323 gears at 70

[rt green]

i have 323 gears in a 69 with a 4 speed. 295\50\15 tires on 10 inch slots. what can i expect the rpm to be at 70mph? any ideas? stock engine

[68RT4ME]

Try this site made by one of the members here. Input the info and you will see the results instantly.

http://vexer.com/68rt/speed.html

[tan top]

 about 28 hundred

[Musicman]

  Yea.. about 2850 give or take...

If it was an Automatic you'd add about 8% more for Torque Converter slippage, bringing you in at just over 3000

[rt green]

so....you think gas milage will suck on the hyway?   440 engine

[1970RT]

Your tires are almost the exact height of my 225/70 14's

I have 3.23's and a 727/440

I turn about 3400 at 70.

Not sure how much differene there is between a 4 speed and automatic.

[Musicman]

I have an Auto with a 3.23 Sure-Grip out back riding on 295/50/15's... 70 is roughly 3000-3100 with mine. Mileage suffers a little bit on the highway, but I plan to put a Gear Vendors unit on there when I get the chance.

[1970RT]

295/50's compute out to 2936 rpm at 70 assuming no slip in the drivetrain and using the BFG rev/mile numbers.

My tic tock tach must really be off because it shows exactly 3000 rpm at 60 but my tires comp out to 2535 at 60.  No way can there be that much slip in the 727

[rt green]

wow. i figured that the rpm would be lower than that. maybe an overdrive unit is the answer. here we go again, i'll never be done with this thing. gotta love it though.

[firefighter3931]

295/50's compute out to 2936 rpm at 70 assuming no slip in the drivetrain and using the BFG rev/mile numbers.

My tic tock tach must really be off because it shows exactly 3000 rpm at 60 but my tires comp out to 2535 at 60.  No way can there be that much slip in the 727

Your tach might be correct but your speedo is off. 

When changing tire diameter and rear end gearing it's important to use the correct (matched) speedo pinion gear in the transmission. 

On a stock converter you shouldn't see more than 4-5% converter slip at cruise speed. 


Ron

[1970RT]

I checked the speedo with GPS and it was within 1 MPH.  The car originally had f70/14's and I put back 225/70 14's.

[rt green]

68rt4me, thanks for the site on the rpm+speedo thing. easy to blow one up on that. where in the hell did you find that? thats cool.

[68RT4ME]

68rt4me, thanks for the site on the rpm+speedo thing. easy to blow one up on that. where in the hell did you find that? thats cool.

I know I'm kinda late in replying here so sorry. Anyway, I cannot take any credit for the site. That info was posted here some time back by another member. I remembered reading about it and found the thread with the link.

FYI, I have the same tire setup as you on my '71. I had a Gear Vendors unit installed but switched to 3.91's from 3.23's. I can run 80 mph @ 3100 rpm's all day. If you get one, you'll be happy

[Nacho-RT74]

honestly, I can't understand those tables with RPMs and Speedo relation... I don't get ANYTHING CLOSE to the values stated, unless I'm making something wrong

and I think I have the right speedo gear to my setup... 34 teeht, 3.55 on 255/60-15... is green and I remember have read the 34 number, but didn't count the teeth... unless I read it wrong and really was 31 what is also green

[Musicman]

Nacho, there are a few different green ones as you know, but 34 is one of them and that would be the right one for your setup.

[Nacho-RT74]

yeah I know but weird is that I'm not getting same RPMs reading what tables state, as I told I'm doing something wrong or I do have the 31 teeth gear ( was used so I could missread )

anyway I'll have to recheck for that to be sure, sorry the highjack