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Mclaren Heads

By David Vizard

McLaren, like Cosworth and Ferrari, is a name that for both pro engine builders and race enthusiasts alike is synonymous with high tech performance. Although long a separate entity of McLaren International, one of the most successful teams in the history of Formula One, McLaren Performance Technologies was originally the engine development division of Bruce McLaren Motor Racing. During the many years it has been in operation, McLaren Performance Technologies has developed and manufactured numerous advanced products in the field of power train, traction control and differential systems.

However, the company is probably best known for a number of highly successful specialty performance vehicles developed in partnership with major auto manufacturers. During the early ’90s the McLaren 5.0L Mustang made hot media headlines, and the recently introduced supercharged McLaren Lincoln LS appears to be following suit.

With McLaren’s business expanding rapidly, the company needed to step up both R&D and production capability. To meet these needs in 2001 it acquired from Gary St. Denis and his associates, Dart Machining Canada (not to be confused with Dick Maskins’ Dart Machining USA). Dart Machining Canada, which is now trading as McLaren Performance Products, is well known within the industry for its production of cylinder heads, engine blocks and differential housings.

To professionals in the performance business, Gary St. Denis is a familiar name. He has, over many years, carved a reputation as one of the most prolific and respected cylinder head designers in the business. If you have ever bought an aftermarket head, be it Ford or Chevy, there is probably at least a 50/50 chance that Gary was involved in its design or production somewhere along the line.

Now in semi-retirement, divested of interests in various other companies, St. Denis has been able to focus his attention on advanced engine and chassis development for his championship Automobile Racing Club of America (ARCA) stock car racing program. A rough draft of a small block Ford cylinder head, with what was hopefully the potential to significantly advance the state-of-the-art, was shown to McLaren Engines. The design concept met with much enthusiasm and resulted in St. Denis’ expertise being retained to see the project through.

The harnessing of external resources such as St. Denis is a strong indicator that, as a corporate group, McLaren Engines is not prone to falling foul of the "not invented here" syndrome. When presented with the new cylinder head design, Steven Rossi, McLaren’s CEO and president, commented, "this is just the sort of high octane opportunity that Bruce McLaren would have envisaged when he originally founded the company."

Teamwork is what wins races in F1 and the essence of that appears still to be part of McLaren’s policy. To this end, in-house talent is often augmented with outside expertise. In this case, not only did McLaren retain Gary St. Denis but also brought in Don Losito of Ultra Pro Machining in Charlotte, NC, and Carl Foltz of CFE in Eastpointe, MI, two of the nation’s premier cylinder head development engineers. Both of these gentleman have, amid the pro ranks of all major forms of competition, built race-winning reputations spanning several decades.

My involvement in this project began when McLaren Engines’ Director of Product Development Bill Gardner (late VP of Product Development at World Products) called and asked if I would like to get involved at an early stage so as to get a more in-depth story on the development of the new ProKing heads. As far as I was concerned, anything that looked like new technology with potential was of major interest.

Drawings And Prototypes
Shortly after my talk with Bill Gardner a UPS package containing Gary’s original drawing and the prototype flow bench model arrived. The drawing (Figure 1) depicted a head configuration having a 10-degree valve angle and steeply down-drafted ports. Looking at the ports in the prototype model revealed that about 70-85 percent of the backs of the intake and exhaust valves were in the line of sight. If pushrod motors, with two parallel valves per cylinder, were mandated for Formula One, the Pro King is about what I would expect to see.

Although subsequent development would inevitably bring about changes and refinement, I ran the model received on my well-equipped (and accurately calibrated) flow bench. These initial tests revealed the raw ingredients of a potential super head. The model intake port displayed good high lift flow with exceptionally strong mid-lift flow.

Equally important, and often overlooked, even by some of the most recognized head porters in the nation, was the good port velocity distribution and high overall port velocity. Along with flow, the swirl measurements also displayed desirable characteristics and, by adopting the 10-degree valve angle, the resulting compact combustion chamber could deliver high compression without the possible negative effects of a high piston dome.

In a similar manner the exhaust also delivered excellent flow bench results. The high numbers seen were generated more by virtue of efficiency rather than size.

To confirm the concept viability of the prototype head design, St. Denis put together a 358 cid ARCA (like NASCAR’s Winston Cup Series but with less restrictive rules) motor. The high velocity ports produced results that met expectations by delivering a wide torque curve that peaked in excess of 540 ft.lb. along with enough hp to qualify third fastest in its first race. This much torque represents well over 1.5 ft.lb. per cube, a level achieved by only the best and most highly developed single-four-barrel, 12.5:1 compression, 2-valve, pushrod motors.

