Dart Big-M Block Machined Upgrade - Scratching The Surface
The Dart Big-M Block Goes Under The Knife
From the March, 2009 issue of Chevy High Performance
By Sean Haggai
Photography by Sean Haggai
Anybody who regularly wields a wrench can slam a motor together practically blindfolded. That's the easy part.
If you really think about it, most of the labor is tied up in piecing together the rotating assembly, adding the cylinder heads, and topping it off with the manifold. But if you took a step back and started from scratch, where would you begin? Sure, for the most part our favorite manufacturers are spot-on with their machine work when it comes to engine blocks. However, we're looking to make big power and aren't willing to take any unnecessary chances. When you are in the midst of creating huge reliable strength, why take shortcuts? If you take into account the time and energy, not to mention the cash, that you are willing to throw into your race program, it seems only necessary to have the block machined properly to fit the exact specifications for your application.
This month we left the block in the hands of QMP Racing of Chatsworth, California. Choosing a competent machine/race shop is critical, and over the years we've built good relationships with these race wizards. They've got the know-how to get things done, and they back it up by sponsoring a number of race cars, including a '73 Camaro that recently took a PSCA drag radial championship and an NHRA Division 7 GTO race program. At QMP, expert machinists Mike Consolo and Brad Lagman checked every critical measurements and made sure our tolerances were dead-on. Their combined knowledge was only one reason we chose their shop. They not only facilitate fellow racers with their builds but also utilize an emerging trend and rely on their top-notch CNC machining program, which is where our Dart block was headed. And considering the big plans we have for this Dart block--a monster centrifugal supercharger system--it was vital that we get the job done right first time.
We decided on going for all the beans, pulling out all the stops and getting the block precision-machined with an automated process for much of the work. Our Dart block was delivered to us with a 9.800-inch deck, 4.840-inch bore spacing, and 0.842-inch lifter bores and went through the ringer getting align-honed, decked, bored, lifter-trued, resized lifter bores, and lastly bore-honed with a torque plate. While race shops vary in labor time and prices, we were in and out of the machine shop in a matter of days and spent $1,100 to get the job done. It may seem like a lot, but it's paid insurance and well worth the dough. Plus, when the motor gets put together we won't be running into any problematic issues like the lifters not fitting in the bushings or not having enough clearance for the main bearings once the crankshaft is in. Whether you're into the racing scene or building a boulevard cruiser, any time backpeddling can put a strain on your program.
If you have never seen a block fully machined, it's a sight to behold. Follow along as we take you into QMP's race facility and show you how to get the job done. We show the ins and outs of the machining process, get the scoop on what to look for, and let you know you can expect to pay.
What We Did
Fully machined a Dart Big-M block for big horsepower
What to look for and how much it costs
Starts at $1,100
Like all Dart blocks, our...
Like all Dart blocks, our Big-M block arrived machined, but it's still a good idea to get the block up into the align-hone and measured for accuracy. Mike Consolo led the way, and after learning which crankshaft and main bearings we were using, he started by measuring the mains. Using the bore gauge, he measured each main by checking the front and behind the oil hole, discovering that our mains were 2.936 inches, which is 0.001 shy of what we were looking for. We needed our mains between 2.937 and 2.938 inches. From there, Consolo set the bore gauge to hone the mains.
Align honing can get elaborate,...
Align honing can get elaborate, and costs can be incurred from the extensive labor. Consolo tightened the main caps with oil to 100 ft-lb and loosened them accordingly in order to achieve the 2.937-2.938 inches he was after. Typically, this job alone runs about $140.
Not only are the mains now...
Not only are the mains now properly machined to size, but our main saddles now displayed the textbook crosshatch pattern. This pattern is essential to all bearing seals and oil retention. Plus, it's the sign of excellent machine work.
While most shops don't have...
While most shops don't have a CNC machining program, QMP does--and we took full advantage of it. Javier "Chewy" Dominguez prepared the block by installing the main rings and sliding the main-bar through. He then lifted our Big-M into the CNC machine where we could begin the meat of the machine work.
Once the block is in the CNC...
Once the block is in the CNC machine, Brad Lagman began measuring the block. With the measuring sensor-tool installed and the Dart Big-M program selected, the CNC begins measuring and recording all tolerances and measures everything from deck heights to bore spacing.
The CNC machine begins by...
The CNC machine begins by measuring the deck surfaces and each cylinder bore, all the while recording the information. This ensures that our bore spacing within every cylinder is accurate. The CNC automatically slides the block based on a four-axis program and gently sweeps each key surface point, which also enables it to identify its exact position.
CNC Machining No doubt, having...
