CTR pistons VS .25 oversize??
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From: Bellingham, WA, USA
Re: CTR pistons VS .25 oversize?? (evo)
well, you are cleaning off the cylinder walls, so you can start fresh with the new rings.. And you are going to be increasing displacement slightly, and increasing the compression ratio slightly..
Is that enough?
[Modified by martini, 9:09 AM 8/6/2002]
Is that enough?
[Modified by martini, 9:09 AM 8/6/2002]
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From: WI, USA
Re: CTR pistons VS .25 oversize?? (evo)
To overbore or not will depend on if you think the cylinder walls are scored or not or if you feel you need/want the extra bit of displacement.
I rebuilt the engine in my 85 CRX Si and started with an engine with ~160k on it. I only needed to recrosshatch the cylinder walls and use new rings and it ran great. This was in a street car and I did not want to pop for new pistons so just bead blasted the old ones and reused them.
Good luck
I rebuilt the engine in my 85 CRX Si and started with an engine with ~160k on it. I only needed to recrosshatch the cylinder walls and use new rings and it ran great. This was in a street car and I did not want to pop for new pistons so just bead blasted the old ones and reused them.
Good luck
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From: Renton, WA
Re: CTR pistons VS .25 oversize?? (martini)
The oversize will increase the compression ratio slight. THey CTR pistons will increase the CR significantly.
Stock (PR3): ~10.2
.25 Over PR3: ~10.25
CTR Standard: ~10.8
CTR Over: ~10.85
10.85 CR should still be able to use 92 Octane fuel without detonation... should have a fairly significant hp/torque improvement, how much I'm not sure.
Stock (PR3): ~10.2
.25 Over PR3: ~10.25
CTR Standard: ~10.8
CTR Over: ~10.85
10.85 CR should still be able to use 92 Octane fuel without detonation... should have a fairly significant hp/torque improvement, how much I'm not sure.
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From: San Diego
Re: CTR pistons VS .25 oversize?? (rotten)
you wont feel the dif between std and os... but it is nice to know that your walls are in perfect shape after the bore and hone when using os pistons
[Modified by cl4show, 7:40 AM 8/22/2002]
[Modified by cl4show, 7:40 AM 8/22/2002]
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From: Trinidad, W.I.
Re: CTR pistons VS .25 oversize?? (sparkz)
Basically honing means the process giving it a crosshatch.
To the guy that said there would be a compression increase from the 0.25 overbore.... how do you figure an increase in displacement to give an increase in compression ratio ?
CTR's will give more compression= more Hp/tq and the overbore will give you more displacement=more hp/tq... might only be like.. 2-4hp (from overbore)... but something !
X2
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From: PASADENA, CA, USA
Re: CTR pistons VS .25 oversize?? (evo)
I'm still unsure what's the difference between Crosshatch and Hone??
Can anyone explain to me, Thanks..
Can anyone explain to me, Thanks..
Crosshatching is either performed during the honing process or after the honing process. Crosshatching ensures a good seal for the piston rings. They're criss-crossed lines that you can visually see on the cylinder walls, created by a honing tool.
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From: Trinidad, W.I.
Re: CTR pistons VS .25 oversize?? (Katman)
Honing is when the cylinder walls have a very small layer 'sanded' off to create a smooth, cross hatched surface... the cross hatch is a RESULT of honing... it's not done at the same time. Honing gets rid of small imperfections and the seating created by the previously used rings. Without it done, you can get some compression loss thru deeply seated gooves.
BORING (to get the cylinder BORED) is when you increase cylinder wall internal diameter for a larger piston.
Honing still does widen the wall (very slightly), but is not meant to increase bore, just to smooth the walls, which is one of the reasons you should ALWAYS use new rings on a freshly honed block.
X2
BORING (to get the cylinder BORED) is when you increase cylinder wall internal diameter for a larger piston.
Honing still does widen the wall (very slightly), but is not meant to increase bore, just to smooth the walls, which is one of the reasons you should ALWAYS use new rings on a freshly honed block.
X2
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From: PASADENA, CA, USA
Re: CTR pistons VS .25 oversize?? (X2BOARD)
Honing is when the cylinder walls have a very small layer 'sanded' off to create a smooth, cross hatched surface... the cross hatch is a RESULT of honing... it's not done at the same time. Honing gets rid of small imperfections and the seating created by the previously used rings. Without it done, you can get some compression loss thru deeply seated gooves.
BORING (to get the cylinder BORED) is when you increase cylinder wall internal diameter for a larger piston.
Honing still does widen the wall (very slightly), but is not meant to increase bore, just to smooth the walls, which is one of the reasons you should ALWAYS use new rings on a freshly honed block.
X2
BORING (to get the cylinder BORED) is when you increase cylinder wall internal diameter for a larger piston.
Honing still does widen the wall (very slightly), but is not meant to increase bore, just to smooth the walls, which is one of the reasons you should ALWAYS use new rings on a freshly honed block.
