Here's author Mark Weymouth's '70 R/A-IV GTO launching. It's capable of 12-teens at 115 mp
You roll up to the burnout box in your Ram Air IV Judge. When the starter gives the signal, you blip up the throttle and snap the clutch off the floor, while immediately sliding your foot from the clutch to the brake pedal. Hold the rpm at 4,000 while smoke starts to billow out of the fenderwells. After a long 10-count, you ease off the brakes and feel the motor pull higher. Then you slowly roll out of the gas while laying down another 25 feet of rubber, finally bringing it all to a stop before the staging beams.
As you clear the motor a few times, you let the victim in the other lane pop the staging bulb first. As he becomes a bit anxious, you clear out your nasty rattling Ram Air IV one last time. Stage nice and shallow so you can ride the clutch right on the edge of engagement, while giving yourself a good long rollout. With the second staging bulb lit, you pull the motor up to 3,000 rpm, then wait for the last amber bulb to show the slightest glow.
This 455 H.O. engine on the dyno is destined for a T/A. Notice it has the air cleaner and
When this happens, the clutch swings up as you raise your left foot, while your right foot dives for the pavement via the gas pedal. The tires dig in, the motor starts pulling down off the cam and you hold steady on the clutch release, letting the motor build momentum. With a burst of forward motion, you release the clutch fully, while probing for tire slip. The direct engagement from crank to differential is now complete and your backside sinks into the Morrokide as the scenery begins to blur.
Just as the engine nudges the far side of 6,000 rpm, you half-heartedly kick the clutch and violently wrench the Hurst lever back-your right foot never considers leaving the carpet.
You repeat the procedure two more times and now the 4.33s are really pulling in Fourth before the 1/8-mile has even passed. The half-track traps flash by at over 90 mph. Now you have nothing left to do but keep her dead straight and vacuum up the 440+6 this, LS6 that, or SCJ something on the big end like it was left for dead.
Dan Jensen makes a secondary metering rod change to the 455 H.O. on the dyno. Strict rules
A certain Pure Stock Oldsmobile record holder says it's "like being crop dusted by a Pepper Green F-14." Congratulations-you just made a Pontiac record-setting pass in the low 12s at 115 or so mph, while simultaneously embarrassing another big-cube brand X wonder wagon.
If this sounds exciting, then you're the right hobbyist to come join the fun at the Pure Stock Muscle Car Drags (PSMCDR or PS). The PSMCDR was founded by Bob Boden and one of the quickest all-time Pontiac racers, Dan Jensen. Dan and Bob have created such a remarkable event over the last decade that for the last few seasons the F.A.S.T races have also adopted the PS rules for their Factory Stock class, expanding the amount of events we can all participate in. The original and granddaddy of events, though, is still the September Pure Stock event run by Bob and Dan in Stanton, Michigan.
In this story, we'll provide the engine rules with Dan and show you how to build a representative Pontiac racer. In an upcoming article, we'll cover the remainder of the drivetrain and chassis setup and their rules. Remember, all who represent the spirit of the rules are welcome and you don't have to go to the lengths to prep your Pontiac described here to have fun and be competitive.
Pure Stock Muscle Car Drags Basics
All participants are paired with the qualifier closest to their e.t., beginning with the number one qualifier who races the number two and so on. This creates incredibly close and fun best-two-out-of-three heads up shootouts. No bracket racing here!
The important thing is not worrying about setting new race records, but rather a new personal record each time you race. Year after year, improvement is what all the racers are really interested in, whether you show up in a '74 Goat or a 421 2+2 Cat.
The subject motor for the next series of photos is a '69 Ram Air III from a four-speed GTO
It was on its original bore, and since it's a matching block, a +0.030 bore was chosen to
Any binding of the cam in the bearings will soak up power and reduce reliability, so prope
Evaluate Your Pontiac And Your Intentions
It's important to honestly review how you're going to use your Pontiac before you prep it for PS racing. Answering these questions before you start the project will help you balance any compromises needed:
- Will it primarily be a PS race car or will it be used more for cruising?
