924s Forced Induction Page
8 Valve Normally Aspirated 944/924s

UPDATE August 10, 2009

Please read my supercharge section on this page (scroll down) as there is allot to think about when adding forced induction to a car.  However I have changed directions and I am now going down the turbo path.

I have changed my direction with this project a little bit.  I am still going forced induction but with a low pressure turbo instead of the supercharger.  The biggest reason for this is packaging.  In my book an intercooler is a must with any home brew boost project that will see use over 6lbs. In fact due to the uncontrollable urge to add boost to any car once it is up and running under pressure it is best to install a intercooler as part of your original build.  Every build I have watched/read always sais something like "Since I am only going to boost it to 5lbs to start I don't need an intercooler"  This is followed a couple pages later by the tale of the blown up motor and the engine rebuild and the tale of trying to up he boost to a "safe" 7-9 lbs.  It never works.  There for I have decided to actually design my system around the intercooler.

I had originally wanted a front mounted intercooler unit from a 951 mounted under the nose piece from a 931.  But the way the 924s is constructed this is just not going to happen with out some serious cutting and fabrication. One of the original requirements of this project has always been that the project ahs to be reversible.  Cutting radiator supports is not to reversible in my book so that option was just not a good one.  To I turned my thoughts to turbo.  This would allow me to use 951 intercooler in a top mount position where the supercharger was going to go.  Yes this requires cutting a hole in a hood. I am going to get another hood to play with and keep my good paint matching hood in storage during this project.  I will probably paint the experimental hood flat black as it would go good with my dark green paint.

The abbreviated plan is to fabricate a log type exhaust manifold (I will fabricate it and tack it together and then have a local shop TIG it up)  The turbo will then be mounted/hung off the header down next to the head/block.  This should make the fabrication of oil lines and the return rather simple by putting a "T" in where the Oil pressure sender mounts. The drain will be to a hole drilled in the pan or I was actually thinking of loosening the pan and drilling through the basket and then putting a copper tube through the gasket and re tightening the pan bolts to real.  I am not sure if this will work but it seems better then drilling holes in the pan (yes I have a couple spare pans around and I do need to do a bearing replacement soon so we will see how I finalize this one.  I may see about mounting a 951 pan to the car but the return for it is on the other side of the pan making this a bit impractical..  Coolant for the turbo will come from a  "T" into the cooling line that is for the heater core and just put a return on the other side of the core.

I am getting a core motor that I will be mounting up in my shop complete with motor mounts and what not that I can sue for fabrication purposes.  I hope to get things fabricated over the winter ready for a spring install.

Another change to the plan came from me re evaluating the engine management system for this project as well as me wanting to come up with a way to eliminate the need for the speed and reference sensors.  This came in the form of a programmable Ford EDIS based ignition system.  I have installed it using a 72-2 cam mounted trigger wheel instead of the standard crank mounted 36-1 wheel.  I also used a VR sensor from a FC RX7 due to its ability to cense finer toothed trigger wheels.  The programmable ignition unit that controls it is made by Autosportlabs.  I am using there Megajolt Light Jr. (MJLJ)  Google it and you will find it. This is now controlling the ignition n my car and allows complete programmability.  Yes it si a wast spark system COP would be cool but in the real world it is not necessary.  I have been running it over a year now as a daily driver with no issues.  This is the first step in converting my car over to Micro-squirt based engine management system using the EDIS system for the ignition.  This will replace the various parts and bits I was going to use in my original plan.  No more special FPR.  Instead I am just using a stock unit from a 951.  No more need for the MSD universal spark control.  The use of the AFM is also up in the air. There are allot of other variables that can change and in the long run the Microsquirt seems to be the least expensive way to go when you add up all the things it will end up replacing.

Anyway I will be posting up more o the build and its new direction. I have been researching turbo's and what would be the best to sue for this project.  so far a Garrett from a 88 Volvo 740 turbo or one from a Saab 95 seems to be good candidates.  I am also looking at going strait to Garrett and seeing if I could get one of there small framed turbo's that could be sized to work with this application. There ahs been lots to learn and I will post up more as time allows

If you have any questions please email me at dsmith@radio.fm.

UNDER CONSTRUCTION-UPDATED 10-17-2008

SUPERCHARGER SECTION

So you want a faster 944 and you have come to the conclusion that a supercharger is the answer.

So you want to supper-charge your 944.  I am sure that allot of people have told you that you should just go get a 951.  Now that is not necessarily a bad option for many.  Lets face it going down the road less traveled is not for the faint of hart and it is most certainly not with out risks.  For starters if you screw up your can and will damage you motor.  Blowing up your motor is a real possibility if you screw up or take short cuts.  The other possibility is that you get into the project and end up not finishing it turning your 944 into lawn art.  Do not be fooled and think that this is an easy project.  What I am going to outline here is allot of work.  Weeks and in some cases months of time were spent trying to figure things out. What I cover in a photo or two and a couple of sentences may be the end result of weeks or even months of researching reading and asking questions.  If you are going to do this project it is assumed that you have the ability to do light fabrication and/or you understand what it takes to custom make things and have access to getting it done.  The second thing is that you have a basic understanding of what it takes to convert a normally aspirated car to forced induction.  Things like timing and fuel have to be manipulated as well as the need for inter-cooling. I am also going to assume that you understand the how's and why's of this.  At the end of this I will post up a bunch of links to things that I tracked down on the web that helped me wrap my brain around this.

