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Discussion Starter · #1 ·
07 Mustang GT,automatic. Just installed the Flowmaster Axle-back kit and it sounds sweet, but 2 days later I began to notice a loss in power, but I'm sure if its related to the exhaust change. Whats happening is while I'm accelerating and I reach 40 mph the transmission shifts and I get a load groan and the RPM goes to about 1700. I continue to press down the throttle and I get almost no response or just a little response. The only way to get out of that is either back off the throttle and re-apply or just slowly bring it to wide open throttle which would force a shift to get back the power band. It always has done this on occasion but now its worse after the exhaust install. 1 other note, I have heard people say that exhaust clamps alone without welding is a bad idea. And that a leak can develop at the slip-fi connections, could that be why for loss of acceleration/power? And can a leak there actually rob power?
 

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axleback should not affect the car's performance like that at all. It is purely a sound thing. Heck, the SLP axleback deletes the mufflers, and no performance losses there. I've been running a set of cutouts after the cats, which basically bypasses the back half of the exhaust, and I have no performance losses.

Then again, I have a manual, so IDK about your shifting issues.

The clamps are perfectly fine for an axleback install, as long as they're properly torqued.
 

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Discussion Starter · #5 ·
axleback should not affect the car's performance like that at all. It is purely a sound thing. Heck, the SLP axleback deletes the mufflers, and no performance losses there. I've been running a set of cutouts after the cats, which basically bypasses the back half of the exhaust, and I have no performance losses.

Then again, I have a manual, so IDK about your shifting issues.

The clamps are perfectly fine for an axleback install, as long as they're properly torqued.
Flowmaster does not specify how much torque to apply for the final tightening in the install instructions.
 

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This is like the second unfounded complaint about Flowmaster in the last two days. Wonder if a competitor is trying to put out a bad rumor?
 

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if you slam the gas at 40 mph on a stock mustang automatic you will get exactly what your talking about, try 45 mph and i bet you'll get thrown back in your seat, its the same with 30 mph, if you do it at 25 mph you get thrown back as well :bigthumbsup
 

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Discussion Starter · #8 ·
if you slam the gas at 40 mph on a stock mustang automatic you will get exactly what your talking about, try 45 mph and i bet you'll get thrown back in your seat, its the same with 30 mph, if you do it at 25 mph you get thrown back as well :bigthumbsup
god, you are right to a point. There have been occasions where that hasnt happened which still leaves me asking why?
 

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Have flowmasters on my GT automatic with 26,000 miles and don't have any problem.Sounds and runs great.
 

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True I have noticed that there is a lag a certain rpm's or mph when I hit the gas. I can almost hit the gas and come out of it and then get the response after I have already done the action, It really aggravates me I also drive a 52000 lb ladder truck with drive by wire and it is the same hit the gas and wait for a response. Drive by wire not a good thing unless you are at a stand still and give full throttle all the way through the power band.
 

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True I have noticed that there is a lag a certain rpm's or mph when I hit the gas. I can almost hit the gas and come out of it and then get the response after I have already done the action, It really aggravates me I also drive a 52000 lb ladder truck with drive by wire and it is the same hit the gas and wait for a response. Drive by wire not a good thing unless you are at a stand still and give full throttle all the way through the power band.

Hmm, pretty sure a tune fixes this problem.
 

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Maybe its just me, but don't newer car ecu's adapt to your style of driving. If you drive like a grandma for a long time and expect your cars throttle response to be better, it probably wont happen. You should drive you car hard for some time and maybe it will improve? If i missed the point of this or offended the OP then i am sorry.
 

