Rear axle ratio opinion

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Billbo

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Hi all. I was wondering if any one can advise me on rear axle ratio for my 67 Valiant 360. At the moment I am running a 3.23:1 ratio 4 pinion LSD and I was interested in lowering it to 3.50:1. Now for the cost on this change is it worth while doing it? Will it be significant on the performance of the car. The running gear is a 360 with Eddy heads, max rpm is about 5500 rpm and a Torqueflite 904 with a 3000 rpm stall with stock 14" wheels. The car is no heavier than 3200 Lbs.

Regards
Billy D...
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Not much of a change in ratio, might not be worth the price to change it! 3:23 is considered the "maximum performance" ratio!!
 
While you would feel a difference in performance, It is slight and only you can decide if the cost is worth the little bit of extra acceleration off the line. If your rear end is the Chryco 8.75 or a ford 9" purchasing a second dropout gear section set up with the gears you want, while sometimes pricey, can be resold when removed to recover much of the cost. If your rear end does not have the drop out center section, AND you have to pay for the labor to switch out the gear sets it does not seem worth it to me personally for the little more quickness you'll feel off the line. If you do ring and pinion changes your self, and it's only the cost of the new gearset, then perhaps its worth trying as gear sets aren't terribly expensive by themselves.
 
Thanks guys. I was just considering the stall of 3000 and the rear axle ratio whether the converter would be slipping too much at low speeds. No I do not race the car. I use it on the street and for cruising. I addressed this years ago and decided 3.23. But now I have the hi stall does it need the the lower gear? Also what do you mean 3.23 :1 is the optimal performance ratio?

Regards
Billy D.
 
Since you are running 14in wheels and tires I would leave it alone , should be enough gear with those short tires
 
I have a 3000 stall convertor, short 14 inch tires and 3:55 gears in my car. They work GREAT in the city, but rev a little to much on the highway. It all depends on what you plan on doing with the car. JMO
 
Billbo said:
Thanks guys. I was just considering the stall of 3000 and the rear axle ratio whether the converter would be slipping too much at low speeds. No I do not race the car. I use it on the street and for cruising. I addressed this years ago and decided 3.23. But now I have the hi stall does it need the the lower gear? Also what do you mean 3.23 :1 is the optimal performance ratio?

Regards
Billy D.
Click to expand...

If you look in the catalog, or old Mopar brochures, they themselves call the 3:23 their "maximum performance" ratio! I went from a 3:23 to a 3:91 in my GTX hoping to dip into the 13's in stock trim, didn't pick up not even a couple 1000ths! Still at 14:06!!

Most times, when changing things like torque converters, rear ends and such, one component change does little or no good unless more components are changed to compensate for the increased performance capabilities of the change! That's how the snowball gets rolling! I recently had to rebuild my trans, and had a new 2800 converter sitting around so I threw it in! WOW, what a difference! However,'I think my rear ratio change is now benefitting from the converter change, where no change was detected before!! Take that for what it's worth, but I can see where changes should be made with other changes in mind!! If you have the 3:55 and can just swap out the centers real quick and try it out, worth the change! If you have to spend $100's to buy the parts and have them changed, maybe not worth it!!
 
properly tuned with a quick distributor curve your car should break traction at will and pull hard now,unless your cam is too big.
 
The camshaft is not that radical. Its a hydraulic lifter cam with 228 degrees on the intake and 235 degrees on the exhaust at 0.050". Lift is small at .460 on the intake and .485 on the exhaust (.307 & .323 at the lobes 1.5 rockers). Advertised duration is 273 and 280 degrees. Its similar to the extreme energy cams that Comp do but with a little less lift. So it does have very good bite down low rpm. And thats why max power is at just under 5500 (rev limiter set at 5500)

EXTRA INFO:
Intake centerline 106 degrees and lobe separation is 110 degrees. Dialed in at .078" lift on No.1 intake at TDC.

RAgards
Billy D...
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what is your cruising rpm? probably less than 3000, and a 3000 stall converter is probably actually around 2800. If the converter is slipping too much the trans will be hot. a 3.55 gear will match your cam better, but may not be worth the $ to switch, cuz it is only slightly more than 3.23 . and 3.23 is not the maximum performance ratio, I think it may be considered the best overall average street ratio. I have run a 4.88 gear in my 340 4 speed street and strip Duster for 30 years with 28" tires, 3600 rpm at 60mph, 7200 at 120
 
3.23 was always considered to be a good compromise between a highway gear and a drag strip gear. That's why just about all the mid-level performance cars came with that ratio standard back in the day.
 
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