Our In-Depth Look the Camaro SS's LS3 Page 2
Major Cylinder Head Evolution

If there's anything GM Powertrain knows well, it's cylinder heads and air flow. GMPT's "ruthless pursuit of power" has paid-off in five different high-performance heads since MY97: the original LS1 head, those for LS2 and LS6, the super-trick LS7 head and, now, the LS3 along with its offshoot, the LS9 head.

The high-performance, 6.2-liter L92 debuted in 2007 GMC Yukon XLs and Denalis (380hp) and Cadillac Escalades (403hp) and was the source of the casting used for the LS3 head assembly. It's key improvement over the Camaro LS1 and LS6 heads is revision of the intake and exhaust port shapes, volumes and locations. Those changes were influenced by the '06 Corvette Z06's 427. In fact, the L92 head was the "first" LS7 head. Part way through development, when the power target was raised to 500hp, that head was set aside and development began on a second, more aggressive design which eventually went on the C6Z's engine.

Later, when a high-performance, six-two was needed for premium SUVs; Powertrain put that first LS7 head back on the front burner and, after more development, it went to production for the L92. Shortly thereafter, when the upgrade program for the high-performance V8 in the Camaro SS was initiated, GMPT took the L92 casting, added some parts unique to Camaro's performance envelope and used it on the LS3. This same head design, with a few additional enhancements specific to supercharging, is also used on the ZR1's LS9.

While this new head is not a "clean-sheet-of-paper" design, it is a major evolution in Gen 3/4 cylinder head architecture and its effect on performance is profound. There were a multitude of changes which we'll discuss in detail and, for this part of our GMPT visit, the Design Responsibility Engineer (DRE) for Small-Block Cylinder Heads, Lou Oniga, joined John Rydzewski. A "DRE" is a key person on any project at GM. "The buck stops with the DRE," Oniga told us. "If anything goes wrong with their part, it is their responsibility to make it good–casting, machining, assembly, testing, drawing, dimensioning, validation, or field issues, etc. It is the DRE who is responsible. No one else! Humans sometimes make mistakes. That is why most DRE's you meet are such a strange lot. We always worry–we always are concerned that everything we do is as close to perfect as possible."

The Camaro Homepage staff hopes there are more DREs like Lou Oniga working on the 5th Gen car's engines.

The most noticeable feature of this head is vastly different intake port location and geometry. The change was inspired by cylinder head work Mike Chapman, an under-the-radar type with a near-mythical reputation in the racing head business, did for the C5-R engine program Katech, Inc. ran for GM Racing from 1997 to 2004.

Lou Oniga takes it from here, "Based on Chapman's airflow development work, we went to a large, square intake port and did away with the 'cathedral' port we had in the older (LS1/2/6) head. The numbers say what we have now flows better than the cathedral port."

"A key enabler of this," John Rydzewski pointed out, "is moving the pushrod over. Now we had a bigger space, so we moved the port up, gave it a straight-on approach, made it larger, wider, with less turns and have less bosses in the way of the flow path. The result is a huge improvement in performance."

How did GM "made room" for the wider LS3 intake port? They moved the intake pushrod sideways. Image: CHpg Staff.

This new head was going on an engine having 500-cc more displacement than the one for which the previous Camaro head was designed so, not only was the shape of the ports changed dramatically, but their volume was increased. Just how much larger are the ports? Lou Oniga told us that LS1 port volumes were: 200cc for intakes and 70 cc for exhausts. LS3 intakes are 257cc and exhausts are 86cc.

The "short-turn" or "short-side" radius in the intake port is the holy grail of cylinder head airflow. It is where the floor of the intake port turns downward to the area of the valve seat closest to the port entry. There are differing opinions amongst cylinder head experts about some issues, but one upon which they all agree is the importance of the short-turn radius.

"It's incredible," Oniga went on, "how much effort we put into the short-turn radius. Just a few thousandths of an inch change can affect airflow significantly–as much as 7-10 grams per second, so that's where we focused a lot of attention.

"We took the UG model of the Chapman-derived racing ports," Oniga continued, " which were fully CNC-machined, sent it to our pattern shop and they made a flow-box, based on this geometry."

"UG" is "Uni-Graphics", a high-end, 3D modeling, software application. A "flow box" is a plastic model of an individual cylinder head port from port entry or exit all the way to the valve seat.

"Then, we took these flow boxes and we flowed them, made modifications, and flowed them again, repeating this process multiple times. Next we digitized the port shapes and sent the resulting models to our foundry to manufacture a representative casting. Besides the optimized port shapes and size, metal shrinkage, manufacturing requirements, parting lines, even the coarseness of the (core) sand, all affect airflow. It took 15 iterations of the LS3 intake and exhaust ports to get the airflow to where it is, today. That was rather stressful."

"Typically," John Rydzewski interjected, "we do a lot more analysis nowadays, but to get that extra few percent we sometimes have to do it the old-fashioned way."

Look at these saw-cut sections and you can see why the new head flows better. The key enablers are 1) flat port floor, 2) improved short-side radius and 3) shorter distance the intake air flows around the short side radius. Image: CHpg Staff.

A closer look at the LS6 head's short-side radius area. The radius is not that sharp but the curved area is quite large and the port floor is inclined. Image: CHpg Staff.

