MSD 7530 Series Digital 7 Programmable Ignition

A good friend was kind enough to let me use his 7530 Series 7AL Digital Ignition for a couple of races in September (See the chassis tuning article under suspension modifications).

The cool thing about this ignition system is that it is easy to install and if you happen to be using the MSD 8517 Pro Billet Distributor along with 8261 HVCII coil all of the wiring connections are a snap.

Once installed the unit allows for infinite programming of the ignition to accommodate all types of track conditions as well as the ability to program out some of the deficiencies of your chassis via ignition tuning. The ability to save different tune-ups to separate files is also a great benefit. For example if you end up at a track with marginal traction, in 25 seconds you can download your pre-saved tune-up which kills some of the power at launch. From this baseline program and a couple of passes it is possible to adjust the launch retard and duration until you get the most power into the track without spinning.

This unit will also tell you how efficient your chassis is at getting all of the power into the track. If you leave all of the launch retard out at the hit and the car hooks, your 60’ times are consistent and your eighth mile ET’s are consistent with your power level (see chart on this site) you know that your chassis is extremely efficient at converting the available power into forward motion.

If the converse is true meaning you have to retard the launch timing for a long duration then there is more work to be done on the chassis to take advantage of the available power. You are wasting time and money finding more horsepower via engine modifications until you can get all of the power into the track. Chassis modifications are cheap by comparison to engine modifications.

Learning to program the digital 7 can be daunting at first glance so I am including a few simple tips to get you started. You can read the .PDF file on the MSD website (53 pages) for more advanced functions. Once you hook up the digital 7 to your laptop, it will confirm the correct software version, download the current program from the MSD to the computer and open the editor for making changes. Her are the steps for obtaining the latest version of the software and programming your digital 7:

1) Navigate to MSD’s home page at http://www.msdignition.com/ , hit the software radio button and download MSD PRO DATA SOFTWARE.

2) This is 12MB file that takes a bit to download.

3) Install the software and open up on your computer.

4) Open Graphview 3.19

5) Go to the file tab and select open then select your product model number (i.e. 7530)

6) For starters select one of the preinstalled programs (i.e. 7530v01.ign)

7) The editor will open and you will see a gear retard curve, gauges file, data editor file, etc. Where do you start?

8) Select the data editor box or you can press the view button in the upper left hand corner and place a check next to the tree. Here is what it all looks like:



9) Work your way down the tree and set your various rev limiters. This unit is so versatile you can set your burnout rev limit, max rev limit, launch rev limit – basically a two step as a starting point.

10) Decide on where you will set your distributor timing based on atmospheric conditions, tune-up etc. NOTE: with these ignition systems you can only retard timing you cannot advance timing beyond the initial setting.

11) Next move to the timing retard section and select your start retard – for fixed timing distributors this retards the timing at start-up to minimize the chance for a backfire – a good starting point is to retard the start-up timing to 20 degrees. This retard only lasts until the car is started then you go to full timing.

12) Next set your launch retard. A good starting point here is DEG 0 and RAMP 0 for your first pass. If the car spins put in 2-4 degrees for about .5 seconds and make another pass. Keep taking timing out until tire spin goes away.

13) You can also retard timing in each gear plus build custom timing curves based throughout the entire rpm band depending on what you are trying to accomplish – this is where you will need to read up on all of the features in the http://www.msdignition.com/instructions/graphviewdemo.pdf file for advanced functions.

14) Once you are done inputting all of your changes you can save the file to your computer and or download directly to the 7 al unit by hitting the transfer button.

15) Again there are several options here to confirm your changes have been received This unit does self diagnostic checks plus builds in safety features to make sure if a file is corrupted you don’t destroy your engine.

The previous set-up in my car was a 6AL box. Although a great inexpensive ignition I am now hooked on the programmable 7AL unit.

Hopefully this write-up will help you get started. Good Luck!

Helpful Chart for Chassis Tuning

This is very useful guideline if you are trying to determine what your 60' time should be based on your 660' ET.

Again thanks to Dave Morgan of Door Slammers fame for this information sheet.

Chassis and Tuning Tips For Maximum Efficiency

Suspension Maintenance & Tuning Tips
For Maximum Efficiency
by
Tom Rix

EFFICIENCY: When changing the suspension or driveline components, what you are looking for is the LEAST amount of power to move the car the quickest!

