We had a really good run with our EA82T RallyX wagon yesterday. I finished 1st in class and 2nd overall (look for Richard Nuss in the results), which was a big improvement over past races. I beat several newer cars that had race tires. And my co-driver Marek was 2nd in class and 10th overall.

Classes: http://thscc.com/rallycross/events/2008/2008-0928class.pdf

Overall: http://thscc.com/rallycross/events/2008/2008-0928overall.pdf

 

After the morning runs, we realized that the car's power delivery had felt different all morning - it was much smoother.

 

In the past, this car had a definite boost "hit" that was dramatic and would shoot the car into oversteer. This was with a manual boost controller (TurboXS) set to 5psi (our engine is hurt, so we turned the boost down).

 

I took the stock exhaust off the car just before this RallyX, although it was already missing the muffler (fell off in first race of the year). It now only has the downpipe and the first cat. The car still makes 5psi boost, but seems much more linear, more controllable.

 

For instance, the car used to bog down in second gear if we had slowed down for a corner, then all of a sudden it would spool up and take off in an uncontrollable way. But at this past race, we could leave it in 2nd almost the whole track, and it never bogged - was just smooth. Is the turbo just spooling sooner because of the decreased exhaust backpressure?

 

How does the boost act on your cars? Does it "hit", or is it smooth like this?

 

Could just pulling off the exhaust make the difference we're seeing? I knew it might make a difference, but didn't expect to notice much.

 

The reason I ask - we also just started venting the crankcase pressure to atmosphere. PCV and breathers are plugged. Had to do this because one cylinder is real low on compression is pressurizing the crankcase, and would cause oil to be sucked thru breathers. I realize this is not the optimal configuration for this car, but it's keeping it running until we can work on the engine this winter. So I was wondering if our newly "smooth" car is a freak thing that will go away once we get a good engine in there, or is it normal for a properly running EA82T?

 

For fun, here's passenger-hand-held in-car video of some of our runs. You can play it at that site, but it runs better if you download to your PC and play via Quicktime. http://drop.io/thsccrallyx20080928 .

The smoke out the hood is a tube from the center crankcase vent. The valve-cover vents are running down under the car.

Edited September 30, 200817 yr by thecarman

Boost on my XT turbo is very noticeable, but after it's boosting it's very lineair and power keeps increasing with the RPMs. It's not a very sudden "hit" transfer, more like a smooth transition. It also has plenty torque/power down low to pull 4th gear from 1500rpm and starts seeing positive inlet pressure from as low as 1800rpm (full pressure at 2500rpm or so). I consider this a healthy EA82T :-p

 

Only mod is an open catless 2,5'' TBE.

Is the turbo just spooling sooner because of the decreased exhaust backpressure?

 

I think that's definetely a possibility. The faster you can flow air over the compressor wheel the faster the turbo will spin up. Larger diameter pipes from the turbo-back allow better flow. In a turbocharged application the goal is to get rid of exhaust as quickly as possible. Any tuning of the exhaust has got to be done before the turbo - anything after just needs to be large and free-flowing.

 

The 3" catless turbo-back system on my SS makes for smooth power with the stock turbo. It spools very easily at 1500 to 2000 RPM and makes for smooth power all the way through the driving RPM range. It's not the same engine, but the turbo size relative to the engine size is very similar and they were designed with similar goals of low RPM spooling and smooth driving characteristics. They both boost at about 8 lbs stock.

 

GD

Like a F-4 Phantom kicking on the afterburners :-p

TD04 with WRX IC, Spider intake and 2.5in exhaust.

I think if I gutted the DP, I might get even better flow.