Ah, good stuff. looking forward to that video!
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Ah, good stuff. looking forward to that video!
hey tim...just a question how is is that you have made it so that pressure can build up in the 2 stroke combustion chamber without valves? how does it not just blow through? or have you added valves?
It does not blow thru because the turbine holds it back.
That's the big advantage of turbos vs mechanical superchargers that have nothing to hold the charge pressure in.
With the turbo, it is as if the regular motor is in a giant pressure cooker
Regarding scavenging: Sam's answer is correct, the turbo restricts exhaust gas flow. I've given passing thought to installing a butterfly (and pressure guage) in the exhaust duct to test the effects of increased back pressure. More power, but more heat too. The power would reduce time to blowover, the heat would reduce time to piston meltdown.
Another often asked question is: Do the reeds close while under boost? I'd like to believe they do, but at high rpms and boost pressure it makes me wonder. Obviously they close for starting and lower power settings, but my guess is at some point they float. If I had access to an endoscope, the answer could be found within minutes in a test tank. Perhaps one of the factory engineers out there might answer the question?
The engine will be tested this weekend with all improvements previously listed, and possibly one more - a cockpit adjustable boost controller. It's an animal at 11-1/2 PSI. The controller will allow 15 PSI if desired......... Hmmmmm. Will report the weekend's outcome as time permits.
Tim
http://www.boatracingfacts.com/forum...t=7707&page=10
Here's an exercise on your exhaust valve concept.......... scroll way down the page.
Tim
The old Detroit Diesel that went into production as the Gray Marine motor sometime around 1930 and sold as Detroits starting in 1938. The design was a supercharged 2 stroke with intake ports and cam operated exhaust valves. GM engineered the motor and tooling but GM bean counters were afraid it would not sell so they leased it to Gray.
There were even versions without exhaust valves in the head, 2 rows of ports
Its an old time proven design
if you lose pressure out of the exhaust port, surely you just lower ther port.....
easier said than done
Sam's right on again. The idea for my "HKS" Cosworth-Johnson came directly from Loctite customer Detroit Diesel in 1977. I was amazed by those big two-stroke cylinders with a low row of intake ports and four-valves for exhaust in the heads. It occurred to me it would make a great gas burner - an experiment finally accomplished some 30 years later.
As a sales engineer, I spent years developing sealing solutions for the "Dirty Detroits" (because they leaked so much oil). Despite this moniker, they were known to deliver more power per pound than any other diesel on the market at that time. The 53, 71, 92, and 149 series (cubic inches per cylinder) were classified by number of cylinders first, followed by the cylinder displacement. Example 453, 671, 892, etc. Drag racers / street rodders made the 671 roots type supercharger famous (6 cyls in-line with 71 CI/Cyl).
Anyway, Bud Parker and I built the beast in secret from 1993-1998. The basic differences between the DDC and HKS was the lack of blower - crankcase scavenging was used for HKS, along with spark ignition. The head is a Cosworth Indy (sawed in half); all four valves are used for exhaust. Asymmetrical valve timing events allows it to develop 240 PSI cranking compression. Starting is accomplished by positioning the crank TDC on cam lobes before hitting the starter button. Even at 24V, the starter cannot pull one compression or valve opening event and needed the valve spring "push" to start!
A technically successful conversion, development was cut short due to cooling difficulties with the head. Designed to cool laying down, steam pockets form near the valve pockets in the vertical. Twice the chambers have "slumped" due to softened aluminum - valves loose their seats with resultant compression loss. Cosworth suggested EDM relief of steam pockets near the combustion chamber. Perhaps someday. Too heavy, complex, and expensive for racing, I decided to concentrate efforts on more conventional engines.
There's the short course!
