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# Selecting a supercharger

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Hey all, im toying with the idea of adding a supercharger to my Nissan KA24DE 2.4L 4cyl just for something different.

Can anyone help with the calculations for selecting a supercharger? will most likely be a roots type as that seems to be what most factory cars have and id be looking to pick up a good second hand unit, something like a M45, M62 or M90

I found the performance maps for these chargers which use M/hr for the air flow.

So let me know if I got these calculations and working is correct

2.4L 4 stroke engine flows 1.2L per revolution.

with a redline of 6000rpm I multiply 1.2 x 6000 = 7200L/min

I need m/hr to suit the performance map so multiply by 60 to get to hours (7200x60=432,000L/hr)

divide by 1000 to convert to m3 = 432m3

Engine isnt perfect so working on a volumetric efficiency of 0.85 (432x0.85=367m3)

Thats without any boost, i'm thinking of running up to 10psi which is a pressure ratio of 1.68

So am I correct in just multiplying the 367m3 by 1.68 = 616m3

So I plot that point on the map. Redo the calculations for 2000rpm and get 205m3 @ 1.68 pressure ratio and plot that point and end up with this on a M62 map (Red line)

did the same but for 7.35psi (1.5PR) 183m3 @ 2000rpm, 550m3 @ 6000rpm (Green line)

So yeh first of all just wanted to make sure my working out is correct?

what happens if you operate to the left of the map? I notice the lowest supercharger speed on the map is 4500rpm what happens below that speed?

I got a bunch of other questions but I will stick to those for now.

Budget and power/torque level aimed for?

The former is the sticking point for many as, unless you have the equipment and smarts for it to build from scratch, a kit is often the cheaper, overall, option even if it is a big chunk of change.

On that, there are several on the market and, either way, screw type may be best overall and centrifugal for top end - which should be a bit higher than the 6k you cite.

I’m a mechanic and Fabricator.

I will be putting the KA24DE into my Datsun 620 Ute, she is my workshop parts car and general utility vehicle and gets use for collecting loads of firewood, quite light car around 900kg so big power levels are not required. Neither is a high rpm screamer. Torque is the aim.

which influenced the choice of a KA24 over a SR20 or CA18.

factory KA24DE spec is about 110kw @ 5600rpm and 217nm @ 4400rpm (engine)

7-10psi from a roots or screw SC would just be a nice bump across the range without me needing to build a serious motor.

Compression ratio standard on the truck motors is around 9.3:1 not sure if that will cause issues?

but yea once I’ve chosen a supercharger I plan to get a bare unit and will fab intake manifold and belt setup to suit.