X2
you 'honed' my reponse
[Modified by Katman, 9:12 AM 8/22/2002]
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From: Bellingham, WA, USA
Re: CTR pistons VS .25 oversize?? (X2BOARD)
To the guy that said there would be a compression increase from the 0.25 overbore.... how do you figure an increase in displacement to give an increase in compression ratio ?
Increasing the bore will increase the volume of the combustion chamber at BDC by quite a bit, at TDC, you will be very close to having the same volume as the stock bore. Take into consideration the piston-to-deck clearance is only .0762mm, and the headgasket bore may be increased slightly, but the head remains untouched.. So as long as the piston-to-deck clearance plus the headgasket thickness times 10.2 (or whatever your compression ratio was before the bore), is less than 89 (or whatever stroke you are using), it will increase the compression ratio.
I could go into all the math and such of it, but I think if you think it through, you'll understand, it's pretty simple. Maybe I just confused you more though.
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From: Trinidad, W.I.
Re: CTR pistons VS .25 oversize?? (martini)
To the guy that said there would be a compression increase from the 0.25 overbore.... how do you figure an increase in displacement to give an increase in compression ratio ?
Think about it.
Increasing the bore will increase the volume of the combustion chamber at BDC by quite a bit, at TDC, you will be very close to having the same volume as the stock bore. Take into consideration the piston-to-deck clearance is only .0762mm, and the headgasket bore may be increased slightly, but the head remains untouched.. So as long as the piston-to-deck clearance plus the headgasket thickness times 10.2 (or whatever your compression ratio was before the bore), is less than 89 (or whatever stroke you are using), it will increase the compression ratio.
I could go into all the math and such of it, but I think if you think it through, you'll understand, it's pretty simple. Maybe I just confused you more though.
Think about it.
Increasing the bore will increase the volume of the combustion chamber at BDC by quite a bit, at TDC, you will be very close to having the same volume as the stock bore. Take into consideration the piston-to-deck clearance is only .0762mm, and the headgasket bore may be increased slightly, but the head remains untouched.. So as long as the piston-to-deck clearance plus the headgasket thickness times 10.2 (or whatever your compression ratio was before the bore), is less than 89 (or whatever stroke you are using), it will increase the compression ratio.
I could go into all the math and such of it, but I think if you think it through, you'll understand, it's pretty simple. Maybe I just confused you more though.
I am trying to understand your explaination, but a .25 overbore is an OEM option and it does not require modification to the combustion chamber nor does it require changes to headgasket diameter
X2
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From: Bellingham, WA, USA
Re: CTR pistons VS .25 oversize?? (X2BOARD)
ok, so if it requires no modification to the combustion chamber or headgasket, then how is there an increase in displacement?
When putting in the .25mm overbore pistons, you need to have the cylinders bored out by .25mm.
When putting in the .25mm overbore pistons, you need to have the cylinders bored out by .25mm.
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From: Renton, WA
Re: CTR pistons VS .25 oversize?? (martini)
First, it helps to think about C/R from a physical perspective--i.e. the volume uncompressed vs. compressed.
When you have a stock bore, say the volume of the cylinder 400 cc's when at BDC and 40 at TDC, which would be a 10:1 compression ratio.
When you overbore, you're only increasing the total volume when the piston is at BDC (uncompressed), it remains the same at TDC (compressed--picture the piston at TDC... the cylinder volume/bore doesn't matter because the piston is all the way at the top).
So basically you're going from
400 10
---- = ---
40 1
403 10.075
--- = -------
40 1
Its only ~8 100ths, but it definately does increase the C/R.
When you have a stock bore, say the volume of the cylinder 400 cc's when at BDC and 40 at TDC, which would be a 10:1 compression ratio.
When you overbore, you're only increasing the total volume when the piston is at BDC (uncompressed), it remains the same at TDC (compressed--picture the piston at TDC... the cylinder volume/bore doesn't matter because the piston is all the way at the top).
So basically you're going from
400 10
---- = ---
40 1
403 10.075
--- = -------
40 1
Its only ~8 100ths, but it definately does increase the C/R.
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From: Trinidad, W.I.
Re: CTR pistons VS .25 oversize?? (martini)
ok, so if it requires no modification to the combustion chamber or headgasket, then how is there an increase in displacement?
When putting in the .25mm overbore pistons, you need to have the cylinders bored out by .25mm.
When putting in the .25mm overbore pistons, you need to have the cylinders bored out by .25mm.
But following the simple explaination, I think I get it now. Although almost inconsequential, the bore does affect compression.
School's out !!!
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From: Bellingham, WA, USA
Re: CTR pistons VS .25 oversize?? (X2BOARD)
ah, but the combustion chamber does increase in size slightly, because your piston to deck clearance (distance from the "surface" of the piston to the deck), and the space between the top compression ring, and the "surface" (not the dome) of the piston.
and you're right, for hondas the stock headgasket works fine with a .25 overbore, but other engines you have to modify the headgasket.
anyways. I'm done.
cheers!
and you're right, for hondas the stock headgasket works fine with a .25 overbore, but other engines you have to modify the headgasket.
anyways. I'm done.
cheers!
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