Go Karts of Western Maryland

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The information herein is intended to be used by new and inexperienced kart racers and is designed to teach the basics of LTO or “left-turn only” oval kart setup. We are sharing our knowledge and experience so you can run up front and win! The information will show you how to setup an oval chassis or a standard straight up chassis to run ovals, dirt or pavement, competitively.

The article will expose karters to the how and why of oval track setup. The first point that we are going to cover is that most karts can be setup to run competitively on an oval track. We have all heard you can’t set up a straight up chassis to run ovals competitively. Not true! Yes, there are many advantages to a kart chassis that was built to run ovals only, since many of the adjustments are designed in. But, on a straight up chassis, you can make adjustments to the kart setup to give it a left turn bias.

The most important thing you need to know about oval track racing is that cornering is everything! You cannot go down the straightaway fast if you cannot get through the corners. We are going to learn how to adjust your kart to improve cornering speed and handling.

We are going to discuss the basic track setup for dirt/clay and pavement racing. We will cover balance and weight, selecting tires and wheels, aligning the tires, positioning the seat, scaling and adjusting weight.

Once you are at the track, changing conditions mean changing set ups. We will cover the basic adjustments that you can do between practices, heat races and at intermissions, which may give you that extra boost you need to take the checkered flag. We will teach you how to make a “push” go away and how to tighten up a “loose” kart.

Getting power to the track is essential if you are going to run up front. Each racer in a class has essentially the same horsepower – but what good is power if the power is not helping the kart move forward? You will learn how to turn horsepower into speed.

Basic kart setup is a balancing act. Your goal is to select the perfect balance between forward traction and turning traction.

If you have too much forward traction, the kart does not turn in the corners. A “push” causes the front of the kart to slide out in the corners.

If the kart is setup with too much turning traction the back end of the kart slides out (loose) causing the rear of the kart to slide out in the corners.

We will explain push and loose in more detail later. It is important to remember that anything that improves forward traction hurts turning traction. You need to find the perfect balance.

Our goal is to increase corner speed so we can get down the straightaway faster. The kart with the most speed exiting a corner should be the first kart into the next corner. You can have all the horsepower in the world, but you need to get it to the track to be fast!

Front weight: This is the amount of weight on the front tires. Front weight affects how a kart turns.

Cross weight: This is the diagonal weight on the right front and left rear tires and vice versa. Cross weight affects how a kart turns.

Left side weight: This is the amount of weight on the left side tires. Left side weight affects side bite and how much weight is transferred to the outside tires.

Stagger: This refers to the difference in size of the rear tires. Stagger affects how a kart rolls in the corners.

Weight percentage: This is the static weight of each corner of the kart. Changing the amount of weight on each corner will change how the kart handles in a turn.

What do these numbers mean? For example, if you are racing the Briggs Light class at 305 pounds, your corner weights should be:

LF = 68 pounds RF = 68 pounds
LR = 95 pounds RR = 74 pounds
Total = 305 pounds

Front percentage = 44%
Left side percentage = 53%
Cross weight percentage = 54%

Now, let’s start putting all this information to work setting up an oval kart chassis. The static corner weights tell what each corner of the kart weighs when the kart is “at rest”. In a turn, the centrifugal force transfers the effect to the outside (right side of the kart) and forward. Too much weight on the front makes the kart feel loose. Too much weight on the rear makes the kart push, not turn in the corner.

First, we need to choose the tires you want to run. Selecting the proper tire depends on your driving style and approach to the race track. The driver who wants the kart to run loose will start with a harder compound tire. Drivers who want the kart to have a lot of turning traction will start with softer tires. Some tracks make the tire selection easy if they have a tire rule. Look around at the track at what tires the front-runners are using. That’s a good place to start.

Softer tires give you more grip in the corners, but they wear faster. Too much grip can make the kart tight. A condition when you lose speed going through a corner. On shorter tracks and low traction tracks, softer tires are the tires of choice.

Harder tires wear longer and they maintain driving characteristics for a longer time period. The lower grip may make a kart looser in the corners. On faster, long tracks, harder tires are the tires of choice.

Not everyone at the track will make the same decision on what kind of tires to use. There is not always one right answer to the tire question. You may be able to make a hard tire or soft tire work on the same track depending on how you set up a kart. I guess that’s part of why karting is such an interesting sport.

When selecting tire and wheel combinations, start with the right rear tire on a wheel equal to the width of the tire. The left rear wheel should be approximately 1 inch wider than the tire. This combination will give you approximately ½ inch of rear stagger. We will discuss stagger later in this report.

Seniors should run wider tires and Juniors a little narrower. Senior class drivers should start with a 7 or 8 inch tire on the right side and a 6 inch tire on the left rear.

The front tires are a bit easier to figure. They should be mounted on wheels equal to the width of the tires.

The placement of the wheel/tire combinations on the kart is the next step. Start with the front wheel assemblies in the middle of the spindles. This will give you lots of adjustment. Adding and subtracting spindle spacers on the front spindles will allow this.

Next are the rear tires. Start with the left side of the kart. Align the outside edge of the left front and the left rear tires. Now the right side. Align the inside edge of the right front and right rear tires. This is one area that is easier on an oval chassis because the rear of the kart is offset allowing the rear wheels to be adjusted. Those of you with straight-up karts may have a little trouble here, so you will need to take a little time and get as close as you can with the rear wheel adjustments.