Then there is the car its self.  I am going to deal exclusively with the 2.5 liter 8 valve motors with the Pre 85.5 DME.  This being said I am sure that allot of what I do will be useful for other iterations of the 944 but do your home work. I am only talking about my car in this write-up not yours.  I also assume that you understand these cars.  I mean really understand it.  You understand the weaknesses of the 944 as well as what makes it shine.  If you are a 944 owner there should be two or three things that come to mind immediately.

You are going to have to visualize what you need and then be able to make it.  I have found that being able to adapt things to suite your needs is a huge help.  Just because something is in the exhaust section of your parts store does not mean it is not potential intake tubing.  Then there is the old debate of to scrounge or not to scrounge.  If you enjoy wandering around the local pick and pull yards you can potentially save your self allot of time and a couple of buckets of cash.  It will also help with the whole visitation thing helping you formulate ways of solving problems.  In short always be on the look out for something that may be useful. You will never know where you are going to find that part that you need or some new interesting bit of information that makes it all come together. 

Asking for help.  If you don't understand something ask.  There are some hugely helpful resources out there on the web.  Pelican's web site and Clarks Garage are the basic must read 944 sites. Renlist has also been a help but they tend to be a bit more of the Porsche purist type.  I have had allot of questions answered I just don't tell people exactly why I am asking the question. 

There are also a whole bunch of supper charger related sites out there.  Many people have added superchargers to there cars.  I strongly recommend that you read there accounts of what they did right and also what popped there motors.  Learn from this!  This is how I eventually came up with the recipe that you see here. 

Lastly.  Put things on paper.  Make lists.  This is a complicated exercise and most of the things are interdependent.  There for if you make changes or upgrade one thing you will more than likely need to make adjustments to other things.

Ok Enough of the speech on to supercharging things.

Getting Started

The first thing you have to do is have realistic expectations.  This is usually in part dictated by monies and time.  Remember that you are taking a normally aspirated car and adding forced induction.  There are limitations to what you can do just because of what you are starting with.  If monies is no object you can do what ever you want but  if you are like most normal people monies is an issue and it will get to a point where it will be more cost efficient to just purchase a 951.  It is very important that you sort this out as early as possible (one reason why making a list with expenses is important). 

Some of the questions you have to deal with are: How much boost / hp do you want?  Be realistic here. This will dictate if a 951 is in your future or as I have pondered starting with a 951 and converting it to a supercharger (This may be my next project).  This is where you need to make a choice.  If you don't have a money tree in your back yard, and you want 300HP from you 944, just stop and go get a 951.  If you are looking for 200-225Hp from your 944 then read on.

How much can you spend?  This is the tough part.  What ever the amount is budget fifty percent more.  I was aiming for under $1000 originally.  I thought I could do it for $750 or so but things changed that necessitated that I spend more.  With the $750 figure in my head I went to my wife and told her that I was going to be spending $1200 - $1500 to supercharge my car. 

An example of this is:  I was originally going to have 6-7 LBS of boost.  But due to getting a pulley that is smaller than I expected I was all of a sudden looking at 9-11PSI.  This made inter-cooling and some form of timing control a necessity not an option to be added later.  It also mandated that I get better control of my fuel.  This included a M2035 fuel pressure regulator from BEGi Engineering   

My goal is to get roughly the same hp as a stock 951.  I am trying to get to around 200-215 hp at the rear wheels.  Anything more than this and I think that and will find that keeping it at a cost that is reasonable will be a is the problem and that reliability will become an issue. The end result is to have a care is more drivable.  This inevitably means that you want torque and it is wanted as close to idle as possible.  In short you want the feel of a V8.  While I am on the subject of V8's it should be noted that this is another possible solution to your HP needs. My limited research sais that you should expect a minimum of 3-4K (I bet more) out of pocket and a whole bunch of fabrication.  This is a whole different road to travel and then if you want you can add in forced induction and the sky is the limit in terms of HP.  I have always wanted to put the motor from C5 Z06 in to a 944/951/968 but that is another project for another day with a whole different budget.

My goals.  To make my car faster.  Make my car more fun. Ya I know but that is really it.  Now how much faster and how much fun is where you have to start making decisions about.  Honestly I did not know the answer to this question because it involves several huge variables.  However the two that always seem to come to the front are time and money.  The other problem is that if you don't have the time you can spend money so even with in just these two variables choices will need to be made.

