Build A Faster Car - helping drivers engineer

This article is to address the lack of and confusion of information on this forum about intercoolers. Since I've also made this mistake myself (I once posted a silly thread about the speed6/speed3's intercooler being "tiny") I feel I'd like to share what I've learned with the community. This is merely a combination of information retrieved from the internet, personal conversations with shop/shop owners, road course guys, and a few books. This page mainly discusses "replacement" intercoolers, mainly front-mounted units, though much of the information still applies to replacement top-mount intercoolers as well.

Summary: (For lazy people)
The best intercooler is the one properly sized and designed for the application. Going too large in intercooler design can have negative effects on vehicle performance and drivability. A smaller intercooler, with proper venting and design, can be just as effective as a large mouth style. When shopping for a replacement intercooler its important to do proper research on your purchase. A new intercooler can be extremely beneficial to the performance of a car, but it can also have negative effects. Make sure to check with the manufacturer of the intercooler that proper R+D has been done on it's efficiency, psi loss, design, effect on the vehicle, etc. If you see someone just selling an intercooler without any actual data on how or why it was designed the way it was, steer clear, or wait until additional information is available as to why that purchase will be beneficial to your car. It is very easy to fiddle with air/fuel ratios and boost pressure in the design of an intercooler to show a "dyno" gain. Intercoolers are not "power bolt ons". They are bolt on's meant to address the efficency of the charge cooling system present in the vehicle, either to reduce the chance of detonation, or provide for growing room on a car that will see additional upgrades. (Larger turbo's, standback/hybrid/flash tuning)

What's the Point of an Intercooler Anyway?
The function of an intercooler is to reduce the amount of heat generated by the compression of air by the turbocharger. It does this by passing the charge temp air through a series of channels/vanes which are externally cooled by either ambient air or water. The primary reason for reducing the charge temp is to help reduce the chance of detonation. Excessively high charge temps can increase the chance that the air/fuel mixture will combust spontaneously outside of the main flame front. Detonation is insanely bad, it causes excessive stress to drivetrain components. Secondary benefits include cooler air (and thus denser) which contains more oxygen per cubic inch then warmer less dense air. The more oxygen you can fit in a given space, the more fuel you can add to it, and thus the larger the resulting boom. (Hopefully a controlled one). ) Formula's below for those who like math. Intercoolers are measured by efficiency, which is basically the % of heat they can remove from the charge temp (caused by the turbo compressing the air) , prior to the air entering the engine. The higher the efficiency, the greater the temperature drop. Of course the problem with efficiency (and why it isn't stellar on stock cars) comes down to design. The more efficient an intercooler is, generally the larger the pressure drop of the air traveling through the intercooler. The denser the intercooler is, the more pressure loss. It is this balance of pressure loss vs efficiency that drives intercooler design.

Judge Me By Size, Do You?
When looking at intercoolers, its important to remember that size is not indicative of efficiency or "maximum obtainable hp". You can have an intercooler the size of a mac truck, but if it doesn't get airflow through all its vanes, those vanes will not be contributing to cooling the charge temp. At the same time, if there is not an even distribution of charge through the internal passageways of the intercooler, it doesn't matter how much ambient air is flowing through the intercooler, because internal vanes aren't being utilized.

It's a fast car. It has a huge intercooler... thus my car will be fast if I have a big intercooler too!

One of the major problems with intercooler designs is sizing. Many manufacturers (including some big name brands like APS) try to figure out how to shove the absolutely largest intercooler into the front of the vehicle as their primary concern. Thoughts such as efficiency, and flow, are merely byproducts of their attempts to turn the front of a vehicle into a source of global cooling. This is not entirely their fault. Owners of vehicles see tricked out car's and race setups with enormously huge intercoolers taking up the entire front of the car...and feel that means its the end all of performance. (see wings and wheels).

