hey guys. so my s40 is tuned, running a 12psi... SAFELY. its been tuned and checked. but I would like to make this thing run better on the highway. So with a 3 inch downpipe and 2.5 inch straight pipe and the tune its fast. It burns the front tires easy. But on the highway it sits at high rpm here in texaswhere you can go 80 for long periods of time. is there any trans mod for the autos where you can do something about this. thanks! also im about to throw a 14t turbo in.

 

Should have said which year your car is.What do you consider high rev at those speeds?

 

The Gen 1 S40s have a 2.76 final drive and .98 4th gear - so the overall drive is about a 2.70 - which is pretty long legged. That works out to about 26.5 MPH/1000 RPMs on 195/60-15 tires (I used a 24.2" diameter) to calculate about 3000 RPM at 80 MPH. My son has our S40 so I can't test out my math... That's not very stressful on an L4 engine which can turn 4000 RPM all day (say at Autobahn speeds).