||Last Updated: Aug 16th, 2006 - 11:01:00
Iím going to try and cover some of the most popular and effective methods of ignition and fuel control for forced induction motors, but please understand there is a huge diversity in products out there and I might miss some of them. Also, I should say now that I wonít be talking about carbeurated setups, since I honestly donít have enough experience with them to pass on any knowledge. So without further delay, letís just jump right into itÖ
The all important air/fuel ratio has a big impact on how strong the ignition system needs to be to ignite the mixture. For ignition to most easily occur, the a/f ratio needs to be right about 11:1, with anything richer or leaner quickly causing minimum voltage needed for ignition to increase (and sometimes dramatically). Yet optimal power production in FI motors will occur between 12:1- 13.5:1 a/f ratio (on most engines), so already we are asking the ignition system to do a tough job. In addition, the more densely packed the combustion chamber is, the harder it becomes to ignite the mixture. So for the average forced induction motor, the ignition system needs to be very solid system to reliably get the job done.
Which spark plugs you choose is completely up to you, just make sure you donít buy too much into the idea that a specially grooved tip or electrode shape is really going to make a difference in performance. The only important thing to mention here is in regards to plug heat range, and the fact that you should probably go with a plug 1 to 2 heat ranges colder than stock for forced induction use. Since there are so many different engines and forced induction systems out there, I recommend you speak with a knowledgeable tuner (of your car) to find out what heat range and plug will work reliably. But as a general rule of thumb, one heat range colder is about the average in my experience.
On heat ranges: in case you are not familiar with this term, it refers to how easily the plug can transfer the heat absorbed from combustion to the cylinder head. Hotter plugs either have thinner porcelain jackets around the electrode, longer porcelain jackets, or both (when compared to a colder plug of the same manufacturer). The thinner the porcelain is, the less heat it can absorb and so the less heat it can transfer from the electrode tip to the metal body of the plug, and likewise, the longer it is the harder it becomes for heat to transfer from the tip to the body. The more power you make from a given size engine, the more heat you are creating from combustion, which means that the plug is exposed to greater temperatures during engine operation. The different heat ranges allow you to keep the spark plugís tip at the proper temperature for reliable operation; too much heat and it wears excessively (and can cause pre-ignition), to little and deposits will form that eventually prevent the plug from creating a spark. So know that as you increase the heat of combustion, you must move to progressively colder plugs to keep the plug tip at the right operating temperature. More information can be given later on how to know when a colder/hotter plug is needed.
Ignition Coil http://www.msdignition.com/1msdcoil.htm
The coil is probably the most important thing to upgrade when it comes to forced induction performance, because of the additional voltage needed to jump a spark in a high pressure, high temperature combustion chamber. MSD is an excellent maker of coils, but again, choose any you like that fit your budget and taste. Also, in the case of external coil ignitions (one where the coil is located away from the distributor body), make sure you choose a coil that can be mounted very close to the distributor. This is for best performance and lowest resultant RF interference, so simply remember to keep the coil lead as short as possible.
Also, when upgrading to significantly more power coils than stock, itís usually a good idea to upgrade plug and coil lead wires too. The extra voltage they will be carrying, as well as the additional heat the boots will be subjected to (this is mostly in reference domestic V8 motors), will warrant a purchase in this area. Choose whichever name brand manufacturer best fits your budget and taste, just make sure they are well shielded and have, if possible, boots specifically designed for high heat environments. Porcelain boots are best in my opinion, but not necessary. Thicker wires generally have more insulation and not thicker wire, which is exactly what we are looking for. If you can get some 8.5mm wires, do so, if you can get 10mm wires that fit everything fine (including your budget), why the hell not?
Basic Ignition Controllers
By far the most widely accepted and popular controllers are the MSD 6 family (which currently includes the 6A, 6T, 6AL, and 6BTM), and this is for good reason. MSD stands for Mutiple Spark Discharge, an ingenious idea that helps ensure combustion through sending multiple sparks to each plug at the outset of every power stroke. Again a good coil is recommended with any system like this, since coil soak time (the time it takes for the coil to build up a full charge) can limit the ability of multiple spark technology to work well in a stock system. Good aftermarket coils generally have shorter soak times than stock coils.
