Topic: Superchargers: Centrifugals

[Jeffy]

Ok, lets talk Superchargers again.  This time focusing on centrigufals.

Why?  Because they are a simple design and easier to set up without having to do a lot of custom work.  Now, the biggest difference in centrifugals and screw type is the spool up speed.  Screws start making pressure at very low RPM and give you a full range while centrifugals need to spool up and make power higher up.

Well, I never saw this as a problem with the 2.5L since low end power is fine.  Its those times when you need to punch it that it would be nice to have that extra 'oomph'.

So where do we start?  Well, 6-9psi is supposed to be the range for a stock engine.  This is controlled by the pulley size.  There seems to be two different type of compressors out there; internal compression and external compression supercahrgers.  Internal compression, compress the air internally.  External compression push the air out and compressit between the intake and the pump.   From what I've read, this setup creates more heat.  Although the internal compression create more parasitic drag when not operating.  External compresson doesn't have them problem since they have use a wastegate or BOV to get rid of the excess pressure when not under boost.

To keep it simple lets leave out the intercooler for now.

Next there is the supercharger itself.  Some require external oil while others are self contained.  Some are even dry.  I think for a Jeep a selfcontained or dry compressor would be best.  This leaves out the extra plumbing required to oil the system.

The big problems are the air/fuel mixture and detonation.  I think for 6-9psi you might be able to use a modified MAP but an piggyback system might be better.  Those with SC's already can chime in on this.  I think changing the fuel pressure regulator might be an option.

Timing can be retarded with a external controller.  Would it be needed for such low pressure?

The big players in the Centrifugal game are Z Engineering, Powerdyne, Paxton and Vortech.  The later 3 are very popular.

Another consideration is emissions.  A Centrifugal would be simple to remove and reinstall with no major wrenching so that's a big plus.

I know I'm leaving a lot out but that leaves plenty of room for discussion.

[spyros'89]

before installing my turbocharger i did some research and asking/driving around. the centrifugal is an interesting type of SC. the output (as in hp and torque gains) and the way of its operation is simillar to the turbo but a bit more refined. i would always vote for a screw type because of the extra boost down low. i went the turbo-way for these reasons: it was the lowest cost and it takes 30 minutes (give or take) to return to stock. you defenitely get RAW power, and you get much better fuel economy (compared to centrifugals and screws). you just have to take a bit more care of your system, e.g. you have to warm it up patiently and let it cool down (or get a turbo timer) properly.

[Jeffy]

Like I said, a screw or roots type would be optimal for a full range BUT to get one installed requires a lot of custom work.  Which is why Avenger wants almost $4K for theirs.

In all honestly, the 2.5L is fine down low but lacks up high.  As for difficulty, they would be able the same.  Although people might have an easier time making brackets then routing exhaust.

But again, I wanted this to be focused as talk about how to make it work not bash one setup for another.  :roll:

Things like how do you manage air/fuel and detonation....

[Jeffy]

What no takers?

I think bare minumum, a wastegate and a air/fuel gauge would be necessary.  I still haven't seen anything that would suggest that it would need suplimentary fuel with low boost.

Would 4.0L or even 5.0 injectors be necessary?

[wildman4x4nut]

Jeff,
I will agree with you on most points but even with minum boost I think you will need extra fuel. And to control the timing and fuel management the best I have found is the SplitSecond piggyback. As you know I bought the Rimmer supercharger from Trailblazer. I'll be putting this on in about a month and will let you know what I think about the extra power.

[Jeffy]

How much boost does the Rimmer with the Eaton M45 make?

I've been looking at the Powerdyne and they have as low as 4.5psi used for Camaro's.

I'm wondering it the stock injectors have enough leeway to compensate.  With a centrifugal or turbo, I don't think you can use an adjustable MAP.  After thinking about it, when not under boost, the engine will opperate like it does normally.  So increasing the flow across the board isn't good in this application.

It looks like the Split Second takes over some of the duty from the PCM.  Hook up looks straight pretty forward.

I'd like to see picts and installs of the Split Second.  Sounds like the way to go though.

Split Second has developed an FTC1 Fuel/Timing Calibrator specifically for the Jeep 4.0L, in-line six engine. It is the perfect complement for either a supercharger or turbo. It allows the use of larger injectors to appropriately fuel the motor in boost. The FTC1 has it own 2 bar MAP sensor which replaces the stock MAP sensor. This makes it possible for the stock ECU to read boost. Map table A programs the fuel over the entire load range of the engine while map B programs the timing retard required to avoid pinging.

