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Intercooler Pressure Drop Theory - those last couple HP

16K views 21 replies 9 participants last post by  P.Gadget 
#1 ·
As I understand it - pressure drop occures when the air "backs up" behind the intercooler and causes a higher pressure before the intercooler than at the manifold. Ok, I'm comfortable with that. This happens when the airflow through the compressor exceeds the max airflow of the intercooler right?

So how bad is the pressure drop on our stock I/C when running 22PSI at the intake manifold? 1PSI? 3PSI? Has anyone measured it?

The next (and bigger) question is are we more limited by the compressor or turbine flow on the stock turbo, stock hardware, and 22 PSI? I HPtuned my car myself and left a drop off of boost after 5500rpm for longevity of the turbo, but I'm wondering if I can free up other hardware restrictions, can I push 22PSI to redline? Is the cat and exhaust more restrictive of the system, or the intake and intercooler?

This may be a lot of speculation, but hardware upgrades have to start somewhare ;) No matter what I do, I can't seem to break 32lbs/min on the MAF (usually around 5500 rpm incidentally), so if hardware upgrades are in order to push 34-35 lbs/min, so be it!

P.S. water-methanol injection is in my immediate future as well.
 
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#3 ·
Can't give you the hard numbers you are looking for. However, I can share what I have seen, heard, learned, and measured.

1) '07 Redline, Wester's tune, K&N air filter, Magniflow exhaust Solo catless downpipe.
2) The catless downpipe made a HUGE difference BEFORE the Wester's tune. I mean REALLY big. Yes, it threw a cat effieciency code, but the computer did NOT "learn down" the power, even after driving the car for days.
3) The stock turbo is built for max performance in the middle of the rev range. It loses efficiency above 5000 rpm.
4) At a recent autocross I used an IR heat gun to check inlet and outlet pipe temps after a run. The ambient was about 75 degrees. The inlet was about 145 degrees and outlet was about 90 degrees. I have spoken with some tuners who have said that they saw LOWER than ambient temps on the discharge side of a bigger intercooler on their 2.0 Kappa.
 
#4 ·
Thank you for this info, especially about the catless DP.

Regarding point number three - there are two reasons why it could be loosing efficiency above 5000rpm -either the backpressure on the turbine, or compressor efficiency. I was trying to get at if we have a 2-3PSI pressure drop on the stock IC @ 22PSI, then it would make sense that the power could carry out to higher revs if the IC is upgraded and the car is retuned.

Regarding point number 4 - i think it is physically impossible to have lower than ambient temps with an air-to-air intercooler. The lowest is ambient, and i'd call BS on those making other claims. If they were using an IC sprayer or meth injection thats a differnt claim altogether :)
 
#9 · (Edited)
I have checked my 2.4 DDM stage II boost pressure

On both sides. Right off the S/C manifold and then after the I/C and the DDM I/C is awesome!! it only dropped about 11/5 PSI and it keeps this baby cool!! It will keep your intake air at ambient temperature or because of physics "As air speed increases temperature decreases" sometime even cooler then that but not much . Now considering that the boosted air coming out of the S/C is supper hot it cools it a ton!! We My friend Gary "GaryH" and I took my car for a brisk drive and right after opened the hood and felt both pipes. The one coming out of the S/C and the one after the I/C and there is a huge difference!! The Pipe after the I/C was actually cool but the one on the other side going into the I/C was so hot you couldn't even put your hand on it. That tells me that the I/C is working great! :thumbs:
 
#10 ·
On both sides. Right off the S/C manifold and then after the I/C and the DDM I/C is awesome!! it only dropped about 11/5 PSI and it keeps this baby cool!! It will keep your intake air at ambient temperature or because of physics "As air speed increases temperature decreases" sometime even cooler then that but not much . Now considering that the boosted air coming out of the S/C is supper hot it cools it a ton!! We My friend Gary "GaryH" and I took my car for a brisk drive and right after opened the hood and felt both pipes. The one coming out of the S/C and the one after the I/C and there is a huge difference!! The Pipe after the I/C was actually cool but the one on the other side going into the I/C was so hot you couldn't even put your hand on it. That tells me that the I/C is working great! :thumbs:
As air velocity increases through the intercooler the delta temperature of the inlet and outlet of the intercooler will decrease because the air has less time to transfer heat.At the same time the delta pressure of the inlet and outlet increases The object would be to keep air velocity relatively low through the intercooler with as much coil surface area as possible to keep the delta temperature as high as possible.
Although if the intercooler becomes too large internally turbo lag could start to become an issue.Because on acceleration the compressor would have to fill a larger void before pressure at the throttle body can increase.
 
