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Discussion Starter · #1 ·
So I put a magnaflow 2 in 2 out muffler in place of the resonator, had the rear muffler cut out and used the stock tips.

Right away the butt dyno could feel a loss in low end torque. I went to Test n tune at the local track a few hours later and my suspicions were confirmed, in worse air I ran a 12.97 and my fist run out after the exhaust was a 13.40 @ 102, best I could do in cooler air late in the evening was a 13.01 @ 105.

The car pulls decent in the mid range but not as good as it did in the low end.. Not sure what's going on but giving up 3-4 tenths is not worth the better sound..


No exhaust leaks , boost seemed okay, peak of 22 psi

Any ideas?
 

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That's exactly what I posted happened to mine. I said it was due to the back pressure being removed but people started telling me that back pressure is a myth again. Once I got my tune it took care of it.
 

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Discussion Starter · #3 ·
That's exactly what I posted happened to mine. I said it was due to the back pressure being removed but people started telling me that back pressure is a myth again. Once I got my tune it took care of it.
From what I thought I understood For a NA car you do want some Back pressure, but for a turbo car the less the better. I did note that the stock resonator was straight through and the magnaflow that I replaced it with had a little obstruction in the middle in both chambers.
 

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So I put a magnaflow 2 in 2 out muffler in place of the resonator, had the rear muffler cut out and used the stock tips.

Right away the butt dyno could feel a loss in low end torque. I went to Test n tune at the local track a few hours later and my suspicions were confirmed, in worse air I ran a 12.97 and my fist run out after the exhaust was a 13.40 @ 102, best I could do in cooler air late in the evening was a 13.01 @ 105.

The car pulls decent in the mid range but not as good as it did in the low end.. Not sure what's going on but giving up 3-4 tenths is not worth the better sound..


No exhaust leaks , boost seemed okay, peak of 22 psi

Any ideas?
what was your mph on the 12.97, also what day did you run the 12.97 and when did you run the 13's? where are you running ?
 

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NM i saw one of your previous posts... talk to torrie and see what he says... might need to make adjustments
 

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Discussion Starter · #6 ·
I did talk to Torrie yesterday, he said "Less is more when it comes to Turbo Motor Exhaust"

A question I have, perhaps someone knows here. Does it take a bit of time for a car to "learn" a new exhaust? I went right to the track from the shop pretty much. and the car was faster at the end of the night, most noticeably in the trap speed going from 102 to 105, I just don't know if that's the DA getting better as it got cooler
 

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I did talk to Torrie yesterday, he said "Less is more when it comes to Turbo Motor Exhaust"

A question I have, perhaps someone knows here. Does it take a bit of time for a car to "learn" a new exhaust? I went right to the track from the shop pretty much. and the car was faster at the end of the night, most noticeably in the trap speed going from 102 to 105, I just don't know if that's the DA getting better as it got cooler
Yes. Doing an exhaust change is a drastic change in airflow through the engine. Removing the restriction of the exhaust, allows the turbos to spin faster and push more air. Your CPU will need to re-learn a bit to compensate for this change.

Also post sound!
 

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Back pressure is not a myth per se but the more free the exhaust is the better it is up top.
You can lose low-end torque and I know that's a fact not a myth as I experienced that from two supercharged Mustangs. Deleted the cats on both with the proper tune and on both cars, it took more peddle/RPM's to break the tires loose at 20 and 40 miles an hour.
The free flowing exhaust caused my boost to drop 1.5 psi due to the lack of back pressure in the lower RPM's.
 

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Discussion Starter · #10 ·
Back pressure is not a myth per se but the more free the exhaust is the better it is up top.
You can lose low-end torque and I know that's a fact not a myth as I experienced that from two supercharged Mustangs. Deleted the cats on both with the proper tune and on both cars, it took more peddle/RPM's to break the tires loose at 20 and 40 miles an hour.
The free flowing exhaust caused my boost to drop 1.5 psi due to the lack of back pressure in the lower RPM's.
Sounds exactly like what I'm experiencing, perhaps I've gained a little power up top, but not enough to offset the torque loss in a 1/4 situation. The tires don't break loose anymore off the line, but break loose more after the shift to 2nd when the rpms are up and the turbo's spooled.
 

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Back pressure is not a myth per se but the more free the exhaust is the better it is up top.
You can lose low-end torque and I know that's a fact not a myth as I experienced that from two supercharged Mustangs. Deleted the cats on both with the proper tune and on both cars, it took more peddle/RPM's to break the tires loose at 20 and 40 miles an hour.
The free flowing exhaust caused my boost to drop 1.5 psi due to the lack of back pressure in the lower RPM's.
Boost is a way to measure resistance of free flow. Or better way to word it.. less boost means your engine is more efficient. So if all you changed was exhaust and your boost went down, you made your air pump pump air more effectively. This is especially true on a supercharged application where boost is mechanically connected to engine rpm compared to turbo where you have many factors creating a "power band so to speak"

I have put exhaust on many many engines from dirtbike, truckn car, diesel, gas, 2 stroke, 4 stroke, generator you name it. All respond differently but a trend is almost always better throttle tip in. That response when ya "jump on it". The loss and gain at the top end is more noticabke on dyno but harder to feel in your butt. Trap speed and how well the engine revs out are good indicators but not fool proof.

