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High Compression Onan CCK & LK Heads

Mariner

Subscriber
Last Subscription Date
06/12/2019
Are high compression heads limited to gaseous fuel only? What are your thoughts on the usage of high compression CCK OR LK heads with gasoline?

Thanks
 

turtmaster

Subscriber
Last Subscription Date
07/01/2020
Do you mean the 7:1 ratio heads? They were standard on the cckb gasoline lawn tractor engines, for 87 octane gasoline, they will work just fine on gasoline, but the same can't necessarily be said about other engines like the Jb and JC engines.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
When I restored an old LK, I replaced the low compression head with a left side CCK high compression head. I run gas and gasoline and never had a problem with either using the high compression head. One thing I want to say is that the high compression head really woke up my LK big-time! Is was well worth it.

JohnnyC
New Jersey
 

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turtmaster

Subscriber
Last Subscription Date
07/01/2020
The part number that you listed for that high compression cylinder head, is correct for the 7:1 compression ratio cylinder head, will be fine for running on gasoline.
 

lokay5

Registered
Last Subscription Date
01/11/2015
"...the high compression head really woke up my LK big-time!"

And you determined this how, exactly? :shrug:
 

Mariner

Subscriber
Last Subscription Date
06/12/2019
Thanks for the info. I feel better about putting a heavy load on it with the HCH/Gasoline combo.
 

Motorhead

Subscriber
Age
67
Last Subscription Date
07/09/2019
And what exactly was the difference?
I put a high compression head on my 2.5lk and it produced more amperage and stayed at 60hz than it did with the 5.5 to 1 head. and YES.... I tested the difference by a load test also. I'm sure you will have something else to say about this. :rolleyes:
I have a set on my 5.0CCK that runs vapor or gasoline. I added timing to the engine. When I run gasoline, I usually run mid grade. With 87 regular the set would knock once in a while with a HOT shut down.
 

lokay5

Registered
Last Subscription Date
01/11/2015
If this works so well, it begs the question: Why didn't Onan make 'em that way?:shrug:
 

turtmaster

Subscriber
Last Subscription Date
07/01/2020
The really weird thing is, my 2.5LK with I believe a cracked ring, because of the huge white clouds of smoke upon startup, but none when running,
And approximately if I remember correctly ~90-95 psi compression, can still handle a 500 watt overload, in other words, a load test of 3000w, I still have voltage and frequency within acceptable limits, both with and without load. :shrug:
Btw it also has over a thousand hours on it, now does any of the above info add up? I think not!, How though, I have no clue.
 

Mariner

Subscriber
Last Subscription Date
06/12/2019
Motorhead, did you have to adjust the timing on your LK when you added the high compression head?
 

Motorhead

Subscriber
Age
67
Last Subscription Date
07/09/2019
Motorhead, did you have to adjust the timing on your LK when you added the high compression head?
You don't have to adjust if you are not gong to be running slower burning vapor fuels. I run mid grade in my onans so I can tolerate timing advance. the high compression head will help in economy and adding advance can help too.
On my 5.0CCK that car run either, in my case, gasoline or natural gas, I set the timing up to 22*.
 

Sooty Jim

Registered
If this works so well, it begs the question: Why didn't Onan make 'em that way?:shrug:
A higher compression ratio produces more power but the reason why high compression engines are not often used on continuous or heavy duty-rated gasoline engines is that the higher ratio produces higher combustion temperatures. That's harder on the piston crowns and valves, and it increases general engine temps, including oil temperature. All of that tends to decrease engine life and lessen reliability. Remember these engines are designed to run our after hour, day after day.

Remember when big trucks still have HD gas engines? Same deal, they were low compression so they could operate safely for long periods at a high load factor.

As was stated, higher octane fuel is needed and the timing must be remapped (generally by decreasing advance or base timing).

You can compensate to some degree by adding cooling capacity to an engine updated with a higher ratio but with air cooled engines, cooling efficiency is often dictates by ambient air temperature, making the cooling system more efficient on cool days than on hot ones. I learned this the hard way by putting 9.0:1 pistons in an engine built for a VW bus. Thing was a real goer (relative to stock ( : < ) but when I started doing a lot of running the hills at highway speeds in hot weather, it only took a summer to pretty much smoke the upper end.

If the generator was running at it's original rated load, there is probably enough of a safety factor in the design to carry the engine thru a more or less normal life. That's usually true with all machines. In the case of these engines, that would not be true if it was run in hot weather or if the load was increased to match the extra power. For occasional use or as a collector piece, no problemo.

The HC heads were designed for high altitude operation to gain back some of the power lost to lower atmospheric pressure.

The original designer selected the compression ratio as a compromise between output, common fuels and reliability with a 100 percent load factor, or some other similar parameter.
 

Vanman

Subscriber
Last Subscription Date
06/10/2020
The heat rejected by a generator set engine at rated load will be less with a higher compression ratio. Same power out, less fuel (heat) in equals less heat out.

The higher compression ratio will increase the maximum hp capability of the engine, but the stress on the engine remains the same because the (generator) load remains the same.

Vehicles are different as higher hp from higher compression can and will be used. It seems to me that gasoline must be better than it was in the early days of gasoline engines.

My '31 Ford is only 4-1/2 : 1 CR and makes 38 hp from 200 ci. Obviously this could be much higher, but the bottom end was not designed for it, and no doubt would not tolerate too much more power.

Keith
 

zuhnc

Subscriber
Last Subscription Date
12/08/2019
My 1951 Ford 8N tractor has 6:1 compression and makes about 25Hp@ 2000 rpm, 120 cu. in. Designed to run all day at 1500 pulling a plow or other implement. Still running, and has about 110 psi compression. Specs say minimum of 90. Hasn't been rebuilt, best I can tell. Very long life at that compression and speed:). zuhnc
 

flyerguy

Registered
You don't have to adjust if you are not gong to be running slower burning vapor fuels. I run mid grade in my onans so I can tolerate timing advance. the high compression head will help in economy and adding advance can help too.
On my 5.0CCK that car run either, in my case, gasoline or natural gas, I set the timing up to 22*.
Hey Motor Head can you point me to a pair of higher comp. heads for a 6.6 NH series
 

Motorhead

Subscriber
Age
67
Last Subscription Date
07/09/2019
I am not familiar with the 6.6 NH. Is that a VAPOR set? Look at the spec sheet for your set and in the specifications section for the engine, it should have the compression ratio.
 

luc102

Registered
Well my 15 jc was built from factory on propane and definetly has hchs .. if over heat ever became a problem id use a water-meth injector and just add it to the equation.. really cools down your explosions .. cleans the cylinders and improve combustion..

For those not familliar with it . Its generic name is basically windshiel washer at 15% methanol.. wall mart brand has it.. or alcohol based windshield washer..but meth is the best.. very cheap solution..

Go to your local scrap yard get a gas pump from a car .. order a 0.05 mil injector and tap in the intake in front of carburator and.. voila you have a water- meth injected genny... very efficient .. should be on a separate switch as you would need it only on heavy loads or could be triggered by a temp switch ..

I built that car from scratch .. way to much HP couldent get engine temp down enough then added water meth and worked great..

3000 hp dragsters use it not for power .. they use it to keep the engine from meltdown...if any interests give me your engines HP and ill tell you the injector size and you need at least 75 psi .. car pumps deliver that easilly..
 

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