Eric Dvorak

Bernie, I think if you go with 40# injectors you'll have fuel dripping out of your tailpipe, or poor atomization/ flame propagation. FAST calls for 30# and I've heard some have used stock 24# injectors with increased fuel pressure for un-intercooled 4-5 PSI boost applications.

Z

Just to help clarify (maybe), the outside air temperature on the day of the dyno was in the upper 40's as Tim mentioned. The car had been outside waiting for it's turn on the dyno, and so the water temperature in the intercooler would have been the same as that outside air temperature. The temperature that the dyno recorded and corrected the horsepower numbers to was 60.08 degrees, so maybe 10-15 degrees higher than the water temperature in the intercooler. So maybe roughly a 3-4% difference in power compared to the dyno corrected numbers as a result. This would have been on the first pull when the car was put on the dyno. The dyno run pictured was the third pull in a series of pulls. No temperature measurements of the water were done, so there's no telling how much the water had heated up from the first two pulls, but it would have increased to closer to the 60.08 degree temperature to at least some extent, reducing what corrected power difference there was from that maybe 3-4% difference on the first run. In other words, the biggest discrepancy due to the colder water would have been maybe 3-4%, that would have occurred on the first pull, and the discrepancy would have been reduced to some extent on each successive run.

Eric Dvorak

Marc, If your friend is using freon as the cooling medium you better stock up on the SPF 200 sunblock due to the increasing size of that ozone hole. <img src="graemlins/c.gif" border="0" alt="[ouch]" /> I've talked to people that have used their a/c evap. coils as intercoolers but found out through dyno runs that the coil didn't flow well at high cfm's, couldn't maintain a good temp. drop across the coil and lost quite a few hp running the compressor (and load resistance on the alt. from the a/c clutch). It sounds good in theory but the truth came out that the water to air ic was much more efficient. Hey what about nitrogen, -325F, now thats cooling!

Dozman

Eric,

To solve the problem of refrigerant flow one could use a refrigerant pump. Costly yes, but it will solve the problem definitely. We use refrigerant pumps all the time in the commercial refrigeration industry for instances like this. <img src="graemlins/wave.gif" border="0" alt="[byebye]" />

John D

Z

The most practical approach I've heard of as far as using an A/C based intercooling system is something patented by Ford a couple of years ago. The A/C is used in addition to an air/water intercooler. The A/C is used to cool the water in the air/water intercooler's reservoir, keeping that water below the ambient air temperature. The water has a large thermal mass, so acts as kind of a "cold storage facility" until it's needed. Flooring the gas pedal cuts off the A/C compressor and the power it consumes, and the intake charge is cooled by the stored cold water. The water will eventually warm up, but because of it's large thermal mass it's not going to happen right away. You aren't going to keep your foot to the floor for too long if you're making good amounts of boost, so the cold water would last long enough for the period of time on boost. When you back off of full throttle, the A/C compressor kicks back in to start cooling off the water in the reservoir again, and building up the stored cold factor.

Dozman

Z,

Thats a very good idea. The system your describing is called a cascade system. Great application. That will work.

I will have to sketch that in the to do list. Maybe not I won't be needing that much cooling but its a great trick.

Have to love thermal dynamics.

John D

Weissach1982

Does anybody have any opinions on what would be the overall best supercharger for the 928, concerning, reliabilty, power,price, etc..Also..where can you put the air/air or water to air intercooler under hood and how does the plumbing affect the space in there?

Bernie

Hey Eric,
Thanx for the info on the injectors. I am going on a lot of hear-say with some stuff so it is nice to get all the opinions. Good, 24lb injectors that have been flowed / matched will stand for the 4-5psi install until someone brings up something else.

Cheers

Z

The best supercharger really depends on what exactly you want. Space, ease of installation, how much power you want, how much you want to spend, and noise are some of the different factors to consider. There's kind of a comparison that might help at <a href="http://reviews.stangnet.com/Power_Adders/" target="_blank">http://reviews.stangnet.com/Power_Adders/</a>

There are some pictures of Quick Carl's supercharged '78 at <a href="http://www.p-caronline.com/directory/quick_carl/" target="_blank">http://www.p-caronline.com/directory/quick_carl/</a>
The air/water intercooler is that thing mounted back by the firewall, and a little towards the passenger side. There's actually a fair amount of room under the hood because the stock airbox isn't used.

You may notice Carl's favorite quote listed there on that web page. I'm guessing Carl heard that a few times before he put the supercharger on his CIS 928, and that probably also goes for Jim Nowak before he put one on his CIS Mercedes.

srv

Hey Z...

Nice posts; very clear, articulate, and informative! How did you learn all of this??

