Backpressure woes

csledd

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Aug 18, 2001

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Paducah, KY

May 10, 2005

#1

• May 10, 2005

• #1

So I've got my exhaust setup complete and I LOVE IT! I put on SLP Creamic LTs, SLP Short O/R X-pipe, and the Steeda cat-back. Now I was expecting to loose low end power, which I did. I missed the low end power cuz if im in 4th gear and i put the pedal to the floor and im below 2k rpms.. nothing seems to happen. Well I let my friend drive the car and he said it really feels like the power is there but something is just keeping it back. Well I figured it was because I lost a lot of backpressure, the car feels AWESOME up at 4k but I was curious if there is anything I can do to fix the problem. Would getting a bigger TB/Plenum help any by letting more air in? Thanks in advance.

 

csledd

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Paducah, KY

May 10, 2005

#2

• May 10, 2005

• #2

oh and another thing, I drove the car for about 5 days before the SES light came on, I plan on buying rear o2 simulators to fix this problem. Whenever I park and get ready to turn the car off the rpms jump a little at idle, happens almost everytime. Anything to be worried about?

 

RedBullitt

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Jul 7, 2004

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Morgantown WV

May 10, 2005

#3

• May 10, 2005

• #3

no not for the short term, but its annoying. I dont know about in the long run though, I would get those o2 sims when you can so the light doesnt drive you crazy, i am neurotic though, so you know. You will lose some down low, but you gain it back and more high up. Of course more mods will help, but i would go for gears, 410s, they will give you much more bang for the buck.

 

csledd

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#4

• May 10, 2005

• #4

yeah that light bothers me, I'm definately getting 4.10s but it's gonna be 2 or 3 months first.

 

WRXracer

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Feb 28, 2003

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May 11, 2005

#5

• May 11, 2005

• #5

I didnt notice any power loss with my xpipe..

 

csledd

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May 11, 2005

#6

• May 11, 2005

• #6

Well I'm sure the LTs probably play a big part in releasing backpressure since they open up the exhaust a lot more.

 

300bhp/ton

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Apr 4, 2005

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May 11, 2005

#7

• May 11, 2005

• #7

but its done exactly what is supposed to, to increase power without going for a bigger cc or FI is to move the powerband further up the rpms.

When I posted my planned setup you questioned why I had excluded LT's. And I explained that they move the power band up the rpms.

There is little you can do about it, if you try and make more power, better flowing heads, high lift cams, bigger air intake it will move it further up again. You may get a slight increase down low but in % terms no where near as good as mid/higher end rpm power.

Gears will allow you to remain in the new power band better and as they are a numerically higher number each gear should require less effort to turn giving a sense of more power.

Torquey engines are usually big cc low reving small bore and long stroke engines.

The only real way to get lots of low down grunt on a 4.6 is by a Roots or twin screw blower, all other types of FI will produce massive torque gains BUT higher in the rev range.

 

csledd

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May 11, 2005

#8

• May 11, 2005

• #8

300bhp/ton said:

but its done exactly what is supposed to, to increase power without going for a bigger cc or FI is to move the powerband further up the rpms.

When I posted my planned setup you questioned why I had excluded LT's. And I explained that they move the power band up the rpms.

There is little you can do about it, if you try and make more power, better flowing heads, high lift cams, bigger air intake it will move it further up again. You may get a slight increase down low but in % terms no where near as good as mid/higher end rpm power.

Gears will allow you to remain in the new power band better and as they are a numerically higher number each gear should require less effort to turn giving a sense of more power.

Torquey engines are usually big cc low reving small bore and long stroke engines.

The only real way to get lots of low down grunt on a 4.6 is by a Roots or twin screw blower, all other types of FI will produce massive torque gains BUT higher in the rev range.

Click to expand...

Ahh.. makes sense. I figured this was the answer but I wanted to see if anyone had any other suggestions first. I honestly love the way it feels now because it is my daily driver and has made daily conditions A LOT better. I guess cuz my friend drove it and said something about the down low power it got to me lol. Oh well, I'm happy with the exhaust none the less but thank ya for helping me out

 

csledd

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May 14, 2005

#9

• May 14, 2005

• #9

Hmm.. let me ask this questions..

Why does my idle bounce around? Like if I've been driving and I stop to park it goes from like 700rpms up to 1000-1100 all of a sudden. I was at a red light yesterday and it kept moving up and down like 200rpms. Is this because it's getting a misreading from the o2 sensors or something? Would the simulators fix it? Thanks!

 

RedDaemon

10 Year Member

Mar 31, 2005

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Atlanta, GA

May 14, 2005

#10

• May 14, 2005

• #10

i had tha problem with mine with the rps bouncing around...the problem was that i had an exhaust leak in my midpipe that i installed a day before...i knoew thats what was causing it and when i fixed the leak...the rpms leveled out...check and make sure ur midpipe and lt (if possile) screws are tightened down all the way...u should also be able to hear if u have an exhust leak or not so if u dont hear a leak im not sure what it could be....u can not stop for red lights?

 

0

007

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Jan 29, 2002

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Broke

May 14, 2005

#11

• May 14, 2005

• #11

Check for exh leaks. Get gears. You may benefit greatly from a dyno tune with the longtubes in there. I'd at least get a dyno with AF to check it out.