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I have heard that they do but if you disconned the batt for a day or so it re-sets the PCM. Then you can drive like a nut again. :scratchchin
 

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Discussion Starter · #14 ·
I have heard that they do but if you disconned the batt for a day or so it re-sets the PCM. Then you can drive like a nut again. :scratchchin
There is another trick that fixes things for a short time and thats to recalibrate the throttle pedal. Turn the key on, but dont start the engine, when most of the dash lights go off after you turn the key, quickly push the pedal to the floor and release just as quick. turn the car off and wait 15 seconds, restart the engine. You will feel a difference....for a little while. And yes, the ECM has an adaptive learning curve thats SUPPOSED to learn YOU and then its sets it parameters for up to 80 drive cycles. The biggest frustration I'm seeing as far as complaints regarding the lag is not saying WHEN it lags..if people would mention when it lags, it may answer questions. Also to think about is the variable valve/cam timing which the ECM is playing with to. ALOT of calculations going on and it cant keep up with most aggressive drivers. Ford makes it a point that we all dont drive the same and Ford has to compensate for everyone...The way I look at it is, if you dont wanna haul ass, DONT BUY A MUSTANG GT! GET YOUR GROCERIES WITH A V6 INSTEAD!
 

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The way I look at it is, if you dont wanna haul ass, DONT BUY A MUSTANG GT! GET YOUR GROCERIES WITH A V6 INSTEAD!

So, you have some kind of weird belief that a V6 Mustang is faster than a GT? Eh, it's late Friday night; I need to grab a few beers myself. ;-)
 

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I'm pretty sure the lag is just the car downshifting. I was going to race my friends stang on an open stretch...He downshifted manually into third and I just floored it on the 3rd honk...He was 3 cars ahead until my car downshifted itself and got moving lol. Such a big difference manually downshifting at least on a highway. I have a tune too which helps a little, but not 100% at all. I get the same type of "lag" and lack of exhaust noise when I'm at 50-55. The exhaust gets low and the gas pedal only responds if you really push it down. Its pretty aggrivating actually. Your not alone, its been this way on my v6 and my GT at the same MPHs.
 

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Discussion Starter · #18 ·
I'm pretty sure the lag is just the car downshifting. I was going to race my friends stang on an open stretch...He downshifted manually into third and I just floored it on the 3rd honk...He was 3 cars ahead until my car downshifted itself and got moving lol. Such a big difference manually downshifting at least on a highway. I have a tune too which helps a little, but not 100% at all. I get the same type of "lag" and lack of exhaust noise when I'm at 50-55. The exhaust gets low and the gas pedal only responds if you really push it down. Its pretty aggrivating actually. Your not alone, its been this way on my v6 and my GT at the same MPHs.
Exactly what I am feeling to..I was looking around for a while and I finally found my answer...OK good, I thought there was something broke on the car until I read your post...
 

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I'm pretty sure the lag is just the car downshifting. I was going to race my friends stang on an open stretch...He downshifted manually into third and I just floored it on the 3rd honk...He was 3 cars ahead until my car downshifted itself and got moving lol. Such a big difference manually downshifting at least on a highway. I have a tune too which helps a little, but not 100% at all. I get the same type of "lag" and lack of exhaust noise when I'm at 50-55. The exhaust gets low and the gas pedal only responds if you really push it down. Its pretty aggrivating actually. Your not alone, its been this way on my v6 and my GT at the same MPHs.
Ever tried to accelerate hard and turn the OD off first?
 

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There is another trick that fixes things for a short time and thats to recalibrate the throttle pedal. Turn the key on, but dont start the engine, when most of the dash lights go off after you turn the key, quickly push the pedal to the floor and release just as quick. turn the car off and wait 15 seconds, restart the engine. You will feel a difference....for a little while. And yes, the ECM has an adaptive learning curve thats SUPPOSED to learn YOU and then its sets it parameters for up to 80 drive cycles. The biggest frustration I'm seeing as far as complaints regarding the lag is not saying WHEN it lags..if people would mention when it lags, it may answer questions. Also to think about is the variable valve/cam timing which the ECM is playing with to. ALOT of calculations going on and it cant keep up with most aggressive drivers. Ford makes it a point that we all dont drive the same and Ford has to compensate for everyone...The way I look at it is, if you dont wanna haul ass, DONT BUY A MUSTANG GT! GET YOUR GROCERIES WITH A V6 INSTEAD!
I've heard of that. I just never tried it. I just had CR from Tillmans change some of the throttle values in my tune and What a difference.
 
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