Cylinder Heads

ALL RAT Engines are based on our brand new head castings with either or CS, RS or LE port and chamber profiles. We do not offer any engines with old, junk, 40-year-old heads like our competitors.

Please read the below text first before viewing detailed information about a particular cylinder head offering from the expandable menu on the left side of your screen. This will give you a better opportunity to understand just what goes into a truly developed component. Remember, the more you understand- the better you’re engine will be. We are sharing our data to help you make a wise decision, not many companies have any data, much less share it.

Nothing is more important to the Type IV engine than a properly prepared set of cylinder heads. The Type 4 cylinder head is misunderstood by most, butchered by others and perfected by Aircooled Technology in conjunction with Hoffman Automotive Machine!

Len Hoffman of Hoffman Automotive Machine is our head technician. Len has years of experience with the Type IV cylinder heads and with our working relationship we have configured the best cylinder head packages ever arranged for the Type IV engine. In years past the Type IV engine gained a bad reputation for having head related problems, and with developments and refinements Len and I have solved all those problems- No more dropped seats and no more valve failures- period!

Many people make the mistake of confusing the Type 4 head with any other aluminum head, those that are “lost” the most compare the Type 4 head to the Type 1- yet the two share literally zero in physical dimension or the thoughts and ideas and even procedures that are a necessity to properly manipulate them into solid, reliable performers. Hell, these days most shops can’t even be trusted to make simple repairs or even do a valve job on a Type 4 head!

It is never ending… The calls and complaints and failed engines that we see from misconfigured heads that have been worked with by less than knowledgeable persons! Most issues concerning the type 4 cylinder head are the direct result of a human being that didn’t care enough or wasn’t lucky enough to have the experience that is demanded by the Type 4 cylinder head!

A few days ago I was visiting an online forum that I frequent and saw a post from an individual that had just received his spit-shined cylinder heads back from a local professional. I was absolutely amazed when in his posted photos there was a very significant void in the combustion chamber of one of the heads! The worst part of it was the fact that this was visible to the naked eye, yet the “pro” told him that “It would be okay, just don’t remove the exhaust stud that’s under that hole”!!!!! Blasphemy!!!


Issues like these are why we no longer complete procedures on used cylinder heads and also the reason why we have persevered with the development of our “Leading Edge” cylinder heads that you will read about within these next few pages of information.

These cylinder heads are the answer to the shoddy rebuilds and head cores that HAVE BEEN CYCLED FOR THE PAST 30 YEARS OF ABUSE, NEGLECT AND OVERHEATING! Nothing makes a Type 4 engine like a brand new head casting, especially one that has been fully rebuilt right out of the box to the tolerances created by the leading Type 4 developers in the world!

So…. what makes our cylinder heads so much different than the rest????

Below I will break down many facets of our cylinder head program that puts our head program in a totally different classification than any other.

1. Direct benefits of in house testing to offer back to back comparatives concerning the effects of material and procedural alterations.

This basically means that we make changes, note the differences and apply the results to each engine or cylinder head profile. When testing a component the test is only as good as what data is collected and how it is factored into the overall product. Few companies test components, a fewer amount do anything with the data other than just forget it!

Here we have been known to assemble complete engines simply to use as a basis for direct comparison of similar cylinder head offerings!

2. Direct Benefits of using our components in our Racing Applications

The exact same components that are used in ALL of our cylinder head offerings are also used in the Aircooled Innovations Racing Porsche 914-4 race engine. This includes valves, valve springs, valve seats and all other major components! We have been known to run 23 consecutive races (two seasons of SCCA competition) with these same components without a single failure. Keep in mind that this engine spins as much as 8,500 RPM for 30 solid minutes. What does this mean to you??

Well, even if you want a low compression, low-speed engine for your Bus or a high CR Performer engine you can know that the components that are used to comprise your cylinder heads are completely overkill engineered.

3. Material and hardware selection

This is BY FAR the biggest benefit to our cylinder head program. All the testing and the vast amount of engines we have built has given us direct feedback on not only our theory and procedures but also what wear and tear and street and race abuse and neglect can do to the materials that comprise the cylinder head package. Below I will break down most of the materials and components we use and why we use them.

Head Castings- The head casting is the foundation in which all other valve related components reside. The head not only sees the most heat of the entire engine but it also has the biggest role in determining the reliability and especially longevity.

We use BRAND NEW cylinder head castings to base our heads from. This separates our head program from most others simply because other companies would rather dig up a 30-year-old head and clean it up rather than just accepting the fact that it’s just plain worn out and has been heated cycled (and generally overheated) for its entire life!
Replacing the 30-year-old heads with new components is just plain smart and that’s why we do it as a standard. Trying to build an engine that’s based on a 30-year-old head would be equal to painting up an old house that’s full of Termites and rotting down- it’ll work, but not very well and not for very long!!

Starting fresh gives the engine the best chance of living past that 100,000-mile longevity goal without needing attention and without carrying spare tools in the trunk!

4. Valve Seats

Absolutely, without a doubt valve seats are the hottest topic concerning the Type 4 cylinder head! The valve seats that were installed in the stock heads featured 1970s technology for material composition and also the procedures for their install were not as refined as we have today.

Most of the specifications about material and installation of our valve seats are proprietary to our cylinder head program and cannot be shared here. I can, however, tell you that the valve seats that come in the new castings are removed and thrown away, in favor of our own seats installed our own way.

