Ok guys now that I've put some miles on my new Duster I've realized that I need to take more gear out of the car for those longer distance car shows.

I have a stroked big block with alot of torque, 727, 3.55 gears, and 28" tires(275/60/15), converter is a 9.5" Dynamic. It is great around town but when I hop on the highway it gets a little annoying to me since I had a car with a 6 speed manual before.

On a 55 mph road I'm around 2500 RPM's, on the highway at 60 I'm at 2800 RPM's.
I cannot afford an overdrive or a manual trans right now, there's a place near me that can cut a converter apart and re-stall it for less than $200, sometimes with 3 people in the car I can feel the converter slip a little, but my highway RPM's indicate that it locks up fairly well at speed.

So I'm thinking that for around $400 I could switch to 3.23 gears and have the converter tightened up a little. Maybe this would put me at around 2300-2400 at 60 MPH?
What do you guys think? This car is a blast, just trying to make it a little more drivable as we are starting to venture out to more and more car shows/cruises.
Thanks.

I have always been a fan of 3.23 gears, I had them in a 69 GTX with a 572 stroker it ran 11.0 @124.95 thru the quarter mile, I also drove it to Vegas to Mopars at the strip many times from Phoenix. If the car has decent HP 3.23 gears work great all around

Ran 4.10's with 28" tires forever in my 64 300.

Running 3.55's with 26" tires in my 65 Cuda.

No OD in either.

Nice Duster! It sounds like you spend more time on the hiways than I do.

I have ran 3.91s behind my big blocks forever. But I am comfortable running 55ish on my trips which are usually an hour or two at most. The bulk of my driving time is stop and go kinda stuff around the local towns where lower gears are more fun.

Thanks! To be honest the longest I've been on the highway is 30 minutes and that was enough for me lol. We are planning some cruises that are an hour each way so I'd really like to bring the RPM's down and as mentioned, the 500" motor doesn't care what gear is back there, it's an animal with 3.55's so I'm sure 3.23's would be fine, heck a 3.08 would be great but I've only seen 3.23 and old 2.76's available.

I had a friend that put 3.23's in his car and his converter would slip to 3800 just trying to drive around town since it was way too loose for highway gears and wasn't locking the converter up, that's why I'm thinking of tightening mine up some since I've already experienced some slip with 3 people in the car.

My last couple Mopars ran 9's in the 1/4 mile with 4.56 gears and 8" converters so this highway cruising stuff is new to me lol. I'm dying to get a GearVendors overdrive $$$.

I have been around the block on this and have THIS to report:

High stall converters and taller (Lower numerically) gearing do result in excessive slippage, sorta negating the advantage of the taller gearing. I ran a Gear Vendors overdrive with a 3.91 gear, 28" tire and a slippy 9.75 converter. Not fun. The car felt lazy at freeway speeds, like a boat in the water in terms of part throttle feel. The combo was fine for wide open throttle, it just sucked for everything else. I don't care to drag race, I enjoy distance drives, cruises, cornering on twisty roads and such.
I eventually sold the GV and went with a 3.55 gear and an 11" converter that made a huge difference in how the car feels. I really like this combination.

FrankenDuster I love that Charger! What RPM are you at when going 55 and 60?
We were at the GoodGuys Columbus show a couple weeks ago and I am hooked on Pro-Touring. A nice looking good handling car that you can drive anywhere is awesome. I've always been a drag car guy, so with this Duster I had to figure out the cooling, now I'm trying to sort out the converter slippage, next will be getting rid of these skinny bias-ply front tires that suck on the road with big radials out back.

I think what I need to do is to change converters, or have this one adjusted(might call Dynamic), THEN if the converter doesn't make a huge change I'll go to 3.23 gears/

i run 3.23's in both my cars, one with 28" tire. holding out for a "deal" on some 2.94's.

A stroked big block don't need 355s on the street, I think 323s would be perfect also.

I made the mistake of putting 354s behind my 440/6 10 years ago and it don't need 354s, 323 or there a bouts would have been better. It ain't no SB.

Funny when I was young it was 411s for years, no ands, ifs or buts about it. Cars rarely ever saw the highways.

Then I went to 355s and 354s about 15-20 years ago.

Now I'm thinking 323s would be more my style, sucks getting old!

