TIP Ranking Test Change

The first two rounds of Turbo Inlet Pipe testing (round 1 and round 2) showed a trend of the larger diameter pipes having greater airflow.  This association leads to a logical conclusion that all that needs to be done to have the highest flow inlet elbow is make one with the largest diameter possible.

BMS (L) and MST (R) inlet elbow discharge cross section
BMS (L) and MST (R) inlet elbow discharge cross section

As the collection of inlet elbows grew in preparation for Round 3 a couple of questions arose; why would MST build an inlet elbow with the largest inlet by far, yet have the outlet sized smaller than any but the stock inlet?  Why are the APR and Unitronic outlets both on the small side, and both the same dimension, ~48.7mm?  These are two companies that claim to have put forth a significant effort designing this part yet they have outlets that seem to limit the flow of the part compared to others in this test group.

These questions led to reconsidering how the test is being performed, specifically with respect to the adapter that connects the turbo inlet pipe to the flow bench.

Mk7 GTI Straight Coupler Test
Straight Coupler Test

This coupler is a straight piece of silicone.  It has the benefit of fitting with all of the inlet elbows, providing consistency.  This universal fit also means that it won’t impede the airflow out of the inlet elbow, which may not be the case when these inlet elbows are attached to an IS20 or IS38 turbocharger compressor housing.

If the cross section of the throat of the compressor housing is equal to the inside diameter of the Unitronic and APR elbow outlet, 48.7 mm, then these elbows that have larger outlets might create an uneven transition between the elbow and turbo, causing uneven airflow and possibly having a negative affect on the maximum flow rate.

After confirming that the throat diameter is around 48-48.7mm a decision was made to revise the method of attaching the inlet elbow to the flow bench to more closely match the turbo compressor inlet.

Turbo Compressor Inlet Throat Model
Turbo Compressor Inlet Throat Model

The revised adapter has an inside diameter of 48.5 mm and should more closely model the interaction between the inlet elbows and the IS20/IS38 compressor housing.

Of the inlet elbows that were tested during rounds one and two all are still available except for the Unitronic.  Round three will be a re-test of the available round 1 & 2 inlets along with the turbo inlet pipes from CTS, Neuspeed, Leyo, and Induct.