AT HOME PREPARATION:

• Get car race ready: Tire pressure, shock settings, air bags, anti-roll bar, etc.
• Bounce car on all 4 corners. Listen and/or feel for any bind.
• Inspect all suspension components; including factory welds.
• Inspect tires, front & back. Rotate rear tires every race! Preserve the sidewalls.
• Measure the distance from the floor to the center of each fender wheel well and write it down. This is your baseline setting for future reference. “VERY IMPORTANT!” Any changes you make to the car will affect this!

THE TOW:

• Inflate rear tires to 25-30#. The tow is harder on the slicks if under inflated relative to actual racing tire pressure! Or you can tow with street tires and put the slicks on at the track.
• Inflate rear air bags to 20-25#.
• If using adjustable shock absorbers set them firmer for the tow. If a longer tow to the track consider changing at least the rear shocks to a firm street set.
• If you have a temperature gun, measure how hot the shocks get after a long tow! If the fluid gets too hot, 180 degrees +, it will lose its viscosity and effectiveness.
• Use 4 tie down straps; 2 at each end and criss-cross.
• Put the car as forward as possible on the trailer so it is supported by the trailer and tow vehicle suspensions.
• If it is too far back, consider additional measures to secure the car’s suspension.

AT THE TRACK:

• Return the car to race ready condition.
• Bounce on all 4 corners. Listen and/or feel for any bind.
(A simple trick once your car is “working” properly is to shut the car off on the return road after a pass and just coast. You will learn to identify the “normal” noises your suspension, transmission and rear end make while moving. Again, this gives you a baseline for future reference. I do this at least once every race day!)
• Measure the distance from the ground to the center of each fender wheel well and compare to your baseline settings.
• Mark white stripes on your front and rear tire sidewalls. This will be easy to see tire movement if you have someone watching or even better, video taping your run.

BURNOUT:

Pull through to the edge of the water box. Heat tires
enough to match the track temperature for maximum adhesion.
Remember the tires will “cool” a little from burnout to launch.
NO DRY HOPS!

STAGE:

Be consistent in your “spot”. I just barely turn on the
second yellow so I have consistent comparisons from run to
run.

Assuming all suspension pieces and tires are correct for your car
then proceed as follows:


STEP 1:

Make a pass. If the car violently wheel stands or bounces in
the gear change, adjust the front shocks first. If there is rear tire
shake, wheel hop, or excessive body separation, adjust the rear
shocks first.

STEP 2:

Adjusting front shocks. The goal here is to obtain a smooth
transition in the front end movement from the launch through
the first gear change. You want to eliminate all jerking and
bouncing movements.

Too loose a shock setting for extension can be diagnosed at the initial launch by a violent chassis separation and the front wheels jerking off the ground. During the gear change, loose shock settings for the extension and compression cause the car to bounce off its front travel limiter, fall down on the suspension and bounce back up again.

Too tight a shock setting for extension will keep the tires from easily lifting off the ground. During a gear change, a stiff shock in compression will cause the chassis to bounce off the tire when the chassis settles down.

To tune the shock, adjust the settings a little for each launch
until you have a smooth transition from launch through the gear
change. Watch your E.T. – if the time gets slower, back off the
shock adjustment a little bit.

STEP 3:

Rear shock adjustment. The goal is to shock the tire as hard
as track conditions will permit. Shocks control how large a force is put on the tire. Too loose a shock in extension causes excessive separation between the tire and body. Too tight a shock in extension or compression will cause high tire shock loads and cause extreme flattening of the tire. To tune the shocks, tighten the adjustment a little per pass.
Again, watch your E.T., then back off the adjustment a little bit.

KEEP RECORDS:


Write down all track and weather conditions, chassis settings,
tire pressure, engine oil and water temperature, and transmission temperature if available. Include carb jetting, timing, transmission shift points, EGT’s orO2 sensor data if available.

On your time slip not only compare 60’,330,660’,1000’ and 1320’, ET and MPH from one run to another, but more importantly compare the difference between these incrementals: i.e. – subtract 60’ time from the 330’ time so you know how long it took between those points.