If development of the ProKing had stopped at this point it would be very competitive. But it didn’t. Instead McLaren handed off both wet and dry airflow, swirl and velocity development to Losito and Foltz to see what more could be wrung out of the basic casting while they attended to other developmental and production aspects.

The basic reason for this, according to Losito, was the promise of some innovative high tech porting. A secondary reason, also worth a mention, is that Losito has proved easy to work with on projects such as this. Those people well acquainted with Don Losito know him as someone who is big on results rather than ego. The string of high caliber people that go through his Charlotte shop reads like the who’s who of big time motor racing be it Pro Stock, Winston Cup or even Top Fuel Harley. If you are wondering why you have not heard Don Losito’s name before now it’s because he is too busy looking for results rather than public recognition.

As events were to show, the ProKing’s ports as developed by Losito were cutting edge technology because, at the early stages of development, the ProKing’s casting patterns were still open to changes. Losito decided to investigate the effect of some radical changes. This proved very interesting, and a little out of the ordinary.

Intake Development
After running an extensive test regime on the original flow bench model Losito commented that St. Denis had designed a great casting from which to work. A check on Losito’s flow bench figures showed they matched mine, mostly, to within about 1 percent. I’m stressing this point because I regularly check my bench’s accuracy with special calibration orifices. Using those same plates on other benches I have seen user-friendly numbers to the tune of 30-40 cfm more.

The first major step was to develop the induction side of the head. This meant investigating more than just the port contained within the head casting. In practice, factors influencing the induction side of the head start well within the intake manifold and end deep in the cylinder.

The most fundamental goal was to maximize flow starting at the point the valve leaves the seat. Although achieving high flow is a substantial part of the development of a successful head it is far from the whole picture. Optimizing the often more complex interactions of port velocity, swirl and mixture quality make the difference between a sure-fire winner and a strong mid-field finisher.

Port Evolution
Because of his considerable Winston Cup and Pro Stock success with 50-degree intake seat designs, Losito’s first move was to cut a seat on the pre-production casting which the CNC model was to be made from. Here he had a virtual library of seat forms to choose from. Many of these were developed from his single point, CNC driven, experimental seat cutting machine. The form chosen was based on proven results in a head having a similar intake bowl and chamber form to that anticipated for the ProKing.

Now is not the time for an in-depth look at seat designs but suffice to say there is greater difficulty finding good low lift flow with a 50-degree seat than one of 45 or 30 degrees. The payoff with a 50-degree seat comes at higher lifts. Only by having a highly efficient form will a 50-degree seat produce good low lift numbers. As subsequent flow tests were to show, Losito’s first choice of seat form, when combined with the rest of the port package, delivered just that.

Once the seat had been cut, work started in parallel on the intake port and combustion chamber because of their inter-dependence. In general, we find the greater the port’s flow potential is the more the chamber needs to be de-shrouded around the valve. Generating a successful form, be it a port or chamber, involves far more than just finding airflow. Without considerable attention to mixture quality, which is a function of fuel droplet size and mixing, port velocity and swirl, the head may only be an also-ran. Detailing port/chamber development would fill many more pages than we have here so I’ll deal only with major issues.

First the intake port went through four major iterations in form (left to right in Figure 2). Initially it was a conventional rectangle of moderately tall form with average radius corners and flat walls. It ended as an almost square form having a curvature on the roof and floor. Going this seemingly obvious route maximizes the ports average downdraft angle. In this final form the port floor is over three inches from the head face. Putting that into prospective, we can see from Figure 3, that it produces a short side turn of greater radius than on the long side of most performance heads.

Although the obvious advantage of the fourth generation wide, high centerline port is added airflow potential, there were other significant and exploitable benefits. Other than producing the optimal port entry area for the valve flow efficiency, it also allowed the desired swirl characteristics to be realized. Also, with some refinement, a very interesting (and possibly unique to Ultra Pro) port velocity distribution pattern was achieved.

This pattern proved an effective means of countering the ill effects poor mixture homogeneity brings about. In practice this produces a head that is far less sensitive to carburetor atomization problems than would normally be the case.

To better understand how Losito’s intake port works, take a look at the computer generated intake port velocity map (Figure 4) as measured on my flow bench. Such measurements revealed two significant factors. First, this is truly a high-speed port. The velocities look more like those of an F1 head rather than a two-valve pushrod head. Secondly, the velocity distribution was nothing short of excellent and, for a pushrod motor, pretty much in a class of its own.

The fact the port measured out at such a high velocity may cause concern as it might appear to fall foul of the limiting port Mach speed before reaching the rpm typically seen by today’s top competition engines. Let me allay any fears on this score. The more uniform the port velocity is the higher the limiting Mach speed becomes. Whereas 0.55 the speed of sound represents a practical limit for a pushrod engine with typical port velocity distribution a figure of 0.65 is common to an F1 style motor. On a scale, Losito’s port is nearer F1 than the typical pushrod.

