http://www.v6power.net/articles/99.html
Installing 99 heads/intakes on a 94-98 V6 Mustang
By Gaston Teran
with help from Greg Singer
Pic1 provided by Erdkamp Motorsports
The remaining pics were obtained from theponyexpress.com
Last edited on March 19, 2000
As most people know, a large portion of the 40 HP increase in 1999 V6 Mustangs was made by the completely
new intake and heads. Naturally the question arises if these new revised heads and intakes can be used in
a 94-98 car. I will try to list what is involved to accomplish this. Since I have not done the procedure myself,
proceed at your own risk.
Below is a clear photo of the 99 3.8L. Note the relocated TB. It now lies closer to the air filter. As with
just about any fuel-injecter Windsor engine, air goes goes through the air filter, MAF, then TB, crossover
tube, plenum, upper intake runners, lower intake runners, runners in the heads and to the combustion chambers
when the intake valve opens. The 99 intake has dual runners. That means there are 2 (not 1) runners per cylinder.
You cannot use a dual runner intake with single runner heads, so if anyone wants to try this, you need the heads too.
Continue to look at the picture above. The crossover tube travels back towards the firewall (blue line) rather
than to the passenger side as on 94-98 cars. So the plenum in the 99 sits very close to the firewall. Then it
splits into two main tubes (green lines). One goes down the driver's side and one down the passenger's side,
both straight towards the front of the car.
Here is where it gets interesting. As shown by the red lines, the passenger's side "air tube" feeds the
passenger's side head via a short runner and the driver's side head via a long runner. And naturally the
driver's side air tube feeds the driver's side head (teal line) via a short runner and the passenger's side
head via a long runner. The long, more narrow runners promote torque at low and mid rpms while the short,
wider runners help the engine breathe and make HP at high rpms.
Here is a pic of the 99 upper intake upside down. Note how it looks nothing like the 94-98 upper and has
12 (not 6) runners.
Here is the lower intakes installed in the car with the upper removed. Again, there's 12 runners.
I don't know what the round things are in the runners, so don't ask.
Here is a close up of the upper intake sitting upside down. Note the bigger (60mm) TB and crossover tube.
OK now let's get into the details of what is needed for the swap. Before I begin let me state that the
following has never been done and should therefore not be taken as concrete facts. But the curiousity is
there and we will try to explain what is needed as best we can.
Fuel system changes (the tricky part)
The 99 Mustang has a returnless fuel system. That means that the EEC controls the flow rate of the
fuel pump directly and all the fuel that is sent to the engine is used. In 94-98 cars, fuel is sent via the
fuel pump at a predetermined flow rate to the fuel rails and the fuel pressure regulator (using manifold
vaccuum to determine fuel needs) returns all the fuel that is not necessary back to the fuel tank.
Also the injectors are not equally spaced out on the 94-98 cars but they are in the 99's. So you cannot
use your 94-98 fuel rails as is. And you can't use the 99 fuel rails as is because there is no FPR (fuel
pressure regulator) nor return rail. The easiest method to get around this problem is to modify the 99
fuel rails. You will probably want till cut into the rear of the 99 fuel rail setup and cut at the same
place on your set of 94-98 fuel rails and keep the return rail (that runs on the passenger side intact).
Then toss the back end of the 99 rails in favor of the back end of the 94-98 rails (with return rail)
since this include the FPR. You will need to weld the two different rails together at both cuts. The new
return rail should be able to work with its entire length (from FPR to the rubber return hose) intact.
You will need to either tie or spot weld the 94-98 return rail (loose except at connection with FPR)
to the '99 passenger side rail (which is fixed in position due to the passenger side injectors).
Now you have working fuel rails. The '99 rails will accept their new 21# injectors and plug into the
'99 heads.
The heads
This may be the only true bolt-on parts. They will bolt on to the 94-98 stock block. 94-96 cars have bolt
lengths the same as on the supercoupe cars so you can use the ARP supercoupe studs if you like. '98 cars use
longer head bolts (not sure about 97). I am guessing that 99 blocks also use long head bolts so 94-96 guys
doing this swap cannot use 98-99 head bolts. And 98 guys doing this swap cannot use regular supercoupe ARP
studs, you have to get a custom set ordered which costs the same but is roughly 1" longer. The '99 valves
should clear the 94-98 pistons.
The lower intake
The lower intake may be an easy bolt on. You obviously need the '99 gaskets and likely the bolts too. The
thermostat housing appears to be in the same location so you may be able to reuse you upper radiator hose.
The two main coolant lines that travel from the water pump to the heater core in the cabin are different,
so you will need to use '99 parts here too. I expect the water pump connections to remain unchanged.
The EGR valve
The point at which the EGR tube plugs into the upper intake is vastly different in the 99 engine. Instead
of bolting onto the back of the intake, it plugs onto the front.
For those who are familiar with the emmission components of the 96-98 cars, you will recognize these parts.
The silver box and EGR look identical. I cannot confirm if they match the 94-95 emmission conponents.
Nevertheless you should use '99 parts here but the electrical connectors/plastic plugs will work. On the
downside, you will have to lay plenty of new wire. The stock 94-98 harness will NOT reach this far.
So plan on extending the reach of at least 4 electrical plugs by about 10"-12".
The headers
This is an area where I will have to guess. Note the new EGR tube marked in red:
You will need to use the '99 EGR tube because the 94-98 one is completely different. I will guess that the
'99 EGR tube will NOT plug into the 94-98 header so you will most likely need to use the 99 headers. This
cascading waterfall of problems continue since the outlet of the 99 headers may be different than the 94-98
ones. You may have to obtain a '99 stock catalytic converter pipe if you don't want an exhaust that you
know will fit. Or you can painstakingly modify your 94-98 cat pipe (very possible to do, but not easy).
If MAC ever releases their promised 94-98 and 99 performance exhaust products, you could kill 2 birds with
one stone and just order 99 Mac shorty or long tube headers. But at the time of this writing, those have
not been released.
Vaccuum
Vaccuum lines have been moved. You will likely need to purchase vaccuum lines the same diameter as on the
99 engine to add length and "T"s to split 1 line into 2. While these modifications may require careful
planning as far as space, the actual connections are quite easy to make.
The DIS
The DIS is drastically relocated. The stock wiring harness will NOT reach so you will have to extend the
connector for the DIS as well. You will also need '99 plug wires as 94-98 passenger side plug wires are
much too short.
Conclusion
This conversion is no walk in the park. If you were lost during any part of this article, it is likely
you will have a tough time making this work. Expect more problems than the ones stated here.
Swap to 99+ Heads and Manifold? 
