Ahmet

I'm looking at a supercharger for a total of <$500, with 5-6psi of boost for around a 50+hp hike. I just started my new job as a mechanic again, and can use the shop for this on afterhours/weekends. Anyway, I'm thinking a roots type from a Thunderbird, it would be mounted above the alternator, probably with no intercooler (but possibly a water injector, just picked up some windshield washer pumps, don't know if they can provide enough pressure though). However, I'd consider mounting it where the AC compressor is, if I need the space (but I'd rather keep the AC if possible).



Anyway here's how I'm planning to handle the possible problems:

Readjust the DME baselines to 3% retarded timing, and 6% richer air/fuel mixture. If further modifications to the fuel/air mixture is needed, I'd consider a 5th injector, or replace the injectors with something larger, or possibly a boost dependent fuel pressure regulator (or if I'm coming close to budget limit, a generic high pressure fuel pump near the tank).

If timing retard of 3% isn't enough, I'll consider the cheapest MSD unit I can find that'll retard the timing based on boost and/rpm. I'd like to avoid this step, and I think I can, considering that the DME can retard the timing further then stock, since the baselines are already knocked back 3 degrees. An even more cost effective way to deal with this could be to reprogram the EPROM chip in the DME. I've talked to some dude on the net who says he can burn an EPROM to any necessary input, within somewhat reasonable parameters for $>60.

I already have a straight pipe in place of the cat, I'll probably go to a straight through muffler as well.

The intake on this unit would be very near where the brake booster is on my 84 944, if mounted in place of the air box. From there, I'd have one bend down, and stick the AFM, and right after that the air filter (probably a K&N cone).

The boost(-ed) side of the supercharger would end up under the unit (if mounted in the usual way, it COULD be mounted upside down without much trouble, and have the boost side above it, or on it's side which would be a good bit harder btw, and have the boost exiting on either side. I'd have to route it to the throttle body, the problem is the supercharger outlet is a square openning...



(the intake side is also a weird shape, but since the intake side won't be boosted, fitting something shouldn't be a problem there):


Anyway, there are three main problems I see with this thing, these are mounting/brackets/plumbing, and vacuum for the brake booster/other engine related vacuum possible problems(I think I can fine tune the rest of drivability problems that are sure to arise without too much trouble).
And I plan to deal with them as follows:

Get a supercharger off an intercooled model, as those come with perfectly round fittings on both intake and boost sides, which would be much easier to work with. Make brackets bending metal, and can bolt them to engine lift points by the stock AFM location, as well as balance shaft housing bolts. Alternator, AC, and supercharger would be driven by the same belt, tension adjusted via the AC compressor, as it is now. Vacuum would probably be provided by a vacuum pump, and a small reservoir somewhere, (how's this done on 944 turbos btw?) unless the supercharger has a vacuum port on it, as I'd imagine some would.

If I can incorporate piping, I'd definetely consider an intercooler, but I'll probably stick to a water injector on the boost side for now. To keep the cost low, I'll probably use PVC, or steel where I can afford it for the plumbing.

Does anybody see if this is impossible for a certain reason, or a good idea, etc.?

I welcome all ideas, ups downs to this, and all comments.

PS: I'll also consider a 3.8 GM eaton supercharger intended for use on GMs (are these units really different?), but those seem to be impossible to find intercooled, and I need the square to round fittings for the supercharger. BTW, does anybody know if it's physically impossible to fit that SC under the hood at my planned location? I wouldn't mind cutting the hood for clearence (and covering with a 924 Carrera GT hood scoop). But if the supercharger is simply too long to clear the brake booster, I'll have to look at another model, which is where the GM eaton comes into play (don't even know if that one would fit). I'm seriously thinking about just buying a used set up, and starting this, instead of taking too long to think it out...

Thanks,
Ahmet

Matt O.

Ahmet,

That sounds like you've planned that all out. I don't know much about making superchargers, but I'm really good at helping. I'm only 2.5 hours away from you so when you start this please give me a holler and I will drive up and help you. The only thing I would request in return is that I can do it to my 944 if it works! The <$500 is right down my ally. This $4K for a supercharger is sick.

I'm serious about my offer, let me know.

-Matt

Ahmet

I've started contacting a few places, and finding more specific info right now. Once I'm ready to actually go through with this, I'll make another post...

I'm new to superchargers too, and I've been doing some research for about a week now, I figure a week or so more should have me covered. There's a few things specific/weird to eatons I need to perfectly understand before I undertake this, but I'm optimistic. There's a couple of things I need to do very carefully, such as the throttle body being before the supercharger (and not after like I posted), in about a week I'm guessing I'll really know what's going on. I'm taking out my alternator tuesday, and I may not want to put it back in before the supercharger takes shape, so who knows.

Thanks for the offer for help, I'll get back to you on that one. Even if I don't need the help though, I probably wouldn't mind if you stopped by (as long as we planned it out ahead of time) to checkout how things are going with my car...
Ahmet

Danno

If you're only going with 5-6psi of boost, you probably won't build up too much heat, so I wouldn't worry about intercooling.

Look at some of the rice-car market for boost-dependent ignition and fuel-controllers. MSD I think makes a bolt-on ignition unit that will retard the spark based upon the manifold pressure. Also Apexi I think, or Accel makes a 5th injector unit that meters additional fuel based upon boost pressure as well.

