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Old 10-08-2009, 07:07 AM   #1  
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Default exhaust cutouts, what do you think of them?

Well I was intrested in some electric exhaust cutouts for my fox, probably either the Pypes or QTP kit. My question is, what's the controversy with them? Some people say they will blow up your engine (highly doubt it), some say they do nothing but change the sound, and some say it helps shave time off at the track. Also, what are the laws on them? I use my Fox as a daily driver, but I would only open them for car shows, cruises, and when people ask to hear em (and of coarse the strip). Also, my car is an 87, so do I still have to pass emissions? Will these create a problem with emissions? The car is over 20 years old so I THINK the emissions laws are easy. So what do you say about the topic?
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Old 10-09-2009, 01:16 AM   #2  
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open headers sound like sh*t, its illegal to use them on the street and if your exhaust isnt a restriction, opening the exhaust wont gain any hp
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Old 10-09-2009, 07:32 AM   #3  
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See, I would have to disagree about there sound sometimes. A lot of people say they sound good on big cams, but I think it sounds terrible on big cams. Stock 5.0's sound great with them, I think.

those are two video's of near stock 5.0's that I think sound awesome with open headers.
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Old 10-09-2009, 09:30 AM   #4  
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My friend has them on his 69 just after the headers. Sounds cool as hell! No smog issues because its a 69! I'm going to get some and put them after the cats so the smog police cant mess with me.
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Old 10-10-2009, 05:55 AM   #5  
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I also think they sound like crap. and would find something that is gone to help your car run faster or better then cut outs
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Old 12-28-2009, 08:17 AM   #6  
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I know it's an old thread, but if I can find it on Google, it's worth updating.

I read this long *** article on how backpressure and whatnot works right...and here's what I took from it:

In short, effectively, the exhaust pipe is like an electric cable. The thicker it is, the more resistance. But you don't see thin cables transferring 1000 volts, do you?

In other words the smaller the diameter is, the more suction it'll create for less amount of exhaust gas. The bigger the diameter, the more exhaust gas it'll require to get that flow going to create the same suction.

You're making less exhaust gas in low RPMs, so the flow is poor with your large diameter pipe. But in higher RPMs, it should give you a similar flow it used to with the original pipes at low RPM because you're making more exhaust gas and it needs a larger diameter to actually flow well. You basically shift the high backpressure RPM range from high RPM to low RPM. Which is good for racing but at low RPMs that extra backpressure might hurt your engine. This is why ricers have huge exhaust pipes and terrible low end torque. :P

So yeah. It's all the above. It makes no difference because the overall performance should stay the same, only slower take offs and better top end. If someone is racing on the top end the entire time sure, it shaves off some time. If you're idling and moving around town at low RPM sure, it'll definitely hurt your engine.

Ferraris actually have a system that opens different exhaust pipes depending on the RPM. Kinda like VTEC only not for the air its taking in, but the air its pushing out.

What's best? Get an electric one, and only open it when you're gonna push the car hard enough. Run some pipe before the cutout, don't go all the way back to the header. You want some flow, you know? Now I dunno what kind of exhaust or how big it should be but I know you gotta have some pipe to create that suction when you get to high RPMs.

Last edited by AmirGTR; 12-28-2009 at 08:22 AM.
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