70mm or 75mm Throttle Body? Then what?
 

I'm looking at getting one of these:

Stack Racing Polished 75mm Throttle Body
Stack Racing Polished 70mm Throttle Body

along with this:

Stack Racing Upper Intake Plenum

Here is the problem: The 75mm TB says its for supercharged or heavily modified GT's, and the 70mm TB says its for stock to mildly modified GT's. I'm not sure which one to get because I do not know when you make that transition from mildly to heavily modified.


Here is my list of performance mods (on my 2000 Mustang GT):

Cold Air Intake (JLT, I believe)
90mm Lightning Mass Air Flow Sensor
Flowmaster Catback Exhaust
Magnaflow X-Pipe w/ High Flow Cats
Hurst Billet Plus SST Short Throw Shifter
SCT 4-Bank Eliminator Chip w/ Tune
3.73 Gears
Power Slot Performance Slotted Front Rotors
Hawk HPS Performance Street Brake Pads


Also, I was wondering what my best bet is for my future modifications. I thought it would be best to get the TB/Plenum, then go for underdrive pulleys. Other than headers (I don't think its even worth getting shorty, and I want to keep my car legal right now), what are my other bolt-on options?

Thanks for the help as always guys.

With your current mods, I would do the 70mm. If you plan on headers and cams later you should do a 75mm.

You can find a 70mm FRPP throttle body off of a 5.4l Ford truck for next to nothing.

I put a 70mm Accufab combo on my 2003 vert and hated it.
Lost low end torque and had idle hang problems.
Nothing wrong with it, TPS fine etc.
Gave it a week to try and re-learn and sent it back.

Only mods I have are Magnaflow catback and KN filter silencer removed.

Waste of $$$ unless you are going FI IMHO.

I have an auto so that may be why.

..I have the Accufab 70mmT/B and Plenum combo as well ..but... I like it. I saw power gain in Hp and TQ on the dyno especially after I got it Tuned which helped my Air/Fuel ratio balance. I would recommend getting a 70mm T/B and plenum combo...and maybe a SCT 4-bank Custom Chip and ger it DYNO TUNED. Whether you get the 70mm or a 75mm T/B IT WILL NEED A TUNE..trust me.

I also have Steeda pullies, Mac Catted H-Pipe, Flowmaster Catback, K&N Intake

Just get the 70 and plenum...at least then, they will both match. I doubt you will feel any seat of the pants gains. If you want some power gains that you will feel. Just save up for nitrous instead of spending a couple hundred here and there for minimal gains.

This whole stigma of 70-75mm is stupid. You want the most air into the motor as possible. Get the 75mm. I only have a TB/Plenum combo on my car because I got it used for a great deal. Otherwise I would of never bought them. Very little gains for the money. You could have a nice safe 75shot of nitrous on the car for the cost of the UD pulleys and a TB/Plenum combo.

Food for thought as the nitrous car is going to be so much faster. You already have a tuner so all you need a nitrous tune on it and you are good to go.

I think you've got a really mismatched set of mods on the car already and you need to stop and decide on a direction.

put your stock MAF back on, 70mm tb and plenum and have the tune updated for the MAF change.

Toss on a 100hp shot of nitrous and quit nancy'ing about with the money wasting mods. no bolt on is worth the cost on our cars IMO.

Yeah I'm not happy with the mismatched mods I have right now either. I bought the car with the mods, otherwise I would have gone a totally different direction. Like an o/r H and SLP I's or something. And I really don't know much about how good the SCT 4-bank tune thing is compared to a traditional tune.

I don't have the stock MAF. I guess I'll have to look into the nitrous as thats the thing everyone is telling me to get.

The 4-bank is a chip. It's a good option but your tuner really needs to know his craft so the quality of the tune could be in question if you bought it with the chip in it. The chip method is traditional. I prefer a custom tune loaded in a handheld and flashed onto the ECU... but that's me and I'm prone to such flights of fancy. Chips are removable and there's almost no risk to the ECU with one. You could theoretically brick the ECU with a handheld but I don't know of that ever happening when directions were followed.

90mm MAF is great if you have a blower but it's probably reducing the view resolution that the ECU has of air intake status. That's the mismatched part. Everything else is fine except that. See if you can find a stock 96-01 MAF body on ebay. They're usually pretty cheap. Or don't... your call. It works now so it's not "hurting" anything other than the tuners feelings. Before you put it on you'll need the tune updated. I'd take a stock maf to a tuner and hand him the maf and the car keys and come back in 2 hours.

With nitrous you'll want to make sure that the tune you get takes that into account. The tuner will need to back off the timing a bit for the nitrous. This is one of the reasons I like a handheld with adjustable parameters. You can have a street tune that's pretty aggressive and then when you want to use the nitrous you just hook up the handheld and back off the global spark a bit.

Throttle Body
 

The best gain I felt was with my Dragon Plenum and factory 65 MM TB, then I went with the Dragon 75 MM TB, I felt it hurt my low end a little. Right now I have a FRPP 70 MM TB and it is just about right.

Dave

01 GT Vert, Auto
3.73 Gears
Dragon Plenum
FRPP 70 MM TB
CAI ( Tuneable)
SCT Tune by VMP
Flows
FAST A/F meter
Best ET 13.8

Thanks for the explanations to those few things, it really cleared up a lot of things I was thinking about. As far as the chip, the previous owner took the car to a place called Evolution Performance in Aston, PA. They are supposed to be one of the best Mustang shops, and I think they specialize in GT500's and high end cars like that. I'm going to look for a new MAF, and I can get them to give me a new tune, they don't charge much for it. I will look into the nitrous too, maybe they can give me a tune for that, and I'll do some research too.

Checkout the power adder section for tons of nitrous info.

That shop does good work I hear so I wouldn't worry about the tune. A chip is fine its just a way to hold the tune. All a tuner does is flash the ECU with a new tune was as the chip is piggy backed to the service port on the ecu. Does the same thing regardless.

The only thing that makes me go WTF is the random ass Lmaf. You have no reason to need that at all.

Agreed on the tune.
I didn't get a tune because AM amongst others said it was not necessary and that the PCM would learn itself again.
Didn't happen :(

A tune probably would have solved the problems but I didn't feel like spending even more than the couple of hundred I already had spent because I didn't really have any other mods except a Magnaflow cat back.