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New Edge Cobras
Highest compression for boost?
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<blockquote data-quote="SlowSVT" data-source="post: 13061231" data-attributes="member: 20202"><p>Even some dished piston engines require race gas when they are packing big boost why would a flat tops be any different?</p><p></p><p>I think some people are overlooking something here that goes way beyond compression. It's "charge volume".</p><p></p><p>That diagram I posted illustrated this but I think a few have either not made the connection of refuse to acknowledge it :nonono: Here is an other way of looking at it. A flat top piston mod motor chamber volume not including deck height and head gasket thickness is 52 cc's, A dished Terminator slug adds another 17 cc of charge volume to the chamber which is a 30% increase. That translates directly on how much fuel the engine process before the point of detonation with most of the added energy going directly to the crack shaft. The laws of physics comes into play here and to argue otherwise is going to be an uphill battle. <u>Under no circumstances would I choose to use flat top pistons in a blown application</u> (with the exception of E85) and to do so you are leaving hp on the table.</p><p></p><p>As stated, a 99 Cobra engine with a forged bottom end and a PD blower will hit a brick wall around 425 hp on pump gas where an 03/04 can get close to 600 <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" />idea: Hay! that's about a 30% power advantage imagine that) Switch both engines to race gas and that gap will still be there. <strong>What ever combo you can come up with that 30% charge volume disadvantage thing will be literarily impossible to overcome.</strong></p><p></p><p>For a centrifugal or turbo bumping the compression will help reduce the effect of lag and a poor throttle response which is a good idea plus the fact they make mad hp "on top" to begin with but the more you add the less potential the motor will have not being able to pack more boost into the engine. 9:1 tops for me. A PD blown car works great at 8.5:1 and to raise it is pointless and detrimental.</p></blockquote><p></p>
[QUOTE="SlowSVT, post: 13061231, member: 20202"] Even some dished piston engines require race gas when they are packing big boost why would a flat tops be any different? I think some people are overlooking something here that goes way beyond compression. It's "charge volume". That diagram I posted illustrated this but I think a few have either not made the connection of refuse to acknowledge it :nonono: Here is an other way of looking at it. A flat top piston mod motor chamber volume not including deck height and head gasket thickness is 52 cc's, A dished Terminator slug adds another 17 cc of charge volume to the chamber which is a 30% increase. That translates directly on how much fuel the engine process before the point of detonation with most of the added energy going directly to the crack shaft. The laws of physics comes into play here and to argue otherwise is going to be an uphill battle. [U]Under no circumstances would I choose to use flat top pistons in a blown application[/U] (with the exception of E85) and to do so you are leaving hp on the table. As stated, a 99 Cobra engine with a forged bottom end and a PD blower will hit a brick wall around 425 hp on pump gas where an 03/04 can get close to 600 (:idea: Hay! that's about a 30% power advantage imagine that) Switch both engines to race gas and that gap will still be there. [B]What ever combo you can come up with that 30% charge volume disadvantage thing will be literarily impossible to overcome.[/B] For a centrifugal or turbo bumping the compression will help reduce the effect of lag and a poor throttle response which is a good idea plus the fact they make mad hp "on top" to begin with but the more you add the less potential the motor will have not being able to pack more boost into the engine. 9:1 tops for me. A PD blown car works great at 8.5:1 and to raise it is pointless and detrimental. [/QUOTE]
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