Both of these would add boost-sensing logic to your stock computers and saves you the hassle of trying to mess with them.

Ahmet

Danno, I'm going to adjust my DME regardless, as it's very easy to do. If this isn't enough (but I'm thinking that it will be), I'm going to have custom values burned into the EPROM. That should be enough for only running 5-6 psi of boost. I'd like to avoid anything fancy to keep this thing cheap.

Thanks for the response.
Ahmet

jim968

Ahmet... it should be possible to find a metal fab shop that can make you a square-to-round adapter, once you have accurate dimensions. It might not be elegant or flow-optimized for cheap $$, but it shouldn't be too expensive. I'm picturing basically a wedge-shaped box, w. a flange around the top, and a round outlet coming out of the deeper side wall. Dunno if it'd fit space-wise, tho'. Mild steel'd work, esp. at low pressures.

Jim, wishin' ya luck...

Craig944

Let me know if I can help...
I have alot of extra parts around for my porsche (extra injectors and stuff).

Tim Too

I have an Eaton 3rd generation M62 Supercharger in a Rimmer install. Looks like it would be easy to do with the 4th gen. that has the built in bypass like your diagram. Just need to have someone fabricate an adaptor from supercharger outlet to intake manifold. Air goes from round K & N in place of stock airbox, to the airflow meter, to the charger, to the manifold. Uses stock chip, increased fuel pressure. Needed water injection to avoid knock on pump gas. Water kicks in at 3psi boost, blower makes 9lbs max boost with at least 7lbs by 2000 rpm.

Matt O.

What sort of numbers do you get in performance if you don't mind me asking? Quarter mile? 60? HP? etc? Thanks for your time.

-Matt

Ahmet

Jim968, I'm sure I can find a metal fabrication/machine shop that can do the work, but I don't want it to get to that point, as to keep my investment in this VERY low, comparatively speaking. If all it is, is going to be a crude round to square fitting, I can weld thich square metal plate to a rather thick, and large piece of piping! I just want the factory fittings that the SC was originally used with, to avoid all these 'extra' steps. I think mounting the thing will be just as hard as plumbing, besides the boost side of the SC to intake plumbing, and possibly the intake side of the SC to a round fitting, there should be no other significant problems.

Danno, I can offer a more indept explanation of my reply to your post now that I have some time: It seems that many have supercharged (to higher pressures than me, with no intercooler, OR water injector), without even backing off timing, or any other mods BUT a rising rate fuel pressure regulator. I think adjusting the DME to 3degrees retarded timing, and %6 richer mixture, along with a fuel pressure regulator should be good for me. Ofcourse I can modify things if I become power crazed later...

Craig, I doubt it'd be necessary, as I have a lot of parts available to me at cost, as well as many parts cars... I do appreciate the offer though.

Tim Too, I don't agree with parts of your post, such as water being necessary to avoid detonation. That may be the case at 9psi, but not for up to 6. Also, I'm mainly considering a 2nd/gen supercharger, as used in some Thunderbirds. I think one of the hardest parts of this conversion (for me) will be working with that relief (or recirculation) valve if I get 2nd or 3rd gen. But a 4th gen has an outlet that's quite complicated, so I don't want to work with it, maybe you have reason to tell me otherwise? I mean I'd be looking at:

instead of something like:

I'd like more info on your set-up, as well as pictures, and anything else you wouldn't mind sharing with me.
Ahmet

Danno

Yeah, the rising rate FPR should allow you quite a lot of tuning possibilities. Better than the DME switch because an FPR adjusts fuel over the entire RPM-range. The DME switch only adjusts for a 6% richer mixture only in the mid-range. At high-RPM, the fuel-injectors will still be hitting their duty-cycle limit. When you set it for 6% richer, it hits this limit sooner.

Definitely spend $100 for some dyno tuning time to get an accurate graph of your air-fuel curve. For a copy of your dyno run, I may even sponsor you!

Ahmet

Danno, I'm going to be working part time for up to 7 more weeks (until I come up with $5k, kinda hard to do with school and all that brings along!), and buy some more CDs on a two year plan (as my 21st birthday present to myself), but after that I should be free to mess with this supercharger/idea. I just can't believe the insane prices people are considering!

ANYWAY, I think the DME adjustments change the baseline value, and 6% richer shouldn't get the injectors even within %90 of their available duty cycle. However, going over 6% richer would probably push them over to an operating speed that reduces their efficiency, but available adjustments on the DME shouldn't IMO. I think the FPR is going to be the route I go.

I won't turn free dyno time down! Where are you located? I'm in Cary NC.
Ahmet

Matt O.

CD's as in from a bank? I would go money market if I were you. Not to change the pace of this conversation but you'll get a better return with minimal risk.

-Matt

Ahmet

Money market? If you mean stock market, I think it's obvious that CDs have MUCH less risk to work with than do stocks. I mean I'll be FDIC insured to whatever I'm suppose to get back at the end of the agreed term (for me would be around 2 years). Not only do I get a pretty good interest rate, but I can be positive that my money (the anticipated amount mind you) will be there when the term is up... I'm planning to play stocks with a friend, but not with the first $5k I raise up.
Ahmet

Tabor

Money market accounts are savings accounts with a very high minimum balance. They too are FDIC insured if you get them through a bank. But CDs give better intrest rates becasue you are promising the bank that they can keep your money for x amount of time.

Maybe Matt meant to say Mutual Funds.