Muffler size/type question...

Wednesday, 17-Jan-01 14:08:49 writes:

My new 2,110 has one of Art's 1 5/8" merged systems with heater boxes. Art included the pieces to put together the muffler since we weren't sure

of clearance requirements in the Porsche roadster replica, so Intermeccanica has to do the final fitting. The muffler Art included is a 2 1/4" (I

think it's a Flowmaster).

Like everyone else I'm looking for the most BHP out of the engine build and plan to replace the 44 IDF's with 48 IDF's, put a Compufire in the

009, and install one of John's "Tiger" CD ignitions.

Which brings me back to the exhaust on the 2,110 with 6,500 RPM redline - in your experience should I switch to a 2 1/2" muffler? If so, any

particular muffler brand/type "better" than others?


george brown


Click here to reply


When I inquired about this with MM, he recommended a 2 1/2" Dynomax, which I went with. This is on a 2.0 liter, and a 1 5/8" merged header. (n/t) (Jim Brown) (17-Jan-01 15:16:17)

The only down side i have found with the simple D-max $29.95 model i use is, it doesnt like to be back fired with alky on the limiter. it has a tendency of bulging and pulling the seams

apart. (this is why i welded the seams up on mine.) (n/t) (Muffler Mike) (17-Jan-01 17:09:00)

Re: Muffler size/type question... (Steve Arndt) (17-Jan-01 15:43:39)

Also. . . (Steve Arndt) (17-Jan-01 15:48:31)

Re: Re: George, On my race car im using the 2 1/4 on the berg 1 3/4 header. Im producing a good HP, with 48 IDAs and 42 vents and shift at over 7000+ easy. Just for info (n/t) (Art

Thraen) (17-Jan-01 16:57:59)

Manual @ A-1 is currently building me a 2 1/2" Stainless Dynomax muffler for my merged heater box 2 liter. I inquired about Flowmasters (like their sound) and he stated that they are very

load on engines bigger than 1800cc, especially because I'm running 48IDA's. My friend has a flow master on a 1641cc and it sounds great but is pretty load for that size motor(his 1641is

pretty maxed out though 044s, 120 cam dual dells) Hope this gives you an idea of what to use. (n/t) (Ollie Frey) (17-Jan-01 16:30:15)

Mine is a 1 5/8 Merged witha 2 1/2 Magnaflow, performance is great, sound is even better, muffled yet mean... (n/t) (Greg Ward) (17-Jan-01 16:50:02)

Re: I depends... my experience with mufflers on race engines (Tom Simon) (17-Jan-01 17:04:21)

Well said. (n/t) (Muffler Mike) (17-Jan-01 17:14:16)

Just use it. You already have it so why waste money. It will work fine. Just look at Art's post above. Mine is 2.25" and it is fine, as is Chris Larson's who you modeled your engine after.. (n/t)

(Matt Harris) (17-Jan-01 17:10:32)

Mac also makes a good muffler called "Flowpath." They are quieter than a flowmaster and many people say they make more power. A couple of guys that I know have them on 1776cc

engines and they sound better than a Flowmaster on a VW engine. (n/t) (Jersey Joe ) (17-Jan-01 17:29:20)

Thanks for sharing, guys - I'll use what I've got for now... (n/t) (george brown) (17-Jan-01 17:29:30)

Check out a Borla muffler...I have a 2" one and a 1 1/2" Berg system on my 1776 that I really like. (n/t) (Craig Merrow) (17-Jan-01 17:30:35)

Flowmasters can drone like crazy, how many chambers? Super Turbo is my choice. (n/t) (Lanny) (17-Jan-01 20:10:55)

Flowmaster! 2 1/4? and a small Berg(Flwmstr) one for my turbo motor 2 chamber. (n/t) (Panel) (17-Jan-01 22:07:48)

Hey George..... I have a similar car and if you have the rear suspension lower than stock, You may run into ground clearance problems. I am running a stinger with a baffle that does'nt have

much of an upward angle to it and I have to watch where I go or it will scrape. I was at the Bug Jam here in Florida, and the guys with lowered cars and the type of muffler you are looking at

had only a few inches of clearance I don't think These would work for me unless I raised the rear back to stock hight .(o\/o) (n/t) (Fl. Tom) (18-Jan-01 12:06:41)


From what I've read, the sizing of the primaries is most important to create the bump in torque and to not lose too much bottom end. The

secondary isn't that critical. In one example in my book "21st Century Performance" by Julian Edgar (KILLER BOOK) he does a dyno

comparision on a 5.0 Holden w/ I think 1 5/8" primaries. They gained horsepower with each step up from 2" all the way up to 3.5". There was

NO reduction in torque or a lower of the torque peak with the larger exhaust secondary setup. In my headers by Ed comparision sheets they don't

make it sound this simple, but proper primary sizing is most important. If you already have the 2.25" then run it. If you need to buy another

muffler, buy a 2.5" or 3" because you shouldn't lose any bottom end from it! (stepping up to a 1 3/4" would most likely result in loss of bottom


Steve Arndt


I am not going to use a Turbo muffler. From what I've read they have a huge pressure drop compared to a straight through modern muffler design.