If you pick up .04 in ET, you need to understand at what point(s) on the track you improved. I pay attention more to the 330’ time when making comparisons from one track to another as 60’ clocks can vary. If racing/testing at the same track, then 60’ is more meaningful. Almost all chassis changes will show up in the first 330’.

HAVE FUN!!!


OTHER TIRE TIPS:


Remember that your 2 rear tires act like an extra “set” of shock
absorbers. Tune with them also. According to Dave Morgan,
most sportsman/bracket cars run with too little air!

Learn to read the pattern on your tires. You are looking for a slight
“grainy” pattern straight across the entire tread.

If you video tape your launch pay close attention to the sidewall of
slick. As you watch the car launch from the driver’s side you
want the “wrinkles” to be from the 9 o’clock position down to
6 o’clock position or slightly past on the tire! This is what
works best for me.

The white stripe on the front tire tells you if you “dead hooked”
(pulled front tires straight up out of the beams) or drove
forward as the car hooked. See how fast the white stripe
rotates in the air to gauge this.

Tire screws, if you use them, make sure they are indexed from side to
side. Absolutely critical!

Check tire circumference with a tape. They need to be within a ¼ “of
each other

Rotate frequently!


I would like to acknowledge Dave Morgan for his Chassis Seminars, Books and Videos. Many of the concepts discussed here come directly from his literature and classes as applied to my race car operation.

I would also like to acknowledge Chris Alston Chassis Works especially regarding shock absorber concepts. http://www.cachassisworks.com/

1970 Buick Stocker Suspension Data

Below are links to my YouTube postings in which I spent the past week trying to make my 3700 lb stocker hook up a 9" radial tire on a marginal track.

The first video was taken 9-13-2008 at Spokane County Motorsports Park (SCMP) in Spokane Washington. A little word about this track before we get started. This is an old AHRA facility in which very little care and almost no upgrades have been done in at least 25 years. It has an asphalt launch pad, grooves in the pavement and is in pretty bad shape.

The county recently purchased the facility and a great group of volunteers - Spokane Pro Gas Racing Association - has been leasing the track and putting on Saturday racing events throughout the month of September. They have been seeing between 200-300 cars show/day for each event. These guys are doing an excellent job with what they have to work with.

Pure nuts and bolts - very little VHT, the burnout box and launch area look like a topographic map of the Rocky Mountains and the last time the rubber was scraped was probably sometime in the 1970's. My goal was to make my 1970 Buick GS 455 Stocker hook on a 9" radial tire at this track, something I had thus far been unable to do the past three seasons.

My thinking was that if you can hook in Spokane, Wa you can hook anywhere in the country.

Please also note the timing system currently in use at SCMP has a correction factor built in that is supposed to correct the runs to sea level - the guy that used to own the facility had a very favorable factor indeed - big numbers on the scoreboard kept the fans coming! So please do not take the run data and try to compare to your track. The data below is only good for SCMP and run to run comparisons at this track only.

Both sets of runs were performed in the same lane 1 week apart.

The first video is a run in which I had a very stiff rear set of springs in the car K= 780 lb/in, antiroll bar, double adjustable shocks up front and single adjustables in the rear. Good Year 9" drag radials on the rear. Front rebound and rear shocks set to "0", Launch RPM on the two step at 2500. SPIN, SPIN, SPIN.

9-13-2008

60ft - 1.8629
1/8th - 7.4262 @ 96.95
1/4 - 11.50 @119.37

Made three other runs that day - the best 60' I had was 1.733 and ran 11.44 @ 109.71 on the brakes in an elimination round.

Air was about 4000 ft
Timing set at 32 deg
Lauch Retard set at 12 degrees for 1 second to kill the launch

Sorry boys no incrementals - timing system doesn't have them!





Set-up for this run was stock soft springs K= 110 lb/in springs in the rear-end. No air in the air bags and anti-roll bar. Hoosier 9x30x15 9" radials. Rear quarters at 27" and fronts at 26". All shock settings set to zero and front end travel limiters set to lowest setting possible - 6" total front end travel. (This set-up was as loose as a goose!)

