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Home > Help Needed / General Tech Chat > 18cc Piston Help | |||||||
13 Posts Member #: 11468 Member Milton Keynes |
13th Sep, 2017 at 01:54:29pm
Afternoon all,
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307 Posts Member #: 11231 Senior Member |
13th Sep, 2017 at 02:01:16pm
To my knowledge in the past there used to be the 15cc Omegas but I guess there aren't being produced anymore. I had the same problem when buying mine for the twin cam build. |
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7259 Posts Member #: 1268 The Boom Boom speaker Police! Essex |
13th Sep, 2017 at 02:32:00pm
You could have a small amount skimmed from the head.
In the 13's at last!.. Just |
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13 Posts Member #: 11468 Member Milton Keynes |
13th Sep, 2017 at 02:37:17pm
Yep I guess so, or deck the block slightly. I'd rather not touch the head as its a nicely ported N/A head.
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450 Posts Member #: 10396 Advanced Member Formerly mk2turbo Stoke-on-Trent |
13th Sep, 2017 at 02:55:15pm
Get some more material removed from the 10cc omegas? |
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7259 Posts Member #: 1268 The Boom Boom speaker Police! Essex |
13th Sep, 2017 at 02:58:38pm
Ah. I'd definitely get the pistons flush with the deck. In the 13's at last!.. Just |
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2618 Posts Member #: 1246 Post Whore Lowestoft, Suffolk. |
13th Sep, 2017 at 07:21:41pm
The 10cc omegas can be opened up to give 14cc, also there is a difference in compressed volume of the bk450 and the af470, only miniamal but this may help.
Edited by shane on 13th Sep, 2017. |
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9502 Posts Member #: 1023 Post Whore Doncaster, South Yorkshire |
13th Sep, 2017 at 09:28:21pm
reading between the lines on what you have put is sounds like you already know this but im going to write it anyway
Yes i moved to the darkside
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2618 Posts Member #: 1246 Post Whore Lowestoft, Suffolk. |
13th Sep, 2017 at 11:39:20pm
Someone may want to double check this but based on ;
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13 Posts Member #: 11468 Member Milton Keynes |
14th Sep, 2017 at 08:40:40am
Cheers for the replies.
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12307 Posts Member #: 565 Carlos Fandango Burnham-on-Crouch, Essex |
14th Sep, 2017 at 08:46:45am
block decking is irrelevent, any motor should be decked to get the pistons pretty much flush.
On 28th Aug, 2011 Kean said:
At the risk of being sigged... Joe, do you have a photo of your tool? http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1 https://joe1977.imgbb.com/ |
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13 Posts Member #: 11468 Member Milton Keynes |
14th Sep, 2017 at 08:51:32am
Hi Joe,
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12307 Posts Member #: 565 Carlos Fandango Burnham-on-Crouch, Essex |
14th Sep, 2017 at 10:56:48am
basically squish band as below,
On 28th Aug, 2011 Kean said:
At the risk of being sigged... Joe, do you have a photo of your tool? http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1 https://joe1977.imgbb.com/ |
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13 Posts Member #: 11468 Member Milton Keynes |
14th Sep, 2017 at 12:34:49pm
Ok that all makes sense.
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Forum Mod 10979 Posts Member #: 17 ***16*** SouthPark, Colorado |
14th Sep, 2017 at 02:33:44pm
Good points bought up here, but I can't help wonder if getting the pistons flush with the deck is good (as we all know is considered "optimal"), is having them proud - say half the gasket thickness - better? Basically, can you have too thin of a squish thickness? Maybe these 18cc pistons with their very small radial width of squish band (about 3-4mm) would benfit more than a piston with a wider land?
On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY |
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307 Posts Member #: 11231 Senior Member |
14th Sep, 2017 at 04:28:43pm
So then with a standard stroke and standard deck, how much will the 18cc forged omegas sit below the deck ? |
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12307 Posts Member #: 565 Carlos Fandango Burnham-on-Crouch, Essex |
14th Sep, 2017 at 06:39:02pm
ummmm a fair bit, pretty sure I had 50 thou taken off my block, but that could have been the build before.
