Is my 3B intercooler project a failure?

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Oct 3, 2008
Melbourne - AUS
I have tried to intercool my BJ40 / 3B with an AXT turbo with an air to air intercooler.

I think I have failed as I seem to have a significant pressure drop across the cooler. Before intercooling I had set the Boost limit to be 15 PSI. With intercooler plumbed in - I am barely pushing 10PSI. (measured near inlet manafold) I already playing the boost vs EGT game so losing 5PSI is not good..

I used a ebay IC ( I thought this one might fit easiest (same side ports, only 70mm thick). Noting I have battery trays that need to be negotiated around...

I also assumed that it probably would be big enough for a low HP engine like a 3B. And it meant I only had to move the radiator back by 8mm... And I had just enough space to bring both hot and cold 2.25 inch pipes up the radiator shroud and then around a 90deg bend and on down the engine...

To check if I had major leaks - I have tried plugging both ends (welded up 2.25 inch pipe) and pumping up the IC and pipes with a compressor. The pipes do leak very slowly (15psi down to 10psi took 30 seconds and another 5min to get to 5psi)

I have also tried removing the IC and shorting the in/out intercooler elbows together.. I think roughly I lose about 1.5PSI in total in the piping..

Therefore I have to assume I am losing 3.5 PSI in the cooler...

Have I done something wrong here? Is my ebay IC crap? Is my design flawed?

Should I have invested more heavily in a better IC?

thanks in advance to those who respond..
Gahh. Your pipe work looks very well done. I wish you had asked opinions before you built it. The intercooler you chose is probably the worst design I can think of. Because it has to make a 180 turn on the far side to run back out near the inlet, the core is not nearly asgenerous asit appears. In essence you have an intercooler that's one very very long pipe. This design will absolutely maximize pressure drop all things considered equal. I would keep your inlet piping and reroute your outlet to the other side and get a much larger cooler and chuck it in front of your rad. You would want to keep it close to the rad so your mech fan will be forced to pull through it.
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cooler.jpg If you rerouted your top heater hose to it move more to the center of your engine bay, it would make a bit of room where I bet you could pull your intercooler piping up from beside the rad. Basically mirroring the driver side plumbing. I notice your intake from your snorkel crosses over your engine. Wrapping that would also help lower your egts as it will want to heat soak, raising your intake temps. Without getting into the quality issues with ebay coolers, I think this cooler design would work much better for you.
Thanks gerg...

I will take a look at how I can route the outlet out the other side...

Two more questions:

a) Would you recommend that I stick with Air to Air or take the opportunity to just switch to a Water to Air?

b) I assume I should aim to position the cooler within the boundaries of the bezel and extend down as far as the bottom of the radiator as this would be most efficient?
So for simplicities sake id stay air to air. Im bias towards air to air cus air water has space advantages, but sacrifices effeciency. Im sure ill get some flack for that, but it is what it is. Id go for basically the largest surface area cooler that will fit your bezel but keep thickness to under 75mmish (3 inches). So now when both pipes come off the same side of the cooler (top or bottom) there are flow bias that can make them less effecient coolingwise and cause backpressure to increase, but in your case id say leave the cooler as is and not modifiy it. Your battereis and such make fitment a bit of a challenge. Looks like inlet and outlet have to be both on the bottom. Lots of folks have fitted coolers very near the same as yours and had great results. The 1.5lbs backpressure is sort of unavoidable due to the extensive plumbing front coolers require. I like top mounts, but they are dependent on electric fans and thus have a weak link there too. You should be able to reuse most of your old piping and a new ebay special wount run you that much. There pretty much around 150$.
My Intercooler looks to be of similar dimensions to yours but doesn't require the 180 degree turn. It's off of a 944 Porsche.

My bad ..... The photo is on the next post.
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I was thinking more along this for it.
The problem with those long narrow coolers is that because of their small volume and long design, they tend to have high internal velocities which not only give you more back pressure but less time for actual cooling. A cooler like the one above allows the air strem not only more surface area, but also the air stream physically slows giving it more time for heat exchange. Because friction is directly related to velocity, the more your air stream slows, the less back pressure you can achieve. Don't get me wrong. It is far from ideal, but might be the best for your application. Because it also fills the front if your rad, it won't easily allow the incoming air for your rad to cheat around it. This would be especially hard with those narrow coolers as the incoming air doesn't like resistance and will just bypass the narrow core unless you force it through. Air is pretty lazy that way. Those little narrow coolers can fit into really small areas. That is their only advantage. They trade a lot if effeciency and give you a lot of back pressure to achieve it. It is interesting to note that your resistance across the core is not related to pressure, but rather gas velocity and core length. Because the core above is approx four times as deep and just as long it essentially will have 1/8th the backpressure. So now that is just backpeessure. When you get into discussing cooling ability the larger core wins hands down. Their are better designs for cores than I showed you, but that would be the easiest to fit.
Now if you Peel back the onion of the intercooler one can really get caught up debating differences that can account for several percent of effeciency. I'm not really into that sort of thing. For your application I was after greater gains than that. You always go for the low hanging fruit first.

I believe I was off on the difference from the one you have fitted compred to the larger one pictured. 4 times the cross section but half as long would net 1/16th the back pressure. If the gaps between the intercooler and the rad were sealed correctly your egt gains would be significant.
id measure your rad to the outside and get a cooler just a bit smaller. The taller the cooler the easier your job will be to seal it to the rad. It won't necessarily make the cooler much more effecient as the flow is bias to go straight from one opening to the other and less evenly across the whole core, but it is still better than narrower. That's why cross flow ports are better as they somewhat force the air to evenly go across the core. That's when the ports are kiddy corner to one another. Your fitment doesn't really allow for that. That being said I'd measure up your rad knowing that the 600mm measurement is to the outside of the ports and not the outside of the end tanks. I think they do that cus it makes it sound bigger than it actually is. That cooler you posted looks more like what I was thinking, but I'm without measurements its hard to say for sure. It also comes down to how tuff you want to make it for yourself fitting it. I'd be more inclined to make it easier on yourself if possible.
Something to think about, which is a much smaller issue, is the right angle you welded off of your air box connected to the 90 silicone bend feeding your turbo. I'm pretty sure that little turbo would much appeeciate a smooth welded 90 as oppose to that abrupt corner. perhaps something to consider after you run out if things to work on
I reckon I can change that elbow to a mandrel bent pipe in version 2....

I am going to give this 400x230x65 IC ( a go..

The OEM radiator is about 480 x 400 - so I am comfortable (I think) shoe horning 400 x 230 in there.. And if I kept it skinnier than 70mm I wouldnt have to relocate my radiator again...

thanks gerg (and all)... I will post up how I go..

You could also rotate the top of the air filter housing to aim more directly to the turbo and eliminate quite a few degree's of bends. Then aim the intercooler outlet towards the intake at a 45 angle and eliminate a couple more bends. Just some ideas.

Here is what my set up looks like, same general idea. The intercooler is the factory Isuzu unit for the 4BD2 engine I used in my swap.

started install of new intercooler today..... i have turned the turbo housing to point under airbox and modifed dual battery tray to squeeze cooler pipes beneath. On cold side i think i will replace the last 90 degree pipe with a 45 degree.....

Any suggestions before i go any further? inter_front.jpg inter_front3.jpg inter_top.jpg
That looks great. Nice routing of the plumbing. I think I'll copy it on my 3B.

The only suggestion I would make is to not use a silicone elbow on the last bend to the intake manifold. It will be fine for a while. That area will absorb the majority of the reverse pressure wave as the throttle plate closes. I'd suggest a cast aluminum elbow with small silicone connectors.

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