I have a 91 5.0 formula 5 speed and was wondering what the largest lift cam I can use with the stock heads.and how much lift will the stock springs take?
I'm looking for a cam with a rough idle but still good low end.I have a posi with 373 gears .

 

can I run a comp cams thumpa cam?

 

Street use?

A cam grind isn't just about lift. "Stock" heads are pushing it what you're still under .500" lift. Duration, LSA and overlap can make a radical cam without a lot of lift but going too much doesn't make it very streetable.

 

yes its going to be street,once and a while I'lll bring it to the strip

 

a ZZ4 cam can help and its cheap. you can get them almost new for less than 100.00 and probably get the heavy duty springs and retainers as well as the push rods thrown in.
you can also get the LT4 Hot Cam. they are all around too.
you will need to pin the head studs or get screw in ones.
there are a lot of other things you can do to.

 

whats a good cam that will give me a rough idle?what do I need to look for in lobe seperation and duration for a thumpy sound?

 

A low LSA with a long duration will give a lumpy idle. The cam in my 540 has .740 lift and 286/298@.050 but with a 112 LSA it idles smoothly at 1000 rpm.

You're not going to find many street cams with less than 110 LSA.

Assuming you have hydraulic flat tappet lifters, a Comp Cams 12-210-2 will probably suit what you're after. Next choice would be a 12-212-2 but it may be at the limits of your stock valve springs.

 

I have a factory roller cam motor

 

It's all going to depend on your valve springs. Going above .480 lift means you may have valve train problems.

12-412-8 should work
08-422-8 and 08-423-8 will give a noticeable idle but I doubt they'll work with stock springs.

For what you want, there's very few selections. If you want a good camshaft with a lumpy idle, you need to get rid of the factory heads and valve springs.

 

COMP Cams 12-412-8,will this cam give a lumpy idle?

 

also I am going to change to springs to a .600 maxx lift

 

and I'm gonna need a cam that will work with the computer,none of those will

 

COMP Cams 08-414-8,would this cam be a good choice

 

It's not just about the valve spring when going to a high lift cam.

You need to check the piston to valve clearance to make sure there's no contact.

Factory heads use small OD springs. Going to a spring that accepts a higher lift, also means going to a larger OD valve spring. The spring pocket may not be large enough for the larger OD spring and there may not be enough metal to make the pocket larger.

Higher spring pressures have a tendency of pulling rocker studs out of the heads. Pinned or screw in studs are required.

There's also clearance issues between the top of the valve guide and the bottom of the spring retainer at full lift.

The cost to get all the proper machine work done to the heads to accept a high lift cam can be more expensive than buying aftermarket heads.

Factory rockers won't work. The slot cut in the rocker can only allow so much lift before it hits the rocker stud. Roller rockers or long slot rockers are required for higher lifts.

 

Go with either comp 08-501-8, or 08-500-8. I would not go above 0.5 lift. Stock heads will not flow more past that point. Any cam upgrade will require new springs and verifying that all clearances are met. Any cam upgrade will also require tuning in order to make it work properly. Computer compatible means that the car is going to run with the cam, but doesn't mean it is going to run very efficiently.
When I upgraded the cam in my car, which is basically the same thing as yours, I did not get the car tuned for about 11k miles. Needless to say, that killed my spark plugs. The thing was running too rich at the low and, and too lean up high. Now it rips.

 

Go with either comp 08-501-8, or 08-500-8. I would not go above 0.5 lift. Stock heads will not flow more past that point. Any cam upgrade will require new springs and verifying that all clearances are met. Any cam upgrade will also require tuning in order to make it work properly. Computer compatible means that the car is going to run with the cam, but doesn't mean it is going to run very efficiently.
When I upgraded the cam in my car, which is basically the same thing as yours, I did not get the car tuned for about 11k miles. Needless to say, that killed my spark plugs. The thing was running too rich at the low and, and too lean up high. Now it rips.