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As the title states I put a dual in/out flowmaster 40 series in place of the resonator and deleted the stock mufflers. The sound is great!

The problem is the butt Dyno makes it feel like I’ve lost power on the lower end. Kinda feels like the exhaust is restricted. Maybe it’s the tires are spinning more (lol) or the computer adjusted timing because of a more free flowing exhaust.


I drove it around for a bit today and I kinda want the stock exhaust back on. It’s only been a day and maybe it just needs some breaking in.

Any thoughts on this set up? Anyone ever run this setup before on an LS motor?
 

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Butt Dyno is not the most accurate but if it feels slower, it's less fun for sure, so from that perspective it is very accurate.

Flowmaster mufflers are not known to be the best flowing and I would guess that dual in/out doesn't flow any better than single in/out. Just more pipes on ends of it. You could install x or h pipe in place of that muffler and see how it feels. Just for fun of it. If it feels better on butt dyno, there is your answer. It may sound pretty good too.
Most people think h pipe sounds better than x pipe. Universal h pipe kit can be found super cheap. Around 30 bucks.
 

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the noise and vibration are just messing with your head. at most you lost a few horsepower, and you won't be able to tell the difference.
I agree. On the few rare instances that I ran open headers, it 'felt slower' but I think that's just my mind paying attention to the noise over the accelleration.
 

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I agree. On the few rare instances that I ran open headers, it 'felt slower' but I think that's just my mind paying attention to the noise over the accelleration.
I bet you felt it just right. Open headers will make less hp at low and mid rpm and feel slower. It's only at high rpm WOT that open headers make more power. Especially on stock engine. With big cam that equation changes a little.
BTW, louder usually feels faster to your brain.
 

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many of the muffler tests i have seen show a gain pretty much everywhere when restriction is eliminated, not just up high.

if you run a full exhaust, if the piping is oversized (like a 3" exhaust on a stock motor, for example) you will lose low to mid range, but even in this scenario, the loss is generally in the single digits. generate more power, that loss becomes less as more gas is travelling through the exhaust system. I think on a H/C/I LS, even though 2.5" exhaust is supposedly good for well north of 500 horsepower, you will not lose anything with a 3" system.

with an open header, you want some added collector length, or you lose a lot of torque. that resonance provided by the extra "chamber" that the exhaust sees matters a lot. you want mufflers and and an exhaust system on a street car, so at that point it simply doesn't matter. the exhaust no longer "sees" the collector length. running open headers with a header designed to be hooked up to an exhaust system is a no-no. you want to stick an 18" pipe on there, or really do the math and see what the engine will want to see at the end of the exhaust system.

best case for a street car, power-wise, is running the right size piping with straight through mufflers. i used to think certain types of chambered mufflers flowed just as well as a straight through, like a spintech, but i kind of doubt that at this point. i remember reading on LS1Tech of the mufflex dudes (a y-pipe system that uses a single spintech muffler) gaining like 20 hp from dropping the system. The muffler is obviously too restrictive for that system, and mufflers like the 6000 and 9000 series flow much better, but they are still chambered mufflers that have obsticles to airflow. With any chambered muffler that is the correct piping inlet/outlet size, at worst you lose nothing, at most you will be at a loss of a few horsepower. On a street car, if that really matters to you, then you should probably get straight through mufflers and have the extra few horsies at 6000 rpm. most people won't even notice the loss, and will enjoy the sound much better.

so 90% of the time, unless becozracecar, go for what sounds best.
 

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I personally think most of the muffler test I've seen are useless. They usually say something like; with spintech mufflers hp loss was 4 hp and with magnaflow was 2 hp and with flowmaster was 5 hp without going into details of where in rpm range was the hp loss, average or peak hp loss, muffler type, size, engine configuration, etc...
To say that chambered mufflers are more restrictive compared to straight through mufflers is misleading. All you have to do is exaggerate to see that this theory doesn't hold water. For example, if you have 1" diameter straight through pipe muffler, will it flow more compared to chambered muffler that is 20" x 20" x 6" with internal openings that provide say 60 square inches of free flowing area? The obvious answer here is no. It is matter of sizing it correctly.
No different from tubing sizing. If you are running 500 hp +, 2.5" tubing starts to be restrictive. Under 500 hp, it does the job as well or better compared to larger tubing. Between 500 and 550, best tubing size probably depends on other factors like cam, heads ports type, etc...
Intercoolers are another good example. You would think they are restrictive no matter what, with all those small passages and fins, but make it big enough and it flows just fine.
Unfortunately, it is very hard to know exactly which muffler would perfectly mach any given configuration. Best is to call muffler manufacturer, give them all the available info, and hopefully they can recommend correct muffler for any given application...
This is just my take on never ending mufflers theories. Not saying it's right or wrong, not muffler expert here, just my 2 cents.
 

