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Exhausting advice please.

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jgregg13
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Exhausting advice please.

Post #1 by jgregg13 » Wed Jul 03, 2019 1:16 am

My 4.9 EFI swap into a '48 Chevy is at the point where I will be building the exhaust system. I am using two front EFI manifolds to facilitate mounting two turbos directly to the manifolds with adapter plates. The turbo setup will be mild, 8 to 10 psi max boost. The exhaust system from the turbos back will be independent dual pipes with no mufflers and no cross or X pipe connection. I'm expecting the turbos to keep the noise level low enough for normal driving. I'll have a removable section so I can put mufflers in if it's too loud. All bends in the pipes will be done with mandrel bends. And there will be two 90^ bends in each pipe near the back to get around the fuel tank.

So the question is; What size pipe should I go with so as not to hurt performance, but not be overkill either? I'm leaning toward 2-1/4" OD (about 2.10" ID). Thoughts???

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THE FRENCHTOWN FLYER
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Re: Exhausting advice please.

Post #2 by THE FRENCHTOWN FLYER » Wed Jul 03, 2019 8:10 am

I like your plan. Two 2 1/4 pipes should be fine at your boost levels.
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sdiesel
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Re: Exhausting advice please.

Post #3 by sdiesel » Thu Jul 04, 2019 2:54 am

2.25 more than adequate.
2 is fine if it is fed by only 3 cylinders.
if u will rev her to stratosphere u might want to reconsider ....
and why no X pipe or H pipe connector?
also i like to use flighting inside the pipe
its popular with the saturday evening bunch who race at the fairgrounds, and have to keep the noise down.
i believe there is a commercially produced muffler out now with the same principle design.
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jgregg13
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Re: Exhausting advice please.

Post #4 by jgregg13 » Thu Jul 04, 2019 1:55 pm

sdiesel wrote:if u will rev her to stratosphere u might want to reconsider ....
and why no X pipe or H pipe connector?


Thanks gentlemen for the guidance.
I don't want to rev it over 5G, It's basically to be a daily driver lead sled that can get out of its own way.
No X pipe just because I want it to sound like my '52 Chev with the split manifold and glasspacks from the '60s. The X pipe will kill the reverberation and make it sound like a dump truck. The old 216 was too loud, but it was running at WOT most of the time, so I'll have to play it by ear and add mufflers if I need 'em.
If I need mufflers, I'll look at making something up with those auger baffles (I hadn't heard of them before).

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Re: Exhausting advice please.

Post #5 by THE FRENCHTOWN FLYER » Thu Jul 04, 2019 2:14 pm

In this case I don't think a crossover pipe will do much good, save for making a boost control valve easier to plumb. Nor do I think it will sound anything like a 216 with split manifolds, what with two turbine blades chopping up the exhaust pulses into hummy little bits.
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Re: Exhausting advice please.

Post #6 by jgregg13 » Thu Jul 04, 2019 4:39 pm

Okay then! Once I get 'er done I'll do some decibel checks and post a recording so we'll see what sort of tune it's humming. :)

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Re: Exhausting advice please.

Post #7 by Max_Effort » Fri Jul 05, 2019 7:59 pm

Restrictions after the turbo are never good, so go as large as you can. Especially with a couple of 90’s in each pipe. Come out of the turbo and then step up. I’d like at least 2.4” ID per pipe/turbo

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Re: Exhausting advice please.

Post #8 by Soldmy66 » Fri Jul 05, 2019 9:10 pm

You should be able to get away with a far less sound attenuating muffler than if the car was naturally aspirated. As others have pointed out, a turbo goes a long way to kill exhaust sound.

Taken from the linked article: "The turbo has a similar effect on exhaust systems, where the exhaust-side impeller disrupts the exhaust flow by creating an extra gate for the sound to have to flow through. When talking about cars with exciting exhaust sounds, most people gravitate to sounds where the individual “pluses” of cylinders firing are very defined, creating an exciting burble or rhythm to the engine’s sound. Unfortunately for turbos, the turbo itself acts as a sort of “revolving door” where the air has to enter (and therefore exit) the turbo in a smoother, more consistent pattern. Much like the effect on the intake, this results in a flatter, more sinusoidal tone to the exhaust, which most people would say is less exciting than an NA engine of similar design. The turbo also tends to make the exhaust quieter as a byproduct."

http://designingsound.org/2014/07/30/tu ... oundscape/

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Re: Exhausting advice please.

Post #9 by THE FRENCHTOWN FLYER » Fri Jul 05, 2019 10:20 pm

Kinda like my shop vac
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Re: Exhausting advice please.

Post #10 by jgregg13 » Mon Jul 08, 2019 4:48 pm

Max_Effort wrote:Restrictions after the turbo are never good, so go as large as you can. Especially with a couple of 90’s in each pipe. Come out of the turbo and then step up. I’d like at least 2.4” ID per pipe/turbo


While I agree that the less restriction the better for maximum performance, I have looked at a couple of friends here with turbos, one a single Holset from a Cummins pickup engine on a 4.2 L GM Atlas 6 cyl. (sorry for the profanity) and a Chinese GT35 on a 2.9 L Atlas 4 cyl.

The 4.2 L example has a 2-1/2" OD pipe from the turbo to just ahead of the rear axle where it splits into two 2" tail pipes. This is a '49 pickup daily driver that also goes to the 1/8 mile car club drags once a year. It runs mid to high 9's. The engine is otherwise stock. It has no muffler and is quite quiet.

The 2.9 L tried running without a muffler with a 2-1/2" pipe, but was too loud so a low restriction muffler was added. I assume the difference in noise level is a combination of turbo size and fewer cylinders.

So I'm thinking that two 2-1/4 pipes, considering that I've only got 2.5 L per turbo at lower rpm and smaller turbos feeding them will work for the level of performance I want. My engine mods are expected to be minimal. Clean up the combustion chamber to minimize hot spots, High volume oil pump, Silvolite hyper pistons and head studs would be about it.

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Re: Exhausting advice please.

Post #11 by MechRick » Mon Jul 08, 2019 8:20 pm

jgregg13 wrote:So I'm thinking that two 2-1/4 pipes, considering that I've only got 2.5 L per turbo at lower rpm and smaller turbos feeding them will work for the level of performance I want


From experience, bigger down pipes will help the turbos spool quicker.

Ford Turbo Coupes (Garrett T3 turbo and IHI RB52 in later years) ran a 2.5" down pipe stock, so yes, it will work.
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http://fordsix.com/forum/viewtopic.php?f=2&t=73244
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