Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - 1968 firebird , highway RPM way to high
View Single Post
  #3 (permalink)  
Old 04-08-2013, 05:15 AM
cobalt327's Avatar
cobalt327 cobalt327 is offline
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 595 Times in 545 Posts
Quote:
Originally Posted by starin View Post
Hi Guys and Gals,

So i have a 1968 firebird with a BOP TH350 it, i'm planning on throwing a 200r4 in it in a few months because the RPM on the freeway is so high. The th350 transmission is used, no idea how many miles. The rear diff is a gm 12bolt it was rebuilt before i bought it but no idea what the gears it has in it.

so at 56mph i am taching 3500 rpm and i have 28 inch tall tires, i used several gear calculators and everything says that equates to 5.21 gears. is it possible that my gearing in the diff can really be that high or maybe my transmission is not shifting into second gear??

thanks
Your math is right, but is the tach?

If the trans is in second, the gear ratio would be a more realistic ~3.5:1. But like poncho said, checking the gears yourself is a good idea.

I'd also be checking the shift linkage to be sure the trans is actually shifting into high gear.
Reply With Quote