Modular FAQ Power Adders

1.I want more power out of my car, what is better Nitrous or a blower?
2.What does an FMU do?
3.How do I pick the correct injector size for my car?
4.What is a power-pipe and why should I buy one?
5.What size intank fuel pump should I buy for my supercharged car?
6.I just installed my supercharger, do I NEED a tune right away?
7.What is a good A/F ratio to shoot for during my dyno tune?
8.How much timing do I run with a supercharger?
9.What are the advantages of having an intercooler?
10.I want to buy one the Air/Fuel gauges I saw in a magazine, can I buy this instead of going to the dyno to tune my car?
11.Does anyone make an ignition system with a timing retard function for mod motors?
12.What is the difference between a centrifugal supercharger and a Roots/Screw type supercharger?
13.How many miles will my car last with a supercharger?
14.Is there such a thing as a Safe tune?
15.I want more power, how do I increase boost?
16.Do I need any gauges when I buy my supercharger?
17.What does the term "pegged MAF" mean?

Q: I want more power out of my car, what is better Nitrous or a blower?
A: There is no correct answer for this question really. The two poweradders both have their pros and cons. What it boils down to is price and application. A blower generally costs in the 2500-4000 dollar range, this includes all pieces needed to use the blower right out of the box. The nitrous system costs in the 500-700 dollar neighborhood, but the bottle needs to be refilled after 8-10 mile passes, at forty dollars a refill the costs can meet and exceed the cost of a blower.

Q: What does an FMU do?
A: A FMU increases fuel pressure in relation to boost. The ratings are expressed in a ratio, e.g. 8:1. For every 1psi of boost pressure, fuel pressure will increase 8psi. An FMU is considered by many to be a band-aid for undersized injectors for the application needed. Fuel injectors are rated at say 36lb/hr at 40psi. If you increase pressure, the injector will flow more fuel than it could without the FMU.

Q: How do I pick the correct injector size for my car?
A: There are a few equations needed to solve for this problem. I will include them here with an example.

Fuel requirement:
Brake Specific Fuel Consumption (BSFC) is the amount of fuel per hour required to make 1hp. BSFC ranges from 0.4-0.6. For blown applications I like to use 0.6 because it errors to the rich side. Pounds of fuel per hour = Brake Horse Power/ BSFC. Using 800 flywheel horsepower we get:

800 x 0.6= 480 lb/hr fuel required

Injector sizing:
Since there are 8 injectors divide the fuel requirement by 8.
480 / 8 injectors = 60lb/hr
This is with the injectors at 100% duty cycle. Normal operating injector duty cycle is 80% max.
60lb/hr / .80 = 75lb/hr injectors required at injector rated fuel pressure (40psi).

FMU: there are two more steps (formulas) to sizing the injectors depending on the FMU, boost psi, and fuel pressure.
If you increase the fuel pressure, the injector flow rate will increase by:
F2 = SQ(P2/P1)*F1
F2 = new injector flow rate @ new pressure
F1 = injector flow rate @ pressure P1
P1 = injector rated pressure
P2 = new fuel pressure
Given the static flow rate of the injectors:
50lb/hr @40psi (100% duty cycle) and increase the pressure to 60psi:
61.23lb/hr = SQ(60psi/40psi)*50lb/hr
0.5 * base + (boost * FMU) for max fuel pressure

Q: What is a power-pipe and why should I buy one?
A: Many supercharger systems use a flexible drier hose for the inlet, which is around 3-3.5" in diameter. Power-pipe's are usually 4" in diameter and made out of metal with rubber connectors between the supercharger and MAF. There are 2 main reasons for replacing the drier hose. The first is the drier hose tends to get cut or torn resulting in an air leak, which can lean out the car, if the tear is large enough the car may not even start. The second is the bigger 4" tubing reduces the inlet's restriction making the blower more efficient and increasing boost by 1-2psi. They are generally good for about 10-20rwhp.

Q: What size intank fuel pump should I buy for my supercharged car?
A: Fuel pump requirement calculations can be seen in the Fuel injector sizing question, but a good rule of thumb is to get the biggest intank pump you can. We recommend the Holley 255lph forced induction pump or equivalent. These pumps flow 50gph@60psi compared to 30gph@60psi of a standard 255lph pump.

Q: I just installed my supercharger, do I NEED a tune right away?
A: Superchargers are generally sent out with a very rich tune up from the blower manufacturer, but as a precaution and for bragging rights we suggest you atleast throw it on the dyno with a wideband Air/Fuel meter to check the Air/Fuel ratio and to check the timing.

