With the recent thread about installing a straight through muffler, such as a Borla, Dynomax, or what not into the midpipe, I've recently had one installed.

Initially I had just a straight midpipe. Incredible power, but incredible noise as well. I then installed a high flow cat, nice deep exhaust tone, no smell, great torque, but noticeable drop in HP. How much? I measured a 20-30 RWHP drop from the straight midpipe.

So recently I installed the straight through muffler in the midpipe with great anticipation. It's louder than the cat, doesn't have as deep as an exhaust tone, but it's much better than straight MP. Horsepower numbers? Well get this, I measured the exact same as with the cat; 20-30RWHP drop compared to the straight MP!! This doesn't make sense.

Now I'm confused. I thought the straight through muffler would only result in a slight decrease in HP from the normal straight midpipe, but the numbers aren't agreeing. I've heard alot of talk about numbers but has anyone actually "measured" the HP difference after they installed their midpipe mufflers???

If anyone else has measured similar RWHP levels before/after with the midpipe muffler, please let me know!

 

Which muffler did you use?

 

were these tests done on a dyno?

I have on a midpipe with a borla XR1 in it and notice very little difference at all than without it

 

A Borla XR-1 Muffler will yield better performance than a $10 muffler found at the local mom & pops autoparts store....

 

Probably because you're going from a laminar flow to a highly turbulent flow. Makes a big difference in pressure. I Did fluid dynamis in my degree, and air (in this case exhaust) acts in a very similar way as fluid.

 

Interest find. I was considering doing the same thing and depending on noise level I might still take it on. Anyone else have any data on this?

 

air IS a fluid.

(but it's not a liquid, which I guess is what you meant)

 

wait, you took a fluid dynamics course, and you don't know that air IS a fluid?

 

Did you do the tests back to back on the same day? Perhaps the calibration was different for each dyno if done at seperate times. You wouldn't be able to compare readings then. Also, what sort of setup do you have? Straight vs. muffler in the midpipe would have different results with the twins vs. a single too with the twin manifold being so restrictive to begin with.
Michel

 

I believe the muffler is a Dynomax, and it's definitely a straight through. It's installed into the midpipe. The rest of the exhaust system is straight through DP, with an Apex N1 can.

The measurements were made with the GTECH. BUT Before anyone discredits the GTECH, let me say that I've learned the proper way of using the device for getting HP numbers (most people don't know how, simply because it doesn't tell you in the manual). Anyhow I've always GTECHed my car right after each dyno trip, and the numbers have always been dead consistent with my dyno numbers within 1-3RWHP, so I know it's a trustworthy device. I can usually do 5 GTECH runs consistently all within a few HP of each other, and of the dyno results.

Anyhow, I'm running the stock twins. Here's the thing, the day before I installed the hi-flow cat, I measured the RWHP @12 psi using my GTECH. Then immediately after the installation of the cat, I measured again and noticed an overall 25-30RWHP drop. Oh well I figured, it's to be expected. After I got the new Dynomax muffler installed into the midpipe in place of the cat, I was expecting the numbers to go right back up, but it's been exactly the same as it was with the cat.

There's been nothing but rain all week (except yesterday), so I'll try to make some more measurements to confirm the findings. I know it doesn't really make sense.

Has anyone else made actual measurements with the mufflers? Any tangible numbers? Most of the comments regarding this setup on the forums have usually been along the lines of "it should flow similiar to the midipipe with very little power loss" but I haven't seen anyone who has data on it.

 

I would rather have turbulent boundary layers in an exhaust system because the flow would be more likely to stay attached around the bends. Besides, you'll trip the turbulent BL way before the midpipe!

 

what is the proper way to use a G-Tech?
have you used the new one (that sells for like $250)?

 

are you getting the same amount of boost w/ the muffled midpipe as w/ the regular mp?

btw, you should post this in the single turbo forum as well. they might be able to answer why you're getting considerably less hp.

 

You need to get you A midpipe (with A resonator).
They are as quiet as the stock main cat!It raised my boost from 10 to 11.-11.5 lbs.

 

That hp number would be correct..I've seen as high as almost 40 rwhp peak gain with a midpipe over a HF cat..only it's over 6K rpms - under that the HF cat will consistently have 20-25 rwhp more than the midpipe - again, another tradeoff. I had a midpipe for a few weeks with non-sequential stock twins and my car ripped above 6K rpms but was pretty doggy before that - I installed a good HF cat and had a lot more power in the low and midrange.. a lot more torque it felt like..but noticed a dip in hp up high although it wasn't too significant. Believe it or not on my car, the HF cat makes it feel more zippier. I know it's different with most other FDs though.

 

Am I the only one on the forums, out of hundreds and hundreds, whose actually tried to measure the HP difference between a straight midpipe and midpipe with muffler??

 

Nope, it was done before but I have the links at home. Basics from his dynos it shows the 30HP shift to from the mid to high end when using a strait pipe.

The Borla XR-1 is the most common muffler to weld in. Only a small handfull have the Dynomax. You could also use the Edelbrock Victor Race muffler #5539 which someone mentiond has better internals to handle the heat. I asked both Borla and Edelbrok about this but received no reply.

 

are you sure its between a midpipe and midpipe+muffler NOT a high flow cat? The only reference that people keep making is to Wael's dyno tests awhile back ago, but those results apparently were due to other tuning issues more so than the exhaust. Please post up the links, since most people are saying there shouldn't really be any significant power loss over straigh midpipe.

 

goracer, which muffler is that one in the picture you just posted?

 

Edelbrock Victor Race muffler #5539

The dyno chart was with hi-flow cat (not muffler) vs mid pipe. I still can't find the link though.

 

well the only feedback I've gotten was the suggestion that it may not be so much the muffler being too restrictive (since it is a straight through) but rather that it's more restrictive than just a straight pipe, and enough to change the air/fuel ratio...ie/running richer than before.

 

Looks like my butt dyno numbers were about right with the Dynomax Ultra Flow. $79.00 at your local hot rod shop with a $20.00 Internet rebate.

"But how can it work because it's so inexpensive and isn't one of the big ricer brand names?"

 

the perfect combination is what I have:

dp
mp
apex gt exhaust
apex gt silencer

With this setup I get good hp, good torque and believe it or not quiet as stock from the inside

When I want loud and feel like going fast, off the silencer and watch me peel from 2nd to 3rd!

 

the perfect combination is what I have:

dp
mp
apex gt exhaust
apex gt silencer

With this setup I get good hp, good torque and believe it or not quiet as stock from the inside

When I want loud and feel like going fast, off the silencer and watch me peel from 2nd to 3rd!

 

Yes, but do you have actual numbers, or just going from observations?

I'm surprised to see that out of all the people on the forum, a very small percentage seems to have actual numbers (ie/ dyno or at least GTECH).