You say you work on turbo cars yet you're asking such an amatuerish question.

Something's not right here.

 

You are 100% correct and I just verified this in a different situation. After installing my DP, I put on a catback with a straight through *free flow muffler* (not as radical as cutting it off). I could really feel the lack of throttle response and in general what appeared to be less lower end torque. At first I thought this was *in my head* and I did verify (60-100 timed run) that my TOP END was possibly slightly better than the DP alone.
I finally decided to put on a silencer (READ>>RESTRICTION) on the muffler's 4" tip, but modified it for top end power by drilling holes in it (less restriction). Man was I surprised! The throttle response was amazing! Night and day! People will say a Turbo needs unrestricted flow PERIOD....not with this car! I guess with lower gas temps out the muffler, you need some narrowing (ie, restriction) to keep the velosity up. Whatever the reason, Muffler delete or a huge straight through muffler will HURT throttle response...unless you're pushing some serious HP with a bigger turbo.

Here is a pic of the modified silencer:

I drilled 4 holes in the front plate as well.


Before:



After (you cant's see the holes in the back plate in this view):

 

my car actually felt quicker, losing about 20lbs had something to do with it, these cars love you back when weight is removed, and it's never loss any pressure, it's always been between 14 and 16.5 when I hit it hard, but I don't do it for long and when I do it I rarely look at the pressure gauge, as long as it still feels fast I'm happy

 

My straight exhaust is way better. There is no backpressure. I think its all in how its tuned.

 

Very true.
BUT....are you SURE you haven't lost throttle response in the lower rpm range? Off the the line?
I can only relate how my car responded....very similar to the OPs.
I was just surprised by the dramatic increase in throttle response with the silencer added..amazing. BTW, my top end didn't suffer at all either. I think I *invented* a *dual* action silencer! In lower/mid RPM range the central smaller tube is working. As the exhaust flow increases with higher RPMs, the gases are further routed around the space between the inner tube and the larger original exit pipe and forced out through the holes in the plates around the tube. I can actually hear a neat *whistle* sound as exhaust is forced through the holes on WOT

 

I found that with the free flow muffler, boost was unchanged. With the silencer on, the boost is still the same but much more stable... ROCK STEADY...doesn't spike much and really stays put at 20-21 lbs. The needle doesn't waiver as much as it did either stock or with straight through muffler.

 

To be honest, I drive my car like a 2 strok dirtbike high rpm when I want to move out. Throttle response has improved across the whole RPM range. I notice less of a difference owhen I use the "stock tune" on the trifecta. I notice less responsiveness in general even before the straight exhaust with the "stock" tune. It runs at less psi and doesn't take advantage of the free flowing exhaust. The 22psi tune is very very responsive becuase the turbo spools so darn fast.

 

lols at the concept of losing power from a muffler delete....

That like replacing a tubular segment of the exhaust somewhere else with the same exact diameter of pipe and saying it lost power/trq.

 

Joe..

You can gain torque lower down and lose HP on top. You can also do the opposite. That's the *conundrum* of exhaust theory. I'm not gonna go into it here..do a search on the topic when you have a LOT of spare time.
I can say WITHOUT a doubt I lost throttle response with the larger exhuast (muffler) and gained a ton back when I restricted the tip with the silencer. My 60-100 (read>>high rpm) run with full open muffler was maximed, so I didn't lose HP with it...just lower end torque.
Yes, you can have that scenario. It effects day to day driveabilty..unless you drive like
RyRidesMotox ..reving the **** out of it.
BTW..this mod with the silencer (and Catback with DP mods) is AWESOME...I wish you could drive it. It friggin takes off at the SLIGHTEST TAP of the throttle...in any gear.

 

Yep..I figured you were reving the **** out of it. If you try and drive *normally*...in part throttle situations, you'll see what I'm talkin' about.

 

I do drive normally. I have traffic on the way to work. I only rev the **** out of it when I get on the freeway... GOtta speed up to merge everyone knows that hehehehehehe. But seriously I really think that something was wrong with the OP's car because mine lost no power with the straight exhaust. The thing you have to know about torque is that the design of the exhaust matters. Like scavenging headers from hooker or edlebrock work better than stock for torque. I can't tell you the exact reason just that mine is running damn good without the muffler and cats.

 

I had the total HP with the free flow muff...60-100 times were very good. Just that part throttle responses were sluggish. In my car..as most tuned here...the torque curve is biased at lower/mid rpms. I know mine is for sure ..take a look:



With larger pipes and the free flow muff, I gave up torque down low..and you can see that has a huge impact on driveablity with this torque curve..for me at least. Anything after 4500 RPM with the free flow wasn't impacted so my 60-100 runs (4000-6000ish) were fine. Thing is, 80% of the time I'm under 4500 RPM and I DON'T like a sluggish throttle response!

