The head buzz of the LS community for the last couple years has been focused on the new L92/LS3 style ports. It’s true the new rectangular port style as cast from the factory is pretty incredible. Add some after market ingenuity, a CNC, and watch out. However, the cathedral head – the same one that was installed on every F-Body, many Corvettes, and today’s Trailblazer SS is still capable of making MONSTER power, and some of the hottest head manufacturers in the after market have been pouring resources into making the best “traditional style” LS1 heads on the market.
This is our guide to cathedral port head technology as of April 2008.
The first thing we want to tell you. WAIT! Don’t go throwing out your cathedral port designs just yet. Don’t forget the old adage, a chain is only as strong as its weakest link. That applies to engines as well; even the best head can be choked by a mediocre intake or undersized throttle body. In other words a head is only as good as the intake bolted to it.
I started counting all of the different intake manifolds available with the cathedral port and quite frankly ran out of fingers. On the other hand, when you look at intakes currently available for the L92 ports, and quite frankly it’s not good. A cast aluminum carburetor style is available and pretty good if you need that style. The factory one works a decent, but it certainly was not designed to meet after market needs. If you have a deep wallet, there are some very nice sheet metal and billet intakes for L92’s. That is why the cathedral port heads are still so relevant.
Let’s get started – we’re going to take a look at each manufacturer’s latest Cathedral Port heads:
GMPP offers 2 flavors of CNC ported factory heads – a CNC ported LS-6 head which features 2-inch hollow stem intake valves designed to push rpm limits, and a CNC ported LS2 package with factory valves for the more budget minded racer. Both styles from GMPP feature large 250 cc intake ports.
Here’s the basic layout and specs of each of these GMPP OEM offerings:
Livernois Motorsports, one of the most reputable shops in the LS1 aftermarket has a little bit more extensive line up of ported factory options on the GM castings. Led by famed street legal drag racer Dan Millen, Livernois is currently offering 4 stages of cathedral port cylinder heads.
Stage 1 starts out with brand new GM castings, and are 5-axis CNC machined to a 220 cc intake runner that flows 305 cfm, with 235 cfm of exhaust flow. The Livernois single coil valve springs are good to .580-inch lift.
Livernois’s Stage 3R heads are Millen’s answer to what is the baddest cathedral port head available in the market place. Starting with the same casting, Livernois applies a monster 240cc intake runner that flows upwards of 335 cfm. Exhaust is 262 cfm with a pipe on the flow bench, and 2.100-inch intake runners get the call. At a street price of less than $2,100 – that’s some major power for low bucks.
• Livernois Stage 3R
Flow: 335 cfm intake, 262 cfm exhaust
Valve Sizes: 2.100-inch intake, 1.575-inch exhaust
Street Price: $2100 or less
Pros and Cons – Using the LS1/LS2/LS6 OEM Castings
They are an excellent option for most heads and cam packages, because they offer the performance flow buys and the factory valve angle makes a good fit for factory pistons. Of course nothing is perfect, factory LS- heads were designed for a specific purpose, which means the deck surfaces were not designed to make over 600 hp, but like the work of most good engineers, they have been proven capable of more. That doesn’t mean pushing them to far is a good idea, because they will have some durability issues, especially with head gaskets in a serious forced induction environment.
That being said, the factory LS1/LS2 and especially the 243 LS6 heads have some major performance potential.
Cast for Perfection – After market LS Cathedral Heads
By custom casting a head, manufactures have a clean slate to do virtually whatever they choose, and several companies have chosen to do just that. AFR, All–Pro, Dart, ET Performance, World Products, Edelbrock and Trick Flow, all have designed their own cathedral port head castings. The great thing is that instead of everyone trying to do essentially the same things, they have chosen to attack their designs in several different ways.
Everyone has their favorite head or head manufacturer. We generated this article to give you an overview of some of the newest head technology coming from the Cathedral head manufacturers.
What do companies do with a clean slate?
Add Deck Thickness
The cylinder head deck is the sealing surface face, by adding thickness, the deck is less likely to flex and cause dreaded gasket leaks. The factory cut away we demonstrate has a 0.400-inch thick deck, while after market heads are cast considerably thicker up to 0.750-inch deck.