After the rear wheels and tires are adjusted, it’s time to set the front-end “toe in”. Toe-in is when the leading edge of the front wheel/tire assemblies are slightly turned inward. These adjustments are made by rotating the tie rod ends slightly. (Editorial note: For safety sake, make sure you have at least twice the diameter of the tie rod threaded into the rod end. Example: ¼” tie rod = at least ½” of rod threaded into the rod end. If, when doing this, the tie rod is too short, don’t take a chance. Use a longer tie rod.)

With a tape measure, yard stick or toe-in tool, measure the distance between the back edges of the front tires, then measure the front edge. Adjust them until they measure the same. Now, adjust the toe-in slightly to 1/6” . As you get more comfortable driving ovals, you may want to try a little tow-out on the left front tire.

Now set the “camber” to the factory specifications, if it is adjustable. Camber is when the wheel are closer together at the bottom than at the top.

The next step - the king pins. Center the spindles with spindle washers. This will give you more adjustment for the front end weights.

When this is all completed, the front tires will have equal amount of weight while the left rear will be much heavier than the right rear.

Basically, the same kart on the same track would be set up narrower for harder tires compared to softer tires. In addition, your wheel base will be narrower if you run on dirt rather than asphalt.

In the second part of this Special Report designed for the beginner, I will be discussing the following topics for basic oval track setup for both pavement or dirt. The topics are:

· Positioning the seat
· Scaling and adjusting weight
· Basic adjustments you can make at the track

Note: In Part One, I discussed selecting and aligning wheels and tires, and understanding weight and balance. Part One can be found in the Archives section.

The Seat. The next step in setting up your oval track kart is installing the seat. It is important to remember that the weight distribution of your kart changes depending on where you place your seat. The driver is usually the heaviest part of the kart. Take your time to analyze this important step. Here are some significant things to keep in mind.

The rear of the seat back cannot go behind the center of the rear axle. Most tracks have a minimum seat back height. In most cases, the driver should be sitting to the left of the kart’s centerline. This helps give the kart left hand weight. A larger percentage of the driver’s weight should be on the left rear tire. This helps increase cross weight and keeps the left rear tire on the track. Note: If you have a straight-up kart with the seat mounts welded in place, you will not be able to do this.

Remember, when you add weight you will want to start at the left rear corner of the kart.

Place a sheet of plywood under the frame of the kart (without the wheels on the kart). Set the seat on the plywood. This will make the seat the same height as the bottom of the frame. Now, have the driver sit in the seat and find a comfortable sitting position for the drivers arms and legs. Mark the seat position. Drill the necessary holes in the seat and begin bolting it in that position. (Note: Don’t get too excited as you may want to move the seat after you scale the kart).

As a general rule, the seat should be to the left of the centerline of the kart. The seat must be inside the frame rails, and the back of the seat should be in front of the center of the rear axle. In this position, the driver can easily reach all controls and feel comfortable.

Scaling the kart - The basic setup. Before we discuss the actual methodology, I need to explain how to figure weights and percentages. The math is very simple. First, you will need the weight of each corner of the kart with the wheels and tires on the kart. Second, total the corner weight.
Model:
               Front Weight: Right Front + Left Front = 100
               Cross Weight: Right Front + Left Rear = 100
               Left Side Weight: Left Front + Left Rear = 100

Note: The manufacturer of your kart should have a setup sheet for different types of tracks and what percentage work best for your kart. If you kart did not come with a weight sheet, ask for one. It should be part of the service they sold you.

Weight Percentages:
               Front: 43% - 45%
               Left: 54% - 56%
               Cross: 52% - 54%

Example: If you are racing Briggs Light at 305 lbs., your approximate corner weights should be as shown:
               Left Front = 68 lbs.
               Right Front = 68 lbs.
               Left Rear = 95 lbs.
               Right Rear = 74 lbs.

Front Weight: 68 +68 = 136 lbs. or roughly 44% of 305 lbs.
Cross Weight: 95 + 68 = 163 lbs. or roughly 54% of 305 lbs.
Left Side Weight: 95 + 68 = 163 lbs. or roughly 53% of 305 lbs.

Now, to scale your kart. Scaling the kart can be done with the new computerized scales or with four simple bathroom scales. A new computer scale will sell for as little as $1000 up to $2500. Bathroom scales can be purchased at a discount store for as little as $20 each ($80 for four). Note: If you do use bathroom scales, make sure they are the same brand and the same height. Also, make sure they all weigh the same. Test each by setting them on the floor and standing on them. Do this until you find four scales that weigh the same.

Important: The spot you use to set up the kart needs to be level. Use a 6 ft. long carpenters level to make sure your scales or pads are level. Your scales must also be the same height as well. Floor tiles make good shims to adjust the height of the scales. Mark the four spots on the floor; 1,2,3,4 and the scales, too. This can make scaling easier the next time.

The driver must now sit in the kart, with his/her helmet on in a normal driving position. The driver should not try to look at the scales. Moving the driver’s head over the outside of the kart will change the reading on the scales.

How to move weight on a kart. Take some time to make adjustments to the kart to see what they do to the corner weights. Moving a washer on the front spindle will change the corner weight. Now is the time to find out how much.