On 28th Aug, 2011 Kean said:
At the risk of being sigged... Joe, do you have a photo of your tool? http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1 https://joe1977.imgbb.com/ |
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307 Posts Member #: 11231 Senior Member |
14th Sep, 2017 at 07:08:24pm
50thou ?? Thats a lot !! |
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11046 Posts Member #: 965 Post Whore Preston On The Brook |
14th Sep, 2017 at 08:32:47pm
Good squish also promotes 'Quench'. Basically, the space is so narrow the charge is difficult to ignite due to the boundary layers of the piston and head. Quench is good since detonation tends to start around the squish band. Charge in this area of the cylinder is usually known as the 'end gas' (the charge that tends to burn towards the end of the burn initiated by the spark). If the charge wont burn in this area, the cylinder less detonation sensitive. This also leads on to when detonation occurs. Detonation is reasonably predictable in most cases in that it occurs somewhere around 14 degrees after TDC. Basically the piston is starting its travel down the bore and this 'squish' or 'quench' area is getting taller, if it is tall enough by the mechanical make up of the fitted parts, that allows the charge in this area of the cylinder to burn, detonation can occur more easily. This is not to say that it prevents detonation, just that it makes the cylinder less detonation sensitive.
On 26th Oct, 2004 TurboDave16v said:
Is it A-Series only? I think it should be... So when some joey comes on here about how his 16v turbo vauxhall is great compared to ours, he can be given the 'bird'... On 26th Oct, 2004 Tom Fenton said:
Yep I agree with TD........ |
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307 Posts Member #: 11231 Senior Member |
14th Sep, 2017 at 09:03:28pm
Good info sprocket. There is a golden book on this subject really. It's called "Internal Combustion Engine Fundanentals" |
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307 Posts Member #: 11231 Senior Member |
14th Sep, 2017 at 09:07:10pm
Now thatyou started the subject I'm a bit wooried as I didn't know about this problem that the 18cc sit do low below the deck. I've handed the block over to the machinist this week. So I guess when I'll get it back I will check the piston to deck clearance and off it goes again to have a little bit chopped off the deck. I'm aiming for 9:1 but with the 50thou Joe mentioned, that'll get me down to around 8:1. |
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11046 Posts Member #: 965 Post Whore Preston On The Brook |
14th Sep, 2017 at 09:27:52pm
On 14th Sep, 2017 Barrieri said:
Now thatyou started the subject I'm a bit wooried as I didn't know about this problem that the 18cc sit do low below the deck. I've handed the block over to the machinist this week. So I guess when I'll get it back I will check the piston to deck clearance and off it goes again to have a little bit chopped off the deck. I'm aiming for 9:1 but with the 50thou Joe mentioned, that'll get me down to around 8:1. Surely you mean 5 thou or 0.005"? On 26th Oct, 2004 TurboDave16v said:
Is it A-Series only? I think it should be... So when some joey comes on here about how his 16v turbo vauxhall is great compared to ours, he can be given the 'bird'... On 26th Oct, 2004 Tom Fenton said:
Yep I agree with TD........ |
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307 Posts Member #: 11231 Senior Member |
14th Sep, 2017 at 11:24:55pm
Is it 5 Thou or 50 Thou Joe ? |
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Forum Mod 10979 Posts Member #: 17 ***16*** SouthPark, Colorado |
15th Sep, 2017 at 01:29:18am
I suspect it's 50 thou - stock na Pistons are about 30 thou down iirc, and I recall hearing these big cc pistons are a way down. On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY |
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Forum Mod 4823 Posts Member #: 154 Post Whore Midlands |
15th Sep, 2017 at 04:20:22pm
On 14th Sep, 2017 danllew said:
I've had a look but has anyone got any details of how much meat can be taken out of either the cast omegas or 21253's? I've seen the 21253's out at 14.7cc before, I ran them at 11cc On 20th Oct, 2015 Tom Fenton said:
Well here is the news, you are not welcome here, FUCK OFF. |
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