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Discussion Starter #1
So after all basic maintenance and tr6 iridium plugs, CAI with heat shield, 180tstat and new gaskets and o rings I scanned the 2003 PAU. Having only .5* KR at WOT I went ahead and dropped the pulley to a 3.5. Scanned again and got 5* at WOT and maybe half or less of that on the highway at high throttle. I'm ready to order a downpipe now if need be, but i was curious how much knock can be taken out with a good dyno tune. I'm trying to be done spending extra money on this car, what route should I take? Can I go ahead and tune now, or should I opt for exhaust? A bonneville downpipe with cat is $200 and the speed daddy's are right there with it. With the SD I would need a cat, but I could live with that. I don't plan on rockers or cam or IC or any of that. Please let me know what y'all think. Thanks.
 

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The stock exhaust is extremely restricting and any upgrades you will see a great improvement with, a proper tune will also give you great results but with 100% stock exhaust its more of a bandaid for removing KR. The exhaust restriction will still be there. Just a downpipe should take care of all the knock your seeing and a tune afterwards should allow you to see another 20hp or so on top of that. The general rule of thumb is 1*KR = -5hp.
 

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The stock exhaust is extremely restricting and any upgrades you will see a great improvement with, a proper tune will also give you great results but with 100% stock exhaust its more of a bandaid for removing KR. The exhaust restriction will still be there. Just a downpipe should take care of all the knock your seeing and a tune afterwards should allow you to see another 20hp or so on top of that. The general rule of thumb is 1*KR = -5hp.

Cool, that's kind of what I wanted to hear. Now, should I go 3" or 2.5" downpipe? If im not upgrading the rest of the exhaust, will 3" be significant over 2.5? And I don't have to get em missions testing so I could go catless, but if I'm about to get fined for it I'll just pay for a cat. Appreciate your help.
 

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If you dont have regular e-testing then go catless, the only roadside inspections Ive gotten (and ticketed for) is noise issues. They have asked if I ran a cat and didn't bother to look underneath. Stock catback is 2.5", and the rear manifold connection is 3" so its a tossup if 3" is needed over 2.5" but I think bigger is always better so spend the extra $20 or whatever for the 3".
 

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If you dont have regular e-testing then go catless, the only roadside inspections Ive gotten (and ticketed for) is noise issues. They have asked if I ran a cat and didn't bother to look underneath. Stock catback is 2.5", and the rear manifold connection is 3" so its a tossup if 3" is needed over 2.5" but I think bigger is always better so spend the extra $20 or whatever for the 3".

Ok I got you... Thanks for your help man
 

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Speed daddy headers would be the way to go over a downpipe, as they give more room for future upgrades.. I got a set and still holding up after a year. The only issues I had was with the crossover pipe fitment and the O2 sensor hitting the body. The bends were wrong on the crossover. A little cutting and welding and some good band clamps solved most of that problem, and a hammer solved the o2 to body contact.
 

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That exactly why I hate those cheap eBay headers, there fine of you can cut and weld them yourself but if you need to pay a shop $70/hr for likely 2hrs your into SLP header pricerange. if your not planing any future mods the downpipe and a tune will do just fine, an hrs work to install a downpipe (or less depending on your skill level) vs 3-4hrs for headers plus any shop time for welding.
 

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Discussion Starter #9
Wow, almost 1 month later and I just now saw this... Is narrow band volts the 1st o2 bank? What kind of numbers should I be seeing? I know I'll see ya in a few days but I'm bored and feel like tinkering...

Any idea what your narrow band voltages are at WOT?
 

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Cool, that's kind of what I wanted to hear. Now, should I go 3" or 2.5" downpipe? If im not upgrading the rest of the exhaust, will 3" be significant over 2.5? And I don't have to get em missions testing so I could go catless, but if I'm about to get fined for it I'll just pay for a cat. Appreciate your help.
I would go with a 3" down pipe , and for that matter, if you have the funds I would make the exhaust 3" all the way back to the rear where the exhaust splits for dual pipes. I did this on my GTP with a 2.5" pulley and all worked most excellent. I would suggest you scan the car under hard throttle to see how much KR is showing up...... just to be safe and not hurt anything. High amounts of KR is a killer on the PISTONS! I would also recomend having Dyno Tune motor sports do a tune on your PCM. That would be the finishing touch. One last thing that should be done is to scan it under hard throttle to see where the KR is under mild and hard throttle. Excess KR is a quick way to FRY PISTONS!! I personally run my GTP at about 600MV under hard throttle. No problems showing up that way for me. ONE last thing I personally suggest is to run the engine at cooler operating temps. Because my GTP is highly modded, I run my GTP at cooler temps. This will also help keep KR in check....... My heater isn't real warm but my engine has no failure issues.... been there done that..... it ain't pretty Best of luck...Mr Goodwrench Jake One last thought.....using better flowing mufflers will also help keep things in a safer condition...... check out JEGS or SUMMIT for different muffler choices.
 
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