ok what is better wide14in 4in tall or 9in wide 6.3/4 tall . what flows more???

Bob,
If I had to guess I would say the second of the two. I realize your not looking for a guess so I would send Brain41 a PM and ask him about his Dyno results with flame arrestors. It is pretty interesting to say the least. I am using 5 X 10 Gafrig minus the 13 ft. of inner screen. It actually makes more power than having no flame arrestor at all.

Give him a shout.

John

thanks i try to email him

john do you have his email . ? i can not find it

http://www.offshoreonly.com/forums/members/brian41.html

breathers are WAY over rated.

All things being equal, the second has more square inches to allow air in. That does not necessarily mean it will flow better though. BTW, those are huge flame arrestors. A 9x4 is more than enough for 500-600hp.