Front Weight. What does front weight do? Front weight controls how well the kart turns. More weight on the front wheels gives the kart more turning traction. Front weight also takes away traction from the rear wheels. If you add too much front weight the kart becomes loose.

How do you get more front weight? 4 Ways: 1) The front of the kart can be lowered by moving the washers on the kingpins (lowering the front of the kart adds front weight), 2) Moving the tires in on the spindles (This also lowers the front end), 3) Moving the driver forward in the kart, and 4) moving any added-on weight forward on the kart.

Left Side Weight. Left side weight is much more important to dirt racers. If you have too much left side weight, it makes it difficult for dirt karts to get the right side wheels to work in a corner.

It is very difficult to have too much left side weight on pavement. Some karts run up to 60% . But remember, left side weight may change your cross weight.
Pavement racers take heart. It’s hard to have too much left side weight, but too little left side weight will cause the kart to “bicycle”. Bicycling is when the kart tips up on the right side wheels.

On dirt, too much left side weight makes it harder for your right side tires to get traction. This will feel as if the kart is both loose and pushing at the same time.

Cross Weight. Cross weight controls how the kart transfers weight in the corners. Increasing cross weight tightens up the kart. That means the kart has more forward traction. The kart also has less turning traction.

Decreasing cross weight loosens up the kart consequently the kart will have less forward traction and more turning traction.

How do you change the cross weight? Remember cross weight is Right Front + Left Rear = 100%. So to increase cross weight , you would add weight to the right front or remove weight from the left front. NASCAR guys call this “wedge”. You can move the left rear tire out on the axle, which increases the weight on that wheel.

To recap: To increase cross weight, add weight to the right front or left rear. To decrease cross weight, remove weight from the from the right front or left rear.

This adjustment can also be made by moving the front spindles up or down or moving the rear tires in or out on the axle.

Stagger. Stagger is difference between the diameter of the inside tire and the outside tire. The rear axle in a race kart is fixed so both wheels turn at the same speed. Stagger helps the inside wheel not turn (as quickly) going around a corner.

Changing the width of the wheel that a tire is mounted on, can change the diameter of the tire. A wider wheel will give you a smaller diameter tire. The diameter of a tire changes the base of the air pressure in it. If you increase air pressure, the diameter increases.

Increase stagger loosens the kart up while decreased stagger tightens (removes push) from the kart.

Keep in mind that tracks with long sweeping corners require less stagger than tracks with short tight corners.

Camber. Camber is the degree to which the front wheels lean toward or away from each other. If the tops of the tire are closer together than the bottom, the camber is negative. The opposite is positive camber. To maximize grip when cornering, it is desirable to have as much of the outside tire rubber on the track as possible. Camber is the setting particularly for maintaining maximum rubber on the track in the corners.

Camber is adjusted using the camber adjusters at the stub axle mounting. Many karts have adjustment pins to change the angle of the kingpin. Not all karts have adjustable camber, but it is not usually difficult to fit adjusters if you need them. Karts have very little body roll therefore they need very little camber.

Toe-in and toe-out. This is the degree to which the front wheels point toward or away from each other. Front wheels pointing toward each other is toe-in while wheels pointing away is toe-out. Toe-in makes a kart track in a straight line better, but can contribute to poor turn-in to corners. Toe-out can cause the kart to wander, but can assist the kart turn-in to corners. With toe-out, the inside front wheel move down in relation to the chassis more than it will with zero toe-out or toe-in. Toe is adjusted by lengthening or shortening the tie rods.

Push or Understeer. Push or Understeer is when you turn the steering wheel and the kart wants to go straight. This is caused because the front tires do not have enough traction and they are slipping on the surface of the track.

Loose or Oversteer. Loose or Oversteer is the opposite of push. The rear tires want to swing out around the kart, even though you only turned the steering wheel a little. This condition is caused because the rear tires do not have enough traction. This makes the kart hard to control and you could easily just spin around. If the kart is controllable, a loose kart can be very fast.

Karts can be loose going in to or coming out of a corner. As a general rule, if a kart has trouble entering the corner you need to adjust the front end, but if you have trouble exiting a corner, you need to adjust the rear end.

There are two basic rules to remember that will help you become fast.
A. Adjustments to the front end effects how it enters a corner
B. Adjustments to the rear of the kart effects how it exits a corner

It’s time to go to the track.
1. Learn what adjustment changes the way your kart works.
2. Practice - know what changes in track conditions require what setup changes.
3. Practice making adjustments to the kart
4. Don’t be afraid to ask questions

LOOSE ON ENTRY:

1) Reduce rear stagger (do so in .125" - .250" increments)

2) Reduce Front Weight % (1/2%-1% increments)

3) Increase Cross Weight %

4) Increase RF stagger and readjust your camber back to previous settings

5) Decrease LF positive camber

6) Change RR to a slightly softer compound or put your RR on a narrower wheel

7) Widen the front track

8) Use a harder compound front tire

LOOSE IN CENTER OF TURN OR TOO MUCH ROTATION

1) Decrease air pressure in the LF (1/4 - 1/2 lb. at a time)

2) Move LF in ( 1/8" - 1/4" at a time)

3) Increase air pressure in the LR and RR (1/2 lb at a time)

4) Move RR in as close as possible (always use lock collar if possible)

LOOSE COMING OFF OF TURN

1) Move the LR IN(1/4"-1/2" increments)