The link to the horsepower calculator is a nice tool.

What I really liked was the link with all the 928 dyno information as it gives one an idea of how much power you can expect from a given set of mods.

By far, it appears that supercharging is the way to go.

Not only are the two supercharged cars making more horsepower than the rightfully vaunted 'White Car', but it's waaaay cheaper too.

Now I am saying this with the perspective of owning a street car, versus the demands of owning a race car that has to conform to strict rules, etc, and run at high RPM for a long time like the White Car, so please, I'm not knocking anyone nor their car.

But that chart does illustrate what a great horsepower value a supercharger is, especially for a street car as it's a relatively simple bolt-on.

Again, for the hundreth time, it's emissions legal which should be foremost in everyone's mind contemplating an engine mod which still has to pass a smog test every couple of years.


Hi Bernie...

Where did you get your brackets and all? I'm glad other guys are considering this mod too!


Hi Randy...

Since we both have the same car, can you please provide some details on your setup? Please feel free to provide as much detail as you'd like! :-)

Such as which supercharger, where did you get the aftercooler, how many cores, was it a kit, etc...

George 911-V8

What about that guy marcus in southern california isn't he the 928 blower motor wizard. I have never heard his comments on the blower application since this thread started. He claims to be the man with the plan. I have been waiting for almost two years for him to finish a friends motor.This guy has been paid up front, I guess rome wasn't built in a day. Still waiting

George 911-V8

I hope marcus does respond to this thread. I went to visit his shop in southern california back in early november of 2002. He told me then that the motor was only a couple of days away for shipping, still no motor but a lot of bull**** stories.

George 911-V8

<a href="http://www.marcus3.com" target="_blank">marcus3</a>

John..

Regarding fuel enrichment:

Simply plugging in large injectors will more than likely yield a rich mixture under normally aspirated conditions, since the fuel injection brain might not be able to correct the mixture at idle.

My car left Callaway with (8) 30 lb. injectors, and two additional 30 lb injectors powered by the microfueler. To compensate for NA conditions, Callaway wound the spring tension up on the air flow meter. This worked, but the car was still fat NA. It was so fat, I could run with only one extra injector firing under boost... I would bet I could have even gone without....rich down low and matched under boost wastes a lot of fuel...and power.

I switched back to the stock 19 lb injectors, set the fuel pressure to stock and adjusted the AFM until it ran properly. I estimate at least 20 more ponies, just from bringing the fuel mixture in line with where it needed to be. Remember, I still have two 30 lb injectors which richen up the mixture under boost. Without these I would be in big trouble...

My setup has a microfueler system, which is a total stand alone piggy-back block box. It reads engine RPM and manifold pressure and dials in the proper amount of fuel. There are some adjustments, but it is still a crude way of doing things by today's standards.

Changing all 8 injectors will probably work, but the car will be rich down low off the manifold pressure. In my case, in closed loop, there was absolutely no way for the brain to compensate, there was just too much fuel in there. Thus the reason the car left Callaway without an O2 sensor. There are other stand alone piggy back systems available today which would work well, or one could use a MAP sensor and a programmable black box which sends a tricked signal back to the brain telling it where to set the pulse width on the injectors. Callaway ran 10 lbs of boost on their Vettes with stock injectors at all 8 ports and two additional with the Microfueler.

I don't think simply changing injectors is the best way to go. You could do the same thing but have more resolution with an adjustable fuel pressure regulator. Going from 19 lbs up to 24 lbs would be very, very easy, plus you can go less or more if you really need to and stop anywhere along the way. Remember, fuel pressure is automatically increased when the back of the regulator sees positive manifold pressure...clever way of doing things.

Check with Devek for an adjustable pressure regulator and a new damper. The old cars have two pressure regulators, you replace one with a pressure damper and the other with the new regulator...then you plug the extra return line to the tank. I put my adjustable regulator on the PS and the damper on the DS....it worked flawlessly.

Randy Page

Hi Folks,

As for fuel changes for a supercharger, if you are currently running 24psi injectors, and only plan on running 5psi, you should be fine. Just have the injectors cleaned/balanced by someone like Tim Marren at Marren Motorsports.

I know of three of us with supercharged 87+ 928's, and one with an 85 (all with LH-Jetronic) that are running 30 PSI injectors and approx. stock fuel pressure. Three of us are using RRFPR's with Vortech FMU's to increase the FP under boost, and one guy is running with only a RRFPR. AS far as I know, none of us are having issues with the cars running rich when not under boost. It seems that the LH brain is smart enough to compensate for the larger injectors by reading the output from the O2 sensor.

Randy

87 S4 Auto Black/Black
Supercharged & Intercooled