3 speed would like lower rpm's hwy?

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witteman

Test & Tuner
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Hi,

I have a 1968 DartGTS 340, whats the cheapest way to get lower rpm's,
Tires/axel would that really make much difference? I have 391 rear end and don't want to change that becuase i do take it to the 1/8mile track. Anyway any ideas would would be great help to this weekend warrior!

Thanks Tom
And Merry Christmas
 
Cheapest way would be to buy larger diameter tires for the rear of the car. Don't know what tires you currently have but you might be able to get up to a 10% reduction in rpm. This would make your 3.91s equal to about 3.5.
 
Tom, theres no easy way out. The above advice is 1/2 the catch 22. And it is the cheaper of the catch 22. And that would be an overdrive trans. The Chrysler version has a .69 OD ratio giving you a final ratio of;

3.91 X .69 = 2.6979 (2.70)
 
Is this car an automatic or manual trans? Had the same problem with my Valiant. The car was a pain to cruise at highway speed (poor slant was screaming) but I liked the dig it had due to the gears. Since it was a three speed manual, I swapped in an OD 4 speed. Now I have the best of both worlds. I have the same gearing I had before with an overdrive 4th that gives me sane cruising revs. All I had to swap was the bell and trans, front driveshaft yoke, and cut a hole in the floor for the shifter. It's a little more complicated if you have an automatic though. Basically your options are a 500/518 swap which is not a straight bolt in, or a Gearvendors overdrive unit. Kiesler has an OD auto swap kit but it uses a Generic Motors transmission. Don't know about you, but the thought of GM parts in my Mopar makes me want to:puke:
 
Thanks Guys,

The tires are P245-60R14
Automatic Trans,
Trany swap is out for now, low funds!
What about 14 to 15" axel change?

As for GM parts No thanx, that would just give my buddies at the track somthing to raz me about.
 
Going to a bigger rim will not help. It just changes the size tire on the rim. You can get 26 inch tires for 14 or 15 inch rims. Ride quality should improve with 15's. But not drop in RPM's.

You have 2 options. Bigger tire or overdrive the tranny via auto 4spd, auto w/gear vendors. I don't know if theres a 5 or 6 spd auto that can do the trick, but if the tranny gets bigger, fitment becomes an issue.
 
Starting to sound like your options are severely limited. If it was me I'd pick up a 2 something open 8 3/4 chunk for daily driving and swap in the 3.91 for track days. Shouldn't take more than an hour or so to make the swap. You should be able to pick up an open chunk fairly cheap. I paid $175 for a 489 case 3.23 open that had just been checked, cleaned, and had new bearings installed. You should be able to find a 2.76 or 2.94 in that price range. The open rears are almost give aways for some reason. I'm assuming you have an 8 3/4 in your GTS, haven't seen one yet that didn't. Hope this helps and you find one under the tree.
 
grumpuscreature said:
Starting to sound like your options are severely limited. If it was me I'd pick up a 2 something open 8 3/4 chunk for daily driving and swap in the 3.91 for track days. Shouldn't take more than an hour or so to make the swap. You should be able to pick up an open chunk fairly cheap. I paid $175 for a 489 case 3.23 open that had just been checked, cleaned, and had new bearings installed. You should be able to find a 2.76 or 2.94 in that price range. The open rears are almost give aways for some reason. I'm assuming you have an 8 3/4 in your GTS, haven't seen one yet that didn't. Hope this helps and you find one under the tree.
Click to expand...

Ditto!
 
I would get some 15" rims to match whatever you have now and the biggest tire you could fit in the wheel well and put them on when you are cruisin' around. There are more choices in tire sizes in the 15" range than the 14's. I am thinking about doing the same thing because I can't stand the high rpm on the highway either. The tire that would fit with no problems on my 72 Swinger is 235/70/15. It is a little narrower but is taller than my 245/60/14. It depends on your rims backspacing for fitment. There are some good calculators on the web that you can play around with, just google tire size calculator and you will find something.
 
the cheapest way is a taller tire. but you would need 15" wheels... wheel vintiques sells a 15 x 6 and 15 x 7 small bolt wheels... then throw a set of 235/70-15 on there.. it will mellow then 3:91 gears quite a bit. still probably have $500 into it though... there really isn't any real cheap way to do it... http://wheelvintiques.com/shopsite_sc/store/html/page52.html
 
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