When the heads come off of my Toyota 3VZE, I want to see if I need shim gaskets. So, I'd like to calculate the comp. ratio, and compare it to stock.
Please tell me how to calculate compression ratio
- Thread starter Stelth
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Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
l
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Originally Posted By: Chris142
l
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Or you overbore. +.10", .20", all the way up to .60".. = Compression ratio is raised.
Higher compression ratio = Requires higher octane gasoline?
Last but not least, some speculate that carbon buildup on pistons actually increases compression a minute amount, and "helps" combustion due to the carbon getting hot...
l
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Or you overbore. +.10", .20", all the way up to .60".. = Compression ratio is raised.
Higher compression ratio = Requires higher octane gasoline?
Last but not least, some speculate that carbon buildup on pistons actually increases compression a minute amount, and "helps" combustion due to the carbon getting hot...
Oversized pistons are often destroked to keep the ratio the same
Head gasket thickness comes into the equasion also. Ed
Originally Posted By: asand1
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Originally Posted By: Stelth
Originally Posted By: asand1
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Yes. Or you could just run premium.
Originally Posted By: asand1
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Yes. Or you could just run premium.
Last edited:
.600" overbore ?
Originally Posted By: asand1
Originally Posted By: Stelth
Originally Posted By: asand1
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Yes. Or you could just run premium.
This...I am curious...as the owner of a 3VZE that's never been apart, you're on your second head removal? Why? How is the bottom end of the engine?
As far as cc'ing them, you could, because the thickness will change a minute amount, but if you've only removed a tiny bit, then the change will be minor, this wasn't a very high compression engine.
One other thing that might change with a difference in deck height on the head, is the valve timing...not much, but the camshaft pulley will be a tiny bit closer to the crankshaft pulley, right? So, that will rotate the cam by a degree or two...so there is more to keeping the stock deck height than just compression...I wouldn't worry about compression (those things need all the help that they can get) but I wonder about the camshaft/crank angle relationship if the pulleys are moved closer together....
Originally Posted By: Stelth
Originally Posted By: asand1
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Yes. Or you could just run premium.
This...I am curious...as the owner of a 3VZE that's never been apart, you're on your second head removal? Why? How is the bottom end of the engine?
As far as cc'ing them, you could, because the thickness will change a minute amount, but if you've only removed a tiny bit, then the change will be minor, this wasn't a very high compression engine.
One other thing that might change with a difference in deck height on the head, is the valve timing...not much, but the camshaft pulley will be a tiny bit closer to the crankshaft pulley, right? So, that will rotate the cam by a degree or two...so there is more to keeping the stock deck height than just compression...I wouldn't worry about compression (those things need all the help that they can get) but I wonder about the camshaft/crank angle relationship if the pulleys are moved closer together....
OVERKILL
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Originally Posted By: TechnoLoGs
Originally Posted By: Chris142
l
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Or you overbore. +.10", .20", all the way up to .60".. = Compression ratio is raised.
Higher compression ratio = Requires higher octane gasoline?
Last but not least, some speculate that carbon buildup on pistons actually increases compression a minute amount, and "helps" combustion due to the carbon getting hot...
I'm hoping you mean 0.010, 0.020, 0.030....etc.
Originally Posted By: Chris142
l
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Or you overbore. +.10", .20", all the way up to .60".. = Compression ratio is raised.
Higher compression ratio = Requires higher octane gasoline?
Last but not least, some speculate that carbon buildup on pistons actually increases compression a minute amount, and "helps" combustion due to the carbon getting hot...
I'm hoping you mean 0.010, 0.020, 0.030....etc.
Originally Posted By: OVERKILL
Originally Posted By: TechnoLoGs
Originally Posted By: Chris142
l
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Or you overbore. +.10", .20", all the way up to .60".. = Compression ratio is raised.
Higher compression ratio = Requires higher octane gasoline?
Last but not least, some speculate that carbon buildup on pistons actually increases compression a minute amount, and "helps" combustion due to the carbon getting hot...
