Last issue, we showed you what was involved with putting together MTI's mighty 427 cubic-inch LS1 shortblock, and this issue we plan to show you how MTI tops it off with a killer set of its Stage III cylinder heads, but before we do that we need to inform you of a new development at MTI.
The Motorsport Technologies crew had used a proprietary method of installing the new bore sleeves using heat and liquid nitrogen, but they now have what is considered to be the next technology. Using a brand new Rottler F65A boring machine, MTI prepares the blocks for the Modular Integrated Deck or MID from Darton Sleeves. This is where MTI believes the future is headed, and the company is already ahead of the game now.
Getting back to the towers of power, it's no secret that the cylinder heads are what make the Gen III small-block so great. With stock airflow numbers that rival and sometimes exceed many aftermarket earlier-style heads, it's easy to see why they make so much power from the factory, and why they can pick up so much more with just a simple camshaft swap.
However, a 427ci small-bock requires something just a bit more radical and MTI's Stage III LS6 cylinder head is the answer. MTI's Stage III service is available to both the LS1 and LS6 heads, and pulls out all the stops when it comes to modifying the factory castings. From raw casting to the finished work of art, MTI invests over 40 man-hours of labor to produce flow numbers of 341cfm intake and 229cfm exhaust at .650-inch lift. These impressive numbers are the result of the hand porting and larger 2.08/1.60 valves that are installed. The heads also receive heavier-duty springs and bronze valve guides.
"The cylinder heads really are a blessing from GM," says MTI's Jayson Cohen. "The 15-degree valve angle allows us to run relatively small camshafts and achieve 500-550 horsepower that can be driven daily and still get great mileage." The cylinder heads also indirectly aid in the remarkable drivability of such a stout powerplant. "The key to drivability is primarily camshaft selection," notes Cohen. "The wrong cam can kill drivability and gas mileage. I've learned from customers and from myself that the lure of a big cam disappears when the car is driven daily."
Comprehension ratio also plays a big part, and MTI prefers to keep it at or below 11.25:1. Without the heat transfer properties of the aluminum heads and block, high ratios like this would not really be possible. MTI believes that 11.25:1 is the limit before you have to pull out timing or run high-priced, high-octane race fuel, neither of which are beneficial to the daily commute. Rear gearing is also important for the daily driver, and MTI recommends no more than 3.23/3.42 for automatics and 3.42/3.73 for manuals. Track applications can go up to a 4.10:1 ratio, but better have an aftermarket rear in the car as well as a sticky tire.
In addition to the high-performance hardware that MTI creates, an extensive interview process with the customer determines what he or she wants and/or expects from the final product, which ensures a happy customer when delivery is made. 550 streetable horsepower should definitely put a smile on anyone's face, and if you want to play with the exotics but don't have the bankroll for one, MTI's 427 package might just be your ticket.
The valve seats obviously need changing to accommodate the mammoth 2.08-inch intake and 1.60 exhaust valve combination. This is the old one, which will be replaced with a new nickel chrome piece. | 
Here Robert is installing the new Ferrea bronze valve guides, which are used instead of the stock cast iron ones. | 
Inside the runner, you can see the rocker arm bolt hole. From the factory, there is actually a large and obtrusive casting boss, but MTI mills it smooth for better flow. When the rocker arm bolt is bottomed out, it still does not protrude into the runner, so there is no need to have the boss there. |
Robert uses an air hammer to install the new nickel chrome valve seats. | 
Here the new valve seats have been installed. Since the new valves are much larger, new seats are required mostly by size... | 
...and MTI also changes the shape to its liking as well. |
The valve seat is first cut using a Kwik-Way seat and guide machine. Once the required size of the opening has been reached, it then gets smoothed out with a 70-degree cutter. | 
A lapping stick and blue ink is used in conjunction with Clover Leaf lapping compound to provide a good seal between the valve and seat surfaces. | 
With the addition of a larger camshaft and larger valves, the MTI heads require larger valve springs to make sure everything is rocking and rolling like it should. The stock castings however do not have a large enough seat for the new springs, so MTI uses a 1.440-inch tool to widen it for the new spring cups. Without the new steel spring cups, the valve springs could tear up the soft aluminum. |
Here you can see the new bronze valve guide has been installed along with the new spring cup on the right. The old spring cup and cast iron valve guide remains on the left, but not for long. | 
The stock LS6 head features lighter hollow stem valves for better performance at the engine's higher rpm range, but MTI's Stage III heads use all new valvetrain parts. From top to bottom: Ferrea bronze valve guides, Martin Wells valve seats, Ferrea 2.08 intake and 1.60 one-piece, swirl polished stainless steel valves, Ferrea double valve springs, steel spring cups and titanium retainers, factory GM valve seals and keepers and Jesel 1.7:1 SS series rocker arms. | 
MTI utilizes a SuperFlow SF600 flow bench with FlowCom hardware and software to verify that the heads have been ported to their required specifications. |
As you can see, the MTI heads offer a major improvement in airflow. Intake flow comes in at 341cfm at 28 inches and exhaust is 229cfm, both of which arrive at .650-inch lift. | 
The Gen III cylinder heads use this lifter tray to keep the lifters from turning, which keeps the roller flat on the camshaft. | 
Here our finished Stage III cylinder heads are fitted to the 427. MTI uses Fel-Pro gaskets (part No.1041), which offer the proper 4.125-inch bore opening and a compressed thickness of .0041-inch. |
MTI has been tuning LS1s since day one, and when they load the shop's base tune-up, they are 95 percent done. Cohen said that each car requires just three or so hours of driving, part and full throttle dyno time to nail the computer program. MTI also recommends that you start researching aftermarket rear ends, as the massive amount of torque and horsepower that is generated by these engines can fry one in a hurry. Sounds like a tough problem to have. | | |