Is it a good idea to bore only one cylinder?
01-29-2013, 10:07 PM
#21
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Wow, so the Asshat Mechanics Society is still going strong and looks like they could've suckered in more prey. That custom piston they talk about, that'll be a condom piston. I along with all others here think you should get that car right outta that shop, not tomorrow, not today but NOW. Ask again on this site for any suggestions as to reputable engine shops in your area if you're not sure.
01-31-2013, 09:11 AM
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I’m taking the official stance that yes, do all 6 or nothing at all.
However, I’m bored and feel like playing the devil’s advocate. So…
If you only over bore the cylinder by 1mm (~0.040”) the gain in mass of the piston can easily be balanced out since you’ll only be adding probably a couple of grams and most of them are only balanced to +/- 1 gram anyway.
Next, yes you’ll have a larger bore hence you’ll be pulling more air and possibly running that cylinder lean. Looking at the surface area of a stock piston it comes out to about 3581.5 mm^2 and a 1mm over bore comes out to 3656.9mm^2. This is roughly about a 2% increase in surface area and thus 2% more volume in the cylinder under static conditions. However, due to volumetric efficiencies (VE) at various rpms and choke points in the air path the actual change in cylinder air mass will probably less than the theoretical 2%. I would argue no one’s air fuel curve hold within 2% of the engines target value. There are just too many variables to control.
Compression ratios….yes that could possibly change as well, but being a ‘custom’ piston it could be made to correct this. But since I’m arguing on the side of ridiculous, let’s run with it. So we now have 1 cylinder with a higher SCR and more air with a leaner mixture. Let’s assume it also makes more power. Since only 1 cylinder fires at a time and it is probably more powerful by a very very small amount (<5%), it is probably still going to be operating within the ‘noise’ of any given cylinder anyway. Power comes from your dynamic compression ratio which is a mix of your static compression ratio (SCR) and your given VE at whatever particular rpm/load condition you’re under. I’ll argue your VE from cylinder to cylinder, especially on the VQ, varies by far more than 5% due mostly to the flow path of each cylinder has to take in order to reach the combustion chamber is drastically different. This is part of the reason plenums spacers and larger volume aftermarket plenums make decent power on this engine.
That being said, and poorly at that, don’t listen to my advice.
Cheers!
However, I’m bored and feel like playing the devil’s advocate. So…
If you only over bore the cylinder by 1mm (~0.040”) the gain in mass of the piston can easily be balanced out since you’ll only be adding probably a couple of grams and most of them are only balanced to +/- 1 gram anyway.
Next, yes you’ll have a larger bore hence you’ll be pulling more air and possibly running that cylinder lean. Looking at the surface area of a stock piston it comes out to about 3581.5 mm^2 and a 1mm over bore comes out to 3656.9mm^2. This is roughly about a 2% increase in surface area and thus 2% more volume in the cylinder under static conditions. However, due to volumetric efficiencies (VE) at various rpms and choke points in the air path the actual change in cylinder air mass will probably less than the theoretical 2%. I would argue no one’s air fuel curve hold within 2% of the engines target value. There are just too many variables to control.
Compression ratios….yes that could possibly change as well, but being a ‘custom’ piston it could be made to correct this. But since I’m arguing on the side of ridiculous, let’s run with it. So we now have 1 cylinder with a higher SCR and more air with a leaner mixture. Let’s assume it also makes more power. Since only 1 cylinder fires at a time and it is probably more powerful by a very very small amount (<5%), it is probably still going to be operating within the ‘noise’ of any given cylinder anyway. Power comes from your dynamic compression ratio which is a mix of your static compression ratio (SCR) and your given VE at whatever particular rpm/load condition you’re under. I’ll argue your VE from cylinder to cylinder, especially on the VQ, varies by far more than 5% due mostly to the flow path of each cylinder has to take in order to reach the combustion chamber is drastically different. This is part of the reason plenums spacers and larger volume aftermarket plenums make decent power on this engine.
That being said, and poorly at that, don’t listen to my advice.
Cheers!