I'm hoping you mean 0.010, 0.020, 0.030....etc.
Yes, you are correct, it was the .01 .02 .03 etc. My bad
Also, what is "de-stroked to match" ? How can that be? I thought overbore = bored AND stroked = more power..
Originally Posted By: TechnoLoGs
Originally Posted By: Chris142
l
Originally Posted By: asand1
Compression ratio does not change over time. You need change piston crown or heads or something else. If your engine is stock it still the same ratio.
true unless the heads have been milled.
Or you overbore. +.10", .20", all the way up to .60".. = Compression ratio is raised.
Higher compression ratio = Requires higher octane gasoline?
Last but not least, some speculate that carbon buildup on pistons actually increases compression a minute amount, and "helps" combustion due to the carbon getting hot...
I'm hoping you mean 0.010, 0.020, 0.030....etc.
Yes, you are correct, it was the .01 .02 .03 etc. My bad
Also, what is "de-stroked to match" ? How can that be? I thought overbore = bored AND stroked = more power..
Mis-print. Stroke is determined by crank throw. Pistons can have a different height (or shape) above the wrist pin...leading to different compression...
it only proves you are human, but arent we all? if that was the biggest mistake i ever made i would be doing great
Originally Posted By: Astro14
Originally Posted By: asand1
Originally Posted By: Stelth
Originally Posted By: asand1
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Yes. Or you could just run premium.
This...I am curious...as the owner of a 3VZE that's never been apart, you're on your second head removal? Why? How is the bottom end of the engine?
As far as cc'ing them, you could, because the thickness will change a minute amount, but if you've only removed a tiny bit, then the change will be minor, this wasn't a very high compression engine.
One other thing that might change with a difference in deck height on the head, is the valve timing...not much, but the camshaft pulley will be a tiny bit closer to the crankshaft pulley, right? So, that will rotate the cam by a degree or two...so there is more to keeping the stock deck height than just compression...I wouldn't worry about compression (those things need all the help that they can get) but I wonder about the camshaft/crank angle relationship if the pulleys are moved closer together....
OK. I got this vehicle ('91 4Runner) free from a friend who doesn't want to do the head gaskets again. The 3VZE is a well-known head-gasket-blower, and the people that owned this 4Runner before put a lot of money into it, including what they called "new" heads. I've done head gaskets in the past, and I really don't feel like doing it this time. So I have it up at my mechanic, who is pretty inexpensive. He is also a smog guy, and says that if the heads are milled too much, the compression will go high enough to cause higher NOx emissions, and it may not pass smog. Therefore, I want to keep the compression close to the stock figure.
As far as the bottom end, I'm not really sure, except that it passed smog the last time around, which usually indicates that things aren't too bad. If this vehicle ends up needing a new engine, I'll scrap it, and consider the money I pay for disassembly well-spent.
Originally Posted By: asand1
Originally Posted By: Stelth
Originally Posted By: asand1
Bore x stroke for cylinder vloume.
Cylinder volume + combustion camber volume
Divided by combustion chamber volume = compression ratio.
Thanks. The heads on this engine may have been rebuilt before, and, once they're off, we'll see if they need to be done again. If they need to be resurfaced, then I can cc them and see if I need shims. Right?
Yes. Or you could just run premium.
This...I am curious...as the owner of a 3VZE that's never been apart, you're on your second head removal? Why? How is the bottom end of the engine?
As far as cc'ing them, you could, because the thickness will change a minute amount, but if you've only removed a tiny bit, then the change will be minor, this wasn't a very high compression engine.
One other thing that might change with a difference in deck height on the head, is the valve timing...not much, but the camshaft pulley will be a tiny bit closer to the crankshaft pulley, right? So, that will rotate the cam by a degree or two...so there is more to keeping the stock deck height than just compression...I wouldn't worry about compression (those things need all the help that they can get) but I wonder about the camshaft/crank angle relationship if the pulleys are moved closer together....