- Is race gas readily available in your area or do you need to run pump gas?
- What is your e.t. goal?
- What is your budget?
- If you race and cruise your car, how steep of a gear can you tolerate on the road?
Make Your Stock Pontiac Quicker
What follows is the application of the rules (see sidebar) that Dan has laid out for us.
Let's look at several important items individually to give you an idea of what it takes to build a highly-potent Pontiac Pure Stock motor.
First, you need to choose a trustworthy, competent machine shop. From all the stories circulating and the amount of motors we have had to redo for competitors, this may be more difficult than it seems. Try to find someone who understands and has experience with Pontiacs. When you have so few items that vary from factory original, every small detail needs to be addressed, as this is how you will ultimately make all the power these motors are capable of.
Aftermarket steel main caps were chosen for this engine strictly for durability because th
The machining must be precise and should start with the crankshaft main saddle alignment. This provides the reference for decking and cylinder boring. We also check and make sure the cam journals are bored dead straight. A torque plate isn't necessary for boring the block, but is mandatory when honing and should be installed and torqued to the proper headbolt specs. This puts the block/cylinders under the same stress as when the heads are installed and will help to create accurately dimensioned and clearanced cylinder walls for the assembled motor.
The crank preparation will begin with an assessment of its condition. This is most often done with a magnetic check. The machine shop should be able to resize and polish the crank journals, if needed. Careful crank prep requires knowledge and care to maintain proper radiuses at the corners. Additionally, we make sure that none of the oiling holes have burs. After all the necessary machining is accomplished, then the reciprocating assembly must be balanced. Some racers at this time will have the crank Nitride treated, but that isn't a necessity for PS motors.
The stock crank was machined and retained.
Rod choices are numerous and you can let your wallet or durability concerns be the driving factor here. Stock Pontiac rods have unjustly earned a reputation for being weak. This isn't true, particularly for our venue. If they're properly resized and upgraded rod bolts are installed, they can more than adequately handle the requirements of our blueprinted motors. Using the stock rods may save as much as 50 percent of the cost of going to an Eagle rod.
If you choose to buy new rods, we've used Eagle H beams, SCAT and Oliver successfully. The Olivers are the strongest items available and they've worked very well for us, but they can be a budget-buster and overkill for PS racing. They cost at least double that of the Eagles and SCATs. We've also tested CAT rods and they've held up well in dyno testing and racing in one competitor's motor, but we wouldn't recommend them as they took a substantial amount of extra setup time and reworking to get them to repeat the recommended torque setting before installation and match each other. All the additional work wiped out any cost savings that was realized up front.
Even with new rods, we check every measurement and preassemble them until we believe each rod will hold its torque when installed.
Eagle forged H-beam rods and forged pistons were chosen because a numbers-matching block w
Pistons can be chosen from several NHRA-approved sources and really come down to personal choice. The two best options are hyper-eutectic or forged. Hypereutectic pistons generally have decent strength and dimensional stability. They require additional care when following the ring gap instructions. Any deviation from their proper setup has been known to shorten their life span. Another item to note is that hypereutectic pistons don't transfer heat as readily as cast pistons and may have your motor running at higher temperatures.
We prefer to file-fit our rings for a more accurate and customized fit. By doing so, we're trying to increase our sealing performance. You may also buy pre-sized rings. There is likely very modest performance difference between the two types of rings, but again, we're trying to leave no stone unturned in maximizing our power potential.
With the additional performance all of the above machining has provided, we don't want to skip this important process. We like to have all our piston/rod sets balance within one gram. It takes time, but the motor will spin free and easy when you're charging down the track.
Adequate oiling has three components:1) make sure casting flash isn't interrupting the oil's ability to return to the block; 2) a windage tray will help control oil frothing and ease the load on the crank's ability to turn; 3) don't put too much oil pump into your motor. Too much psi not only costs a great deal of power, but will also prematurely wear your distributor and cam gears.
