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Blower and Turbo Information

What Does a MAP Sensor Do, and Where does it go?


What Is A MAP Sensor & What Does A MAP Sensor Do?

Remember science class when the teacher shouted “Pay attention! You might need this someday!” ? Well, as much as I don’t want to admit it, that teacher was right. Let’s touch upon the basics and see if it rings a bell?

The Basics:

  • First off – MAP is an acronym for Manifold Absolute Pressure. MAP sensors measure the air pressure in your intake manifold which helps the engine’s computer determine air / fuel ratios. MAP sensors are set to “zero” from the factory. So with the car off, and the key on, the MAP sensor will read “zero” at sea level.
  • On earth, we have 14.7 Pounds per Square Inch (PSI) on us at all times at sea level.
  • “Bar” is a measurement of pressure. 1 Bar = 1 atmospheric pressure, which is 14.7 PSI.
  • The absence of pressure is measured in “Inches Of Mercury” (in. hg). (Finally we get to use the periodic table of elements in real life!)
  • -1 Bar = -29.4 in. hg
  • 1 Bar = 29.4 in. hg
  • Naturally Aspirated = without a turbocharger or supercharger. Also known as “N/A”.
  • Forced Induction = with a turbo or supercharger
  • In forced induction applications “Boost” is automotive slang for PSI
  • Stoichiometric Air Fuel Ratio = The ratio of the exact amount of air it takes to burn a fuel completely.
  • Stoichiometric for Gasoline Engines = 14.7 : 1 (14.7 parts air to 1 part fuel).

What Does A Map Sensor Do

Now some of that good stuff:

With a N/A engine running, the MAP sensor may see readings anywhere from -29.4 in. hg to 0 PSI depending on how hard you smash the pedal. The more you hit the throttle, the closers to 0 psi the MAP sensor will read because there is less vacuum in the intake manifold. On an engine with forced induction, the MAP sensor will also measure boost (finally above zero!).

When MAP sensor data is combined with an air temperature sensor and a known engine speed, the ECU (engine’s computer) can accurately calculate the air flow rate of the engine, which then means it can calculate fuel. It does this with fuel maps that are programmed into the ECU. The fuel map guides the engine to its happy stoichiometric place. Easy enough right?

So what is so great about a 3 or 3.3 Bar MAP sensor? Why do people use them on cars that they don’t belong on?

Some cars that come stock with superchargers or turbochargers have 3 or 3.3 bar MAP sensors from the factory. So horsepower addicts like to take their own project car, stuff more boost into it than it was ever intended to have (More Powahhh!), and run a tunable computer system to handle the changes. Since a 1 Bar sensor can only read up to 14.7 psi (which is really zero here on earth), a 1 Bar sensor can’t handle any forced induction applications. EEEK! Any type of forced induction puts pressure (above zero) into the intake manifold, and therefore horsepower seekers need a MAP sensor that can accurately read those pressures. This is where the 3 or 3.3 Bar comes into play. A 3 Bar sensor can read up to 44.1 PSI (Subtract the 14.7psi of atmosphere, and it can actually can read up to 29.4 PSI.) So, if a person were to put a 1 Bar sensor where a 3 Bar goes, the ECU would freak out when the boost arrives, and wouldn’t know what to do with the air/fuel ratio because the numbers on the fuel maps don’t add up anymore. The moral is that the 3 and 3.3 bar sensors are perfect for this type of thing because of their simple 3 wire connector, reliability, and accuracy. Oh and the price is great too!

Goes in the blower manifold or intake manifold Blown or Unblown  

What Does A Map Sensor Do

Lobe Separation Angle and how it works with Blown and Unblown engines


TECH QUICKIE: Camshaft Lobe Separation Angle And Power Relationship

December 29, 2015

Selecting a camshaft for a given engine’s purpose usually involves a compromise between low- or high-end power options, and the lobe separation angle (LSA) is one of those factors where engine builders have to make a choice between those priorities.

“The lobe separation angle is the angle in camshaft degrees between the maximum lift points, or centerlines, of the intake and exhaust lobes,” says Eric Bolander of Erson Cams. “It affects the amount of valve overlap; that is the brief period of time when both the intake and exhaust valves are open.”

click here to read the entire article and see all the images

Some Q and A about boost and pump gas vs E-85 and methanol


Is it possible to have a blower on 93 octane pump gas without the stripping in the rotors?

Why stripped or not? Does Compression ratio matter? 

If yes that I can get a blower without the stripping in the rotors, what is the max horsepower cutoff without the stripping and 93 octane pump gas?

This is one of the most misunderstood elements of blowers. Stripping is done in levels. So a stripped blower is always more efficient than a non stripped one.  The degree of tightness is what is to be considered.  All of our Blower shop Blowers are stripped for specific fuels. Gas  requires more clearance and thus looser stripping to eliminate heat. Alcohol and E-85  can accept much tighter stripping since alcohol is a cooling fuel, and the tighter the stripping the more boost a blower can make.

Gas is such a low octane (resistance to detonation)  that if a blower produces much boost, and when coupled with a high static compression, it will eclipse the ability of 93 octane to  not detonate, and that is how engines are destroyed. So we have a chart in our technical area which tells how much boost you can have with pump gas and be safe. Think of a blower as a compressor or like piston rings-  Tighter clearances = more ability to work.

Pump E-85 can be dangerous to try and figure out because it can be as low as 100 octane or as high as 105 at any given time.

Drum C-85 is always approx 117 octane usually good up to 18-1 compression.

Methanol doesn’t have a  boost limit for all practical purposes and will resist detonation to over 30-1  compression.

The “Effective” compression ratio has to be calculated by first knowing the engines compression (Static), then adding the blowers boost which gives an answer called  “Effective” which is what the engine is seeing as the compression ratio.

