Above diffuser muffler - LotusTalk - The Lotus Cars Community
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post #1 of 16 (permalink) Old 03-20-2019, 08:35 AM Thread Starter
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Above diffuser muffler

As the title says, I'm looking for a cheap above diffuser muffler.
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post #2 of 16 (permalink) Old 03-20-2019, 09:53 AM
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I am a massive skeptic of the value of these $700+ exhausts. I just used a $90 Magnaflow, some tubing, and some doodads, and I am thrilled with it. It is a bit loud when hitting redline but otherwise nice, which is perfect in my mind. It weighs within a pound of the lightweight guys, and who gives a care that it isn't rebuildable - it costs $90 for a new one for crying out loud.

Okay, rant over, haha.
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post #3 of 16 (permalink) Old 03-20-2019, 09:55 AM
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That didn't show the tip, so here is my original setup. I started with brackets, but I like the rod better.
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post #4 of 16 (permalink) Old 03-20-2019, 11:16 AM Thread Starter
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Originally Posted by cyow5 View Post
I am a massive skeptic of the value of these $700+ exhausts. I just used a $90 Magnaflow, some tubing, and some doodads, and I am thrilled with it. It is a bit loud when hitting redline but otherwise nice, which is perfect in my mind. It weighs within a pound of the lightweight guys, and who gives a care that it isn't rebuildable - it costs $90 for a new one for crying out loud.

Okay, rant over, haha.
I was just reading some threads about magnaflow mufflers, did you use the 14"?
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post #5 of 16 (permalink) Old 03-21-2019, 05:41 AM
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I was just reading some threads about magnaflow mufflers, did you use the 14"?
I honestly don't remember, but I can try to remember to measure it for you. I think I also extended the exit pipe into the muffler, too, which effectively shortens it. Tuneable sound

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post #6 of 16 (permalink) Old 03-21-2019, 06:06 AM
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Originally Posted by cyow5 View Post
I am a massive skeptic of the value of these $700+ exhausts. I just used a $90 Magnaflow, some tubing, and some doodads, and I am thrilled with it. It is a bit loud when hitting redline but otherwise nice, which is perfect in my mind. It weighs within a pound of the lightweight guys, and who gives a care that it isn't rebuildable - it costs $90 for a new one for crying out loud.

Okay, rant over, haha.
Someone with common sense finally speaking up
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post #7 of 16 (permalink) Old 03-21-2019, 06:35 AM
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Well I never!

but I might on the XJS restoration... Thanks, I was wondering about that route!

L O T U S
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post #8 of 16 (permalink) Old 03-21-2019, 08:10 AM
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Think this thread just saved me $600+. I was just looking at those $700 mufflers.

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post #9 of 16 (permalink) Old 03-21-2019, 08:15 AM
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Interesting use of closed turnbuckles for your diffuser. Now I know how to repurpose some of my boat turnbuckles when I get around to getting a diffuser.
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post #10 of 16 (permalink) Old 03-21-2019, 09:22 AM
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Originally Posted by Catsailr27 View Post
Interesting use of closed turnbuckles for your diffuser. Now I know how to repurpose some of my boat turnbuckles when I get around to getting a diffuser.
At first they were out of necessity - the diffuser tabs at the clam were broken - but I love that I can actually adjust the angle of the dangle. I have since added a second horizontal plane so I have a dual plane diffuser with enough rigidity to not need the license plate mount. This gives me a couple inches of adjustment, but the turnbuckles do rattle if they aren't preloaded or have rubber added in the right places. That's just due to my cheap selection. When it is all painted and cleaned up, I am going to make a thread for it.

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post #11 of 16 (permalink) Old 03-21-2019, 01:14 PM
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Think this thread just saved me $600+. I was just looking at those $700 mufflers.
Yeah, no catback is worth more than $200 on a Lotus. There's just not that much material there, and mufflers and pipes size directly to horsepower produced, because horsepower in turn correlates directly to fuel and air burned in an Otto cycle engine. If you're paying more than $200, you're enriching somebody instead of improving your car with the difference.

If you do a little quick math using the most optimistic numbers (2 litres for a 2ZZ, 9000 RPM, 100% VE) you get the grand sum of 9000 litres/min = a bit less than 320 CFM. That's it. The world is full of inexpensive, decently made mufflers meant for half a high performance 5.7+ L V8 that will work very well indeed on a 2ZZ ([email protected] = 301CFM) . The hardest part is packaging, but Lotus was pretty generous with space behind the engine, so it's not that bad.

Yes, you need higher flow if you have a supercharger. The math isn't any harder, and there are still plenty of cheap mufflers that will do the job.