A similar view of the LS3 port shows a radius that is actually slightly tighter but the critical area of the port floor curving down to the valve is actually smaller. The net sum is improved intake flow. Not the larger "cavity" beneath the intake port entry. That's the larger space needed by the AFM hardware on other engines, such as the Camaro's automatic V8, the L99, which use this head casting. Image: CHpg Staff.

"Our analysis tools are getting more sophisticated with each passing generation of cylinder head." Oniga continued. "Computer software tools such as GT Power, Uni-Graphics, CFD and NASTRAN (software designed and licensed by NASA to private companies) are necessary tools of the development process, but there's a human touch needed as well. We'd take development heads to the Warren airflow room. There's a gentleman working there named Dave Suminski. He's a wizard. All he does is flow heads. He analyzes the flow data and makes subtle modifications to the port sets to optimize the air flow to (meet) our desired number. Dave is very good. He's from the old school of porting, polishing and flow testing. We'd take his input, then go back and make additional samples then, flow them again–fifteen times–until we finally got what we wanted. We really sweated the details, right down to the last 2 grams per second (of air flow), which are within the measurement capability of the equipment utilized.

"We wanted to create a port design that provided the flow numbers required for the desired horsepower, but that could also be reproduced in a mass production foundry on a day-to-day basis .

We made sure casting shrink rate (of the aluminum as it cools) was as accurate as possible. We changed an aspect of casting technology, too. We use a different foundry sand on both the intake and the exhaust ports. We went to a finer silica sand so the inside of the ports are smoother. Many cylinder head experts will state that surface finish does not affect airflow. I have conclusive and repeatable data that, for this particular head, significant flow improvements came from changing to a finer sand."

Flow-wise, the LS3 intake port pulls ahead of the LS3/LS6 port almost at valve opening. Image: GMPT Communications. Click Image for Larger View.

The exhaust port in the new head, also, benefited from GM's ruthless pursuit of power. The port roof was raised slightly and the floor was lowered slightly which increased cross-sectional area and port volume. The short-turn radius is not as important in an exhaust port as it is in an intake, but flow still benefited somewhat from its being recontoured. To further improve flow, the valve guide boss was recontoured and the port roof just upstream of the valve was smoothed. Lastly, exhaust flow also benefitted from the finer core sand.

In spite of all that, the exhaust port didn't change near as much as did the intake because one thing GM didn't want to do was effect a practical reduction exhaust port cooling jacket volume. It was imperative that the head have good cooling around the exhaust port. Nevertheless, the port changed enough that a new exhaust manifold with revised shape at its port entries was required.

The LS3 exhaust port's flow also surpasses that of the old head. Image: GMPT Communications. Click Image For Larger View.

To compliment larger ports, LS3s have bigger valves. The intake diameter is 55- mm (2.165) the exhaust is 40.4-mm (1.59"). Larger valves forced a 2-mm (.078") increase in valve center distance because, on this head for "durability reasons" (ie: the supercharged LS9), the "valve bridge"–cylinder head structure between the valves–needed to meet a minimum width.

In another example of aftermarket high-performance and racing processes migrating to production applications, back in 1998, GM Powertrain began making Gen 3 heads with multi-angle valve seats and faces. The LS3 head continues that with 60-46-30-degree multiangle finishing on the seats and a 45° on the valve faces.

The combustion chamber in the LS3 head changed from what was used in the LS1. The chamber is shaped differently and it's a little larger. The change in shape is the addition of a "bulge" in the chamber wall, on the opposite side of the intake valve from the short side radius.

The best combustion quality occurs when the air fuel mixture in the chamber is distributed uniformly, or is "homogenous", throughout the chamber. The process of becoming homogenous, or as close to it as possible, occurs in the latter stage of the intake valve event and continues once the valve is closed and the piston starts upward. Not only does the upward piston movement compress the air-fuel mix but it also causes it to swirl and tumble and that further mixes it up making it more homogenous. The LS6 chamber had great swirl but not very good tumble. The air fuel mix needs to be doing both if the goal is homogenity right when the spark comes.

The bulge in the LS3 chamber exists solely to get the air-fuel mix to tumble more as the piston nears the point at which the spark lights that mixture. The bulge is also responsible for a slight increase in chamber volume, from 67.3 cc. on LS1 to 68.7 cc . on LS3. The chamber volume, combined with the LS3 piston make for a compression ratio of 10.7:1.

While the spark plug location remained the same, just about everything else in the L92/LS3 combustion chamber changed. The shape is quite different, the valves are larger and the valve centers are 2-mm father apart. Image: CHpg Staff.

The biggest change in the LS3 combustion chamber was the area outlined in red. That change improved the chamber's tumble characteristics and that enhanced combustion efficiency. Image: CHpg Staff.

 "The flow numbers," an understandably proud Lou Oniga told us, summarizing the new head, "are (average) 17% improvement on the intake and 6.2% on the exhaust."

"That's very impressive." Rydzewski continued. "(The intake port has) more of a straight path, right down to the valve and that was very important to air flow. Lou did a good job, taking what the race guys came up with then refining that–tweaking it in our airflow facilities–to get where it is with LS3. It's a great high-volume cylinder head design which performs very well."

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