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juan ruiz's Avatar
 
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The question is how quiet does the muffler have to be?

Good Question! Heck I don't even know if the one I have can be consider"Quiet"

I'm thinking something down this lines which will allow me to come from turbo to the muffler and straight to the left side without any bends I'm not sure how effective this could be since they will be so close

(Photo borrowed for illustration purposes)

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Old 05-14-2010, 06:48 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #41 (permalink)
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I've tried Brian's Zork, and Muffler with the 180 degree bend, exiting the stock cut out in an '82 930.

Seat of the pants dyno; no difference between the Zork and Muffler. Boost comes on strong and early.

The Zork is a little loud for the street. Ran it for a week and my Tinnitus has gotten noticeably worse. There are some peculiar harmonics in the cabin at cruising speed. Full tilt; women take children off streets, buildings lose bricks....

I've had the muffler on about a month. Nice reasonable sound off boost. Nice rumble during engine braking. On full boost, good bark, but nowhere near the volume of the Zork.
Old 05-14-2010, 08:33 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #42 (permalink)
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Here is an idea.

Put a butterfly plate in the tail pipe run so you can throttle back the exhaust and this should quiet your system substantially.

You could set it to trigger manually from the dash with a solenoid or program your EFI system to drive a stepper motor at low load and RPM and let it open progressively or 100% with WOT'.

You could put it in your existing pipe or better yet, build a 3.5" right side exit like David's and you might pick up some more ponies.

After all, from what we are hearing your shortie headers and expecially your chambered muffler are holding you back.

Quote:
Product Description
The ECV was created as an alternative to the standard silencer typically fitted in the tip of performance exhaust systems to lower the sound output. The ECV (Exhaust Control Valve) is a spring loaded butterfly valve that can be installed to the main piping of an existing exhaust system. The angle of the valve can be modified on the fly from within the cockpit to provide complete control over exhaust decibel output.


Would be cool.
Old 05-14-2010, 08:59 AM
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An active exhaust system is a whole different ballgame. We need more info.

Specifically, WHY does this system need to be quiet?
HOW QUIET does it need to be? (stock quiet?)
WHEN does it need to be quiet? Always? On the street only? Off boost only?

Keith that is an interesting valve. I have not seen one with a spring, only step motor, solenoid or vacuum pot. Do you know of a supplier for the vacuum pot style valves such as used by BMW, Porsche and Corvette? I have uses stepper motor valves with ill results; they bind in to bore and coke up.
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Old 05-14-2010, 07:35 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #44 (permalink)
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Brian,

Sorry, I just did a Google search and that was the first picture that came up that could better convey the idea. (Something like Exhaust Butterfly Valve).

Maybe put is at the end of the tail pipe like the Corvette.

Then if coking is an issue just hit is with some brake cleaner.

I do not know if a turbo would respond to using a steeper motor, with an exhaust butterfly valve, and ECU to tune for a wider power band (guessing not).

Last edited by 911st; 05-14-2010 at 09:35 PM..
Old 05-14-2010, 08:11 PM
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Juan, Eddie didn't tell you about the 5 pound exhaust system on my 930? Not too loud
Old 05-15-2010, 10:46 AM
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JR,

My vote is do what David did.

Perfict transistion out of turbo up to 3.5", then turn toward the muffler.

Light weight big can Coast / Burns rebuildable muffler with right side exit. (WG exit on drivers side.)

If you want they can do a two stage muffler where he puts a section in with no packing and a section with packing for a bit more noise control. The bigger the can the better.

If not quiet enough might try a removable or adjustable restrictor in the tip.

This is going to be a hard combo to beat (straight through, minimum bends) and should out do your existing muffler. Might be as good as your Zork.

The best.

Oh that is pretty:
Quote:
Originally Posted by David View Post

Last edited by 911st; 05-17-2010 at 05:38 PM..
Old 05-17-2010, 05:24 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #47 (permalink)
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just heard the report back on the monty we modded (cut all the guts out of) and made 2.5" 19" long 180 perfed tube and welded back inside of the monty. so bascially flow through now no change in power on the dyno vs zork and basically what I did was a downsize version of Brians muffler (2.5" vs 3" of brians) so it proved bends did very little to total power output but he did say boost threshold changed some.. dtill need to get pictures posted.
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Old 05-17-2010, 06:14 PM
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Ben,

My apologies but I am not getting what you are saying. Could you please clarify for me.

1) Are you saying you put a 2.5" tube (not 3") with a tight 180 deg bend inside the Monty?

2) That it made as much HP as a 3" Zork?

3) Also, you note the threshold changed. Was that an earlier or later boost threshhold?

4) What HP level are we talking about please?

Thank you in advance.

Last edited by 911st; 05-17-2010 at 06:53 PM..
Old 05-17-2010, 06:50 PM
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Quote:
Originally Posted by 911st View Post
Ben,

My apologies but I am not getting what you are saying. Could you please clarify for me.

1) Are you saying you put a 2.5" tube (not 3") with a tight 180 deg bend inside the Monty?

2) That it made as much HP as a 3" Zork?

3) Also, you note the threshold changed. Was that an earlier or later boost threshhold?

4) What HP level are we talking about please?

Thank you in advance.
1. yup as this is all that would fit, 2. yup, 3 later threshold, 4. 400 whp . This is the same engine being discussed on the header thread of brians.
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Old 05-18-2010, 04:09 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #50 (permalink)
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Ben,

As you know, boost occurs when the differential pressures about the turbine wheel reachs a minimum threshold level. Increase pressure in the area after the trubine and we need to wait for more pressure to be made by the motor up stream to before we see boost.

Thus, the later boost threshold in this case would imply an increase in back pressure in the low rpm area of operation.

But why are we not seeing any impact on peak HP over a 3" Zork?

For some reason it seems the hot side of this turbo dose not need to flow anymore exhaust volume to support the 400hp.

This may indicate the turbo's turbine has become the restriction (choke point) and not your improved 2.5" system.

Thus, we probably can put as large of an exhaust on this thing as we want and it may not make any more HP as the turbine probably just can not flow any more.

Interesting thoughts.

Thus, I do not know the modified Monty is any indication that a 2.5" can support big HP or even 400hp in all cases. On a turbo with a larger flow rate hot side this may not be the case.

It is also probably not conclusive evidence that a tight 180 turn would not have an effect on back pressure at some point or even in this case, as evendenced by the later boost response.

It may be that anything larger than a well designed 2.5" straight through muffler on a smallish hot side turbo or K27-7200 hot side may not be needed to make HP.

Thus, it is not peak HP that may be determining exhaust size after the turbo but the flow rate of the turbo's hot side.

Very interesting!
Old 05-18-2010, 08:26 AM
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I agree just wanted to share the little info I had
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Old 05-18-2010, 06:01 PM
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All info appricated Ben.

The best!!!
Old 05-18-2010, 08:42 PM
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