Changing your axle gears helped the 1/4 mile by how much?

[timk225]

My question here is mainly for lowered powered cars, like Slant sixes, mildly modded, in my case. On a more or less stock vehicle, no crazy mods like boost or nitrous, changing your rear end gears helped your 1/4 mile time by how much?

I'm doing some mild performance improvements on my 1973 Duster, and although I'd like to put better gears than the 2.76's it has in it, I have to think about the overall driving experience.

Yes, some 3.23s or 3.55's would help acceleration and 1/4 mile, but how often will I be on the dragstrip (twice a year would be a lot) compared to how often do I want to run 80+ mph on local highways (almost every day I drive that car).

Not having an overdrive gear in the 904 is a real limiter, and it is definitely not worth the trouble of adding a Gear Vendors OD unit at any price.

But if you did do a gear change, like from 2.76 to 3.23 or whatever, what did you gain in things like 60 foot and 1/4 mile times and speeds? I imagine mph changes wouldn't be much, unless the previous gears weren't enough for the engine to get to its best HP range.

I took my Duster to the dragstrip a couple weeks ago, and at 3630 racing weight with me and tools in the car, I got an 18.32 @ 74.3 . I was shifting the Slant 6 (stock except for a Holley 350 2 bbl and a 2-12" TTI exhaust) at 4000-4100 rpm, and crossing the finish line at the top of second gear, shifting to 3rd as I got to the end of the 1/4.

Higher stall converters aren't a good choice, as my typical rpm range would have the converter slipping all the time, and making unnecessary heat.

I don't imagine putting 3.23's in the car could help the 1/4 by more than .3 to .4 second at the most, but the impact on daily high speed driving would be bad.

 

[Locomotion]

An option to consider is getting an OEM 904 low gear set (2.74 vs the usual 2.45) 2nd gear is a bit better too. Chrysler started using those in lower HP/torque applications while putting tall gears in the rear for fuel mileage. Lock-up converters were also used but that limits converter options. All this started around 1978. A trans shop familiar with Torqueflites shouldn't have a problem identifying and/or mixing/matching parts to put together a low gear, non-lock-up 904. There may be other parts in a small block case that can be swapped into a /6 case for durability. End result is better acceleration off the line without hurting the final drive ratio. Build one while still driving the car.

There is a lot of range between gearing for optimum 1/4 mile times and fuel mileage. Just like an OD unit, will the net results be worth the investment.

 

[Oldmanmopar]

My wife drove a 69 Dart GT with a /6. I put a 294 sure grip 8 3/4 rear in it. I also added a part throttle valve. The car worked great . Totally change performance and drivability around town and on the highway. I liked the 294's. I eventually put the fenders doors and rear in the primered 318 car because it had AC. That car also was a great everyday driver with the 294's.

So you don't have to go from 276's right to 323'. There are also 331's before 355's. Most Imperials we stripped were 331 suregrips. 331's in a 4 speed car are a good gear with the 247 first gear trans. The 247 1st gear usuall came with a 355 set to make them easier to pull out with the higher 1st gear. 331's gave you that little higher gear without affecting pulling out as much as the 323's ,

Having access to a lot of parts and cars years back we would try different sets.

 

[timk225]

Yes, way back around 2001 I built a 904 with the wide ratio gear set. I guess that is an option, and it'd give me the chance to install 4 disc clutch packs instead of the 3 discs that Slant 6 904s came with, at the same time. It may not need 4 discs, but better too many than not enough.

I'm planning to install an 8-1/4" axle when I eventually break the 7-1/4. I killed 6 of them in various ways back in the 90s to early 2000s with my lead foot and a Slant 6!

I'd like to put 2.94 gears in an 8-1/4", but finding one has been difficult so far. I don't want an 8-3/4". Not right for the year of the car and unnecessarily heavy.

 

[Dana67Dart]

Top down, arm on the window sill. Totally chill! If only I could secure the Surf Board properly!

This is what I weighted in at with the 2.93 gears (Car, driver and junk in the trunk)

These are the timing slips with 2.93 gears

(this slip has a reaction time close to the 3.32 slip)

This is a timing slip with 3.32 Gears

 

[TF360]

Most people don't look at Tire diameter either. We all put taller tires on our Duster's, but having that taller tire changes the gear ratio too. So, you have a 2.76 which is most likely like a 2.45 with a larger tire. Making it a real dog off the line

 

[jrc4y4]

I have a mild 318. And don’t have time slips after changes but typically ran best of 15.4s with it with 2.76 gears. Now has 3.92s. Was a good pickup on the butt dyno, but heads and headers were significantly more gain than the gear swap. Which I was surprised because the car has a stall. Dragy shows mid 14s and I’d say 2/3 of the gain was engine and 1/3 from gears.

That said I went from being able to cruise at 75 to hating life above 55 lol. Blast around town but if a show is 40 miles away it’s no longer enjoyable. If you’re regularly on the highway, imo it’s better to add power than to change gears. Shave the head and add a 4 bbl and headers before doing the gears if highway driving is still desirable.

 

[timk225]

I can simulate having 4.10 gears in my Duster quite easily. Just put the shifter on 2 and get on the highway. 2.76 * 1.45 in the 904's second gear = 4.002. That's not fun for long, especially with a low revving Slant 6!

 

[TT5.9mag]

Probably be more of an improvement to take the tools and junk out of the trunk when you go to the drag strip. 3630 is an absolute porker of a duster. Keep it a street car. If you want a race car to go fast build a race car.

 

[DFX 340 Duster]

@Dana67Dart There's surfing in Colorado? Where?

