944bucky

I've been looking into supercharging my 87 944S and was running some numbers to see what kind of power I can expect. This led to the question of what kind of power can I get and that’s what this is about right.
So after reading a how to supercharge book and using its equations and assumptions, here are the numbers I came up with.
Now I live in the desert so I have driven my car in temps of 120 degrees F and it has survived through that.
Using 120 degrees ambient temp and 10.9:1 compression ration I find a charge temp of 1132K. Compare this to 90F ambient and I get 1074K charge temp.

Using my known max combustion charge temp and assuming an 85% efficient intercooler on a 90F day I can calculate that the charge leaving the supercharger can be 200F hotter than ambient. Intercooler results in .15 x 200F = 30F elevated temp above ambient into combustion chamber. 90F + 30F = 120F entering the combustion chamber.

Now for the fun part, assuming the 200F allowable increase in air temp after the SC it can be calculated that a pressure ratio of 2.24 or 18psi will keep the charge temp with in my 1132K max temp!....on a day no hotter than 90F.

Sounds outrageous for a 10.9:1 compression engine right...well just wait.
This would result in 360bhp from a stock 944S accounting for sc losses etc.

Not that this is my plan, but it would be fun as hell. Plus how often does theory match reality right?

GodSpeed

at 18psi and 10.9 cr your gonna hear knock ... knock ... boom

zoxx2004

click-click---boom

Imo000

Hate break this to you, but with a 10.9:1 comp, you’ll be lucky if you can get 10 psi without detonation, let alone 18. Your calculations might be correct on paper but they won’t hold up in the real world. I would say what is achievable (using stock internals) is not more than 8 psi WITH a good air-air intercooler.

spazegun2213

If there is one thing i have learned in my short car years, its dont try to add forced induction to a car that does not have it. You will just spend more money and time than if you were trying to add hp to a car with a turbo or S/C.

its even worse with a "high strung" car. any car with a high compression ratio you cant add that much boost to. good luck if you do it though.

My advice if you want more power, sell it and buy a turbo and go from there.

Dr.Porsche

Did you carry the 1?

inactiveuser92616

I heard that the 959 used the same combustion chamber, albeit lower compression ratio. Look to the figures experienced in that engine and you probably have your answer.

Fishey

18psi and 10.9:1 is fine unless you are running crap gas...

We ran 17psi on our 306mustang with a 11:1 compression. There are ways to control knock but apparently people on this board are blind to them.

944bucky

Thats right, and less you live up north the 90F temp max would present quite an impedance to daily driving fun.

Imo000

Not blind. It’s a bit more complicated than you think. I’m not sure if the 944s ignition systems is anything like the 928, but on the 928 it’s not possible to hook up an MSD 6BTM or anything equivalent to it. One of the guys on the 928 board followed MSD’s direct instructions (they were on the phone with him) and still managed to fry 2 of them. MSD couldn’t figure out the problem so no one is using it. I have two on the shelf that I could use in the SC’d 928 but I don’t want to fry them.

Were the itnernals forged in the 306?