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Best Pressure Tap Location On Tuned Pipe?

Old 10-28-2008, 12:09 PM
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CrateCruncher
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Default Best Pressure Tap Location On Tuned Pipe?

Hi all. I'm setting up my Super Tigre G-61 with a MACS 10cc tuned pipe. What is the best place for the pressure tap in your experience?
Old 10-28-2008, 12:51 PM
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ChrisAttebery
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Default RE: Best Pressure Tap Location On Tuned Pipe?

http://www.macspro.com/pressure.asp
Old 10-28-2008, 01:43 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

Thanks but that link offers two possibilities and I've also seen some installations with the fitting in the header pipe itself. MACS says they prefer the tap way out on the body of the pipe at its largest diameter. I'm not a 2Cycle boffin but my general experience with engines inclines me toward putting the tap closer to the throttle for the best match with instantaneous throttle setting. Does it even matter?
Old 10-28-2008, 02:20 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?


ORIGINAL: CrateCruncher

Thanks but that link offers two possibilities and I've also seen some installations with the fitting in the header pipe itself. MACS says they prefer the tap way out on the body of the pipe at its largest diameter. I'm not a 2Cycle boffin but my general experience with engines inclines me toward putting the tap closer to the throttle for the best match with instantaneous throttle setting. Does it even matter?

Yes, it does mater. You have a fluid gas flowing in a pipe, the pressure will drop as velocity increases and goes up as velocity decreaces. Therefore the pressure is highest at the widest point. The throttle setting will have no differance on the best location. If you have enought pressure on the smaller header, then more pressure may be of no additional benifit, but if you do need more pressure then there will be some additional pressure at the widest point.
Old 10-28-2008, 02:55 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

In theory, the widest part of the exhaust system will provide the greatest pressure Bernoulli says so and he's smart!

However...

Since the exit area of the pipe is smaller than the inlet area, the average pressure inside the exhaust system will always be greater than the ambient pressure outside so you can actually put the tap *anywhere* and still see a positive *overall* pressure.

I've run taps on the manifold and on the pipe both work.

A pressure-tap on the manifold/header *will* fluctuate from positive pressure to negative pressure. However, the *average* of those two variations will always be positive so the tank will still pressurize.
Old 10-28-2008, 03:12 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

A one way valve in line will improve the pressure also...I have read!
Old 10-28-2008, 03:27 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

Even the pipe manufacturers put taps in different places. My Rossi pipes, the ones with taps, come with the tap in the belly of the pipe. Of the two examples of the Hatori 601, popular in '80s pattern, I have the earlier model has the tap in the straight part before the divergent cone and the newer model has it halfway up the divergent cone. I have installed taps in the belly/widest part of pipes with good results. Managing the pressure tube length is another factor to consider.

Terry in LP
Old 10-28-2008, 04:38 PM
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ChrisAttebery
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Default RE: Best Pressure Tap Location On Tuned Pipe?

The most consistant spot is the wide point of the pipe.

The pressure is going to travel much faster than you'd ever be able to measure.
Old 10-31-2008, 08:41 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

Despite some misgivings I ultimately located a 6-32 fitting on the top of the manifold block. The engine ran fine but I haven't had it in the air yet.

I had a chance to tune the system today and went from a baseline of 12300 with manifold and no pipe to a final 13200 with the tuned pipe and manifold shortened about 1.25". I may be able to get a few more out of it. Is there any indication that you are getting close before you actually get to optimum length?

P.S. the sound is a wicked "snarl". I'm going to love this pipe.
Old 10-31-2008, 08:54 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

I have tried both the header and the tuned pipe. On my .46 the point at the widest part of the pipe is the best for constant pressure.

Mounting the fitting at the header (close to he engine) gave me the lowest pressure and made my engine un-reliable operation.

Just my $.02 worth....

larry
Old 04-16-2010, 10:46 AM
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Default RE: Best Pressure Tap Location On Tuned Pipe?


ORIGINAL: ChrisAttebery

The most consistant spot is the wide point of the pipe.

The pressure is going to travel much faster than you'd ever be able to measure.

I agree with my boy Chris! I will tap and Drill mine this weekend (if I can find the stuff to do it with, I have never done such a thing). I need to do it to my warbird very soon.
Old 04-16-2010, 11:26 AM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

Kevin, you better get on it. The race is next weekend. I'd like to see you have a good day instead of chasing gremlins all day.
Old 04-16-2010, 01:32 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

As a rule I tap the header next to the engine and so far have never had any issues with not enough tank pressure.
What I have ran into tapping out the larger diameter of the muffler itself is the thin wall, it won't take much to strip one out
As for to tell when your getting close to or the correct length, when your close only cut off 1/4 inch segments untill the engine no longer raises in RPM"s or drops at WOT, if it drops then add the last piece you cut off to obtain the higest RPM gain you had. Just slide it up inside of the tube, the pipe won't know it's been cut. Hope that helps some.
Old 04-16-2010, 02:04 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

Don't drill and tap the pipe. MACS makes fittings specifically for thin wall pipes. They have a flange inside the pipe and a nut on the outside.
Old 04-16-2010, 10:52 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?