With its high and more even velocities, this head can not only get away with a port of some 10-15 percent less cross sectional area but also capitalize on it by delivering significantly superior ram charging around BDC. Unlike pressure wave cylinder filling, which is only a positive benefit over about 400 rpm, inertial ramming due to air mass times velocity squared operates over an rpm range wider than is typically used by a race engine.

At this point Losito’s port looks pretty good – but there’s more. Take another look at Figure 3 and you may spot the fact that, unlike typical Ford heads (aftermarket or otherwise), the highest velocity occurs on the cylinder wall side of the port and the port floor. This is opposite of what normally occurs. In most instances Ford-style ports normally flow more air on the wall nearest the center of the cylinder and almost all ports, Ford or otherwise, flow faster on the roof than the floor.

This reversal of the high velocity location positively impacts the mixture quality arriving at the cylinder. Normally, fuel fall out is from the high velocity air on the roof of the port to the low velocity air on the port floor. For fuel to fall out of suspension in this fashion in Losito’s McLaren ProKing port it would have to fall upwards!

Intake Manifold Compatibility
Other than countering gravity-influenced fuel drop-out, there is more to this port yet, so let’s stay with it a while longer. The intake manifold’s bends and the runner approach angles to the head have a significant effect on mixture quality, especially in carbureted engines.

Looking at the bigger picture first, we find that fuel droplets large enough to be influenced by gravity or the approach angle of the intake manifold (coming in from the right on Figure 4) hit high-speed – rather than the more normal low- speed – air. This significantly reduces the amount of fuel that ends up streaming on the port wall.

For those intake port runners arriving from the left of the head port, any large fuel droplets will be dumped onto the port wall on the side of the cylinder center. The bulk of the air flowing on this side of the port is subsequently dumped into the middle of the cylinder. Going this route takes much of the large fuel droplets over the edge of the intake valve in the area of the fastest flow. As a result, considerable fuel shear can take place off the edge of the intake valve in that area.

Now for the smaller picture of mixture preparation. The velocity probing of the port revealed a small but highly active vortex that followed a path from the high-speed corner of the port and ended up on the cylinder center side of the intake valve as per Figure 5. Even large fuel droplets thrown into this aerodynamic threshing machine arrive at the cylinder pulverized into small droplets.

The bottom line here is that the velocity distribution and the small, strategically located, highly active vortex generates user-friendly port characteristics. In practice it matters little whether the intake runner approaches the port in the head from the left, straight on or from the right. Regardless, there is a strong tendency to counteract and minimize fuel drop out and to dump the more fuel-laden air toward the cylinder center and less on the cylinder walls where it simply fails to burn.

Flow, Velocity And Swirl
The way the air flows on the cylinder wall side of the ProKing’s Ultra Pro intake port proves an asset not only for mixture quality but also for swirl. Often heads with Ford orientated ports are dead players when it comes to swirl. Those heads that do develop swirl, for the most part, only do so at high lift when the flow "windows" by streaming almost totally across the back of the valve. When this is taking place the air’s exit angle is predominantly 30-45 degrees from the port centerline and results in a very strong swirl action.

High swirl is normally good, but if the ports are not taking care of mixture quality the larger fuel droplets will tend to centrifuge out to the cylinder wall. This leads to poor combustion qualities, increased fuel consumption, greater bore wear and reduced output.

This centrifuging action has prompted many race engine builders to condemn swirl for high rpm race applications. Granted, having the fuel of a poorly prepared mixture centrifuged out on the cylinder wall is counterproductive. However, the fix is not to kill swirl but to improve mixture quality! From what has been discussed already we have seen the Ultra Pro port does just that.

With the velocity distribution that the Ultra-Pro intake port has the swirl (Figure 6) is moderate until valve lifts are high. At this point the port velocities existing then tend to keep the fuel broken up and in suspension so it is least likely to centrifuge out. From this you can see that by taking care of wet flow the positive effects of swirl for a faster burn can be harnessed to better advantage.

Flow – Size Versus Efficiency
High port velocities with high flow can only be achieved by means of an efficient port. This port displayed exactly such qualities. I made some calculations here and came up with an efficiency number only a little less than 100 percent for the area about 1/4-inch in from the manifold face.

As far as SAE flow efficiencies at the valve are concerned, some impressive numbers were produced. At valve lifts from .025˝ to .900˝ the lowest figure seen was at .050˝ where some 65 percent was recorded. This is a very creditable figure for a 45-degree seat and extremely good for the 50-degree seat used.

