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PostPosted: Sat Mar 09, 2019 1:37 pm 
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Joined: Mon Oct 14, 2002 6:08 pm
Posts: 651
Location: Raleigh, NC
Getting ready to fab up an exhaust system for my FP MGB. What are people running for mufflers? And what is the typical pipe size? My current header has a 2 inch outlet (but I am thinking of going larger). I've also noticed that the Flowmaster's start at 2 1/2 inches. Help!

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PostPosted: Sat Mar 09, 2019 1:43 pm 
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Joined: Tue Aug 20, 2002 10:01 am
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Location: Belmont, CA
How much space do you have, and where do you want to mount it? It also depends on what the sound restrictions are at the tracks that you race at.

Full length systems (rear exit) weigh more than simple side exit systems, but ride height limitations might come to play with side exit systems.

@Neil Verity might have some suggestions

I run a 2.5" Cherry Bomb unit that exits right in front of the rear axle with a 45 degree down pipe. Obviously my car is different than a "B"

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PostPosted: Sat Mar 09, 2019 2:48 pm 
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Joined: Fri Aug 12, 2011 4:03 pm
Posts: 207
Location: Northeast PA
I had run a Hooker Max Flow welded muffler for years, sounded great, no sound issues at 103 tracks and was solid.
After I think 8 seasons it finally cracked open on a backfire. I immediately got a new one and it failed in 2 weekends on a similar backfire.
Apparently they used to make them in the US, now outsourced somewhere.

I then tried a Walker welded DynoMax, that failed in a few weeks.

I called Summit and spoke to a customer service rep, explained my car, what I was doing etc, he recommended a Flowmaster 40 series RACE muffler.
He said the Flowmaster race mufflers have much more serious construction than all the rest of their mufflers and if I blow one of those apart I have bigger problems than my mufflers failing.
Its been in there since 2016 and working perfectly. Im converted.

Hopefully those data points help somewhere.

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88 BMW M3 - SPU #98


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PostPosted: Sun Mar 10, 2019 3:20 am 
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Joined: Wed Jul 06, 2011 3:48 am
Posts: 590
Location: Florida
Had to put a muffler on our 16.1 948 engines we use in one of our cars. Went directly to Flowmaster Tech Support and they recommended the single chamber, one baffle (which is nothing but a "V" in the can), 2" in, 2" out unit using an 8" end pipe. We got the unit from Summit and went from 110 db to 98 db and according to Flowmaster should have picked up at least 1 to 2 hp. We run through the tunnel exhaust with the muffler just behind the left mount for the panhard rod. These units were originally designed for the IRL Indy Lights cars. One other note... I had an old article listing the most efficient race mufflers which rated brands like Borla, Flowmaster, etc. at the top of the list and Cherry Bombs and Supertraps at the bottom. List went away in our '17 hurricane or I'd post it for you. BTW, our 1275 limited Prep engines use the 2" pipe system but don't need the mufflers for 11.1 cr. They are around 97 to99 db.

Bob

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PostPosted: Sun Mar 10, 2019 4:09 am 
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Joined: Thu Jan 22, 2004 3:31 pm
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I like https://spintechmufflers.com/. They quite the car and don't hurt HP. There a chambered muffler. Charlie and Tom Campbell still use it on the FP Miata I sold them years ago with obviously good results.


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PostPosted: Tue Mar 12, 2019 4:32 pm 
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jimmypet wrote:
I had run a Hooker Max Flow welded muffler for years, sounded great, no sound issues at 103 tracks and was solid.
After I think 8 seasons it finally cracked open on a backfire. I immediately got a new one and it failed in 2 weekends on a similar backfire.
Apparently they used to make them in the US, now outsourced somewhere.

I then tried a Walker welded DynoMax, that failed in a few weeks.

I called Summit and spoke to a customer service rep, explained my car, what I was doing etc, he recommended a Flowmaster 40 series RACE muffler.
He said the Flowmaster race mufflers have much more serious construction than all the rest of their mufflers and if I blow one of those apart I have bigger problems than my mufflers failing.
Its been in there since 2016 and working perfectly. Im converted.

