89 Trans Am GTA T-5 5 speed .... Installing new 355 (L98) motor with 280-300 horses ( engine alone)... Added parts will be as follows : Underdrive pulley kit, air foil , custom burned chip , 24# accell injectors , headers, Turbo Thrust ? mufflers, strut tower brace (3 point) , and a set of sub frame connectors... I THINK the stock rear end is a 3.45, but both rear tires dont always spin together..... SO ARE THE ANY GURU's out there that can possibly give me an educated guess on 1/8 and 1/4 mile times and speed ???? PLEASE HELP AND THANK YOU ! Rocky

higher part of the 13's.......13.7 to 13.8ish if you launch it very well, but if your posi is not quite locking up both tires, that may hurt you a bit. possibly mid 13's tho depending on those gearsl if its 345....if its a nice bolt rear end, the tag on the diff cover will tell you.

i think 3.73's would match the T5 very well. you should buy a pinion and gear install kit and freshen up that rear end. then sell the 3.45 gears to me! LOL

Hep posi is nice, but you ment to say nine bolt. I think low,low 14's to hi 13's.

it will be fine,, here is your rear diff, These are RPO's look in your center console.

<P align="left"><A name=axle><B><font face="Arial" size="3">Rear Axle Codes</font></B></A><font size="2" face="Arial"><BR></font>
<TABLE width="40%">
<TBODY>
<TR>
<TD><B><font size="2" face="Arial">6HB</font></B></TD>
<TD><font size="2" face="Arial">3.08:1</font></TD>
<TD><B><font size="2" face="Arial">6HP</font></B></TD>
<TD><font size="2" face="Arial">2.73:1</font> </TD>
<TD><B><font size="2" face="Arial">8EW</font></B></TD>
<TD><font size="2" face="Arial">3.45:1</font> </TD></TR>
<TR>
<TD><B><font size="2" face="Arial">6HE</font></B></TD>
<TD><font size="2" face="Arial">2.73:1</font></TD>
<TD><B><font size="2" face="Arial">6HT</font></B></TD>
<TD><font size="2" face="Arial">2.73:1</font> </TD>
<TD><B><font size="2" face="Arial">9ER</font></B></TD>
<TD><font size="2" face="Arial">3.45:1 Locking</font></TD></TR>
<TR>
<TD><B><font size="2" face="Arial">6HF</font></B></TD>
<TD><font size="2" face="Arial">3.08:1</font></TD>
<TD><B><font size="2" face="Arial">8ET</font></B></TD>
<TD><font size="2" face="Arial">2.77:1</font> </TD>
<TD><B><font size="2" face="Arial">9EQ</font></B></TD>
<TD><font size="2" face="Arial">3.27:1 Locking</font></TD></TR>
<TR>
<TD><B><font size="2" face="Arial">6HK</font></B></TD>
<TD><font size="2" face="Arial">3.08:1</font></TD>
<TD><B><font size="2" face="Arial">8EU</font></B></TD>
<TD><font size="2" face="Arial">3.27:1</font> </TD>
<TD><B><font size="2" face="Arial">9ET</font></B></TD>
<TD><font size="2" face="Arial">2.77:1 Locking</font></TD></TR>
<TR>
<TD><B><font size="2" face="Arial">6HL</font></B></TD>
<TD><font size="2" face="Arial">3.42:1</font></TD></TR></TBODY></TABLE>
<hr>

Also if your not locking check out clutch/cone in the diff

i bet the posi diff is just plane wore out my buddys GTA did the same thing

but on 1/4 mile times im gonna say 13.5s if ya hook and you know how to work that stick

Well, I am hearing alot of 13 sec times... That is where I wanna be... (Dont wanna be embarrassed by a NEON again) LOL ... By the way, I just changed to roller tip rockers... Think that will help too ? Scott