Tim
Tim, very nice job on the 3-cylinder. First OMC with turbo that I am aware of was a V4 built by Jim Booe and Bob Thompson in 1972. Jack Leek, Jimbo and I went to test it on Bob's pond in Indianapolis. The pond was small but Jimbo was impressed. Jim Booe had used a mechanical injection system which made calibration somewhat difficult. After the test in Indy Jim B brought the engine to Waukegan and did some more development on our dyno. A few years later we built our own turbo V4 followed by a V6. Both ran quite well, but added cost and complexity did not justify performance increase for a fishing motor.
Hi Jim
Any photos in existence?
Cheers
The problem with running poppet valve exhaust valves in a two stroke is that they are severely rpm restricted. Where as a 4 stroke opens the valves every other stroke, a 2 stroke would have to open them every stroke--think 14,000 rpm like operation in a 7,000 rpm motor. True, present Formula One motors run 18,000 rpms (and could rev higher if allow by the FIA), but they're not reliable enough for operation for more than a few hours (using nitrogen gas springs).
The Aussie Orbital 2 stroke used such a system, and quite successfully. Ford and other Detroit auto makers seriously considered installing one of them in compact cars. (I recall seeing a Ford Escort with one that had great performance.) With direct injection AFTER the intake closed, they were clean enough to pass 80s emission standards, but looking stricter standards are what probably killed the idea. Mercury ran a few test power heads using Orbital power--I recall a video of one--but they dropped it as well. Perhaps the time to resurrect the idea has arrived?
Jeff
Mr. Nerstrom,
Thank you for your kind comments regarding project Virgo - I'm pleased and honored - also for sharing historical information regarding OMC turbo projects. 1972 was very early in turbo application technology. I'm sure Jim and Bob had their hands full forging a new path! Interesting that they used mechanical FI at that time. The need for boost biased enrichment would have been difficult to say the least. Also, it's interesting you developed V4 and V6 turbos. I'm sure the test rigs were popular! Understanding the challenges, your explanation regarding the cost/complexity of production makes sense. A less costly, easier to service solution would be a larger displacement conventional powerhead.
With a little luck and decent weather, you'll see more video following the September 9 test day at Hillsdale. Stay tuned.
Tim
You're quite right about RPM limitations. But you might be surprised: The 1990 Cosworth cylinder head used for HKS was rated to 13,800 RPM with conventional springs. Dividing by 2 gets you 6900 RPM - quite useable given the correct prop. My plan was to swing an 8-1/2" X 17" with the 1:1 45SS gearcase. The math worked. Sadly, the engine didn't deliver. Too heavy, too complex, too expensive, but a cool project!!! Perhaps this winter the VHS video might be digitized for YouTube.
Regarding the Orbital process, it seems to me the Mercury Opti-max is the air assited Orbital system in two stroke application. Can anybody comment?
Tim
Re Orbital
Way back when Ralph Sarich was working on his custom engine the things that let it down were all the perifererals like injection/ignition etc.
He very cleverly worked out that direct injecting fuel with a blast of air would create great atomisation and direct injection also allows for stratified charge i.e only fuel to combust is in the middle of the combustion chamber. Light years ahead hence just about all engines guys bought licenses to the technolgy.
He then worked out making existing tech work better was a better idea.
Ford ( or Orbital?) built a dozen or so 3 cyl oil injected 2 strokes and put them in a fleet of Escorts for testing.
Did everything better then the current 4 stroke tech could deliver, also cheaper and lighter used less oil over its life which is where directed computer controlled oil injection comes into its own.
Ford said sounded funny and we dont have a plant to built it so stick with what we have?
What changed was very high pressure direct injection which competes with it( but thats 30 years on) but without the compressor so simpler although I cant help thinking how an engine would be with a large air pump so the blast of air via the injector can add to BMEP?
Right where you want it When you want it!!
2 stroke combustion process still has significant advantage over 4 stroke in idle to mid range ( hence Etecs 50% less CO at this range than any other 4 stroke)
Bit of history here
http://www.chainsaws.com.au/chainsaw...roke-comeback/
In the mid-late '80s I saw one of the 2-stroke Ford Escorts you discuss at the FORD-OCP plant in Techumseh, MI. Quite impressive, it absolutely fried rubber off the otherwise sedate little econobox. Reason was Detroit Diesel was in decline and some of my customers went with the OCP startup effort - they called me in to discuss Loctite sealing technology. The facility might have been in operation for a couple years when for reasons I can't remember, the project was canceled and the plant closed. Bummer!
