IMpreZeR
Originally Posted by Imprezer
Belt's placement has everything to do with compression. Not the belt itself. Like I said wording...
Jacob, yes, that was me in Oaktown.
Jacob, yes, that was me in Oaktown.
Wow, crazy. Mostly I remember really wanting an RS, and being amazed at how you could drive while wearing gigantic boots. Usually I showed up in a black WS.6 trans am, or a black turbo Z. Always #57. Finally got my GM6 two weeks ago.
-Jacob
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Originally Posted by ish
i like fish
I <3 White Girls
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Originally Posted by Scott@S-S
oh wtf zoeb, you cannot post in this thread because ish did not list you as viewing
STOP POSTING WHILE YOU ARE NOT VIEWING THE THREAD !!!!
STOP POSTING WHILE YOU ARE NOT VIEWING THE THREAD !!!!
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What Alex is talking about is effective compression, which is affected by valve timing, and not the compression ratio. Cranking the engine to get a simple compression reading is determined by ring sealing and valve timing. The latter factor is important because if even one valve is even slightly open, it will leak compression pressure during a reading.
This is explained better by the late Smokey Yunick, the small-block Chevy engine guru:
From Chapter 5 - Camshaft and Valvetrain, page 74:
Intake closing will also have a tremendous influence on the pressure conditions in the (combustion) chamber during the compression phase of operation. This is the primary reason that it is possible to use a high compression ratio in an engine that has a relatively long intake duration. In actual fact, the so-called static compression, the mathematical comparison of the maximum chamber volume to the minimum chamber volume, can be somewhat misleading. Even if the mechanical compression is relatively high, the operating compression (pressure) may be lower when there is a long-duration cam in the engine. When you use a long cam, which will have a late intake closing, much of the mechanical pressure developed during the compression phase will escape past the open intake valve. As a result, the dynamic compression, the thing that really counts, will be reduced.
I guess the best way to illustrate this is to look at an example. If you dry-cycle a late-model stock engine and hook a so-called compression gauge to the chamber, the pressure reading, a relative indication of the dynamic pressures in the chamber, will be quite high. Even though the compression is relatively low, the camshaft in this type of engine usually has an early intake closing, consequently the pressure of mechanical compression is more efficiently trapped in the chamber during cycling. If you then take this same engine and install high-compression pistons, increasing the mathematical static compression, the pressure readings will increase if all else remains the same. Buth then, if you take this engine, with the high-compression pistons installed, and put in a long-duration cam, the pressure readings in the chamber will be significantly reduced.
Here is an online calculator for figuring effective compression in an engine.
--
0==WW==0
"…axles of evil…" - george w. bush
This is explained better by the late Smokey Yunick, the small-block Chevy engine guru:
From Chapter 5 - Camshaft and Valvetrain, page 74:
Intake closing will also have a tremendous influence on the pressure conditions in the (combustion) chamber during the compression phase of operation. This is the primary reason that it is possible to use a high compression ratio in an engine that has a relatively long intake duration. In actual fact, the so-called static compression, the mathematical comparison of the maximum chamber volume to the minimum chamber volume, can be somewhat misleading. Even if the mechanical compression is relatively high, the operating compression (pressure) may be lower when there is a long-duration cam in the engine. When you use a long cam, which will have a late intake closing, much of the mechanical pressure developed during the compression phase will escape past the open intake valve. As a result, the dynamic compression, the thing that really counts, will be reduced.
I guess the best way to illustrate this is to look at an example. If you dry-cycle a late-model stock engine and hook a so-called compression gauge to the chamber, the pressure reading, a relative indication of the dynamic pressures in the chamber, will be quite high. Even though the compression is relatively low, the camshaft in this type of engine usually has an early intake closing, consequently the pressure of mechanical compression is more efficiently trapped in the chamber during cycling. If you then take this same engine and install high-compression pistons, increasing the mathematical static compression, the pressure readings will increase if all else remains the same. Buth then, if you take this engine, with the high-compression pistons installed, and put in a long-duration cam, the pressure readings in the chamber will be significantly reduced.
Here is an online calculator for figuring effective compression in an engine.
--
0==WW==0
"…axles of evil…" - george w. bush
Last edited by Wingless Wonder; Dec 31, 2004 at 08:20 AM.