To our knowledge, we have not had a set of heads, or a customer’s engine “drop a valve seat” since 1997! Many things impact valve seat failures, heat being the most prominent, yet even with engines that have been severely overheated these seats still have not failed! I have purposely overheated engines to the sum of 550-degree head temps only to find the seats have not moved!

5. Valve Springs

STOCK VALVE SPRINGS ARE ONLY COMPATIBLE WITH 100% stock cams! That’s right, and since we do not promote the use of stock cams (even for 100% stock engines) all of our heads come with “Heavy Duty” valve springs. Some heads feature dual valve springs, but most of the most popular offerings provide plenty of valve control for the port work they feature and unless severely over revved would not have an issue of valve control with just a single spring. Keeping a single spring increases the fully seated and fully open pressure just enough without producing wear from “over springing” the valves. This keeps cams and lifters especially “Happy”.

Stock valve springs are easily overworked and I have broken them on even low RPM engines with only .030 more valve lift than stock. For this reason, I NEVER promote the use of the stock valve springs, better springs are one of the cheapest and wisest upgrades that one can do to the cylinder heads.

6. “Better” Springs

are a standard in all the heads you will see mentioned here.
Retainers- It’s the job of the “retainer” to do just that, Retain! These very simple but very important parts play a big role in valve control and engine failures.

The stock Type 4 retainers are “stamped steel” and when being used with any camshaft other than a 100% stock grind or when operating above 5,000 RPM (even with a stock cam) the stock retainers are being asked to do way more than they are designed to do!
Retainer failures generally allow the engine to “swallow a valve” as the valve keepers are generally pushed through the center of the valve retainer allowing the valve to simply slide right through the retainer and into its meeting place with the piston, in the combustion chamber. This immediately creates a catastrophic failure and wastes the engine.

The retainers we use as standard equipment are Chromoly steel and offer much more material strength than the stock, stamped steel units. The stronger material resists the forces that spread the retainer and allows the keepers to push through. These retainers help to create a very good sense of security within the valve train and I can honestly say that I have never seen one of these chromoly units fail!
When RPM demands lighter and stronger components we offer Titanium retainers as well.

7. Valves

The valves we use are modern stainless steel units that are made primarily for us by SI industries. These valves far supersede the composition of older stainless steel valves and they offer extreme reliability and feature resilience to wear, even when not adjusted timely and even when downright abused!

These stainless valves can take extreme conditions of heat and RPM between valve adjustments, they have very minimal stretch and this allows for increased intervals of valve adjustments for typical engines. All of my personal engines feature these valves and as of this writing, one of these vehicles has 3.7 years on its valve adjustment without being touched, with over 60,000 miles racked up during that time!

We do feel that these valves are far superior to the “Sodium Filled” valves that were OEM equipment on some Type 4 engines- none of our heads are available with these sodium filled valves that can fail and leave you with an engine that’s just a pile of rubble!
Even our lowest performance offerings right up to some full race, 8,500 RPM beasts feature stainless steel valves and the stock valves that come new in the heads when we receive them new, are removed and trashed as they are substandard.
Our most extreme cylinder head offerings, the LE 220, LE 230 and our Billet “Ultra” heads come with proprietary valve options that open up new doors for RPM levels.

Valve guides- Valve guides are an often overlooked item for quality because most people really don’t know the differences from one guide to the next- I have even been guilty of this generic way of thought!
The fact is that valve guides are THE BIGGEST wear item associated with the cylinder head! This is mainly because they are made of softer material than the valves they are supporting and sometimes with improper valve train geometry their wear is accelerated. With worn valve guides, valve jobs are short lived and oil consumption and crankcase pressure is also elevated, both of which impede performance and tuning.

The valve guides used in all our heads are resilient to wear and are made of a harder material than the stock guides. Stock guides are removed from all of our heads and replaced with our proprietary guides as standard procedure.

Modern thoughts and procedures- Here we don’t follow the leader- Raby’s Aircooled Technology and Hoffman Automotive Machine ARE the leaders!

That’s right, the procedures we use to complete cylinder heads are not the industry standard, they generally far exceed the standard; hell they CREATE the standard.

The procedures in which we create our cylinder heads are “Leading Edge”. Using modern CNC digitization of our most popular port and chamber profiles we are able to replicate each port and chamber with incredible accuracy! Each port being the same volume and shape  helps to create a “balance” for the engine that promotes efficiency and with efficiency comes cooler running, smoother running and better fuel economy. Chamber volumes being exact within tenths of a cc helps to make for an engine that can be better “blueprinted” as the compression ratio of each cylinder is equal.  The point blank truth, is that doing this type of work with the human hand is just not accurate, and even if it could be done accurately it would take dozens of hours and be much more expensive to do than the CNC procedures cost.

The latest generation of our cylinder heads are the best performers, ever.

Currently NO OTHER company offers a CNC cylinder head program for the Type 4 engine. Even if they did, these would still kick their asses.

In Closing:

A set of cylinder heads must be matched to the rest of the engine combination to be effective at creating the proper power band, drivability and running temperatures. This is where our combinations of camshaft, cylinder heads and overall engine combination come into play big time!

 Our empirical data has proven that the valves and ports arranged on our heads are *perfect* so please don’t ask us to use larger valves or ports on your heads! There is a good possibility that the larger valves won’t perform as well as the smaller ones, that are optimum.

Remember that a performance engine is heavily dependent upon its cylinder heads and that if you can’t afford a set of heads you can’t afford a higher performance engine!

Remember: Any engine is only as good as it’s cylinder heads and the cold hard fact is that with any other cylinder head you are starting a project based on a compromise and the result of the project will undoubtedly also be a huge “Compromise”.