Our calculator has all the detailed math built into it… this post has some oversight for sure…

As far as pressure ratio vs density ratio goes… I’m adding that feature into our horsepower calculator as we speak… maybe I should write up all my work as it’s been a while since I’ve blogged on here…

I’ll give you an example i just ran on the beta version of the new calculator…

160 hp engine at 2.0 pressure ratio with a 60% efficient supercharger puts out 188hp
Same setup adding in a 70% efficient intercooler spikes the density ratio giving us a final power figure of 272hp
Both figures are less than the ideal power figure of 320hp because the density ratio lags the pressure ratio based on the heat rise due to the compression process…

Water/Alcohol injection also follows this same principal where you trade off some volumetric efficiency (as the water/alcohol mixture displaces some intake air) in exchange for lower intake temps and a higher density ratio… doing this properly gives an overall positive result on horsepower where you trade off 5% of your volumetric efficiency for example for a 20% increase in density given you an overall boost of 15% horsepower …

All this math is coming in the power calculator version 4.0 … and people will be able to get exact modeling of their engines including the inherent VE of the motor and how that affects intake flow as well as full temperature modeling for the supercharger and intercooler and water injection system to find a realistic (rather than idealized) setup to reach their power goals safely

I just wanted to point out what I think is a slight error in the beginning of this entry. I think I have seen it correctly in another post, but here you say that a 1.5 liter motor would ingest 1.5 liters of air per revolution. Since we are typically talking about 4 cycle engines, it should be 1.5 liters for every two revolutions.

The pressure ratio is a little hard to figure too. If you pump twice as much air through the supercharger than the engine would normally ingest, you will only get a 2.0 pressure ratio if there is a perfect intercooler and no temperature rise. Even if you have 100% adiabatic efficiency compression there will be temperature rise and you will see more than a 2.0 pressure ratio.

Maybe people would appreciate an entry talking about the different types of efficiency and what they mean. The terms get thrown around a lot, but I don’t think people really understand them. A description of how an intercooler, even with no restriction, lowers supercharger boost and increases hp would be good too.

Peter

For supercharger sizing, I’ve built the power calculator found here:

http://www.superchargerperformance.com/the-power-calculator/power-calculator-v2-3

Which gives you a list of the 10 ‘smallest’ superchargers that can meet your power , flow, and boost requirements. The reason I list from smallest to largest is that the smaller chargers typically have less drivetrain loss associated with them so the software recommends the smallest supercharger that is capable of meeting your power / boost / flow goals with minimal drive loss.

As far as gearing goes… the equation is very simple:

Supercharger pulley diameter = drive (crank) pulley diamter * (engine redline / supercharger redline) * (supercharger peak horsepower / target horsepower)

Let’s put some numbers to the equation:

Say I have a 120mm crank pulley, a 7200 rpm redline engine, and I’m using a supercharger capable of 450hp @ 18000 rpm supercharger redline.

If I’m shooting for 350hp from this buildup the results are as follows:

My snout pullet = 120 * (7200 / 18000) * (450/350) = 61mm

to check this

when the motor is at 7200 rpms
the supercharger rpm = engine rpm * crank pulley diameter / supercharger pulley diameter

supercharger rpm = 7200 * 120 / 61 = 14163 rpm

Because of intercooler pressure drop, and depending on how much boost you are running you might have to ‘over gear’ the supercharger by some 10 to 15% to get the correct boost at the motor.

For example, building on the last example, if your target is 350hp @ 8psi …. and you have an intercooler with a 2psi pressure drop then to get your exact gearing for the supercharger you really want to run the previous equation shooting for 380hp of charger flow @ 10psi of boost

which will leave you with 8psi in your manifold.

The resultant pulley size if you re-run the numbers is :

56mm as opposed to the original ‘ideal’ calculation of 61mm

I don’t do supercharger gearing calculations in the power calculator yet, but it’s coming soon in a version update.

OK, something that is never stated anywhere, it seems: what sizes of superchargers are best for given engines, and what gearing (pulley sizes)? For instance I am thinking of putting Lysholms on two three of my cars: 1) 1989 FWD CE96 Corolla DX diesel commercial (no back seat, leaf rear springs) on which I’d like to replace the factory 2C-T turbo unit with a Lysholm to hopefully keep the head from cracking; enginew revs to 5000 2) 1996 AE111 Toyota Carib BZ Touring 1.6-liter 20-valve redline 8000 3) Subaru Alcyone SVX EG33 3.3-liter (year unknown) fitted to a 93 VW Microbus, assuming 7200RPM redine. For all of these I want as much power and torque as possible without affecting reliability or drivability; the vehicles will be daily drivers, not racers. Can you e-mail me suggestions, or tell me where I can get good answers?

As far as I know manguson has two types of coatings , one is the typical Teflon seal coating used by OEM’s on later generation roots style compressors. The other is a harder coating that is water / alcohol / methanol / fuel / nitrous injection compatible where spraying liquid before the supercharger will not hurt the rotors nor strip the coatings.

http://www.magnusonproducts.com/reman/index.htm

Make sure you explain to them what kind of setup you’ll be running and they’ll be able to give you the right coating service.

As far as DIY coating I have no idea, but my best guess is that this technology trickled down from power generation turbines… here’s an example:

http://www.calltru.com/services/coatings.html

Thanks, Jirka