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Intercooler properties - Is there a defining value?


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Hi all

I have just started breaking my Wife's Renault Scenic due to a cam belt failure and even though it's a puny 1.5 diesel the intercooler seems quite big, which got me thinking. I have seen and read about people taking intercoolers off other vehicles to put onto their hybrid Land Rover's to give them more performance, as well as buying the bespoke performance ones designed for the Land Rover engines and I wondered if there is a defining value to an intercooler that can be measured. What I mean is, if I try to fit this intercooler to my 110, how would I know I would get any improvements over the factory 200Tdi intercooler that I have already fitted? Is there some sort of airflow/cooling formula that is available for normal hobbyists to look at? I know it doesn't make a whole lot of difference without a pump tweak, but I would think that just because it looks bigger that doesn't mean it's any better.


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It's quite probably going to be better than anything fitted to your 200TDI, a) it's 10-20 years newer b) It's most likely a PSA diesel engine which are widely renowned for their efficiency and design, which means it's likely to be a good one.

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Compressing air makes it heat up. If you run the truck with a temp probe on the intercooler exit and it is high, like 50 or 60 deg.c, then there is a gain to be had. If it's doing 40 on a warm summers day I wouldn't bother. It's typically coming down from 150 (turbo exit), and the last bit is the hardest to do. And while you are increasing intercooler size to bring the hot air down as cold as you can, you are acquiring turbo lag.

Many big engines these days hope for a 40 deg.c inlet manifold temp, but the not-so-old 450hp cats used water exiting the main rad. (charge cooler) So they are happy with air at 80+, which is way better than 200+.

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The only answer is to measure the intercooler temperature in and out and the pressure in and out, before and after the change, then compare. There are 3 things to consider, being pressure drop, temperature drop and volume. You can easily improve 1 of these, and maybe 2, but very difficult to improve all 3. I had a play with the standard 300 tdi intercooler, measured temperature in and out, and pressure difference in and out. my view of the standard intercooler core is that it is very, very good, only let down by the cast tanks, giving a restriction in the in and -outlet pipes. The total flow area through the pipes in the core is very large, much larger than the 2" pipes. So I just modified the pipes to thinner wall ones, to remove the bottlenecks. It gives better pickup and marginally better pressure drop.

Also very important is the fan and the cowling to it, and channel all the air going through the grille to go through the intercooler.

I would start with buying some k-thermocouples with read out displays, I bough mine on ebay for about £10 each. You can than verify every mod you do and see the difference (Or not...). I also used a cheap digital readout to measure ambient. You will be surprised how much difference a few degrees difference in temperature makes. I still run the temp readouts, and get regularly a temp drop of 60 degrees or more. As Idris says, the last few degrees are very hard to achieve.

Here is the write up, if you hadn't already seen it:



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The science behind it is quite complicated. A better intercooler than standard is basically any intercooler that is big and thin. Lots of surface area with a thin core helps shed heat way quicker than a small thick core. I've used a saab intercooler, from memory it's about the same size as the core of a 2.5NAD or V8 rad, but only in inch thick.

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There is a bit you can visually check to compare intercoolers, first the core, number and size of the runners, this is a double edged sword lots of runners, means you get alot of surface area to cool, smaller tubes means better cooling but slower air movement (restriction) bigger tubes less restriction but also less cooling

Cooling fins or turbulators, more is good as its more surface area to transfer the heat to the outside air but the slower the outside air can move through the intercooler, a fan and good ducting will help this, mud or anything that blocks them is bad, good intercoolers will have internal turbulators as well

Thickness of the core, thin is good if you can get a large surface area but if your hard on space a second best is thickness, the reason thicker doesnt work as well as area, is as the outside area travels through it takes heat from the intercooler now with a thick intercooler the front adds its bit of heat so when its in the thicker section its already warmer so cant take as much heat from that section

Looking at your outside, are the runners rounded off at the ends or sharpe sqaure edges, rounded corners are better as they cause less drag to the outside air

As for what you can see in the top tank, if its a top tank does it have baffles to help spread the flow. Tank design makes a difference too, if the air flow has to make lots of hard turns as it flows in and out this will create turbulence and reduce flow, flairs, trumpets etc are way better than tubes that just butt up against the tank

If you can see into the top of the core in the tank, do the runners come up like in the old school copper radiators this is the worst type this is called extruded and causes turbulence at the mouth of the runners, better are flush ones called plate core they flow better, and the best type and as far as I know only available on after-market intercoolers is bell-mouthed, they have a half round shape either side of the runners this works the same as an air intake trumpet and can get as much as 3% improvement in air flow

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