How to limit mechanical advance in a mopar distributor, tuning for street, strip or all out racing, cure that rich stinky idle, win races

FBO Ignition

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Mopar Distributor Limiter Plates only $39.00

No More Welding and Filing!

This FBO Advance limiter plate will allow you to have the limiting abilities of a TRUE Mopar Performance Distributor in minutes.

Quick easy and changeable as you build your engines performance level.

One Masterfully Engineered Part gives you 0-10-12-14-16-18* of Mechanical Timing limits, changeable at any time.

Click for full size images

We all are aware that in order to run a performance engine especially with today's fuel formulations we need to have more initial timing in the motor but we still need to control the total timing which on most Mopar Engines is 34* or they will detonate.

Note: Max Compression Ratios on pump gas with Iron heads is 9.5:1, aluminum heads 10.5:1, 1 point of compression will add 2-5HP but if you have to retard your total timing by 1* it could take out 5-20HP out unless you running very high RPM's there is little to no gains achieved by building a motor with too much compression for pump gas, race gas is whole different set of rules.

In the past the you stripped down the distributor to remove the T-Bar and then guessed how much to weld up the slots to shorten the total mechanical advance limit or the amount of travel the weights have, which is the mechanical timing limit.

Once you had it all welded and filed smooth then you reassembled, ran the engine and checked the amount of total mechanical timing, then you took it all apart again and filed or welded more by guess and by golly and tried it again.... repeat several times to finally get it close and hope you have the slots both the same length.

J685S Install Instructions on line Click Here

No more! Whatever the amount of mechanical timing you want just select the correct slot, drop in the plate and your done!

The laser etched numbers on the disc designate the amount of mechanical advance so for instance...
If you want 18 degrees of initial timing you just set the plate on the 16* slot 18 initial+16 Mechanical= 34* total
If you want 24 degrees of initial timing you set the plate on the 10* slot for 24 +10= 34* total
If you want to lock down the distributor with NO Mechanical timing at all then just drop the plate over the 0 round hole.

Now you can have all the adjustability of a True Mallory style Mopar Performance distributor (not a Chinese Copy) for a fraction of the cost. Simple installation with NO welding and filing and dead on perfect timing accuracy.

J685S Install Instructions on line Click Here

Click Images for full size

Shows the J685 over the 12* Holes (22* Initial)

FBO-J685S Limiter discs are MADE IN USA from 100% American Stainless Steel and carry a

LIFETIME Warranty on Workmanship and Material... yours or ours whichever is shortest.

J685S Install Instructions on line Click Here

Now Lets Perfect The Tune-Up!

Now you've got 1/2 the job done, you've taken the time and invested in an excellent product to give your ignition a chance to operate correctly, but your only 1/2 way there.

Now you need to address your old antiquated transistor type ECU which is working hard to take away everything you just achieved. Those old style Transistor ECU's from the 60's start retarding the timing at about 3200 and by 5200 most have pulled 8-10* of timing out of the motor! How can it possibly perform correctly when it's retarding the timing so drastically?

Retarding the timing will take out 5-20 HP out of the motor for every degree, depending on the performance level of your engine.

The reliability of a Made In China Transistorized Orange, blue, green, pink, black whatever color ECU combined with the quality of the old unreliable ballast resistor makes your ignition a crap shoot, better carry spares, your going to need them.

Rich stinky Idle? Carb won't respond to your adjustment? Stumbles?

Poor Mileage?

It's all in the timing events, get it fixed before you damage your engine!

Need a new distributor?

The HRR688 a fully computerized ECU with the matching Pertronix coil bypasses that unreliable ballast resistor (5.5V) and feeds your ignition system at battery voltage, 12-15V...

More Power In = More Power Out

Will Not retard the timing to 7000 RPM
10 position REV Limiter 5200-7000 (200R steps)
Algorithm DEAD Stop REV Limiter
Plug and Play, stock mounting pattern
Billet housing
EPROM Microprocessor controlled

5 YEAR WARRANTY

MADE IN AMERICA!

How can we offer a 5 year Warranty?

It's a simple formula, design it using the best engineering and components, use ISO 9000 certified suppliers to guarantee consistency in manufacturing. Do your research and apply your nearly 50 years of experience, do 6 years of R&D and testing so that it's right from the 1st piece made to the latest piece.

