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JasonS · Post by **JasonS** » Thu Sep 06, 2007 8:40 pm

I don't have any hard data, but I've been involved with recording the audio for a bunch of cars on a dyno for a video game. We often do power-pulls with the muffler both on and off. The most HP gain I've seen with the muffler off is around 5 hp. I think Michael might actually have posted some dyno shop print-outs with the actual figures for a 3 liter with the exhaust on and off. I'll see if I can find them.

Jason
'85 gtv6

JasonS · Post by **JasonS** » Thu Sep 06, 2007 8:51 pm

Found it:

http://www.alfagtv6.com/bb/viewtopic.php?t=1846

You have to search through the thread but the dyno results showed a 7.1 hp gain without the muffler on Michael's 3.0!

Jason
'85 gtv6

GTV27 · Post by **GTV27** » Fri Sep 07, 2007 12:21 am

Well, that's still a gain I suppose. Worth it for the sound alone.

A note to Brisbane residents on the weekend, that noise you'll be hearing is not an F111 flyby, its Jason gratuitously road testing his Alfa!

PietereQ · Post by **PietereQ** » Sat Sep 08, 2007 8:51 am

GTV27 wrote:mine's fairly tame, a 2 inch stainless system with a straight-through resonator in the middle and a centre chamber muffler at the back. It is very quiet unless you wring its neck, and even then, its mostly engine noise.

However, as I use it on the track this is just not acceptable - it is virtually silent compared to the other cars.

So I've had a new rear section made up that I can swap the muffler out for at the race track - about 50 cm of straight pipe.

Fitted it up last night and took the car for a spin...holy f@#$!

At idle it sounds deep and bassy - more like a 5 litre engine!

Up about 3000, its loud, but not completely over the top.

Over 3000 it begins to develop a howl. As it climbs onto the cam, it shreiks like a banshee, all the way out to the limiter at 6,5.

When you back off, it pops and bangs and splutters.

My only problem is I don't want to put the road exhaust back on! Can't wait until the next track outing!

Now, apart from sharing the enthusiasm with like minded individuals , I wanted to seek a view on the performance benefits.

It FEELS like it has more torque and power, particularly reving more freely from 4000 onwards.

I have no data to support this and it could just be psychological.

Anybody else had a similar experience going from a baffled to unbaffled exhaust.

Hell I know what you mean

http://www.youtube.com/watch?v=5vecF-szqow
http://www.youtube.com/watch?v=7w0MBAHwdSA
I'm currently running more civilized setup. I have remus resonator and custom made pipe exists with stainless steel ulter tips. Looks pretty much like stebro/ansa

And still sounds great, thanx zam for the tips

excuse for the mess in garage, I'm just after major house refurnish

Rookie ROX · Post by **Rookie ROX** » Wed Nov 14, 2007 12:29 am

So just bumping this thread..

I have the same issue with the resonance at around 3-3.5k RPM after dropping the centre muffler whilst I was changing my cat to a single out for a full single 2.5" system.

Can someone suggest the best way to remove the resonance? I was thinking of simply slotting in a hotdog resonator, as I'm really not that keen on putting a centre muffler back in. Is that the best way to get rid of the resonance, or is there another way?

Apart from the resonance the exhaust sounds great, but I feel like a little riced out econobox with a child eating sized cannon muffler everytime I put the boot in

ROCK ON
R~R

5yearplan · Post by **5yearplan** » Fri Nov 16, 2007 6:50 pm

I think the whine of a supercharger would def. solve your problem.

Other than that, what size pipe are you running. It seems to me the bigger diameter (and switching form two small to 1 big) adds some resonance to the exhaust on 3.0 and smaller cars, as they are not pushing enough air, so it sounds hollow, i.e. fart can

Rookie ROX · Post by **Rookie ROX** » Sat Nov 17, 2007 12:11 am

I'm three steps ahead of you, waiting for Greg to get the crank pulley for the kit in actually

It's a 2.5" system

ROCK ON
R~R

Jarle · Post by **Jarle** » Sat Nov 17, 2007 1:16 am

See many of you use 2.5" systems.
Recording to Graham Bell`s 4 stroke performance tuning and other big "tuner names" a 2.5" system is "rated" to a good 170 hp setup. . . . .
200hp + is recomended with a 2.75" setup (NB! This is for N/A engines..)