2) Increase cross weight percentage (1/2%-1% increments)

3) Softer compound on LR

4) Reduce the negative camber on the RF

5) Reduce stagger in the rear tires
6) Stiffen rear torsion bar
7) Increase rear weight
8) Decrease stagger in right rear tire
9) Add air to left rear tire

VERY LOOSE CAUSING 4 WHEEL DRIFT

1) Reduce Left side % to get more side bite

2) Increase VCG (Vertical Center of Gravity)

3) Reduce air pressures all the way around (same amount each tire)

4) Go to softer right side tires

5) Go to softer compound on at least RR

6) If softer compound unavailable use new uncut tires over cut tires

7) If you start out with this condition and are 10" wheels, go to 9.5"

8) Increase castor 3's on both RF and LF ( do this in equal increments)

4) Increase front % in .25% increments (do not go crazy, only minor adjustments)

7) increase cross weight
8) Move right front wheel out
9) Soften front torsion bar
10) Increase rear brake bias
11) Use a softer tire compound front tire
12) Narrow the front track

Note: Stagger change is a productive to the push but the resulting camber changes are not. Readjust your camber back to the previous setting before stagger change

4) Increase the negative camber on the RF
5) Increase rear stagger
6) Increase rear torsion bar
7) Decrease rear weight
8) Increase air pressure in rear tires
9) Increase stagger of rear tires
10) widen the rear track

And finally… Record Keeping
Keep good records of how the changes you make effect the kart. You will not be able to remember what changes you made and what the effect was. Your kart will be effected differently than everyone else’s, even if it is the same brand and model. What takes a ½ inch adjustment for you may take someone else a ¼ inch or 1 inch. You can keep records with a simple notebook or on a laptop with one of the new kart racing computer programs. If you do not keep records of what changes do to your lap times, all you will ever be doing is guessing. A few minutes in the pits may give you the extra edge on the track.

STOCK BRIGGS

HEADER PIPE - .312" MAX. THICKNESS OF THE FLANGE - HEADER MUST BE SAFETY WIRED AND THE WIRE MUST GO ALL THE WAY AROUND THE PIPE TO KEEP THE BOLTS WITH THE PIPE

AIR FILTER ADAPTER - .250" MAXIMUM. FROM TOP OF ADAPTER TO CARBURETOR MATING SURFACE -- TOP MUST BE FLAT

THROTTLE SHAFT - .040" MINIMUM FRONT EDGE -- .086" MINIMUM BACK EDGE -- .030" MINIMUM BACKSIDE RECESS -- MUST RETAIN STOCK CONFIGURATION

BUTTERFLY SCREW - .322" MINIMUM LENGTH

AIR HORN - 1.011" MAXIMUM TOP AND BOTTOM

METERING HOLES - .062" MAXIMUM MAIN METERING HOLE -- .028" MAXIMUM IDLE HOLE

FRONT RECESS - .726" MAXIMUM AND MUST BE AS CAST

CARBURETOR BORE - .695" MAXIMUM ENTIRE LENGTH OF BORE

SHORT PICKUP TUBE - .066" MAXIMUM HOLE SIZE

HEAD GASKET - .043" MINIMUM CHECKED IN 4 PLACES ONE ON THE FRONT, REAR AND ONE ON EACH SIDE

HEAD - .011" - .408" - .300" MINIMUM - .315" MAXIMUM IN DEEPEST PLACE -- BOLT HOLES .3480" MAXIMUM

PISTON POP-UP - .005" MAXIMUM ACROSS THE WRISTPIN AND FRONT OF PISTON

BORE - 2.6025" MAXIMUM

STROKE - 2.437" - 2.444"

INTAKE VALVE - 30° FACE -- 1.115" MINIMUM DIAMETER -- .035" ON THE EDGE OF THE VALVE (no knife edging allowed)

EXHAUST VALVE - 45° FACE -- .990" MINIMUM DIAMETER

INTAKE SPRING - 1.240" MAXIMUM LENGTH -- .087" MAXIMUM WIRE SIZE

EXHAUST SPRING - 1.300" - 1.500" LENGTH -- .088" - .093" WIRE SIZE -- .625" - .640" INSIDE DIAMETER

RETAINERS - PART # 23184 .50" - .058" THICKNESS -- PART # 555147 .015" - .025" THICKNESS

INTAKE SEAT - 30° SEAT ANGLE -- 1.004" MAXIMUM INSIDE DIAMETER -- .199" - .215" SEAT THICKNESS

EXHAUST SEAT - 45° SEAT ANGLE -- .880" MAXIMUM INSIDE DIAMETER -- .199"
- .215" SEAT THICKNESS

FLYWHEEL - 6 lbs. 4 ozs. MINIMUM

PISTON OLD STYLE - 1.869" MINIMUM LENGTH -- .937" MINIMUM LENGTH TOP OF PISTON TO TOP OF WRIST PIN -- .084" MAXIMUM RING LAND WIDTH

RAPTOR III PISTON - 1.671" MINIMUM LENGTH -- .937" MINIMUM LENGTH TOP OF PISTON TO TOP OF WRIST PIN -- TOP TWO RING LAND WIDTH: .0603" - .0612" -- OIL RING LAND WIDTH: .1020" - .1032"

