Technical DIY Exhaust Baffles

My Son redid the exhaust on my 56. It was 3” with Flowmasters with dump prior to rear end. New system is 2 1/2” all the way out to the back bumper but still retaining the 3” Flowmasters. We were both shocked that it rapped so hard (near low rider like). My Son added an H pipe and what a difference.

 

Bet it ran better too?

 

Don’t have to yell at each other anymore as well.

 

H pipe almost there, worked out great for locate under trani. spirals goin in fer giggles,will grab pics. slow go today, she's like 32 celsius.

 

Speaking of that another full subject for sure would be carb versus fuel injection with crossover.

 

Ready to mount, should b interesting to c what sound comes from all this

 

Yes, I try and keep up with technical hp stories, I know that the optimal muffler placement is 15-18 inches behind the collector, and it seems that most H-pipe placements is at the transmission crossmember.

 

Yes an H pipe will help quiet it down alot.

Built a nice rowdy pontiac 455, nice nasty sounding beast, added to H pipe and it sounded like a small cammed original motor.

I like to keep it within 18" of header flange.

.

 

Well, after dual spirals and H pipe fab n install the Big Blocks maybe 10% quieter, Haha... Driver!!

 

So, if adding an H pipe makes it quieter, would adding two H pipes make an even greater difference? What I'm thinking is an "X" pipe with an "H" pipe slightly behind it ........
To me the perfect exhaust would be one that had a mellow sound above 2200 rpms but was very quiet at lower rpms when in overdrive on the expressway.

 

Maybe it won’t be a “sound-a-like”. Every Saturday at our car gathering you don’t need to turn around and look at what drives in most times.. cammed big blocks with a 3” exhaust all seem to sound the same.

 

Check this out…doesn’t have to be stainless. Can be done step by step (with pipe still on the vehicle), until it is a quiet as desired:
https://www.jalopyjournal.com/forum/threads/cheap-stainless-steel-muffler-tech.123933/

 

An X pipe before an H pipe would certainly change the tone, but not sure it would affect the actual sound level.

Now, adding some resonators after the mufflers will drop the sound level without hindering flow.

Exhaust systems are tricky to get "right" because everyone has a different perspective and/or preference of sound level, and tone.

 

Well, I believe I have caused excess crankcase pressure by hindering exhaust flow installing spirals with stock style mufflers. I have oil pushing out of pan gasket only . Pcv system working ,plugs look good and no dip stick push. Also annoying exhaust tone whistles. Can that much crankcase pressure b result of restricted exhaust? Thinking yank the spirals out , reseal pan and test before doin leak down etc etc.All new motor with several hundred on her.update::: pulled pan today, the felpro has split inside pan at base of timing cover ?? Also At request of my p***enger removed the whirling spirals .Moroso pan gasket on way. Is it possible a backfire would damage this seal?

 

Pull the breathers and check for blowby!
No amount of backpressure is needed for an engine [that is an old timer myth]

As for spiral baffles , the only thing they benefit is the bank balance of the vendor.
I have spent time on a flowbench testing developing mufflers and these were near the worst.
We started removing spirals but the flow never improved


I have managed to get a car down to under 95db without a muffler [motorsport sanction rules]
This was done with an "atmosphere box" in the system [Volume = CID x 2.5]
The box needs to be sound deadened externally to get rid of reverberations . [we didn't care about this]

I don't know what your end goal is, but mine was minimal HP loss and not get "pinged" at the track.


One of the most simplest and effective baffles we built worked amazingly well [Muffler manufacturers won't promote this because they will put themselves out of business]
On a Formula5000 with headers and pipes dumping out the back , we literally welded a piece of 1" Angle steel across the tube [approx 12" from the outlet]. we had to "V" slot the tubing to drop it through and weld it.
BUT this piece of angle was installed backwards to capture flow.

This ^^^^ started out as an experiment originally replicating a f***master, and we started removing baffles and testing flow and Db readings

 

" 1" Angle steel across the tube [approx 12" from the outlet]. "

Does the attached image show it about right ?

 

I just stuffed a bunch of chicken wire down this pipe! Hahaha!!

 

Yes, exactly like that!
The angle was small enough in size to allow unrestricted gas flow around it.
And the gases that intercepted the angle built up pressure and spilled around it [into the outer gas flow]

But the sound waves "deflected" at 90° sideways into each other cancelling each other out.

We also develop another "Gl*** pack" style muffler that was better , but this ^^^ was easier and a lot cheaper. [and had longevity]
In road racing there was no significant advantage between the 2 that diving skills couldn't overcome [HP doesn't overcome track position]

 

Pipes running hot downstream could be too little ignition advance and/or excessively rich fuel/ air mix !
Do some reading about how gun silencers work , same principles as exhaust muffling . Companies have spent untold millions producing quiet ,efficient power , just copy what they've done .

 

Modded Back to just the dual mufflers with H pipe

 

Does it sing like a whistle

 

Good topic to open a rabbit hole for those who like technical "snacks", look up Helmholtz resonators:

https://pressbooks.pub/sound/chapte...use,especially ported speakers and subwoofers).

 

These can be found on the intake side, too, on many OT vehicles.

 

Race Cars with open exhausts don't whistle.

 

57dood;
If you have the room, you might try an X-pipe in place of the H-pipe, The X should help split the flow, utilizing both sides for each exh pulse, mimicking ~dbl-size muffler-effect. Try to make it flowing, not abrupt.

On the original Patent(s) that resulted in the X-Pipe, the header-termination point/collector, was a t****zoidal-shaped wedge, w/the singular pipes welded to the large-end of the wedge, a "U" bend for the outlet & half of the outlet pipes dia blocked w/a small plate. Claimed nothing more was needed. Started on a bike, went to v8s, same thing, For the race engine testing, he unblocked the outlet pipes. He claimed better power curves, & 3 noticeable power-bands. Also claimed, iirc, primary dia & length didn't matter much. Did give a very odd exhaust note. Too complicated for m***-production(although I've seen some acvw headers done by him), so he simplified it into the X-Pipe. Everyone copied that...

Kerry;
Did you do any math on the angle-iron placement, or further testing? Reason I ask is, it seems that the added steel "obstruction" would appear similar to the atmosphere at the tailpipe end, w/regards to what the exhaust frequency sees & how it reflects back into the combustion chamber & ports. Full-wave, half-wave, qtr-wave, etc.
Any pics of the "atmosphere" box & it's installation?

Some of you guys are getting dangerously close to practicing what Phillip H. Smith wrote about in "Scientific Design of Intake & Exhaust Systems" years ago. .
Marcus...

 

I have used these in the past to reduce exhaust noise. Cheap off ebay and easy to try just drop it in the pipe upstream of the muffler.

 

What is that? A short round Cat? Even that should modify sound.
Marcus...

 

Its called a DB killer. Used to reduce noise in motorcycle exhausts. Got mine on ebay

 

Thanks. Different diameters available? Stainless steel construction? How many in a row did you need to adequately drop the noise level?
I'll have to look those up.
Marcus...