14:1 static compression ratio on pump gas and the "Its all about the tune" excuse...
11-28-2009, 02:06 PM
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14:1 static compression ratio on pump gas and the "Its all about the tune" excuse... A rather misinformed friend of mine has been telling me for awhile that you could run a built LS1 with 14:1 static compression ratio ON 93 OCTANE PUMP GAS... WTF?!?! He said that all you would really have to do is to take out a lot of timing in the tune to however low you could go, i.e. 14 degrees of timing at WOT and the car will still run decently and still have a lot of power... Now, please help me put this argument to rest because I'm thinking that running an LSX motor with a 14:1 static compression ratio on 93 octane pump gas is either next to impossible to tune unless you are a superior LSX tuner or simply 100% BS... FWIW, I will show him this thread so please sound professional in your responses. Thanks!
11-28-2009, 02:14 PM
#2
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Well it also depends on the DCR, if DCR is respectable range it is possible.
I run 12:1 on 93 with a 9.0 DCR still make good power 24* max timing.
Also to do that you would have to factor in tight quench and dual pads would not hurt either along with proper plug heat range..
Basicaly it is not imposible, but why go through the trouble if lesser compression would make equal power or perhaps even more.
I run 12:1 on 93 with a 9.0 DCR still make good power 24* max timing.
Also to do that you would have to factor in tight quench and dual pads would not hurt either along with proper plug heat range..
Basicaly it is not imposible, but why go through the trouble if lesser compression would make equal power or perhaps even more.
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NewOrleansLT1 (06-25-2023)
11-28-2009, 02:36 PM
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Of course, wouldn't it be logical to have a rather big cam in a higher compression motor in order to bleed off excess compression to deter detonation? This does sound a little counter productive IHMO. And if you had a small cam in that high compression motor that didn't really bleed off a lot of compression, would you still be able to tune a motor with say a 10.8:1 dynamic compression ratio to run pump gas as long as you pulled out even more timing? I'm still wondering about this whole deal because my guess is that there is most likely much more precision and $$$ involved building a 14:1 compression motor vs a motor that only has 11:1.
11-28-2009, 04:02 PM
#7
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Very dumb idea. You want to run a cam that traps or creates as much VE as possible in the rpm band you actually are using whether racing or street and run just enough compression with that so you can run full timing and actually make some power. We have stuff running mid 9s on pump gas and it's never higher than 11.50 to 1 and usually lower.
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no way it whould last on pump gas
11-28-2009, 05:16 PM
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Nothing is ever impossible, but if he wants a higher compression ratio, go diesel. These motors aren't durable enough to withstand the beating of high c/r constantly. It really isn't worth trying for or arguing over.
11-28-2009, 11:40 PM
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And if you didn't have cats, you'd think that the egts would be hot enough for the headers and exhaust pipes to glow red hot and melt exhaust pipe hangers... Well I'm just guessin' at this point. It probably would backfire like crazy...
11-28-2009, 11:47 PM
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That kind of static compression would require pop up pistons. You just couldn't get a combustion chamber small enough for flat tops. My point being with pop up pistons and pulled back timing, you would have such a convuluted flame front, complete combustion would be nearly impossible. I have to agree with the others. Sounds like a bad plan.
11-29-2009, 12:08 AM
#12
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That kind of static compression would require pop up pistons. You just couldn't get a combustion chamber small enough for flat tops. My point being with pop up pistons and pulled back timing, you would have such a convuluted flame front, complete combustion would be nearly impossible. I have to agree with the others. Sounds like a bad plan.
Last edited by PREDATOR-Z; 11-29-2009 at 12:21 AM.
11-30-2009, 12:43 PM
#13
Yes, it would backfire quite a lot. With the headers ceramic-coated inside and out, you could keep from melting everything nearby, but try a 12:1 build before going off the deep end. And to get high compression with flat tops, you want all the bore and stroke you can get. GM's LSX block can go 511 ci. That might get you in range. I'm not doing the math, because it's not a good project.
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NewOrleansLT1 (06-25-2023)
11-30-2009, 02:13 PM
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A rather misinformed friend of mine has been telling me for awhile that you could run a built LS1 with 14:1 static compression ratio ON 93 OCTANE PUMP GAS... WTF?!?! He said that all you would really have to do is to take out a lot of timing in the tune to however low you could go, i.e. 14 degrees of timing at WOT and the car will still run decently and still have a lot of power... Now, please help me put this argument to rest because I'm thinking that running an LSX motor with a 14:1 static compression ratio on 93 octane pump gas is either next to impossible to tune unless you are a superior LSX tuner or simply 100% BS... FWIW, I will show him this thread so please sound professional in your responses. Thanks!