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I did talk to Torrie yesterday, he said "Less is more when it comes to Turbo Motor Exhaust"

A question I have, perhaps someone knows here. Does it take a bit of time for a car to "learn" a new exhaust? I went right to the track from the shop pretty much. and the car was faster at the end of the night, most noticeably in the trap speed going from 102 to 105, I just don't know if that's the DA getting better as it got cooler
Yes it most definatly needs to relearn, but depending on how these cars are programmed wot may be a set table and it may not realy look at o2s that much for its fulling at wot. Or it could take a long time to reset that table.

Im assuming this was same dragstrip bith times? What are the Time of day, air temp differences and what was your trap spead on these runs?

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Discussion Starter · #13 ·
Yes it most definatly needs to relearn, but depending on how these cars are programmed wot may be a set table and it may not realy look at o2s that much for its fulling at wot. Or it could take a long time to reset that table.

Im assuming this was same dragstrip bith times? What are the Time of day, air temp differences and what was your trap spead on these runs?

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Same drag strip different days

Pre exhaust work run
DA-2593
60 FT 1.8445
330 FT 5.388
1/8ET 8.3251
1/8 MPH 83.64
1000ft ET 10.844
1000MPH 97.09
1/4 ET 12.97
1/4 MPH 106.21

After Exhaust 2nd run (I tossed the first run slip away .. it was a 13.44 @102
DA-1700
60ft 1.835
330 FT 5.414
1/8th ET 8.395
1/8th MPH 8.395
1000ft ET 10.974
1000ft MPH 94.46
1/4 ET 13.162
1/4 MPH 102.39
 

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Discussion Starter · #14 ·
Yes it most definatly needs to relearn, but depending on how these cars are programmed wot may be a set table and it may not realy look at o2s that much for its fulling at wot. Or it could take a long time to reset that table.

Im assuming this was same dragstrip bith times? What are the Time of day, air temp differences and what was your trap spead on these runs?

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Same drag strip different days

Pre exhaust work run
DA-2593
60 FT 1.8445
330 FT 5.388
1/8ET 8.3251
1/8 MPH 83.64
1000ft ET 10.844
1000MPH 97.09
1/4 ET 12.97
1/4 MPH 106.21

After Exhaust 2nd run (I tossed the first run slip away .. it was a 13.44 @102
DA-1700
60ft 1.835
330 FT 5.414
1/8th ET 8.395
1/8th MPH 82.28
1000ft ET 10.974
1000ft MPH 94.46
1/4 ET 13.162
1/4 MPH 102.39
 

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It was definatly slower in all except 60ft. Traction control off i assume? Did it seem to spin more tire after launch? It is completly possible your xpipe magnaflow is causing a minor restriction... havta go back and tray again after some miles. There is so many variables.

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Discussion Starter · #16 ·
It was definatly slower in all except 60ft. Traction control off i assume? Did it seem to spin more tire after launch? It is completly possible your xpipe magnaflow is causing a minor restriction... havta go back and tray again after some miles. There is so many variables.

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It spins less off the line but about the same when the RPM's are up at the 1-2 shift., also I've lost 4 tenths on my 0-60 when measured on my tuner (not super accurate I know but it's a baseline) 4.7 before exhaust 5.2 after.

I'm thinking that perhaps Food knew what they were doing with the stock exhaust. the flaps in the stock muffler have pretty weak springs.. I'm wondering if they are to aid in low end TQ before the turbos have spooled up adding a bit of back pressure.
 

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That was my theory on the flaps on the stock mufflers. Aids in the low end. Freeing up the exhaust lost our bottom end until I requested another tune from Torry after I datalogged it with the new exhaust.
 

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Discussion Starter · #18 ·
That was my theory on the flaps on the stock mufflers. Aids in the low end. Freeing up the exhaust lost our bottom end until I requested another tune from Torry after I datalogged it with the new exhaust.
I've never done data logging before, though I see the function on my tuner/gauge display. Did he tell you what he changed?
 

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You mentioned the stock resonator was straight through? No baffles what so ever? Were you able to see if it had a cross over built in? Depending on if the factory ine has a cross over could be the cause for a performace loss. Theoretically a cross over is bettee then 2 straight pipes. But put in the wrong place too close or too far from the engine could make it less efficient.

I really dont think blocking off the exhaust with a flap, no matter how weak a spring, can help the turbo spool. At the turbine in the turbo there is a huge pressure drop. That is what contols spool. Any resistance after the turbine will hurt performance. I dont think the stock exhaust is as restrictive as it apears, that huge rear muffle has such a large volume that the little 2.7 would have to fill it up and pressurize it with exhaust to cause a true restriction. I think the flaps are more to keep the exhaust pulses from bouncing off the inner parts of the muffler and goinf back up the wrong way, back towards the engine.



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