RINGS OLD STYLE - .105" MINIMUM WIDTH TOP TWO RINGS -- .085" MINIMUM WIDTH OIL RING -- .083" OIL GROOVE MINIMUM

RAPTOR III RINGS - .090" MINIMUM WIDTH TOP TWO RINGS -- .058" + OR -.005" THICKNESS -- .035" MIN. THICKNESS OF THE NARROW CUT OF THE SECOND RING -- .070" OIL RING MINIMUM WIDTH -- .100" + OR - .005" THICKNESS -- IF OIL RING IS BROKEN ALL PIECES OF RING MUST BE IN RING LAND

WRIST PIN OLD STYLE - .290" INSIDE MAXIMUM DIAMETER -- .490" OUTSIDE DIAMETER MAXIMUM

RAPTOR III WRIST PIN - .291" INSIDE MAXIMUM -- .490" OUTSIDE DIAMETER MAXIMUM - LENGTH - 1.732" + OR - .005"

AFTERMARKET ROD - NO ALTERATIONS ALLOWED. LEGAL AFTERMARKET RODS: ARC ROD PART #6328, #6330, #6348, #6350, CKI PART #3875, HORSTMAN PART #H-498100, #H-498101, #498105, RIX ROCKETS / EBERT PART #3.875, WMS ROD PART # 7070, 7575 -- 135 GRAMS MIN. TOTAL WEIGHT -- 113 GRAMS MIN. ROD LESS INSERT -- 22 GRAMS MIN. INSERT WEIGHT -- 1/4" ROD BOLTS

ROD - 3.120" - 3.1333" LENGHT - ROD MUST BE STOCK OR APPROVED AFTERMARKET

CAM - .770" BASE CIRCLE MAXIMUM -- (SEE 701.17.1 FOR CAM PROFILE)

LIFTER - .982" - 1.005" HEAD DIAMETER -- 1.606" MAXIMUM LENGTH -- AFTERMARKET LIFTERS ALLOWED MUST MEET STOCK SPECS

CRANKSHAFT - .990" MINIMUM JOURNAL DIAMETER -- .775" MINIMUM DIAMETER AFTER CLEARANCING FOR BEARING

SILENCER - RLV 8-91 SILENCER -- .1285" NO-GO INTAKE SIDE BAFFLE AND EXIT SIDE BAFFLE

BRIGGS CONTROLLED STOCK

HEADER PIPE - .312" MAX. THICKNESS OF THE FLANGE - HEADER MUST BE SAFETY WIRED AND THE WIRE MUST GO ALL THE WAY AROUND THE PIPE TO KEEP THE BOLTS WITH THE PIPE

AIR FILTER ADAPTER - .250" MAXIMUM FROM TOP OF ADAPTER TO CARBURETOR MATING SURFACE -- TOP MUST BE FLAT

CONTROLLED CARBURETOR - .715" MAXIMUM BORE (FULL LENGTH OF BORE], NO MATERIALS ADDED INSIDE OR OUTSIDE, MUST HAVE SOME STOCK RECESS SHOWING, BOTH PICKUP TUBES MUST WORK

SUPER CONTROLLED CARBURETOR - ANY TILLOTSON HL-SERIES CARBURETOR
-- .850" MINIMUM VENTURI - .900" MAXIMUM VENTURI -- MUST BE STOCK APPEARING ON THE OUTSIDE

HEAD GASKET - .043" CHECKED IN 4 PLACES ONE ON THE FRONT, REAR AND ONE ON EACH SIDE

HEAD - .400" MINIMUM IN SPARK PLUG AREA-BOLT HOLES -- .3480" MAXIMUM MACHINING OF VALVE AREA ALLOWED MUST NOT HIT THE BACK OF HEAD, MUST NOT BE MACHINED BELOW FLAT CYLINDER PORTION OF HEAD

BORE - 2.6025" MAXIMUM

STROKE - 2.437" - 2.444

VALVE BREATHER - AFTERMARKET BREATHER ALLOWED -- CRANKCASE BREATHER ALLOWED

INTAKE VALVE - 30° FACE -- 1.115" MINIMUM DIAMETER -- .035" ON THE EDGE OF THE VALVE (no knife edging allowed)

EXHAUST VALVE - 45° FACE -- .990" MINIMUM DIAMETER

INTAKE SPRING - 1.240" MAXIMUM LENGTH -- .087" MAXIMUM WIRE SIZE

EXHAUST SPRING - 1.500" - 1.300" LENGTH -- .088" - .093" WIRE SIZE -- .625" - .640" INSIDE DIAMETER

RETAINERS - PART # 23184 .50" - .058" THICKNESS -- PART # 555147 .015" - .025" THICKNESS

INTAKE SEAT - 30° SEAT ANGLE -- 1.004" MAXIMUM INSIDE DIAMETER -- .199" - .215" SEAT THICKNESS

EXHAUST SEAT - 45° SEAT ANGLE -- .880" MAXIMUM INSIDE DIAMETER -- .199"
- .215" SEAT THICKNESS

FLYWHEEL - 6 lbs. 4 0zs. MINIMUM

SUPER CONTROLLED FLYWHEEL - ONLY FLYWHEELS ALLOWED ARE THE ARC BILLET, J. R. RACE CAR AND UNITED MACHINE AND FAB. FLYWHEELS -- 4 lbs. 12 ozs. MINIMUM

