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[scurvy_bandit]

jeff?
raceland -148$


supersprint- 707$

[yokust]

Techtonics and do it right

Some of those short headers like that are no better than manifold and dp

[mjohnson]

Just get rid of the muffler altogether.  That's my plan.

I've been rockin a straight pipe for a while.  It started as 2.5" TB w/ high flow cat and an electronic exhaust cut out after the front wheels.  I lose too much power going with the cut out open (dyno proven) and then I threw it back on the dyno when I lopped the muffler off (still 2.5" w/ hiflo cat) I gained some power over the cutout being open but still not like when I had the muffler on.  I decided to go w/ 3" TB w/o a cat in to a magnaflow muffler and 2x 2.5 out.  I know it's going to sound sick, but as far as power goes, we'll see.

[MileHighAssassin]

Just get rid of the muffler altogether.  That's my plan.

I've been rockin a straight pipe for a while.  It started as 2.5" TB w/ high flow cat and an electronic exhaust cut out after the front wheels.  I lose too much power going with the cut out open (dyno proven) and then I threw it back on the dyno when I lopped the muffler off (still 2.5" w/ hiflo cat) I gained some power over the cutout being open but still not like when I had the muffler on.  I decided to go w/ 3" TB w/o a cat in to a magnaflow muffler and 2x 2.5 out.  I know it's going to sound sick, but as far as power goes, we'll see.

That doesn't make any sense.   On a forced induction car you shouldn't lose power from losing the muffler or having a cutout.  How far apart were the dynos done?  Could it have been something else, maybe conditions, temp, etc?

[mjohnson]

I've gone to the dyno 3 times and this is how I did my pulls.

Jan 08 col spgs:
session 1  pull 1 - cutout closed w/ muffler and stock (modified airbox) [base]
                 pull 2 - cutout closed w/ muffler and stock (modified airbox) [another base]
                 pull 3 - cutout open w/ muffler and stock (modified airbox) - whp & tq less than pulls 1&2

Feb 08 same dyno:
session 2  pull 1 - cutout closed w/ muffler and cone filter (clamped directly to the maf housing)
                 pull 2 - cutout open w/ muffler and cone filter (clamped directly to the maf housing) - whp & tq less
                 pull 3 - cutout open w/ muffler and stock (modified airbox) - whp & tq higher
                 pull 4 - cutout closed w/ muffler and stock (modified airbox) - whp & tq higher yet

Aug 09 dothan AL:
session 3  pull 1 - cutout closed w/o muffler and cone filter (clamped directly to the maf housing)
                 pull 2 - cutout open w/o muffler and cone filter (clamped directly to the maf housing) - whp & tq less
                 pull 3 - cutout open w/o muffler and stock (modified airbox) - whp & tq higher
                 pull 4 - cutout closed w/o muffler and stock (modified airbox) - whip & tq higher yet

I'd post numbers but 1: I don't feel like looking for them, 2: the exact numbers shouldn't be relevant since the pattern of power loss/gain should speak for itself.

As you can see I tested the different variations each time I was at the dyno so I highly doubt conditions played a factor.  Especially since the power loss/gain patterns were very similar and as predicted in each session.

[MileHighAssassin]

That is seriously strange.  There is no way in hell you should have better numbers with a muffler and more restrictive exhaust on a turbo motor. 

The numbers might shift up a bit but you should still have better numbers

[scurvy_bandit]

Something else to consider is the exhaust turbulence.

[mjohnson]

Something else to consider is the exhaust turbulence.

as far as?

[mjohnson]

Got the car back from the exhaust shop today.  Alls good, except that he said he couldn't bend the 3" around the axle, so he did as much as possible 3" and over the axle 2.5"  I was kind of disappointed because I know people have fit 3" through the whole thing (at least that's what people have said).  Could it be because of the style of bends?  He doesn't have a mandrel bender.

I digress.

I started the car...then thought to myself "didn't I just start the car?"  I was so used to straight pipe or cutouts that I didn't recognize the quietness of a brand new muffler.  Sounds too prissy for me (at idle).  Can't wait for it to be broken in.  It does sound nice under load though.  The 3 gave it a much nicer deeper growl instead of the slightly raspy growl of 2.5.

I must say though.  A piece of me was tore out when the cutout was removed    I've grown attatched to bleeding ears at the touch of a button... 

[yokust]

That is seriously strange.  There is no way in hell you should have better numbers with a muffler and more restrictive exhaust on a turbo motor. 

The numbers might shift up a bit but you should still have better numbers

This has been proven time and time again. It is all based on your ecu tuning.

If your ecu is meant to have a cat in it, removing the cat can cause lower power levels EVEN on a turbo car. By opening his exhaust boost levels came in harder, faster, and HOTTER. By having the hotter air charge the stock ecu will cut boost and timing levels to get back to what it thinks is normal. Even more so on a stock intercooler that is barely capable or functioning on a fully stock car.

The ME7 Bosch ecu also needs to see the same exhaust flow and temps on both O2 sensors. Surprising or not the ME7 ecu the rear O2 sensor has overall main control of fuel mixture and timing maps. The front O2 only controls short term fuel mixtures and settings.

[mjohnson]

so could a person theoretically just move both sensors in front of the cut out and trick the ecu?  or how about resistors?  Obviously going standalone is the way to go, and I likely wouldn't do the resistor part, but I'm just tossing ideas out there, trying to learn a thing or two.

[scurvy_bandit]

I think he meant by hotter faster air, it was in reguards to the pressurized air entering that tiny throttle body.

About the turbulent air, when hot air expands say.... as much as just a cutout allows it, the result is the loss in streamline of airflow. The air is flowing down a nice smooth path from the turbo then into the open. Think of it like throwing a rock in a pool, the pulses of exhaust gas also help to pull themselves out of the way of the fresh hot pulses. If you just have everything going to open atmosphere eventually the ripples probably disrupt the smooth air flow from the turbo. (why nobody runs an open turbo without some type of DP)  Think even race drag cars have some nice pipe exiting somewhere..

[yokust]

so could a person theoretically just move both sensors in front of the cut out and trick the ecu?  or how about resistors?  Obviously going standalone is the way to go, and I likely wouldn't do the resistor part, but I'm just tossing ideas out there, trying to learn a thing or two.

That only fixes half of the problem, but would help somewhat. You still have an issue with the tune in the ecu not meant for what you are doing. And other items you would need to upgrade in order to make it function correctly

I think he meant by hotter faster air, it was in reguards to the pressurized air entering that tiny throttle body.

I meant both as well.


To do it right with an open exhaust/cutout you would need supporting mods. ECU tuned for open exhaust, and intercooler capable of handling higher intake temps made by turbo.