If we ran duals into a Y into single pipe like many Ilmore V10's, life would be better. Double amt of exhaust pulses per pipe. Would be almost like doubling the engine rpm.

Here's what they look like
[ATTACH=CONFIG]542226[/ATTACH]

[ATTACH=CONFIG]542227[/ATTACH]

B- Break
O- Out
A- Another
T- Thousand

That's not what I was referring to. I just did a search and didn't come up with anything. It seems to me Merc had a 1 way exhaust check valve, like a reed valve on 2 stroke motorcycles that mounted close to the riser.

Read this thread, have them make you a pair similar to these. These will not revert...

http://www.offshoreonly.com/forums/d...e-exhaust.html

are you running a circulation pump or crossover..thermostat? water temps makea huge differance on emis

circulation pump

you mised a ? ..oh well..installed many many many emi thunder exhaust.no issues..oh well good luck..

you have used several sets of risers on the same manifolds. were they pressure tested? it is only reversion if it is not a leak. you say fairly mild cams but they came in these engines. it is a pain but doable to degree cams in the engine compartment. you gotta hog out center of degree wheel so balancer socket fits thru.