Custom exhaust - exhaust note question

AlfaBeta · #1 (**permalink**) 12-25-2006, 08:07 AM

Hi Gang,

I have an 88 Milano verde and I was hoping someone from this list could help. I completely changed the exhaust system (I'll give details in a minute), the car burbles nicely at idle and sounds great on acceleration. However at harder acceleration and at semi higher rpm (4000-4500 rpm maybe) there is a terrible "metallic sounding resonance" that comes from the tailpipe. It almost sounds like a Honda Civic. Anyway, I'll list below what I did but if anyone has any ideas as to what is causing this or what I can do to limit it please let me know!

*CSC headers
*Each downtube is mated to an open flow Random Technologies catalytic converter
*The catalytic converters then exit to a Y tube
*The Y tube then exits to a 2.5" exhaust pipe with no center muffler
*Magnaflow muffler at rear. This is the open flow type with a perforated tube. The tube has a slight S bend in it so the outlet matches up with the stock bumper cutout

Thanks

AlfaBeta

JoeCab · #2 (**permalink**) 12-25-2006, 10:10 AM

I used to run the CSC headers and Random Tech cats, mated to a stock center section and an ANSA tailpipe, and it sounded really amazing at high rpms, with no resonance at all.

So, I would venture to guess the problem is with straight pipe center section or Magnaflow tailpipe. I know the Magnaflow is a good product, but perhaps that particular muffler is not suited to the system you have.

Joe

AlfaBeta · #3 (**permalink**) 12-25-2006, 11:58 AM

Hi JoeCab,

I agree with you, I think the problem is somewhere there too. Maybe there is too little backpressure for the higher running rpm with this set up. I may change the rear magnaflow muffler to something more "common" for Alfa's

thanks

AB

Gilles · #4 (**permalink**) 12-25-2006, 01:26 PM

I also have the same set up (CSC's & cats) but have center and rear sections from Stebro, it sounds really nice.
I agree with Joe, and suspect the magnaflow portion.
Gilles

AlfaNewB · #5 (**permalink**) 12-25-2006, 03:06 PM

when i bought my verde is had a resonator and a magnaflow muffler, no cat, so i added an aftermarket cat and removed the resonator, and it was deap and loud at idle, i could say it was close to a boat, that sound lasted for about 3 days, i guned it on the fwy and the sound was totally gone, somehow it became quieter then before and at high rpms it sounds exatly like a honda.

AlfaBeta · #6 (**permalink**) 12-25-2006, 03:30 PM

I noticed Random Technology also makes a performance muffler (PowerMax). Their cats are really good, I wonder if this muffler is good also?

AB

Rookie ROX · #7 (**permalink**) 12-25-2006, 05:10 PM

If you find a good exhaust should, you *should* be able to get them to work with you on selecting the best sounding one by temporarily fitting, testing and seeing what you like.

I'd agree with the rear muffler being the problem though.

ROCK ON
R~R

Biscione · #8 (**permalink**) 12-25-2006, 10:35 PM

Quote:

Originally Posted by AlfaBeta

Hi Gang,

......I completely changed the exhaust system (I'll give details in a minute), the car burbles nicely at idle and sounds great on acceleration. However at harder acceleration and at semi higher rpm (4000-4500 rpm maybe) there is a terrible "metallic sounding resonance" that comes from the tailpipe.

Giorgio68 · #9 (**permalink**) 12-26-2006, 11:16 AM

Alfabeta,

I think your problem is the center pipe convert that to a stock center muffler and leave the magnaflow the way it is. That's what I have on my car and sound very throaty and fine.

Giorgio

racingswim2006 · #10 (**permalink**) 12-31-2006, 12:45 PM

I've built about 3 different exhausts for my 164 and two different ones for my verde - the two cars sound dramatically different even with the same 3.0 engine - maybe from the manifold differences? Anyhow - to solve this metallic resonance issue: I found in both the 164 (which is de-catted) and the verde is to use an empty (preferably padded - Dan at Stebro could ship one in the neighborhood of $100 to your dimensions) resonator to help disperse some of those higher frequencey sound waves earlier on in the exhaust system (I may be able to post a few videos later on of both cars to give you an idea of sound). Right after the Y pipe sounds like a good spot to me - just my two cents though.

p.s. - I've used magnaflow many times, and always had great results - HOWEVER they need an adequate "burn in" time. The stainless wool packing takes a bit to achieve this.

Peter A · #11 (**permalink**) 12-31-2006, 01:36 PM

While I have never run any of my Alfa's without a center muffler, I did once have a Saab 99 that used a resonater in the center and a rear muffler, a bit like the long run you have designed from the cats to the rear muffler. With the resonater replaced by a long straight pipe to the back, there was a very strong metallic ringing at certain RPM levels and on hard acceleration. The long pipe sets up it's own harmonic. Inserting a center section muffler or even just a resonator-type open section will likely solve your problem.

AlfaBeta · #12 (**permalink**) 01-03-2007, 09:33 AM

Thank you for the replies. Peter A, Random Technologies also makes an open tube resonantor so that may be something I could try. Racingswim2006, you mentioned a "burn in" period for the magnaflow. What exactly do you mean by this? How many miles does it typically take to complete this burn in?

thanks

AB

racingswim2006 · #13 (**permalink**) 01-11-2007, 10:21 AM

the "burn in" time is the time required for the stainless wool packing in the magnaflow to be coated with carbon deposits - if your car runs rich (as most alfas do anyways) it wont take very many miles. I'd say a few weeks of driving the burn in should be significant enough to hear a difference. Obviously the packing will continue to be coated, but once there is somewhat of a layer inside the canister and packing there will be more sound absorption, without decrease in flow.