There is a lot of data on the net about this phenomenon, especially in TMIC enabled vehicles (where everyone wants to get an FMIC as quick as possible. Basically individuals slap these huge intercoolers in the front of the car, and the following can occur. (These apply to oversized cores [for the application])

1. Charge temps drop.
2. Boost Lag increases.
3. Coolant temps increase.
4. In the case of a poorly designed intercooler, psi demands increase.
5. Vehicle air conditioning becomes less effective.
6. Drag times increase (the car is slower in the 1/4)
7. Impossible to tune out rich spikes (drivability issues).
8. In the case of some vehicles, crash protection is removed to allow for better flow. =/

Air-->Intercooler-->Warmer Air-->Condenser-->Hot Air-->Radiator-->Sad Face Coolant.

Cooling
When looking at FMIC's (Front Mounted InterCoolers) you have to remember the basic airflow diagram entering the car. First air enters the intercooler, secondly it passes through the condenser (air conditioning), then finally, through the radiator. This means that the larger the intercooler in the front of the car, the more airflow it's both blocking, and heating up, prior to that air reaching the condenser or radiator. In this way the FMIC effects the entire vehicles cooling, not just the intake charge. Too large, and too thick an intercooler can actually result in requiring to upgrade the vehicles radiator, just to take up the slack due to loss of airflow, and increased ambient temps flowing through the radiator. Such is the extent of this problem, that some manufacturers will over a V mount style intercooler/radiator combination, which angles the two < to allow unobstructed airflow through both. This also helps to showcase later points, in that a much smaller, but well designed intercooler, can be superior to a fat momma style.

Air Conditioning
Dealing with condenser issues is usually a mute point when talking about performance...because who cares about air conditioning when you've got races to win! But then of course if you do care...any airflow blocked by an intercooler will reduce the condensers effectiveness, both due to less airflow, and higher ambient temps passing through.

Charge Temps and Efficiency:
It's pretty much a given that any aftermarket intercooler is going to give you better efficiency then a stock TMIC unit. What's efficiency? Efficiency is the % of heat removed from the air as it passes through the intercooler. A higher efficiency intercooler will tend to have a denser core, which will drop temps more, but also tend to increase pressure loss. (the denser intercooler slows down the air as it passes through it.) One of the arguments for larger intercoolers is that they tend to have higher efficiency for a given pressure loss, as the core can be less dense (as it has more space to work with). Of course when the intercooler gets enormous, you can then have issues with taking time to fill that sucker up. ie, LAG.

Boost Lag:
It takes time to fill a large volume of space. Even with compressed air, and screaming turbines, a larger intercooler can result in a slight delay between the turbo spooling up, and that air reaching the engine. This results in the familiar topic of "turbo lag". Depending on the amount, and lack of tuning (if someone just slaps on a huge intercooler without tuning, it has a whole other set of problems., this can actually reduce the initial acceleration of the vehicle from a stock configuration, increasing 1/4 mile times.

Rich Spikes:
In MAF based vehicles, and excessively large intercooler (not properly sized for the application) can result in an untunable rich spike during acceleration. This occurs when there is a delay between the time the air is read by the maf, and the delay caused by the intercooler being filled with air. The MAF reads an huge amount of air being sucked into the vehicle, and signals for fuel to be added, but because of the delay in time, that air has not yet reached the engine, so BAM, nice rich spike. This results in the vehicle bogging, and possibly choking, creating erratic acceleration patterns. Considerable engine management would be required to tune this out of the vehicle.

Example of What Happens to the A/F if you use the wrong type (too large, poor design)

Example in Question of Spikes
http://www.iwsti.com/forums/showthread.php?t=71375

Designing an Intercooler
So what qualities should a good replacement intercooler have?

1) Properly sized for the application.
2) Not blocked by the design of the vehicle. (Maximum utilization of size, through careful selection and/or ducting)
2) Not drastically effect the vehicles cooling systems. (ie, not being so large as to impact significant airflow).
3) Provide an increase in efficiency, and hopefully a lower pressure drop then stock. (Or at least properly balanced)
4) Endtank and core design should allow for even flow through all internal passages. (See below)
5) Bar and Plate design for strength and durability.
6) Not cause spikes or variations in A/F due to excessive lag between maf and intercooler.
7) Works with current and future planned mods.