5yearplan · Post by **5yearplan** » Sat Nov 17, 2007 10:11 am

2.5 isn't bad. If you are gong FI I would wait until the supercharger is in and purring before adding anything. On my '85 535i I took out the cat and center muffler, put in a cheap turbo II resonator and 2.5 single into dual (1.75 as per factory settings) because I kept the stock rear muffler. It sounds pretty good, a touch louder, but it really growls nice and cleanly throughout the RPM band. next I will be cutting into the stock rear muffler and cutting out some baffling until I get the tone just right. My friend however ran single 2.5 with a cherry bomb on his 535i (a year older than mine) and it sounds like a banshee part 3-3.5 RPM with lots of resonance, we even set off a random car's vibration sensor/alarm while idling past it

So I recommend you add another resonator to the system, but if you are concerned about back pressure, up the pipe to 2.75 How much boost are you planning on running? You will have to post some pics/vids for us addicts.

5yearplan · Post by **5yearplan** » Sat Nov 17, 2007 10:12 am

2.5 isn't bad. If you are gong FI I would wait until the supercharger is in and purring before adding anything. On my '85 535i I took out the cat and center muffler, put in a cheap turbo II resonator and 2.5 single into dual (1.75 as per factory settings) because I kept the stock rear muffler. It sounds pretty good, a touch louder, but it really growls nice and cleanly throughout the RPM band. next I will be cutting into the stock rear muffler and cutting out some baffling until I get the tone just right. My friend however ran single 2.5 with a cherry bomb on his 535i (a year older than mine) and it sounds like a banshee at/above 3-3.5 RPM with lots of resonance, we even set off a random car's vibration sensor/alarm while idling past it

So if it's still too raspy I recommend you add another resonator to the system, but if you are concerned about back pressure, up the pipe to 2.75 How much boost are you planning on running? You will have to post some pics/vids for us addicts.

Rookie ROX · Post by **Rookie ROX** » Sun Nov 18, 2007 3:03 pm

Jarle that's very interesting. I have always been of the understanding that 2.5" was always the ideal size for most N/A 6 cylinder engines. For some reason I've never even thought of 2.75". However discussing with Greg, he's of the opinion 2.5" is fine with FI and I trust his opinion.

Depending on how long I have to wait, I probably will hold off until the S/C arrives, but if the resonator seems the only option, at least I know for future reference. As I said it really does sound quite good, and it only resonates for about 500rpm, after that it just howls

Problem is that 500rpm just happens to be in the exact same place as the perfect shifting point for average driving

I'll be sure to keep you updated on the S/C side. I'll be running the MP62 with a Coolingmist trunkmount water/meth injection kit and Gotech Pro, probably in the 10 pound range. From there I may add a water/air intercooler and then look at internals, hopefully I'll be kept happy for a while before I decide to look at that though!!

ROCK ON
R~R

turtlerich · Post by **turtlerich** » Thu Nov 22, 2007 7:43 am

Rookie ROX: have you considered putting on one of these as a center resonator?
http://hushpower.com/
they make a 2.25 and 2.5 inch inlet/outlet size. I bet a small inline resonator would cut down the vibs! but maybe too much noise reduction?

I run:
South African design headers
custom flanges/pipes to a Magnaflow Cat
Xlerator muffler (in place of a center resonator)
and dual side-out exits.

resonance at high-load/low-RPM can be droning, but with windows up its not too bad. High RPM exhaust note is insanely loud, but deep, round and full bodied!! In my opinion, it's a perfect Italian engine scream!! No hint of the razzy, tin-can sound.

cheers,

-rich

Rookie ROX · Post by **Rookie ROX** » Thu Nov 22, 2007 6:41 pm

Thanks for that turtle.

I haven't looked too deeply into the different types or brands of resonators yet, I was just wanting to confirm firstly that it would be the only way to go to get rid of the resonance. I can't hear it with the windows up, but I live in sunny Australia, so it's rare

I will look into those ones though! Cheers!

ROCK ON
R~R

ferrari_f50_2 · Post by **ferrari_f50_2** » Mon Aug 11, 2008 1:32 am

Hey, This is how mine sounds like.

http://www.youtube.com/watch?v=AmhxRshe ... re=related

I read some of these threads beforehand and decided on this setup.

Its a stock 2.5. Got the whole system redone after the manifolds. Pipes from the manifold collect into a hot dog in the middle and a free flow exhaust at the rear.

Rookie ROX · Post by **Rookie ROX** » Tue Aug 12, 2008 12:31 am

Sounds very nice ferrari!

For the record, the resonant buzz in your other video (the 21 second one) is exactly what mine sounds like. Frustrating..

ROCK ON
R~R

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