PISTON OLD STYLE - AFTERMARKET PISTON ALLOWED MUST MEET STOCK SPECS -- 1.869" MINIMUM LENGTH -- .937" MINIMUM LENGTH TOP OF PISTON TO TOP OF WRIST PIN -- .084" MAXIMUM RING LAND WIDTH

RAPTOR III PISTON - 1.671" MINIMUM LENGTH -- .937" MINIMUM LENGTH TOP OF PISTON TO TOP OF WRIST PIN -- TOP TWO RING LAND WIDTH: .0603" - .0612" -- OIL RING LAND WIDTH: .1020" - .1032"

RINGS OLD STYLE - .105" MINIMUM WIDTH TOP TWO RINGS -- .085" MINIMUM WIDTH OIL RING -- .083" OIL GROOVE MINIMUM

RAPTOR III RINGS - .090" MINIMUM WIDTH TOP TWO RINGS -- .058" + OR -.005" THICKNESS -- .035" MIN. THICKNESS OF THE NARROW CUT OF THE SECOND RING
-- .070" OIL RING MINIMUM WIDTH -- .100" + OR - .005" THICKNESS -- IF OIL RING IS BROKEN ALL PIECES OF RING MUST BE IN RING LAND

WRIST PIN OLD STYLE - .290" INSIDE MAXIMUM -- .490" OUTSIDE DIAMETER MAXIMUM

RAPTOR III WRIST PIN - .291" INSIDE MAXIMUM -- .490" OUTSIDE DIAMETER MAXIMUM - 1.732" + OR - .005" LENGTH

ROD - 3.120" - 3.1333" LENGHT - AFTERMARKET ROD ALLOWED MUST MEET STOCK SPECS.

CAM - MAY BE CENTERED ON BOTH ENDS -- .265" MAXIMUM RUNNING LIFT-CAM GEAR MUST REMAIN AS CAST

LIFTER - OPTIONAL INCLUDING RETAINERS

CRANKSHAFT - .990" MINIMUM JOURNAL DIAMETER -- .775" MINIMUM DIAMETER AFTER CLEARANCING FOR BEARING

SILENCER - RLV 8-91 SILENCER -- .1285" NO-GO INTAKE SIDE BAFFLE AND EXIT SIDE BAFFLE

BRIGGS LIMITED MODIFIED

HEADER PIPE - .312" MAX. THICKNESS OF THE FLANGE - HEADER MUST BE SAFETY WIRED AND THE WIRE MUST GO ALL THE WAY AROUND THE PIPE TO KEEP THE BOLTS WITH THE PIPE

CARBURETOR - ANY TILLOTSON HL-SERIES CARBURETOR - .850" MINIMUM VENTURI - .900" MAXIMUM VENTURI -- MUST BE STOCK APPEARING ON THE OUTSIDE

HEAD GASKET - NOT A TECH ITEM

HEAD - .400" MINIMUM IN SPARK PLUG AREA-BOLT HOLES -- .3480" MAXIMUM MACHINING OF VALVE AREA ALLOWED MUST NOT HIT THE BACK OF HEAD, MUST NOT BE MACHINED BELOW FLAT CYLINDER PORTION OF HEAD

BORE - 2.6075" MAXIMUM

STROKE - 2.437" - 2.444"

VALVE BREATHER - AFTERMARKET BREATHER ALLOWED -- CRANKCASE BREATHER ALLOWED

INTAKE VALVE - 30° FACE -- 1.115" MINIMUM DIAMETER -- .035" ON THE EDGE OF THE VALVE (no knife edging allowed)

EXHAUST VALVE - 45° FACE -- .990" MINIMUM DIAMETER

INTAKE SPRING - NOT A TECH ITEM

EXHAUST SPRING - NOT A TECH ITEM

INTAKE SEAT - 30° SEAT ANGLE -- 1.004" MAXIMUM INSIDE DIAMETER -- .199" - .215" SEAT THICKNESS

EXHAUST SEAT - 45° SEAT ANGLE -- .880" MAXIMUM INSIDE DIAMETER -- .199"
- .215" SEAT THICKNESS

FLYWHEEL - ONLY FLYWHEELS ALLOWED ARE THE ARC BILLET, J. R. RACE CAR AND UNITED MACHINE AND FAB. FLYWHEELS -- 4 lbs. 12 ozs. MINIMUM

PISTON - ANY FLAT TOP ALUMINUM PISTON-COATING OF PISTON IS ALLOWED
ROD - ANY ALUMINUM ROD ALLOWED

CAM - TWO PIECE CAM ALLOWED-SIDECOVER MAY BE GROUND TO ALLOW FOR CLEARANCE OF ADJUSTABLE CAMSHAFT BOLTS-NO ROLLER CAMS ALLOWED

LIFTER - OPTIONAL INCLUDING RETAINERS

CRANKSHAFT - .990" MINIMUM JOURNAL DIAMETER -- .775" MINIMUM DIAMETER AFTER CLEARANCING FOR BEARING -- MAY BE CLEARANCED ON COUNTERWEIGHT TO CLEAR CAM-ENTIRE COUNTERWWEIGHT CANNOT BE CLEARANCED

BLOCK - MINOR GRINDING TO CLEARANCE ROD AND LIFTERS ALLOWED

OTHER - THIRD BEARING SUPPORT ALLOWED - GIRDLE STRAP ALLOWED-USE OF SEALANT ON GASKET OR JUST SEALANT ALLOWED ON INTAKE AND EXHAUST SURFACES AND HEAD TO BLOCK