Beware the Marketing Department: "New design, New for 2018, New Improved features." These statements are only telling you that there were problems in their original release. Check their warranty! Will anyone match our 5 YEAR WARRANTY?

Beware of ridiculous claims of massive HP gains over MSD or others I could write a book on why that statement doesn't make any sense. Wait, I did write a book!

Compare our Warranty/Engineering/Quality to any other Manufacturer!

The Mystery of the Vacuum Can?

Ported or Constant?

Lets clear this up.... Generally, emissions equipped vehicles use Ported and they are connected to a computer, OBD1 or 2 to retard the timing based on information gather from a multitude of sensors in the vehicle.

Non-Emissions Hot Rods and Street Muscle Cars Pre-emissions use Constant. Many vehicles were built with specs that designated Ported, that was fine in 1975 when we used real gas and we could set the total advance to 25 with 5* initial and have the vac can pull the timing to 34 under load and fuel economy, formulations and costs were not an issue. These cars ran horrible and got terrible fuel economy, more gas ran out the tailpipe than got burned in the combustion chamber.

GM always used Constant Vacuum and built over 300 different set-ups for all there product lines until computers were introduced and everything changed to meet EPA emissions regulations.

So Your Hot Rod gets connected to CONSTANT manifold vacuum and the distributor needs to be set up properly to burn today's fuel formulations. The Vacuum Can needs to be adjusted to pull enough timing in the motor to allow it to burn the today's fuel and limiters installed to set the part throttle cruise timing numbers so they don't pull the timing too high and cause a lean miss at cruise, it's a delicate balancing act to get it all correct.

Your carb has 4 Venturi's, as the air speed or velocity increases with throttle position a venturi creates high pressure in the center to fracture the fuel into small particles and "Opposite and Equal Reaction" is negative wall pressure.

The negative wall pressure is what draws the fuel through the booster and feeds the engine based on throttle position or air velocity. A carburetor is a simple metering device that delivers fuel and mixes it with the air to create clean combustion, the higher the velocity the more negative pressure the more it delivers, it's a pretty simple device.

How They Work

Ported vacuum: With that thought in mind consider if the distributor hooked to Ported Vac, as air speed increases the ported vac activates and starts to pull more and more timing in the motor as velocity increases. So if you set you total timing to 34* at 3000RPM that's when the ported starts to do it's job and advances the the timing to the total stroke of the vacuum can arm, usually 12-18* (without Limiters) so now have your total of 34* PLUS the stroke of the Canister arm of say 16* net result=50* of total timing under hard acceleration and your motor WILL "Detonate". If you had a OBD1 computer it would pull that timing back to the 34* as all the sensors feed information to it.... and no detonation.

Now to Constant: At idle/part throttle cruise you have high vacuum, the carb is nearly closed causing a restriction which creates the high vacuum level. Under this light load condition and lean AF ratios the motor needs more timing to burn the fuel (Lean Mixtures take Longer to Burn than rich mixtures) so you need more timing at idle and cruise to burn the fuel correctly and completely. When you stomp the throttle you have NO manifold Vacuum so you have NO vacuum timing and at NO time under high load will it ever advance more than the mechanical "All In" numbers. Stop pointing your finger at the carb for rich idle and top end lean conditions.. It's In Your Distributor Tuning! If your Buddy tells you to hook your Hot Rod distributor to Ported Vacuum, find a new friend because that guys advice is going to blow your crankshaft through the oil pan. Same goes for the guy who say's to disconnect it, they obviously have no idea of how it works or what it does or why we use it.

This not hear-say or an opinion its engineering, based on physics formulas, calculated by people who are a lot smarter than me and I know that so I do what they tell me. They come up with the numbers, we set them up accordingly.

If the Motor Makes 10" of vacuum or less at Idle with 30* of timing in it then it needs a properly calibrated Vacuum Can, we have Mopar and GM vacuum cans that will read 5" of vacuum.

There's all sorts of unqualified guy's on the "Internet" and so called "engine builders" who will try and argue this point with me, I give up. They have no clue how the vac can works or what it does, if they did they would realize how ridiculous they sound to us, Jim and I account for over 100 years of experience with thousands of happy customers.

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