|02-19-2004 02:04 AM|
I like big intercoolers as much as the next bloke, but you all should know that higher flow doesn't necessarily result in higher horsepower. In fact for a small displacement engine with high boost you need surface area WAY more than you need flow.
Also a restrictive intercooler can be useful in some sense. If your car is flowing lots of air (such as in the Viggen) but not running high boost at high RPM (the Viggen's boost tapers significantly) then putting a restrictive intercooler will put your turbo in a happier place on the map.
Contrary to popular belief most turbo's, including the ones on the stock Viggen and Aero, are happiest with a pressure ratio of about 2.5:1. That equates to a boost pressure (at the turbo outlet) of 22 psi, if you assume inlet pressure to be ambient.
In the case of the Viggen the restrictive, but long intercooler, combined with the restrictive intake pipe is designed specifically to put the turbo at the best place on the compressor map for stock boost. At max power the Viggen is at about 13.5 psi of boost ... if we assume 5 psi pressure drop across the IC, and 1 psi pressure drop from the air filter and intake pipe we can calculate the pressure ratio at the turbocharger as follows:
14.7(ambient) + 13.5 + 5(IC restriction) = 33.2 psi of absolute pressure @ turbo outlet
14.7(ambient) - 1(drop from air filter) = 13.7 psi absolute pressure @ turbo inlet
33.2 / 13.7 = 2.42
2.4 pressure ratio isn't the most efficient place on the map, BUT it is the most efficient place on the high flow side of the map, which is where you are going to be before the intercooler restricts anything. This means that in stock form, getting a larger intercooler, and better intake pipe may actually result in higher intake temps, and increased turbo wear because you are spinning the turbo outside its ideal map.
For an upgraded Viggen the higher flow IC and intake pipe help at high revs, but you might still see more benefit from a water sprayer for the IC, or water injection. And some B234i naturally aspirated camshafts would help out more with top end.
|02-15-2004 12:21 PM|
|02-15-2004 12:16 PM|
|JABM||The Viggen IC is only $159 New from Genuine Saab without the hoses, so it doesn't seem worth while to buy off Ebay for only a few bucks less....|
|02-15-2004 09:33 AM|
I recently was able to find a VIC on ebay, for $150 new, without the hoses. I asked him to hold it for me, but I may go for an aluminum universal IC on ebay instead.
I suggest if you don't know how to work with custom hosings, then it would be best to order it from Genuine Saab.
Nick, may have more to say about this.
|02-15-2004 07:33 AM|
So what was the cost of the VIC from the Saab dealer? I see http://www.genuinesaab.com/detail.asp?product_id=ic-kit at $375...is that completely unreasonable? I was considering this as one of the mods for 9-3. Do you guys suggest going a different route or is the genuinesaab.com kit a good price?
|01-12-2004 03:12 AM|
Standard IC or VIC? Diagrams!
So, this weekend I switched IC to a VIC. Took a lot of time, and was quite difficult. If you are to do this, buy the hose from the turbo to the VIC at SAAB, making that hose from "spare parts" was hard work!
And, did it make any difference? Hm, perhaps I should wait a little longer to let the adaptation take place, but I ran a test as soon as it was assembled
The temp was not much affected, it rises almost the same amount (perhaps getting 3" will make the VIC more worthwile here).
The most interesting part is that the pressure from the turbo was much more stable using the VIC, the second dip in pressure was also eliminated. This can most probably be credited to the VICs better flow.
Note that the pressure is divided by 10 to fit the diagram better. Max pressure with the VIC was 215kPa.