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Working on upgrades for my 04 SXT uplooking for some guidance/opinions

Posted: Mon Jul 27, 2020 6:42 am
by JaeDolo
Hello everyone! So I'll start with where I am at progress-wise. I've already installed a CAI (generic eBay one with K&N paper filter), under drive pulley (also generic eBay one),Amazon cat back, soon to be headers as well. I had to ship them out of state and just need to pick them up. The improvement with just those alone has been pretty awesome but there is a few things I've noticed and I'm curious as to whether this is common or not and also I'd like to kind of get an idea of where to go from here. Since installing all of this stuff I've noticed a pretty sharp drop in fuel economy. That could just be my lead foot but it's noticably worse. Also there is a kind of "dead spot" when accelerating hard, it's only slight and lasts between 2-3 k RPM but it's there. O4 SXT 5 Speed. 194k miles. I have about a grand left earmarked for add-ons. Any help or advice is greatly appreciated. Also if this has been covered my apologies and thanks for reading!

Re: Working on upgrades for my 04 SXT uplooking for some guidance/opinions

Posted: Mon Jul 27, 2020 11:08 am
by JeremyJ
If I remember correctly, the dead spot is pretty normal. The N/A cars don't make much power below 3K, so it's not going to do much down there. If you don't have emissions testing in your area, I'd suggest a long-tube header instead of one of the short eBay headers. You'll make a bit more power, but it'll remove the catalytic converter to do so. Also, with that many miles on the car, you should really change out the timing belt and water pump. I'd add some solid motor mounts while I was in there, because they feel fantastic and I'm sure your mounts have to be really worn by now.

Go here for parts: www.modernperformance.com

Re: Working on upgrades for my 04 SXT uplooking for some guidance/opinions

Posted: Mon Jul 27, 2020 11:57 am
by occasional demons
None of your current mods are going to significantly add more air and fuel going through the engine. The drop in mileage is probably mostly from your foot, being sucked into the more aggressive sound the motor is now making.

I was still getting up to 40 mpg with my '01, with a 60mm TB, short ram intake, '02 Magnum cam, ghetto blaster intake manifold, header, '02 R/T PCM, and a cat back system.

The only thing that dented the fuel mileage was the mildly ported Magnum head. It dropped to about 32 to 36 MPG, if I drove it normally.

It could be a tired o2 sensor at that mileage, that is showing it's limits. I replaced mine at 172,000 miles, and it made a far bigger increase in throttle response with the 60mm TB than the UDP I removed. UDP didn't make a noticeable difference, and only got me a flashing CEL with the '02 PCM.