Before installation of the FTC1, this Jeep has a serious lean spot in boost. Both problems were fixed by the FTC1. An added feature of the FTC1 is that you can download different calibration files as needed. If this Jeep goes to the back country where premium unleaded is not available, the owner can download a calibration map that takes out enough timing to run on regular unleaded. The performance is not as good, but it is safe to run without worrying about pinging.  

Can you control fuel management with one of these?  

FUEL MANAGEMENT UNIT (FMU)

What is an FMU?
The letters FMU stand for "Fuel Management Unit". Basically, an FMU is a fuel pressure regulator. The FMU is used on fuel injected, supercharged engines using the factory electronic engine management system.

When an engine is supercharged the air delivered to it is greatly increased. For the engine to run properly and make max power a 11.5:1 air/fuel ratio must be maintained. Since the factory electronic controller can compensate for this increased air flow (it was not designed for supercharger use) another way has to be found to supply the necessary additional fuel. The FMU is the device that does this.

The FMU is installed just down stream of the stock fuel pressure regulator. It does not control fuel pressure until the engine manifold pressure comes under boost from the supercharger. As the manifold pressure increases, a pressure line from the manifold to the FMU causes the FMU to increase the fuel injector rail pressure. The increased fuel pressure causes the injectors to deliver more fuel to the engine. With this system the stock factory electronic controller can be used without modification on a supercharged engine with good results. The reason the Vortech supercharging systems are smog legal is because the stock controller is retained unmodified and at part throttle the engine's performance and emissions are not effected.

Some other questions I've got are more related to turbo's.

Wastegates and BOV's.  Do you need a BOV if you run a wastegate?  I know the wastegate will bleed off excess pressure with a spring attached to a valve.  While the BOV is vacuum dependant.  Turbo's usually come with wastegates but do centrifugals need them too?  I'm guessing not.  Actually the more I look the more I just see a BOV.

[Jeffy]

Found this while looking arouns but it still leaves a lot of questions.

Do It Yourself Turbocharging Part 1
By: Overboost Staff
10/18/1999
PLEASE READ OUR DISCLAIMER

   

Note: Part 1 is intended to provide background information to your average performance laymen. This covers the absolute basics, and should be considered as part of a series rather than a complete guide. Future chapters in this series will go in depth into the more advanced factors involved in turbocharging.

The advent of improved international standardized manufacturing techniques and standards has led most folks to come to the realization that cars are made a lot better than they were ten years ago. Simply put, improved mechanical tolerances and increased reliability have greatly increased. If anything, that should encourage you to coax a little (or a lot) more power out of your car.

A lot of folks go down the path of traditional powertrain modification. They do your average "breather mods" (intakes, headers, exhaust), play with fuel maps, modify ignition timing. Those with more time, know-how, and money on their hands resort to headwork -- porting, polishing, cams, etc. However, it's the dream of many an automotive tuner to seek power through forced induction (turbocharging, for one) and creating more power from less displacement, which, essentially, is what turbocharging is. For most people, there are some VERY expensive aftermarket turbo kits out there. Those with money will trust experts to install such a setup. For those who don't have so much money but KNOW WHAT THEY ARE DOING, there are turbo setups that cost in the hundreds of dollars rather than in the thousands. This article is just to give you insight on some of the possibilities that exist. IF YOU DON'T KNOW WHAT YOU ARE DOING, don't proceed! Turbocharging your engine improperly is a VERY easy way to cause thousands of dollars in damages, not to mention serious risk of damage to one's self. If you do something dumb, we take NO RESPONSIBILITY. Please take the time to read our Terms of Use