No doubt, having access to a CNC machine is a great resource for engine machine work. Is it worth it? Yes, the advantages outweigh the cost. Not only do you have the ability to run specific programs, but they can be tailored to your specific race applications. The CNC is more precise than a human, and the machine work gets done faster and more accurately--so you get to the track sooner. Typically, machine work on a CNC program might cost around $750.
After the measuring and recording...
After the measuring and recording were complete, our Big-M was ready to begin the machining on the CNC. Initial measurements showed that our lifter bores measured 0.842 inch, but we needed 0.904 inch for our lifter bushings. A lifter bore cutting tool was added, and the CNC began to hog out each lifter bore in order to gain the clearance for our CHE lifter bushings.
Here the lifter bores are...
Here the lifter bores are enlarged for the CHE bushings. The walls of the lifter valley were also cut, otherwise the lifters will not fit properly.
The initial deck height measured...
The initial deck height measured between 9.803 and 9.804 inches. However, we wanted to clean things up a bit, and give the deck a mirror finish. A cutting-tool specifically designed to deck the surface was added to the CNC, cutting exactly 0.004 inch off the deck on both banks to square off the surface.
You can see the difference...
You can see the difference before and after the deck was cut. Notice the slight imperfections in the deck surface before...
...and the mirror finish achieved...
...and the mirror finish achieved after. Not only will this make the deck surface true throughout, but it'll improve gasket seal under extreme cylinder pressures.
The bore sizes of our Dart...
The bore sizes of our Dart Big-M measured in at 4.500 inches, but we needed it bored 0.030 over to fit our pistons. Lagman was at the controls of the giant, and before we could begin boring the block, he started measuring the bore depth. With the boring-tool added to the CNC, it began the automated process of removing unnecessary material from the walls of each cylinder.
CHE Lifter Bushings There...
CHE Lifter Bushings
There is no sense completely machining an engine block for a race application and not machining for lifter bushings too. Machining for lifter bushings will add some cost to the bill, but it's well worth it. The Lifter Tru process corrects for angles and positions the lifter exactly where it's supposed to be and even corrects for any casting flaws. Also, the lifters will endure less friction and, as a result, have an extended life; the lifter bushing is smoother over the cast iron walls.
With the final cuts complete,...
With the final cuts complete, each cylinder measured exactly 4.525 inches. While this wasn't the final measurement, it got us close enough to begin honing out the rest.
|SHOPPING CART |
|Manufacturer ||Description ||PN ||Price |
|CHE ||Lifter bushings ||1002-904-175 ||144 |
|Dart ||Big-M block ||31263444 ||2,400 |
|QMP Racing ||Align-hone ||BO4 ||140 |
| ||Deck block ||CNCB09 ||136 |
| ||Lifter true ||CNCB25 ||465 |
| ||Bore block ||CNCB10 ||150 |
| ||Power hone with torque plate ||B13 ||195 |
| ||Detail block (hand-finish deburring, wash, paint) ||B15 ||100 |
| ||Total ||$3,730 |
There's no pretty way about...
There's no pretty way about it: The lifter bushings must be pressed in using a driver and a hammer. Dominguez placed each bushing in its bore (tapered side down) and drove each bushing into the bore, all the while making sure not to drive them in too deep.
Dominguez checked his work,...
Dominguez checked his work, ensuring that each bushing is pressed in properly; too far or not enough can cause lifter failure.
Out of the box, the CHE bushings...
Out of the box, the CHE bushings needed to be bored to 0.904 inches in order for our lifters to fit. Dominguez first drilled through the oil galleys of each lifter bushing, which feeds oil to the lifters, and then he prepared to set the block back onto the CNC machine.
Lagman measured the lifter...
Lagman measured the lifter bushings and programmed the CNC to begin removing material. The CHE bushings' inside diameter measured 0.902 inch, requiring a final finish bore for the additional 0.001.
The bore honing process could...
The bore honing process could begin by using a torque-plate that was torqued to 65 ft-lb, in oreder to simulate the cylinder wall stress of an actual cylinder head. Without this plate, false cylinder bore readings can be had. Depending on your shop of choice, bore-honing a block with a torque plate could run around $200.
Lagman measured the low-compression...
Lagman measured the low-compression pistons and took into account piston ring clearance. Before the block was honed, it measured 4.525 inches, and to get proper ring seal, an additional 0.005 inch would have to be removed by honing. Bore honing will also give us the crosshatch pattern we desire, and the pattern will retain a film of oil on the walls of each cylinder.
From here, our Dart Big-M...
From here, our Dart Big-M block was ready for a thorough cleaning and paint. Expect to shell out another Benjamin for a general detail job.