RPM Project - Pace Car/Race Car Part 2

RACE CAR PROJECT PACE CAR CAR

Biro

PART 2: CHOOSING OUR SBF PISTON

Last month we gave RPM readers the entire rundown on how the Project Pace Car Race Car came to be and left you wanting more with a photo of our assembled short block. Ok, maybe we got a bit ahead of ourselves, so instead of giving you information overload in one article we’ll break things down a bit, and this issue we will focus on our piston choice. Having a place to work on your project is great but having all

the equipment and tools available at your fingertips is something totally different. As we’ve said many times over the past 21 years in RPM, we’re just like you, our readers; hardcore car people, and because of past years in the business of horsepower, we find ourselves very fortunate to have all these things and more at our age. Not to say that I am in advanced years (insert LOL here), but when you start as a teen, 30+ years makes for a lot of experience. It takes much dedication to build cars

and the builder doesn’t usually get to enjoy the fruits of his/her labour in the end. In short, it takes a momentous amount of time to acquire the knowledge and the equipment to carry out others’ dreams. Through many years of building relationships with people in our own circle and people across many countries, states and provinces, one acquires a wealth of information and resources literally at our fingertips with the technology we have today. Throughout this pandemic, we have

had to social distance and do all the good health practices our health officials deem safe. But by human instinct, we must make contact with people. My phone and computer have been my best friends the last couple months and they keep our contact alive. We have been able to stay in contact with all members of the Pace Car Race Car (PCRC) build and deliver the next segment of our project. As the health restrictions are now easing up a bit, tracks are opening, people

story and photos by TIM

can be seen in larger groups, and we pray, our lives may return to some type of new normal.

When we left our readers last month, it was clear that the PCRC short block needed some serious attention. When planning and building a project, our experience tells us to keep in mind the time process parts have to go through before you actually get them in your hands. If you are ordering in-stock or stocking parts, you may receive them in a day or two. But when ordering custom parts, which are non-stocking, they may have a longer delivery time and obviously a higher price point. Both are completely justified as the custom parts must be designed and manufactured correctly, which simply takes more time and resources.

For many years, hot rodders have talked about boring and stroking engines. The process of boring is to increase the bore size of the cylinder the piston travels. The stroking process relates to increasing the length from the rod pin to the centerline of the crankshaft. Stroking increases the distance the piston travels in its bore. The increase in bore, say from 4.00” to 4.125” is significant. The stroke increase from 3.50” to 4.00” is also significant. By boring

1: Our Wiseco 2618 high strength alloy pistons boast a 360 degree skirt for extra rigidity. The top of the piston has been totally radiused in all the critical areas, no heat risers here! Note the thickness of the forging at the pin and skirt area. Also note the pin and its thickness. High strength and reliability is present in every design aspect of this piston. The Wiseco engineers designed and built this piston for poweradder applications.

and stroking, you have effectively made more cubic inch displacement from the same dimensionally sized engine block. Every engine builder knows that there is no replacement for displacement. With a little math, you can see, using the previous numbers, what was once a 351 cubic inch (CI) engine has now turned into a 427 CI monster.

Math example:

CI Displacement= (Bore/2) x (Bore/2) x 3.1416 x Stroke x Number of cylinders

(4.125 in./2) x (4.125 in./2) x 3.1416 x 4.00 in. x 8 = 427.634 cubic inches.

In the early days, you could increase the stroke of a certain crankshaft by offset grinding the rod pin of the crank centerline, obtaining a smaller diameter rod pin to achieve a longer stroke. Today, there are many cranks available for all sorts of applications when you need more stroke.

There are limitations to boring and stroking an engine, though. Obviously material must be removed from the cylinder block for the process, which will weaken the cylinder blocks integrity. The builder must know the maximum bore and stroke their block can safely withstand. The aftermarket is filled with manufactures of quality blocks who cast extra thick blocks for all the major engine designs. For the PCRC, we choose (due to original plan and budget) to use our stock 351W, 2 bolt main block. It is old, well seasoned and ready for a little hit of the juice - just a little hit, though. The max cubic inches I believe we can safely design within this

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4: Here you can see the ring pack design. The first ring is placed a longer distance from the top of the piston which increases the top land dimension to keep the area alive in a heavy nitrous oxide application. You can also see the different valve angles that the TFS R cylinder head has, by evidence of the valve reliefs in the piston dome area.

5: The valve relief pockets in the top of the piston were designed for our TFS R cylinder heads. We supplied our camshaft specification to Wiseco in order to obtain a dome that would net maximum compression and correct valve to piston clearance during engine operation. One of the critical assembly steps is to check the valve to piston clearance.

stock block is 410. We have designed our combination around a used forged crank that we had, with a stroke of 3.750” and our block bore of 4.040”. These dimensions will net us 384.569 cubic inches, let’s just call it a 388 CI, it sounds cool!

