dreadstealth
Registered Member
i want to know what the maximum compression anyone has heard of in a gas or diesel motor any and all info able to be provided would be helpful.
thanks
thanks
CK5
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highest compression ratings
- Thread starter dreadstealth
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BadBob
1/2 ton status
The 6.2L diesels were 22.5:1, that's about the highest I remember seeing on anything.
I believe the top fuel stuff is up around 15:1, and I've heard that gasoline direct injection also allows higher compression ratio. Obviously fuel plays a large part in tolerance to compression.
On a gas engine, more compression really doesn't get you much power, it's the engine combination.
Need to know where you are going with this.
On a gas engine, more compression really doesn't get you much power, it's the engine combination.
Need to know where you are going with this.
Agreed on both, I've heard Top fuel as low as 12.5:1 at sea level tracks, and 15:1 at Denver.
The old GM 5.7 diesels have 22.5 if I recall correctly. Thats the highest I've heard of.
The old GM 5.7 diesels have 22.5 if I recall correctly. Thats the highest I've heard of.
desertrat67
Hawk Driver
On the topic of the Olds 5.7 diesel, it was a 350 gasser converted to diesel. Hot rod guys/racers use these to build high compression gas engines. The fuel injectors are pulled and spark plugs are put into the same holes. Different pistons are used to achieve a lower compression than the 22.5:1 one, but it is still 15+
dreadstealth
Registered Member
well im trying to see how much pressure an engine can take without going boom. i was looking at a single piece long block. no removeable heads or gaskets. running an extremely high "octane" fuel. would it be possible to run 50-75:1 compression or would the motor find the weekest point and go boom?
The engine would go BOOM. Pretty sure that the diesels with 22.5:1 compression ratio is about the max you're gonna find. Also there are only a few engines that don't have a removable cylinder head and no V/8's that i'm aware of.
dreadstealth said:
My understanding is that there is more to it than just compression ratio.....cylinder pressure is also affected by cam timing. If you play around with the overlap of the valves, the valves will still be open slightly during the beginning of the compression stroke so the amount of "squeeze" you get is not as high as the CR would suggest....some of that air/fuel is being pushed out before the valves are both closed. That reduces the amount of cylinder pressure.
I am pretty sure that programs like DeskTop Dyno have features that will show cylinder pressure as a function of cam overlap and timing.... someone with a more brain power will need to chime in to confirm/deny all of these ramblings of mine.
smalltruckbigcid
1/2 ton status
2 kinds of engines come sort of close, top fuel drag, and some tractor pullers. The top fuel motor because it runs at almost the point of hydraulic lockup, so if the cylinder cuts out, it generally pushes the head off and bends the rod and other parts.
The tractor pullers who run 2 and 3 stage turbos that push something like 175psi boost might be closer to what you are talking about.
If your trying to achieve more useable power (higher effiency) then I think your chasing the circle of diminshing returns. In short the more you do to make this viable in terms of strength the more power it will consume to run. That much compression will require a reciprocating assembly built so heavy a crane will be needed to move it. And that much weight means high drag on the rotational force.
Instead try this on your next engine. With a fully assembled long block with no spark plugs check the torque needed to turn it over. A standard rebuild needs 35~50 lbft of tq to turn it over but a pro stock or nextel cup motor the goal is to achieve less than 20lbft of tq. Kill the parasitic drag from the internal assemblies and things go much better.....
George
The tractor pullers who run 2 and 3 stage turbos that push something like 175psi boost might be closer to what you are talking about.
If your trying to achieve more useable power (higher effiency) then I think your chasing the circle of diminshing returns. In short the more you do to make this viable in terms of strength the more power it will consume to run. That much compression will require a reciprocating assembly built so heavy a crane will be needed to move it. And that much weight means high drag on the rotational force.
Instead try this on your next engine. With a fully assembled long block with no spark plugs check the torque needed to turn it over. A standard rebuild needs 35~50 lbft of tq to turn it over but a pro stock or nextel cup motor the goal is to achieve less than 20lbft of tq. Kill the parasitic drag from the internal assemblies and things go much better.....
George
3 on the tree
1/2 ton status
Back in the 60s/70s, the big 3 had their hottest motors with up to 13/1 comp ratios. My 70 429 has 10.5/1 factory. That is as high as I would go on a "street" motor. Even that will probably require judicious timing and octane booster.
smalltruckbigcid said:
The drag engines are "loose" to achieve those low parasitic losses, only to the point it detracts from the "gained" performance of that certain part. They don't have to live long, so running greater clearances on bearings, and other parts, has a benefit of freeing up horsepower. Not what you might like for a street engine to live long.
The cylinder pressure is what I think your zeroing in on. That generally comes from a combination of CR, boost, fuel, cam timing, etc. It has to be the combination of all these to know how the engine will respond, or blow because of to much pressure.
Thats one of the reasons the Hemi ruled, built loose... They where estimated to have a 50,000 mile life from the factory...
Highest compression motors I see are obviously diesel... Some marine diesels push 25, 30 to 1, at about 500, 600 lbs of cylinder pressure..
Highest I would ever consider these days with gas is 10.5, maybe 11 to 1.. I had a bud back in the 70's running a BB at 13.5 to 1...
What I'm curious as to is, what he's talking about with a 1-piece block, never heard of such a thing, and can't imagine it being feasable within reasonable means...
Highest compression motors I see are obviously diesel... Some marine diesels push 25, 30 to 1, at about 500, 600 lbs of cylinder pressure..
Highest I would ever consider these days with gas is 10.5, maybe 11 to 1.. I had a bud back in the 70's running a BB at 13.5 to 1...
What I'm curious as to is, what he's talking about with a 1-piece block, never heard of such a thing, and can't imagine it being feasable within reasonable means...
smalltruckbigcid
1/2 ton status
Some marine inline 4 cylinders are one piece like that with the block and head as one...mercrusier maybe? I saw one about 20 years ago.
Tight versus loose. Its really more of how you spec the ring pack, low drag rings will last a long time if not heavily abused. And wouldn't you say that a nextel cup engine that lasts 500 miles at 8000 plus rpm lived a long time.
Tight versus loose. Its really more of how you spec the ring pack, low drag rings will last a long time if not heavily abused. And wouldn't you say that a nextel cup engine that lasts 500 miles at 8000 plus rpm lived a long time.
Doubt it was Merc, more than likely a Kohler gen set, or even an Onan...
Pretty certain the Hemi's bearing clearences are what was considered "loose" back in the day...
Either way, it's all a balance... CR, Cam profile, etc.. Or at least it should be..
Pretty certain the Hemi's bearing clearences are what was considered "loose" back in the day...
Either way, it's all a balance... CR, Cam profile, etc.. Or at least it should be..