For the laymen who can't distinguish a camshaft from a halfshaft, here's turbocharger theory 101 in a nutshell. Engines are designed to work like a pump. Air and fuel are mixed together, and then ignited. The explosion provides power. Air and fuel must be combined in a specific ratio -- 14.5 of air to one part of fuel. If there is too much fuel in relation to air, the engine runs in a state of "richness". This leads to poor performance and lower fuel economy. An excess of air in relation to fuel will cause the engine to run in a state of "leanness". This leads to bad bad things -- detonation (explosions happening before they should, when the engine is in a poor position to receive the benefits of it), and high combustion temperatures (which, if hot enough, WILL melt parts of your engine). The point is to maintain that magical "stoichiometric" ratio of about 14.5 to 1. Ok. Pay attention -- this part is where power comes in. The more of this 14.5-to-1 air/fuel mixture you can force into your engine and ignite, the more power it will make. A turbo charger is essentially a double-sided pinwheel. The rapidly flowing exhaust gases spin the exhaust side (the hot side). This is connected via a turbine shaft to the compressor side (the cold side), which spins up in the range of tens of thousands of RPM. This action pressurizes the air intake charge -- thereby forcing more air into the engine. Now, if you've been following along this whole time, you should be asking yourself, "won't all this extra air cause the engine to run in a state of leaness?" That's correct! Specially designed fuel injection setups provide the extra fuel your engine needs.

At this point, you reach the two most important questions involved with turbocharging. 1) How do I get a turbo attached to my car and 2) how do I provide enough extra fuel in the right amounts at the right time to accommodate this influx of air?

The easy way.

If there is a turbocharged version of your engine on the market, you'll have an easier time finding parts and doing the installations. This makes things MUCH easier and cheaper, seeing as a) chances are, your car's manufacturer has designed proper clearances and tolerances into your car to accept turbocharging and b) these parts are quite plentiful and cheap at your local junkyard! This includes (but isn't necessarily limited to) 3rd and 4th generation Toyota Supra, all generations of the Nissan 300zx, 1st and 3rd generation of the Nissan 200sx, 2nd generation Toyota MR2, 91-99 Mitsubishi 3000GT. In part four of this series, we'll do our best to post a more complete list -- including the myriad of turbo Saabs, Volvo's, and Porsches out there. The parts you'll need from your car's turbo big brother will include the turbo, oil lines, turbo manifold, intercooler, compressor bypass valve (more commonly known as the blow-off-valve), downpipe, ECU, injectors, fuel pressure regulator, fuel pump, air flow meter, and as much as the intake/intercooler piping as possible. Here's a breakdown of what each part does.

The Turbo

It's the power adder, silly. When picking one up from the junkyard, make sure the turbine wheel spins freely. Also, make sure the wheel has no play. It should spin--period. It shouldn't wobble, it should wiggle, it shouldn't move in and out. The average price of a used turbo is in the $100-$200 range. Try to get the factory oil lines that go to and from the turbo. You will need to tap the sender line into the block someplace, and the return line into the oilpan to ensure a flow of oil through the turbo.



Turbo Exhaust Manifold

This replaces your stock exhaust manifold. Rather than guiding spent exhaust gases straight into your downpipe and out of your tailpipe, the turbo manifold directs the exhaust gases into your turbo to spin it. If one isn't in existence for your vehicle, it can be manufactured for anywhere in the $400-$800 range.

Turbo Downpipe

Chances are, your factory non-turbo downpipe will not mate up properly with the turbo exhaust outlet. If the turbo downpipe is unavailable for your car, your local muffler shop can fabricate one for about $150. An aftermarket unit will cost upwards of $200.

Make sure you get the downpipe to mate with your catalytic converter and exhaust system.

Intercooler

Much like a radiator for the incoming air charge, the intercooler cools the intake air charge to temperatures closer to ambient, condensing it and allowing you to fit more into each combustion stroke. This also helps in reducing combustion temperatures (bad) and helping prevent against detonation (also bad). Stock units from the junkyard can usually be had for between $25-$75.

Compressor Bypass Valve (CBV) or Blow Off Valve (BOV).

This is what usually makes that cool pffffsssshtt sound on turbocharged cars. This valve does more than make that funny noise, however. Its main purpose is to relieve the pressure on the intake air charge between shifts. When you shift, you usually let off the gas pedal. That in turn slams the throttle plate shut. Your pressurized intake charge now has no where to go. What the CBV does is vent this pressurized air -- either back into the metered intake stream in the plumbing before the turbo, or out into the atmosphere. If this air is not vented, it will send a pressure wave back down to the turbo, trying to reverse the direction that the turbo is spinning. This is not good for turbine longevity. Decent OEM CBV's will usually retail for about $30-$50. There are benefits of going with aftermarket units like the Greddy Type S, which is adjustable.