The bottom end of the Ram Air III was buttoned up with the forged rods and steel aftermark
We've gotten around six horsepower in the past by lowering the psi from 80 to 65 pounds. A safe guideline is to make sure you have 10 pounds of pressure for every 1,000 operational rpm.
When assembling the motor, we adhere to Pontiac's factory specification for clearances. For example, all Pontiac motors, except the 455, use main bearing clearances of 0.0002-0.0017 and rod clearances of 0.0005-0.0025. We would look at these specs, then run on the loose end of the spectrum to try and maximize performance by lessening friction. If your project car will see more driving than the typical race car, you may want to run a bit tighter clearances than we use.
Cam And Valvetrain
Before we choose a final installation position for the cam, we check and see if it really does match the manufacturer's cam card by degreeing it. Most cams arrive slightly off due to their build tolerances. Take note of any discrepancies and make adjustments as necessary.
When installing the camshaft, there are two options. If we're running a 3.23 gear with an automatic and 9.5:1 compression, it makes little sense to retard the camshaft to create more top-end hp when what we really need is additional torque to get the car moving quickly. Advancing the cam two to four degrees will help create more bottom-end response.
A Melling 744 grind cam was employed, as they've shown consistent performance compared to
Conversely, if we have 11:1 compression, a four-speed and 4.33 gears, we consider retarding the cam for more speed at the traps. A good starting point for most builds is to install the cam straight up as directed by the cam manufacturer. Remember, as the timing chain breaks in it will automatically stretch, which creates one to two degrees of retardation on the cam.
Pure Stock racers aren't allowed to alter the valve seat angles. Most Pontiac heads have 30-degree intake seats and 45-degree exhaust seats with the notable exception of the SD-455, which uses seat angles of 45 degrees on both valves. This doesn't mean we don't want to have accurately machined seats. This actually is one of the areas that will pay off with lots of power, if the machinist is careful. A proper seal with the valve and seat is crucial. This is helped along by not skimping on valve choice. We primarily use Manley valves, but there are other high-quality valves out there. The valves must match the factory items for stem and head diameter. Under no circumstances are lightweight valves, such as titanium, allowed.
A high-quality double-roller chain was used to reduce stretch.
Dyno Tuning: Carb And Ignition
We prefer, when possible, to dyno any engine we build. Dyno testing helps us to continue matching the entire driveline as a whole or system. This will maximize the power output and address any flaws that are detected before the motor goes into the car, possibly saving work later. It gives a solid baseline for jetting from which to begin track testing. If the motor is well set up on the dyno, we'll need to do little more than change the secondary hanger to address weather changes at the race.
We also find a good base timing setting for each motor. We like to have the timing curve all in by around 2,500 rpm. We're not afraid to push a lot of timing into a Pontiac. Most race best in the 36-40 degree total range.
Dyno testing also gives us the power output and rpm levels at which the motor is functioning. With these two items available, it'll be easier to choose our proper gearing.
The heads were milled near the minimum NHRA spec of 65cc's. This results in approximately
Remember not to get caught up in the semantics of the words "Pure Stock." These cars are actually amazingly close to how the factory shipped them, but they're nearing or have already passed their 40th birthday. With this in mind, there are few actual cars that could be, or are truly virgin enough, to be factory fresh. What we're trying to demonstrate is the level of detail it takes to create a fun Pure Stock car like the ones in the Pavement Pounder Shootout article. Whether your car simply meets the spirit of the rules or is a full-out Pure Stock racer, we hope you'll come out and enjoy the venue.
Pure Stock Musclecar Drags History and Engine Rules
It's hard to believe that Bob Boden and I have been hosting the Pure Stock Muscle Car Drag Race for 15 years now. It started back in 1993 when we rented Milan Dragway and invited 20-30 of our friends to bring their musclecars out for some friendly racing.
When we moved the race to Mid-Michigan in 1995, Bob and I worked extra hard to get the word out about our race. We came up with a flyer to hand out, and we courted Tom Shaw at the old Muscle Car Review magazine (MCR) to check us out. Fortunately, he took the bait, and has been a strong supporter of the Pure Stock Drags ever since. Thanks, Tom!
