03 M45 Exhaust "Spring"?

Post by **RAGTPZ** » Tue Nov 29, 2005 7:48 pm

Ok, so two posts in a row.

Tonight when looking under the car I noticed there was a spring attached to one of the exhaust pipes going towards the rear of the car. The spring was located on the pipe that is on the passenger side of the car. Does anyone know what this is??

Something to note, the pipe on the driver side definitely looks heat cycled but the pipe with the spring still looks like relatively new stainless steel. Just strange, we were thinking maybe it was a flap that would open up at WOT for better perfomance and sound maybe? It has an electronic actuator as well. The spring itself was seized on mine but after some soaking in PB blaster for a couple of minutes it's moving freely again.

Thoughts?

Thanks!

Randy

Post by **szh** » Wed Nov 30, 2005 8:07 am

The 2003/04 M45 has a "Dual-Mode Muffler" with valves that open and close at certain engine speeds and accelerator pedal position sensor info. You can check this by revving the engine

For reference, the M45 service manual says:

1. when the the pedal position sensor is "below half at no-load condition", the valve should open at rpm's above 4800 and close at rpm's below 4700.

2. when the pedal position sensot opening is "over half in loaded condition", the valve should open at rpm's above 2600 rpm and close at rpm's below 2500.

I am not sure if the springs you noted are related to that system or not ... I will look further in the service manual!

Z

Post by **szh** » Wed Nov 30, 2005 8:15 am

Okay, the exhaust diagram does not show any springs attached to it. Is this spring "in line" with a cable that goes to the actuator? If so, then it is probably something that takes up the slack in the actuator when it opens the valve in the exhaust!

Z

Post by **Rex** » Wed Nov 30, 2005 8:29 am

Maybe a pic would help?

Z, maybe a call to Joe to see if he lists a PN for it, and description?

Post by **RAGTPZ** » Wed Nov 30, 2005 9:53 am

I will see if I can get a pic of it tonight, I didn't have a camera with me at the time.

Randy

Post by **szh** » Wed Nov 30, 2005 10:56 am

I'll also take a look at mine when I get home (my wife has the M45 today.)

Z

Post by **alexf20c** » Wed Nov 30, 2005 11:15 am

I didn't notice any spring on mine...?

I'll go check.

Post by **elwesso** » Thu Dec 01, 2005 8:01 am

That flap there is just to reduce noise complaints..... I say wire it so it stays open or just remove it if you can...

Post by **szh** » Thu Dec 01, 2005 10:37 am

elwesso wrote:That flap there is just to reduce noise complaints..... I say wire it so it stays open or just remove it if you can...

Hmmm, I don't know if it is that simple, Wes!

Having some back-pressure on the exhaust system at the engine has value in controlling engine performance and fuel use, etc.!

Z

Post by **elwesso** » Thu Dec 01, 2005 10:52 am

we already covered this earlier..... people want it loud on high acceleration, and quiet at idle... The easiest and cheapest way to make stuff quieter is to cause a restriction..... Destructive interference is your friend.

zerothread?id=89149

Not getting into that argument again, but theres the information... Chose to believe what you want, the facts are there.....

Backpressure is never good.

Post by **szh** » Thu Dec 01, 2005 11:03 am

Okay ... a good link and discussion!

But I remain unconvinced ... and in Brian's (maxnix) side of the fence!

Z

Post by **elwesso** » Thu Dec 01, 2005 11:28 am

Im not getting on your case Z, but if your so unconvinced, why dont you just try it... Make the valve stay open, do some performance tests and see what you come up with... I coudl see you making a nice spreadsheet about that or something.....

If it comes back with brians side, ill shut up and always agree with brian... however, i have a better feeling on the results.....

Post by **szh** » Thu Dec 01, 2005 1:03 pm

elwesso wrote:Im not getting on your case Z, but if your so unconvinced, why dont you just try it... Make the valve stay open, do some performance tests and see what you come up with... I coudl see you making a nice spreadsheet about that or something.....

I wish I had the time! There is a local dyno place in Los Gatos that I keep meaning to go to ... hmmm ...

Z

Post by **alexf20c** » Thu Dec 01, 2005 4:56 pm

elwesso wrote:Backpressure is never good.

A highly tuned engine needs backpressure to effectively scavenge exhaust gases from the combustion chamber.

Post by **elwesso** » Thu Dec 01, 2005 5:48 pm

There is a difference between backpressure and maintaining velocity...

YOu dont want back pressure... You do want to maintain the maximum velocity of the exhaust gasses, for the reasons you started.....

Back pressure is when there is enough restriction to cause the gas to have positive pressure...

Post by **alexf20c** » Thu Dec 08, 2005 5:19 pm

Yes, there's a difference, but you can't have the latter without the former.

If you don't want backpressure (which you claim to be any positive pressure), then we might as well not run exhaust systems at all - just run it straight from the cylinder head. That's just flat out wrong, and you know that.

You can still maintain velocity in an exhaust system with excessive backpressure. Some backpressure is required to synchronize the exhaust gas pulses with the valvetrain. The magic number for me has been 3-5psi.

03 M45 Exhaust "Spring"?

03 M45 Exhaust "Spring"?

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