2.5" or 2.75" OD Intercooler tubes for daily driver?
 

87 TII 13BT with hybrid turbo. S5 exhaust side with 60-1 compressor. 15psi. Mild street port. Stock exhaust ports. daily driver

Low end torque and throttle response are important to me. I compete in autocross. No interest in drag racing.

The previous owner used 2.75" exhaust tube. The housing were ported huge. They were ported down and wider. I think the exhaust ports we so big they affected low end. The car didn't really have much power until 3.5k+ rpms when the boost came on full. It wasn't much fun to drive around town.

I'm rebuilding the engine. I was thinking of keeping the exhaust ports stock, just cleaning them up a little and using 2.5" OD 6061 0.065" wall aluminum tube for the intercooler tubes. I'm thinking the increased intake velocity will improve the throttle response.

Will this give me the low end I'm looking for or will keeping stock exhaust ports be enough to maintain low end and run 2.75" OD tubes to gain better top end flow?

2.5 is perfectly fine for what you want. Larger pipes only benfit for hi hp applications cause they are less restrictfull at maximum flow. The small pipes will keep the air intake velocity higher (which is what you need for improved low end torque). FYI 2.5" is the actuall inlet diameter of stock 20b and 13brew intake elbow entry.

Thats good to hear. I'm running a 70mm (2.75") tb but only because it makes the intercooler tube routing easier. I'll pick up some 2.5" OD tube and get a 2.75" to 2.5" reducer for the tb elbow.