Cylinder Head Selection: New -vs- Used

As with the engine block a used part is usually just as good for you as a new off-the-shelf part.  We would love to sell you a new set of cylinder heads but never overlook what you already have.  Often we see people buying new heads because of some magazine article they read – often heads that are not setup for what they need or don't match their application. 

Just like the block cylinder heads tend to warp with initial use.  By starting with a good used head you can simply re-surface the head to get back to perfectly flat and square and you will have less warp-age than a new head. 

Another benefit of a used head is the valve seats tend to settle on initial use, this results in a less than perfect valve seal after initial installation.  After the seats have settled in (after a few thousand miles) they are most likely not going to move again.  Subsequent valve jobs will last longer and seal better because of this. 

And finally a used set of heads will show you if your valves are “cupping”.  Often with high spring pressure or high RPM’s (or if your valves float) you will “cup” the valve resulting in a poor valve seal.  With used heads you already know if this is happening and can fix it by installing heavier duty valves or by solving the valve float problems.

This doesn’t mean you should be afraid of new heads.  There are heads that have less problems than others and there are things you can do with new heads to help reduce the problems.  Give us a call and we will help you select the best head and head work for your application.

(Picture a head/manifold combination that has been proven to work well together)

Cylinder Head Coatings:

Did you know that if you had two identical heads, one cast iron and the other Aluminum, the cast iron head would make more power?  The reason is very simple, the heat of combustion makes power!  An aluminum head conducts (transfers) heat more efficiently than a cast iron head.  This means a cast iron head will hold the heat in the combustion chamber more efficiently than an aluminum head.

The problem is most of the “good heads” are aluminum and aluminum is so much easier to work with!  From porting to repairing an aluminum head is always easier to improve than a cast iron head.  On top of that aluminum heads way far less than cast iron.

What is the solution?  Special coatings can be applied to an Aluminum head to help it hold the heat in the combustion chamber and them move this heat into the exhaust.  By doing this you get the best of both worlds.  Our coating process can not only help improve power but also helps stop detonation!  This allows you to run more boost and more compression.

(Picture of combustion chambers and exhaust runner coated on a set of Aluminum cylinder heads)

Re-surfacing:

Just like an engine block a cylinder head will tend to warp with use.  Some heads warp more than others but all heads will move a little.  Re-surfacing the cylinder head will make sure your head is perfectly flat and square to your engine block.  This is critical for keeping head gaskets from blowing.

Another use of re-surfacing the head is to increase an engines compression.  If you mill a few thousandths off the head surface you can increase static compression without changing pistons!  It is always important to check piston to valve clearance but often a significant increase in compression and power can be made by simply milling the head a little.

(Picture of a set of aluminum heads during the resurfacing process, uneven machine marks show how badly the head is warped)

Porting:

Cylinder head porting is a way to dramatically improve the performance of your heads.  Even if it isn’t high lift numbers you are looking for smoothing out the air flow can increase the air velocity and make dramatic improvements to low-end torque.  Of course for big horsepower numbers high lift numbers are important and the only way to get there is with a competent porting job. 

Always remember, a good porting job will help and a bad porting job will hurt!  Done wrong you can drop airflow and really mess up the combustion chamber design.

(Picture of hand porting in process)

Valve Job:

Everyone has heard of 3-angle and 5-angle valve jobs.  Everyone thinks that one is better than the other but the truth is both have an application.  Multi-angle valve jobs (5 angle) provide better low lift air flow.  The reason is the angles in the valve job provide more clearance for air flow at low lift.  The increase in flow goes away once the valve has moved a significant distance away from the valve seat.  This is great for classes where cam lift or duration is limited or for high torque, low lift applications.  Once you start running long duration and high lift a 3-angle valve job will provide the same results.  In the end a competent valve job is very important but knowing the correct valve job for your application is the most important.

(Picture of heads having the valve seats machined)

CC’ing the combustion chamber:

The purpose of cc’ing the combustion chamber is to verify the size so you can calculate final compression.  Did you realize that on factory heads we have seen the combustion chamber size very up to 5 cc’s between one set of heads to another.  This is with heads that are supposed to be identical!  To give you an idea a change of 5 cc’s could change your compression ratio by a full point!  This means your 9:1 engine could end up at 8:1 or 10:1.  Now imagine one head is one size and the other side completely different!  How can you set proper ignition timing with half your engine at 10:0 and the other at 9:1? Of course this is an extreme case but it is always a good idea to cc your combustion chambers.

(Picture heads being cc'd) 

Flow testing:

So you have your killer set of heads with the trick port job, trick valve job, combustion chamber size is set, and everything is ready to go.  How do you know how much an improvement you made?  How do you justify the money you spent getting your heads race ready?  The only way is to flow test your heads and document air flow.  We will typically flow test a head several times during the porting and assembly process, and make changes based on your engine requirements.  We measure both intake and exhaust and take into consideration the difference between the two.  Knowing how you want your engine to run we can use the flow testing process to match your heads to your exact engine requirements.  At DG Motors we have a SuperFlow SF-600 flow tester.

(Picture of SuperFlow SF-600 flow bench)

Coating:

Power is made by the combustion of the air/fuel and the resultant expansion (heat) from the combustion process.  To optimize power you want to keep the heat in the combustion chamber and not transfer the heat into the head.  The heat that is transferred into the cylinder head ends up in your water jackets and is what makes your radiator hot.  This heat loss is a loss of energy that could be used to push the piston down the cylinder and generate more power. 

Once the combustion process is done you want the remaining heat to exit the head and enter the exhaust system without transferring into the cylinder head.  This is especially important for turbo applications as this heat entering your exhaust is what is powering your turbo.

Finally any heat that is transferred into your cylinder head will result in higher head temperatures and a higher likelihood of pre-detonation.  If the head is already hot the chance of your air/fuel igniting early is much higher.  Lowering head temperature will allow more ignition timing, more compression, and more boost!

The process of coating the cylinder head and exhaust runner helps control this heat and keep it where you want it.  It will help increase the life of your engine and the power gains are “free power”.  What this means is you don’t have to burn more fuel to gain the extra power!  The overall efficiency of your engine is increased!  If gas mileage is important to you coating the heads will help!  If being able to run a full race without re-filling is important then coating the cylinder heads will help!

We have the ability to do the coating process for you.  This allows us to first get your heads to where they need to be in terms of flow and combustion chamber size then coat the final product!  If something changes down the road and we need to service the head we can re-coat just what is needed!

Don’t forget to coat your pistons, the same benefits apply!

(Picture of a set of Aluminum cylinder heads and forged pistons that have been coated)