01-31-2013, 09:27 AM
#25
my biggest thing is that he bent a rod meaning its likely he is already detonating, while on a good tune with a good build it might theoretically be possible to do it with no issues he dosnt have that. so the detonation that is already happening and caused his issue in the first place is just going to be worse doing it that way =P
I’m taking the official stance that yes, do all 6 or nothing at all.
However, I’m bored and feel like playing the devil’s advocate. So…
If you only over bore the cylinder by 1mm (~0.040”) the gain in mass of the piston can easily be balanced out since you’ll only be adding probably a couple of grams and most of them are only balanced to +/- 1 gram anyway.
Next, yes you’ll have a larger bore hence you’ll be pulling more air and possibly running that cylinder lean. Looking at the surface area of a stock piston it comes out to about 3581.5 mm^2 and a 1mm over bore comes out to 3656.9mm^2. This is roughly about a 2% increase in surface area and thus 2% more volume in the cylinder under static conditions. However, due to volumetric efficiencies (VE) at various rpms and choke points in the air path the actual change in cylinder air mass will probably less than the theoretical 2%. I would argue no one’s air fuel curve hold within 2% of the engines target value. There are just too many variables to control.
Compression ratios….yes that could possibly change as well, but being a ‘custom’ piston it could be made to correct this. But since I’m arguing on the side of ridiculous, let’s run with it. So we now have 1 cylinder with a higher SCR and more air with a leaner mixture. Let’s assume it also makes more power. Since only 1 cylinder fires at a time and it is probably more powerful by a very very small amount (<5%), it is probably still going to be operating within the ‘noise’ of any given cylinder anyway. Power comes from your dynamic compression ratio which is a mix of your static compression ratio (SCR) and your given VE at whatever particular rpm/load condition you’re under. I’ll argue your VE from cylinder to cylinder, especially on the VQ, varies by far more than 5% due mostly to the flow path of each cylinder has to take in order to reach the combustion chamber is drastically different. This is part of the reason plenums spacers and larger volume aftermarket plenums make decent power on this engine.
That being said, and poorly at that, don’t listen to my advice.
Cheers!
However, I’m bored and feel like playing the devil’s advocate. So…
If you only over bore the cylinder by 1mm (~0.040”) the gain in mass of the piston can easily be balanced out since you’ll only be adding probably a couple of grams and most of them are only balanced to +/- 1 gram anyway.
Next, yes you’ll have a larger bore hence you’ll be pulling more air and possibly running that cylinder lean. Looking at the surface area of a stock piston it comes out to about 3581.5 mm^2 and a 1mm over bore comes out to 3656.9mm^2. This is roughly about a 2% increase in surface area and thus 2% more volume in the cylinder under static conditions. However, due to volumetric efficiencies (VE) at various rpms and choke points in the air path the actual change in cylinder air mass will probably less than the theoretical 2%. I would argue no one’s air fuel curve hold within 2% of the engines target value. There are just too many variables to control.
Compression ratios….yes that could possibly change as well, but being a ‘custom’ piston it could be made to correct this. But since I’m arguing on the side of ridiculous, let’s run with it. So we now have 1 cylinder with a higher SCR and more air with a leaner mixture. Let’s assume it also makes more power. Since only 1 cylinder fires at a time and it is probably more powerful by a very very small amount (<5%), it is probably still going to be operating within the ‘noise’ of any given cylinder anyway. Power comes from your dynamic compression ratio which is a mix of your static compression ratio (SCR) and your given VE at whatever particular rpm/load condition you’re under. I’ll argue your VE from cylinder to cylinder, especially on the VQ, varies by far more than 5% due mostly to the flow path of each cylinder has to take in order to reach the combustion chamber is drastically different. This is part of the reason plenums spacers and larger volume aftermarket plenums make decent power on this engine.
That being said, and poorly at that, don’t listen to my advice.
Cheers!
01-31-2013, 09:47 AM
#26
I’m taking the official stance that yes, do all 6 or nothing at all.
However, I’m bored and feel like playing the devil’s advocate. So…
If you only over bore the cylinder by 1mm (~0.040”) the gain in mass of the piston can easily be balanced out since you’ll only be adding probably a couple of grams and most of them are only balanced to +/- 1 gram anyway.
