Apexi

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!

nocab72

Did you tune before/after swaping MP, Muffler, Hi-Flow Cat? I measured a 40-50rwhp gain by removing the silencer in my JIC Bullet. I believe the majority of this gain was due to the increased flow and higher ARF's.

I conservatively tuned for 11.2:1 with the silencer in.

I removed the silencer and measured the 40 - 50rwhp gain and a AFR of 12.2:1 !!!

I figure 30rwhp of the gain was due to running leaner.

In your case, it is probably the opposite, you were tuned for 11.5 with the midpipe. Adding a more restrictive muffler or high-flow cat, reduced your ability to "flow" and probably dropped your AFR's below 11:1. That would account for 1/2 your HP lose. By leaning the car back out after putting the muffler or high-flow cat on, you should be able to gain back 1/2 of the HP you lost (10- 15rwhp).

Hope this lends a possible bit of insight to WTF is going on with your car and exhaust flow...

k

Astro

yikes!
i thought the borla, etc only caused like a 5 hp loss at the most.
Hmm..may have to rethink installing one now

Apexi

well yes in theory. Problem is, seems like not many people have actual data to support before/after results using the midpipe mufflers. Some guys have done some tests with high flow cats, but none seem to have done it for the mufflers, which is kind of surprising with all the hundreds of members on the forums.

Well I shall be the first one then. I did some further testing yesterday and the results seem more positive. Closer to how it was before, with only 5 HP difference, but I need to do some further testing to make sure. I'll update you guys when I find out.

forcefed7

I have done actual testing, on the subject. On my car with a PFS cat back, and center muffler (Borla) I didn't gain ANY HP when I removed them and ran just a 3" down pipe on the dyno. Without the exhaust it did seem to pull a little cleaner, but the car was making 620rwhp at the time. I've done through cat back and center muffler over 650rwhp. So at lower power levels I wouldn't expect to see any losses when installing a center muffler. Just my experiences.

-Ray

Cheers!

how does the flow rate and exhaust gas velocity differ between the straight through borla/dynomax compared to a presilencer (ie Racing beat )?

Apexi

Ray did you mean 3" straight midpipe? So you've actually done before/after dyno pulls between straight midpipe and midpipe with muffler and didn't notice any power loss/gain??

Apexi

while on this topic, just wondering if anyone has actual numbers of what kind of power difference the following would typically make:

1. poor spark plugs
2. dirty intake filters
3. running a little too rich

From my experience, I know a loose plug wire can easily account for 50-60RWHP, and running too rich can account for 10-15RWHP. I don't have any experience or know what fouled plugs or dirty intake filters would do.

rx7racer11

um.. wg

forcefed7

This was early summer when everyone was saying I was full of crap when I posted my dyno sheets, and wanted be to back up my numbers on another dyno. Well, we went to another dyno to verify the numbers. I can't remember the exact numbers it laid down, but it was like 618rwhp with a 3" catback and a 3"center pipe with a borla welded in. I took the cat back and the center muffler off and bolted on a 3" side pipe, so with no exhaust (mufflers) it only picked up like 3-5 HP, it was hard for even us to believe such a small increase. That was at about 30-32 psi of boost. I personally would run a center muffler, I can't stand how loud the cars are with just a center pipe.

Jodeny

iTrader: (3)

Who welded the muffler on. Sometimes muffler guys weld the exhaust pipe INTO the nipple of the intake or exit of the muffler. If they stick the pipe inside too far it actually cuts off flow and chokes the exhaust. Take a look at if the exhaust pipes are inside the muffler or just welded seam to seam (as they should be).
John

carcrazy

I have accomplished testing with the same results. I had a high flow cat (Random Technologies) with a Greddy SP exhaust. The exhaust sound was extremely loud! I was running 393 rwhp. They installed a Dynomax muffer (3") and immediately dyno'ed with the same results - 393rwhp. With some more tuning a/f, they got 403rwhp as the original setup was rich to begin with.

regards

Rick

Jodeny

iTrader: (3)

.............but the gtech is accurate............................
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John

Apexi

Does this mean that your midpipe muffler technically resulted in the same power loss as a high flow cat? In other words, I'm wondering if installing the dynomax muffler resulted in similar HP numbers as the original straight midpipe.

It wouldn't make sense that the Dynomax straight through muffler which is high flowing would result in the same power loss as the much more restrictive cat.

carcrazy

I would of thought the Dynomax muffler (3" in/out) would be much more power than the cat - I was wrong. Looking at the muffler is quite awesome. It is a fairly short box with a 3" straight thru design. There is virtual no back-pressure at all. There is a big difference in sound pressure though. Either my Greddy SP exhaust is the limiting factor or the Random Technologies cat is quite good!

regards

Rick