In blue on the left is a sectioned Dart head with a .500+ -inch thick deck, on the right is a GM head with a .400-inch deck.
Enhanced Rocker Arm and Spring Options
When people change heads they almost always have more aggressive cams and higher valve seat pressures. All of that means a bunch of extra forces which the factory heads really were not designed to handle, even though like most things, they can handle more than they were designed to handle. With after market heads, you have the possibility for larger valves, and for enhanced rocker arm mounting surfaces.
Years ago, an after market head upgrade meant going on a diet from a cast iron boat anchor, to a sleek aluminum part. Now-a-days aluminum is a given, but not all aluminum is created equal. There are so many variations of aluminum alloy, that people make careers out of studying them. Manufacturers, who create their own casting, can choose the alloy, which gives them the best balance of properties.
Standing up valves relative to the deck surface allows better flow. Looking back to the production days of the small block Chevy era, 23 degree valves were typical. When engineers decided to build a better mouse trap with the LS-1, they stood the valves up to 15 degrees for production. Manufacturers produced heads decreasing the valve angle for SBC to improve flow, and now some companies are choosing to do the same with LS heads.
Port & Wall Thickness
When porting a factory head, the wall thickness around the ports limits just how far the CNC can cut. When doing a custom cast head, the designer can shrink water jackets and such to buy more space for monster port volume if they so desire. It also gives a clean slate for manufacturers to modify the combustion chamber for the desired swirl and flame propagation.
Additional Design & Engineering Options
I know that sounds like a real catch all and it kind of is. Head gasket sealing has always been a concern when increasing power on an LS engine. Four head bolts are a limiting factor which led to the adaptation of six bolt designs becoming standard and optional for LS heads and blocks. The factory valve covers and rocker design don’t allow a lot of room for bulking up, but some head manufacturers have tried to design ways to help the situation.
The Guide to After market Cathedral Port Heads
There isn’t room to review every single after market LS1/LS2/LS6 head here, but we will cover the newest releases from the head manufacturers.
Dart has recently introduced their new Pro 1 CNC LS1 head with a larger 250 cc intake runner. Dart has made some key improvements to the durability of the casting – and – as with all Dart products – it is made of premium aluminum and machined on world class CNC machining centers.
Some upgrades include: extra material above the ports, bronze valve guides, interlocking valve seats, an extra thick casting, and radiused exhaust seats.
Dart’s Pro 1 CNC LS head maintains stock valve angles, features the 250 cc intake runner and a larger valve package, makes it a good option for bolt-on heads and cam packages with aspirations of taking it to the next level in the future on 4.00-inch and larger bore engines.
The head comes bare or assembled by Dart with monster 2.08-inch intake valves!
• Dart Pro 1 CNC
250 cc Intake Runners
Flow: 322 cfm intake, 240 cfm exhaust
Valve Sizes: 2.08/1.60
Street Price: $1,500/set unassembled, $2,200/set assembled
A few years ago – to be honest – I don’t think Edelbrock was much of a player in the LS1 game. Frankly, they had only a few selections of products and they were geared to the entry level market. Well, that has changed and Edelbrock makes some top-tier Cathedral port heads which we are going to review. Edelbrock has long had a Lingenfelter-ported version of the LS1 head, which is a 202cc CNC-ported head which flows about 300 cfm on the intake. However, we’re going to focus our attention on the new RPM Xtreme LS Edelbrock heads and the Pro Port heads.
Edelbrock’s RPM Xtreme head is an as-cast port design that has some CNC porting. Edelbrock says that it’s as-cast port design along with the CNC work in the chambers, intake entry, exhaust exit and intake/exhaust bowls give you the best both worlds – an affordable head which offers tremendously increased performance. Plus, you can still CNC port the head!
A few interesting things Edelbrock brings to the table with the RPM XT:
• 5/8-inch thick deck
• 214cc intake and 80cc exhaust runners (unported) flow 286/215 cfm at only .600 lift.