Of particular interest to the forced induction crowd, the 6BTM controller allows for boost dependent ignition retard as well as multiple spark discharge. Without going into depth here, letís just say that boost dependent ignition timing retard is one of the best ideas for ignition controllers EVER, and that almost any forced induction motor can benefit from it, especially if the ECU wasnít tuned for forced induction use from the factory. A 6BTM additionally has a control knob so you can set the amount of ignition retard induced per pound of boost, where the user can select anywhere from 0-3 degrees of retard per pound of boost. Of note: the 0 setting allows you to prevent any ignition retard during boost, meaning that (among other things), this controller can be purchased and installed before the s/c or turbo is installed. So if anyone is looking for an ignition controller and is also planning on forced induction, this might be the one for you.
Check http://www.msdignition.com/1ignstre.htm for more details.
While MSD has taken the pro-active approach to ignition control in the way of their BTM units, J&Sís basic controller covers the reactive side of the equation. The J&S Safegaurd uses a knock sensor (standard on most late model ECU equipped cars) to ďlistenĒ for detonation, and if it senses any, retards the timing in an effort to prevent engine damage. The J&S units are very fast and sophisticated, and can even retard timing on a per cylinder basis if you so choose. J&S Safegaurds, for their modest asking price of $450-500 dollars, should be considered the best insurance policy for your engine money can buy, and for a small extra outlay in cash, will show you if and when they are pulling out timing. In essence, a J&S unit is a tuning tool and insurance policy all-in-one, not a bad investment for less than the cost of pistons alone.
The new kid on the block from J&S is their Ultra Safegaurd, combining boost dependent ignition retard with the welcome insurance the standard Safegaurd supplies. Although these units donít offer the multiple spark discharge of a 6BTM, in my opinion they offer the absolute best setup when it comes to a single purchase system for forced induction motors. You can essentially tune the J&S with itself; upon seeing that the unit is pulling out timing under boost, you can alter the retard amount to tune out detonation. And with their dual monitor gauge, you can even see the a/f ratio the engine is running at the time of detonation, allowing you to most accurately pinpoint the cause of the problem. What other product costing less than $600 can you make that claim with?
Check http://safeguard.20m.com/ for more details.
Yes, the all important fuel system. Nothing is quite as basic as this when it comes to engine performance, and yet sometimes nothing is more blatantly overlooked. There are 4 principle ways to increase the fuel supply to the motorÖ
There are two common types of fuel injectors, pintle and disc (Lucas style). Pintle injectors have a superior spray pattern to disc actuated injectors, but disc injectors are less expensive and generally flow large amounts of fuel easily. If possible, always choose high flow pintle style injectors, as fuel atomization at anything other than full throttle (high velocity port flow) is superior, leading to better drivability and economy. Below is a picture illustrating what I mean about the spray patternsÖ
So when do you upgrade to larger fuel injectors? The general rule of thumb is that anytime the injector duty cycle goes beyond 80% (meaning the injector is open and firing over 80% of the time), you should upgrade. Fuel injector performance can become unstable beyond this point according to some experts, plus it doesnít pay to have a proper sequential fuel injection system working as a simple always open spray nozzle (which is neither efficient or powerful). Of course upgrading their size is only one way to add more fuel, and although a very good idea, it works best on carís that can be easily retuned to work with them. In the case of MAF cars (Mass Air Flow sensor), system recalibration is generally just a matter of changing the sensor (many of the available larger sensors offer multiple calibrations). For speed density fuel injection systems (the other type of airflow sensing), its generally necessary to have an ECU capable of recalibrating itís fuel tables for different injector flow rates. This is a problem mainly for the Honda people out there (all of which come with speed density systems), in which case you should think seriously about giving Zdyne or Hondata a call. Both offer very nice programmable ECU systems capable of keeping a big time forced induction motor running reliably and strong. Or, you can read on and see a few other ways to increase fuel flow without changing injector size.
Fuel Pressure Regulators (FPRís)
All fuel injected motors have high line pressures when compared to the older carbuerator technology, generally somewhere in the area of 25-40 psi. Changes to the line pressure will have a direct effect on total fuel flow from the injectors, but itís important to realize this pressure vs. flow relationship is NOT linear. By one estimate I have read, to double fuel flow through an injector you must quadruple the line pressure. However most fuel systems will not tolerate more than 60-100 psi of pressure (even with upgraded fuel pumps; more on this in a moment), so just know that changing fuel pressure works great until you need to add anything over about 50% more fuel, at which point you need to do something else besides simple line pressure changes.
