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Compression question for pump gas...
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<table border="0" cellpadding="1" cellspacing="1" width="99%" align="center"> <tr bgcolor="#000000"><td> <table border="0" width="100%" cellpadding="3" cellspacing="0"> <tr bgcolor="#000099"> <td colspan="2" align="left"> <font size="2" color="#ffffff" face="Verdana, Arial"> <b>T O P I C R E V I E W</b> </font></td></tr> <tr bgcolor="#dedfdf"> <td valign="top" width="18%"> <font size="2" face="Verdana, Arial"> <b>Fox89GT</b> <br /><small>Member # 1539</small> </font></td> <td width="82%"> <font size="1" face="Verdana, Arial"> <img src="https://californiafords.com/ubb/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.writeln(timestamp(new Date(2002,8,25,9,4,0), dfrm, tfrm, 0, 0, 0, 0)); </script><hr /> </font> <font size="2" face="Verdana, Arial"> Whats the highest compression ratio you should go while using 91-93 octane pump gas? Would the higher compression also hurt emissions? Also, whats the highest octane gas around here? I think I've only seen about 92 whereas the east coast might have about 94. Bummer huh... <br /> </font> </td></tr> <tr bgcolor="#f7f7f7"> <td valign="top" width="18%"> <font size="2" face="Verdana, Arial"> <b>2000BlackGT</b> <br /><small>Member # 283</small> </font></td> <td width="82%"> <font size="1" face="Verdana, Arial"> <img src="https://californiafords.com/ubb/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.writeln(timestamp(new Date(2002,8,25,9,11,0), dfrm, tfrm, 0, 0, 0, 0)); </script><hr /> </font> <font size="2" face="Verdana, Arial"> </font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by Fox89GT:<br /><strong>Whats the highest compression ratio you should go while using 91-93 octane pump gas? Would the higher compression also hurt emissions? Also, whats the highest octane gas around here? I think I've only seen about 92 whereas the east coast might have about 94. Bummer huh...</strong></font><hr /></blockquote><font size="2" face="Verdana, Arial">you can get 100 octane at the pump on Almaden @ the 76 station <br /> </font> </td></tr> <tr bgcolor="#dedfdf"> <td valign="top" width="18%"> <font size="2" face="Verdana, Arial"> <b>gR40coupe</b> <br /><small>Member # 698</small> </font></td> <td width="82%"> <font size="1" face="Verdana, Arial"> <img src="https://californiafords.com/ubb/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.writeln(timestamp(new Date(2002,8,25,9,19,0), dfrm, tfrm, 0, 0, 0, 0)); </script><hr /> </font> <font size="2" face="Verdana, Arial"> I believe you can run 11"1` <br /> </font> </td></tr> <tr bgcolor="#f7f7f7"> <td valign="top" width="18%"> <font size="2" face="Verdana, Arial"> <b>Mean2001GT</b> <br /><small>Member # 1750</small> </font></td> <td width="82%"> <font size="1" face="Verdana, Arial"> <img src="https://californiafords.com/ubb/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.writeln(timestamp(new Date(2002,8,25,9,33,0), dfrm, tfrm, 0, 0, 0, 0)); </script><hr /> </font> <font size="2" face="Verdana, Arial"> also depends on if you have alunimum heads. if you do you hould be able to bump it up .5 more compression. <br /> </font> </td></tr> <tr bgcolor="#dedfdf"> <td valign="top" width="18%"> <font size="2" face="Verdana, Arial"> <b>Fox89GT</b> <br /><small>Member # 1539</small> </font></td> <td width="82%"> <font size="1" face="Verdana, Arial"> <img src="https://californiafords.com/ubb/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.writeln(timestamp(new Date(2002,8,25,10,54,0), dfrm, tfrm, 0, 0, 0, 0)); </script><hr /> </font> <font size="2" face="Verdana, Arial"> I'm thinking specificly thinking about the GT40P heads and wanted to mill it a bit. So this is an iron head with about 60cc chambers. I think if I shave off about .030 my compression should be close to but not quite 10:1 and would be okay running 91RON and still pass smog. Are my assumtion reasonable? <br /> </font> </td></tr> <tr bgcolor="#f7f7f7"> <td valign="top" width="18%"> <font size="2" face="Verdana, Arial"> <b>shade-tree</b> <br /><small>Member # 298</small> </font></td> <td width="82%"> <font size="1" face="Verdana, Arial"> <img src="https://californiafords.com/ubb/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.writeln(timestamp(new Date(2002,8,25,11,29,0), dfrm, tfrm, 0, 0, 0, 0)); </script><hr /> </font> <font size="2" face="Verdana, Arial"> If you back off on the timing a bit, an iron-headed 10:1 or 10.5:1 should survive on 91. I would suspect you would need a little octane booster to run optimal timing. <br /> </font> </td></tr> <tr bgcolor="#dedfdf"> <td valign="top" width="18%"> <font size="2" face="Verdana, Arial"> <b>93PONY</b> <br /><small>Member # 60</small> </font></td> <td width="82%"> <font size="1" face="Verdana, Arial"> <img src="https://californiafords.com/ubb/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.writeln(timestamp(new Date(2002,8,25,13,41,0), dfrm, tfrm, 0, 0, 0, 0)); </script><hr /> </font> <font size="2" face="Verdana, Arial"> A little known secret....<br /><br />Run straight water w/2 bottles of water wetter. It'll keep cylinder head temps down & help eliminate hot spots in the heads....thereby reducing the octane requirement of the motor.<br /><br />You should be fine on 91 w/ 10.5 to one & Iron heads. Like Shadetree said, if it's pingin', drop the timing a few degrees. Or get a custom chip that pulls timing at peak torque (most likely were you'll ping) & throws it back in at higher rpms.<br /><br />Minor changes in compression doesn't effect emissions too much....as long as you run on pump gas that is. Cam specs are much more important.<br /><br />BTW, cam profile will also play a BIG part in cylinder pressure. Cams can bleed off cylinder pressure, or help increase it. With a good cam *cough* custom *cough* you can maximize cylinder pressure without having to shave the heads. <br /> </font> </td></tr> </table></td></tr></table> <br /> <br />
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