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This may be a dumb question, but bear with me, ok? There was no exhaust on my '70 GT when I got it, so I quickly fabbed up an exhaust all the way out the back just to keep the fumes from coming in through the rust holes in the floors (which are now being repaired). I had a nearly new complete exhaust from a '73 Datsun 240Z that had been in my garage for about 8 years, so I used and reshaped pieces of it to make the exhaust and even used the small stock barrel muffler. Now, I just recently purchased a very good GT rear resonator with dual tips and I had a question regarding what muffler to use with this. The short little barrel muffler on it now was really fairly quiet when I ran it on the Datsun with a straight six, but either due to it's age or other factors, it seems excessively loud on the GT. I was wondering how much difference the resonators really make and if this would just amplify the already too loud exhaust? I'm wanting a fairly throaty exhaust note, but I don't want to get too overly loud and offend the "noise police". I am considering replacing the old Datsun muffler with a turbo muffler of some kind from either thrush or dynamax, and I was wondering what some of you might have tried and what you would recommend. I am wanting to keep the exhaust fairly cheap right now, especially since everything on the motor is stock. I've used the dynamax turbos and turbo II's ($14-$26 and widely available) many times over the years on V8's, but I have no idea what these would sound like on the GT with the 4 cylinder and resonator/dual tips. Has anyone ever used one of these on a GT? Also, would this type of muffler have any affect on the performance of the stock engine, either good or bad? How does this compare to a stock GT muffler? As I said at the beginning, this may be a dumb question, but I don't want this thing to sound like a swarm of bees going down the highway so I thought I'd see what some of you have used on your GT's and go from there. Thanks for any replies on this topic and sorry for such a long post. :D

John
 

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4 cylinder motors have different noise characteristics than V8's.

The 'fart tip' crowd is noisy on account of they place the muffler at the very end of the exhaust system and go with a large outlet. This makes the exhaust tone very flat and harsh. To tune the note, you have to have a fairly long length of pipe AFTER the muffler. It also helps to increase pipe diameter as you go along.

After much experimentation, a good setup is to run 2" pipe from the 2-1 collector on the GT, a Dynomax just behind the rear seat, and a 2-1/4" pipe over the rear axle to the dual tip exh. This will give you a good overall tone.

The problem is harmonics, tho - there will be a spot where the natural frequencies will be amplified. For Maggie the Opel, this is right at 2500 RPM - 50 ish on a 4 speed Opel. Unless you have access to a NVH lab, this is hard to get rid of.

FWIW, Maggie runs 2" to a Dynomax, 2" over the axle to a single bullet resonator and a down tip. Nice mellow tone - you can hear it - but not so obtrusive as to be nasty. Sound quality has not degraded over the years.

My '73 GT ran sidepipes for a while - those 4" outlets carrying 2 cylinders each sounded like a Harley. When I took them off for the winter, I went with a single Thrush glasspack on the stocker headpipe - undercar exit.

Damned thing sounded like a chainsaw.
 

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This is a pretty important topic. I always thought the sound of the GT's was
rather cool with the resonator, etc. I like the way it sounds when you're shifting and keep a bit of gas pedal down while you're putting the clutch in. Doesn't sound like American cars of the time. Has a bit of a snarl to it.

I think that the muffler set up should make the car sound powerful, a bit loud, but not too loud. The car should not be quiet or completely muffled.

It should sound like some European racing car with a mellow tuned sound when idling and which has a different sound when shifting.

Whatever that means.

The sound should be as neat, exotic and as unique as the cars look. The Harley and Bumble Bee sounds are out.

I'd like to hear what people have done that's successful.
 

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Mine has that perfect sound to it, is very simple, just a header going to 2-1/2" tube, into a big Flowmaster muffler, then a big resonator tip. Of course the way it is routed and rigged won't work on a street GT with a passenger seat, but it could all be done underneath if necessary. The street Honda kids tell me it sounds great when it is the only car on the track, in traffic it is quieter than most of the others...
 

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hahaha lmfao, yeah thats what I was thinking, kinda curious to hear that though. I have a flow 40 on my v6 ranger and it sounds good no idea what a CIH 4 would sound like with one though. hmmm, the gears are turning. Time to start experimenting. I'm just now tearing into my GT, it still has the stock pipe that look like no more than 1.5". Pretty restrictive I say.
 

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I have headers going to 2" pipe and then a large magnaflow muffler, 2.5" over axel and a resonator with 4 ansa resonated tips. It's not loud, it sounds good and it sounds great on an upshift or downshift. It doesn't really have a rumble it, it's a smoother sound but still catches people's attention. Look in my photo album to see pictures of it.
 

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On my Gt I run a sprint to a 2" pipe with dynomax muffler dumped before the rear end. It is rather loud on the freeway but tolerable in daily driving.
 
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