Hey guys it’s me again


New Member
Jun 25, 2019
Oahu, HI
So I came about this 99 mustang gt for a great price. It’s got quite a bit of work in it but the catch is that it needs a tune. I’ve been tracking down exactly what’s been done to the car for a bit and I think I’ve got a pretty good idea of what’s been done to it.

So when I got the car it came with a SCT x4 tuner and in it it had a custom tune, don’t know if it’s a canned/email or custom tune but as for now it runs ok.

I live in Hawaii where muscle cars aren’t really a thing. I heard there’s a handful of people who can tune mustangs on island but it’s next to impossible to get ahold of them. I have a friend who feels pretty confident he can tune my car, I trust him enough to believe it. But I’m also a skeptic and I’ve been reading LaSotas book on tuning with SCT so I can at least know what’s going on.

We’re going to do a part throttle street tune for the time being and get some dyno time for WOT/ boost tuning.

So I guess my question is what do I look out for or pay extra attention when tuning? Never tuned a car and after reading into tuning I may be in over my head. Any input or advice would be greatly appreciated!

Manley rods h beam
Manley pistons -10 dish
Melling oil pump
Beehive valve springs
Oem valve seals
Steel retainers
Oem retainer clips
Comp cam xe278ah cams
BBK headers
Trickflow valve covers
Accufab throttle body
Delphi 50lbinjectors
450 fuel pump
Egr delete
On3 turbo kit
Pt7675 turbo
Aem wideband
McLeod rxt twin disk clutch
Tr3650 trans
Detroit rear end 4:10
strange 31 spline axles
Accel super coils
Tail 44mm waste gate
Tail bov
Boost controller grimspeed
  • Sponsors(?)


Active Member
Aug 22, 2007
New Orleans, LA
I take it your friend has the prp stuff and yall are using sct?

If this is your buddies first go at tuning a ford his crash course is going to be pretty steep. Yours as well. The ford ecus are all engineer based so its quite extensive if you truly want to fully understand all of the algorithms which is necessary to calibrate it correctly / fully. Being a manual trans will make it significantly easier though since you don't have to worry about dialing in the trans.

It seems like a pretty simple setup it should be straight forward to tune. One issue you are going to have is those small injectors will limit you. If your still running a returnless fuel system you can command a higher base pressure at wot to compensate. If you swapped to return style you will have to raise the base fuel pressure to 65psi or so in order not to peg them. Your injectors are going to require some extensive tuning to get them dialed in correctly regardless since there is no published data for them that I know of. And since the deltap multiplier puts them over the max injector size limit you will have to scale your tune. You did leave out some of the more critical details of your setup though. Whats the compression ratio? What heads are on it and what all has been done to them? What maf are you running? What fuel do you run?

Since you have a wideband a dyno is useless for your setup. You will run in to detonation well before MBT on pump gas.