Question What is the exact combustion chamber size on #643 casting - Page 2 - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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Old 11-08-2010, 04:41 AM   #16
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You can't change your combustion chamber size with spark plugs. Only way to change them is mill the heads, weld, or grind the chambers. Thinner gaskets are an easy way to raise your compression also.
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Old 11-08-2010, 10:27 PM   #17
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Right, but if you installed longer plugs regardless of how small of a gain you would see your still filling the combustion space with more material so you would lower your CC's regardless of how small.

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Old 11-08-2010, 10:32 PM   #18
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Quote:
Originally Posted by BLK95-Z View Post
the stock intake runner is 170cc for a LT1

....and 195 for the LT4. Not sure on the exhaust.
Did you CC these? it would be nice to know the exhaust side too.
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Old 11-08-2010, 11:20 PM   #19
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Quote:
Originally Posted by FueledSoul View Post
Did you CC these? it would be nice to know the exhaust side too.
No, those are the specs given by GM
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Old 11-09-2010, 04:17 AM   #20
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Quote:
Originally Posted by FueledSoul View Post
Right, but if you installed longer plugs regardless of how small of a gain you would see your still filling the combustion space with more material so you would lower your CC's regardless of how small.

There's this thing called the piston that could possibly get in the way. There is also possible detonation from the tip heating up too much. Lastly, if your threads extend a ways out and get all carboned up it's not going to be fun getting them out.
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Old 11-09-2010, 07:01 PM   #21
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Quote:
Originally Posted by FueledSoul View Post
Right, but if you installed longer plugs regardless of how small of a gain you would see your still filling the combustion space with more material so you would lower your CC's regardless of how small.
Things like this come up from time to time on Forums. Discussions and deciding between what "could" be done Vs what "should" be done.

Technically, you're correct. Even the tiniest amount of spark plug protrusion into the combustion chamber will effectively reduce the size of the chamber and result in a tiny increase in C.R.

Assuming we had the ability to accurately measure that small difference, and all things being equal, there would be a tiny increase in C.R. However, the downside far out-weighs ANY benefit.

As already mentioned by MIZ28, if any thread is exposed to the combustion process, it'll/they'll quickly begin to glow red hot and cause detonation. It's one of those MANY things that the best engine builders check for before the heads are bolted on.

So, even though you are technically correct, it isn't something you'll find as being recommended by anyone. In fact, it's something I've seen in the manuals as something NOT to do. So it's not recommended unless the guy making the recommendation has a grudge against you, LOL

Would C.R. increase? Technically/mathematically Yes. Provability is dependent on our ability to detect it using our equipment. I'm betting NASA could though.

Would any power improvement result? No, not within our ability to measure such tiny changes. Even then back-to-back dyno runs don't show the exact same results every tme.

Would doing this be of ANY benefit? No, just the opposite in fact.

Is this something that is recommended to be done or at least done by some guys? No and No (unless done unknowingly)

Are there any more questions I should have asked? No, you asked too many already.

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Old 11-12-2010, 05:20 PM   #22
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I just want to jump in for a minute.As a former NHRA stock class national
record holder. When you make your first attempt at a record run and go under the current nat. record,part of the checking procedure is sealing the spark plugs with a special paint. Now when you make your second run or backup your run you cannot change the plugs (MANY OTHER THINGS ARE SEALED,BUT SINCE WE ARE TALKING ABOUT COMBUSTION CHAMBER SIZE) The reason for this is exactly what you guys have been discussing .Different plugs have different tips and different types of projections,which could change the combustion chamber volume and increase compression just enough to possibly make a few more HP and a faster run. So during tear down when they cc your head they can make certain you were not running a higher than stock compression ratio. Hope I didnt make for more confusion.ed
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Old 11-12-2010, 06:59 PM   #23
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[QUOTE=Racy Roadmaster;369379]I just want to jump in for a minute.As a former NHRA stock class national
record holder. When you make your first attempt at a record run and go under the current nat. record,part of the checking procedure is sealing the spark plugs with a special paint. Now when you make your second run or backup your run you cannot change the plugs (MANY OTHER THINGS ARE SEALED,BUT SINCE WE ARE TALKING ABOUT COMBUSTION CHAMBER SIZE) The reason for this is exactly what you guys have been discussing .Different plugs have different tips and different types of projections,which could change the combustion chamber volume and increase compression just enough to possibly make a few more HP and a faster run. So during tear down when they cc your head they can make certain you were not running a higher than stock compression ratio. Hope I didnt make for more confusion.ed[/QUOTE]

No, you didn't. Thanks for the input.

Jake
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