I went through a version of this excercise on my Corvair van with a warmed-over engine back when. Stock replacement mufflers were restrictive, expensive and an odd shape. I wanted to retain the stock mounts and form factor because of bodywork. Some quality time with the Walker catalog found the OE replacement muffler for a six-cylinder Ford Granada. What was probably an unpleasantly restrictive muffler for a 250 CI low-perf engine was the hot tip for a 164 CI higher-perf engine. Sounds great, too (yes, I have gotten compliments), because the muffler dumps straight out the back of the van with a 6" long tailpipe. Cost? About $50 all up including tubing adapters and clamps. Now admittedly, it's not stainless steel, so will rust out every 50k miles or so, but it's a 1965 collector van, so 50 k miles is 15-20 years.

Exotic money for mufflers for exotics is not a new thing - my father tells me that an Abarth muffler for his Fiat 600D (which was the same part as on a Fiat-Abarth Zagato 750, among other things) was something like $150 in 1963. He went with a custom welded header and glass pack instead, changed the glass pack every year when it started getting too loud, and bought a new set of Pirelli Cincuratos (which did more for the car than any muffler) with money to spare.

Note that this has nothing to do with header/collector/cat selection, which is pretty close to optimized on the NA 2ZZ, but has room for improvement on supercharged or highly tuned engines, as BOE's research shows.
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post #12 of 16 (permalink) Old 03-22-2019, 08:11 AM
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Originally Posted by steelypip View Post
If you do a little quick math using the most optimistic numbers (2 litres for a 2ZZ, 9000 RPM, 100% VE) you get the grand sum of 9000 litres/min = a bit less than 320 CFM. That's it. The world is full of inexpensive, decently made mufflers meant for half a high performance 5.7+ L V8 that will work very well indeed on a 2ZZ ([email protected] = 301CFM) . The hardest part is packaging, but Lotus was pretty generous with space behind the engine, so it's not that bad.
You are ignoring the expansion of the gasoline from a liquid to a gas as well as the thermal expansion of the gas from combustion. It is a little more complicated than just figuring an air pump.
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post #13 of 16 (permalink) Old 03-22-2019, 11:30 AM
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I am using a FLOWMASTER PRO SERIE 3", 13016100 on my elise K20 Turbo... nice muffler with a turbo. The turbo is removing heat from the exhaust flow and the muffler sound like lasting quite well. My exhaust tip is passing thru the diffuser early to reduce the noise level.
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post #14 of 16 (permalink) Old 03-22-2019, 03:12 PM
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You are ignoring the expansion of the gasoline from a liquid to a gas as well as the thermal expansion of the gas from combustion. It is a little more complicated than just figuring an air pump.
Ha! I wondered if anybody would catch that. Yes, and you know what else I'm ignoring? That exhaust flow starts off at an elevated pressure and temperature but dumps into an ambient temperature, ambient pressure plenum. You're ignoring that I did the flow estimate for the 2ZZ-GE with a (larger) engine that doesn't exist: Two litres at 9000 RPM.

Flow capacity of a pipe at a maximum delta-P of 1 ATM is rather different than at three times that, and 3 ATM momentarily at the exhaust valve is not an unusual value. Add in that a chambered muffler is full of expansion plenums, and you really care a lot less about exhaust pressure in a (non-turbo) Otto cycle engine than you do about intake tract restriction from a performance perspective, because gas is very compressible, and exhaust cools (and contracts) as it leaves the engine - we wouldn't need all that heat shielding in the back of the car if it didn't.

Further, the point I made using an extremely optimistic flow estimate for the 2ZZ-GE as evidence remains equally valid regardless of how exact the calculation of exhaust volume is: that half a 5.7+ litre high performance V8 engine needs as much or more exhaust flow capacity as a 2ZZ-GE. The strength of this argument is not affected in the least by the actual CFM of exhaust gas at any particular pressure and temperature in the exhaust tract.

If you want to do the estimations and give me a L/min exhaust flow value for the 2ZZ-GE at 9000 RPM and 100% VE, I will ask: is this number greater than the same calculation done for half the 2005 Corvette base engine (LS2) at rated power (6000 RPM)? My math suggests no: I get 8950.5 L/min with the same calculation that gave 9000 L/min for a 2 litre engine at 9000 RPM.

Therefore, I must conclude that an aftermarket muffler sufficient for dual exhaust on a 2005 LS2 will also be sufficient as a single muffler on a normally aspirated 1.8L 2ZZ-GE at 8500 RPM.

@elise/europa - that looks like a very practical installation for a turbo'd engine. a 3" 'big engine' muffler should give good sound and low backpressure to the turbo.
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post #15 of 16 (permalink) Old 07-11-2019, 02:52 PM
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I have a cheap Larini 6"!
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post #16 of 16 (permalink) Old 07-12-2019, 10:51 AM Thread Starter
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I have a cheap Larini 6"!
I actually ended up cutting the tail pipe off of my stage 2, and having a small elbow welded on to exit above the diffuser.
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