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Last year, when I reworked my exhaust, I used a Thrush turbo type muffler and 2" pipe all the way. I used the Thrush muffler for a few reasons:

1) Someone here said the CIH doesn't like a Flowmaster type muffler (think it might have been RallyBob)
2) The Turbo type muffler was extremely small and cheap
3)Turbo type mufflers are supposed to flow very well with out sounding obnoxious
4) Glass packs usually sound obnoxious on a 4 banger

Well it seems to work ok, butttttttttt, I feel it's too quiet. It has a decent tone, but I'd like a little more sound. Now since I'll have time to develope a new exhaust system while I have the engine out, I'd thought I'd get suggestions from you'll on mufflers.
70 GT future 2.0

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Just FYI, a Flowmaster muffler lost 8 hp on one particular Opel engine compared to a Simons straight-thru glasspack muffler. What is a Simons? A Swedish made muffler similar to a Borla or Magnaflow or any of the other straight-thru perforated-core (no louvered cores!) glass-pack mufflers.

Most of these newer 'glass-packs' are oval in cross-section, not the normal round glass-packs you might be thinking of from years ago. Those smaller glass-packs are louder, since they have very little sound-absorbing packing around the core.

Some rules of thumb I've accumulated over the years, as they pertain to Opels and exhaust systems.

>The bigger the engine, the bigger the pipe diameter it can handle.

>Alternatively, the more hp and rpms you're spinning the engine, the bigger the pipe the engine can handle, even a 'small' Opel engine. So while a stock 2.2 might run best with a 2.25" exhaust, a high rpm racing 1.9 may need a 2.5" or larger exhaust.

>Straight-thru is the way to go with muffler design, with a perforated core. The larger the muffler, the quieter it will be.

>Higher compression makes the exhaust louder, and in general a higher hp engine will make more noise. So a muffler/exhaust that is quiet on a stock 1.9 might be loud as hell on a 2.0 with a hotter cam.

>If you place the muffler closer to the engine, it will be quieter than if it is further back near the bumper. It will also produce less power.

>If you're running over 130 hp or so, you WILL need two mufflers or it will be loud. All my cars have had two mufflers and have been streetable, both by the letter of the law and by my own ear. With a single muffler expect it to be about 95 db. Of course this varies with the muffler size and brand, etc. You won't be able to carry on a normal conversation at highway speeds at this level. My ITB car will have one muffler, but it will be a LARGE one, and the engine is basically stock, so it will be tolerable noise-wise.

>I recommend running a larger over-axle pipe than the rest of the main pipe. So, if you have a 2" main exhaust pipe feeding into a 2" muffler, you would then transition into a 2.5" pipe over the rear axle. Why? Those bends are fairly tight, and a pipe that is bent at that radius will shrink internally somewhat in cross-section. So exhaust gas velocity will drop drastically at that point from the combination of the smaller pipe ID and the three tight bends that are in close proximity to one another. Running the larger pipe maintains the velocity, and torque, HP, and throttle response will improve. It's not uncommon to see 4 ft. lbs. of torque across the board from this mod.

Bob 'I'm exhausted' Legere
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