SILENCER - RLV B-91MO SILENCER -- .1285" NO-GO INTAKE SIDE OF BAFFLE -- .2031" DISCHARGE SIDE OF BAFFLE FOR SQUARE HOLE -- .1935" FOR ROUND HOLES

BRIGGS ANIMAL

SHROUD AND COVERS (STOCK ANIMAL) - MUST RUN STOCK SHROUD AND COVERS -- STOP SWITCH MUST BE PRESENT DOES NOT HAVE TO BE CONNECTED

SHROUD AND COVERS (CONTROLLED AND MODIFIED ANIMAL) - PLASTIC COVER AND CONTROL PLATE MAY BE REPLACED -- MUST USE NEW STYLE SHROUD PART # 555623

HEADER PIPE - 24" MAXIMUM -- .312" MAX. THICKNESS OF THE FLANGE - HEADER MUST BE SAFETY WIRED AND THE WIRE MUST GO ALL THE WAY AROUND THE PIPE TO KEEP THE BOLTS WITH THE PIPE

CARBURETOR (STOCK ANIMAL) - PZ MODEL 15 MUST BE AS CAST -- .874" MAX. THROTTLE BORE -- .792" MAX. VERTICAL -- .615" MAX. HORIZONTAL -- .061" MAX. AIR PICK OFF HOLE -- 1.148" MIN. SLIDE -- 1.149" CHOKE BORE -- .602" MUST NOT GO PASS STEP IN CARB FROM INTAKE SIDE - 1.680" MINIMUM - 1.690" MAXIMUM LENGTH NEEDLE - ANYTHING IN THE FLOAT BOWL OR THAT CAN BE REMOVED THOUGH THE BOWL IS NOT A TECH ITEM.

RESTRICTOR PLATE (JR ANIMAL) - GOLD RESTRICTOR PLATE -- .505" MAXIMUM -BLACK RESTRICTOR PLATE .576" MAXIMUM -- MUST HAVE ONE GASKET ON THE INTAKE SIDE O-RING ON THE CARB SIDE AND NO GASKET

CARBURETOR (CONTROLLED ANIMAL) - ANY HL CARB WITH A MAXIMUM THROTTLE BORE OF 1.005" AND A MAXIMUM VENTURI OF .825" - BUTTERFLY MUST BE HELD IN PLACE WITH A SCREW - SINGLE OR DOUBLE PUMPER STACKS ALLOWED

CARBURETOR (MODIFIED ANIMAL) - ANY HL CARB WITH A MAXIMUM THROTTLE BORE OF 1.005" AND A MAXIMUM VENTURI OF .900" - BUTTERFLY MUST BE HELD IN PLACE WITH A SCREW - SINGLE OR DOUBLE PUMPER STACKS ALLOWED

INTAKE (CONTROLLED ANIMAL AND MODIFIED ANIMAL) - ANY INTAKE ALLOWED

INTAKE (STOCK ANIMAL) - 1.740" - 1.760" LENGTH MAY BE MACHINED TO MAX. LENGTH -- .885" - .905" INSIDE DIAMETER -- .070" MAXIMUM GASKET THICKNESS.

BALL ROCKER (STOCK AND CONTROLLED ANIMAL) - .590" - .610" -- MUST BE STOCK

BALL ROCKER (MODIFIED ANIMAL) - MUST BE STOCK -- MAY BE GIRDLED OR REINFORCED

ROCKER ARMS - 2.865" MIN. LENGTH -- MUST BE STOCK

PUSH RODS - .185" - .190" DIAMETER -- 5.638" - 5.656" LENGTH -- MUST BE STOCK

CYLINDER HEAD PLATE (STOCK AND CONTROLLED ANIMAL)- MUST BE STOCK -- .055" MAX GASKET THICKNESS

CYLINDER HEAD PLATE (MODIFIED ANIMAL)- MUST BE STOCK -- .055" MAX GASKET THICKNESS - MAY BE REINFORCED NO WELDING ALLOWED

CYLINDER HEAD (STOCK AND CONTROLLED ANIMAL) - STOCK PART #558 -- .011" MIN. DEPTH AT SHALLOW PART OF HEAD -- .319" MIN. DEPTH AT FLOOR OF HEAD -- .335" - .360" DEPTH TO TOP OF VALVE SEAT - DEPTH FROM GASKET SURFACE TO TOP OF VALVE GUIDE 1.255" MAXIMUM - THICKNESS OF HEAD 2.420" MIN. TO BE CHECKED WITH GAGE IN FOUR PLACES VALVE GUIDES AND PUSH ROD HOLES

CYLINDER HEAD (MODIFIED ANIMAL) - STOCK PART #558 -- .011" MIN. DEPTH AT SHALLOW PART OF HEAD -- .319" MIN. DEPTH AT FLOOR OF HEAD -- .335" - .360" -- PORTING ALLOWED -- THICKNESS OF HEAD 2.420" MIN. TO BE CHECKED WITH GAGE IN FOUR PLACES VALVE GUIDES AND PUSH ROD HOLES - AFTERMARKET VALVE GUIDES ALLOWED

