Re: freebetonys turbo
Originally posted by FreeBeeTony:<br /> Any other opinions on turbo charging a gas marine engine? I am still considering it and want to know as much as I can before I do it........<br />Why would the operating temp go up? It's not re-circulating the exhaust gases.
for what I know, trying to "turbo" charge a marine engine is not worth it. For one, if they do make a water cooled turbo it's bad from a standpoint of efficiency. There's an inherent exhaust gas temp drop across the turbine inlet and outlet ports, due to the compressor converting that energy into work (giving you boost on the engine intake). So the hotter the exhaust gas, the better the flow and the better the boost and efficiency. Now if you water cool the turbo to reduce heat, you reduce boost and it's efficiency... probably to the point where it's not that beneficial. Of course you can design the compressor to partially compensate for that, but in the end, you're wasting energy. Hopefully I didn't butcher that explaination too much, I sit next to fluid dynamics guys at work that can talk for hours about this stuff. If I can, I'll post a better explaination.<br />Probably because of the whole heat issue, engine bay enclosure along with turbo design and efficiency, is why you see no turbo systems for boats these days and why their life in the marine market was shortlived. Along with that, turbo-charging a carbureted motor is not that easy. The entire carburetor has to have the intake plenum coming from the compressor completely around it and sealed off. With intake manifold geometries and finishes, it's not easy to get a good seal. And when the seal fails, the carb cannot monitor fuel properly and the engine will run poorly. Not to mention there's no way to tune the carb while the engine is running, along with having to possibly resize the entire carb, and definitely jets and power valves and fuel delivery to accomodate the increased fuel need of the motor. If you don't, the motor runs lean, detonates, and burns valves and pistons. On top of all that, there's turbo lag- where the boost doesn't kick in until the engine is under load at a certain rpm to produce enough exhaust gas to spin the compressor blades to produce boost. So now you have to tune the carb for that.<br />In freebeetony's ebay link of the turbo for sale, I don't see any hardware of the intake plenum going from the turbo to the carb. That there would probably cost more than the turbo itself, if you could even find one or have one made. As for the motor it goes on, I'm not familiar with it but I imagine you either replace the entire exhaust manifold with one that re-routes exhaust gas to the turbo then back to the manifold/riser to accomodate the compressor, or the compressor somehow fits between the manifold and rise to get access to exhaust gas flow.<br /><br />"super"-chargers on the other hand, are a different story. The Weiand-root type blowers (fit on top of or replace the intake manifold, what you see on NHRA top-fuel drags) are best for running with carbs and can be tuned. These are the same type Merc uses on their big block race motors found in Fountains. Although now I think these use throttle-body fuel injection and a computer to do the fuel mapping as opposed to straight carb tuning- would give better idle and overall performance in all temperature & sea conditions.<br />There's also centifigual type superchargers- about the size of an alternator, bolt on front of engine and utilize crank pulley belt to spin. They are probably the easiest to install, but for same reasons as a turbocharger, are no good on a carb'd motor because they too are located upstream of the carb and thus requires the entire carb to be sealed off from atmospheric pressure and must only see the boost pressure- the 14.7psi atmosphere + x psi boost, to meter fuel properly.<br /><br />hope this helps, I think you're better off passing on the ebay auction.
