Home: Mustang Tech: Forced induction: Supercharging Q&A's
Supercharging Q&A's

Summary:

This article is written by Jim Roal and answers many of your questions about supercharging engines.

Details:

Q: Which is the best supercharger for the Ford 5.4L truck?
Q: What supercharger do you recommend for the 4.6L 2V Thunderbird?
Q: I just bought a used Kenne Bell but it is missing some parts.  Where can I get Kenne Bell parts?
Q: What is the best supercharger kit for the 4.0L Explorer/Ranger?
Q: Which is more important, horsepower or torque?
Q: Why do you prefer positive displacement blowers so much?
Q: What is an FMU?
Q: What is more efficient, a supercharger or a turbocharger?
Q: Why is inter cooling such a good thing?
Q: How much power could I expect to gain with a turbocharger or supercharger?
Q: How much engine life can I expect to loose when I supercharge/turbocharger?
Q: How much fuel economy can I expect to loose when I supercharge/turbocharger?
Q: I have a blower from a Super Coupe.  Can I bolt it on my engine?
Q: I have a supercharged or turbo charged engine and it have a problem with detonation (ping) under boost.  What is the best way to handle it?

Q: Which is the best supercharger for the Ford 5.4L truck?

A: Fortunately there are 3 very good positive displacement systems out there.  The most expensive is the Holley Thunder kit.  It uses a Holley Roots style blower and a water-to-air inter cooler.  The kit sells for just under $6,000 I heard.  A guy installed one last fall and emailed me.  He was quite happy with it.  Holley bought the supercharger line from B&M Racing a few years back.  B&M had been building these blowers since about 1980.  See the Thunder kit at:
http://www.holley.com/HiOctn/ProdLine/Products/AMS/AMSSIHPS/300-520.html

My personal choice would be the Magnuson kit (sold through Magnacharger http://www.magnacharger.com/). It uses the proven Eaton Roots style supercharger and is also water-to-air inter cooled and bypass valve.  It has a superior intake manifold design as well.  It sells for $3845.  It looks identical to the Allen superchargers of which I have completed 2 installs last year.  I was very impressed with the Allen kit. http://www.magnacharger.com/ford_5_4.htm

The other system is made by Kenne Bell.  This uses a Lysholm (or screw) type supercharger.  These blowers are actually more efficient than a Roots.  It is not inter cooled and does not include a bypass valve.  I have installed many KB kits.  They are much better than any centrifugal but not quite the quality of an Eaton blower.  KB kits usually run about $3500.


Q: What supercharger do you recommend for the 4.6L 2V Thunderbird?

A: The AED kit is by far the best choice for your car, hands down.  The Allen kit uses the best quality (Eaton) blower, comes with a bypass valve, fuel pump, and inter cooler, and has a superior intake manifold design.  The Allen comes complete with everything you need, no custom fab work required.  It is also the recommended kit of the National Thunderbird club.  The Allen uses the same blower you had on your Super coupe and it has the same boost characteristics.  I would definitely recommend you go that route.  It is well worth the money.

Installation of the Allen kit is time consuming.  If you have done basic wiring and mechanics repairs, you should be able to do it yourself.  If you don't want to tackle it, Allen installs them in California, I have friends (professionals) who install them in Seattle and Eastern Washington, and of course I install them here in central Illinois.



Q: I just bought a used Kenne Bell but it is missing some parts.  Where can I get Kenne Bell parts?

A: I have heard that Kenne Bell does not do business with people who buy used kits. I have no idea why they are that way but I have had several people tell me this.   I don't know what KB's problem is.  You could ask on http://www.kenne-bell.com/eBay is another possible source.  Good luck.



Q: What is the best supercharger kit for the 4.0L Explorer/Ranger?

A: The only positive displacement kit I know of is the BBK.  Explorer Express sells that same kit.  These kits use the Eaton Roots blower for instant boost across the entire rpm range.  I have not yet installed one of these kits but they appear to be a solid design.



Q: Which is more important, horsepower or torque?

A: Horsepower is a rate based measure of an engines ability to do work.  In order to accelerate a given mass from 0 to 60 mph for instance, a certain amount of horsepower is needed.  Torque, on the other hand, is merely a force.  Torque can exist with no motion.  Therefore a torque rating really does not tell you much without an RPM that the torque was measured at.  If you have torque and RPM, you can calculate horsepower HP=(torque ft*lbs x RPM)/5252.  So you may wonder why people get so hung up on torque.  Well, given a peak torque and RPM, and the peak HP rating, you can tell some characteristics of the engine performance you won't get with just HP.  If you have an engine with a peak torque above the peak HP, you have an engine that does not care to rev but instead has good power at low engine RPM.  If you have an engine with torque (ft*lbs) and HP ratings about the same, it is a typical automotive engine.  If you have an engine with high HP ratings and low torque ratings you have an engine that has poor power down low but can rev very high.  Bottom line however, any performance estimates will require the HP, not the torque.  More important yet is what is often called "power under the curve".  This is the area under the power curve throughout a given rpm band.  Best case would be to have the most area under the curve to provide the best acceleration.