.
09-15-2014, 06:21 PM
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The Compression Ratio (CR) of an engine is the ratio of the cylinder volume compared to the combustion chamber volume. A cylinder with 10 units of volume (called the sweep volume) and a chamber with a volume of 1 has a 10:1 compression ratio. Static Compression Ratio (SCR) is the ratio most commonly referred to. It is derived from the sweep volume of the cylinder using the full crank stroke (BDC to TDC). Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.
The difference between the two can be substantial. For example, with a cam that closes the intake valve at 70º ABDC, the piston has risen 0.9053" from BDC in a stock rod 350 at the intake closing point. This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch. Thereby reducing the compression ratio. This is the only difference between calculating the SCR and the DCR. All other values used in calculating the CR are the same. Note that the DCR is always lower than the SCR.
Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors. DCR is derived from measured or calculated values that are the actual dimensions of the engine. Therefore, unless variable cam timing is used, just like the static compression ratio, the Dynamic Compression Ratio, is fixed when the engine is built and never changes during the operation of the engine. so you can run the 14:1 if you use variable timing, and as long as you are not driving around with your foot stuck to the floor. On top of that if your looking to raise the compression just to produce more horsepower, Then just spend your money on a turbo and don't waste your time with anything else.
The difference between the two can be substantial. For example, with a cam that closes the intake valve at 70º ABDC, the piston has risen 0.9053" from BDC in a stock rod 350 at the intake closing point. This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch. Thereby reducing the compression ratio. This is the only difference between calculating the SCR and the DCR. All other values used in calculating the CR are the same. Note that the DCR is always lower than the SCR.
Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors. DCR is derived from measured or calculated values that are the actual dimensions of the engine. Therefore, unless variable cam timing is used, just like the static compression ratio, the Dynamic Compression Ratio, is fixed when the engine is built and never changes during the operation of the engine. so you can run the 14:1 if you use variable timing, and as long as you are not driving around with your foot stuck to the floor. On top of that if your looking to raise the compression just to produce more horsepower, Then just spend your money on a turbo and don't waste your time with anything else.
09-15-2014, 07:01 PM
#18
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The Compression Ratio (CR) of an engine is the ratio of the cylinder volume compared to the combustion chamber volume. A cylinder with 10 units of volume (called the sweep volume) and a chamber with a volume of 1 has a 10:1 compression ratio. Static Compression Ratio (SCR) is the ratio most commonly referred to. It is derived from the sweep volume of the cylinder using the full crank stroke (BDC to TDC). Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.
The difference between the two can be substantial. For example, with a cam that closes the intake valve at 70º ABDC, the piston has risen 0.9053" from BDC in a stock rod 350 at the intake closing point. This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch. Thereby reducing the compression ratio. This is the only difference between calculating the SCR and the DCR. All other values used in calculating the CR are the same. Note that the DCR is always lower than the SCR.
Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors. DCR is derived from measured or calculated values that are the actual dimensions of the engine. Therefore, unless variable cam timing is used, just like the static compression ratio, the Dynamic Compression Ratio, is fixed when the engine is built and never changes during the operation of the engine. so you can run the 14:1 if you use variable timing, and as long as you are not driving around with your foot stuck to the floor. On top of that if your looking to raise the compression just to produce more horsepower, Then just spend your money on a turbo and don't waste your time with anything else.
The difference between the two can be substantial. For example, with a cam that closes the intake valve at 70º ABDC, the piston has risen 0.9053" from BDC in a stock rod 350 at the intake closing point. This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch. Thereby reducing the compression ratio. This is the only difference between calculating the SCR and the DCR. All other values used in calculating the CR are the same. Note that the DCR is always lower than the SCR.
Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors. DCR is derived from measured or calculated values that are the actual dimensions of the engine. Therefore, unless variable cam timing is used, just like the static compression ratio, the Dynamic Compression Ratio, is fixed when the engine is built and never changes during the operation of the engine. so you can run the 14:1 if you use variable timing, and as long as you are not driving around with your foot stuck to the floor. On top of that if your looking to raise the compression just to produce more horsepower, Then just spend your money on a turbo and don't waste your time with anything else.
Lets please let this useless thread rest in piece.
