Peter F

Wow Steve that is very impressive, have you made more mods than what's listed in your sig. ?
Any word of advice on bang for the bucks when starting to tune my GT?
Have decided on the x pipe and high flow cats, what else would be needed to get near your numbers?

Cheers/Peter

pappy92651

Hello Peter,

Yes, I have a few unmentioned mods on the car. My list is attached.

Stage I, The best bang for the buck items are:
1)The Ott X pipe with high flow CATs, 2.5" tubing, and free flow mufflers
2) A means to alter your fuel and spark. You will need this if you want big gains from 1 (custom chips, computer, fuel pressure regulator)
3) A means to keep the engine cooler, Devek radiator, 75C thermostat, separate oil cooler (it makes a difference)

Stage II, Items that don't make sense unless you do stage I things are:
1) Headers
2) 968 intake valves or big valves
3) Port work
4) Custom intake manifold
5) High flow injectors

Stage II items are expensive. Unless you have the means to provide more air, fuel, and spark they will do very little. There are plenty of stories from people who bolted headers on and lost power. I had 968 intake valves installed and the only noticeable change was a slight drop in low RPM torque. I didn't gain the power back until I went back to do the job right.

Joseph Fan told me a story about installing headers on his stroked 928 race car. The gains were small. He installed a Phil Treshie carbon fiber intake manifold and gained about 100 HP. The right combinations are required in order to achieve big gains.

You might need to spend time on a dyno tuning the engine for maximum gains. You can play hit or miss while tuning by ear, but you will not know your true AFR at various RPMs. This is like leaving money on the table. The Perfect Power SMT-6 computer can be used to control fuel and spark. It also logs data as you drive. This allows you to check things like AFR at various levels. The GT engine likes an AFR between 13.2:1 and 13.6:1 at higher RPMs.

The stock exhaust manifolds seem to work quite efficiently on the 5.0L and 5.4L engines. Louie Ott did a nice right up:
http://www.performance928.com/cgi-bi...ss_parent=1128

Peter F

Thanks for sharing the details Steve.
Will save the document and read carefully.
No plan for stage 2 stuff at this point, bought the car with need of lots of attention.
I'm currently working my way down my list.
Can't help starting to think ahead and make plans for next stage once the basics are done.

/Peter

IcemanG17

Steve
Heres another ?? for ya. What are the sound levels of your current setup compared with stock? I have heard of modified 928's with really free flowing exhaust getting up to 120db, which is really really loud!