Q: Why do you prefer positive displacement blowers so much?

A: When was the last time you saw a professional race team use a centrifugal blower?  How about a new vehicle manufacturer?  Sure, if you look real hard, you can find a few instances here and there but they are very rare.  Why do you suppose that is?  While centrifugal superchargers will give you the peak HP numbers you are looking for on the dyno, it is only the peak that you really get.  A typical 6psi to 9psi kit will not give you any real boost until about 3000RPM.



Q: What is an FMU?

A: An Fuel Management Unit (FMU) is a special rising rate fuel pressure regulator placed in the fuel return line of the fuel injection system.  This is a very common approach to handling the increased fuel demand required by supercharger kits.  It does work.  It will make the injectors flow more fuel than their rating.  These are used in addition to the factory fuel pressure regulator and only have an affect under boost.  They are rated by the ratio of fuel pressure to boost pressure.  For instance, a 10:1 FMU will give you 100psi fuel pressure at 10 psi boost pressure.  The problem here is that the extra pressure on the fuel pump decreases the flow capacity of the pump.  That is the last thing you need on a supercharged engine.  You can offset that by installing an in-line fuel pump in addition to the in-tank pump.



Q: What is more efficient, a supercharger or a turbocharger?

A: Turbochargers have an adiabatic efficiency in the range of 70% to 80%.  Centrifugal superchargers are usually closer to 70%.  The Eaton Roots blower is typically 60% and the screw type blower (Whipple or Kenne Bell) can be as high as 75%.  Conventional Roots blowers, like the GM 6-71, is about 40% to 50% efficient.  What does this mean?  The lower the adiabatic efficiency, the more heating of the discharge air you will get.  That means less density, less power, more detonation problems.  An inter cooler can pull the heat back out but there is a price for that too.  Now if you want to look at total efficiency of the system, the turbo wins.  It will give you the highest power gain potential of any forced induction system.  Notice that the Pro-Mod 5.0 class now uses more turbochargers than anything else.  If you really want peak power, get a turbo and inter cool it.  I still like the Roots or Screw blower for many street applications since there is no lag or cut-in speed to worry about (although my daily driver is turbo charged).   Most centrifugal blowers will have an even higher cut-in speed than most turbo's and will not offer anywhere near the mid-range power gains of either a turbo or a roots or screw blower.

Superchargers all draw power from the crankshaft where turbochargers draw the power from the exhaust flow and heat.  Both rob power but much of the power the turbocharger uses would otherwise be wasted out the exhaust.  The turbocharger is also more efficient at applying the power to the compressor.  Overall, the turbocharger is the most efficient method of forced induction.



Q: Why is inter cooling such a good thing?

A: Anytime you compress air, it heats up.  Even at 100% adiabatic efficiency (which is impossible), the air will heat up quite a bit.  The inefficiency of the compressor (turbocharger or supercharger) will heat the air up even more.  As the air is heated, the density of the air drops.  Engine power is a function of the amount of air, and fuel, you can get into the cylinder during the intake stroke.  It is not really the volume of air but rather the mass of air that is the key.  As the air is heated and the density drops, the same volume will supply less air mass to the cylinder.  The key is to not only compress the air, but to cool it back down as well to achieve the maximum mass of air, and therefore maximum power.

In addition to this, the hotter the inlet air, the more tendency the engine will have towards detonation and pre-ignition (spark-knock, ping).  These are very damaging to the engine and they rob power.



Q: How much power could I expect to gain with a turbocharger or supercharger?

A: Roughly, you can expect to gain about the same power difference percentage as you gain induction pressure percentage.  The equation is HPafter = ((14.7 + boost)/14.7)*HPbefore.  For instance, if you have a 200HP engine and you add 7.5psi boost, you can expect to have about 300HP.  This is an estimate, not an exact calculation so take it for what it is worth.  In reality, it will likely be just a bit less than that due to inefficiencies and air density losses due to heating.  If you are inter cooled, you will get closer to this estimated power.



Q: How much engine life can I expect to loose when I supercharge/turbo charge?