Tim
You could potentially stagger operation of the the 4 valve head help make the rpm feasible. Use 2 valves per revolution like a four stroke. That would give the valve springs a chance to live. I wonder if alternating side to side or diagonal would make a difference?
I am certain Mercury Optimax is an Orbital license. I recall a few years ago their web site had some technical articles about their work for Mercury. Some of the Bombardier sled or pwc stuff is or was also.
Barry
The reason to operate all four valves at once is to satisfy port-time-angle-area gas flow requirements. Using only two of four valves cuts port/exhaust area in half, greatly limiting engine power. Either way, the valve train apparatus is complex, heavy, difficult to cool (must cool valves, pistons, etc. in one revolution), and expensive for a two stroke. If there were a great advantage to valved two stroke technology Mercury, OMC/BRP, Yamaha, etc. would have it in production.
Side note: Another lighter, but equally complex and still expensive approach would be a sleeve valve like those used in the Bristol radial arcraft engines of WWII. These eliminated valve springs & poppet valves entirely. Again, if there were promise it would already be on the market.
Keep thinking.........
Agreed on the size, weight, complexity, and that cutting the valve area / cycle in half will make a difference but difficult to know without a cut and try. Hard to guess since the valves and ports in the head were developed for such a different set of dynamics inside the cylinder. Of course if two valves per cycle worked that suggests all four per cycle could work better with less lift and duration. Until they failed.
How about a four valve head from a modern V6 adapted to a two stroke triple? Full sleeves and make a four stroke. With a lot of boost:). Perhaps lube the bottom end like the Stihl 4-Mix saws.
This is lots easier this going out to shop and making stuff.
Barry
All above mods were completed and the turbo was tested briefly Saturday which proved the following:
1) It idles nicely; driveability is excellent.
2) On rough water during hard accelleration, the stern spins to port.
3) Water was too rough and boat too squirrely to attempt high speeds.
The propshaft was dead flat and centerline was even with the bottom; too high. Today it was lowered 1/2" to improve rough water handling. All is ready for Hilldale, and the weather is forecast good. See you there!
Tim
A couple of years ago I gave a lot of thought to building a 3 cylinder axial flow turbo 2 stroke, the idea was to use a commercial 2 stroke block with replacable liners, the head was to have 2 desmodromic inlet valves with 2 plugs & a single overhead camshaft.
the breathing was to be turbo,single carb into the 3 crankcases, out into a common inlet gallery somewhere where it could lube the little ends & cool the pistons, then out & up to the head.
The exhaust would be low & very wide more than 180 degrees wide, giving a longer trapped stroke, exhaust ports either side of cylinder block feeding into a turbo that was offset way over on one side in the hope of damping 6 smaller pulses rather than 3 big ones.
The hopes were that the high scavenging efficiency coupled with the longer trapped power stroke & the higher cylinder pressure when the valves closed (dependant on the boost pressure) would raise the torque enough to cover the slightly lower max revs.
Because of the lower bore/stroke ratio required the piston speed would have to be balanced with the valve speed until they were both civilised.
The problems that I never answered were, where to put the crankcase outlet ports (in a block with 3 cylinders that almost touch each other) so they could do some usefull piston cooling, & how was I to lube the camshaft & everything at that end. I did consider putting the camshaft into the inlet gallery.
Fuel consumption was allways going to be poor when you have to clean & cool the piston with that much of the fresh charge.
I must be getting old when most of my waking thoughts are about 2 stroke motors.
Since we're all using our imaginations, how about a leaf blower supercharged two stroke? There was an article (Mechanics Illustrated?) in which two leaf blowers were used to supercharge a Corvette. Worked very well. All one needs to do is plumb the gas powered leaf blower's output to an airbox that pressurizes the carb(s), with an automatic fuel pressure increasing device.
