Thread: I Need More Power Scotty

Originally Posted by County3.9

Ben,
Can I fiddle with this myself or do you recomend getting it done by someone who has a clue???
Col

Anyone who can use a spanner (competently) can time a 4BD1 and adjust the fuelling. I re-timed a (OZ Built) 110 county in the middle of nowhere in Guatemala using only the tools we had with us!!! So it is definitely a DIY job

If adjusting the fuelling yourself, only make very small adjustments at a time, and take it for a drive in between each adjustment - and also get someone to watch how much smoke (if any) is emitted on full acceleration.


EDIT - Justin - Your rangie sounds like a beast - any pics? Will be interesting to see how much extra power I can wring out of my 110... We will have to have a race across the nullabor when mine is finished.

I don't wanna hijack this thread, BUT......

I just can't seem to find any intelligent, free source for sizing an air-to-air intercooler.

And before you all say "biggest is better", it is NOT: in fact, if you go too big, the pressure drop caused by air resistance in the IC causes a DROP in performance. Go read up on this.

So again:
if I have the proverbial Turbo Diesel, let's say a 3.9 Isuzu 4B1DT for instance, how big is the smallest and/or optimum size for an IC?

A 6 liter TD motor runs a 100cm x 64cm x 6.cm core. That's obviously a truck engine, and like our TD motors, built for sustained power output.

A typical after-market core size would be 60x30x7,5cm (24 x 12 x 3 inches for you bloody Imperialists....)

But what is good for a 3.9 Isuzu?

OK, let's get to airflow:

3900cc x 66 revs per sec / 4 cylinders = 3.9 cubic meters per min. (3900cc = 3.9L, 1000L = 1 cubic meter)
That is equal to 3.9 x 35.3 = 137.7 Cubic Feet per Minute.
(Conversion tables Cubic metres to cubic feet)

(Can somebody just verify my maths?)

So we can say our Isuzu at peak revs will be able to flow about 140 CFM.

Some sites state a "rule of thumb" of HP x 1.5 = target CFM.

So if our CALCULATED CFM is 140, then our ball-park HP on the Isuzu would be around 93HP.
Does that sound right for a stock 4B1DT?

OK, so now we want to run a full 1 BAR: that implies a 2 x compression.
So that means our IC must flow a minimum of 280CFM.

Now 280CFM is small bananas when it comes to ICs.

Can we then say that Garrett's web site is correct, and their smallest IC is OK?
TurboByGarrett.com - Catalog

Part Number

Hot Flow
Length (in)

No Flow
Height (in)

Cold Flow
Width (in)

Core Weight
(lbs.)

* Horsepower

Type

703521-6001

6.0

12.0

4.5

9.0

180

BP

So a 6x12x4.5 inch IC will do the trick?

Bell Intercoolers say 283 CFM is possible from a 4.2 x 6 x 3.5 inch core:

Bell Intercoolers | Air to Air Intercooler Cores

But then I found this:
Horsepower (hp) = 0.533 * intercooler volume (cubic inches) + 50.17
So if we want to run 150HP from our 3.9, here's what happens:

150 = 0.5333 x IC Vol +50.17

that means, by substitution:

IC Vol = (150 - 50.17) / 0.533
= 187.3 CFM

So a 280CFM plus IC will work just fine.

An IC that can flow that amount of air is around 12 x 5 x 3 inches (3 inches being the standard core thickness). So 12" x 5" is L x H.

Any combination that totals 60 square inches x 3 inch thick will do the job:
- 5 x 12
- 4 x 15
- 3 x 20
- 6 x 10

In fact, that gives an internal area of 60 x 3 = 180 cubic inches. Hmmmm.

Garret = 6 x 12 x 4.5 = 324 (that's pretty big, but fits the numbers for 180HP)
Bell = 4.2 x 6 x 3.5 = 26.67 (that doesn't look right, does it?)

Then I found this:

Internal Flow Area (in3) =


So:

Internal flow = 6 x (150) / 100
= 9 in cubed

So then the Bell figures son't look too shabby.

Now I'm just confused.

A bigger intercooler has less pressure drop.

A turbo intercooled 4BD1T with 15psi boost at 3000rpm will suck about 300 cft/m.
At that point you're pushing approx 130kw with safe EGT's.

Thanks Dougal.

So my only mistake was under-estimating the power output on the 4BD1T.

OK, so we take a 2.7 non-intercooled TD motor that currently pumps 100HP:

If I add a 6 x 12 x 4.5 inch IC, and we assume 70% volumetric efficiency, can I say that I will get a 30% increase in power without significant fuel pump adjustment?