Help on 550 exhaust valve!

First thought is have you checked that the hoses are connected to the solenoid valve correctly? That valve has, I believe, a vent port. check that it is open to atmosphere.

 

Allan- The valves on the 550 are fail closed, which means they are spring loaded to be closed with no vacuum pressure on them. When the engine is turned off, the valves will be closed. When the Motronic ECU sends a signal to the solenoid valve to open, this allows vacuum to reach the pneumatic controls and the exhaust valves will open. On a 550, the valves are closed at idle and only open at wide open throttle at some rpm in the 3000-4000 range.

Your symptoms would seem to indicate someone in the past has rerouted the vacuum lines to bypass the solenoid valve and have vacuum available at all times so the valves would be open all the time. This is easy to check. If the long vacuum line goes from the vacuum accumulator in the engine compartment directly to the T-connector near the exhaust valves, it is bypassing the exhaust valve solenoid completely. What you need to do is disconnect the long line from the T connector and reconnect it to the inlet of the solenoid valve. You will then need another piece of vacuum hose to go from the solenoid valve outlet to the T-connector. That will restore your valves to normal operation.

Here is a 575M parts catalog page showing the system and a page from the 575M workshop manual showing the bypass valve solenoid with the long vacuum line going into the top of the solenoid. 27 is the solenoid and everything else should be pretty obvious. The 550 is generally the same, just the 575M images are better.

Taz
Terry Phillips
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Sounds to me like the solenoid may be inoperative. Some valves are held open by vacuum, like a 550, and some are held closed by vacuum, like a 599, and probably, BMWs. That is why I said there were fail closed (closed with no vacuum) and fail open (open with no vacuum) valves. It sounds like the BMW valves are fail open and the vacuum from the busted solenoid valve is holding them closed regardless of rpm. The 550 valves are fail closed, so they are open as soon as you start the engine and stay open for the same reason the BMW valves stay closed. The reason the 550 pneumatic valves open slowly when started is that an idling 550 does not generate a ton of vacuum.

The solenoid valve for the 550 is fairly expensive at $233.56, so you might consider a Capristo valve for a little more that offers a remote control capability. Check and make sure you are getting power to the solenoid valve before changing. The solenoid valve is not closing at the present time.

http://www.ricambiamerica.com/product_info.php?products_id=204020

Taz
Terry Phillips

 

Why would you think the cappy exhaust that does not come with a valve should have a valve in it? I don't think you are doing yourself any favors by doing this.

 

FBB- It is an option on Tubi, Kreissieg, Capristo, and Novitec that I know about, plus some more I am not mentioning. Works just like the OEM exhaust. A bit more torque down low and a quiet cruise. My HGTC has valves and I really love them. The right sound for the right time.

Taz
Terry Phillips

 

I agree with FFB, It depends on the internal configuration of the muffler. Just putting a valve on one of the outlets on a muffler that is not configured for a valve accomplishes nothing.
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Dave- The Novitec non-valved system I had was already set up for valves and I think the rest are, too. On the Novitec, you could look right through the inboard pipes to the front of the muffler, while the outboard pipe was more convoluted and probably did not carry any gas at all under most conditions. Putting on a valve would have forced the gas to follow the more convoluted path, quietening it considerably.

The main purpose of this thread was to help Allan figure out why the valves were not working, and I think we did that.

Taz
Terry Phillips

 

Terry,

What FBB and Dave are saying is, indeed, very relevant to this thread. Dave's schematic of the internal configuration of the OEM valved 550 muffler demonstrates an interference-type muffler with Helmholtz resonating chambers. To understand Helmholtz resonance is to truly understand the concepts of exhaust pulses, why straight pipes are indicated for V-12s and X-pipes for V-8s, and variable exhaust geometry and its resultant increased back pressure benefits at low RPM.

I would hope that Capristo, Kreissieg and Novitec have designed their valved mufflers according to the design shown in Dave's schematic. Are you really sure the non-valved iterations share that same internal design? If they did, the result would be a poorly designed muffler for a non-valved application in which case adding valves, as Allan is doing, would be beneficial. But if those manufacturers' non-valved mufflers are properly baffled internally to route exhaust gases in such a way as to at least emulate the differential gas flow of a valved muffler, merely adding valves would not produce appropriate Helmholtz resonance and so would be of little value.

Barry

 

Thank you Barry, you explained it much better than I could have.

Regarding the vacuum problem, its a simple job to determine where the problem lies with just an inexpensive hand vacuum pump and gauge. just basic diagnostics.