 

I lopped em both off READ: cat and muffler and found a slight low to no boost low rpm torque decrease, spools FASTER, midrange unchanged and top end feels better. Yes you will lose a bit of bottom end, but hell you can mess with the cam timing if you want to get most of that back ANYWAYS.

 

Not so sure you can mess that much with these cams
BTW there's a lot more overlap built into this car than you wouldn't *normaly* have in a Turbo car. It's also twin scroll.. Helps with scavaging for sure..maybe that has something to do with running counter to the mantra that you *can't have enough free flow with a Turbo car*??
I only know one thing...huge difference with some corking the freeflow muff with DP and catback added. What can I say? I'm happy with it..no loss of top end either due to my mod. I'm just surprised more people with 3" back and no muff don't notice what I have. The OP certainly did

 

Just found these 2 posts on another forum. Not the same car, but it is a TURBO with 300HP. He doesn't talk about the MUFF per se, but it does address the exhaust pipe size and restriction issue. It also seems to describe my experience loss of torque in lower range while maintaining (maybe increasing a bit) peak HP.

...DSM Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum: DSMtalk.com - View Single Post - Variable Exhaust Restrictor

chad,
your research is correct.
my 2.0 car with 18g turbo lost loads of torque at low rpms when i switched from 2.5 exhaust to 3.0. it was very disappointing for me. the torque loss was in the neighborhood of 50ft/lbs in 4/5th gears.
on my stroker motor. when i first built the car it was running just a short downpipe. the turbo spooled up at about 4100 rpm. when i installed the 3'' exhaust the turbo spooled up 800rpm sooner. i was perplexed , as you hear from many tuners that bigger is better when it comes to turbo exhaust.

DSM Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum: DSMtalk.com - View Single Post - Variable Exhaust Restrictor

when my front wheel drive car was making alittle over 300whp, i switched from a full 2.5 to a full 3.0. the car picked up 15-20hp after 5k rpm, but from 3-5k it lost 40-50 ft lbs torque.

i was dumbfounded at the loss of torque.

i tried a 2.75 full exhaust. it gave up horses and gained some torque. poor compremise

This *phenomenon* is FOR REAL. Why some experience it and others don't??? Ya got me there. But don't tell the OP or myself that we didn't have this happen.

 

But by just removing the muffler ? The op still has the stock down pipe on the car .... that should be the biggest restriction in the stock turbo back exhaust.

 

you do know the stock muffler is free flow right...

 

This thread is absolutely pointless, and is getting way out of control...

 

This car does have a lot more overlap than you would expect in a turbo car even in the high load cam angles but every time I have tried to decrease overlap in the high load areas I have always ended up going back to stock because acceleraton times were slower. Decreasing overlap in the part throttle areas helps the part throttle drivability IMHO but it does decrease fuel economy slightly.

 

It may be pretty good with flow, but it's not as free flowing as the one I put on. That one is a STRAIGHT THROUGH.

 

Agreed that DP is the most restrictive, but the MUFF HAS TO BE RESTRICTIVE to dampen the sound..by definition!. Removing the restictive stock DP which is POST TURBO, can only free up the flow, since the gases are HOT at that point and removing any restriction there increases flow.
However at the END of the system (MUFFLER) the gases are about 800-1000 degrees cooler and don't *require* larger pipes there since cooler temps contract the gas volume and velosity slows given the same diam pipe. That's why removing too much restriction (MUFF DELTE/free flow MUFF) will decrease velosity and adversely effect low end torque. Of course as you get into the HIGHER RPM range that changes due to increased volume and the negative effect is gone. At least that's my take.

I found this on the Caliber SRT forum (Turbo):

Dodge Caliber Forum - Caliber SRT4 Forum - Forums and Owners Club! - View Single Post - Caliber SRT 4 Exhaust Mod results

Originally Posted by ericksrt4
your slipping. im surprised you didnt point this out but it is a bad bad idea to put a chambered muffler (flowmaster) on a turbo car. your should really only use straight through mufflers (magnaflow, etc. you get the idea)

(Reply):
Correct, but in this case (stock boost) I feel that a chambered muffler would be the best way to go. Again we have seen these "open" systems with high flow mufflers loose power on the dyno.

Now, if we were running more boost... do not run a chambered muffler or a "box" muffler with baffells (sp) in it. These will kill power.

 

Then stay away

 

From Evo board (Turbo)

Poor performance with muffler delete pipe?

--------------------------------------------------------------------------------

I've been reading many threads in the archive about increased power by adding an exhaust to a stock Evo. Many have said that their boost pressure has increased with a free-flowing pipe.

My experience has been just the opposite. After installing a muffler delete pipe on my car the hp has actually decreased by 17% (223hp vs 185 as measured by my G-Tech).

I've since heard by a reputable source that installing such a pipe on a stock vehicle will actually lower the boost levels. The manufacturer of this particular pipe has told me that I should expect a 5-6hp increase on my stock vehicle. What gives?

Can anyone else shed some light on this issue? Thx, Mike.


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