The MAP controller does its wonder by faking a signal to lengthen the injectors. There are no if/ands/buts about it. It will not work with larger injectors. It doesn't have any thing to do with fuel pressure; it’s the size of the aftermarket injectors. Many people before you have tried without success.
I'm going to try to hit up all the questions as best I can, so welcome to a crash into forced induction, supercharger style.
To be successful in engine tuning, you are going to need control over three things: more air, more fuel, and the right amount of spark. Bolting up the supercharger covers the “more air” part, but it’s the other two that can really toast the engine.
More fuel- This sounds more wicked than it really is. “How much and how big” are the usual questions. I suggest an aftermarket rising rate fuel pressure regulator (RRFPR or FPR for short). If you ever shop around, you’ll notice some FPR are stated having an output in regards to a ratio. For this example, we will use the FPR that come with the JR kit; it is a 5:1 unit. The first number, “5,” represents how many pounds of fuel pressure the unit will increase, in regards to one pound of positive manifold pressure, being represented by the second number, “1.”So if you are running 7PSI of maximum boost with this FPR, the output will help you decide how to pressure match a fuel pump that will meet your requirements.
Maximum boost X Rate of FPR = Additional fuel pressure ADDED to the system.
6 X 5 = 30 + 52 (stock GSR fuel pressure) = 82 LB total maximum fuel pressure
What does 8PSI produce?
8 X 5 = 40 + 52 = 92 LB
I rave the Cartech 2025 or Vortech S-FMU, as these have adjustable ratios. The grand idea behind these is you get to tune the ratio, as most power is made on the edge of detonation. one can turn to that edge and ride it in comfort, but do the tuning on a dyno. I found a nice linear power gain by changing the ratio to about 4.6:1. The JR FPR is setup to be rich, as it’s designed to bolt-up and cruse. These units also ramp the fuel pressure, while the engine approaches boost. Ramping the fuel pressure in vacuum does the job of creating a smooth transition from vacuum to boost. The JR FPR and any other doesn’t do this, as they only activate on 1lb of boost; this makes the engine operate in a lean spot which can cause hesitation on slow throttle transitions. Drivability is the key here, as well as adjustable performance if you ever get 310cc injectors.
So you’ve got a grasp on how additional fuel is delivered, but now we need to address a constant, reliable supply.Here is how the JR high-flow unit stacks up against the one I recommend at equal pressures. Remember, both pumps are rated as high-flow models at 255LPH.
Pressure--JR High-flow--GSS-342
0---------------75-----------76
10--------------72-----------73
20--------------67-----------68
30--------------63-----------63
40--------------53-----------59
50--------------54-----------54
60--------------49-----------50
70--------------40-----------45
80--------------29-----------37
90--------------0------------27
100-------------0------------11
110-------------0-------------1
“0” means the pump doesn’t move any fuel AKA dead motor.
I don’t know the flow rates of the Comptech, as they are not good about giving information in this kind of detail. Both of the pumps above, as well as the Comptech, are 255LPH and “high-flow” models. You can’t judge a pump based on these two terms above. There are stronger more expensive pumps on the market, but this is the cheapest and most reliable I’ve seen.
Also, the bigger pump flows more fuel at every PSI level. Increase in fuel flow will affect the fuel consumption, at the fuel pump stand point.
Injectors act like a dimmer switch: full on, full off, and points in the middle. The stock ECU doesn’t know the size or cares; it just needs injectors of the same resistance voltage to work. Increasing the total volume of fuel, doesn’t affect the ECU, as it doesn’t have a way to measure the fuel pressure. The ECU assumes the fuel pressure is in the 48~52LB area with a stock fuel pump and is tuned for such levels. By jacking the fuel pressure to 90LB on-boost, the consumption level of fuel is preoperational. This is how all FI engines with aftermarket FPRs operate. This knowledge is also transferable to turbocharging. When one changes the flow rate of the injectors, fuel pump, and FPR, everything changes in a linear fashion. A lot of guys of guys go for the 310cc and readjust all their pressure settings, so they can operate in the strongest part of the fuel pump’s power band. It’s a total system, as not one part is better than another.
Timing- I first suggest you read the articles on cam timing and how it affects cylinder pressure. Cam timing directly affects the spark advance, as the rotor is connected to the intake cam on our cars. The idea for any application is to have the gas burnt and ready to expel by something like 10 ATDC (I don’t remember the exact degree, so don’t shoot me). This places the piston on the down stroke, so all the pressure will transfer the piston down and make the engine work. The ECU still assumes it’s operating as a NA. Being such, timing is modified as high levels of spark advance in mid-throttle and more aggressive at WOT. This is done because fuel burns at a steady rate.When RPM is increased, more time is needed to complete the burn; this is the reason you’ll see 35 BTDC advance at WOT. The timing advance is based off of the static/dynamic compression ratio of the engine. The more tightly compressed the combustion mixture (read as higher compression) the less spark advance is needed. With FI, one is stuffing more air/fuel into the cylinder (read as raising the CR). For this reason, less timing advance is needed during on-boost performance. To get by without additional aftermarket parts, one has to retard their static timing; this is done by twisting the distributor counterclockwise, which forces timing retard to be linear. I believe JR recommends something like 8~10 degrees static advance, where stock advance is 16 degrees. Doing this makes for safe on-boost timing advance, but kills off-boost drivability. The car will feel laggy and unresponsive to quick throttle input at low RPM. Static timing retard will also cause the engine to operate at higher temps, during idle; this is an old trick used to get a vehicle to pass emissions as the extra heat helps burn off the extra hydrocarbons.
The JR BTC and MSD 6BTM are timing retard devices that have a dial. The dial operates as a ratio, again in a timing: boost fashion. This is best illustrated on the MSD unit, as it has number on the dial. “0-1-2-3” are the ratios. Having the dial set to “1” means the timing is retarded 1 degree for every pound of boost and so on. There are increments in between, so you can tune it to your needs. With the BTC, try a 10-o’clock position as a starting place and about 1.75 on the MSD. You only want to advance the timing as much needed, as too much advance will complete the combustion, before the magic ATDC area we talked about before. Advancing too soon is what causes internals break.
Having one of these units will allow for stock or advanced static timing and you have all that off-boost power. It makes for such a better driving car all the way around.
Spark plugs- These are the lifeline of your ignition system. They are rated in a number system, where the higher the number is a “hotter” plug. Having one heat range colder is a good choice, as the ignition of the mixture isn’t as blunt. The gap of the plug is the distance form the electrode to the tip. Stock gap on a GSR is 1.3mm, noted by the “xxxxxx-13” on the end of the plug’s model number. This is a suitable gap for the stock ignition system, but is too wide for FI. FI is all about a more concentrated mixture, so the wide gap makes the small spark travel a greater distance before the ignition can take place. Many times, this can lead to what is called a “misfire.” To combat this issue, the gap is shortened, making the distance shorter.
If you’ve got a MSD unit, the extra spark energy can easily travel thru the dense mixture without a problem. Widen the gap and now the mixture is being ignited more thoroughly. This also shortens the need for on-boost timing advance, so adjust the boost: retard rate accordingly.
The plug I recommended is also a copper plug, as they are very cheap at $2 a unit. I replace them about every 10,000 miles, as they are priced fairly and operate best in like-new condition.
