8-71 NA marine diesels 1

[pitchbait40]

We are looking at purchasing a boat with a pair of 8-71 Naturals in it. We know in a few years we are going to repower it but right now we're gonna have to run these. do they make a turbocharger or supercharger kit for these motors? and if so which one provides the most power?

 

[jomor]

pitchbait40,

I cannot speak for the marine world but I do have that engine in my bus. The intake has a positive displacment supercharger/blower on the intake, it is a 2-stroke diesel. I have some info from people who put turbos on theirs and kept the boost low (6 psi & 12 psi). One had a waste gate and one did not. They used truck turbos and bought them relatively cheap. I have heard mention of being careful not to blow seals on blower. The 6V92 and 8V92 normally are turbocharged. They both claimed power increase was marginal at best but it didn't smoke in the mountains (less air). Since you are going to repower anyway, then it may be better to just tune those 2 since you probably won't be going to the mountians. If your interested respond and I'll post some partnumbers that they sent to me. Let us know what you do.

Sticking with the landyacht,

jomor

 

[TheBlacksmith]

71 series diesels, being 2 strokes, receive fresh air via cylinder ports and exhaust through poppet valves. The mechanical compressor provides motive force to the incoming air. If the exhaust valves close about the same time as the piston covers the ports, the engine is a "natural", as the cylinder pressure cannot exceed atmospheric. Some engines had cam timing that closed the exhaust before the ports, allowing pressure to build up, these were considered "supercharged". Finally there were various turbocharger setups, including bypass setups, that cut the mechanical blower out of the circuit (freeing up power) when the turbo was spooled up. These engines produced over 1 HP/Cubic inch. Look at the old Johnson and Towers engines, they had 6/71's (426 CI) at 450 and 485 HP. I don't know how high they took the 8-71's.

Blacksmith

 

[DesignOutsourcing]

Blacksmith,

I'm looking into the possibility of building small 2-stroke diesels with the poppet/port design and a small turbo. Any suggested websites or reading? What were the shortcomings of these 71 series 2-strokes (and other similar models?) Were they discontinued and why? Thanks a lot.

Wilksch is doing an aero diesel in this design. Interesting little engine. We've booked one of their first 160hp models for one of our Saab/MFI BA14 prototypes.

http://www.wilksch.com

cheers, derek

Join us at

http://groups.yahoo.com/group/opensourcecars

 

[bmunse]

I worked for GM in the 70s and had a lot of experience on the 71 and later 92 engines.
In truck and bus the 8v-71 came in two popular itterations. 318hp was the most popular with 350hp produced with the turbocharger. The inline 6 came in 238hp and the less popular 260hp(I think it was 260) with the same situation with the higher hp being exhaust driven turbocharged.
Both the 318 and 238 were popular and well regarded. The most common problems were the constant oil leaks both from air box drains and from rear seals and the normal gasket leaks that come with age. The next most common problem that I recall was the jumper fuel lines either loosening or cracking and then leaking which would fill the crankcase with deisel fuel if not caught. Generaly they were both good engines. The turbo engines however had a major problem with camshafts and cam roller follower failures. It was determined that the combination of lubricating oil breakdown from turbo heat and or increased pressure on the exhaust lobes and rollers from opening the exhaust valves against the turbo pressure(The exhaust lobe or follower failed in 99% of the cases. I don't ever remember seeing an injector lobe bad.) Newer governor design with better fuel economy in the 92 series doomed the 71s.

 

[bmunse]

I got into a rush and forgot to mention that I feel that the 71 series in marine application is a very dependable workhorse. I think that the nature of marine use(more constant speed rather accelerating /decel)allows them to live longer. There are two other failures that have come to mind. The most severe is engine runaway caused by any number of reasons but the most common being a stuck injector which would hang all the injectors open. later engines had springs that would allow all to return except the hung one. The other weakness is the quil pin that drives the blower from the gear train. When they break, which they do as an engine wears, they cause a runaway engine also which can be disconcerting if you are trying to deftly maneuver a boat into the dock.