9-20-2008

60ft - 1.6121
1/8th - 7.14 @ 97.38
1/4 - 11.209 @ 120.3

Made 6 other runs that day - the best 60' I had was 1.5951 and ran 11.195 @ 109.79 again hard on the brakes at 1000' in an elimination round.

Air was about 4000 ft
Timing set at 32 deg
Launch Retard set at 12 degrees for 1 second to kill the launch

Bracket Racing 102 - "The Dial In"

Dialing in your car to win again falls more into the realm of art than science. Requiring only a few simple tools - cheap weather station, a notebook, a pencil and a simple handheld ET predictor (optional) - you will be able to predict what your car should run based on weather conditions. Predicting your car's ET and actually dialing your car for an elimination run are two different things.

The art of the dial-in is having an idea of what your car should run and dialing your car in slightly slower than this number to compensate for errors and changing weather or track conditions. Some folks call this "sandbagging" as conventional wisdom holds that we dial our car .01 to .02 seconds faster than our best guess of "exactly" what our car might run to avoid breaking out. Unfortunately, this conventional wisdom is a losing strategy and here is why:

1) You can never 100% predict exactly what your car will run no matter how many gadgets you buy to help you do so.

2) You have just handed your opponent a .01 to .02 second cushion the minute you dial your car in too fast. Many bracket races are won or lost by thousandths of a second.

3) Should the air density, windspeed or any other weather related factor change more or less than your last calculation you could be either fast or slow and not know exactly what your car will run. Weather shifts can be extreme during night time eliminations thus causing inconsistency.

4) The guy that beats you every week-end at your local track has figured out what you are doing and knows that you have not given yourself multiple options to win the race should you be slightly late at the tree, misjudged the weather, did not get a great burn-out, etc. Further he knows that if he monkeys around during his burnout and staging he can make your engine take on more heat further increasing his advantage. Bracket racing is more like playing Texas hold-em than racing. Dialing in the car is the first step towards mastering the game.

Dialing your car in slower than the predicted ET will require you to develop your skill at judging your car's position relative to your competitor as well as the finish line or "STRIPE"!

THE ULTIMATE GOAL: Get to the finish line first without breaking out but not taking the stripe by too much!

Deciding how much slower to dial your car than the predicted ET is up to you and your skill at judging your position relative to your opponent at the big end of track in relation to the finish line.

Every Stock and Superstock racer out ther stripe races. The third week-end in September I took my Buick stocker to the local track for some testing and raced in the pro ET category. Due to an extremely old timing system and very crappy track prep, it was almost impossible to consistently predict my cars ET. I stipe raced my way into the final six cars out of 50 total and lost fourth round in a double break-out race losing by .01. 3 out of the 4 cars I raced were delay box equipped!

It works try it for yourself!

Bracket Racing 101 - "The Basics"

Bracket racing is a game of both skill and art! "The Basics" is the first of series of bracket racing articles designed to convey knowledge on both the skill and art of bracket racing.

The skill is in being able to predict your cars performance at any time and at any race track regardless of weather and track conditions and consistently performing the burnout, staging, launch and shifting.

The "art", much like the game of poker, relies on your ability to always keep your opponent guessing and having the presence of mind to make the necessary adjustments during a race to improve your chances of winning.

Developing Basic Skills

The very first step in developing your skill starts with a trip to the racetrack with the goal being to gather information about you and your car. At this point all that is required is a notebook and a pencil.

Recommended Steps Day 1

1) If this is your first time at the track my advice is to sign-up for time only runs to practice getting your skills down without the distraction and pressure of competition.

2)Spend some time at the starting and watch a few cars perform their burnouts, stage and launch to get the idea of the basic technique.

3) Pay close attention to where they stop the car in the burnout box and the approximate amount of time they spend heating the tires - simply count 1-1000, 2-1000, 3-1000 etc.

4) If you are running street tires drive around the water box. Dry-hop the car to get the gravel and dirt off the tread but stay out of the water. The tread on a street tire picks-up water deep in the grooves that ends up dripping onto the racing surface when you are staging the car. As soon as the rear tires hit the wet surface your rear wheels spin and you lose consistency.

