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I found this off a bmw forums.
Thought it was pretty interesting

They wrote----
I had the opportunity to put a Saab Intercooler on the flowbench yesterday. Why post about a Saab Intercooler here? Because it happens to be used on a aftermarket supercharger kit designed for our BMWs. The results were:

176cfm @ 28" of H2O

For reference, 1psi = 27.681" of H2O

What does this mean in laymen's terms? It means that when flowing 176cfm of air through the intercooler, it has a pressure drop of 28" of H2O (which is about 1psi). The more airflow that you push through the intercooler, the higher the pressure drop. Here are some other readings I took as an example:

126cfm @ 14" H2O
176cfm @ 28" H2O
189cfm @ 31.5" H2O
200cfm @ 34.5" H2O

So as you can see, the higher the flow, the higher the pressure drop.
 

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Great Info! The question of course is how many cfm does our engine pull in. I’ve done some quick calculations for 15 and 20 psi boost levels.

15 psi boost
2000 rpm.....120.4 cfm
3000 rpm.....180.5 cfm
4000 rpm.....240.8 cfm
5000 rpm.....301.0 cfm
6000 rpm.....361.2 cfm

20 psi boost
3000 rpm.....211.0 cfm
4000 rpm.....281.6 cfm
5000 rpm.....351.6 cfm
6000 rpm.....422.0 cfm
7000 rpm.....492.3 cfm
 

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At 15 psi you should cut all of those numbers in half.

Your engine does not take in a different volume of air based on manifold pressure. It takes in a different MASS of air, because the air is now the same volume, but pressurized.

The flow through the intercooler will be more dependant on engine volumetric efficiency and size than it will be on boost pressure. In fact, boost pressure should have no effect on the volumetric flow across it. The CFM readings shown for the engine are from the low pressure intake side of the turbo.

At 15 psi the pressure ratio will be approximately 2:1 ... which means as already stated you can divide those numbers by about two. At 20 psi it will be about 2.36:1 ... so you can divide the values by 2.36 ...

Also ... while I haven't checked, I assume your calculations assume 100% volumetric efficiency, which I can assure you the engine never reaches. Typically a pent roof 16 valve engine will reach about 90-95% at peak torque, and about 80-88% at peak horsepower ... by redline it's usually fallen off to about 60-70% VE.

The REAL concern is with spool up. Before the air is pressurized it takes a large VOLUME of air to move through the intercooler to pressurize the side opposite the turbo. If there is a bottleneck, such as in the case of the stock Viggen intercooler, boost lag will be more noticable. A larger intercooler has been shown to significantly reduce this. But once pressurized the volumetric flow across the intercooler is significantly reduced.

Great flow bench results though. Those will be very handy in the future no doubt. :)

Adrian~
 

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Adrian, you are correct in your assessment. I was using the equations from Maximum Boost and did not convert cfm to lbs air per minute, (Done correctly all calculations should be lbs air and then converted to cfm). The calculations are “back of the envelope” and are only meant to show the limitations of the Viggen Intercooler.
I use a volumetric efficiency (Ev) of 0.85

Airflow=(cid*rpm*0.5*Ev)/1728
PR=(14.7+Boost(gauge))/14.7
Airflow*PR

I liked the last point you made.
 

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Sorry if I sounded like I was picking nits with you. The T7 software has, on some occasions, been shown to not like modifications.

I just don't want anyone to go out and buy a big intercooler with the expectation of a huge hp gain.

In reality, once under boost the stock intercooler will flow as much air as the stock engine could ever need. Only changes in VE caused by things like headers, new intake manifolds, new camshafts, porting and polishing, will necessitate a larger flowing intercooler.

Also the stock intercooler reaches a peak efficiency of about 68% and even a very good aftermarket unit the size of your windshild will do no better than about 75% or so. That's only a few degrees difference and not worth the cost.

However, the stock intercooler COULD use more flow for better spool up. Especially with a larger turbo. And it could use a water sprayer and/or water injection to help it cool even more than it does. But more important than anything ...

The stock intercooler needs proper ducting!!

Corky Bell is a big advocate of this and I am as well. Proper ducting will make more difference to intercooler efficiency than size really will. If I buy an upgraded IC it will be for the better spool up and so that I can mount it flush with the IC opening on the bottom of the Viggen front end.