HEAD GASKET - .049" MIN. THICKNESS CHECKED IN FOUR PLACES -- MUST BE STOCK

INTAKE VALVE - 45° ANGLE -- 1.055" - 1.065" HEAD DIAMETER -- .099" - .119" DEPTH OF DISH -- STOCK FACTORY VALVE -- .057" MIN. WHEN CHECKED IN GAGE

EXHAUST VALVE - 45° ANGLE -- .935" - .945" HEAD DIAMETER -- .084" - .104" DEPTH OF DISH -- STOCK FACTORY VALVE -- .060" MIN. WHEN CHECKED IN GAGE

VALVE SPRINGS (STOCK ANIMAL) - .930" MAXIMUM LENGTH -- .103" - .107" WIRE SIZE -- .615" - .635" INSIDE DIAMETER -- MUST BE STOCK

VALVE SPRINGS (CONTROLLED ANIMAL) - AFTERMARKET SINGLE VALVE SPRINGS ALLOWED

VALVE SPRINGS (MODIFIED ANIMAL) - AFTERMARKET DUAL VALVE SPRINGS ALLOWED

VALVE SPRING RETAINERS (STOCK ANIMAL) - .060" - .070" THICKNESS

VALVE SPRING RETAINERS (CONTROLLED AND MODIFIED ANIMAL) - AFTERMARKET RETAINERS ALLOWED

INTAKE VALVE SEAT - 45° ANGLE -- .966" - .972" INSIDE DIAMETER

EXHAUST VALVE SEAT - 45° ANGLE -- .844" - .850" INSIDE DIAMETER

INTAKE PORT - .918" MAXIMUM -- .864" NO-GO CANNOT TOUCH VALVE GUIDE --.860" VISUAL CHECK ON PORT EYEBOW

EXHAUST PORT - .980" MAXIMUM

PISTON POP-UP (STOCK AND CONTROLLED ANIMAL) - .005" MAXIMUM ACROSS WRIST PIN THEN TURN THE BAR STOCK 90 DEGREES TO THE WRIST PIN AND MUST STILL BE .005"

PISTON POP-UP (MODIFIED ANIMAL) - .010" MAXIMUM ACROSS WRIST PIN THEN TURN THE BAR STOCK 90 DEGREES TO THE WRIST PIN AND MUST STILL BE .010"

CYLINDER BORE - 2.690" - 2.725"

STROKE - 2.204" MAXIMUM

IGNITION - 3,000 - 6,000 OHMS

FLYWHEEL - BILLET FLYWHEEL ONLY - 4 LBS. - 8 OZS. MINIMUM - NO PAINTING

CAM (STOCK AND CONTROLLED ANIMAL) - .870" MAXIMUM BASE CIRCLE -- GROUND CAMS LEGAL -- MUST MEET PROFILE IN TECH MANUAL--MAXIMUM LIFT OF CAM TAKEN OFF OF VALVE WITH ON VALVE LASH .255"

CAM (MODIFIED ANIMAL) - MAXIMUM VALVE LIFT OF .310"-- MAXIMUM LIFT OF CAM TAKEN OFF OF VALVE WITH ON VALVE LASH .307" -- MAXIMUM VALVE DURATION OF 248 DEGREES AT .050" LIFT -- MAXIMUM VALVE DURATION OF 153 DEGREES AT .200" LIFT

VALVE LIFTERS - .820" - .860" HEAD DIAMETER -- 1.515" - 1.525" LENGTH

ROD (STOCK ANIMAL) - 2.419" - 2.429" LENGTH -- .185" MAXIMUM OIL HOLE -- MUST BE STOCK

ROD (CONTROLLED AND MODIFIED ANIMAL) - AFTERMARKET ROD ALLOWED MUST MEET STOCK SPECS.

PISTON (STOCK ANIMAL) - .658" MINIMUM TOP OF WRIST PIN TO TOP OF PISTON -- 1.768" MINIMUM LENGTH - MUST BE STOCK

PISTON (CONTROLLED AND MODIFIED ANIMAL) - AFTERMARKET PISTON ALLOWED MUST MEET STOCK SPECS.

RINGS (STOCK ANIMAL) - .095" MINIMUM WIDTH -- .059" - .064" MAXIMUM THICKNESS TOP TWO RINGS -- .065" MIN. WIDTH -- .098" - .102" THICKNESS OIL RING --EXPANDER RING MUST BE INSTALLED - MUST BE STOCK

RINGS (CONTROLLED ANIMAIL AND MODIFIED ANIMAL) - AFTERMARKET RINGS ALLOWED AS LONG AS IT MEETS STOCK SPECS.

WRISTPIN - .624" - .626" OUTSIDE DIAMETER -- .414" MAXIMUM INSIDE DIAMETER -- 1.901" MINIMUM LENGTH

CRANKSHAFT - 1.094" - 1.100" JOUNAL DIAMETER

SILENCER (STOCK AND CONTROLLED ANIMAL) - RLV 8-91 SILENCER -- .1285" NO-GO INTAKE SIDE BAFFLE AND EXIT SIDE BAFFLE

SILENCER (MODIFIED ANIMAL) - - RLV B-91MO SILENCER -- .1285" NO-GO INTAKE SIDE OF BAFFLE -- .2031" DISCHARGE SIDE OF BAFFLE FOR SQUARE HOLE -- .1935" FOR ROUND HOLES