Carver Owners Forum

I have worked around engines most of my life but this puts function and fuel delivery into another perspective. Very interesting for anyone how likes engines.

Hans, that is a really great video!

Very cool indeed!!!!! Thanks for sharing!!!!

Cool video. Would be nice to see effects of valve overlap at the carb but it's more prominent on bigger more efficient engines. This is where the intake and exhaust valves are both open at the same time to help clear as much of the exhaust out of the cylinder as possible just as the next intake cycle starts. I see a little backflow in the video at the carb at one point but I suspect it's more due the rush of air coming to a sudden stop. It's a critical timing more so on marine engines than automotive as we don't want to ingest the raw water being injected into the exhaust at the exhaust elbow. The amount of overlap is controlled by the design of the cam and is another reason you don't use some automotive engine components in marine engines.

I have seen reversion on engine dynos and the results of some relatively simple mods to make power and cut the reversion cloud. Reversion can be handled a few ways, engine tuning/valve timing, proper assembly techniques, a good valve job with attention to flow design thru the head, attention to high back pressure issues in the exhaust are some ( manifold design ).This exhaust design sector is where the marine side is having the most issues in my opinion, even some bad casting flash will do it. It is something that is inherent to regular engines both marine and automotive.......car engines don't have a lake they are trying to keep out though.....like mentioned......

Like the automotive industry, the biggest concern isn't power anymore, it's the environment. The overlap is intentional, so for our application it doesn't make sense for the OEM to then try and minimize it, and they have environmental guidelines to adhere to. You can modify later for performance applications but it's still a happy medium. You won't get the best performance if you don't push out all the exhaust in the cylinder which is the whole reason behind incorporating valve overlap into the cam's design.

Several things including the external exhaust system do contribute to water ingestion due to reversion but difficult to mitigate in the real world while trying to balance the effects with boat production concerns. With this in mind, Mercruiser came out with a simple resonator to help minimize ingestion due to overlap/reversion and the boat's exhaust system. The good thing about it is that it's done outside the engine and doesn't involve interfering with the benefits of valve overlap. At minimum, any 454/7.4L and up should have them in their exhaust systems. You probably have them but just don't know it as they're inside the exhaust tube close to the elbows.

Would have been cool to see the effects of overlap in a video with a high speed camera. Great video as it was though.

VERY cool. Thanks for sharing.