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I personally think most of the muffler test I've seen are useless. They usually say something like; with spintech mufflers hp loss was 4 hp and with magnaflow was 2 hp and with flowmaster was 5 hp without going into details of where in rpm range was the hp loss, average or peak hp loss, muffler type, size, engine configuration, etc...
To say that chambered mufflers are more restrictive compared to straight through mufflers is misleading. All you have to do is exaggerate to see that this theory doesn't hold water. For example, if you have 1" diameter straight through pipe muffler, will it flow more compared to chambered muffler that is 20" x 20" x 6" with internal openings that provide say 60 square inches of free flowing area? The obvious answer here is no. It is matter of sizing it correctly.
No different from tubing sizing. If you are running 500 hp +, 2.5" tubing starts to be restrictive. Under 500 hp, it does the job as well or better compared to larger tubing. Between 500 and 550, best tubing size probably depends on other factors like cam, heads ports type, etc...
Intercoolers are another good example. You would think they are restrictive no matter what, with all those small passages and fins, but make it big enough and it flows just fine.
Unfortunately, it is very hard to know exactly which muffler would perfectly mach any given configuration. Best is to call muffler manufacturer, give them all the available info, and hopefully they can recommend correct muffler for any given application...
This is just my take on never ending mufflers theories. Not saying it's right or wrong, not muffler expert here, just my 2 cents.
i pretty much agree. loss is pretty minimal if you did your homework and picked the correct sizing. the whole thing with chambered and the stock style mufflers is the odd path the exhaust must take to escape, which provides the sound reduction effect, but also does provide a certain restriction. that restriction is pretty minimal if the muffler is large enough for the application, as you said.

in the end it probably doesn't matter unless you are really worried about 2-3 horsepower, or if you are making an absolute ton of horsepower. like 900hp turbo guys saying they gained 40 hp when they switched mufflers. i can believe that. bolt-on LS guy? it's like 2 hp, if that.

take for example the latest engine masters muffler test. they did a 600 hp cleveland motor farting through 2.5" pipe sizing. at that hp level, you usually want to go with a 3" pipe. they made it restrictive intentionally to exaggerate gains/losses. on a 400-500 application, the differences they displayed would be a lot smaller.
 

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Discussion Starter #9
Thanks for the input everyone. I've had the exhaust for awhile and I really like it. Just had to get used to hearing exhaust vs engine I guess. Car has plenty of power.
 

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Butt Dyno is not the most accurate but if it feels slower, it's less fun for sure, so from that perspective it is very accurate.

Flowmaster mufflers are not known to be the best flowing and I would guess that dual in/out doesn't flow any better than single in/out. Just more pipes on ends of it. You could install x or h pipe in place of that muffler and see how it feels. Just for fun of it. If it feels better on butt dyno, there is your answer. It may sound pretty good too.
Most people think h pipe sounds better than x pipe. Universal h pipe kit can be found super cheap. Around 30 bucks.
The dual in dual out flowmaster was put in place of the resonator (same spot) and just straight pipe out the back. It's supposed to be a resonator and muffler all in one or at least that's what it is doing. Car sounds just loud enough.

I see you have chrome stock 17" wheels and they look nice. Bought my car with the same wheels. They have grown on me and I don't think I'll change them out.
 

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I see you have chrome stock 17" wheels and they look nice. Bought my car with the same wheels. They have grown on me and I don't think I'll change them out.
Yes, they look nice. Even nicer when car is in motion. Check out on this video;
I moved on to 18s, wider wheels for racing. And now have big brakes coming, so 17s will never fit again. Probably going to sell it soon...
 

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Yes, they look nice. Even nicer when car is in motion. Check out on this video;
I moved on to 18s, wider wheels for racing. And now have big brakes coming, so 17s will never fit again. Probably going to sell it soon...
Good stuff. Nice to see you're moving that heavy beast.

I was considering widening the stockers in the rear.
 

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Good stuff. Nice to see you're moving that heavy beast.

I was considering widening the stockers in the rear.
Yeah, that was my first race last year. Still on all season tires and no sway bars.
Car got quite a bit faster since then.
I see lots of guys widening the wheels and no reports of wheels breaking, so it should be fine. Maybe it would make me think twice about going really fast, like 150 or more.
Stockers are kinda heavy tho. And limited room for big brakes. Sometimes it’s not a bad thing to think about future upgrades...
 
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