Bob and I believed in the idea of "same place, same time" for our event so people could plan ahead to participate. We think that strategy has worked since we now attract more than 150 cars and more than 1,000 spectators!
We decided to call our race the Pure Stock Muscle Car Drag Race-purposely using the word "Pure" in the name to weed out those cars that were already modified and thus not eligible to participate. Yes, most of the cars that participate at the race are not the literal definition of "pure stock," but you have to remember, these cars are anywhere from 34 to 53 years old now! They weren't bought by speculators, like today's musclecars are. They were more affordable, and bought by young people who drove them like they were intended. It's pretty rare to find one of these cars with the original engine that hasn't been rebuilt today.
To be eligible to participate, the car must be stock, and meet the following criteria:
- Eligible years are from 1955 to 1974
- Cars must have been built in a U.S. orCanadian assembly plant
- Cars must have had a minimum warrantyof 12 months/12,000 miles
- Cars must be factory equipped with aminimum of a four-barrel carb, dual exhaust, and other correct factory equipment that promote highperformance intent and image
Valves and seats must remain stock. No trick angles or blends can be used. Proper valve se
High-performance intent holds greater weight than high-performance image with us. Cars known as "sleepers" have all the intent in the world, but little image, so they're legal. (Note: Cars that come close, but don't quite meet all these criteria will be evaluated on a car-by-car basis, and acceptance is determined by the event organizers.) For example, any GTO is eligible because they show intent and image. However, the '67-'69 two-barrel-equipped cars wouldn't be eligible because they don't meet the intent criteria.
Factory lightweight cars built specifically for sanctioned drag racing, with no factory warranty, as well as dealer built/modified cars aren't eligible to participate.
Before we go into detail about the rules, I want to mention that the Pure Stock Drags does allow cloned musclecars, so long as they are 100 percent correct, inside and out, top and bottom.
No mods can be done to the intake ports, not even a gasket match.
After talking it over with many of our participants, Bob and I decided that since we already had an influx of NHRA-spec'd engines, we adopted the NHRA Blueprint specs as the limit that we would allow participants to machine and build their engines. These specs are available to everyone so we don't have to "play God," and decide what one can or cannot do. Plus, anyone can go onto the NHRA Web site and see what others are allowed to do. Many participants have used the NHRA to help them decide what kind of car to build for the race.
Basically, blueprinting an engine to NHRA specs raises the compression ratio anywhere from a little to a lot. We are now quite familiar with the specs for many of the engines produced in the late-'60s and early-'70s, and we made some interesting discoveries. It's fairly evident that by 1970, many manufacturers were trying to get an edge over the others by altering the specs they gave to NHRA. For example, for the '67 through '69 GTO and Firebird 400 four-barrel engines, all of the cylinder heads show the same combustion chamber volume of 65 cc's. For 1970, the cc requirement dropped to 62 for the same engines and cars, giving them a compression advantage. Buick did the same thing for its Stage I engine in 1970 by whittling 4 cc's out of its chambers, making it stronger in its particular class.
Some of the other NHRA engine rules we adopted include limiting oversized pistons to 0.070-inch, using their specs for deck clearance, head gasket thickness, piston type (with dish/dome volumes), and cam lift. What the NHRA allows its racers to do with the rest of the car is not our game.
We realize that a majority of our musclecars sacrificed their original blocks in their quest for supremacy back in the day. Also, many of our participants whose cars still retain their valuable numbers-matching block prefer to set it aside and build another to race. Therefore, engine blocks don't have to have matching numbers, or have the correct casting number, but they must be a vintage block with the correct cubic-inch displacement-no aftermarket blocks are allowed. However, the engine has to be correct for the year, make, and horsepower claimed.
Cranks And Rods
No lightweight cranks or rods are allowed, either. We want our participants to make the most of the parts the factory provided them. Anybody can spend money on aftermarket parts in order to go fast, but it's not as impressive as doing it with parts as close to factory specs as possible.
