IMPORTDIS

Hello All! I’ve been out of the game a few years but recently purchased a 2004 GT as a non-everyday driver to tinker with. I am in the process of planning to upgrade my exhaust on the GT. Currently I have stock Header/Hpipe with Flow Masters 40’s. I would defiantly want to go with some headers and an Xpipe but unsure if A) long tubes or shorty headers and B)catless or x-pipe w/cats due to wanting to keep the car street legal in the state of PA. I’ve been looking at BBK for both items but wanted to touch base with the mustang community and get some input/ideas. Nothing is set in stone and I have been looking at other products/suppliers such as Pypes and MAC. Pypes appears to be a little less but I am a firm believer in you get what you pay for. I want the car to sound mean and increase the horse power, looking for best bang for the buck. My end result will be to get the car up to 400+ hp and add a supercharger.

Cali_Swag

YouTube is your friend when trying to find an exhaust set up that you might like.

cliffyk

Insomnia has kicked in again, so excuse my verbosity...

It really doesn't matter which mid-pipe or "catback" pipes (brand, catted or not) you buy, all they are are bent pieces of pipe with no intimate knowledge of fluid dynamics or rocket science involved in bending them up.

H-pipes have more of a musclecar tone, X-pipes more of a NASCAR tone, because the X-configuration flows better at higher RPMs where push-rod engines could not go (easlily or cheaply). The overhead cam design allows revving up to well over 6000 rpm without valve float.

There is very little to any power difference between catted and so-called "off-road" pipes, there is a big noise difference which to my ears can often make a GT sound like it's advertising something it cannot deliver. If your state inspection looks for cats, or sniffs the tailpipe you will likely fail inspection, OTH if all they do is check the OBD2 I/M monitors and you have MIL Eliminators installed you may get by.

Many, myself included, feel that chambered mufflers like the Flowmasters sound better with H-pipes and that straight-through muffler like MagnaFlows sound better with X-pipes.

Whatever you do make the exhaust 2-1/2" ID from the manifolds back.

Headers are a whole different thing where good design does matter, and where you need to select them based upon how you plan on driving the car. Full race headers that are optimised for higher engine speeds can be a pain to drive around town with. The good news is that aftermarket headers in the $400 to $800 price range are street headers.

Dead stock, even with an opened up exhaust, you will find that your '04 will put down 225 to 230 rwHP. maybe a bit more, on a dyno. This is because of the very conservative stock tune, designed to run on 87 octane fuel of any quality and to ensure that there is no way an owner can possibly damage that engine while under warranty.

The ignition timing is quite uninspiring, and on the late '02 through '04 GTs with the pink (lavender) 21 lb/h injectors the engine runs PIG rich at higher loads and WOT with the AFR dipping into the high 10:1 range at times. So, after opening up the exhaust resists all the siren calls to get a "CAI" (the stock intake is a CAI and a pretty good one), larger throttle body, TB spacers and all that other stuff--get a tune, optimised for the highest octane fuel you can or are willing to buy.

There are systems out there for those who wish to do their own tuning and fully tweak their setup, and for those who just want have someone else provide a tune that will make you happy and cover their butts. I.e. insure nothing is likely to go wrong, sort of like Ford's plan.

Take your pick.

After the tune install lower (higher numerically) final drive gears, 3.73:1 and 4.10:1 are the most popular choices. The tune/tuner will let you correct the speedometer.

Finally turn to stuff like an aftermarket upper plenum, they all flow better than the stock unit, and to top it of a 70 mm TB. The stock 65 mm throttle body was a carry over from the pre-'99 "non-PI" engines and is a bit too small for the PI manifold/heads. 70 mm does not sound that much larger, but it is a 16% larger hole. You can read more about TBs and plenums here.

IMPORTDIS

Cliffyk, thanks for the response much appreciated! I recently upgraded the following. BBK CAI, BBK 70mm TB, Trick Flow Upper Intake Plenum, Ford Racing Intake Manifold. My plan was to allow the engine to accept more air intake, now my plan is to allow it to breath better by upgrading the Exhaust. I’m unsure if I should go with Long Tube Headers or shorty. I certainly want to go with the X-pipe as my understanding is that I would get more of a gain in HP. Eventually preparing the car for a SC down the road.

scott4.6

Long tube is the only way to go. You will get more HP and TQ.To me shorty headers is a WASTE of time. When i bought my car someone put shorty headers on it , I will put long tubes on it very soon. The x pipe is only worth about 1 hp over the h pipe. I have heard this from a hand full of people. I would go long tube with a h pipe and some good flowmasters( delta flow) . Thats what in going to go with . I have bbk shorty headers a o/r x pipe and a slp loudmouth cat back. It sounds like a bunch of ricers when i let off the gas it pops crackles and sound like ****. But when i smash the gas it sounds pretty good in the upper rpms. I would not ever use the set up i have now on my car ever again.

IMPORTDIS

Thanks Scott! Nice Ride BTW! Love the staggered look. I appreciate the info as I am leaning towards the Long Tubes but wanted to get other opinions.

scott4.6

Thanks, if you need anything just let me know. Clifty is very smart we all kinda listen to him. He will lead you in the right direction for sure. His post just blows me away.

IMPORTDIS

Just wanted to give you guys an update, I decided to purchase the BBK Long Tube Ceramic Headers with the BBK High Flow Catted H-Pipe. I cannot wait to hear how it'll sound! Thanks again guys for the info.

Question, how could I determine if the car has higher gear ratio? If I am doing 70mph the RPM's are at 2.5.

cliffyk

5-speed or automatic, if it's a 5-speed you have 4.10:1 gears.

Here is my "How Fast Can I Go in Each Gear" calculator, its use is straight-forward.

In the upper right corner there is a link to a pop-up "guesstimator" that will make a best effort attempt to determine your rear-end gear ratio based on speed and rpm in 4th gear (3rd for an auto, 4th gear is 1:1 for a 5-speed, 3rd is 1:1 on an auto--making the calculation universal)...

TRexGAWD

Good choice on the LT's and personally I prefer x-pipes but you'll enjoy either.

And like cliffy said you have 4.10s, that's assuming you have a 5 speed and stock size tire diameter.. Are you sure about that rpm and speed?