Tightest "Quench"...
09-12-2012, 03:57 PM
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Tightest "Quench"... Looks like many folks are claiming an ideal .035-0.45 quench on stock bottom end ls1's. How about for an all-forged n/a bottom end? I'm currently building a 383, and am going to have AI do a "216" job on some 243 castings for me, and am just trying to crunch some numbers to help determine ideal chamber vol., gasket thickness, etc....
Any thoughts?
Any thoughts?
09-12-2012, 05:43 PM
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Yep. Got all that covered...just looking to see what is a reasonable quench in a forged bottom end as compared to stock....sounds like .035 is about right then.
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09-14-2012, 04:21 PM
#15
There are two sides of the fence to this argument.
One is build the most powerful N/A motor you can and then spray it to achieve maximum performance.
The other is build the least timing sensitive nitrous motor you can and spray the ever living **** out of it.
The first thought while good will be timing sensitive and will most likely want to be a plug eater unless you are a highly skilled tuner who can read spark plugs and can be patient and take his time. There is only so much you can do with high dynamic compression numbers and tight quench when it comes to steep valve angle cylinder heads and heavy nitrous use. You'll have to run it very low on timing, lower than what is considered "in-line" or normal with other combinations and the camshaft IMO will not be optimal for nitrous as it will retain too much heat in the chamber with an EVO that is not early enough.
The second thought allows you wiggle room. You keep the static compression high like a N/A motor but you up the cam timing to keep the DCR low and this also involves more quench as more quench will also lower the DCR. When this is done you can spray more nitrous safely and not have a motor that is so sensitive to timing and large amounts of nitrous. You also change the exhaust side of the cam timing to evacuate the cylinder sooner of the spent exhaust gases by making the EVO event much earlier to start the blow down of the piston sooner and to allow all that combustion that is being accelerated by the use of nitrous to escape and not be absorbed by the spark plug, cylinder and piston itself.
If I was going to spray more than 350-400hp worth of nitrous I would go with option number two as it allows more room for error and IMO will make the same amount of power if not more and not have a overly sensitive combination that likes to make ash trays out of pistons.
If I was going to stay under 300hp worth of nitrous I would build the most powerful N/A motor I could and try and optimize the cam timing as best I could for that amount of nitrous, basically borrowing cam timing events from both sides of this proverbial coin.
If you're still with me hear I think you will understand now why I said what I did. Hope this makes sense, as I could of explained it better and taken a little bit longer to do so, but in a nutshell that is the theory behind it. Really isn't theory as it's been proven many many times in heads up racing that option number 2 is the way to go for heavy nitrous or boost.
09-14-2012, 05:26 PM
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That isn't really what I consider heavy nitrous but I will elaborate.
There are two sides of the fence to this argument.
One is build the most powerful N/A motor you can and then spray it to achieve maximum performance.
The other is build the least timing sensitive nitrous motor you can and spray the ever living **** out of it.
The first thought while good will be timing sensitive and will most likely want to be a plug eater unless you are a highly skilled tuner who can read spark plugs and can be patient and take his time. There is only so much you can do with high dynamic compression numbers and tight quench when it comes to steep valve angle cylinder heads and heavy nitrous use. You'll have to run it very low on timing, lower than what is considered "in-line" or normal with other combinations and the camshaft IMO will not be optimal for nitrous as it will retain too much heat in the chamber with an EVO that is not early enough.
The second thought allows you wiggle room. You keep the static compression high like a N/A motor but you up the cam timing to keep the DCR low and this also involves more quench as more quench will also lower the DCR. When this is done you can spray more nitrous safely and not have a motor that is so sensitive to timing and large amounts of nitrous. You also change the exhaust side of the cam timing to evacuate the cylinder sooner of the spent exhaust gases by making the EVO event much earlier to start the blow down of the piston sooner and to allow all that combustion that is being accelerated by the use of nitrous to escape and not be absorbed by the spark plug, cylinder and piston itself.
If I was going to spray more than 350-400hp worth of nitrous I would go with option number two as it allows more room for error and IMO will make the same amount of power if not more and not have a overly sensitive combination that likes to make ash trays out of pistons.
If I was going to stay under 300hp worth of nitrous I would build the most powerful N/A motor I could and try and optimize the cam timing as best I could for that amount of nitrous, basically borrowing cam timing events from both sides of this proverbial coin.
If you're still with me hear I think you will understand now why I said what I did. Hope this makes sense, as I could of explained it better and taken a little bit longer to do so, but in a nutshell that is the theory behind it. Really isn't theory as it's been proven many many times in heads up racing that option number 2 is the way to go for heavy nitrous or boost.
