Johnson GT 300 VRO - long question

[thebruce]

Background: I have a pair of 300's acquired for an offshore fishing project. However, I subsequently understood they have not proven particularly reliable so I thought I might use them for an inland waters project. I am seduced by their potential hp:weight ratio.<br />There is a lot of knowledge and experience on this list so a best guess here might be useful/reliable as I am not very experienced with two cycle engines.<br />Question: Since there is no crankcase oil sump, can these vertical shaft engines be inclined to near horizontal for a direct drive? I think they could be adequately aspirated, cooled and exhausted, but my concern is fuel/lube flow. At first blush, the crank might be 'better' positioned for gravity lube (horizontal and down...ie, carbs up) but what do I know? I have seen a throttle body injection system advertised with computer tuning/timing. Anyone with any experience with these? Could one of the new (presumably more reliable and efficient) 2 cycle systems be retrofitted? Rendering this alternative-use idea unnecessary and undesirable. <br />Wrap up: I have very little in this pair of motors so I can experiment a little. As I appreciate it, these motors are a bit of an urban legend...but did not perform well on the racing circuit. Exhaust gas temp probes in each side and removal of the VRO feature seems mandatory before exploring combustion chamber clearance, fuel mixture changes and non-rev limited power pak. <br />Any Ideas or Suggestions?<br />1. Retrofit a more modern fuel delivery system?<br />2. Horizontal orientation problems?<br />3. Experience with aftermarket fuel delivery system conversions?<br />4. Creative suggestions for a winter project?<br />Thanks in advance.<br />b.line

 

[12Footer]

Re: Johnson GT 300 VRO - long question

Wow! Much of this is beyond any experimentation I have done. I also have never worked on the monsters. But from a practical standpoint, your proposals to convert them to FI,and horizontal mounting go hand-in-hand, as the carbs must be upright. I know, a no brainer, but consider manifold-porting as an option...Verticaly mount the carbs to the horizontal powerhead via a riser? Just thinking out loud here.<br />As for the direct drive,an alternative could be a 90deg clutch pack? This would double as your "gearbox",simular to what they run on the drag boats.<br />As for the recirculation system,it should adapt well,as it is all vaccum/compression-powered. From what I have read of problems inherant with the beast, is it's VRO system, so removal would be a good idea, no matter what you do with these engines.<br />But the whole thing sounds so "lake-X" to me...Too kewl. Do keep us posted <br />If ya get bored,,,,Can I play with one? Please? JK

 

[petryshyn]

Re: Johnson GT 300 VRO - long question

I'm not an expert on engine designs by any means, but this sounds like cool a project alright! I would guess a few things to consider about horizontal orientation would be cooling system hot spots(probably could be dealt with by installing air bleeds) Oil puddling in the crankcase (relocate bleeder fittings). And lets not forget the tuning of 12footer's manifold riser. I'm not experienced with the latest and greatest fuel systems, but carbs are cheap, reliable and easily modified to fit your needs. I can't see lubrication being a problem. I would guess that the oil film would hang around longer on a horizontal bearing race. Sounds like fun... good luck

 

[thebruce]

Re: Johnson GT 300 VRO - long question

OK, we came to a couple of good points right away. <br />1) The carb manifold/tuning question...is it reasonable to assume this is beyond mortal men? If the fuel didn't carry essential lubrication I wouldn't be hesitant to play with it. I would prefer carbs as I agree with the cheap and reliable assessment and I think I understand them intuitively. What about separating the lube function to cover the bottom end while testing and tuning. Is it enough to place semi-high pressure injector(s) to cover the bottom end while you test the fuel function? Would this skew the fuel test results? If not, would the tuned fuel manifolds be adequate for the bottom end? This is how I finally arrived at FI...but FI might be more complex still! Still interested in discussion on this one! Efficiency being an operative question.<br />2) Cooling system hotspots is something I hadn't considered!!!a real consideration! I guess a check valve with a back flow ball could be logically placed (high and late) and flow tested. Does anyone know how much compression/vacuum I might expect? I have the shop manual but don't recall seeing this info...necessary for the riser manifolds anyway, I'd guess...and fairly easy to measure<br />3) Oil pooling - would this really be a problem? Where is a bleeder fitting normally located? What does it bleed to?<br />4) I'm a little hesitant to punch holes in the crankcase casting. I'm thinking about seals and temp. The egt probes will measure from 700 - 1200 degrees. I wonder what to expect for crankcase temps. What is the temp difference for this motor, from say, the front to the back? What about inside front to back? This has a a bearing on mounting, seals, insulation and dampening. <br />Thanks for the replies. Actually, this is quite a bit beyond anything I've ever tried either.<br />b.line

 

[Dhadley]

Re: Johnson GT 300 VRO - long question

Mounting an outboard in the horizontal position has been going on since the 50's. Remember the "DU" model OMC sterndrive?<br /><br />The V8's are GREAT motors. They are a breed of their own and cannot be compared to a V6. And by the way -- They worked great on race boats. And they were still one of OMC's best sellers overseas when they quit selling them in the states.<br /><br />Why do want to lay it down anyway? We've mounted many with a right angle gearbox for various applications. You are absolutly right -- the power to weight ratio is something else. Although it's not that hard to make 300 HP with a V6 looper on pump gas.<br /><br />Good luck!

 

[petryshyn]

Re: Johnson GT 300 VRO - long question

To further the question on bleeder location, I'm no expert and I could be wrong, but I thought that bleeder lines were strategicaly placed to channel pooled oil to places within the engine that required extra lubrication. These lines would be subjected to changing crankcase pressures which keep the oil on the move helping to atomize and mix it back into the fuel thus reducing pooling. I could be wrong, so don't quote me, but that was my understanding. If one drastically changed the aerodynamics of a crankcase (by turning it on its side) would it be possible to have oil pooling in a particular area and at some point in time, have a large slurp into the cylinder causing hydraulic lock? I have no idea...

 

[thebruce]

Re: Johnson GT 300 VRO - long question

Thanks Schematic for the logical explanation...makes perfect sense to me... problem is, I don't know how to determine where the "turbulent" areas might be. Got any idea how to locate them? The slurp thing would likely be catastrophic at almost any rpm. The aerodynamics of the crankcase is definitely a issue.<br />Thanks Dhadley.<br />More Cool Info...I have never heard of the DU model OMC Sterndrive, but I'll try to dig something up. I'm really glad to hear that someone else thinks they're great motors too...from the factory they are set to run "pig fat" and last forever...just not very efficiently...I think the term is "gas hog"...to the max. I was shocked, to say the least. These babies can run thru a couple hundred gallons of fuel mix in just a few hours. BUT, they can also reach 500hp (or so) real easy (on pump gas) and at that rate the fuel consumption could be acceptable. <br />My original thought on laying them down was to avoid the differential mechanical efficiency loss of 8-15% (conservative estimate) of a right angle drive. <br /><br />Does anyone know anyone who has inclined an outboard? I hate to re-invent the wheel.<br /> <br />My emerging plan is a displacement catamaran cruiser (read VERY weight sensitive). I hope to achieve slightly better than 1:1 hp/wgt ratio with the castings and cowling removed.<br />Leaves more room for fuel. <br /><br />Thanks again for the input.<br />b.line<br /><br />BTW, what does the term 'looper' mean exactly.