Same goes for the exhaust.
Cam And Valvetrain
We require the camshafts be the factory grind, or as close to the factory specs as possible. If a factory camshaft is unavailable, the aftermarket cam must fall within 1 percent of the NHRA lift spec, and duration as measured at 0.050-inch lift. For example, Pontiac's 068 cam has a duration at 0.050-inch lift of 212-degrees intake and 225-degrees exhaust, with NHRA allowed lift of 0.424-inch. Using our 1 percent rule, the aftermarket cam can have duration of 210 to 214-degrees intake, 223 to 227-degrees exhaust, and lift of 0.420 to 0.428 inch. Engines must be able to idle with 16 inches of vacuum at 1,200 rpm. (Big cammed engines like the R/A-IV are given a variance to this rule.)
We don't allow roller cams, or roller rocker arms, not even roller tip rocker arms. The rocker arm ratio must be correct for the application. We do allow the use of polylocks or crimp nuts to adjust the rocker arms to avoid lifter pump up (hydraulic cams).
Heads And Intake
Intake manifold and heads have to be the correct casting numbers. Porting or gasket matching of heads, intake, and exhaust manifolds is not allowed, not even a simple clean up. We want the castings just as they were made at the factory.
The carburetor must be correct for the year, make and horsepower claimed. Jetting and metering changes are allowed. We don't want to see the '71 Pontiac high-flow or '75-and-later 800-cfm Q-jets on engines that originally had the 750 carbs. Carbs can only be fed by mechanical fuel pumps; no electric pumps are allowed.
We limit distributor modifications to recurving the advance and replacing the points with an electronic module that fits under the stock distributor cap. Aftermarket coils must be of the same shape and color as the factory coil. Aftermarket ignition boxes aren't allowed.
The engine must have factory pulleys in place, and belts to run the water pump, alternator, and power steering (if optioned) at all times. The only belt that we allow to be removed is for the A/C compressor, if so equipped.
The radiator must be correct for the year, model, and horsepower claimed-no aftermarket aluminum radiators. All cars must be equipped with radiator overflow catch cans 16 ounces or larger. The fan must be the correct factory unit for the application-no aftermarket lightweight fans.
We're pretty liberal when it comes to the exhaust systems. They must be routed as original, but we allow participants to upgrade to 2.5-inch mandrel-bent pipe, H or x-type pipes, and any full-bodied muffler(s). Glasspacks and straight pipe are not allowed. Of course, the exhaust manifolds must be correct for the year, model, and hp claimed, and no internal modifications are allowed. Headers aren't allowed.
Those are the basics for preparing your musclecar's engine to compete at the Pure Stock Drags. For further info, go to www.purestockdrags.com. Dan Jensen
Ram Air III Cams And Power Production
An important choice that must be made with all '69 Ram Air III four-speed Firebirds and GTOs is the cam. Early cars came from the factory with the 744 cam (224/236-degrees, 0.050 duration), but mid-year, Pontiac switched to the 068 (212/225-degrees, 0.050 duration) grind. This is an important factor. If you choose to run a lower compression motor due to the way you use your Pontiac or the availability of race gas in your area, you have to take that into account. Also, if you plan on a lot of street driving and you want a mellower rear gear, you need to choose wisely.
In this instance, the GTO was an early build car and has steep gears and the motor will be optimized for ultimate power. This in turn pointed us toward the 744 cam for its extra horsepower production and rpm potential. We will use the steep gears and compression to cover for the loss of the torque that the 068 would have given the build.
As we have built several R/A-III motors that were all dyno'd afterwards, we have a pretty good idea what to expect. For this build, we're looking for a minimum of 435 hp and 480 lb-ft of torque. The e.t. capability for this medium-optioned car is in the 12.50 range at 112-plus mph. We dyno very conservatively, which leaves us near a modern SAE Net rating. We dyno with the water pump, fuel pump, alternator (on but unplugged), exhaust pipes and air cleaner. It gives us a very representative view of a car's potential. MW