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2V Performance Camshaft FAQ Page

Are these cams reground?
All of these cams are manufactured from brand new gun drilled steel billet cores in the USA.

Be careful as the cheaper ones out there are not gun-drilled but rather are solid.  This means they weigh about 2lbs more each than the factory cams they replace.

Who designed the cam specs?
Mark Chacon of Bullet Racing Cams and Nick McKinney of ModularHeadShop worked together many late night hours on these.  Mark in our opinion is probably the best performance valvetrain engineer for the modular motor, and we are deeply thankful for his help.  We learned quite a bit from him and the staff at Bullet with what really works on these engines.  Much of what really works is not well known I found out.


Why do you say so many other cams have piston to valve problems?
I used to recommend the available cams that people were using that made good power, I actually never intended getting into the cam business.  After a few people bent valves I started my own measurement investigation and was shocked to learn that the popular aftermarket cams were not safe with the stock valves even though the manufacturers were saying they were.  I called Bullet to ask about getting a cam to fit with the stock valve, and the rest is history.

Here is a picture of a stock PI piston with a notch from an improper cam spec.

What is this issue with install centerline?
Its simply the location of the lobes in respect to the motion of the piston.  Specifically its showing the location of the peak of cam lift in degrees to the piston after TDC (top dead center)  The below are showing what happens moving the ICL - Intake Center Line to different locations:

A street N/A car running at 7000RPM or below typically wants about 106-110 degrees on the intake location point.  However the smaller you make this number the exponentially fast you lose intake valve clearance.  110 is a good location for cams smaller than 230 degrees of duration at 0.050" lift.  The earlier (smaller) you make the intake centerline the better the midrange torque of the engine. 

110-112 works good for boosted engines as the boost pressure helps to start the intake flow.  The N/A motors don't have boost so the earlier we open the intake valve the earlier we can start moving the air into the bore.  Higher RPM NA cars with restricted intakes can look at ~112 for an install centerline.  What happens here is that if the point is reached that something in the intake tract is restricting, the later you close the intake valve the higher the HP you can get on the top end.  Our "R" series cams are designed with this, it also allows more intake valve to piston clearance.

114+ is used by the factory for emissions reasons, they have been doing this since the early 1970's.  It has been a common trick to "advance" a cam since the 1970's to gain performance.  Basically if starting with a 115 intake install centerline and advancing it 5 degrees you end up with a 110 intake install centerline.  We simply grind the cams this way since its very hard to advance these in car without spending $400 on a good set of adjustable gears.

Is it the maximum valve lift that causes the piston to valve clearance problem?
No the piston to valve clearance is closest around 5-10 degrees after TDC on most all cams.  At this location the valve is open around 0.100~0.200"  Maximum lift has nothing to do with piston to valve clearance.  It is the duration of the cam (larger makes it worse), and the intake installation centerline (smaller number makes it worse)


What are the details to this piston to valve clearance problem?
The stock Ford pistons do not have valve reliefs a.k.a. piston notches cast into them.  The 4.6 PI is the worse offender here as its intake valve is not only designed ~0.060" closer to the piston than the NPI head, it also has a unique valve with a large ~0.040" thick lip that sticks deeper into the chamber.  Here is a picture showing the difference between a stock PI valve and and aftermarket valve on the right:
You can machine this lip off in a lathe on the stock valve.  This will give you about 0.040" more intake valve to piston clearance which is a big help.  The exhaust side you don't need to worry about.
We offer these modified intake valves ready to go. Check out our Valve Section under the Modular Valve Train Parts Section. 

The NPI head ends up with about 0.1" more piston to valve clearance than a stock PI head and 0.060" more than a PI with an aftermarket valve.  You can use a much larger cam as a result before piston to valve interference becomes a problem.

The 5.4 has about 0.1" more piston to valve clearance than the 4.6 as its piston sits that much deeper in the bore.  You can use a much larger cam as a result as well here.

What are the the valve to piston clearance differences between the PI piston, NPI piston, and 4V piston?
There is really no difference when it comes to piston to valve clearance as the valve will hit the extreme outer flat edge of the piston just about the same time as it goes into the center of the dish.  Here is a picture of a stock NPI piston that was hit by a PI intake valve, the notch made by the valve is in the red square near the top:

Also see the picture below of a valve notch and how far to the edge the stock valve is on the piston


What about notching the stock pistons in the short block?
It can be done, here is a picture of a stock notched piston:



Why did you use 525 and 550 intake lifts?
Any modular cam with a lift higher than 550 means it also has a reduced base circle as the commonly available cam cores only allow for 550 lift at the stock base circle.  Going over 550 lift you either lose some lifter preload, need longer valves, or need shims under the lifters. 

525 is a good point for the stock valve springs in both the NPI and PI heads, it also is a good intake lift for turbo cams as they stress the valvetrain more especially with higher boost levels.  550 lift cams should use upgraded springs especially in boosted and higher RPM applications.  550 lift is also the location where we found most PI intake ports stalling that have had their swirl dams removed.  At 600 lift all the heads we have tested so far without swirl dams flowed less than at 550.  Even on heads that have the stock swirl dam and flow slightly more at 600 lift, the power gain between 550 lift and 600 lift is negligible, and the valvetrain is stressed so much more we just don't do it.


Why are the exhaust lifts smaller than the intake lifts?

The exhaust lift doesn't help as much with the horsepower gains on these 2V engines, it is the duration and the exhaust centerline where the real gains are to be found.  Higher lift stresses the valve stem, valve guide, and valve spring more.  If at the track and on the dyno increased exhaust lift is not showing any significant gain, then why do it.

Ported heads are even worse in this scenario as the intake to exhaust flow ratio of most ported 2V heads is highly exhaust biased already.  This lower lift also helps keep the exhaust port from over scavenging the cylinder.  This is a trick well known in the race world that is now trickling down into the street scene for these heads.  The exhaust lobes on these cams are specifically designed for exhaust duty, and there are different shapes between the various series as well.


What is the difference between an NA and a Nitrous only cam?

The intake lobes are the same, it is the the exhaust lobe that is changed.  The exhaust lobe for the Nitrous only versions are not only larger, they have a different ramp rate, and are usually advanced slightly more.  These changes combine to help cool down the cylinder/piston more.  Usually you will get a small loss of low end torque compared to the NA version in the worse case, and the top end HP will be near the same.  Some versions have more overlap and thus a rougher idle, for those wanting the roughest idle possible this is a good option.  There is no problem running the Nitrous only cams NA, and for small shots of nitrous say 125 or less you can run the NA version should you desire but make sure the tune is good. 


When and why did you change from 5 NA specs to 17 NA specs for the NPI and PI?

We learned that each combination prefers something different if NA, even though they all seem to prefer near the same specs when under boost.  After researching it with multiple dyno runs with the same cams in different motors on the same dyno the same day, we decided to make cam specs to target the advantages (and disadvantages) of each combination.  This was done officially the first week of October 2009.  Any NA cams made before then would be under the old specs, and any made after then are the new specs.

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