A: You should not loose much at all as long as you properly maintain the engine.  The amount of time you will be in boost on a daily driver will be very small in most cases.  Even on cars that have small turbo charged/supercharged engines, the engines generally last quite long these days.  Engine technology and engine oil has significantly improved over the years.  Fuel injection has also made a big difference.  Most modern engines should last 250k miles or so.  I would recommend Mobil One engine oil with oil changes every 10k miles.  I had a 1985 Thunderbird Turbo Coupe with the boost set at 17psi.  I ran the car very hard.  The car was totaled in an accident at 177k miles but it never used any oil in it's life.  It ran like new to the end.  This was not an isolated case.  I have seen many of those cars last over 200k miles with the original engine and turbo.



Q: How much fuel economy can I expect to loose when I supercharge/turbo charge?

A: You may loose about 5% or so for a good system.   The amount of time you will be in boost on a daily driver will be very small in most cases.  A good design with a bypass valve (for superchargers) will draw about 1/3HP on Eaton supercharger based kits under normal driving conditions.  Most other types will still be under 1HP under most driving conditions when not in boost.  If you drive with your foot buried in the throttle all the time you can loose quite a bit of fuel economy.  Most people will not loose much at all.



Q: I have a blower from a Super Coupe.  Can I bolt it on my engine?

A: The Super Coupe used the Eaton M90 blower.  While this blower is the proper size for 3.0L to 5.0L engines, the installation parts for the Super Coupe will not fit on other engines.  You would need to develop and build your own mounting, ducting, and blower drive to make it work.  It can certainly be done, and has been done many times, but this is a completely custom thing.  You had better know what you are doing.  Even the Eaton based kits for other applications (BBK, Allen, SVO) use different drive arrangements.  The Super Coupe blower will not fit any of those I know of either.  I have not heard of anyone offering the kit parts to make a Super Coupe blower fit any other applications.  Magnuson has more information about Eaton blowers and kits available on their web site.  They also sell Eaton blowers for custom applications.


Q: I have a supercharged or turbo charged engine and it have a problem with detonation (ping) under boost.  What is the best way to handle it?

A: First of all, always use the best premium fuel you can buy in any forced induction engine, and make sure the engine has plenty of it.  The few pennies you save buying regular are not even worth it.  In order to allow your forced induction engine to run on regular, you must remove so much timing you loose more fuel economy than you ever gain in savings from cheaper fuel.  Besides, if you are that interested in fuel economy you should be driving some econobox anyway.  If you are running high compression (relatively speaking, like over 10:1) you may want consider using octane booster along with premium in every tank.  The air fuel ratio should be around 11.5:1 to 12:1 under boost.  Make sure your fuel system will support this.

If you have a distributor type ignition system, the MSD Boost Timing Master if my personal favorite.  This comes in 2 forms, one is a complete MSD module with boost retard (about $350), and the other is just a boost retard (about $170, MSD part number 5462).  Both have a remote control knob that you mount in the drivers compartment.  The knob allows you to adjust retard relative to boost pressure, up to 3 degrees per psi.  I would not recommend using it for more than about 1 degree per psi however or you will loose power.  Crane sells a similar device (called TRC) that is very easy to install of TFI Fords and other makes.  It connects into the connector where the timing check plug plugs in and has the driver compartment adjuster knob like the MSD unit.  The nice thing about it is if it fails, you can just pop the timing plug back in and drive off.  It can be configured to control boost like the MSD unit if you buy the optional pressure sensor.  It can also be configured to be a base timing adjustment, or to have a step adjustment in timing (great for nitrous).  These systems let you keep your normal timing strategy when not in boost.

Timing control can also be done through software (chips or flash programming).  Some aftermarket engine controls (like the Extreme Performance Engine Computer that SVO sold) can also connect to a boost pressure sensor and retard timing based on boost pressure.  Some more advanced ignition systems can even be set up to use a knock sensor.  I would caution you on the use of a knock sensor however.  While this sounds like the ultimate way to go, it has drawbacks.  First of all, they can be very tricky to set up so they don't retard timing when there are other noises present.  Even if you get past that issue, the strategy is a matter of trade-offs.  If you always start off with advanced timing and let the detonation (knock) sensor sense the ping and back the timing down, you are letting it ping too often.  If you take the knock information to develop maps so you don't let it ping again, then you could be retarding the timing too much and loosing power if noise enters the picture.  A knock sensor is best used to develop optimum timing curves.  It can be used to help prevent engine destruction in continuous use as well but it is tricky to really optimize it.

Inter cooling is always a good idea with forced induction and it will reduce detonation as well.  Lower compression ratios will not ping near as bad either.  Combustion chamber design play a big role in detonation too.  High squish or high swirl chambers will reduce detonation.  Some modern engines with advanced chamber designs can run 10:1 compression and 15psi boost on pump premium fuel.  Camshaft design also plays a role.

Article by: Jim Roal E-Mail

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