Fast Fred's OMC Mod 50 secrets Thread #2

[Tim Kurcz]

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

[clough]

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

i know the questions been asked but what kind of work would it be to setup some kind of exhaust valve? i know it wouldnt be operated by a cam so it is way above my knowledge but im sure theres someone out there that could do it! could be you tim!

[Tim Kurcz]

http://www.boatracingfacts.com/forum...t=7707&page=10

Here's an exercise on your exhaust valve concept.......... scroll way down the page.

Tim

[Mark75H]

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

[Powerabout]

if you lose pressure out of the exhaust port, surely you just lower ther port.....
easier said than done

[Mark75H]

if you lose pressure out of the exhaust port, surely you just lower ther port.....
easier said than done

I don't understand

[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

[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