5) Once you have the basic idea of what you are supposed to do head to the staging lanes to make your first pass. You will be as nervous as a dime store hooker at Sunday mass on your first pass so don't expect too much. Just follow these few basic steps:

a) Pull into the burnout box, set the lineloc or foot brake

b) Put the car in low gear and nail the throttle. Once the wheels begin to spin and the car again comes up on rpm shift into second gear.

c) At the top of your count 1-1000, 2-1000, 3-1000 etc., let off the foot brake or lineloc and carry your burnout up to about 10-15 feet from the starting line by feathering the throttle. The idea is burn a clean path up to the launch area to make sure there is no water, gravel etc under the rear tires.


6) You are now ready to stage the car. There are two staging beams that correspond to the two sets of staging lights on the Christmas tree. The idea here is that once the first beam is tripped and you see the top set of stage bulbs gently ease the car forward until youtrip the second beam so that the bulbs flicker just before coming on.

7)Bring the car up on rpm until it just starts to pull while holding the foot brake. Make a mental note of the rpm.

8) When you see the third yellow bulb, release the foot brake and mash the throttle at the same time. If you wait until you see the green light you will be late. It is necessary to anticipate the green light.

9) Make your run and pick-up your time slip. Once you get back to the pits record all of the information from your time slip into your notebook. For example: launch rpm, reaction time, 60', 330', 660', 1000' and 1320' E.T.

10) Make between 3-5 passes before making any adjustments or changing anything. The idea is to get to know your car. See if you can arrive at some sort of consistency before trying to improve or change things.

11) Compare the data in your notebook between the runs paying particular attention to reaction time and 60' time. We want to see very consistent 60' times to make sure the rear tires are not spinning. If the 60' times are erratic this is the first thing you will need to fix.

12) If the 60' times are consistent then you can start working on tuning your car for reaction time. See the article in this site entitled " A Simple Idea to Help You Win More Drag Races".

13) Once you have mastered the basics of launching your car and tuning for reaction time proceed to "Bracket Racing 102 - The Dial In"

Holley Carburetor Facts

This info is from Tom Vaught courtesy of www.performanceyears.com :

Some Useful Holley Carburetor Facts:

1)Why the Holley Hex Nut above the float bowl has 6 sides (vs say 8 sides)
2)What the actual float moves vs the tip of the needle (away from the seat)
3)Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a higher fuel pressure (vs the Holley fuel pressure spec of 6 psi) is used
4)Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a larger needle and seat is used (vs the Holley .110 needle and seat)
5)Why “Float Drop” is important
6)Why Floats collapse after a Carburetor Fire.
7)What the “Standard” Brass Float should weight vs what the Black Nitrophyl Float
8)Adding Weight to a Black Float
9)Lean Acceleration caused by an improper float level setting
10)Why Bowl Vent Clearance is important
11) “Sight Plugs” Why they are different Front Bowl to Rear Bowl and why some people have carburetor problems when swapping out Holley Bowls for aftermarket fuel bowls
12) How to use a Primary Float Bowl on the Secondary side of a Holley carburetor
13) Float Bowl Screws can be different
14)Never use “Hot Rod” needles and seats parts vs the “Holley Design” needles and seats
15) Differences between Holley needles and seats
16) Viton tipped needles and seats vs steel needles and seats

1) Why the Holley Hex Nut above the the Float Bowl has 6 sides (vs say 8 sides):
The thread used on the needle and seat that screws into the top of the float bowl is a 3/8-32
thread. There are 32 threads per inch cut on the needle and seat where it goes into the bowl.
One full turn of the Hex Nut will move the needle and seat 1.00” divided by 32 or .03125”
or for easy math about .030” upward or downward.

2) What the actual float moves vs the tip of the needle (away from the seat): The float has a 6 to 1 multiplication ratio so you turn the needle and seat hex nut one full turn downward, the float movement will be .03126 X 6 or .1875” lower in the float bowl and the average fuel level in the bowl will be for easy math .180” lower. Two “Flats on the Hex nut works out to about a 1/16” of fuel level change in the float bowl. If you keep accurate records of your float level position you can track the air/fuel ratio change (with an accurate air/fuel meter and get the fuel bowl fuel level vs the mail well fuel level dialed right in for your intake manifold/ carburetor/ engine installation angle dialed right in for best fuel control.


3) Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a higher
fuel pressure (vs the Holley fuel pressure spec of 6 psi) is used:
When the needle and seat (.110” size) is used with a factory float bowl and at the Holley fuel pressure calibration point (6 psi), the average float level height will be close to the “design fuel level” in the bowl and and the carburetor will will meter fuel properly. In some of the old Holley Books they used to show an external gage mounted on the fuel bowl to check fuel level before the “Sight Plug” type bowls were designed. If you add extra fuel pressure to the fuel line going to the bowl the needle and seat will have a higher pressure acting on the tip of the needle and seat. A small change here in force acting on the tip of the needle vs a fixed float buoyancyforce X a 6 to 1 float ratio mentioned above means that the FUEL LEVEL IN THE BOWL WILL RISE TO A NEW AVERAGE LEVEL WITH INCREASED FUEL PRESSURE.

4) Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a larger needle and seat is used (vs the Holley .110 needle and seat).
In the previous paragraph 3), the fuel level went up because the pressure on the float was higher due to the fuel pressure. The other way the level can go up is by using a larger area needle and seat which also imparts more force against the float, (raising the average fuel level.
A Holley 6-504 part Number is Holley's standard .110” Viton Needle and seat assembly
A 6-505 needle and seat will flow about 170-180 lbs of fuel per hour at 7 psi (depending on the
specific gravity of the fuel used). 175 x 2 = 350 lbs of fuel per hour. About 630 horsepower if
assuming a .55 lbs/horsepower/hr. Using the larger needles and seats naturally will move more
fuel BUT flue level changes in the bowl will have to be monitored for each combination vs
expected air/fuel ratio and drivability.

5) Why “Float Drop” is important:
If you have the wrong float drop, the float can “hang” against the needle as it rides on the “hump” on the float level. There are two needle and seat lower needle dimensions. One needle has a 2 cm lower diameter and the other one has a 4 cm diameter. Naturally the 4 cm diameter needle and seat will not “hang” as easily as the “footprint” (diameter) is twice as large. If the float “hangs” you will have open flow into the bowl with no fuel control and flooding, fuel coming out of the vents, and potential “hydra-locking” of the engine. As second issue with the wrong float settings is that the fuel level in the bowl could be too low and uncover the power valve on acceleration. Special power Valves can help eliminate this issue.

6) Why Floats collapse after a Carburetor Fire:
If you have a carburetor backfire, and the carburetor is burning inside the venturis, the main-body gets hot quickly. This heat transfers to the air in the carburetor heating it and the also to the parts around the air. The brass floats have air inside of them when they were made. The air in the float gets hot, expands, and trying to get out of the float. Many times there are very small places where the air can escape but fuel cannot get into the floats. As soon as the engine is restarted, the cold fuel enters the bowl, the float is still hot. The float cools rapidly vs the lost air inside the float. Because the air pressure outside is now higher vs the inside of the float the float collapses (just like it would under boost). Now you have a big problem. The black Nitrophyl floats do not suffer this problem therefore as we know are a better component to use in a boosted carburetor. At least now you can explain to your buddy why his float looks like Chit when he was not running any boost through the carb, LOL!

7) What the “Standard” Brass Float should weight vs what the Black Nitrophyl Float weighs
A Brass float weighs around 15 grams. (An average paper clip weighs 3 grams). The black nitrophyl float weighs about 11 grams. When you cut notches in the black float to allow for jet extensions, (or if you buy a black float with the notches already there), you should check the weight of the float on a gram scale to see if it is close to the right factory weight. You never know how much epoxy the guy used sealing the float, how deep he made the cuts, etc. Some floats for the road race guys and NASCAR guys are heavily modified. If the float is too light, (less than 11 grams stock, or if you want to make the float the same weight as the brass float you can add extra lead shot to get up to the brass float weight of 15 grams.

Cool Adding weight to a black float:
You drill a hole in the black float, add the weight, do a trial measurement on the gram scale, and when you are close you add the light coating of epoxy to seal the whole deal up. I am not a big fan of the making the black float weight the same as the brass float as the black float dimensions are different vs the brass float. The brass float has a longer arm therefore more force on the needle and seat vs the float weight.