Jeff
Thanks for that Jeff, but I was rather hoping one of the techies would have torn it apart techniically if there were major flaws in my logic.
The "axial flow" arrangement you discuss is called "uni-flow" in engineering circles. The low row of ports is used in the Detroit Diesel two stroke and my "HKS" two stroke and are actually 360 degrees around the cylinder. Your concept is sound except four valves are needed for area, and can easily be verified by running Gordon Jennings port-time-angle-area equations. Desmodromic valve actuation (ala Ducati) would tolerate high RPM better than conventional spings, but parts (like titanium valves, etc) would be extremely expensive for a one-off. Can't speak to splitting up the exhaust except the plumbing and cooling would be a nightmare. Otherwise, your (global) 1-bbl carb with a plenum intake is the berries. Virgo uses this arrangement and it's been the easiest engine ever to tune.
For all you engine enthusiasts, search for SAE technical papers online. You'll find hundreds of technical papers written about 2 strokes, 4 strokes, rotary (Wankel), Sterling, Rankine cycle engines and more by the leading experts in the industry............
Keep thinking!
Tim
BTW: The twin cams used on my HKS Cosworth-Johnson 45SS twin were converted to roller bearings and lubed with a simple OMC diaphram fuel pump delivering 5W engine oil to all three main bearings. Spray from the bearings lubed the follower buckets and lobes.
Tim the axial-uni flow expression depends of who's work you read last.
Using someone elses cylinder block precluded the use of 360 degree ports & I wanted to get any heat away from the lower portions of the liner as fast as possible, without dropping it's velocity & pressure & 90 to 100 degree wide ports were a lot quicker for me to machine in situ.
With regard to the inlet side of things & the 2 - 4 valve question I felt that Jennings & everyone elses port time areas were made with the assumption that the transfer pressure would drop during the port open time to 1 atmosphere, without exhaust assistance, at a constant boost pressure the flow would greater, how much greater I never calculated as I didn't want to spend a fortune on Blair's 4 stroke book.
Using only 2 valves also gave some uncooled head area to transfer heat into the camshaft gallery where I was hoping to get more fuel vapourisation leaving some lube on the cam gear.
I was also hoping that 2 valves might give less mixing of the fresh charge as the valves could be opened when the boost pressure was slightly greater than the cylinder pressure which would fall much faster with such a large port time area.
Variable valve timing could also be used with a fancy cam chain tensioner.
As Fastjeff said this was just a dream as it would never start without 9 sets of reed valves, even then it would need high speed starting! Which would be more work than the cylinder head.
The valves I planned to obtain from one of the Japanese motor cycle manufacturers as I didn't want to re invent the wheel
What the MOD 50/M31 needs is to have E Tec injectors
Waiting for Dave Bush to be able to mod e-tec paks..
Get computer control of your fuel curve
engine might pass EPA - green racing engine
Slight boost to volumetric efficiency as no fuel coming in the front
Not sure what to do with the oil though, drop in in the front I guess
Will require oil pump
Might need customs pistons
Will need custom head
ok just put e tec 90 on race mid and lower
Fuel coming in the front increases volumetric efficiency by evaporating and cooling the air causing the air to contract.
Yesterday's test session was scratched in favor of demo rides as Virgo performed almost perfectly from the start. Weather was 70F+/- with a heavy overcast and mist, but no wind. All were impressed with the incredible power and relative quiet. Racers Eric Vanover, Rich Welch, and Jimmy Robb (Jr.) all drove. From memory, initial comments included: OMG! Holy SH&%!, Vicious, etc. If the boat was top ended, Eric made it happen as you’ll see in a video (or two) to be loaded soon to YouTube.
On the subject, friend John Mitchell shot well framed video with my pocket camera. Unfortunately quality is lacking compared to prior work by Vic Banta, but the sound is great: You’ll get a good feel for performance. Not to worry, though. There’s one more opportunity to secure a quality shoot at Dixon Smith’s where it will run side-by-side with his 2.5 Merc drag hydro.