Next, yes you’ll have a larger bore hence you’ll be pulling more air and possibly running that cylinder lean. Looking at the surface area of a stock piston it comes out to about 3581.5 mm^2 and a 1mm over bore comes out to 3656.9mm^2. This is roughly about a 2% increase in surface area and thus 2% more volume in the cylinder under static conditions. However, due to volumetric efficiencies (VE) at various rpms and choke points in the air path the actual change in cylinder air mass will probably less than the theoretical 2%. I would argue no one’s air fuel curve hold within 2% of the engines target value. There are just too many variables to control.
Compression ratios….yes that could possibly change as well, but being a ‘custom’ piston it could be made to correct this. But since I’m arguing on the side of ridiculous, let’s run with it. So we now have 1 cylinder with a higher SCR and more air with a leaner mixture. Let’s assume it also makes more power. Since only 1 cylinder fires at a time and it is probably more powerful by a very very small amount (<5%), it is probably still going to be operating within the ‘noise’ of any given cylinder anyway. Power comes from your dynamic compression ratio which is a mix of your static compression ratio (SCR) and your given VE at whatever particular rpm/load condition you’re under. I’ll argue your VE from cylinder to cylinder, especially on the VQ, varies by far more than 5% due mostly to the flow path of each cylinder has to take in order to reach the combustion chamber is drastically different. This is part of the reason plenums spacers and larger volume aftermarket plenums make decent power on this engine.
That being said, and poorly at that, don’t listen to my advice.
Cheers!
However, I’m bored and feel like playing the devil’s advocate. So…
If you only over bore the cylinder by 1mm (~0.040”) the gain in mass of the piston can easily be balanced out since you’ll only be adding probably a couple of grams and most of them are only balanced to +/- 1 gram anyway.
Next, yes you’ll have a larger bore hence you’ll be pulling more air and possibly running that cylinder lean. Looking at the surface area of a stock piston it comes out to about 3581.5 mm^2 and a 1mm over bore comes out to 3656.9mm^2. This is roughly about a 2% increase in surface area and thus 2% more volume in the cylinder under static conditions. However, due to volumetric efficiencies (VE) at various rpms and choke points in the air path the actual change in cylinder air mass will probably less than the theoretical 2%. I would argue no one’s air fuel curve hold within 2% of the engines target value. There are just too many variables to control.
Compression ratios….yes that could possibly change as well, but being a ‘custom’ piston it could be made to correct this. But since I’m arguing on the side of ridiculous, let’s run with it. So we now have 1 cylinder with a higher SCR and more air with a leaner mixture. Let’s assume it also makes more power. Since only 1 cylinder fires at a time and it is probably more powerful by a very very small amount (<5%), it is probably still going to be operating within the ‘noise’ of any given cylinder anyway. Power comes from your dynamic compression ratio which is a mix of your static compression ratio (SCR) and your given VE at whatever particular rpm/load condition you’re under. I’ll argue your VE from cylinder to cylinder, especially on the VQ, varies by far more than 5% due mostly to the flow path of each cylinder has to take in order to reach the combustion chamber is drastically different. This is part of the reason plenums spacers and larger volume aftermarket plenums make decent power on this engine.
That being said, and poorly at that, don’t listen to my advice.
Cheers!
01-31-2013, 09:47 AM
#27
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I fully agree, I would take a long look at my tune if this were my engine. I don't know what, if any, mods are done to this car but if it has this much knock I would think it would be evident on the remaining pistons. Possibly bad gas, very bad. Plus the rods in the VQ are not notorious for being the strongest link either. But I had a few breathing mods on my old VQ (revup) and I tracked the hell out of it and when I pulled it with 75k miles it still ran like a champ with no issues and I had a stock tune.
01-31-2013, 09:50 AM
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We'll you really shouldn't overbore a vq without sleeves more than .5mm. A 96mm piston has about the minimum wall left to be considered safe. I had the choice to use a 30 thou block with custom pistons, or buy a new block, re-machine it and use 20 thou pistons. I chose the 20 thou (or .5mm) because that's about as far as you'd want to go on a vq35 w/ stock sleeves.
