How far should I go on my npi/pi swap?

PinkieT

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Ok, I've assembled parts for years now but my back is preventing me physically and retirement is restricting me financially from doing my full PI swap plan on my 98 GT by myself. So far it has a BBK CAI and an Accufab plenum with larger than stock throttle body I installed. In the garage I have a set of PI heads with cams nabbed cheap from Summit's discount area - they are either brand new or fresh rebuilds - and an extra set of used PI cams picked up for a good price. I have a PI intake, a set of BBK shorty equal length headers, 2.5" H-pipe with high flow cats, and a used Flowmaster cat back. I have a cherry picker and plenty of jack stands but no lift. My plan was to drop the engine on the k-frame, take the engine to a shop to do the head and intake swap, install the BBKs, put the engine back on the K-frame, put it back in the car, and then do the exhaust. The minimum I'm going to do is leave the engine in the car and do the PI intake swap (which I can probably tackle myself) and pay for headers to tailpipe exhaust work. I figure that may cost me $500 to $800. Next step is paying somebody to swap the PI cams into my low mileage car, or pay somebody large coin to do the whole head swap. If I go low, I can sell the heads and cams for some good money. How much extra power will I get from the cam upgrade vs. the money involved, and the head swap vs. the money involved? At this point I'm thinking go cheap and do just the intake and exhaust, but change my mind. BTW the car is a cruiser, not a racer.
 

07GtS197

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Cams and intake net the biggest gains. Pi heads do flow better but IMO it’s a lot more work for not much more gain. And it will increase compression. Also it’ll limit your cam choices due to the npi pistons.
 

delling3

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Very limited experience here, but I just finshed a cam and intake swap, and all I can say is it's a completely different car. I guess the '98's had a bit more power as compared to the '96 from the factory, and yours has the benefit of a 5-speed as compared to my automatic. I can tell you my car now pulls strongly to 6000 RPM, whereas before it was wheazing by 4500. I wanna wake mine up a bit more with some exhaust tweaks and a set of 3.73's in the pumpkin. I decided that the cam and intake swap was within my ability and budget. I went back and forth on the heads, but ultimately I am very pleased with the performance gains I got. My cams are not PI cams - they were made by Bullet Cams specifically for the NPI engine. Not sure how they compare to the PI cams.
 

Flade

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I’ve got a set of PI heads with the cams, and intake. Looking forward to putting them on my wife’s 98GT. Just have it had the time. Not much room to work with either to get those heads swapped.
 

96blak54

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Npi heads arent the turds people make them out to be. Its the whole pi head swap package along with the compression bump that brings the car to life and people make the npi out to be boat anchors. Ill admit the pi head is a step above the npi head for many reasons, but it takes forced induction to extract their potential. The potential being a larger exhaust valve.

Shimming the intake lasher .010-.020" in the pi head along with a tweek on the exhaust lobe will wake up a set of mustang pi cams. Remember their are pi cam model differences from other platforms, mustang cam being the best, exploder cams being the worst in terms of performance. Its mostly their max lift values and some of it being duration. On the pi mustang cam, only the exhaust gets more lift. It offers a tad bit of more exhaust duration at valve float during high rpm, extending valve opening during overlap. Adding the shims to the intake lasher broadens the intake cam lobe much like how a higher ratio rocker does for a push rod engine. Therefore opening sooner, closing later. Knowing the pi heads ability to flow phenomenal at low valve lift during duration, doing these tricks broadens overlap for a stock cam. Just another way to pull out power from stock parts and keep the tuning the same.
 
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Flade

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Thanks 96blak54. All great info. Are the stock cams marked? I’ll need to see what is installed in these heads. I know they we’re in a Mustang, but no idea if the cams were stock. The heads were newly fresher by the previous owner who then decide to go with aftermarket heads after a couple thousand miles. I got the heads for a great deal, they have been wrapped tighly in plastic waiting for me to get time to install them.
 

96blak54

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And A little bit of info on the npi heads. I have yet discovered a set of npi head with lashers like the pi heads which leads me to believe the npi lashers cause the valve train to actuate different. In my findings, Npi lashers bleed out faster and takes more oil psi to overcome valve spring pressures. In other words, the lashers makes the valve train variable rate as rpm increases. Which makes sense in todays engine performance. Im thinking this is fords 1st attempt at variable cam rate. Ford nailed it better with the pi heads and its components.

As the opening and closing ramps on the cam lobe transfers function to the follower, the lashers bleed out to a certain lift point making the lobe like a small cam but as rpm bring oil psi up and the lashers bleed slower(just like hydraulics) it gains more of the opening and closing ramps of the cam lobe. Making the cam lobe more of a performance cam. Couple this idea with npi's higher valve seat pressure over pi, roughly 30lbs more, one can understand more of npi heads downfalls. Simple solution is to change out the intake lashers for pi lashers and retain the npi exhaust variable rate function.

Taking this a step further with npi heads. Reduce the valve seat psi by swapping in a lower valve spring. Npi heads have really light valves compared to pi heads. The pi heads valves gained a significant amount of weight over npi valves. Heavy valves dont articulate the cam as well as lighter valves. Heavy valves are slower to respond closing after being opened. Hanging open at the closing ramp. We call that valve float.

So cognitively putting this together.... pi heads low valve seat psi, heavy valves, and stiffer lashers makes the pi head just like a stock strict rules class dragracing head setup. Where rules restrict any performance cam, the racers utilizes valve weight, possibly rocker weight, and reduced valve spring weight to gain more duration at high rpm.
 

96blak54

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Thanks 96blak54. All great info. Are the stock cams marked? I’ll need to see what is installed in these heads. I know they we’re in a Mustang, but no idea if the cams were stock. The heads were newly fresher by the previous owner who then decide to go with aftermarket heads after a couple thousand miles. I got the heads for a great deal, they have been wrapped tighly in plastic waiting for me to get time to install them.
The mustang cams are marked. There are part #'s along the cam length wise. You be wanting to look for parts #'s that are not along the length. IIRC Parts #'s will have the name krupp as well.

Check this thread out. It could be helpfull

Thread 'NPI & PI cam specs' https://www.sn95forums.com/threads/npi-pi-cam-specs.72717/
 
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