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Buddy of mine is looking to get his stock exhaust redone on his 89SC. I know a guy that can custom bend him a true dual exhaust (he did for me) for fairly cheap... and remove the 3rd cat, resonator, and replace the mufflers. Pipe size would probably be between 2 1/4 or 2 1/2 inch in size... or have him just get an aftermarket catback that's around 3" in size.

Which would be the better way to go?
 

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If he's modded or plans to mod - true dual...

If he's stock and doesn't plan to mod - true dual anyway.

With MN12 Exhausts being restrictive, I'd advice opening it up. How much to open, I'm not sure about. But I recommend true dual if he can afford it.

-Andy "Melon"
 

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Jason,

Mine wouldn't accept the true dual exhaust without changing fuel tanks. I just went with the Dual 2.5" into 3" into dual 2.5" system from SCP. I don't think my exhaust system is holding me back, because I've still got cats.

David
 

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True Dual vs. Single Center. The whole purpose of the H or X pipe, is to even out the exhaust pressure pulses. For that purpose, the large single center section is the ULTIMATE way to accomplish equalization. True Duals won't equalize anything!

The whole idea of "True Duals" goes way back to early hot rodding days, when replacing a RESTRICTIVE single exhaust with headers & large pipe, gave a significant increase in power.

The single LARGE center section will flow better than true duals.

68COUGAR
 

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Going dual will improve your performance signifigantly but it will come at a high cost on an '89. It'll make no sense to stop half way. You'll need to install a pair of hi-flow cats ( because the stock units suck large ). Then you should go 2 1/4" or 2 1/2". I have heard of some guys going without the resonator altogether without getting the "Coffeecan full of Hornets sound" but they went for the big Borla muffs and that means $$$. You must turf the stock resonator too because it's horribly restrictive. I found some hi-flow cats that came with seperate left & right mini resonators followed by a "Y" pipe for a stock setup but I had them cut off the Y and replace it with a Magnaflow "X" pipe and I went 2 1/4" dual all the way back to a pair of Stainless Magnaflows. You can buy a hi flow dual in/dual out resonator instead of an "X" pipe if you prefer. On an '89 you will need to replace the tank as well because you'll never get twin pipes to do the Zig-Zag around the stock tank. I found a big difference after I got my system in (Last Saturday). Buckets more power, a fun growling idle, cool WOT roar and quiet highway cruising. I love feeling the slight vibration in the seat while accelerating.

Lots to think about for you. Good luck

Marty:zbounce:
 

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You're preaching to the choir!

I'm running SCCoA headers, 2.5" down pipes, NO cats, No Resonator, & Big DAWG exhaust. Of course that means that I've already changed the gas tank.

Yeah, it gets ricey when I'm racing, but I don't care about that. The Big DAWG does exactly what I want it to do. It doesn't contribute to blown HG's via. back pressure.

Could you Please explain why you think that performance will increase significantly with true duals, vs. a single LARGE center pipe?

68COUGAR
 

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68COUGAR said:
You're preaching to the choir!
Yeah, it gets ricey when I'm racing, but I don't care about that. The Big DAWG does exactly what I want it to do. It doesn't contribute to blown HG's via. back pressure.
68COUGAR
Well said, I have 2½ Duals and its very quiet. I rather peace of mind, more than any sound that my exhaust makes.

Calvin
 

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Could you Please explain why you think that performance will increase significantly with true duals, vs. a single LARGE center pipe?
It has to do with airflow capacity. Two pipes side by side have a certain volume and the single pipe would have to be close to twice as large as the duals to have the same volume. Larger volume = lower backpressure. The "X" pipe or dual to dual resonator also compensates for the firing order (and sounds really cool) by sharing the bursts from each side of the block equally on both sides of the exhaust system without being large enough to bottleneck the system. Some people do swear by the 2 1/2" dual - 3" single -2 1/2" dual system (I myself prefer duals all the way down).

It is unfortunate that you can't feel or hear what a system will be like on your vehicle before you have it done. Listen to anyone's and everyone's system in your area (if there are any) as that is the most accurate way to decide for yourself. There is nothing I can tell you that will be anything more than my opinion and it might quite possibly differ from yours. I felt and heard it immediately, but others may tell you that everything I told you is bull. You will have to decide for yourself.

I hope you get what you're looking for.

Marty
 

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Thank You for making my point. I was careful to mention that I was referring to a LARGE single center pipe, & not the oem size pipes.

The dual in - dual out (common chamber) resonator performs the same function as the LARGE single center pipe. The exhaust pulses from both banks will flow equally through the rest of the exhaust system.

The Big Dawg (3.5" center section) flows nearly the same as the two 2.5" down tubes.

True duals provide no equalization of exhaust pulses, which means higher back pressure, than a comparably sized single pipe or common chamber resonator.

68COUGAR
 

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well guys, im the guy that this wonderful thread is all about.
i have the 89 SC 5-speed. gettin ready to toss some 3.55s in there
and then get my exaust. im gonna have someone make mine custom.
im just gonna stroll on down to summit and buy some Dynomax super turbos
and order a magnaflow reso. from SCP. www.supercoupeperformance.com
im cuttin off the damned 90 degree cats. screw em, i just got my e-check anyways
and the bastards are packin up and leavin town soon so hell, ill let my car flow!! my design will basically resemble the SCP exaust for over $700 but should only cost me around $250 max!! then i figure ill throw on a 10% pully to make up for the slight loss of torque most people talk about when slappin new exaust on and havin the loss of backpressure. then hopefully the mods will just keep coming, theres not enough room on here to list em all. but my car will looks mostly stock on the outside other then some 03 cobra wheels.
thanks again, Adam

my stock 89 SC 5-speed runnin 15.3s @92mph well i did a couple, lil things... its on the site.
RAGE RACING!!!!
 

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[my stock 89 SC 5-speed runnin 15.3s @92mph]

I have a '89 XR-7, 5-spd with a few mods, that runs 14.5. Lets compare notes. My E-ddress is: [email protected] (that's lower case QTM.NET)

68COUGAR
 
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