Since our crank now has a longer stroke we cannot use stock length rods and stock compression height (CH) pistons. Keep

in mind, it all must fit inside your block height. In our case, the deck height of our block is roughly 9.500”. Cylinder block deck height is measured from the crank centerline (main cap centerline) to the top of the cylinder bore surface, known as the deck of the block. The piston compression height is measured from the top of the piston to the centerline of its piston pin.

Swinging just the extra .250” of stroke manipulates the rod length and piston compression height. To fit it all together, our math tells us that the rods are now 6.250” long and the piston compression height must be 1.375 inches. Our TFS R cylinder heads discussed last month,require a certain piston. When designing your engine, the builder must keep in

6: Wiseco supplies coatings for their pistons and we ordered ours with their skirt and top coatings. You can see the ArmourGlide skirt coating which is a Molybased solid film lubricant on our piston skirt. The ArmourGlide coating reduces friction, increases power and reduces piston rock. The top of our pistons are coated with Wiseco ArmourPlating which lowers the crown temperature 20 degree C on average and reduces the effects of detonation on the dome. ArmourPlating also provides a hard smooth surface for the rings to prevent microwelding in the ring grooves. Notice the oil drain back holes in the oil ring groove for superior oil control.

mind the cylinder head type due to the combustion chamber design. Other dimensions like compression height (CH), ring pack location, material and pin type are key factors in your engine’s success. If you are lucky, you may find an off-theshelf piston to work with your combination. Since we wanted to make as much squeeze (static compression) as possible, use a little nitrous oxide, and require an uncommon compression height, we thought it would be best to have a custom piston designed for PCRC.

The “wise” choice for this project was to use Wiseco for our pistons. For over 75 years, Wiseco has been known for quality pistons. They offer pistons for every conceivable engine, including engines in ATVs, bikes, sleds

and more. Their corporate headquarters in Mentor, Ohio, boasts of over 150,000 square feet of state-of-the art forging and CNC machining equipment. Their engineers utilize the latest in 3D design and finite

element modeling software and the Wiseco research and development facility boasts an in-house Dyno that is equipped with the latest technology. This, along with their

rigorous field-testing network, ensure that their products meet the expectations of every engine builder. Their ordering network is very knowledgeable and seamless, with a quick call

and a few questions answered, our pistons were on the way. With all the math and the short block out of the way, we turned our attention back to the top end of our engine. With

7: Here you can see the piston in mock up. Fits perfectly with having the flat part as high as possible in the bore. With our .040 head gasket we have a desirable quench area to make good power.

the Trick Flow head ports capable of solid torque and awesome high rpm power numbers, we needed a valve train to support the same. Knowing how much and at what lift a port flows can assist you in your selections. We must also keep in mind the design of our engine and realize the limits of each component in our build. We all want to make 2000 horsepower, but soon realize the size and complexity and cost of an engine producing that much power is beyond most people’s reach. Not to mention the chassis required to contain that amount of power. Plan your build and build your plan. Keeping that in mind, we know the power we needed to produce to take the Pace Car to our desired ET.

Excessive rpm can kill many parts in an engine. We need to spin the engine to a peak rpm of 7500 rpm and would like it to stay under 7200 rpm for many reasons. Early on in my drag racing and engine building I saw a

few engines fly apart from trying to extend the design engineering specifications of engine parts. Examples include; main caps walking, block cast cracking, melted/broken pistons, etc. Heck, I remember one time, a customer came in after rippin up the street, pedal to the floor, in front of my shop and said “Tim, I think she is down a cylinder.” Sure enough, after a quick diagnosis, it was. I found the head of his intake valve laying on the pavement, It broke and dropped straight down the header tube, then through the collector, and onto the road. Nowadays in-

stead of overextending stock parts, we have excellent support from manufacturers that test and produce high quality parts that far outlast the stock parts of the OEM world.

NEXT MONTH

After a quick visit to the machine shop to touch up our balance we were ready for the next phase of our build and returned back to the RPM shop with the custom Wiseco pistons, rings, bearings, crank, rods and block, and prepped each part for final assembly of the short block. We cleaned, measured and assembled the rotating parts into the

cylinder block and will dig into the step-by-step assembly of the short block and also finish the top end of the RPM Pace Car Race Car build next issue.

Soon we will be steps closer to being a part of a larger goal, one that is enjoyed by friends and family at a track hopefully soon. This is why I have a passion for race car design and assembly, drag racing and engine building.

8: I am setting the TFS R cylinder on in the mock up stage to check piston to combustion chamber fit, piston to valve clearance and head gasket fit.