01-31-2013, 09:52 AM
#29
I fully agree, I would take a long look at my tune if this were my engine. I don't know what, if any, mods are done to this car but if it has this much knock I would think it would be evident on the remaining pistons. Possibly bad gas, very bad. Plus the rods in the VQ are not notorious for being the strongest link either. But I had a few breathing mods on my old VQ (revup) and I tracked the hell out of it and when I pulled it with 75k miles it still ran like a champ with no issues and I had a stock tune.
02-02-2013, 12:47 PM
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I fully agree, I would take a long look at my tune if this were my engine. I don't know what, if any, mods are done to this car but if it has this much knock I would think it would be evident on the remaining pistons. Possibly bad gas, very bad. Plus the rods in the VQ are not notorious for being the strongest link either. But I had a few breathing mods on my old VQ (revup) and I tracked the hell out of it and when I pulled it with 75k miles it still ran like a champ with no issues and I had a stock tune.
now that i think of it i was having alot of random misfire but i was told it is the split second box causing that code. I am looking into haltech.
02-02-2013, 01:02 PM
#32
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at a bare minimum you need to do an entire bank with a custom tune to compensate, altering the bore on just one cylinder is going to cause the afr on that cylinder to be off.
next i would find new people to work with since thats a bone head recommendation, doubly so because oil starvation dosnt cause bent rods it causes spun and destroyed bearings and bearing journals. bent rod means too much power for the rod, manufacturing defect, or a **** poor tune thats detonating. if its detonation then doing what they are suggesting is just going to make it worse.
next i would find new people to work with since thats a bone head recommendation, doubly so because oil starvation dosnt cause bent rods it causes spun and destroyed bearings and bearing journals. bent rod means too much power for the rod, manufacturing defect, or a **** poor tune thats detonating. if its detonation then doing what they are suggesting is just going to make it worse.
02-02-2013, 01:16 PM
#33
I can't see how it could be too much power for the rod as they were Carrillo SA rods, CP pistons, ARP STUD KIT. I was getting random misfire codes. I was told there was dried up oil in the oil pan indicating the car was ran low on oil causing starvation. I changed the oil every 3k. I'm thinking manufacturing error or bad gas, or tune as i was using a split second box.
02-02-2013, 02:32 PM
#34
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[QUOTE=e30cabrio;10030942]I was just about to post this.
If you are ok with doing this silly bandaid repair why ask?[/QUO
They are changing all of the pistons I misunderstood. after spending 20k trust me i don't want a band-aid
If you are ok with doing this silly bandaid repair why ask?[/QUO
They are changing all of the pistons I misunderstood. after spending 20k trust me i don't want a band-aid
02-02-2013, 03:07 PM
#36
read completely i said too much power, manufacturing defect OR **** poor tune. according to carrillo the SA rods are rated about the same as eagle rods but alot more cost(although much better quality control).
if you where using the ss box im willing to bet money thats what it was your not going to see very many manufacturing defects from carillo theres a reason you pay a premium.
you could have had some oil starvation however that guaranteed dint cause a bent rod. no oil means bearings catch, bearing catching means something has to give, crank, rod or bearing. i dont care what combo your running the bearing will be the weakest link every single time.
if you where using the ss box im willing to bet money thats what it was your not going to see very many manufacturing defects from carillo theres a reason you pay a premium.
you could have had some oil starvation however that guaranteed dint cause a bent rod. no oil means bearings catch, bearing catching means something has to give, crank, rod or bearing. i dont care what combo your running the bearing will be the weakest link every single time.
I can't see how it could be too much power for the rod as they were Carrillo SA rods, CP pistons, ARP STUD KIT. I was getting random misfire codes. I was told there was dried up oil in the oil pan indicating the car was ran low on oil causing starvation. I changed the oil every 3k. I'm thinking manufacturing error or bad gas, or tune as i was using a split second box.
02-03-2013, 08:42 AM
#37
I am an expert in oil starvation on built engines... the bearings will go first. If the tops of your pistons are all pitted, that will be signs of detonation. For an aftermarket rod to bend like that something must have been seriously off in the tune somewhere.
02-05-2013, 08:47 AM
#38
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I don't disagree. My point was simply it may be in the noise of the existing variation and depending on how the car is used you may never notice, but I still wouldn't do it. Especially, now that I see it's a very well massaged motor and is probably driven as such. Or at least it was...
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