Okay, so the Ecotec in the 02-05 Cavaliers has 2.2L of displacement. Also, if I'm correct, they're running roughly a 10:1 compression ratio, right? So tell me if this next statement is correct based on the previous statements. If one were to buy pistons which lower the compression ratio from 10:1 to 8.9:1 / 9:1, it then lowers the displacement of the engine from 2.2L to 2.0L, right?
Also, if the pistons have a .020" overbore, where does that put the displacement on a 8.9:1 compression ratio 2.0L Ecotec, does it not really make much of a difference for it to change the displacement? What about handling higher power levels for things such as boost? What are the benefits of a .020" overbore on 8.9:1 Pistons?
Thanks.
P.S. I know it's a lot of questions, and they're all probably pretty simple/strange, but I'm attempting to learn all I can, and this would help me out a lot. Thanks again.
displacement has nothing to do with compression ratio. displacement is all about bore and stroke
Okay, so then buying .020" overbored pistons would increase the engines displacement, gotcha.
About the stroke, I thought that buying pistons with a larger compression ratio would decrease the stroke, apparently that's wrong, could someone explain to me how that works, or link me to something that does then?
Thanks PJ. And thanks to anybody who answers the new questions.
.020 overbore wont increase displacement that much. i think you neeed at least .040 overbore
Im a Xbox 360 fanboy...and damn proud of it!!
no higher compression pistons just push the air/fuel mix into a tighter space to produce more compression of the mix and a more powerful explosion in the chamber thus creating more power
overboring isn't for displacement increase, its for getting into fresh cylinder wall if the engine is worn.
the onlytime that will increase to a noticable effect is if you go 2mm or more and that (i'm pretty sure) isn't possible without sleeves.
stroke is effected only by the crank. no matter what the compression of the piston is (the height of the piston will change) it still travels the same distance because of the crank.
same if you were to run shorter rods. the stroke is still the same. the only thing that changes stroke is changing the crank.
Alright guys, thanks tons for the help and info. I feel like I'm a little more less stupid now.
DaFlyinSkwirl (PJ) - BPU++ wrote:overboring isn't for displacement increase, its for getting into fresh cylinder wall if the engine is worn.
the onlytime that will increase to a noticable effect is if you go 2mm or more and that (i'm pretty sure) isn't possible without sleeves.
stroke is effected only by the crank. no matter what the compression of the piston is (the height of the piston will change) it still travels the same distance because of the crank.
same if you were to run shorter rods. the stroke is still the same. the only thing that changes stroke is changing the crank.
Theres a kit for the fiero .040 overbore and its supposed to increase displacement by .3l. For Js that'd probably translate to about .2l. As far as the rods go: its how big you go. Doing something small on the rods won't change anything, but going say 1/4 an inch longer would make a difference in compression ratio and torque (longer piston stroke = more torque rather than hp).
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a long rod would change compression, but a longer rod does not change stroke
think about it... the journal offset on the crank is what makes the rod move. if the rod is longer.. it still moves the same distance.
for example.. the crank is set for a 94mm stroke (like the 2.2 eco) it doesn't matter if the rod is 2" long or 24" long, its only going to move up and down 94mm.
you're not gaining .2L with a .040 overbore either.
86mm bore x 94mm stroke x 4 cylinders = 2185cc or 2.185L
0.040 overbore = 1mm
87mm bore x 94mm stroke x 4 cylinders = 2236cc or 2.236L
so by overboring .040 (or 1mm since the eco is a metric engine) you gain 0.051cc or 0.051L
like I said. overboring that little bit is only for fresh cylinder walls, nothing more. Don't belive muscle car jargon, hear-say, and old wives' tales. they have ricers too, they're just harder to spot.
don't overbore unless you have to. the only thing you're doing is taking away from a possible future rebuild because you used up too much of the cylinder wall for an increase of displacement thats not much larger than a table spoon
Rob Durrett wrote:
Theres a kit for the fiero .040 overbore and its supposed to increase displacement by .3l. For Js that'd probably translate to about .2l. As far as the rods go: its how big you go. Doing something small on the rods won't change anything, but going say 1/4 an inch longer would make a difference in compression ratio and torque (longer piston stroke = more torque rather than hp).
Im not sure where you read that. I know that a 350 sbc is different than a 2.2 eco but the rules of cubic engine dispalcement and liters still apply the same. If you bore out a 350 .030 overbore then you only get a 355. There are approximately 61.4 cubic inces per liter so a 350 is a 5.7 and a 355 is somthing like a 5.78. therefore there is no way you could chage the displacement in a small fiero motor or eco by that much and only an overbore of .040. In a 2.2 liter there is not that much change in displacement that would be a noticable in power difference. As far as longer rods go you do gain horsepower because they cause less friction in the rotating assembly. This causes the engine to free up more of the power it is already making somewhat similar to a lighter pulley making things easier to spin. Thats why you always hear about people building 350's with a 6" rod. You would also need different pistons because i believe if you could find a longer rod for an eco without changing the piston it would crash into the head. There is no way possible that a rod can change displacement of an engine thats all in the storke of the crank and the bore of the motor as stated above. Changing the rod length only changes the angle at which the crank pushes the piston up the bore giving it more leverage and has nothing to do with more or less stroke.
Thank you very much. Very nice post
I appreciate all the help guys. Thanks again.