There are two sides of the fence to this argument.
One is build the most powerful N/A motor you can and then spray it to achieve maximum performance.
The other is build the least timing sensitive nitrous motor you can and spray the ever living **** out of it.
The first thought while good will be timing sensitive and will most likely want to be a plug eater unless you are a highly skilled tuner who can read spark plugs and can be patient and take his time. There is only so much you can do with high dynamic compression numbers and tight quench when it comes to steep valve angle cylinder heads and heavy nitrous use. You'll have to run it very low on timing, lower than what is considered "in-line" or normal with other combinations and the camshaft IMO will not be optimal for nitrous as it will retain too much heat in the chamber with an EVO that is not early enough.
The second thought allows you wiggle room. You keep the static compression high like a N/A motor but you up the cam timing to keep the DCR low and this also involves more quench as more quench will also lower the DCR. When this is done you can spray more nitrous safely and not have a motor that is so sensitive to timing and large amounts of nitrous. You also change the exhaust side of the cam timing to evacuate the cylinder sooner of the spent exhaust gases by making the EVO event much earlier to start the blow down of the piston sooner and to allow all that combustion that is being accelerated by the use of nitrous to escape and not be absorbed by the spark plug, cylinder and piston itself.
If I was going to spray more than 350-400hp worth of nitrous I would go with option number two as it allows more room for error and IMO will make the same amount of power if not more and not have a overly sensitive combination that likes to make ash trays out of pistons.
If I was going to stay under 300hp worth of nitrous I would build the most powerful N/A motor I could and try and optimize the cam timing as best I could for that amount of nitrous, basically borrowing cam timing events from both sides of this proverbial coin.
If you're still with me hear I think you will understand now why I said what I did. Hope this makes sense, as I could of explained it better and taken a little bit longer to do so, but in a nutshell that is the theory behind it. Really isn't theory as it's been proven many many times in heads up racing that option number 2 is the way to go for heavy nitrous or boost.
09-15-2012, 05:15 PM
#17
Not really. Higher or lower DCR is just a by-product of tightening or loosening the quench.
Tighter quench speeds up the flame front in the combustion chamber and makes for a faster burn in the chamber. In a N/A motor that operates at atmospheric pressures and isn't using an accelerant like nitrous or creating huge amounts of cylinder pressure with a lot of boost a tight quench helps to speed the burn of the combustion mixture up to create more power with less ignition timing being required to do so, making higher amounts of timing inefficient.
When you introduce a lot of boost or nitrous it will speed the flame front up on it's own, and combined with a tight quench it can be even harder to control the flame speed and you end up running so little timing to compensate that it becomes inefficient at making power. Also when using large amounts of nitrous or boost, cylinders will become uneven and require slightly different amounts of timing and fuel to stay happy and having a very fast burn combined with a power adder that makes the fast burn characteristics worse can make ashtrays of your pistons.
A looser quench in those applications will be a lot more forgiving on the tune-up and also to weather changes. Like I had mentioned above DCR is a by-product of the quench used and adjusting static compression to compensate for the added quench is done for best results. So you end up having the compression you want to make power while giving yourself a slight margin for error.
The amount of compression, fuel, power adder, the amount of boost or nitrous being used cam timing and the application will determine what should be run as far as quench.
Hope this helps.
Tighter quench speeds up the flame front in the combustion chamber and makes for a faster burn in the chamber. In a N/A motor that operates at atmospheric pressures and isn't using an accelerant like nitrous or creating huge amounts of cylinder pressure with a lot of boost a tight quench helps to speed the burn of the combustion mixture up to create more power with less ignition timing being required to do so, making higher amounts of timing inefficient.
When you introduce a lot of boost or nitrous it will speed the flame front up on it's own, and combined with a tight quench it can be even harder to control the flame speed and you end up running so little timing to compensate that it becomes inefficient at making power. Also when using large amounts of nitrous or boost, cylinders will become uneven and require slightly different amounts of timing and fuel to stay happy and having a very fast burn combined with a power adder that makes the fast burn characteristics worse can make ashtrays of your pistons.
A looser quench in those applications will be a lot more forgiving on the tune-up and also to weather changes. Like I had mentioned above DCR is a by-product of the quench used and adjusting static compression to compensate for the added quench is done for best results. So you end up having the compression you want to make power while giving yourself a slight margin for error.
The amount of compression, fuel, power adder, the amount of boost or nitrous being used cam timing and the application will determine what should be run as far as quench.
Hope this helps.
