Hello,I own a 2001 996TT and I installed the blownsix intercoolers today,I have the K16/24 but when we made a test drive the car felt less agressive ,seems like the power comes a little later and not so brutal anymore,could this be because the blownsix intercoolers have larger cores and that it would take the turbo's more time to fill these up with air?
I run 1.2 bar pressure,have the silicone boosthoses and whe checked that we had no leakes on the hoses..For some information about the blownsix intercoolers ,you have to make some adjustments to make them fit on the plastic caps .
Maybe they are only good for the bigger turbo applications and not for the K16 ?
Please let me know what you think ....
Thanks a lot.....

 

I looked into the blownsixes but went w/ the Evo's because the end tanks seemed to flow better.

 

MAYBE THATS WHY DR JITSU. HE HE HE

 

dixie
The most obvious reason is that you have an oversized intercooler for your application that is dropping pressure too much and creating lag. I am not sure I understand why you would change from the stock Porsche setup to an aftermarket IC given the turbo size that you have, and if you really need it, I would go for a GT2 IC.

Assuming that the reason for this is not any leaks in the setup following installation, I would return the IC to Blownsix and get my money back. 90% chances that you are loosing performance by going this route, whether with more lag or not, regardless, a stock or GT2 will be better IMO.

 

The 30% larger cores really shouldn't make any difference to transient losses, with respect to the size of the turbos we use and the size of the intercooler cores. Your pair of K16's are big enough to fully pressurize an intercooler of that size in a matter of milliseconds.

Basic theory:

http://www.gnttype.org/techarea/turbo/intercooler.html

Could be an end-tank design issue, as Dr jitsu stated.

 

IMO, more likely the larger core size and increased volume. Same reason a larger Y-pipe on K16/24's creates more lag.

 

The lag increase (not boost threshold) as a result of the 30% increase in surface area will be also 30% more than stock, and this is what is driving increased lag when the stock intercooler is just perfect for this partcular setup.

Lag time= volume/flow rate x2

The reason for the 30% increase in volume vs. stock is to show nice temp drop efficiency numbers, since better cooling cannot be achieved with superior core streamline design or the use of prohibitevely expensive materials, the next best thing and easier to achieve, is to increase volume, therefore increase air travel, which increases pressure drop as a direct result of the larger volume traveling inside the core.

All else being equal in the setup, this is the only reason for the "lag increase" perceived. End tank design doesn't have much to do with lag, since the results of a sharper corner here and there form end tank design differences hardly would result in a 5% increase in the overall intercooler flow, vs. 30% due to surface area increase.

 

No, it will be nowhere near 30%.

The core on a blown6 intercooler is 16" x 9" x 3.4" per side. That's about 490 cubic inches.

It uses a bar & plate style core. The internal volume on a bar & plate type intercooler is about 25%. In other words, though the core is 490 cubic inches, you'd only be able to pour about 122 cubic inches of water into it.



Tube & fin style cores typically have marginally less internal volume, however, the difference is close to nil. Let's call it 23%. If the core is 30% smaller than the Blown Six one:

490 * .7 * .23 = 79 cubic inches

We'll ignore for now the fact that bar & plate tend to flow better than tube & fin.

So, two BlownSix intercoolers have a total core volume of 244 cubic inches, and two stock intercoolers have a total core volume of 158 cubic inches.

Stock intake piping on the 996TT is 2.25" in diameter. That's a cross-sectional area of 3.976 square inches. Let's call it 4 square inches.

There's about 5 feet of it or so, pressurized (after the turbo) per side. That's about 10 feet total.

So the volume if the intake piping is 480 cubic inches.

The cores are rather small on both models. Let's call it 20 cubic inches per side for 40 total.

Total intake volume stock: 480 + 40 + 158 = 678 cubic inches
Total intake volume blownsix: 480 + 40 + 244 = 764 cubic inches

So, the total increase in volume is:

(764 -678) / 678 = 12.7%

Now, if we consider that bar & plate tend to flow a little better than tube & fin, the time it takes to pressurize that volume difference will be lower than 12.7%.

On top of this, there's the consideration of how long it takes turbos of this size to fully pressurize that amount of volume. Remember, at about 3000rpm, that 3.6L lump is taking in about 5475 cubic inches per second.

 

what he said...

 

SallyMobile

Thanks for the time taken to do the calculations. I will go through them in more detail.

I don't know blownsix intercoolers as I never took the time to research them, and what I am saying has literally nothing to do with the brand or company, but if he is seeing increased lag, it is due, most likely than not, to the increased volume inside the intercooler that air has to travel, and inappropriate sizing vis a vis his turbosystem setup.

The 30% I used were the numbers you posted earlier, I had assumed (mistakenly maybe) that you were quoting 30% increased volume, not simply size, since it is irrelevant as such.. The formula I posted above is the way to calculate increased Lag as a result of intercooler changes in flow and volume. The denominator part takes care of the IC design overall including fin and turbulator design etc which I obviously did not address here , and the numerator, of the volume.


The point is that the increased lag (whatever that percentage is in Dixie's car) after the addition of these ICs is a direct result of the pressure drop in the overall turbosystem design, and, to some smaller extent to the improved flow in the IC.

Cheers

 

I agree with you. I just think though, that the overall effect in this case should be relatively small.

To think of another way, the system gained 86 cubic inches with the two bigger intercoolers. That's roughly the size of a 4.4" cube.

With the motor ingesting 5500 cubic inches of air a second at 3000 rpm, it takes roughly 0.016 of a second to fill that extra 86 cubic inches. Even at a low 2000 rpm, it takes a mere 0.024 seconds. I don't think my personal butt-dyno is sensitive enough to feel that difference (admittedly, I never bothered to calibrate it).

I think this is why intercooler theory says that the right sized intercooler is better than one that's too big, but building one big enough to make a perceptable difference in transient response is not a practical reality.

Perhaps in a front engined vehicle there will be a difference switching over to a huge front-mounted intercooler. However, with the 996TT's size/location constraints, I think it would be difficult to design an intercooler big enough that the core internal volume difference could be felt in transient response.

What do you guys think?

 

They are K24's w/ K16 compressors, yes? I think the B6's might be a little on the big side, but that is just my guess. W/ straight K24's at 1.2 bar I don't think they are too big. I would prefer a bit too large to too small, since a lack of cooling could lead to detonation and BOOM. Of course Belgium isn't that hot.

 

Thanks for your opinions,but the only thing we have changed is the intercoolers ,we double checked all hoses and they were fine,I also have 1.2 bar immidiatly but the car feels a lot less brutal in acceleration.I will put in the stock intercoolers next week,so probably there will be blownsix ic for sale...

 

Maybe it's just a little warmer outside, causing a slight power drop.

 

Sally Mobile,
Thanks for your calculations and explaining it. While It might be over my head, I think I understand it.
My question is, given a larger core, there is more surface area to cool the air (which is the IC job) shouldn't the cooler and more dense air make a difference??
Elliot