#12 ·
Ah guys just so you know you are NOT talking about pressure drop, you are talking about flow. The pressure drop is the amount of boost lost in the intercooler do to it's size and design, this is why you can have to big an intercooler, if it slows the air down to much because it is to big or poorly designed you have pressure drop. The Dejon was tested against stock and the pressure drop was about 1 PSI over stock with a much larger intercooler and much cooler denser air at the outlet. This is the result of a good design by Garrett on the intercooler and decent end tanks by Dejon.
 
#13 ·
No We do mean pressure drop of PSI between the inlet and outlet of the I/C.

Yes we are aware of flow but on this post my self anyway are talking about true boost pressure into the engine. I am worried about flow as well but I am mainly talking about pressure drop from in and out. :)
 
#14 ·
I have the Dejon intercooler and see no pressure drop at all.
In 3 th gear temperature under full boost stays the same as outside temperature
In 4 th gear with stock intercooler temp raised with 23 degrees celcius
In 4 th gear with Dejon temp raised with 10 degrees celcius,so 13 degrees better than stock intercooler.
I have the BSR tune because with stock tune temperature won't raise so high.
Bigger intercooler is not always better...That's why I bought the Dejon,because I don't like the pressure to drop..
 
#15 ·
Guys, pressure drop is the pressure difference between the hot side of the IC and the cold side of the IC. A smaller, lower flowing IC will have a greater pressure drop when it is taxed with more flow than it can handle. An IC that is too large will not have a pressure drop, but will cause more lag because of the higher volume to pressurize. Don't confuse the two concepts.
 
#16 ·
That is not true entirely, smaller IC's will not flow the same amount of air due to to restriction of flow, you just can't push that much air through the pipe. The pressure drop is based on the delta of what you can put in and what comes out. If you can only put in 15 psi because of restricted flow and you get 12 out that is a pressure drop of 3 psi. With a bigger well designed intercooler you might be able to put in 25 psi because the flow is not restricted it may output 24 psi so a 1 psi drop. If the IC is to large the 25 psi in comes out as 15 psi because it takes more pressure to fill the larger volume and the flow is slowed creating a drop in pressure so 25 psi in 15 psi out. There is only one way to change pressure drop and that is to modify the IC, pressure drop is a measurement of the capability of a particular IC and is static. You can not change it with a tune, the flow is also static. The right IC has a good flow, can't be to high or it won't cool the air and it has a low pressure drop. Neither have anything to do with temperature, but it is very important they are correct to get the temperature reduction desired. Spearco makes some huge intercoolers that are very effective at cooling the air but only work well on really big high HP motors because they have a huge pressure drop due to the size. RPI makes a very effective intercooler for our cars it is much smaller that anything else out there except stock, but due to a correct flow and low pressure drop it cools effectively and works very well.

Bottom line we have all bought blind as none of the intercooler makers for our cars have ever listed the pressure drop or flow for the intercoolers. I have asked everyone of them for the numbers, Dejon didn't have the equipment but sent an intercooler to Lyndon Wester who does, intercooler is now on Wester's car numbers were good. RPI did not know didn't have the equipment. Werks same thing and Bill Hahn never replied.
 
#17 · (Edited)
Pressure drop is always a bad thing for two big reasons -

1) the turbo is working harder to achieve manifold pressure than it would with no pressure drop. This is the big one for those pushing the stock turbo to its limits. Its working hard enough to achieve 22 PSI at the mani without having a 3-4PSI drop.

2) the increased pressure behind the IC heats up the air even more. In otherwords, it is not effiecient.

The penalty of an IC that has a higher flow rating (CFM) and hence a higher core volume is the lag in pressurizing it.

Edit: I should say that I agree that pressure drop cannot be "tuned out" persay. It is a function of the hardware, but not just the intercooler. It is a function the the airflow produced by the turbo and the airflow capability of the IC. When the airflow of the turbo exceeds that of the IC's capability, pressure drop will occur.
 
#18 ·
Here is the scoop on pressure drop, you are still a little off oldskool, Volume has a big effect on pressure drop as does design, small does not always have a lower pressure drop, and a large intercooler can have the same as a small one if it designed correctly. I would be willing to bet the RPI has a smaller pressure drop that the stock, and it is larger. I am not sure at all where you came up with a larger one will not have a pressure drop, larger typically has a higher pressure drop and lower flow rate. No pressure drop and air won't move. See below.

