It's the number of tubes, not the length of them which matters.
To make a basic comparison, you have a guy who can run a marathon and you stick a drinking straw in his mouth, tell him to breathe through it and send him off, he gets 1/2 a mile before collapsing with exhaustion, why? Because he cannot get enough air to his lungs, so you pick him up, dust him off and give him a drink and a rest then stick a 3" pipe in his mouth (!!) and send him on his way again, he finishes the 5 mile marathon..... Your engine is just like the marathon runner.
Now for some basic maths, if you look inside a 'cooler:
You will see that roughly half is tube and half is blank, so only about 50% of the total area will actually flow air. Lets take the integrale cooler and compare it, a quick sum gives us sq" remember, only is half is tube so:
8 x 3 (x .5) so = 12sq"
This:
Is a pathetic 7.5 sq" (6 x 2.5 x .5) So although it looks bigger it will actually flow less air...
And then we return to this complete mess of an attempt, oh yes, the good old 3 x 12 x 24 double pass! (oh my god):
The air has to travel a whopping 48" (4 times further than an integrale IC) to get through it and it has a flow area of 9".
It flows less air than the OE cooler.
Jeez, I bet you could measure the turbo lag with an egg timer.
Turbo lag
Yes we just brushed on it there, you wanna know where lag comes from where tube area and pipe diameters are concerned? Well I'll let you into a secret, lag comes from the fact that not enough air can get through in the first place, not too much volume.....
How do we know for certain we are on the right track? Where to look for good designs? Other newer cars of course, here are a few good examples:
The first one is a VW, check out the well shaped end tanks, designed to give well balanced flow to all the tubes. Also note Subarus nice job, short tubes, compact and the idea of twin pipes to equalise the flow again. The Pug one is just good basic design, tapered end tanks, lots of tubes, a very bad 90' bend on the end pipe, but still, you get the idea.
So, an off-the-shelf good design? Let's look at this:
Core size is 3 x 18
This looks like a good design, 3" thick x 12 wide and 16" long tubes:
Now you've just got to do the hard bit - fitting it in the cramped space......
