Harley's 818S

[MrDude_1]

My tubes, (early kits) used 1-1/4" od tubing. That might be why the thick adaptors don't work.
Bob

I have chassis #15, so I likely have the small diameter tubes as well. It was super tight.

Why was there a design change from 1.25 OD tubing to 1.5?? Did the car need a bigger ID tubing for flow?

[Mechie3]

Why was there a design change from 1.25 OD tubing to 1.5?? Did the car need a bigger ID tubing for flow?

No idea on official reasons, but I'm glad I found out about this. Might just have to buy my own tubing to step it up. Certainly the fewer times the ID changes size the less fluid energy losses you'll have.

[MrDude_1]

No idea on official reasons, but I'm glad I found out about this. Might just have to buy my own tubing to step it up. Certainly the fewer times the ID changes size the less fluid energy losses you'll have.

I was having the opposite thought. Water is heavy, and the OEM subaru system didnt need an increase in capacity. I kind of want to run whatevers the smallest that works.

[Bob_n_Cincy]

I was having the opposite thought. Water is heavy, and the OEM subaru system didnt need an increase in capacity. I kind of want to run whatevers the smallest that works.

The cooling system on a wrx has multiple paths to bring water back to the water pump.
1. oil cooler/warmer
2. throttle body warmer
3. heater core (bypass loop)
4. radiator: when thermostat is open
5. turbo cooler/ expansion tank

The amount of flow through each path is controlled by the restriction of that path.
Be careful if you add any restriction. You may not get enough flow through that path. This problem will not show up until heavy loads. (racing)
My 2 cents.
Bob