1. What exactly is done to the heads to create horsepower? Is it just porting and polishing. Is it cutting or plaining the head? Do you put in bigger valves?

2. What does a cam do differently that the stock cam. My understanding is that a cam controls valve lift and duration. Do performance cams hold open the intake valves longer to get in more fuel?

3. Let's say I've bolted on enough stuff (cold air intake, cat back exhaust, LT 13/4" headers, ud pulley) to get 350 rwhp. How much will H/C add?

 

Great post idea. We're gonna get a lot of opinions about these topics :D

Where to start? Headwork can consist of many different things. The ideal setup would be to have straight and direct ports so the porting and smoothing of the ports is important. Increasing volume and velocity is the major goal of these two. This is where flow bench testing comes into play. Larger valves can be incorporated to allow for more flow as well but you want to keep the valve weight down as much as possible. Valve size is very dependent on cylinder bore size. Port matching is also important to remove any turbulence that may occur between the manifold and heads. A good 3+ angle valve job is also important for proper compression. Milling or decking the heads is a good idea to remove any warpage and/or increase compression. Combustion chamber and valve sizes should match the bore size...chamber size will effect compression ratio as well. Balancing all of these variable is what makes for a good set of heads.

I don't have that much experience with camshaft profiling/design but I'll give my opinion. A camshaft change should match the characteristics of the intake and exhaust. Higher lift will allow for a larger volume but heavy springs must be used to make sure the valve gets closed properly...this will wear the valve seats more quickly. Duration is the amount of degrees that the valves are open. The longer the valve is open, the more it will flow. I think that matching the camshaft duration to the combuston chamber is more important than lift for making power. Lobe seperation is the amount of time in degrees between intake and exhaust cycles. All I really know about this is that the lower the number the more lope you'll get because of the increased overlap. The more the overlap the longer amount of time you can allow for the valves to be open.

The main goal of heads and cam work is to increase the amount of A/F mixture and exhaust gases that are allowed to flow in and out of the cylinders. The internal combustion engine is truly an air pump with an explosion in the middle to generate the reciprocating motion. The more air it can push/pull the better.

A good stage 2 heads/cam combo is capable of netting an additional 100 rwhp.

 

Great explaination! :cheers:

 

just to add. cam lobe seperation angle...

Overlap assisists in scavenging.

This is when the intake valve begins to open while the exhaust valve is still shutting. This serves to "suck" in more air. Sort of a supercharging effect.

 

[QUOTE]Great post idea. We're gonna get a lot of opinions about these topics :DQUOTE]

You did such an excellent job on your reply that no one could add anything and the post dropped off the front page, so I'll add another twist to get it TTT.

When you go to a tuner for this work, is it completely custom or is it a standard 3 cut head work and a matched cam? What can you expect to pay for that?

 

I'm really suprised that there hasn't been more input here. Everyone has their opinion and I'm sure someone can take it to another technical level.

All of the tuners I know of do a real good valve job with a heads and/or cam package. So, the cost of such is included in their package prices.

Thanks

 

Is there any standard to go by to get the scavenging effect? 114 or 112? What are the variables involved?

Thanks