So I had to then come up with realistic time and money goals and let this limit / guide my project. 

The Monies.  I want to get it done for under $1,000 in parts / fabrication costs (Actual cash I spend).  Time is also important as I have 4 kids and a wife that get jealous of my car if I send to much time with it so time versus cost has to always be balanced

So now it is time to start a balance sheet.  I am including a market value column for things that will reflect what something would cost if you had to purchase it from a supplier or even worse new.  Basically it is the cost if you don't want to spend the time looking for a good deal.

Note: This is a work in process and at any given time there will be stuff on this list that will probably not be used and re sold or I will trash it while trying to figure out something.  When I finally get this thing finished I will publish a complete parts list of exactly what I used that will eliminate the R&D stuff.

So has this list scared you yet? It scares me. It is my $$$ and is adding up!  Like I said earlier this is not a cheep undertaking I am betting I will be in to this for 1.5-2K  One of the first questions you have to answer is do you want to get into the motor?  This can mean new pistons or head work or possibly a new or better head gasket.  

The second thing is you have to figure out what boost levels you will be running.  This is key to determining how much you will be spending.  that I don't want to blow things up. I will need to make a maximum boos of around 7-9 PSI with inter-cooling and say.  With out an intercooler I would not go above 5-6PSI.

Ok this sounds simple enough.  Now all I have to do is get a supercharger that will make up to 9 psi with my stock crank pulley (5" is what the 944 has).  I probably could have used a M90 but they are quite large.  Looking at the math a M62 seemed to be a much better "fit"  This was based upon the recommendations of several places that sell them. I also noted that the motors that use the M62 were much closer in size to the 944's 2.5l than those motors that used the M90.  Other considerations when selection a supercharger was how they mount to the motor and how you are going to plumb the intake tract to it.  Both the M62 from a Mercedes Benz C-230 Kompressor and a M90 from a Ford Supper coupe seemed to be the best when looking at these two issues.  The intake and exit ports on both these units make the fabrication of the hose connections rather simple.  I also found that the mounting holes on the housings were in good locations that make mounting of the units rather simple as well. while allowing space around the unit for plumbing.  I also looked at the GM M90 superchargers and it became apparent very quickly that they were not going to be as adaptable due to them having an odd shaped exit port that is designed to bolt directly to an intake manifold as well as a built in 90 degree bend in the intake that world be difficult to adapt and plumb to.  This makes mounting more complicated in a custom design more complicated as they use the outlet port as the mounting point.  The M90's from T-birds (supper coups) were an option, a good option, but they are very long making fitment more difficult than the m62.  I also noted that the M62 would be in is "sweet spot" in terms of RPMs when paired with the 944's motor as they are very close in displacement to the 2.3l motor form C230.  The drawback to the M62 from the C230 is it has a huge magnetically activated clutch assembly that has a 3 1/2" pulley on it.  After doing the math  (reference my spreadsheet) It became clear that if I ran the stock pulleys on both the c230 unit and the 944 motor I would end up with only 2-3lbs of boost.  This was definitely not worth it the effort of the install to only get 2-3 lbs of boost!.  Put that through an intercooler (although it would not be really worth it) and you would be down to some where in the 1-2PSI.  Basically unless.  So then I started to think.  One option was to see if the front section of the M62 would bolt to a M90.  I was told it would.  I have since purchased a M90 off eBay and the tow shouts are not interchangeable.

The other option was to see about getting a custom made pulley for the 944.  This looked plausible but I think there would be some fitment issues with the timing cover and I really did not want the added mass at that distance spinning on the crank especially since the oil pump is right there and is kept secured by the friction fit of the crank bolt compressing everything starting with the pulley.  If there was a failure of the pulley it could lead to an oil pump stoppage and that means almost instant motor death. (This happened to my car but the pulley failure was caused by hitting a battery at the glen "at speed")

I have looked at both the M62 and the M90.  Both mount very similarly.  The M90 as tighter fitment issues with the plumbing then the M62 due to size and the length of the shout compared to that of the M62.  Both plumb the same way.  Both mount independently of the plumbing.  It should also be noted that the M90 seems to be the unit of choice if for no other reason they are uch more available at any given time there are 5-20 of them on eBay.  They have been used with success making them a good choice. But since I like the plumbing of the M62 better and that the snout is much shorter on the M62 and they mount with 4 bolts instead of the three on am M90 I am going to go with the M62.  Additionally the short snout on the unit moved the unit forward. This gives more room behind the unit for plumbing as well as keeping it clear of the motor mount and the brake and clutch maser cylinders..  The short snout also reduces the lever effect that the long snout on the M90 creates.  The short snout of the M62 allows for the unit to be centered over the mounting bolts of the mounting plate reducing strain/flex on the mounting plate allowing for me to use aluminum instead of steel saving about 10 lbs   This also reduces stress on the mounting points of the housing of the unit as well.

So in short I will be using the M62.