Stock 2003 GT Convertible - Now What????

Super Dragpack · Mar 6, 2010

Hi guys.

After all the success of modding the 5.0's, and the death of my Fox when it ran into a wall (not me driving), we now have a new toy - a 2003 GT Convertible Manual with 33k miles and stock in every way. Its a nice car, Shadow Grey, Mach 1000 upgrade, 3.27 diff etc etc etc

Anyway, what now?

I have planned the following but have a few questions for each. Thanks in advance for any assistance.

1/ Cold Air Intake - Any particular CAI that is notably better than others?

2/ Drop FRONT suspension 2 inches - Anyone know how much roughly is needed to be removed from stock springs to acheive this?

3/ Cat Removal - This is the one needing the most advice. If I remove the cats and replace them with straight through pipes, will the light come on? Will the engine run any better (or worse)? Is it worth doing? Does anyone know what cats (obviously there are a few) make the most difference and what ones are worth keeping?

4/ Is a tuner worth getting and can this help sort issues with the cat removal and any emmisions tests etc? What tuner is the best to get for all round features and tunability?

What other mods are worth doing? It is missing a lot of the power I am used to in a 5.0 or 428 engine and I would like to increase it while keeping it streetable obviously.

1996mustangGT · Mar 6, 2010

1) Will get little to no gain from this. Does it help, yes but your looking at very little whp gain.
2) IIRC the first two coils are dead coils. I think with my buddies 01 we did 1 1/2 coils and it did a good drop. Cut 1 coil reinstall and check the drop. Or just save yourself the trouble and pick up some springs for 175-200. The cut stock springs will ride realllllyyyyy rough. If you dont mind that then go for it

3) You'll be fine. Just be sureto get some MIL eliminators to override the codes.Your basically making your own O/R H pipe..nothing different than the MAC one i bought. Get estimates on the labor though...only cost me $110 shipped plus 2 hours of my time to get a O/R H pipe
4) YEs and no...it will clear codes, and without constant datalogging and some other good upgrades it will make little to no difference.

If you want my first recomindations: for PI - get some 3.73's installed, good mid-pipe, CAI, tb and plenum. You'll get a good bump in HP. The gears will be the best though, cant beat em.

Welcome to the forums BTW

Super Dragpack · Mar 6, 2010

1996mustangGT said:
1) Will get little to no gain from this. Does it help, yes but your looking at very little whp gain.
2) IIRC the first two coils are dead coils. I think with my buddies 01 we did 1 1/2 coils and it did a good drop. Cut 1 coil reinstall and check the drop. Or just save yourself the trouble and pick up some springs for 175-200. The cut stock springs will ride realllllyyyyy rough. If you dont mind that then go for it
3) You'll be fine. Just be sureto get some MIL eliminators to override the codes.Your basically making your own O/R H pipe..nothing different than the MAC one i bought. Get estimates on the labor though...only cost me $110 shipped plus 2 hours of my time to get a O/R H pipe
4) YEs and no...it will clear codes, and without constant datalogging and some other good upgrades it will make little to no difference.

If you want my first recomindations: for PI - get some 3.73's installed, good mid-pipe, CAI, tb and plenum. You'll get a good bump in HP. The gears will be the best though, cant beat em.

Welcome to the forums BTW

Cheers for the reply.

I fitted 3.73's in my Fox and it did run very well with the AOD. I MAY consider the same swap in the 03 SN95, but it doesn't seem too bad with the 5 speed and 3.27's at the moment, but we'll see.

I will be doing all the labour myself. I retired a few years back (at 33) so have a lot of spare time and a fully equiped workshop where i do a lot of engine rebuilds, mustang repairs and restorations and keep myself busy with one project or another.

As I am in England, the shipping is a little stupid, so I prefer to make do with what I have than pointlessly ship new items.

On the 5.0 SN95 I simply made a support frame for the exhaust and one at a time I removed the cats and welded in suitably sized and shaped sections. I also did a lot of porting and an entire engine rebuild with smog and egr removal too, so I don't know how much of a difference the cat removal made, but it really does like to rev now - especially for a 5.0. It really improved the sound too, even with stock rear boxes.

Anyway, what Throttle Body and Plenum is worth having then?

Is it worth removing the smog and egr on these motors too?

MustangChris · Mar 6, 2010

since you are in england, i suggest finding some 4.10s somewhere... after that, porting your cats and "patching up" your exhaust will give you emission problems and will cause the check engine light to come on, but that bay be your only option.

since you have a shop, i suggest making your own cold air intake.

I'm not a fan of cutting stock springs, but that may be your only option with your current location.

if you are going to change the TB/Plenum, accufab is pretty much what everyone "drools" over... but a home-port job might be your only option.

and no. removing smog/egr on these cars is pretty much useless at this point.

as for the tuner. most people go for SCT products or Diablo Sport. both have good hand helds.

1996mustangGT · Mar 7, 2010

+1 on the EGR...it really doesnt help much to remove it for whatever reason.

I got an ebay 75mm throttle body, and a C & L plenum for around $150, much much much cheaper than accufab.

The gears are nice, but I agree that the 3.27's are a great gear. To be honest I would've stayed stock if I'd had that ratio, but alas I had 2.73's lol.

As far as a t-45 to 4R70W swap..honestly its not that hard. I went the opposite way (manual to auto) and if I had not had to torch one of the transmission bolts out it would have only taken a day and a half to do the entire swap.