Why run something designed for the Corvair in the early 60s? The muffler section is also covered in detail on and in Julian

Edgar's book.

I am going to use a 3.5" core cat, and a 3" straight through muffler on my 1 3/4" merged system from TG Fab. This is on my 2599 Typ Vier

conversion in my beetle project. This will allow all components to migrate to a low boost turbo setup in a year.

Steve Arndt


I have some experience regarding mufflers, exhausts and such. I should preface this by saying it is limited experience. Two motors, 3 headers, a

couple of muffler and megaphones, during two different dyno sessions. I'm no expert, but I'll share what I learned, and pass on some info shared

with me by others.

My first experience was with a 2165cc race motor, (78X94 12:1 comp, 48mm intake valve, .615 lift (at the valve), 328 duration, 110 lobe

centers, advanced 3 degrees on the intake lobe, 48IDAs w/40mm chokes, 1 5/8 S&S header 32" primary tubes, small megaphone) I was shooting

for 200HP. Roger Crawford (Heads up Performance, Fullerton, CA) broke the motor in and proceeded to make small changes to timing and

jetting to find the "sweet spot" for this particular combination. From his experience, he swaped out the header 1 5/8" for a 1 3/4" Pheonix unit

(also 32" primary tubes, but larger collector and megaphone). It managed about 185HP at 7K rpm. I was a little disappointed, but hey, Roger still

had some ideas, and we were cetainly moving in the right direction. He bolted on a 2 1/2" muffler, and it made more power than the stinger! A

little jet change, and we were at 202 HP @ 7K rpm. I bought the muffler and the header. I think this combo liked a little back pressure.

Second case: I built another motor with the same spces as above, but used an 86mm crank for 2386cc. I dynoed this engine at Geoff Hart's shop.

Geoff thought this larger displacement combination wouldn't like the 1 3/4" header, so I borrowed a 2" Berg unit. You could see a difference in

the torque curve between the two. With the smaller header, it made more torque below 5K rpm, but wouldn't pull much beyond 7K rpm as the

power really fell off, as compared to the 2" header. (Geoff uses 5K 6.5K and 8K as test points) We got every thing set up around the 2" system

w/megaphone, then I started to play with mufflers. The 2 1/2 muffler I brought along, would'nt bolt up to the Berg flange, so we "C" clamped it on

the 2" header. It didn't like it, as upper rpm torque went "in the tank". Geoff had a 3" Dynomax tube muffler that we tried, gained about 2 hp

(probably within the error bar of the test, so no change) I then switched back to the 1 3/4 system and 2 1/2 muffler (the one that worked so good

on the 2165cc engine, above) Again, the lower rpm torque improved, and the usable rpm range went from 5K down to 4.5K, but the upper end of

the usable range really went down, also, as the torque fell off even more sharply above 7K, than the 2" hedaer w/ 2 1/2" muffler.

I spoke with Brian Hyerstay (NHRA G/Dragster record holder, 167?cc VW powered) at an event. He claims to have tried 10-12 custom exhaust

systems. When I ask if there was really that much power to be gained, he gave me one of those silent looks while nodding his head and smiling.

Further evidence is the custom "over-the-top" exhausts showing up lately on Pro Stock VWs, with shorter primary tubes. Anothe rlittle known

fact, is some teams use an inserted venturi in the collector of the header, in an attempt to improve performance. One guy that I know does this,

owns a dyno, I'll bet he does it because it works!

My conclusions: Every engine has an exhaust system that is too big for it, and one that is too small for it. Also, intended rpm range is a big part of

the equation. From my experience, above, the 1 3/4" system would have been better on the street, sacrafice a little high rpm torque for a little

more down low. Mufflers (or a restriction after the collector) make a difference. How great that restriction is makes a difference. Both dyno

operators asked the same questions before recommending an exhaust size (to use as a baseline) Engine displacement, Intake valve size, cam

specs, compression ratio, at what rpm I intend to use the engine at. These items must have the greatest influence on the exhaust system needed. I

also conclude that at street operating rpm, with some high rpm blasts, close is good enough. If you are "Heads up" racing (PRA Pro classes,

NHRA heads up classes), and 10 lb/ft of torque at 8000 rpm horsepower makes a big difference, then you need to experiment on an engine dyno

to find the best combination(s). But, someone with (more dyno experience than I) can get you real close from their past experiences. Good luck!

Tom Simon


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