 

Dave,

I did a lot of reading on the subject two years ago when I replaced my center resonator with straight pipes. And as a result, I've tenaciously stayed with my OEM valved mufflers.

These two articles summarize nicely what I read and learned:

http://www.jagweb.com/aj6eng/technics.php

http://en.wikipedia.org/wiki/Manifold_(automotive)

Barry

 

As have I.

A couple of years ago I bought every thing I need to make up a remotely controlled solenoid valve bypass including a very nice remote controller.

It sits somewhere in my workshop unassembled and all but forgotten.

 

Dave,

As I mentioned, I prefer to stay with valved mufflers. They tend to be rather expensive though. But then I found out that X-OST Maranello makes valved mufflers for the 550/575 for about the cost of a non-valved system offered by the others.

Classic Coach, where I service my cars, is a distributer for X-OST and they have ordered several of their systems for installation on Challenge and road cars. X-OST has offered to build me a custom "550 Marmitta Corsa con valvola terminali slant" (valved race muffler with slanted tips). We expect delivery in about two weeks and I'll have them installed prior to my next track event.

Terry, now I'll have the chance to install those screens you found for me on eBay to replace my existing bent, cut-up, and paint-bare original muffler screens.

Barry
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Allan,

There's been page after page of threads on the subject valves but this classic one word post sums it all up: http://ferrarichat.com/forum/showpost.php?p=134522876&postcount=5

Barry

 

Dave, Barry- I understand all the theory, but, like I said, I think the valved exhausts do not differ from the unvalved exhausts except for the presence or absence of a valve. The unvalved Novitec I had was certainly set up that way. Not optimum, but the guys building aftermarket exhausts are not rocket scientists.

Barry- There have been problems on the V8s with X-OST on the mufflers coming apart (unwelding or breaking at the welds). Be careful. May not be a problem with our cooler running mufflers, but there are other makes, admittedly more expensive, that have had no problems.

Taz
Terry Phillips

 

Terry,

Quality aftermarket exaust systems are given a lot of thought and testing of their internal designs and are made of at least 304 Stainless Steel. I've seen several X-OST systems on Classic Coach's 355 and 360 Challenge cars as well as a few on street cars. They are all doing just fine. The tips appear to be made of an alloy which does not discolor and the welding and finish are excellent; on a par with Tubi. Their trademark tips do project a bit further than other systems to obviate condensation dripping on the bodywork. They build custom exhausts on request for Classic Coach. They took the time to discuss the valved system they were making for me and its ability to provide the dynamic exhaust geometry specified by the nearby Ferrari factory.

I'm confident the engineers designing these systems are knowledgeable and I'm happy they are not rocket scientists. A case in point is the Mille Miglia system on my 1976 GTB. Fitment has always been an issue for the fiberglass GTBs. The muffler sent me bolted right on with precise exhaust tip clearance fron the unique valance on my car. The hanger brackets have single round holes rather than the usual elongated slots found on other systems. That's how precise their patterns and manufacturing are!

I'm sure the X-OST system will be a repeat performance, this time for the Maranello.

Barry

 

Barry- Would have felt remiss if I had not warned you. They certainly look pretty.

Taz
Terry Phillips

 

So are all straight pipes created equal?? I am considering replacing center resonator with straight pipes just for an inexpensive change in sound and curiosity on my part. Product recommendations anybody??

Also, from what I have read I believe straight pipes are preferred over X pipes??

 

Rick- As long as they are SS, no problem with wherever you get them. Bradan has them for sale for a reasonable price or any good exhaust shop can make a pair for you in stainless. Dyno runs have proven the straight pipes will give you more hp than X-pipes, although the X-pipes are not far behind and a big improvement over the original center muffler.

Taz
Terry Phillps

 

What is the purpose of having the valves? I have a stock 550 Maranello. Thank you.

 

Drive by noise requirements set by law in various countries.

If your car is stock you have valves, that's a good thing IMHO

 

Thank you. Frank

 

I'd like to know the circumstances where this has happened in V-8 applications. The internal baffles can detach in cases where the air/fuel mixture is very rich and combustion occurs in the muffler body. This can happen with any brand muffler.

Again, what you term a "convoluted path" is actually a baffled chamber in the muffler which, in addition to quieting the exhaust, sets up Helmholtz resonance beneficial to low RPM performance. But how just by sighting through an non-valved Novitec muffler's inboard pipe you can can determine the internal design of all valved and non-valved muffler systems truly amazes me.

Thanks for the warning.

 

Barry- Obviously, I cannot determine the internal configuration of all the mufflers.

Taz
Terry Phillips