ORIGINAL: captinjohn

A one way valve in line will improve the pressure also...I have read!


A one way valve in line will over pressurize the fuel tank, throwing the carb's metering out of kilter. Don't do it unless you are also running a fuel pressure regulator.


Ed Cregger
Old 04-17-2010, 02:10 AM
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Default RE: Best Pressure Tap Location On Tuned Pipe?


ORIGINAL: captinjohn

A one way valve in line will improve the pressure also...I have read!
No way, Jose (or is it John)!

Using a one-way valve will make the engine run erratically, because the fuel-pressure at idle; following even only a few seconds of full-throttle, will be much higher than the engine will have it 'naturally' at idle...
The engine; after being set to run perfectly while idling, will be way too rich to run well.

If instead, the low-speed needle is set after a full-throttle run; i.e. with maximal tank pressure, the mixture will be way too lean to allow the engine to start...


The simple nipple is there to allow free two-way flow of gas and to allow pressure changes according to needs of the engine.
Using a larger diameter hole in the nipple, as well as a larger diameter fuel-line, between the tank breather and the muffler, will allow pressure to equalize faster and stabilize engine operation.


The silicone tubing and length attenuate the pressure pulses; and at a constant throttle and RPM, pressure is virtually unchanged, i.e. there are virtually no 'pulses' to be felt.
So, the ultimate placement for the nipple, would be where the flow is slowest.

The higher average static pressure (yes, [link=http://en.wikipedia.org/wiki/Bernoulli%27s_principle]Bernoulli[/link] WAS pretty smart) will allow the most reliable engine operation.
Old 04-17-2010, 02:32 AM
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Default RE: Best Pressure Tap Location On Tuned Pipe?


ORIGINAL: ChrisAttebery

Don't drill and tap the pipe. MACS makes fittings specifically for thin wall pipes. They have a flange inside the pipe and a nut on the outside.
Chris,


The problem is that it is not very easy to get to where that flanged fitting should be set, from the inside...

Macs should have made a threaded 'bunghole', where the pressure-fitting should be set.


Alternatively, if one has access to an argon welding machine, that area can be 'welded' thickly enough, to allow a hole to be drilled and 4-5 threads to be tapped into it; so a 'normal' pressure nipple could be fitted.
Old 04-17-2010, 02:33 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

another trick for adding the nipple on the Mac's pipes.

I purchased some aluminum welding stick, we all know them as the ones that the guy's demostration is using a propane torch and a aluminum beer can.

The rod has a very low melting point and I just use a propane torch, heat p the area I want to build up, gob some of the welding rod and let it cool, clean it up with a dremel and drill and tap my nipple hole.

On you first time using, I recommend you practice on something other than you tuned pipe.

Pratice makes perfect



Larry
Old 04-17-2010, 03:00 PM
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ChrisAttebery
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Default RE: Best Pressure Tap Location On Tuned Pipe?

What I do is take a piece of bailing wire, stick it into the hole and run it down to the inlet side of the pipe. I slip the flanged part of the tap over the wire and tie a knot in it so that I can pull the tap through the hole. I then run the nut over the wire and tighten it down. Their taps work very well and I never had a problem with them.
Old 04-17-2010, 07:10 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

Is this tap made by Macs???

I dont remember seeing it on there website.

Larry
Old 04-17-2010, 11:13 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

http://www.macspro.com/accessories.asp

They are listed as "Thin wall"


Chris




ORIGINAL: lbarnes

Is this tap made by Macs???

I dont remember seeing it on there website.

Larry
Old 04-18-2010, 09:28 AM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

You know, I have never seen that page or even thought to go to it.

I always used the Dubro fittings and added them to my pipes.

Learn something every day....


Thanks for the link...


Larry
Old 04-18-2010, 10:23 PM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

I have recently acquired a carbon fibre pipe for a .60 size Evolution glow engine I have ...

How do you put a pressure fitting on one?
Old 04-19-2010, 01:00 AM
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Default RE: Best Pressure Tap Location On Tuned Pipe?


ORIGINAL: fiery

I have recently acquired a carbon fibre pipe for a .60 size Evolution glow engine I have ...

How do you put a pressure fitting on one?
Fiery,


The link from Chris gives the best primary solution, although I would add slightly wider, thin washers to that; especially on the inside...

The washers are to spread the load; not to vibration-proof the installation.
Old 04-19-2010, 01:09 AM
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Default RE: Best Pressure Tap Location On Tuned Pipe?

Thanks Dar. Your input is much appreciated.

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