ECU/Injectors/Fuel Pressure Regulator/Fuel Pump

This is primarily, the fuel system from the turbo version of your car. Chances are, the turbo version of your car will have larger higher capacity fuel injectors and have a different air metering system than your normally aspirated car. This system, when functioning properly, will inject the proper amounts of fuel, proportionate with the incoming air, at proper intervals and duration. Several sensors (air flow meter being the major one) detect the volume, temperature, (and in some cases, velocity) of the intake air charge. This information is sent to the ECU, or computer, which in turn computes how much fuel is required to mix with this air. Once this is calculated, the ECU fires the injectors. The fuel pump and fuel pressure regulator are in place to see to the fuel demands of the injectors.

Oil/Coolant Lines

These are very important systems and should not be ignored. Simply put, to remain lubricated and within operating temperatures, a turbocharger needs a constant supply of oil and coolant flowing THROUGH it. Your stock cooling system can usually be teed off with radiator hose and redirected through the turbo to supply coolant. Oil on the other hand will require a certain grade of hose that withstands much higher temperatures. Fittings will need to be created both in your oilpan for the oil drainage line from the turbo and in a source of fresh oil somewhere before the turbo. The easiest solution for that (since most engines require tapping to get a live oil feed) is to install a remote oil filter relocation kit. These attach where your oil filter normally is, re-route the oil to a remotely mounted oil filter, and provides a return line back to the block for the filtered oil. This is the perfect place to tee off the connection and run a line to supply oil to your turbo. Your average kit will run you about $100.

Intake/Intercooler Piping

This is what holds everything together. This piping, held together by friction fit, hose joints, and clamps, will allow air to flow through the air filter to the turbo, from the turbo to the intercooler, and finally from the intercooler to the throttle. Stock factory pieces are usually made of plastic, but tend to fit fairly well. Pieces that you're missing can usually be made from large radiator hoses or pieces of generic muffler piping of varying lengths and bends. If you're feeling extravagant and want a better flowing system, we recommend taking this task to your local muffler shop. You should see to it that beads are welded into the piping where clamps will be used to ensure a fit that will not come apart should you start running large amounts of boost. Follow this up with some powder coating or anodizing, and you've got a pretty trick looking setup.

Gauges/Monitoring Equipment

Ideally there are three different gauges you should have when you embark upon this project. First and foremost is an aftermarket boost gauge. Decent units are made by Autometer for about $40. Best thing is, these units read in ENGLISH, that is, in PSI. These gauges will tell you what kind of negative and more importantly, positive manifold pressure your turbo is creating. Next is an air/fuel ratio gauge that will tell you how far you are from having a stoichiometric mixture by reading the signal coming from your O2 sensor.. Intellitronix makes a 52mm unit that fits into your average a-pillar gauge pod for about $30. Finally there is the EGT (exhaust gas temperature) gauge. When an engine is in good running order, it should be at about 1450 degrees Fahrenheit. Temperatures below that will indicate a state of richness, and temperatures above that will indicate a state of leanness (BAD). An EGT gauge is essentially a voltmeter that displays the output from a thermocouple, or pyrometer, that sits in the exhaust stream and converts heat to an electric signal. A full complement of these gauges, coupled with some good common sense, we go a long ways in keeping you from turning your motor into a metal foundry.

What we've gone over are some basics of a turbo conversion. We don't recommend you consider doing this until we've published (and you've read) the rest of this series. Future installments will include turbo selection, advanced turbocharger theory, intercooler selection, sources for parts, advanced fuel management, pros/cons, monitoring, tuning, and installation.

[spyros'89]

extra fuel will be needed no mater what. otherwise we are soon going to be dealing with cracked pistons and dry-cracked heads. i prefer the secondary ecu/extra injector way because it is easier to calibrate. for the mpi 2,5's, you can re-calibrate for extra fuel for up to 0,5bar of boost. beyond that, you need bigger injectors but forged pistons and more stuff as well so there goes simplicity. for the diy route, 0,5 bar is just enough 'cause you dont mess with the engines internal.

[Jeffy]

Yes, but the answer I'm trying to coax is how broad is the spectrum for the MAP?  I know MAP's vary a bit from vehicle to vheicle. What's the stock fuel regulator set at?  Now would a adjustable fuel pressure regulator work?  If not then why?   Larger injectors are used, would that help?  And again, if not then why? (I'm assuming the fuel regulator controls how much pressure the injectors actually get.  But then would assing the new FMC from above compensate for that?)

