[ndutton]

We started talking about increasing the size of exhaust systems over on the troubleshooting section so I thought I'd move the discussion over here.

The more I think about larger aqualift exhaust systems on our little engines and their ability to expel water, the less I like 'em.

As an example, the difference between the cross sectional areas of 1 5/8" exhaust hose and 2" exhaust hose is about 50%. In terms of exhaust gases, going bigger reduces backpressure allowing the engine to breathe better. No quarrel from me.

In terms of expelling water though (the whole purpose of an aqualift system), it takes a greater volume of water to 'seal' off the exhaust hose so the exhaust pressure will push it along, especially push it up. Also, there's less exhaust velocity to do the job with a larger system. We need to factor in how much exhaust force we have available in the first place, most critically at idle. In sort of a twisted way, I can see where a larger exhaust line could result in more backpressure when factoring in the added volume of water in each 'batch' as the aqualift system batches out the water.

I'm sure there's a sweet spot somewhere between too small a system and one too large. We have pretty good historical data given the number of A4's with aqualift systems but I'm not sold on the 'bigger is better' strategy. The fact we're dealing with wet exhaust systems changes things.

Thoughts??