• 2.02 and 1.57-inch valves
• CARB 50-state legal with part #61949!
The RPM XT Edelbrock heads are not the biggest flowing heads in the LS1 Cathedral port market, but they provide a good, solid value head which has the Edelbrock badge of quality and will offer stellar street and street/strip performance.
LS-Series Pro-Port Raw Head
If the RPM XT is Edelbrock’s happy-go-lucky want to be friends with everybody LS head, the Pro-Port is the street fighter of the line up. “Designed, engineered and cast with porting in mind,” says Edelbrock, as,”the Edelbrock LS-Series Pro-Port Raw Head is the perfect casting for any custom cylinder head porter.”
Edelbrock’s Pro-Port is a raw casting – in fact, the same casting as Edelbrock provides to Lingenfelter for their CNC ported LS1 head. This the perfect head for hardcore engine builders or racers that want a casting with extra material in critical areas and who want medium to large port sizes with serious flow numbers.
Here are some of the features that Edelbrock listed for us:
• Tall intake short turn and small intake cross-section for modern, high velocity port designs
• Exhaust features extra bowl and short turn material to accommodate all exhaust port shapes philosophies
• Extra metal and merged rocker boss pairs for improved valve train stability and support
• Extra material in the spring pockets to allow machining for larger spring diameters
• Heavy deck thickness ensures optimum gasket retention and material for milling of the deck for smaller combustion chamber sizes
Chamber size on these Pro-Port heads can range from 80cc for forced induction cars, to a tiny 40cc for high winding N/A engines. These Pro-Port heads are like the NHRA Pro Stock castings of the LS1 cathedral-port market – they are what you make them. We wouldn’t recommend these for beginners, but your engine builder may think these are a great choice.
To the best of my knowledge, Air Flow Research (AFR) was the first to offer an after market custom cast cylinder head for the LS market. In addition to an as cast version of their Mongoose head, AFR offers a 205 cc and 225 cc intake runner, along with a redesigned 66cc and 72cc combustion chamber to dial in the best compression ratio for your engine. They have also taken advantage of the design flexibility to give the Mongoose a thick .750-inch thick deck surface, and reinforced rocker bosses.
The 225 cc LS1 Mongoose in the head we find most interesting – as AFR claims it is the ultimate bolt-on emission-legal street strip head. It flows great numbers, 320 cfm and 250 cfm respectively intake and exhaust, and the big bore version features a nasty-large 2.08-inch and 1.60-inch intake valves. The Big Bore head really does require a larger bore due to the valve sizes, but the head will work on anything from the preferred 400ci+ engine to the turbo/supercharged 346ci displacement. The head is also available in small bore (small valve) versions and in 62/65 and 72 cc combustion chambers.
All-pro heads has also put a lot of effort into building a very durable casting with a bunch of race specific features. They are currently offering what they refer to as the Generation 3 LS1/LS2 head, with a claimed 50 hp improvement over stock castings.
All Pro has moved the valve cover mounting out and up to maximize clearance for rocker upgrades. Large 244cc and 250cc intake port options are designed specifically to work best with higher power applications. If you need any proof that these are serious race heads, Steve Turly, the number one qualifier at the LSX shootout is opting to run a set of cathedral port All-Pro heads again this year, rather than moving to the square port design. He is also taking advantage of the 6 bolt option which is hugely important for head gasket sealing when your trying to make the power it takes to run 7’s.
The All-Pro heads are really designed for large bore engines, as they come equipped with 2.08-2.125-inch intake valves, and 1.600-1.625 exhaust valves – the largest of the cathedral port heads. All-Pro seems to have a pretty dominant position as a hardcore LS1 head manufacturer with these super ultra-level pieces.
Some information about the All-Pro Generation 3 LS1 Head:
• 244 or 250cc Runners
• Head is unported, but CNC porting is available
• Large Bore recommended
• 2.08-2.125 and 1.600-1.625 valve package
Rewriting the rules of the game, ET performance evolved from a porter, to a manufacturer largely based on the success of their early commitment to the LS market. They now offer several versions of ported factory heads, as well as their own casting. The new casting stands the valves up to 11 degrees from the factory 15 degrees. They also offer a huge variety of five different intake runner volumes to fine tune for virtually any displacement and rpm combination.