OK. I got this vehicle ('91 4Runner) free from a friend who doesn't want to do the head gaskets again. The 3VZE is a well-known head-gasket-blower, and the people that owned this 4Runner before put a lot of money into it, including what they called "new" heads. I've done head gaskets in the past, and I really don't feel like doing it this time. So I have it up at my mechanic, who is pretty inexpensive. He is also a smog guy, and says that if the heads are milled too much, the compression will go high enough to cause higher NOx emissions, and it may not pass smog. Therefore, I want to keep the compression close to the stock figure.
As far as the bottom end, I'm not really sure, except that it passed smog the last time around, which usually indicates that things aren't too bad. If this vehicle ends up needing a new engine, I'll scrap it, and consider the money I pay for disassembly well-spent.
To the OP, I'm really not sure why you are trying to figure out your compression ratio and why on earth you would want to "shim" your head...compression ratio is calculated by taking the swept volume and dividing it by the combustion chamber volume. So deck heights, gasket thickness all need to be taken into account.
Most heads will clean up with less than 0.010 milled off with 0.005 being about average. That amount is worth less than 0.1 on your compression ratio, it which case you would not have to change grades of gas.
I've never heard of de-stroking a piston, I'm not sure how you would even do that??? Custom crank offset grind??? Shorter rods??? Mill the tops of the pistons??? None of this is ever done...
If you are really concerned about the heads being milled before, then go ahead and cc them but if you think you can resurface them again I'm afaid you might be out of luck if they were cut down to the service limit the first go around. Even so, you will likely not need to shim them, Asian engines are not prone to detonation like the old big V8s. I've had 2 Hondas that I took 0.020" off (for added power) during rebuilds with no ill effects and still passed smog testing.
Most heads will clean up with less than 0.010 milled off with 0.005 being about average. That amount is worth less than 0.1 on your compression ratio, it which case you would not have to change grades of gas.
I've never heard of de-stroking a piston, I'm not sure how you would even do that??? Custom crank offset grind??? Shorter rods??? Mill the tops of the pistons??? None of this is ever done...
If you are really concerned about the heads being milled before, then go ahead and cc them but if you think you can resurface them again I'm afaid you might be out of luck if they were cut down to the service limit the first go around. Even so, you will likely not need to shim them, Asian engines are not prone to detonation like the old big V8s. I've had 2 Hondas that I took 0.020" off (for added power) during rebuilds with no ill effects and still passed smog testing.
FWIW...my engine has never been apart. There were some problems with 3VZE HGs in those years, but a second failure isn't right...yours should have been fixed the first time under a recall...by the dealer...and I am really surprised that it needs to be done again. The bottom end on this engine is strong.
My 4 Runner has been a great truck...slow, but reliable under some really trying conditions. It has 240,000 on it.
I would have the heads checked, mill them if needed and throw it back together. Don't worry too much about compression ratio or NOx...you're not taking off enough to change any of that appreciably (unless one got warped by overheating...in which case, I would replace it with another rebuild) .just fix it and drive it.
My 4 Runner has been a great truck...slow, but reliable under some really trying conditions. It has 240,000 on it.
I would have the heads checked, mill them if needed and throw it back together. Don't worry too much about compression ratio or NOx...you're not taking off enough to change any of that appreciably (unless one got warped by overheating...in which case, I would replace it with another rebuild) .just fix it and drive it.
Well, as the first steps of disassembly were undertaken, it became clear that more has been going on. The intake tract and throttle body are very oily, so I'm not sure about rings, etc.
Therefore, I've found a used engine with good compression that is probably going into it.
Therefore, I've found a used engine with good compression that is probably going into it.
Originally Posted By: Stelth
Well, as the first steps of disassembly were undertaken, it became clear that more has been going on. The intake tract and throttle body are very oily, so I'm not sure about rings, etc.
Therefore, I've found a used engine with good compression that is probably going into it.
What condition was the pcv valve in?
Well, as the first steps of disassembly were undertaken, it became clear that more has been going on. The intake tract and throttle body are very oily, so I'm not sure about rings, etc.
Therefore, I've found a used engine with good compression that is probably going into it.
What condition was the pcv valve in?
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