
I have the OS 46 FX.
The DuBro extensions are fine. It is the OS extensions that require the "mods". I forgot to specify DuBro to the LHS when he got it for me and didn't realize the memory had jumped a cog until I went to bolt it up.
The DuBro extensions are fine. It is the OS extensions that require the "mods". I forgot to specify DuBro to the LHS when he got it for me and didn't realize the memory had jumped a cog until I went to bolt it up.