Pressure Drop

Another aspect of intercoolers to be considered is pressure drop. The pressure read by a boost gauge is the pressure in the intake manifold. It is not the same as the pressure that the turbocharger itself puts out. To get a fluid, such as air, to flow there must be a difference in pressure from one end to the other. Consider a straw that is sitting on the table. It doesn't having anything moving through it until you pick it up, stick it in your mouth, and change the pressure at one end (either by blowing or sucking). In the same way the turbo outlet pressure is higher than the intake manifold pressure, and will always be higher than the intake pressure, because there must be a pressure difference for the air to move.

The difference in pressure required for a given amount of air to move from turbo to intake manifold is an indication of the hydraulic restriction of the intercooler, the up pipe, and the throttle body. Let's say you are trying to move 255 gram/sec of air through a stock intercooler, up pipe, and throttle body and there is a 4 psi difference that is pushing it along (I'm just making up numbers here). If your boost gauge reads 15 psi, that means the turbo is actually putting up 19 psi. Now you buy a PT-70 and slap on some Champion heads. Now you are moving 450 gm/sec of air. At 15 psi boost in the intake manifold the turbo now has to put up 23 psi, because the pressure drop required to get the higher air flow is now 8 psi instead of the 4 that we had before. More flow with the same equipment means higher pressure drop. So we put on a new front mount intercooler. It has a lower pressure drop, pressure drop is now 4 psi, so the turbo is putting up 19 psi again. Now we add the 65 mm throttle body and the pressure drop is now 3 psi. Then we add the 2.5" up pipe, and it drops to 2.5 psi. Now to make 15 psi boost the turbo only has to put up 17.5 psi. The difference in turbo outlet temperature between 23 psi and 17.5 psi is about 40 deg (assuming a constant efficiency)! So you can see how just by reducing the pressure drop we can lower the temperatures while still running the same amount of boost.

I have seen some misunderstandings regarding intercooler pressure drop and how it relates to heat transfer. For example, one vendor's catalog implies that if you had little or no pressure drop then you would have no heat transfer. This is incorrect. Pressure drop and heat transfer are relatively independent, you can have good heat transfer in an intercooler that has a small pressure drop if it is designed correctly. It is easier to have good heat transfer when there is a larger pressure drop because the fluid's turbulence helps the heat transfer coefficient (U), but I have seen industrial coolers that are designed to have less than 0.2 psi of drop while flowing a heck of a lot more air, so it is certainly feasible.

Pressure drop is important because the higher the turbo discharge pressure is the higher the temperature of the turbo air. When we drop the turbo discharge pressure we also drop the temperature of the air coming out of the turbo. When we do that we also drop the intercooler outlet temperature, although not as much, but hey, every little bit helps. This lower pressure drop is part of the benefit offered by new, bigger front mount intercoolers, by bigger up pipes; and by bigger throttle bodies. You can also make the turbo work less hard by improving the inlet side to it. K&N air filters, free flowing MAF pipes, removing the MAF itself when switching to an aftermarket fuel injection system, these all reduce the pressure drop in the turbo inlet system which makes the compressor work less to produce the same boost which will reduce the turbo discharge temperature (among other, and probably greater, benefits).
 
#19 ·
Instead of "no pressure drop" I should have said a negligable pressure drop. But all the concepts you are stating are the same as what I was stating:

- a large pressure drop means more air backed up behind the IC and hence more heat (time for an upgrade)
- pressure drop is dependent on the volume of air the turbo is moving, hence the flow rating of the IC (CFM) should be matched to the flow of the turbocharger behind it
- an intercooler that is too large will cause tubo lag - there is more volume to pressurize
 
#20 ·
Yea like he said, that's what I was trying to say, you were talking outside intercooler at the turbo I was talking inside the intercooler. It seems pressure drop can be reduced with better intercooler connection tubes, DDM Works has tried to do this with there new Intercooler/CAI they have straightened the tubes, I don't think anyone else has done this.
 
#22 ·
Nice article. RickyD claims to have a negative number for approach. negative approach numbers are not possible without mechanical refrigeration unless youhave perfected a perpetual motion machine with no friction. If you have I can put you in contact with several high powered Engineers in the HVAC industry. They would love to have a little buisness chat with you.
 
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