Mustang GT, Cobra, and Mach 1 Mod Analysis Thread


Secretary of Defense
It's pretty obvious that the majority of us are V8 Mustang owners and I think it's safe to say that more than half of V6 owners who buy new cars will buy a V8 Mustang. With that said, I think it will be helpful to have a thread were we can post reviews of our modifications and any performance data relating to them.

So basically you can post a brief review of any mods you have done in this thread. Be sure to include your cars year, model (GT/Cobra/Mach 1), transmission, and all information relevant to your mod (i.e. price, etc).


Secretary of Defense
I'll start. Follow this model:

Car - 2003 Mustang GT, 5spd

Mod - Accufab 70mm TB/Plenum, $415

The 70mm TB/Plenum combo is good for about an average of 10 rwhp across the board. Most of it's gains are through the mid-range (many dyno's indicate an average of 17-18 rwhp gains at roughly 3800 RPM). Increased throttle response all throughout the RPMs, especially mid-range. Very attractive design, quality piece. Definately a must have bolt-on.


New Member
3.8MustangSteve said:
I'll start. Follow this model:

Car - 2003 Mustang GT, 5spd

Mod - Accufab 70mm TB/Plenum, $415

The 70mm TB/Plenum combo is good for about an average of 10 rwhp across the board. Most of it's gains are through the mid-range (many dyno's indicate an average of 17-18 rwhp gains at roughly 3800 RPM). Increased throttle response all throughout the RPMs, especially mid-range. Very attractive design, quality piece. Definately a must have bolt-on.
have a 2001 gt not single engine mode but 4.10 gears and 3000 stall torque converter with trany shift kit.
the car take off from the line really fast and it also shift really fast it is a 13.62 but my next mods would be a procharger with 10lb and hopfully I hit the 12s that is my goal


Car - 2002 Mustang GT, 5spd

Mod - I'll give 2 reviews, my NA review and my Blown review..

NA - i had about every bolt on besides a timing adjuster and gears. LT headers, PRochamber, Magnapacks, C&L Plenum, 75mm TB and Pullies.
With just the exhaust and TB i made 259RWHP !! I can only guess i would have been in the low 270s with the pullies and Plenum. It ran great and had alot of power, but i wanted more after awhile:)

Blown - For $4900 shipped, installed, and tuned, i am making 396rwhp and 400tq. is where i got it all from and with this safe tune, my engine is insured not to blow as long as i am not stupid. With the centirfical blower, you get the power when you want it. IF you want to just cruise around town, you can do it like you have every bolt on and then a little. If you want to rip something apart, down shift, punch it and go. To me, it was more then worth the money. Just the intimidation factor alone is worth it :p


New Member
Year: 2001
Model: Mustang GT
Transmission: 5-speed (Not sure which tranny)


MAC 2.5" Cat-Back exhaust system - I feel this is a very good mod for the money ($260 when I got it). It will give your SOHC GT a very mean rumble, and you will turn heads. The chrome plate exhaust piping is a little cheap, and will start to rust if not taken care of. I heard MAC has a new coating though, so it might work Better.


K&N Air Filter - Worth the $45? I would say no. You could buy a cold air intake for a little more money. The K&N is probably worth 1rwhp, and you only have to clean it every 40,000 miles or so.

UPR Billet Aluminum Interior Pieces - It looks good at first, but the UPR aluminum seems to scratch and lose its color over time. I would suggest because I have heard great things.



Mach 1 Chin Spoiler & Grille Delete - This will definitley make the front end of your V6 or GT look alot better. The Mach 1 chin spoiler can sometimes be a little too low even if you are at stock height. The Mach 1 grille delete also cleans up the front end of your car, and I can't help but think it will cool the engine down better at higher speeds because of more air flow.


GoodYear Eagle F1 GSD-3 Tires - These things have AMAZING grip, but with a price tag of $1,200+, most people will turn away. If you have the money, go for it :thumbup:



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Tim S

2004 GT 5speed

Accufab 70mm Throttle Body/Plenum
While Steve gave his review on the same exact tb/plenum, a second opinion can't hurt. Installation is fairly simple. I really only ran into one problem, but it was easily solved. It definetly adds to the look of your engine bay. Power gains only add to the fun of your v8.

Once I install the Steeda UDP's, I'll post my opinion.


I know all about that.
2002 GT 5speed..

