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Straight eight with dual exhaust

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I have a '37 Special with a '40 engine with a dual carb set up from a '41/42 Special/Super.  I want to install dual exhaust but I'm not sure how to run the pipes.  The dual carb set up I got has a modified "X" pipe, standard is a "Y" pipe, so I'm thinking someone had dual exhaust on their early '40s Buick.  I'd like to know if anyone is running dual exhaust on their mostly stock '37-42 Special.  If you did I'd like to see how you did it.



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Dual exhaust might be overkill on a small series Buick. Your flow limitation is the intake, not the exhaust. It also doesn't sound as cool as you'd hope--not like a V8, but like two 4-cylinders. My 320's single exhaust with 2.5-inch tubing sounds awesome, though. Baritone hum with a nice burble at idle.


That said, to answer your question, most dual exhaust systems I've seen that use the factory dual carb exhaust manifolds simply run two smaller pipes as close together as possible. One will have to follow the original path through the frame and the other will have to go below the frame. What you do behind it is easier, whether you want to separate them and run one down each side or run them both down the same side. You will definitely have to get creative since there's no template to follow. Having a skilled tubing bender will be a big asset. It will take a lot of test fitting and experimentation to make sure you clear the steering gear, shift linkage, and brake system, which are all crammed into that same area where you want to run the pipes. There's a definite cool:hassle ratio that you'll have to consider.


When I built the custom headers and exhaust for my Limited, I went with 2.5-inch pipes, which flow considerably better than the stock 2/2.25-inch. It took us about six weeks to get the exhaust right on the Limited and we still had to go back and make the over-axle tubes a second time for more clearance and add a second muffler to get rid of a highway-speed drone. Given the limitations of the Buick engine's flow rates, 2.5-inch tubing is more than adequate, especially on a small series engine. If it's all-out performance you're looking for, your smaller engine probably won't test the limits of a true 2.5-inch system.

5-28-19-12.jpg.2fe0926ee2bcbcb34ff171cc51ffccf3.jpg  5-28-19-2.jpg.2c860b3bfbdfad99e704b0d0eaf1703c.jpg  5-28-19-4.jpg.bc581a1a2b73ecd19672967f3f891c64.jpg  5-28-19-6.jpg.233c9b3cd640c78ce23ffeb202a99108.jpg  ExhaustFinal7.jpg.6af75e4bd62e096be4a0885a453e5edc.jpg



I also have a 1940 Special in the shop that has a dual exhaust but it uses one pipe from the manifold and branches later underneath the car--zero performance gains but someone thought it would sound cool, I guess (it actually sounds kind of farty). Here's how it looks:

078.jpg.0b31025269d3d59303d61038d29b1ff1.jpg  079.jpg.a4a6311c4bc78402c7d0f86ee319e9a5.jpg



You'll simply need to get creative and do a lot of test fitting. Good luck!

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Matt, I am fairly certain you've seen my posts on the Pre-war forum but for those that haven't I'll recap a little.  I am building a Frankenstein '37 Buick.  Started with a complete rusted out junker, got a better frame, better body, '40 248, '36 transmission.  Basically the only things form the original car I kept were the two front fenders and radio.  For some reason I tent to do stupid car things like this.


Anyways, I am trying to build a somewhat period correct modified car, dual carb set up, overdrive unit and I thought dual exhaust would just add to it.  I'm not a hot rodder, usually stay all stock but since this car was a beast from the start I thought I'd give it a try.


I bought an exhaust kit consisting of four straight pipes, four 45°, four 90° and four 180° bent pipes, all 2.25 piping.  I also bought two long stock sized mufflers.  I have friends that have gone this route on other old cars with success and I don't shy away from fabricating parts, have welder and grinder, will travel.  The "X" pipe I have came with the dual carb set up but since the later Buicks had their engines sitting at a slight backwards angle, the '37 leve, the "X" pipe goes into the frame, I will have to cut it and alter it to fit the '37.  I could modify it into the traditional "Y" pipe and run one single exhaust.  My main goal is to have a quiet car, I don't want a noisy, rumbling hot rod.

Thanks for the pictures and any other advise you have to offer. 

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  • 4 months later...

Bob, I seldom visit this site so this reply may be of no value since it's so late. I've got a substantially modified 41 Rdmstr with headers and side by side duals, sounds great. X pipe makes a lot of difference. Firing order is really the contributor in the sound of the exhaust system. Split the pipes to each side and you can't tell a straight 8 from a V8. My x pipe is right behind the collectors where the pipes are very close together. Had a good exhaust man do it in about 4 hours while I slowed him down by helping.

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My 1950 has a homemade manifold/headers. Plumbed such that firing order mimics a 180 degree firing engine. In other words, firing order is left right left right,  no X pipe.  I use Smithy glass pack mufflers. To me, sounds great.



Edited by Ben Bruce aka First Born (see edit history)
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