Outer Limits 4x4 Board

Does anyone know the CFM rate for a Nissan TD42 motor? I am looking to replace the air box on my TD42 with something else (eg Donaldson) and don't know how to figure out what size filter would be required.

Cheers

Steve

Turboed on non-turboed TD42 engine?? Turboed is around 450 CFM or more. Engines running lotsa boost will happily suck alot more than that though.

Cheers
Mitch

it's turbo'd @ 12psi, looking to increase boost to 16-20psi

I would just get the biggest one you can fit that will flow over 500.

If you cannot fit one that big maybe make one.

you can not really have too much air and I know the piddly nissan filter isn't real good.

Hmmmm, might have to rethink this. The donaldson catalogue gives dimensions for a filter housing rated at 500cfm as 14" diameter and 22" long. I could always pull out the motor to fit the air filter in

Might look to use a panel filter off a commodore V8 or something instead of the donaldson option

they guy at hitachi said i would have to run a 500cfm donaldson to get the HP that im getting in my ute ... it seems a bit strange as the standard gear
is quite restrictive

if i did fit a more free flowing intake would i get more HP?

You would be better to look towards freeing up the exhaust, if you haven't already. With turbo exhausts, the bigger the better, as you are trying to generate as much pressure differential across the exhaust side of the turbo as possible. Likwise the shorter the run to the turbo the better. This will also lower the revs at which the turbo comes on boost which is in effect what most ppl want.

Similar principle for the intake, but there are a lot more restrictions (air filter, intercooler, intake manifold, valves) so upgrading only one component is less likely to have such a dramatic effect. The bigger the better again for the air filter, but the main limiting factor to flowing more air is going to be your valves (dia + lift).

There is always compromise between flow and filtration. The Donaldson on our old truck was only 8" dia and 12-14" long and had a CFM rating of about 525, so obviously its filtration properties wouldn't be as good as the one you're looking at.

You just gotta work out what is most important to you.

working out cfm requirements is pretty easy.

first convert the capacit of the engine in litres to cubic feet:

4.2 litres x 0.03531 = 0.1483cu.ft

divide by 2 as each revolution only half the cylinders are filled:

0.1483/2 = 0.0742 cu.ft/rev

for a peak rpm of 4000, multiply by 4000 to get a figure for cu.ft/min:

0.0742 x 4000 = 297cfm

but at this rpm the volumetric efficiency will be pretty bad - guess 70%:

297 x .7 = 208cfm

for turbo boost, every 14.7 psi doubles the free air flow, so for every psi boost add 6.8% to that figure - so for 12psi:

(1+12x.068)x208 = 378 cfm

20psi:

(1+20x.068)x208 = 491cfm

but as a word of warning, high boost is very very bad for indirect injected engines and require decompression and combustion chamber modifications. You also start coming up against extremely high combustion temperatures and pressures which force combustion product back past the injector nozzle (obviously bad), and combustion chambers start melting, cracking and dropping chunks into the cylinder (also obviously bad).