I even have set of 276s I am going to put in for messing around out at Bonneville along with some MT 30" tall tires, should be interesting.

I would also send your convertor to whoever built it if possible and have it made just for your combo...323 gear and all including the camshaft and all. If not the the guy who made it, many places can to do that for you.

I have had Coan Trans build me convertors and trans("street fighter" 727 trans used to cost 600 bucks plus a good core=deal. Convertor was extra but very reasonable, not like a racing convertor, way cheaper) for my 340 and my 440/6 for the street. They did a great job, never ever ever had such great performing trans, seem to match my combo perfectly and could not be happier. And now both of them are over 10 years old and still barking the tires on the upshift.

2800 rpm @ 60 mph = 9.5% slip. That is not good in my opinion but I don't have experience with highway slip only at the track.

I have had converters slip as much as 13% at the finish line. My current Frank Lupo 9 inch in the race car slips 4% through the traps.

My new build will have a Lupo 9.5 inch converter (its currently in the street car). I will be running 4.56 gear with a 30 inch tire but do have a Gear Vendors OD for it. That drops the 4.56 to a 3.55 gear. It will be interesting to see how it behaves on the highway.

Heck, you have the torque. Throw on some 2.76's on there and have some fun.

275/60/15 rear tires that original poster has are pretty large diameter that cuts the effective gear ratio down.

Your overall ratio is about 50 rpm more than a bone stock 71 340 Duster with 3.23 gears and F-70-14 tires. They sold 1,000 of Dusters and Demons like that.

These are not new cars. They drove originally down the road at 3100 at 70 mph.

A F70/14 that originally came with 340 dusters is 26" diameter.

275/60/15 are 28" diameter.

This is a very handy quick visual tool to figure out rear end ratio changes: http://vexer.com/automotive-tools/speed-rpm-calculator

What is the exhaust system on the car? Full to the back, turn downs, Flowmasters even?

My 67 Coronet R/T with the stock 440/727 in it has 294 butt gears.. I feel it still revs too high on the freeway.. The car has 245/15" tires on it. ( I have no idea on tire height...

Have always wanted to install 355 with a GV overdrive...

In high school my everyday driver A12 car had 410 gears in it.. Utterly ridiculous gears to run on the street.. 42 years later I still remember what a PITA that car was with those gears... NEVER AGAIN in a car driven on the street....

245/60-15 are 26.6 inch height..........

That speed calculator is really cool, I'll have to play around with that. But everything else you said I'm already aware of, it's just my personal preference to bring the RPM's down. I've seen guys pound their chest and brag about how they roll down the highway for 2 hours at 3900 RPM's, who the heck wants to do that lol.
I can pretty much drive the car anywhere right now, just want to make the drive more pleasurable, I'm installing my stereo today.

I run 3" pipes with turbo mufflers and turndowns right before the axles. I plan to install some tailpipes this winter to the back bumper.

My 69 Dart had less then 3% slip at the finish line, it was a great ATI converter. I like 5% or less, some 8" converters are useless on the street.
You'll love the Gearvendors, hopefully you're converter is tight enough for it. There's a fine line cuz I had a 10" nitrous converter years ago that was a super tight pig without nitrous of course.

Guys that don't want to pay $2000+++ for high horsepower and high torque handling overdrive conversions.



3" pipe is louder than 2 1/2" but I realize you have a 500 cubic inch air pump to handle.

Pipes out the back will help.

My 67 Coronet has a 493 with a 9.5 dynamic convertor with a gear vendors and 3.55. All I can say is I love the combo. Haven't had it to the track though so don't ask me for a number.

The 68 charger has a mild 406 small block with a TCI Sat night special, probably 2200rpm stall, 904, and 2.94 gears. It slips a bit more than my dynamic while cruising but still isn't that bad on the highway.
I ran it once at the track and got a 13.28 at 101 just using 1st. and 2nd.
I would say not bad for a car with a/c, power steering and lots of sound deadener.

Bob, would going to a 29" tall rear tire help??

Following this.
My 526 made 630lbft at 3600.
i drive it a bunch, and a lot of hiway driving.
i have 3.73's now, and 60 is about 2900 with 275/60's. i'd like to go to 3.23's, so i can at least keep up with traffic.
i had no problem spinning my old motor 4,000+ on the hiway, but not with this engine.
I also have a 2600 Ultimate converter.