Observers on the beach included Mark Suter, Dave Brill, Ed Weinert, Brian Cafarelli, Jim Robb (Sr.), Bob Dunlap, Mark Wheeler, Jason Hay, Steve Hueninck, and many others. All recognized the engine as nicely built, and were stunned by its performance. Perhaps you’ll see a comment or two posted.
During the demo rides, a handful of technical issues were observed:
1) The engine starts easily cold and idles nicely. Unfortunately, the additional fuel bleed caused a rich off-boost condition. It four-strokes heavily, and had difficulty with one hot restart (flooded).
2) The revised oil reservoir is still inadequate. Oil vapors/drips still escape the vent.
3) The Methanol enrichment system works great, except the reservoir size allows only 10-15 minutes of spirited driving – actually might be about right.
Post test inspection found:
4) Gear oil is clean and backlash is good: No external signs of overstress - yet.
5) Cranking compression was appx. 135 PSI for all cylinders – unchanged.
6) Plug reads were dark coffee with black in the recesses - clearly over-rich.
That’s all for this report. Idle re-jetting will be take place tomorrow. More information and hopefully better video will be posted after the next outing.
For those that would like to see/discuss the engine, it will be on display October 22 at Mark Suter’s AOMCI antique meet in Byron, MI (about halfway between Brighton and Lansing). In case you don’t know: Mark and his wife Elaine created a fabulous museum of including appx. 350 outboards, of which 150 or so are racing engines – Alkys, Mods, and Stocks. Google AOMCI and click on “upcoming events” for more information.
Video links:
http://www.youtube.com/watch?v=dMpwqn10czE
http://www.youtube.com/watch?v=OeJltlXMN8I
[QUOTE=Tim Kurcz;110680] Not to worry, though. There’s one more opportunity to secure a quality shoot at Dixon Smith’s where it will run side-by-side with his 2.5 Merc drag hydro.
Tim, I'm looking into my cyrstal ball and I see us side by side right up until you knod your head and reality sets in. Must be the long snowy winter combined with AV gas fumes erased some memory of your ride last fall in the 2.5 V-6 Merc. This reminds me of the time I decieded to take on the school bully after school and wound up in the hospital!
I weighed my hydro today and it was 567# ready to go with motor, 3/4 tank of 110 octane gas, and battery with 330-350 HP, so you better make sure your spray shield is down before we hit it!
Although I have never offically draged it through timers, the previous owner claimed it went 140 in 8.3 sec with a stock 260 HP Merc.
http://www.youtube.com/watch?v=8eGFumvGujo
Hey Dixon,
Hmmmm; the math says you've got about 2.5:1 power to weight on me - yikes! So, you should be happy to spot me a few boat lengths! On thing for sure, the turbo adds enormous punch to the ride. It'll be fun to see how it all works out. Let's hope for better weather next weekend.
Tim
How about that sweet V6 sound!
Tim, I'm glad you brought it to my attention about the 2 1/2 to one HP advantage I have over you. IMO, that's cutting it a bit close, I prefer at least a three to one HP advantage over anyone I line up with so I'll be running the expansion chambers this weekend which should put me in a solid four to one HP over you to avoid any controversial results.
http://i1112.photobucket.com/albums/...onchambers.jpg
Tim, Sunday is way better for me because I won't be getting my nitrous tanks back from filling until Saturday afternoon. Have you ever tried the direct port mega-fogger super blast nitrous system on any of your motors? It works great, but the downside is you only get a couple of short runs out of a motor and it uses an entire tank of premium nitrous for a six second run, but I guess that's the price of tripling your HP.
Dixon
You're going through alot of trouble to wax my little OMC - it must make you nervous! Just took delivery of a 14 pitch Dewald that will carry 115+ 15 PSI boost and the nitromethane shoud narrow the range, nitrous or not........ It will be interesting and fun!
Tim