Q: What is a good A/F ratio to shoot for during my dyno tune?
A: For a power adder car, shoot for the 11.5:1 to 12.5:1 range. Do not go any leaner than 12.5:1 on 93 octane pump gas. Remember, rich is safe and lean is mean but lean kills engines.

Q: How much timing do I run with a supercharger?
A: On a modular motored car with a supercharger on pump gas, 18 degrees of total timing advance, or 28 degrees total ignition timing is the limit. Timing kills motors faster than going too lean, lean burns holes and timing detonates. So keep your timing below 18 and keep the A/F ratio in check.

Q: What are the advantages of having an intercooler?
A: Intercoolers are routed downstream of the blower between the blower and the throttle body. It's job is to cool the air charge temperature, the less heat there is in the incoming air the less prone an engine is to detonate. Also, cooler air is denser air. Denser air contains more oxygen for the fuel to burn than heated air. Discharge temps of a 8psi blower are in the 200 degree range, after cooling it is not uncommon to see a drop of over 100 degrees. The cooler the air the safer your car will be.

Q: I want to buy one the Air/Fuel gauges I saw in a magazine, can I buy this instead of going to the dyno to tune my car?
A: No. These gauges work off the factory O2 sensors and are not accurate enough for tuning. The factory sensors only read +/- 14.7:1, or stoichiometric, the wideband A/F meters will accurately measure from 10:1 to 20:1 A/F.

Q: Does anyone make an ignition system with a timing retard function for mod motors?
A: MSD makes the DIS-4 which has 2 types of timing retard functions. It's retard functions are based on RPM instead of boost pressure like the MSD-BTM. You can pull a set amount of timing after any rpm after 4000rpm, or use the High Speed retard feature which will progressively pull timing from any point after 4000 rpm to redline linearly. For example the first feature can be set to pull 7* of timing at 4000 rpm so your timing would resemble this:
3000 27*
4000 20*
5000 20*
6000 20*

With the high speed retard it progressively pulls the timing depending on RPM. The higher you rev the motor the more timing it pulls.

Q: What is the difference between a centrifugal supercharger and a Roots/Screw type supercharger?
A:

Q: How many miles will my car last with a supercharger?
A: There is no set amount. Some guys last 100,000 miles others only a few hundred. A well taken care of car, with the proper tuning should last a while.

Q: Is there such a thing as a Safe tune?
A: There is no such thing as a Safe tune, there are however tunes that are more safe than others. It's a generally accepted rule that keeping A/F below 12.5:1 and ignition timing below 18* on pump gas is "Safe." However, all it takes a degraded or malfunctioning fuel pump and your engine on the safe tune is a pile of metal in the garbage can.

Q: I want more power, how do I increase boost?
A: There are 2 ways to make more power, increase blower efficiency and increase impellor speed. The easiest way to increase boost is the use of a power pipe which increases the efficiency, after the power pipe going to a small blower pulley or a larger crankshaft pulley will spin the blower faster making more boost. Be sure your fuel system and engine tune is up to the increased power from the smaller pulley. We recommend you get the A/F ratio checked on a wideband O2 meter after any increase of power.

Q: Do I need any gauges when I buy my supercharger?
A: Gauges are not needed, but are a very useful. You will want a Boost/Vacuum gauge and a Fuel Pressure gauge. A Fuel pressure gauge will let you know if your fuel system is up to the task of your motor, if fuel pressure drops off while in boost it's a good sign that your fuel system needs an upgrade. This gauge can save your motor. Get a good electric gauge like the Autometer phantom series if you plan on mounting the gauge in the passenger compartment. Mechanical gauges are unsafe when mounting inside as a line could break spraying fuel all over the interior; not a good thing.

Q: What does the term "pegged MAF" mean?
A: MAF meters are calibrated to measure a certain amount of airflow and give these measurements to the computer in a voltage range of 0-5v. The calibrations are within a given airflow range. X air=Y voltage. If your engine is using up more air than the MAF can measure, you have pegged the MAF. 4.7 volts is about all a MAF can read properly, anything past this and the computer thinks there is a malfunction and reverts back to the MAF tables in the computer. When the MAF cannot properly measure the air, it has lost control of your fuel needs and can lead to big problems, leaning out and killing the engine is possible and likely if no steps are taken to combat this.

To cure this problem, you must either recalibrate your stock MAF for the additional airflow and injectors at Pro-M or buy an aftermarket MAF that will support your engines airflow.

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