MTI Stage III Heads Install - Tri-Power 427 -- Part II

MTI tops off its stout shortblock with these towers of power Part II

Steve Baur Apr 1, 2004 0 Comment(s)

Step By Step

These mild mannered LS6 cylinder heads have become fire-breathing blocks of aluminum capable of leaping supercars in a single bound. Just ask Ron Adee. He is one of MTI's customers who used the Z07 427 package to win the 2003 One Lap Of America race.

This is the modular integrated deck from Darton Sleeves. MTI has chosen to use this design over its previous system as it offers superior strength, among many other benefits. Each cylinder bore locks together with the other ones, forming a single deck surface.

This is the unported combustion chamber. When compared to the finished product...

...you can see how much material has been removed and reworked to accommodate the larger bore of the 427.

MTI's Robert Maenza performs the rough-in porting of the bowl area.

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.

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