I recently tried something- used on full scale EXTRAS-and it works .
We did a WH35% with a ZDZ160 and JMB cans -which fit close to bottom of engine on 5"headers . (absolute rocket!)
This really blocks air flow out the bottom -so----------
I copied the fake louvers in the kit cowl-- and simply put them on top edges of cowl- I used 3 cutoff discs stacked to make the 1.25" long slits- 13 of em in a row
Having seen how well it eliminates the trapped air in the top of the cowl-- I am going to REALLY do up the cowl on my new super snorter Giles 202 with a Super Snorter ZDZ80 single and pipe .
Old hot rodders will recall the multi louver rows on '32 Ford hoods (and '40's)
I found that the best place is at rear corners on EXTRA and on the round cowls - It should work equally well. there are lots of em on a YAK
For those who can't cut holes in cowls -
drill big round ones - not purty but it will get airflow over top of cyls and out the rear of the cowl
Anybody else used this setup?