Saab Link Forums banner

Saab Viggen Intercooler Flowbench Results

30K views 45 replies 26 participants last post by  DC_SAAB 
#1 ·
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.
 
See less See more
#2 ·
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
 
#4 ·
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~
 
#5 ·
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.
 
#6 ·
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~
 
#8 ·
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~
 
#10 ·
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
 
#13 ·
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
 
#14 ·
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?
 
#32 ·
This is interesting. So an upgraded FMIC is actually more apparent than a 3" Downpipe? I would think the DP would add quite a bit more power than a larger FMIC since it's extremely restrictive vs. an FMIC no?

I think there should be a sticky for power mods and which ones add the most power/performance. Something like this hypothetical list:

1) Good tune
2) 3" Downpipe
3) Viggen/9-3 HOT or larger Forge/ETS/Ebay based FMIC
4) 2.5"+ Flex back exhaust

Etc. etc...
 
#24 ·
about the spool up, by adding a larger ic doesn't this mean that there is much more volume to pressurize after the turbo, that cannot be good for the spool up either. I'm refering to the 600x300 cell sized IC:s here.

I think Vigge already mesasured that even adding a larger delivery pipe than the stock one will add lag.
 
#26 ·
so does a larger intercooler flow more air under lower boost pressure. and if so does that explain why I was running 20lb with a small intercooler and now i can't push more 14lb with the larger one ( it's 2x the size ).
 
#27 ·
Actually, it should be the other way around. More CFM flow from the intercooler=more boost potential. Also, I don't see how the Viggen FMIC flowing at 1/2 the rate of even a stock WRX TMIC can possibly be a good solution when the WRX TMIC is aweful vs. larger TMIC's or good FMIC's. Then again, a Subaru engine is a Subaru engine and a Saab engine is a Saab engine...but CFM numbers shouldn't be any different regardless of the car right? I mean, people upgrading turbos to get say, 500CFM of flow aren't saying they'd rather have a turbo that has 340CFM flow...

I don't quite understand how the Viggen FMIC or anything its size can possibly be considered an upgrade for any T7 car that comes standard with the TDO4 turbo.

Can someone point out specifically where my confusion is with all of this and why one would not put on the biggest/best flowing FMIC if you want the car to breathe well and produce power "specifically" in the upper range.
 
#28 · (Edited)
The viggen IC is a normal single pass IC compared to the double pass IC found on the 900's (maybe the T5 9-3's had it too) as shown below. These are very restrictive and to upgrade to a used viggen IC and gain 10 HP is relativity inexpensive. I did this on my 900 back in the day. But yes, just about any aftermarket IC is better then the Viggen IC.

 
#29 ·
The viggen IC is a normal single pass IC compared to the double pass IC found on the 900's (maybe the T5 9-3's had it too) as shown below. These are very restrictive and to upgrade to a used viggen IC and gain 10 HP is relativity inexpensive. I did this on my 900 back in the day. But yes, just about any aftermarket IC is better then the Viggen IC.
The '99 9-3's did have the crappy version except for the H.O.T.'s, they had the Viggen IC and a little more power. (8th place in the VIN is a P).
 
#35 ·
If I had a T5 I would upgrade as follows:

1. Intake
2. IC
3. Sport Exhaust (dump the rear muffler at the very least, heavy and restrictive)
4. 3" DP
5. ECU Tune

The main problem with the Viggen IC is heat soak. But it was a very noticeable upgrade from the two pass IC, in both performance and driveability. An after market IC is the way to go.
 
#36 ·
I had kinda a simillar question to above, I have a T7 HOT with the TD04 and Viggen IC, Im planning on upgrading to a 3" DP and a stage 3ish tune, at what HP point does this IC become a hinderance?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top