9) Lean Acceleration caused by an improper float level setting:
As was mentioned in 5), if the float level drops too low, the “head” that the fuel has to overcome in the main-well gets higher and the engine calibration goes lean. If the fuel level is too high, the “head” that the fuel has to overcome in the main-well, will be much less and the engine runs rich. There is a “sweet spot” that was designed into the carburetor fuel calibration over many years of testing vs the parts used and random “experimenting” will typically cause issues over time. High pressure boosting is adding another level of knowledge to this carburetor database of proper settings.

10) Why Bowl Vent Clearance is important:
The vent whistle at the top of the metering block was added to prevent fuel slosh out of the carburetor bowl vents. A Rivet typically holes it in place. There may be a slight leakage around the vent but typically it is there for fuel control in the bowl. Trimming the vent is commonly done. You do not want the fuel to slam against the back wall of the carburetor under acceleration, climb the back wall, hit the roof of the bowl, move forward, and then enter the vent whistle. A whistle about 1.25' long typically works well. I trim the opening with an exacto knife to allow more area through the vent whistle too.


11) “Sight Plugs” Why they are different Front Bowl to Rear Bowl and why some people have
carburetor problems when swapping out Holley Bowls for after-market fuel bowls:
Few Holley bowls today do not have a “Sight Plug” but the location of the sight plug can be in several different locations. Primary bowls will always have a higher sight plug location vs the secondary bowl location. The number varies all over the map. The average bowl difference will be around .220” difference with some going over .300” difference. Why is this important? Because the sight plug location sets where the “bottom of the threads” location is that everyone sets their fuel level to. As said earlier, you do not want to screw up the Holley Fuel Level Calibration Setting Point if you can help it.

12) “How to use a Primary Float Bowl on the Secondary side of a Holley carburetor:
IF you put a Primary bowl on the secondary side of a carburetor you can typically set the fuel level to the bottom of the threads deal and the LOWER the fuel level 4 FLATS.

13) Float Bowl Screws can be different:
A stock Holley Metering Block type bowl screw is 63mm long from the metal surface the screw gasket seals against to the end of the screw threads. About 2.48” long. The Metering Plate Holley screw is about 48mm long, about 1.89” long. You will notice that neither of the screws is the standard 2” long or 2.5” long hardware store bolts. At one time there were some screws out there that looked the same as the Holley typical parts but they were VERY CLOSE to the 2” and 2.5” length dimensions. You use one of these screws in your carb you are almost guaranteed that you will strip a thread in the main-body as the screw will bottom in the casting, have no where to go, and any additional tightening will pull threads.

14) Never use “Hot Rod” needles and seats parts vs the “Holley Design” needles and seats:
Above in line 13 we had a screw length issues that could cause problems. In this line we have a needle and seat thread issue that needs to be addressed. Holley needles and seats ARE as mentioned above a 3/8-32 thread. Some of the “hot rod” old style needles and seats were a bastard thread then therefore would strip out the threads in the float bowl after installation in the bowl. USE ONLY HOLLEY DESIGN TYPE PARTS.

15) Differences between Holley needles and seats:
Holley used a few needle and seat designs over the years. Initially Holley had steel needles and later offered Viton tipped needles for many applications. Holley offered several orifice sizes, with the .110” needle and seat being the most common. Holley also changed the feed strategy to the needle. The old units used drilled holes in the upper and lower chambers (typically 4 holes). The later generation parts used a “Picture Window” rectangular shaped entry hole for more flow to the carburetor bowls. Today we have the stock type needles and seats and also “Bottom Feed” type racing needles and seats.

16) Viton tipped needles and seats vs steel needles and seats:
Last but not least Viton Tipped needles and seats vs steel needles and seats. The Viton stuff seals very well unless you get metal chips stuck in the viton tip. A steel needle and seat will typically allow the trash if small enough to pass through the needle and seat to the bowl. Steel needles and seats are used on higher performance applications when using exotic fuel blends as the viton tip parts are designed for normal pump fuels and some racing fuels. Most alcohol carbs will use a steel needle and seat for two reasons: Increased orifice diameter required where the viton part is not offered and durability from the corrosive fuel. The increased fuel orifice diameter requirement can be corrected bu the dual needle and seat strategy but the corrosive fuel issue is still there.

Tom Vaught (Former Holley Employee in the 70s.)