Most aftermarket fuel pressure regulators are simply adjustable with a screw (where you will need a fuel pressure gauge to know how much youíve changed things), and are very easy to install. However in the case of forced induction motors, what you need is not the simple adjustable regulator. You need to find a rising rate FPR that can vary fuel pressure according to boost levels, and most people consider Cartechís 2005 the best one available. It has a variable gain rate and the ability to start increasing pressure before the onset of positive manifold pressure (it senses that intake pressures are quickly rising and anticipates the soon to come need for extra fuel), a big plus for positive displacement supercharger applications, which can go from full manifold vacuum to full boost in less than a second. These are very useful tuning tools even if you happen to have larger injectors or other methods of fuel control available, so donít count them out from any forced induction system. Check out http://www.cartech.net/fuelaccessories.html for more info on the 2005 unit.
There are two common choices to what fuel pump setup you can choose to run, internal and external pumps. Internal (the pump is located in the fuel tank) pumps are quieter and sometimes easier to install than external pumps, being that they are more like factory replacements than add-ons. External pumps (which are located somewhere on the fuel line, usually as close to the tank as possible) usually offer the highest flow potential, but they can be annoyingly loud a loud buzz emanating from somewhere under the car). Additionally, there are two things to remember when talking about pump choice and placement. First, pumps like to push fuel, not pull it, so always mount the pump as close to the fuel supply as possible. Second, fuel pump flow drops as fuel line pressure increases, and this is again not linear. Pumps are judged not only by how much fuel they can ultimately flow (called LPH or GPH, being Liters Per Hour and Gallons Per Hour, respectively), but also by how much fuel they can flow at given line pressures.
Ideally, the pump to look for is an in-tank unit that has high flow ability at high pressures (Walbro and Bosch are the primary manufacturers). These pumps will offer quiet and stable performance for virtually any setup, including ones using rising rate FPRís to jack fuel pressure up as airflow increases. Itís also somewhat important to know that you shouldnít just buy the biggest pump you can find, go for the one that best fits your needs. Very large pumps can cause cavitation, and can also (in the extreme) overpower the return lines from the regulator and potentially cause fuel leaks or overly high line pressures. If an external pump is the best choice for you (where a very high flow ability is needed and you arenít too concerned about noise), look to Vortech and Cartech for your pump.
Fuel controllers (I use this term to describe any electronic controller designed specifically for fuel tuning) come in a few different forms, some modifying ECU input data, and most modifying ECU output data. Every oneís purpose is to somehow manipulate injector pulse width to tailor fuel delivery, and they work very well to that end for WOT (Wide Open Throttle) tuning. What they offer is the ability to ultimately control injector duty cycle, and hence the ability to easily tune fuel delivery for maximum performance.
The only problem with fuel controllers is there usual lack of ability to be tuned for anything other than WOT engine operation, but since we like to keep the go pedal on the floor, this usually isnít much of a problem J. Fuel controllers let us tune the fuel delivery curve with precision FPRís can only dream of, and in most applications they work so well that even solidly tuned combos will see power and mileage gains through their use. These relatively new inventions basically ďpiggy backĒ standard ECU tuning, letting the ECU do the fuel delivery work until full throttle is called upon, where they step in to modify ECU signal (in the case of controllers that modify ECU output data) or modify the airflow signal (in the case of controllers that ďlieĒ to the ECU to get the desired fuel delivery from it) to let us modify fuel delivery. This is a very good idea because all that time spent tuning the stock ECU to work perfectly at idle and most throttle openings and RPM (other than WOT) is left intact, with our tuning only taking effect when things really start to stretch whatever setups the factory had in mind. All can offer fuel delivery tuning accurate enough for serious performance applications, and all can be very cost effective when compared to complete engine management systems. Which brings me to my final pointÖ
COMPLETE ENGINE MANAGEMENT SOLUTIONS
Thereís really not much to say here, since you either have a radical enough setup to know why you want this, or are not in great need of one in the first place. The complete and tunable ECU solutions cover a large range in price and features, but donít expect to see anything for less than around $900 (without installation or tuning costs). All attempt to get rid of as many limitations to tuning in the stock system as possible, and all need to be professionally setup to work properly. And please take that advice seriously, as the thing about removing limitations to tuning is also that you remove many safeguards in the system, so itís a lot easier to break things than before without proper tuning.
Having said that, nothing is as powerful as a forced induction motor running solid custom engine management. Race ready Motec M4 setups with tuning can cost well over $5000, but will reward with the best possible power and reliability from the motor. For a look at the products currently available, check these sitesÖ
EFI Systems PMS: http://www.efisystems.com/
Electromotive TEC II: http://www.electromotive-inc.com/home.htm
MSD Digital 7: http://www.msdignition.com/
Accel DFI: http://www.mrgasket.com/accel.htm
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