Although, with the Splitsecond, being able to upload new calabrations is a nice feature.  Being able to run off regular at times would be nice, too.  Although I suspect under regular settings 89 will work.

If by 0,5 Bar do you mean Mega Pascals?  1Mpa = 14.7 psi, if I remember right.  0.5 Mpa would be equilivant to 7.35 psi then.  Sounds about right.  I believe CarTech who made a Turbo for the 4.0L ran their turbo at 7 psi.

[wildman4x4nut]

Jeff,
I can't say for sure but I think the Rimmer is around 6psi stock. I know you could get more out of it by changing pulley size but I am also sure that info is long gone now. The 1 bar MAP cannot understand boost from all I have read. I have seen a few make your own adjustable MAP online but again if your going back and forth from 0 boost to 6psi I'd rather have a computer controling the MAP, Fuel & Timing.

[Jeffy]

That's why I'm wondering if a vacuum controlled fuel regulator would work.  Move vacuum, the more it fuel it lets through.  Although it would need adjusting initially.  A piggyback system would probably be best.

I've located another company which happens to be in CO, that does centrifugals.  Interesting thing is they they add a SC to bring the engine back to sea-level performance.  I think they run around 4psi or so.  They have another one that is used as a performance add-on too.  I haven't tried emailing them yet.

[wildman4x4nut]

Jeff,
On the SC I have there is a vacum controlled fuel reg but on TJ's we do not have fuel reg so I am going to try it without it first and then if I have to with it. At the same time I am pretty convinced I'll run the SplitSecond controller.

[Jeffy]

Hmm, there is no fuel regulator on the front of the fuel rail?

When you do the split second, lets do a How-To so others like me can follow.  :wink:

I'm really thinking about going with a centrifugal.  I drove around today paying attention to my RPM's.  Around town, I wouldn't be under boost unless I punched it.  On the highway, I'm cruising at 65mph in 5th ok but if i hit a hill, I'll be in 4th at 3000rpm.  So, I think it would work out good.  Not to mention, I'd be able to remove it when I have to do SMOG every other year.  Should be as easy as disconnecting it and disabling the computer.

[jpcreep]

Hello Jeffy and Wildman,

I currently have the Avenger supercharger installed pushing 8 PSI.  You need to controll your fuel foremost reguardles of what you use to provide forced induction.  The TJs have a returnless fuel system hich means that an FMU (which throttles the fuel returning to the fuel tank and causing fuel pressure to increase and forcing more fuel through the injectors at each pulse) will most likely not work.  The stock 2.5L Tj comes with 19lb injectors, the avenger is equiped with 25lb and at 8 psi i have installed 30lb injectors.  Another avenue of increasing fuel pressure which would allow you to use a smaller injector is Kenne Bell,s boost a pump http://www.kennebell.net/accessories/boostapump/boostapump.htm.  I also have the split second FTC1 installed which has it's own internal 2 bar map which I belive will sense up to 14 psi.  The stock MAP is a sigle bar which means that once pressure reaches 0 psi it is givinf its max reading which coorsponds to wide open throttle WOT and your injectors should be at max flowrate.  The Avenger setup uses the stock MAP and relies on your O2 sensor to adust fuel while under a vacuum and the  jeep going to WOT to provide the fuel during boost.  This works OK if you either are cruising at low loads or with you foot to the floor. It gets mixed results during periods when you are working the engine enough to be at boost (say 2psi) but you don't have your foot on the floor (the O2 sensor is still trying to controll fuel but get mixed reading from the MAP and throttle position sensor TPS.  Factor X Engineering has a nice setup, but for the 4.0L http://www.off-road.com/jeep/reviews/factorxengineering/  Split seconds FTC1 can also retard timing during boost.  MSD also makes the boost timing master http://www.msdignition.com/tc_19.htm.  At 8psi I have not noticed any detonation so I do not retard any timing at any pressure.  Hope some of this helps.

[wrangler387]

Your FTC1 might sense more then that. I've noticed a lot of companies (and people) when talking about what bar their map sensors are do not account for the vacuum bar. As in they say they have a 2 bar and it's really a 3 bar, etc. I hope that makes sense haha. Glad to see someone on here that has forced induction.