ET has the widest variety of heads that fit the “high end” LS1 Cathedral port market. This is largely because this is the segment that ET specializes in. We will go over some of the variety of LS1 heads ET offers, but you are best served by reviewing their web site product list.
The ET castings are the most radical of the ones reviewed here, and there are versions that flow up to 370+ cfm or more, partially due to the radically modified valve angles. These heads are generally reserved for competition vehicles or race cars, and not for the average grocery hauler. If you’re interested in a top-tier head product, this is an excellent selection.
ET LS1 11-Degree Cathedral Port Heads:
• 215, 225, 240cc
• 255, 265 cc
Trick Flow GenX
Getting in on the action is Trick Flow with their own line of new GenX CNC ported cathedral port heads. They choose an intermediate route, with a handful of common racing upgrades like 13.5 degree valve angles, reinforced deck surface, modified spark plug location, and of course a larger sleeker intake port. CNC and as cast versions with different valve diameters and port size give options to support each of the common LS bore diameters.
Trick Flow offers the GenX in “Fast as Cast” and “CNC Ported Versions, and based on our conversations with Trick Flow – they are SERIOUS about LS performance.
“During the development stage of the Trick Flow GenX Street/Strip CNC-ported cylinder heads, we determined that the valve angles needed to change from 15 to 13.5 degrees to decrease valve shrouding, increase mid-lift airflow, and improve rocker arm-to-valve cover clearance,” Trick Flow explained. Other features include 2 difference CNC programs (215 or 225cc) and several different combustion chamber and valve size options.
• 215 or 225cc Intake runners, 80cc exhaust runners
• 64 or 65cc chambers
• 2.04 or 2.055-inch valves
• Assembled heads come with 1.300-inch dual valve springs for up to .600-inch lift.
World Products is playing the game with their own cathedral port cylinder head – the Warhawk LS1X. They choose to keep the factory 15 degree valve angle. The 235 cc port is a good median volume to work well in most application, and has 64cc and 72cc for some compression ratio options. They also help to address the desk surface stability issue with an injection of some aluminum. One of the more interesting changes they made was to raise the valve cover mounting rails 0.350-inch to buy space for longer valves or maybe different rocker arms.
• Available with 200cc or 220cc intake runners
• 200cc head has 2.055″ intake valves, and 220cc has 2.080″
• Exhaust valves are 1.600″ and all stems are 5/16″
• Choice of 64cc or 72cc combustion chambers
• Made of 355-T6 aluminum and has thick .750″ deck
• Available Bare and Assembled with Different Spring Options
We looked at a bunch of heads, from several different manufacturers, with a ton of options. It is important to realize that you need to do some additional homework prior to making the big decision. Flow numbers are important, but they represent a steady state condition at a certain valve lift. In the engine the heads must work dynamically, valves are constantly moving, air is starting and stopping. So don’t base your buying decisions solely on a flow number.
Port size is an important part of maximizing how the head works in real world dynamic conditions. If the port is too small it will restrict air flow. If the port is too big, yes they can be too big, the air will tend to stall and decrease the flow. A head expert can look at displacement, diameter and how fast you plan to spin the engine, to determine the best port size for your application.
Truth be told, cylinder heads are probably the most complex part on an engine. They serve as the conduit for air flow in and out of the combustion chamber, seal the combustion chamber in three ways, make up half of the chamber, house the spark plugs, collect the majority of excess heat into the engine and physically support the valvetrain, whoo!
If that is not complicated enough, think about everything else to consider when you buy a set of heads assembled with valves, seals, springs, retainers and keepers. If you are purchasing fully assembled heads, there are plenty of other considerations. So what does all of that mean? There are no easy answers! Discuss your application, present and future goals with the manufacturer or an experienced sales agent prior to purchasing. It’s the best way to ensure you get the best fit for your engine, and your budget.
Feel free to ask questions or start a discussion in this thread and I will do my best to answer it or get you the answer!