Steeda Tri-Ax shifter..
I'm surprised this hasn't been covered. :D Installation was super easy. It took a few days for me to get used to the new shifter. Now I love it and couldn't imagine ever driving w/ a stock one - it's like rowing a boat compared to the Steeda. This should be a mandatory first mod for any new GT owner. I picked mine up locally for $130.


Computer Geek
Car - 1998 Mustang GT, 5spd

Mod - Flowmaster Amercian Thunder Catback Exhaust $320

I've always loved the Flowmaster sound and decided to go with one of their catbacks when I got my GT. The quality of the kit is excellent and the tips look great! The sound is a lot better than stock, but not obnoxiously loud. There is noticable drone inside the cabin, especially in the 2500rpm area. I think the drone is expected with Flows though ;) I did notice a bit of lowend loss due to the increased piping size(2.25 / 2.50) , but I also noticed some decent gains in my mid to upper rpm ranges. Once I add a offroad midpipe, it will really wake this exhaust up :thumbup:


01 GT | 87 LX 5.0
2001 GT 5SPD

Magnaflow Stainless Steel Catted X-Pipe and Cat-Back

Installation on both is fairly straight forward...cut out the old and bolt in the new. It's all stainless steel construction for great looks and durability. The sound is deep and smooth at idle and low rpms. Put your foot in it and it will really rumble. It doesn't have the hollow sound that a chambered muffler has, plus it flows much better due to a straight-through design. The SOTP dyno revealed some decent gains up top. I could really feel it when I nailed second gear. :D The price is a bit hefty compared to some other brands, but I think the looks, performance, and durability make it worth it.


The Unicorned Handler
If I had the money Cobra Power, but I still like my little V6er. Good on gas and handles pretty well. But that sound of an x-pipe on the Cobra it's awesome. I wish I could get that sound out of my 6.

Matt :confused:


01 GT | 87 LX 5.0
fastmustangs1 said:
If I had the money Cobra Power, but I still like my little V6er. Good on gas and handles pretty well. But that sound of an x-pipe on the Cobra it's awesome. I wish I could get that sound out of my 6.

Matt :confused:


What the hell does that have to do with this thread? :crazy:


New Member
2004 GT 5 Speed

Mac Performance Offroad H pipe

This made my car much louder than I had expected. It sounds like a race car more or less. Fitment was perfect, went on in under an hour at a local Mustang shop, with the only problem being some o2 sensors we couldnt get unplugged. The cool thing is how there is absolutely no drone. At 65 mph, I cant hear the exhaust at all. It is as quiet as stock. Another cool thing is the price:

Mac offroad H pipe: $139
o2 Wire Extensions (for 04s only): $40
Mil Eliminators: $60

So less than $250 and I'm satisfied... for now. I think a mac catback will be my next modification.


Retired Admin
2004 Mustang GT 4-spd

SCT Xcalibrator Flash Tuner
X-Cal: $325
PC Cable: $50
Extreme Tuning Software: FREE

An awesome piece of electronic and automotive genius. You can get up to 3 custom programs on the tuner (as well as stock). You can also get the PC cable for it and modify your tune(s) on your pc, then send them back to the flasher for customization to your liking.
Running a 91 octane program with all the A/F ratio tweaks probaly provides around a 15rwhp/rwtq or more gain. One of the more appealing tunes is modifying the shift firmness and schedules for the 4R70W. Modifying your programs only takes minutes to perform due to the ease of the tuning software.


If specified
1997 GT

Mac H-Pipe- I cant remember the price, but it wasnt about 200. Made the car so much louder. Great mod, no very hard install if you have another person to help. If you need any advice on the install just PM me.

Ebay CAI- Cheap first mod... You know what it does and easy install.

Up next to install my gears :)


2003 Cobra - T-56

BBK Cai - Probably good for around 10-20 rwhp increase. Cost $200(free to me because it as installed by the previous owner). Probably one of the sweetest looking CAI but I would recommend the JLT CAI or the K&N CAI kits, they provide up to 25 rwhp gains.

Magnaflow Cat Back w/ UPR O/R X-Pipe - Gains of probably 20-25 rwhp. Cost $600 for the setup. Install could be done by most but I couldnt get the jack under the car, $75 to install. Good mods for the price, sounds amazing and so mean. If you get an O/R pipe dont forget to get MIL Eliminators($60) to get prevent the check engine light from coming on.


Street Performance Dawg
99 Mustang GT Auto.

