I posted this question in the technical section:

I have 502 x whipples and stainless marine exhaust x CMI switchable tips.

Question is should I have flappers inside the pipe somewhere? They are straight pipes and if I look up them when the tip is open I can see all the way up to the bend by the riser. I am concerned about reversion or when just plain stopping having water ruch up there. What should I do I cannot put flappers on the outside as it would interfere with the tips.

http://www.jlmwholesale.com/tips.jpg

http://www.jlmwholesale.com/engine.jpg

I am wondering if those with 340's and 380's have flappers in your exhaust pipes?

Yes I have flappers.

As low as the 340 & 380 sit in the water, I would be SURE to have them installed!!!

I have flappers just inside the exhaust tip.

Thanks guys I figured I should have them. Looks like I just found another winter project.

PQ has used CORSA tips, exclusively for years. They have a "fixed" plate just inside the tip. It is tack -welded in 3 spots and approx. 1/4" dia. less than the tip ID for reversion. I removed these on my 260, bought new tips w/rubber salsbury flaps and gained 0. Still probably better than the "Carek" style butterfly damper (no moving parts). My 02