exhaust for 67 bbc convertible - Impala Tech
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post #1 of 11 (permalink) Old 07-02-2019, 12:38 PM Thread Starter
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exhaust for 67 bbc convertible

Classic Industries has a stock setup for around $450 shipped (not stainless). This seems cheap to me. Anyone have any ideas if this is a descent setup? I want it to sound good but not deafening, being a convertible. I'm sure my custom shop will charge quite a bit more than this.
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post #2 of 11 (permalink) Old 07-02-2019, 01:53 PM
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Post a link so we can take a peek.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #3 of 11 (permalink) Old 07-02-2019, 02:27 PM
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Full size cars are body on frame; unlike the Camaro and Nova wich ate uni=body with a bolt on sub-frame in the front. Because these more popular cars have an X reinforcement bolted under convertibles they do have an issue with threading an exhaust through the hoops. Your full size car made the frame deeper and thicker to support your broken in half body (a car with a steel roof is 60% stronger that is it is more rigid than a convertible). It is the fact that your car has a front half and back half but no structural support in the middle where the door gap is that causes convertible Porche, Audi, Mercedes, and Ferarri cars to be 15% slower than their hard top variants (they are also heavier).

Your car's exhaust shouldn't be an issue other than choosing a muffler or a megaphone to affect sound volume. I prefer to speak softly and carry a Big BBC engine than to run around like a one liter Jap car with a coffee can for an exhaust. That is why I used over-sized (longer body with more baffle plates) Corvair muffler made by Flowmaster (70 series PU truck muffler) to quiet down the monster sized engine and ran it through a dual 2½" inch exhaust pipe with a cross-over pipe. Quiet but you could hear the deep rumble of a big engine.

Big Dave
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post #4 of 11 (permalink) Old 07-02-2019, 02:38 PM Thread Starter
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Originally Posted by 68WASAGOODYEAR View Post
Post a link so we can take a peek.
https://www.classicindustries.com/product/ex8007.html
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post #5 of 11 (permalink) Old 07-02-2019, 02:42 PM Thread Starter
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Thanks Big Dave! sounds like you are saying that I should be able to install a kit easy enough. It does look like theres plenty of room under the car, for the most part. So I just have to decide on these mufflers. There are no details given on the site. mabye I'll take it to the shop first and see what the custom price is. I expect it to be at least $600.
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post #6 of 11 (permalink) Old 07-02-2019, 04:20 PM
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Originally Posted by 67ImpalaSSConv View Post
Thanks Big Dave! sounds like you are saying that I should be able to install a kit easy enough. It does look like theres plenty of room under the car, for the most part. So I just have to decide on these mufflers. There are no details given on the site. mabye I'll take it to the shop first and see what the custom price is. I expect it to be at least $600.
Best bet is to go to a car show and listen to what pulls in to the show. If you like the sound ask what they have installed for a muffler (all pipes are the same and unless you are putting it under school bus has no affect on the sound level (harmonics in the really long pipe in a school bus make that annoying noise that they do at least with a gas engine in an older bus). If it is a glass pack such as a Cherry Bomb or Dyno-Max, ask how old it is. The glass fiber filling may have already burned away making it an echo chamber with no muffler at all. Some people like noise. They used to put baseball cards in the spokes of their bicycles as kids.

Bigger the exhaust pipe diameter the more noise it makes. Smaller has no affect on car's performance as on race day I can uncap to go to an open system. There are three types of mufflers:

OEM Walker mufflers are chambered with issolation and vented pipes connecting the front inlet to the rear outlet. Much more restrictive than a chambered exhaust designed to cancel certain frequencies of sound by the angle and placement of interior baffles (more like a weir than a baffle as it doesn't slow down the gas flow).

The chambered exhaust by Walker pioneered for the the Corvair turbocharged Spyder. It was a high volume flow low back pressure muffler that made the engine quiet but allowed a turbo to breath. Flowmaster blatantly copied the design and painted it green to avoid a copyright infringement. Flowmaster did super size the design for larger displacement engines (as well as shrinking it for those who love noise. The bigger the number (series) the quieter it will be. Borla uses this style as well but are much more expensive due to their being made out of stainless steel (you buy only one muffler as it will last the life of the car).

Finally there are glass packs. Muffler shops used to make these for hot rods but Cherry Bomb made a cheap muffler that put them out of business. Cheap mufflers do not last so if you don't like them you can change your mind when you replace them. Glass pack mufflers are a straight pipe with holes drilled in it wrapped with fiberglass fibers. They quickly burn out unless the glass is made of stainless steel wool. Borla sells these stainless steel wool mufflers. For a traditional glass pack look to DynoMax and Cherry Bomb. Obviously a straight pipe is going to be the noisiest of all. Just look to those who rave about the sound to know who has a small motor that he wants to sound louder.

Big Dave

Last edited by Big Dave; 07-02-2019 at 04:45 PM.
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post #7 of 11 (permalink) Old 07-03-2019, 10:33 AM
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I bought a Magnaflow 15165 for my car, same P/N for yours, and have reworked it twice now to make sure it doesn't hit the rear suspension. Overall happy with the sound except at 2000 rpm where it has a horrible drone. Also happens to be where the car sits when cruising on the highway.

Knowing what I do now, I'd have just bought mandrel bent stainless pieces and made my own from scratch.

1969 Imapala convertible build thread here:
https://www.pro-touring.com/threads/...ghlight=impala
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post #8 of 11 (permalink) Old 07-04-2019, 09:48 PM
 
 
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Try checking out Classic Muscle Car Exhaust. They carry complete systems from Pypes, MagnaFlow, and Flowmaster. They have sound clips for most of the systems and a lot of good exhaust information. You can get a Pypes system without mufflers and use any offset/offset muffler you want. They offer Dynomax Super Turbo mufflers which have a great muscle car sound without being loud and they don't drone. Flowmaster offers stock manifold downpipes if you need them. They currently have a 10% off sale and shipping is free.


https://classicmusclecarexhaust.com/
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post #9 of 11 (permalink) Old 10-02-2019, 11:59 AM Thread Starter
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Quote:
Originally Posted by justjohn View Post
I bought a Magnaflow 15165 for my car, same P/N for yours, and have reworked it twice now to make sure it doesn't hit the rear suspension. Overall happy with the sound except at 2000 rpm where it has a horrible drone. Also happens to be where the car sits when cruising on the highway.

Knowing what I do now, I'd have just bought mandrel bent stainless pieces and made my own from scratch.
I ended up having a custom install done at the local shop. They do good work and the cost was around $525. They installed 2.5" aluminized pipe with stainless magnaflows. It was from the exhaust manifold back to the bumper. Sounds very good but is quiet in the cab. I think I'll like that being a convertible.

Thanks for all the input.
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post #10 of 11 (permalink) Old 10-10-2019, 12:16 AM
 
 
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Out of curiosity, what length MagnaFlow muffler did you use?
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post #11 of 11 (permalink) Old 10-16-2019, 12:41 PM Thread Starter
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Originally Posted by Spoffie View Post
Out of curiosity, what length MagnaFlow muffler did you use?
Sorry I just now saw your question.

I'm not really sure what length they used. Looking under the car it appeared to be around 24" but I could be way off. I'll try to remember to measure and post what I find.

The way it is setup, its very quiet in the seat, but sounds pretty good in the rear. Probably also due to the exhaust exiting at the bumper. It might be too quiet for some folks. But it sounds great at higher rpms.
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