FRPP 4.1 Gears
Cut about 0.4 sec from my 0-60 mph time. Great street mod.

Diablo Predator Programmer
Very happy with it. I can adjust shift points, shift firmness, rev limiter, air/fuel, timing, and so on. I get everything the way I like it without mailing chips back and forth.

Accufab 70mm TB & Plenum
Three-eight Mustang Steve documented this and it is true. This mod hit hard from the first test drive. It accelerated so hard I had to move the rev limit from 6050 rpm to 6250 rpm since I bumped it on the 1st to 2nd shift.

K&N Air Filter (drop in)
No complaints here. Many dyno tests show +3 rwhp gains on 99-04 GTs. No expensive CAI. Just dropped it in and called it good.

Magnaflow cat-back exhaust
Very good rumble and performance. Breathes much better from 4000 to 5800 rpm.

Nitto Drag Radials
Solved my traction problems, at least for now. After the 4.1 gears, it would spin the tires all through first gear. Now I can launch hard, about 0.85g according to Gtech Pro SS.

So that's where it stands. It is running very good and is fun to drive. My stock 0-60 mph times were averaging 6.4 sec. Now they are 5.3 sec.

I will probably stay n/a, but I am looking at a PI converter, aftermarket cam, aftermarket intake manifold, and Meziere electric water pump. But it will be some but not all of this.


2001 GT 5 speed

Pro 5.0 shifter- Love the tight smooth shifting :thumbup: $170

Predator Tuner- Awesome capabilities plain and simple. Noticeable gains :thumbup: Traded hood for it

SLP Loudmouth exhaust-I love this exhaust. Once I get the O/R H pipe in this thing will be setting off car alarms when I floor it :D 349

FIPK-I like this Air intake system over the MAC CAI. I recommend switching over to this system :thumbup: $90

Pullies- I have them but I have yet to install them :sleep: $100


Retired Admin
2004 Mustang GT 4-spd

Highly Ported Stock TB - $40
Highly Ported Stock Plenum - $30
K&N FIPK GenII - $194

I tested all these at one time, so I will give the review of them as a package.
The ported TB greatly increased the throttle response and in conjunction with the ported plenum and FIPK, it probaly good for a small peak gain, but bigger gains across the powerband (specifically mid to high end). The exhaust tone was more throatier as well. I believe this was well worth the money and I noticed the difference the instant I pressed the accelerator.
Install Time: 35 minutes

Test 2:
I launched the car on a backroad today and at first I thought the car was pulling less. But it was definately faster. After a few pulls, I reliazed that it only seemed that way because the powerband was flatter and it pulled much earlier than I was used to, so I was expecting the suddent rush when it had already happened and was running a nice steady pace. :thumbup:


I know all about that.
Diablo Predator Tuner: Installed "Performance Tune" - notice SOTP difference, but haven't dyno'd since. Very user-friendly and can adjust a variety of things. You can also do custom tunes. I paid $195 shipped, but they usually go for $300-400. You can get a used one, but only buy from people you trust because the device must be unmarried from vehicle A before it will work on vehicle B.​

FMS 4.10s: You won't get traction in gears 1-3 without sticky tires. It pulls much better - almost feels like a different car. Be sure to pick up a new pinion bearing for the install. I bought the gears brand new for $125 (good friend had them) and had them installed for $150. Definately worth the $295 (tipped gear installer). You'll want to have a Speedcal or tuner handy to adjust the speedo. Don't fear the gear! - a must have for n/a cars!

My car now averages 21MPG with the gears.


Retired Admin
2004 Mustang GT 4-spd

Magnaflow Cat-back - $436.00 shipped
The gain on the power end is minimal due to the fact that the rest of the exhaust is still corked up (ie: stock mid-pipe and headers), but the top end seems to pull a bit harder now.
However, the sound alone is well worth it. I was looking for an exhaust that was quiet when driving normally, but really woke up when the accelerator was pressed. I think I made the right choice. The sound is awesome and I couldn't be happier, especially with the bigger SS tips that fill the bumper holes better.

1/2" Intake Spacer - $28.00 shipped
Definately worth it. I wish I had done it when I switched the TB/Plenum, but it took less than 10 minutes to put on. The gain is definately there once you get deeper into the power band. For 10 minutes and less than 30 bucks, this is definately a mod that people should do. It compliments the tb/plenum & fipk well.