 

[AJ/FormS]

Here is My experience, and what I already did, decades ago, and more than once.
I don't care what anybody else says, cuz this is already 50 years ago. and specifically, I'm Not telling you what you should do.
********************
back in the late 70s
I installed a 2800 into my 68 Barracuda/slanty. Best thing I ever did for her.
When off the throttle, it drove no different, and with 2.73s, 65 was ~2200/2300, and that is a great rpm to tune the VA, for 30 mpgs.
If I had to guess, that 2800 allowed my slanty to spool up to close to double the take-off power. Then I installed N50-15s on her for Zero tirespin. The 1-2vshift was fantastic (shift kitted)
Then a guy offered me about double what the car was worth, so, that was a no-brainer. The deal was bartered in parts. and I mean a pile of parts, some of which I still have. I got complete 340s, a 4-speed with shifter, I think 4 Holleys and an LD340, and a wrecked 71Demon. and a bunchamore stuff.
Later in that same summer, I saw the kid driving around so I stopped to talk. Yeah, he was very happy with the deal, but the engine was driving around with a hole in the block, where a rod had let go. The hole was stuffed with rags and the ignition on that cylinder had been disabled. The piston was still in there, but it was no longer going up or down, lol.
That about broke my heart cuz that engine was a nearly fresh rebuild, from a prominent local builder. She was a stock rebuild, but it was somehow hotter than usual.
If you're looking for a snappy take-off, you can't beat more stall, and IMHO, the 2800 is about perfect. I've been running those on most all my stock automatic Mopar DDs, ever since, from slantys to 318s. My Hotrod 340/360s were all 4-speeds.
And, I found the A999 low gear is a bit better off the line, but that trans is a wider ratio, so Second is further out there. and with a slanty being shifted at ~4500, with the factory lo-stall, I really noticed that 300rpm hole on the 1-2 shift. It's a good idea, but the slanty has no powerband to support it. It's a great idea if you just use it the way it was intended, with a deeper rear gear, and the Lock-up convertor.
*************************
When doing these kinds of swaps, you always have to keep track of what the roadgears are doing.
For instance;
Say your car has 2.73 gears and an A904 (2.45-1.45-1.00) Your roadgears will be;
6.69-3.96-2.73. with splits of .58/.69 and 65= about 2300
Installing an A998 (2.74-1.54-1.00/no lock-up, the roadgears would be
7.48-4.20-2.73; with splits of .56-.65, and 65 still ~2300
Installing an A999 (same gears but with a lock up). and 2.94s
8.06-4.53-2.94, 65= about 2380 in lock up.
Now check out Second gear; 4.53 is 7.7% better than 4.20, and 14.4% better than 3.96, and it only cost me like 80rpm on the hiway.
As for First gear, 8.06 over 6.69 is 20.4% better; which is a lot..
The thing is, say you were ok with a 3.96 Second gear, Theoretically speaking, with the A999LU, it would be possible to run a 2.57 rear gear, and still get a First gear of 7.05 ....... which is still better than, the 2.73 x 2.45= 6.69 combo. and of course, 65 would be about 2080.
Of course there is no 2.57 rear gear in a Mopar, but there is a 2.45 ........
But
Don't forget that the 2800stall, over an 1800, will get you probably 100% more Horsepower to take off with, and costs you maybe a 100/150 rpm at cruising. which you can get back with a LU style convertor.
Now, what happens when you combine an A999LU, with 3.23 gears, AND a 2800.... lol. I know yur thinking it!!
*******************
As for your original question, regarding the quarter mile. IMHO, forget about it.
Concentrate on getting to 65mph in a timely manner, and let the rest be what it is.
The 1970 225 was rated 145 hp@4000, so stock, by 4300, she's already on the downside of the curve. Therefore, For 65=somewhere around 4300 in Second gear @WOT, with 27" tires, the needed gear is about
3.55s, for the A904 ratios, for 65=4375. But for an A999 you would only need 3.23s for 65= about 4230
*****
I didn't get to mess with the A998/999 transmissions until I got me a 1980 Volare.
I rebuilt the engine @9.5Scr, installed a 2.73 rear, and the A999 in it, already had a lock-up. For what I needed, I found it satisfactory with the OEM stall, and I/we drove that car for well over two decades. All my kids learned to drive in it.

 

[318willrun]

Not as much as one would think. Truth: invest in a quality torque converter, like FTI-maybe a 10" 2600, and the slant will be lucky to get 2k out of it BUT....it will drive like a stock converter but the car will respond WAY better off the line, even part throttle, with a converter like mentioned. A slant with 2.76's and the converter mentioned would have no problem beating a slant with 3.23's and stock converter. Without sacrificing highway cruising, drivability,

 

[33IMP]

The way you describe your usage of the car, a gear swap will be 100% disappointment. Gain on track, insignificant. Annoyance during daily usage, significant.
My experiences are irrelevant to your situation, but I took 5.14s out, put 4.57s in, and lost no performance at all.
Same experience taking 4.10s out, putting 3.91s in
Street strip cars.

 

[Dana67Dart]

@Dana67Dart There's surfing in Colorado? Where

Glenwood springs
Glenwood Wave - Endless Waves

 

[timk225]

Probably be more of an improvement to take the tools and junk out of the trunk when you go to the drag strip. 3630 is an absolute porker of a duster. Keep it a street car. If you want a race car to go fast build a race car.

My Duster has a few weight adding options. Power disc brakes, air conditioning, the fold down rear seat, which I saw in one video was nearly 90 pounds, hard to believe! Then the tools in the trunk and me.