If the intercooler you are looking at doesn't have these characteristics, or information on these characteristics is not available, then you should look for another company to provide a solution, or find your own.

Endtank Design

What the heck am I talking about? Well first off, the end tank design of most of the aftermarket intercoolers isn’t optimal. Most of the end tank design seems to be more of an afterthought, then an actual design decision. This tends to reinforce the idea that most of these companies are just trying to fit the biggest intercooler possible in the spot allocated.

Endtank design of an intercooler is extremely important. It determines both the flow and distribution of air through the cooling fins inside of the intercooler. A poorly designed endtank will cause one section of cooling fins to receive significantly more air then the other, basically dropping efficiency, and wasting a good portion of the cooling surface area.

Why are there so many sti examples? Well thats because part of this article was used on the sti forums by myself to argue a point about endtank design being horrible among almost all aftermarket manufacturers of intercoolers. Some of these endtanks below are only utilizing a portion of their massive girth. The rest of the vanes are practically useless. Might as well just taped a hello kitty to the front of the car instead. (This is ignoring any giant intercoolers which leave the stock crash equipment in place...basically losing 40% of their usefulness off the bat).

Here’s some common endtank designs

Now the STI appears to follow the “fitment style” of endtank design. Mainly the _| |_ type. Here is two examples I found searching on the forums.

These type of intercoolers are generally easy to fit, but don’t utilize the entire inner surface area of the cooling fins, as the section directly after the inlet piping receives a majority of the charge air.

A better design is this…where you’ve got a tapering design put into the endtank to help equalize flow.

(This isn't an sti forum anymore, so using multiple examples)

A bit better even…

Optimally, you’d want something like this.

Or additional internal deflectors to do this.

You can see how these designs better utilize the entire cooling surface area by better distributing the air more evenly. My question is this…why don’t more manufacturers use this type of end tank design? Is it because of fitment issues? The 3rd STI photo above could have easily used a taped center endtank design and still had plenty of space. I think it comes down to aesthetics. An intercooler that shows the maximum amount of fins, without any excessive piping or tanks on the end tends to look "nicer" then those fit for the application. Manufacturers know this. They also know that the average person buying their product has done little research other then posting in a forum asking for advice. (if that).

With some FMIC end tank design’s, you’re only partially utilizing the cooling surface area. My point? A properly designed intercooler could be significantly smaller, and still perform the same, or better then most of the intercoolers on the market.

Need an example? Check out the Vmount designs. Compared to most of the FMIC’s, these are significantly smaller in size, but just as effective as some of the larger designs. Bigger is only better if its properly designed and implemented!

There is no need for such giant intercoolers, when a smaller, properly flowing, and well ducted version can support the same horsepower levels without any of the negatives.

Conclusion:
When shopping for a replacement intercooler its important to do proper research on your purchase. A new intercooler can be extremely beneficial to the performance of a car, but it can also have negative effects. Make sure to check with the manufacturer of the intercooler that proper R+D has been done on it's efficiency, psi loss, design, effect on the vehicle, etc. If you see someone just selling an intercooler without any actual data on how or why it was designed the way it was, steer clear, or wait until additional information is available as to why that purchase will be beneficial to your car.

References

Intercooler FAQ
Bell Intercoolers - Technology and FAQs

TMIC Discussion Thread
Is there really any benifit of upgrading to a better TMIC?? - IWSTI.com: Subaru STI Forums

FMIC Core Thread
New Intercooler Design - IWSTI.com: Subaru STI Forums

New Intercooler Design
TSL chargecooler sti air to water intercooler - Factory 2.5L Turbo Powertrain - NASIOC

How Stuff Works Turbo
Howstuffworks "Turbocharger Design Considerations"

Maximum Boost by Corky Bell
Amazon.com: Maximum Boost: Designing, Testing, and Installing Turbocharger Systems (Engineering and Performance): Corky Bell: Books

Forced Induction Performance Tuning by A. Bell
Amazon.com: Forced Induction Performance Tuning A Practical Guide to Supercharging and Turbocharging: A. Bell: Books

Sparco Flow Chart Data
RRE Griffin Intercooler Flow Charts

Below are additional questions/answer posts from the original discussion.

