CFM's for TD42, intercoolers and boost pressure.

[tgaguy1]

Hi all.
I am using my idle time at work to figure out stuff on the up coming turbo charging of my Daily driver/tow truck; a 1990 LWB Safari, Diesel.
I have most components to do this and I am trying to make the calculations to see that all is well with the plans I have.
What I need is opinions on this intercooler plan.

I have a subaru water to air system. They flow 450 CFM max.
My Calculations tell me that it is suitable for a 4.2 Litre four stroke engine at 10 psi (1.66 bar absolute)
Here is how I got to this conclusion. Please correct me if I am wrong with any of this.

4.2l @ 4000 rpm = 4.2l x 2000 induction strokes per minute.
= 8400l/min
=296.64 CFM.
Thats for a n/a 4.2. So if I add forced induction...

296.64 CFM x 1.66 bar(a)=492.42 CFM.

Realistically a TD42 is not going to be revved out to 4000 rpm but more likely 3500 rpm, and certainly not going to be held anywhere near those revs. So 3500 rpm gives me a boosted CFM of 430.87CFM.

4.2l x 3500 rpm = 4.2l x 1750 ind strokes/min
= 7350l/min
= 259.56 CFM

256.56 CFM x 1.66 bar(a) = 430.87 CFM.

So going by this, the Subby intercooler system is up for the job.
Anyone agree/disagree with my logic?

Cheers

Jase

[darinz]

You logic is fine but 10psi on a TD42 is a joke and you'll be increasing it pretty quickly.
When I spec'd the filter for mine I got basically the same result. Eg at 20psi I needed 1,000 cfm so either we are both right or wrong.

IMO the Subbie I/C is too small due to the fact you will want to increase boost and then won't be able to. So I'd either fit a big air to air or get one of the cheap W2A I/C from TradeMe. However keep the pump from the Subbie I/C as they appear to be quite good.

[u13turbo]

I thought 1 bar =14psi? so wouldnt 1.66bar be more like 22psi?

[tgaguy1]

I thought 1 bar =14psi? so wouldnt 1.66bar be more like 22psi?

When calculating gas pressures,absolute pressure is used. So zero psi gauge pressure is 14.7 psi absolute or more correctly written psia or approx 1 bar.

[crazyclark31]

i'd go bigger just because way i see it the longer the airs in the cooler the colder it gets.
fyi when i turbo'd mine i up'd the boost to 1bar within a week as 10psi was bit of a disapointment.1bar brings them alive

[gqsam08]

one thing not to forget is the air temp, cold air is dence and you can fill the box with a lot more, so by fiting an i/c the hot air going in at 10psi
will come out the cold side at a lot less so this changing the cfm flow of the cooler?

am i right in saying this ??
tell me if im not lol

[tweake]

i think the intercooler would be right on the limit and starting to be a big restriction. the other factor is do you want to spend all that time and $$$ to only run 10lb boost ?
mind you that may not be a bad idea on the weaker td42's.

[coxsy]

i had less than 10 psi and engine died, but then its a fn tonne truck not a skyline