Fast Fred's OMC Mod 50 secrets Thread #2

[Tim Kurcz]

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

[NERSTROM]

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.

[Powerabout]

Hi Jim

Any photos in existence?

Cheers

[Fastjeff57]

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

[Tim Kurcz]

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.

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

[Tim Kurcz]

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

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

[MN1]

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.

I think one of the turbos (V4 I think) went to St. Louis one year. With Ken Stevenson driving. I don't think it raced, just tested. Did this happen at St. Louis or another race site?
Mark N

[Powerabout]

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/

[Tim Kurcz]

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

[Barry Strawn]

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