At .250˝ lift the 2.180˝ valve of these heads flowed 186 cfm. This is also very good. It only marginally missed equaling the best small block head my bench has ever recorded (188 cfm by a 2.2˝ canted valve head). Peak flow measured out to 420 cfm with 400 cfm being achieved at .730˝ lift. This equates to an exceptional peak SAE efficiency of 78 percent. By comparison only the best of heads pass the 70-percentile mark.

Combustion Chamber Development
Following through the combustion chamber design revealed a number of interesting points. The original St. Denis flow bench model was well conceived so subsequent development involved painstaking refinement.

As shown in Figure 8 the key areas are arrowed. The slight concave angled at 38 to 40 degrees on the chamber wall (at arrow A) helped mid and high lift by apparently acting as one side of a funnel for a smoother and more directional flow into the cylinder.

The radius (on edge B) influenced fuel shearing and the minimizing of plug wetting. The concave chamber wall (at arrow C) exerted measurable influence on the flow efficiency of the exhaust port’s short side turn. Cutting away to the extent as seen here is normally only effective when combined with steeply angled ports.

The form (at arrow D) blends the chamber’s continuation of the cylinder wall into the seat and port. A radius as large as possible with a 25-30 degree bottom angle proves effective throughout the exhaust valve’s lift range.

The chamber wall form (at arrow E) aids the scavenge process that takes place around TDC. As such, the effect taking place is not replicated by the flow bench so it has little effect on the cfm measured. Adding material (at arrow F) reduced the chamber volume and marginally helped flow.

This (arrow G) proved a critical area were material was added to the original St. Denis chamber form. By doing so and reducing the amount of air that enters the cylinder by this route both overall flow and swirl were improved. This move also helped keep the chamber volume to a minimum.

Exhaust Port Design
Development of the exhaust port progressed at a rapid pace as the flow model port was a very close one used in a highly successful Ultra Pro Chrysler head. As well as finding good flow throughout the lift range (especially in the .250˝ to 500˝ range) effort was also put into refining the port’s velocity characteristics.

The target here was a high overall velocity with minimal velocity variations. As pointed out earlier, these two factors in mutual co-existence means developing a highly efficient port form. The benefits of flow from high efficiency rather than size bring about better combustion chamber scavenging everywhere in the rpm range resulting in a wider power band and greater output.

A look at the port’s velocity map shown in Figure 4 exhaust) shows a near uniform pattern exists. Measurements recorded a variation of less than +/- 4 percent existed over 90 percent of the port area. This is less than half the variation normally seen by some of the best, stock position, CNC ported aftermarket heads. Without the aid of a flow bench exhaust pipe stub the exhaust port delivered top notch results right up to .500˝ lift (Figure 6, exhaust) where it made almost 250 cfm. From here on up, flow climbed to a maximum of just over 260 cfm.

I have seen the exhaust ports with a 1.6˝ valve flow up to just over 270 cfm but this often comes at the expense of some 5-10 cfm in the mid-range. The advantage of a strong mid-range is that it allows the cylinder to dump its contents effectively with less valve lift than is usually required.

During the development of the exhaust port, its flow characteristics with an exhaust header tube (as opposed to a flow bench exhaust stub) were tracked to ensure high flow was retained with either a left or right turn pipe in place. A test with a typical header as seen nearby showed an increase in flow.

Conclusions
What we have talked about here is centered on the developments of the Pro King by Ultra Pro Machining’s Don Losito. Events during the production of this feature indicate that McLaren’s R&D team, Don Losito and Gary St. Denis were willing to put out whatever effort was required to develop a top-notch product.

Based on personal experience developing race winning cylinder heads at national and international levels I believe the Ultra Pro developed heads have all the ingredients to run up front. So much so I am prepared to go out on a limb and make some predictions as to what they may be capable of.

The McLaren ProKing heads, as tested here, have enough of all that it takes to make over 810 hp on an all-out single 4-barrel, 12.5:1, 358 cid motor. Given a tunnel ram intake, 16:1 or more compression, as in ProStock, and that number could go well beyond 925 hp. EB

Sources:
McLaren Performance Products, 32233 West 8 Mile Road, Livonia, MI 48152. Tel: 248-477-6240 Fax: 248-477-3349

Ultra Pro Machining, 6350 Brookshire Blvd., Charlotte, NC 28216. Tel: 704-392-9955 Fax: 704-398-0814 Email: UltraProM@aol.com

Ex-aerospace engineer David Vizard, with over 3,500 published articles and 29 books (5 publisher’s best sellers) is one of the world’s most widely published automotive writers.

He is also a university lecturer, holds numerous patents and is a winning engine/car builder. In his best year he amassed a combined 169 track records, first places and championship wins, from just 8 engines. Technology he has developed has been used on everything from F1 across the board to drag race and dirt cars.