Hopefully those data points help somewhere.



Sorry to hear your DynoMax failed so quickly. Do you recall the part number, or the style, was it round, oval, straight through?

I have used a DynoMax Race Bullet 24244, 5" round on my FP Miata. It is a 2.25 ID pipe. I prefer the rounds over ovals for their durability. The sound levels are good for the track. No "ratty" shell noise either - like my Flowmaster oval that came with the car - the shell failed after two years).

See no change in straight line speed in back to back tests based on my data acquisition.

Had a DynoMax race bullet on my Spec Miata for 10 years, beat the crap out of it, would high center on curbs (Mid Ohio turn 11 exit) it still held together. Was on the car when I sold it, and switched to prod racing.

Hope these data points help. I am a little biased, have been working at Walker for 25+ years now, but real data is real data.

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PostPosted: Tue Mar 12, 2019 8:08 pm 
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Joined: Fri Aug 12, 2011 4:03 pm
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Location: Northeast PA
Mine was an Oval "Dynomax Performance 33274"

There is a picture of the Walker post race / failure on my Instagram: https://www.instagram.com/p/BKD75E0hLKS/

I posted a picture of the Hooker as well, that failed much more spectacularly: https://www.instagram.com/p/BJJIgvtBMzv/

I have a Dynomax bullet on my other race car and it is pretty much indestructable,,, but its also too loud. I wanted a quieter option.
The Hooker Max Flow that I had was perfect for years until if finally failed.
The Walker sounded great, but failed really fast.
As I posted the Flowmaster 40 series race muffler thats in the car now is living on pretty well at a pretty decent volume level.

Cheers
jimmy p

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PostPosted: Wed Mar 13, 2019 8:10 am 
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Joined: Tue Nov 03, 2009 3:15 pm
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Rick,I use a Flowmaster, part no 8325408, on my MGB. Seems to hold up quite well and I never have a problem with sound.
2.5" inlet and outlet
I think I bought mine from Summit.


Jerry


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PostPosted: Wed Mar 13, 2019 9:18 am 
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Joined: Wed Jul 06, 2011 3:48 am
Posts: 590
Location: Florida
My two Flowmaster ovals are now 15 years old and rock solid still.

Bob

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HP 13 '59 AH Sprite FP
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PostPosted: Thu Mar 14, 2019 6:00 am 
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Joined: Thu Oct 01, 2015 8:45 am
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jimmypet wrote:
Mine was an Oval "Dynomax Performance 33274"

There is a picture of the Walker post race / failure on my Instagram: https://www.instagram.com/p/BKD75E0hLKS/

I posted a picture of the Hooker as well, that failed much more spectacularly: https://www.instagram.com/p/BJJIgvtBMzv/

I have a Dynomax bullet on my other race car and it is pretty much indestructable,,, but its also too loud. I wanted a quieter option.
The Hooker Max Flow that I had was perfect for years until if finally failed.
The Walker sounded great, but failed really fast.
As I posted the Flowmaster 40 series race muffler thats in the car now is living on pretty well at a pretty decent volume level.

Cheers
jimmy p



Thanks for sharing the photos. The part number should be 17xxx or 24xxx. It appears to be an Ultraflow welded, that failed by the shell emboss. The shells thin slightly from the "lettering" emboss, and this becomes the weakest point. I have experienced this myself.

Round shapes have higher natural frequencies than oval shapes, and are more durable for this reason. Rounds are also more durable from impacts for the same reason. Production engines that rev to 9K RPM create strong pulses. This assumes you have the package space to fit the round that you need. Oval mufflers exist so you can get more muffler volume in a flatter space, with some risk too.

I assume your exhaust pipes are likely in the 2.25 or 2.5" range. The mufflers I suggest for your application:

Dynomax 17230 6" round 2.5 inch pipe - most volume = most sound control - if you can fit a 6" round
Dynomax 24215 or 24236 4" round 2.5 inch pipe - if you can only fit a 4" round
Dynomax 24244 5" round 2.25 inch pipe. - in the middle for muffler size. I personally use this one.

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