Just going from your factory NON PI (power improved) heads to a set of PI heads like the SHM with a port and valve job you can expect to see atleast 40-50 rear wheel HP over stock.

As stang00 said, port and polished PI heads can expect around a 40 rwhp increase.

From the factory FMS heads alone will get you around 35 rwhp, add the FMS intake, and you're looking around 45-50 rwhp. These are all stock numbers from the factory, so any additional work done SHOULD give you an even better increase....

The worked over PI heads give you an extra 5-10 rwhp at peak, but the FMS heads give a better power output along the curve, lower compression ratios, and room to grow if need be.

Part #s:
M-6049-D46 : heads
M-6067-D46 : Head changing kit
M-9444-D46 : Intake install kit
M-9424-E46 : Intake Manifold

Possibly a new Engine Management Computer (M-12650-A461 Auto trans. or M-12650-B461 Manual trans.) or custom\dyno tuned chip with the stock computer.

I would contact Ford Racing (586-468-1356) or another knowledgable company such as Dallas Mustang (800-MUSTANG) for specifics on your application and help with purchasing the exact parts you may need..

awesome. thanks.

I think your numbers may be rated a bit on the low for both heads, I gained 130rwhp with the FRPP heads+intake and a set of regrind cams and have seen PI swapped cars in the 280rwhp range. IMO a headswap is a must on any pre '99 car.

The FRPP heads outflow ported PIs straight out of the box, throw port work on top of that and they are ther best bet for performance, BUT at a much higher premium. FRPPs will cost near double the PIs new for new, unless they've come down recently.

Another good question for you would be what are your overall plans for the car? If you ever decide to go with a power adder you need to know that the PI heads will increase compression on your motor and create a very N2O happy environment, whereas if you decide to go with forced induction the FRPP heads will leave compression unchanged, a better environment for boost.

I'm quoting numbers on a BONE stock 96-98 car without reground cams using "out of the box" FRPP pieces. The old yellowjacket gained about 65 rwhp with the FRPP head\intake alone, but had a lot of bolt ons to begin with, so its hard to estimate what a "stocker" would do. Ford motorsports quotes a gain of 35 hp with the heads alone. (which I also think is conservative)

I also don't like to estimate high and then see someone disappointed when they get it on the dyno...

I am surprised nobody has brought up the fact of porting a set of 96-98 non-PI heads. The PI swap gained a ton of popularity because out of the box it adds decent power, but 30% of the gain comes from the PI cams. When you start talking about porting, you can get the 96-98 heads to flow better then a set of ported PI's. Then throw in a set of PI cams and you have at least as much or more power for less money.

I personally don't see that porting the "pig" heads is the best option for the money. Why not save up for PI heads and have that same port work done to them for even more flow?

Because when ported, the PI's don't flow better.

Then you're not using the right porter. PI heads when ported properly do flow better than non PI heads.

Bill

Put the pipe down please.

Renegade Racing has been doing this for a little bit now, and they get better intake flow numbers from the ported NPI heads then they do the ported PI heads, but on the same note they get better exhaust flow from the ported PI heads then from the ported NPI heads.

Also, you will probally make a little more power with the ported PI head then with a ported NPI head because you are getting some power from the higher compression that comes with the PI head swap.

There are ups and downs really. If you use PI heads you up your compression so it would be harder to use a supercharger with that much compression. But with NPI heads it will stay the same the compression and you can boost your 4.6 with less fear of detonation.

IMO, the renegade NPI's offer a better bang for the buck then converting to PI heads and the other parts required.

I might concede that from a money standpoint that the renegade NPI heads are a better deal, but port work for port work, there is no way that they will make the power the PI heads will.

Do you have any flow numbers? Not trying to call you out or anything but I can get my hands on some flow numbers from some ported PI heads to compare.

Also just a heads up but the intake side of these heads isn't restrictive it's the exhaust side so by opening up the intake side even more it isn't going to help as much as opening up the exhaust side more.

Bill

Here's what a set of Renegade's heads flowed for a friends street car, and Jim could have gone a bit more, but he wanted to keep the port ratio at around 70% for a good split.
intake:
.100"-68
.200"-120
.300"-166
.400"-190
.500"-208
.600"-220

exhaust:
.100"-95
.200"-142
.300"-161
.400"-170
.500"-172
.600"-178

Something to remember..absolute peak is nothing for comparing flow numbers..
Add up the values from .100-.600,and them add up the same values from the head that is being compared-and see who has more total "area under the curve". Also remember..you spend alot more time at .300-.400 lift than you do at .600 from just the physical aspects of camshaft lobes.

I am not trying to start a war here or anything. I guess I expressed myself wrong in the first couple of posts. I just don't think that the PI's are the all high and mighty for street cars when you get into porting. From what I have seen is the NPI's can be made to work very well, and for less total cost. Sure, out of the box, there's no comparison, PI hands down.

91LX2Bfast - what kind of a price would i be looking at to port my NPI heads? or are you saying that you buy these heads from renegade?

Well, just like any good porting, its not cheap. Your looking at $1500-1800 for the whole meal deal w/ bigger valves, Modmax spings, etc, etc, etc. But you get what you pay for.
I have seen some pics of some of these so called "ported" head kits and the porting is no better then what anybody can do with a dremel in his own garage. If you are going with a ported head setup, no matter what head you are using, choose a porter very carefully.

i found a set of ported stock cobra heads for 1100 bux
if you aren't in a hurry, you might be able to find a deal somewhere...