That's my take on it anyhow. Throwing a big intercooler in the stock location has been shown on a dyno to cause the T7 software to sometimes "learn down" (not always) ... and even if it did not, you would notice little gain in anything but spool up, despite how small it is.

Adrian~
 

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Excellent topic, gents.

Adrian, Eric: Does this the bench testing puts hard numbers on what some folks presumed by the "seat-of-the-pants" dyno, that the Viggen IC and the accompanying ducting are definitely undersized for even mild mods?
 

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I think the "seat of the pants" dyno is misled by the fact that the spoolup with a bigger intercooler is much better. So you feel like it's kicking you into your seat harder.

By proper ducting I mean external ducting to the intercooler. Proper placement in the car's airstream, or proper management of the airstream to duct air over the intercooler. The actual piping to and from the intercooler contributes little if any restriction. Stock Saabs make their power off boost, not flow.

A number of people have dyno'd T7 engines with a better intercooler only to find they lose horsepower because the engine adapts downward for some reason. Same thing with an upgraded exhaust.

I think if anything these results show that the stock intercooler is adequate at flowing (though not at cooling) and that no more than roughly 1 psig of pressure drop will occur at full boost.

Could be better I suppose. But a larger intercooler won't make as much improvement as a better placed one would. At least IMHO.

Adrian~
 

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One thing that I hear from the drifters a lot is its not the peak hp we are looking for when we go up to a larger performance ic, its the ability to have more power for a longer period of time. Viggen ic flows better than a larger performance ic, but for how long? One to two pulls if you really wind it out in my experience where a larger ic may not flow quite as good, but it allows 90% of the viggen flow rate for say 4-5 wot gear pulls. Its balancing efficiency and flow for the perfect ic. I would rather have 85-90% of the best flowing ic out there for all 5 gears than the best flowing ic for 1-2 gears. That is the way I look at it anyway, great post! John
 

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Besides putting a larger bar and plate ic on the car and noticing that you can now go wot for 3-5 gears instead of 1 to 2 gears before the car dumps boost and pulls a bunch of timing, Vigge has data logged a bunch of data showing how the stock viggen ic is heat soaked after one pull and the larger ones never getting as bad as the viggen no matter how long you do a pull or how many pulls you do. Pm Vigge and I am sure he can provide you with as much data as you can absorb...

John
 

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Since it seems that its better to leave the stock viggen ic, would it be possible to drop the ic so that it is inline with the opening in the front bumper, or what about putting a curved piece of plastic under the ic to direct more air up onto it, or what about drilling a whole lot of holes in the front bumper to direct air straight onto the ic? :rolleyes: Anyone tried any of these options?
 

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Since it seems that its better to leave the stock viggen ic, would it be possible to drop the ic so that it is inline with the opening in the front bumper, or what about putting a curved piece of plastic under the ic to direct more air up onto it, or what about drilling a whole lot of holes in the front bumper to direct air straight onto the ic? :rolleyes: Anyone tried any of these options?
It's not better to leave the stock viggen IC.

It's better to get rid of it and sell it to someone with a Honda....:cool:
 

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I've been reading the thread and I'm a bit confused. Is it worth upgrading from the craptastic double pass IC on T5 cars to the viggen/HOT IC's or not?
 

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I've been reading the thread and I'm a bit confused. Is it worth upgrading from the craptastic double pass IC on T5 cars to the viggen/HOT IC's or not?
YES! The double pass and the viggen core are the same volume however the viggen core will be less restrictive and cool better.
 

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With a td04 turbo. (Pick your flavor 15-19T and #5 or #6 whatever.) Bump in size like the forge or mp IC units are a good upgrade. To take it a step further apply ducking to direct air to the IC as well. You will have the best of both worlds IMO.
 

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I've been reading the thread and I'm a bit confused. Is it worth upgrading from the craptastic double pass IC on T5 cars to the viggen/HOT IC's or not?
absolutely. they are discussing between the Viggen IC and aftermarket ones like the ETS etc... THe Viggen IC will absolutely make things better being it has a natural flow through as opposed to forcing air around a U turn.
 

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absolutely. they are discussing between the Viggen IC and aftermarket ones like the ETS etc... THe Viggen IC will absolutely make things better being it has a natural flow through as opposed to forcing air around a U turn.
And by preventing the cooled air from being reheated by the hot charge air in the upper passage.

Do the viggen if your in a pinch if you can find one for a good price.
 
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