I used thin wall Type M for the long runs (which do a lot of cooling) Type L for the 'trombone' which is thicker to be tougher to handle rocks and such.
I figure it will do the job on 2/3s of a flat 6 if Porsche used a similar setup on the 2.7s..If you think about how small the factory coolers are on the 4s, I think a normal cooler would be way too much and then need a louvered cover to protect it. This i can just hose off.
all soldered up with 95/5. This can now be tested first with compressed air and and soapy water.