Ghettospeed6:
I say let the air temps and the dyno be the judge.
Worrying about not using parts of the intercooler core etc etc is only half the story. Remember, if you put diverters in the endtanks its both 1) NOT EASY (especially if you have cast endtanks) and 2) it restricts flow. There is a tradeoff for everything.
Also too there is a picture of a V-mount there that is a recipe for heatsoaking from the AC exchanger.. Not a good example..
I do agree though that using a smaller intercooler than you think you need will probably yield best results, with the placement being the main increase in performance (fmic vs tmic).

Crossbow:
Though I'd debate on the vmount being a poor example (any forward movement would remove any byproduct of the AC effecting the intercooler, especially since the fans are pulling the air away from the intercooler towards the bottom of the car), I'll leave that for another thread.

The big thing I'd like to address was your comment on dyno's. It is incredibly difficult to dyno the effective of an intercooler. This is one of the reasons manufacturers will rarely show a dyno along side of their data...generally they'll stick to showing you proof of efficency, and proof of the psi drops in question. You'll also hear such terms as "supports up to X horsepower," instead of a X gain at X rpm.

When you put an intercooler on a vehicle, especially an oversized unit, the boost tables can be effected. Many times individuals will tune out the change, to reset the vehicle back to stock specifications. The second you bring a tune into the mix, you've changed what effect the intercooler has had on the dyno. Here's an example.

I have intercooler A, which is properly designed for the application, and maintains drivability when installed. There is no bogging or adverse side effects from massive changes in intake volume. This intercooler requires no tuning to properly utilize, though would probably benefit from tuning for maximum gains.

I have intercooler B, which is utterly massive. Upon installing this intercooler, the car drives "funny" and sometimes bogs and jerks from A/F spikes and dips. A stop to the tuner remedies these problems, and the intercooler shows higher gains then intercooler A.

Because intercooler B required proper tuning to utilize, is it really producing more gains then intercooler A? Or is intercooler B merely benefiting from a proper tune (like a protune on an sti), and intercooler A would benefit just as much, if not more from the same tune?

How then do you get both intercoolers to have the same tune, if they effect boost psi in different ways? You really need to see multiple data sets. A dyno, a boost curve, temps, etc. It's way way too easy to manipulate data to make it look like one intercooler is making huge gains over another...especially if you aren't seeing the boost curve.

xxxmonoxidechild
they really didnt get into the difference in top to bottom flow, and side to side. a top to bottom flow will be more efficient then a typical side to side that most people run because of more cores in the same area.

Victory
A lot of good information here. One point I'd like to add here is that for the most part you're approaching the intercooler as a bolt on part that requires no additional tuning or adjustments.

Another approach is that the intercooler is truely a bolt on part that allows you to unlock power through a more aggressive tune, much like higher octane gas. Gas by itself doesn't make horsepower but allows a more aggressive boost and leaner fuel ratios. Like any engine enhancement to get the most benefit from it you should retune. The addition of an intercooler does two things. By itself it adds power, especially if properly sized, and secondly allows a much more aggressive tune to be added due to the cooler more condensed air, as is the case with a very large intercooler.

As you you've mentioned finding the right size is important but for most people their cars are a work in process. Therefore most of us purchase an intercooler which is oversized so that you can grow into it. As the car is modified more and more the intercooler is adequate. As with any part to get the most out of it one needs to retune otherwise you're only getting a small % of the gains each part could attain.

It's a balancing act for sure.