So 8-1 compression +  10 lbs of boost = about 14-1  compression (too much for pump 93 octane) call us for help on this before you hurt something.



Alkydigger’s Turbo/ ProCharger Boost referenced Flow Valve BV1062


Alkydigger’s Turbo/ ProCharger Boost referenced Flow Valve BV1062 Alkydigger’s Turbo/ ProCharger Boost referenced Flow Valve BV1062


Alkydigger’s Turbo/ ProCharger Boost referenced Flow Valve BV1062

This valve provides a way to limit the flow of fuel away from the engine during boost cycles.

The way it works is by normally being wide open with no boost.

When boost is sent to the valve, from any source where boost is available before the butterfly, to the -6 fitting on the valve it causes the valve to begin to close.

More boost which is regulated by the “Air Valve” will cause it to close more quickly – Less boost will make it close more slowly.

The Air Valve uses “Pills” to allow more or less boost to get to the Turbo valve. Larger pill = More Boos t= Quicker Closing = more fuel to the engine sooner.

The -12 Fitting gets returned to the tank. The -12 wants a fairly short hose or direct fit to the tank with no turns if possible.

The -8 Fitting receives the fuel from a direct source from the pump. Fuel pressure BEFORE it gets metered.

So in summary:

Smaller pill in the Air Valve makes it in effect leaner.

Larger pill in the Air Valve makes it richer.

Alkydigger’s Air Valve AV6001 is recommended, using 7009- Enderle pills. You should have pills in the .050 to .100 range on hand.

Alkydigger Fuel Injection




Information About Boost and Various Blower Designs Behavior


All blowers are a compressor. So all blowers will make positive pressure in the manifold.

Weak blowers have dual rec. openings, they are 60 degree twist (Standard Helix), so they have a lot of drag, and are generally set up with loose clearances for Gas. Can you use E-85 or Methanol? Yes. The level of boost will be minimum unless the blower is designed with tight clearances, and has high helix (120 degree twist).

The greater the twist, the less friction they have and a high helix rotor will continue to make boost well up in the 10,000 rpm Blower Speed, where a std. helix will flatten out at around 7000 rpm blower speed.

Blower speed is a product of the drive ratio – so 25% overdrive = 8750 rpm blower speed on an engine turning 7000 rpm.

This is why you are wasting your time and energy spinning a 60 degree rotor blower at anything over 20-30% overdrive usually.

Methanol likes lots of air, and lots of boost since it uses twice as much fuel as gasoline. So high helix, high boost, big butterflies works well in general with methanol.

Blowers designed more for methanol have V Shaped discharges called “Delta” openings – The air is further compressed by forcing it through a smaller opening, thus adding speed and boost.

E-85 is an alcohol based fuel – it also likes boost, and it runs cool, has much higher detonation limits than Gas – Drum E-85 is usually 117 octane.

Gasoline – Burns fast, and HOT. The octane is limited to 93 for pump gas, and some have octane up to as high as 116 – However gas  is difficult to tune in mechanical injection, expensive to buy in high octane form, and runs very hot.  Gas blowers are set up to not make much boost since gasoline is intolerant of high compression in most forms, so not much effort is put forth to create boost.

Boost + Static compression =  Effective compression which puts pump gas out of the picture when effective compression hits around 11:1.

This is why you will hear from many who have some knowledge, but don’t understand the whole picture; they will say that you have to have 8:1 compression with a blower. They don’t know why necessarily, but if their advice is taken without research and  they build a 8:1 Alcohol engine, it will  be a slug. Methanol and Drum E-85 can easily tolerate 11:1 12:1 static compression so when coupled with the blower boost they often have compression ratios of 20:1  which is fine with  alcohol based fuels, but not with Gasoline.

Call Alkydigger 615-457-3192 for more insight into the design of a good supercharger system.

Blower Bottom Openings for Race Blowers

Notice that the  RETRO  has an extra front opening – This is caused from using the gear case to create more cu in of displacement by milling it out – thus causing the blower to have to be moved back 2-1/4”  on the blower manifold, which then centers the  boost discharge.

case sizes


High Helix vs Standard Helix Blower Rotors

There has always been lots of questions about Standard Helix vs. High Helix Blowers.

For many years all blowers had a 60 degree twist to the rotors – this is called a standard Helix.

A 60 degree rotor  will flatline, or quit making more boost at somewhere around 7500 RPM Blower Speed.

So regardless of how much overdrive you continue to try and use, nothing happens that helps make more power – in fact it will slow down a bit due to the effort to drive the blower faster and faster, as well as making  lots of heat. The heat isn’t much of an issue with Methanol, but is with gas, big time.

A High Helix rotor is either 120 degrees, or in the case of our XR-1 Blowers, 124 degrees.

How does this help?

A high Helix blower will go to about 11,000 RPM before it quits making additional boost.

NOTE: We are discussing Blower speed, not engine speed, so if  a blower is driven at 40% overdrive and the engine is turned to 7000 RPM, the Blower is Turning 140% x 7000 RPM = 9800 RPM, so everything after around 7500 and above has been a waste.

High Helix Rotors take less Horsepower to drive, and run much cooler than 60 degree rotors.

The myth is that a 60 degree rotor makes torque and a 120 degree rotor makes high RPM HP. Not entirely true:

Both make the same  torque within  a few %, but the High Helix “Keeps” making power way up the RPM scale, so  it  is, in fact, making more HP at high RPM, since it didn’t quit at 7000-7500 RPM.

Street vs. Race – There is no disadvantage from High Helix;  they are perfectly at home on a Street Rod, Boat, Drag Race, Mega Truck, Pulling truck-tractor, or Land Speed Record, and continue to contribute above 7000  rather than giving it up.