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robert lapointe Apr 23rd, 06, 1:30 PM I just bought a 1970 LS5 number matching motor and 4 speed trans,I think the rear as been replaced,I have a partial buildsheet that show posi but the ratio is not there,the only source I have is the speedo gear code IR F - in block 92 of my buidsheet,could anyone help decode to find original car rear ratio.Thanks Robert. alss Apr 23rd, 06, 2:05 PM Robert, same code in my box 92..my car is a 3:31 posi , code CRV. ALbert Rick_Nelson Apr 23rd, 06, 7:16 PM Al, I don't think that true all the time. I have several 454 build sheets including Greg Boss's (gb70) old LS-6 4:10 car and it also has IR F in box 92 which does confuse me. What stamping is on your rear currently? What does it say in box 29? RV= 3:31 posi RU= 3:31 open RW= 4:10 posi Rick alss Apr 23rd, 06, 10:39 PM Al, I don't think that true all the time. I have several 454 build sheets including Greg Boss's (gb70) old LS-6 4:10 car and it also has IR F in box 92 which does confuse me. What stamping is on your rear currently? What does it say in box 29? RV= 3:31 posi RU= 3:31 open RW= 4:10 posi Rick Rick, rear has CRV stamped and matches my POP..box 29..RV ALbert Rick_Nelson Apr 24th, 06, 12:30 AM What stamping is on your rear currently? Sorry for the confusion Al, that part of the question was intended for Robert. I was curious what might be on his sheet in box 29 since box 92 appears the same on several build sheets for 3:31 and 4:10. Rick mr70 Apr 24th, 06, 9:51 AM IR-F is a manual trans. speedo gear. and not ratio specific. You couldn't get a 4:10 ratio behind the 1970 LS-5 Chevelle from the factory. Only the 3:31 open & 3:31 posi were available. If your buildsheet is showing a posi code,it was built with a 3:31 posi. Prefix code CRV,as Al suggested. CRU is an LS-5 & LS-6 open 3:31 prefix. | ||