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Gear ratio help

jason79

jason79

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Need some advice from people with more experience than myself. Currently running 3.91 sure grip. The problem is 2 fold. First the sure grip is wearing out. Second I drive mostly highway. Rural Illinois closest town is 15 minutes any direction. I have a 489 case that I have cleaned up and ordered a rebuild kit for with a auburn limited slip. I have a set of 3.23 gears in very good condition that will go right in. Is this a good ratio or should I look for 3.55 gears? Engine is a 512 stroker with 9.5 to 1 compression. I have stealth heads, Howards hydraulic roller cam .545 lift, Hughes 3200 stall converter in a 727. I have not run it on a dyno, but would guess 525 to 550 for hp. I want better highway cruising rpms, but still want that low end performance of the 3.91 gears. Am I going to be disappointed with a 3.23 gear ratio?
20210306_234514.jpg
 
A 512 makes enough torque 3.23's will be fine, hell 2.76 might be even better.... When you have enough torque the car ET's practically the same with 3.23's as it will with 4.10's. (seen a number of Mopars with 505's ET within a tenth of a second)
 
With a 3200 stall converter you may be on the verge of trans heat troubles. Depending on your rear wheel height you may run under your stall speed and could risk overheating your trans. I have 3.23’s in my 68 charger with a 2500 stall. 28” tall rear tires. Runs about 3200 at 65mph. I have a 440 that makes 550 ft/lbs torque at 3500 rpm (has run on the dyno) i do not feel the need for a deeper gear. If your not charging your converter I’d suggest 3.55. With a 28” tall tire it’s still an ok gear for the highway and Is great around the city. I used to run 3.55’s in my 67 c-body and loved them.
 
While I have and love 3.23’s, you’re going to find they are a long way from 3.91. Far better on the highway or even open secondary roads but that edge when you get on it will be softened.
 
You may want to consider the Gear Vendors overdrive unit. Keep your 3.91s and kick it into OD on the highway. But if you're going to change, I would go 3.23s.
 
Tman100 said:
I have 3.23’s in my 68 charger with a 2500 stall. 28” tall rear tires. Runs about 3200 at 65mph.
Click to expand...

Maybe I am missing something here but my car has 3.23 rear and 28 inch tires and it hits 65 mph at around 2500 rpms. I went to a transmission calculator and found the same results. I then punched in 3200 rpms all else the same and got 82.56 mph. With 3.55's at 2500 /28 tires was 58 mph and at 3200 was 75.12.
The closest I got to your 3200 at 65 mph is with a 3.91 rear but at 68.2mph. Are you sure you have 3.23's??
I will soon have a stroker 505 and am keeping the 3.23 so I can hit the highways and have some boot with the torque.
 
All that money invested in the engine I would definitely look into gear vendors.
My slant six twin 2bbl webers and headers , 26 inch tyre and 355 rear end . I bought from a guy the wilco adapter plate and boleti on the gm700r4 overdrive lock up tc. I daily drive mine unless its pouring rain.
but she purs at 2200 rpm on the highway at 60 . I love sound of the exhaust crackle in the header as she puts down the highway
 
Turboomni said:
Maybe I am missing something here but my car has 3.23 rear and 28 inch tires and it hits 65 mph at around 2500 rpms. I went to a transmission calculator and found the same results. I then punched in 3200 rpms all else the same and got 82.56 mph.
The closest I got to your 3200 at 65 mph is with a 3.91 rear but at 68.2mph. Are you sure you have 3.23's??
I will soon have a stroker 505 and am keeping the 3.23 so I can hit the highways and have some boot with the torque.
Click to expand...
Sorry my bad... was looking at my Monaco that had 3.55’s... 2750ish is my car at 65. Dad had 2.94’s and is at 2460ish at 65. This can vary depending on air pressure on rear tires.... but that is a non- issue. All I was stating was cruise speed on highway will be below converter stall. And when your below converter stall speed when going down the highway you create excessive heat. My buddy has a 69 cuda with a small block stroker. Had a 3000 stall converter in it with 26” tall rear tires and 3.23 gears. We had issues with trans heating up after about 70 miles of travelling. We were right around the stall speed on that car. So we pulled that converter and installed a 2500 stall. No more heating issues.. those were both Hughes converters.
unless your drag racing you’ll probably be happy with 3.23’s big cubes make big torque and with that you don’t need the deeper rear gears.
 
I too am rural and am running a 3:23 behind a 383. I like the lower RPM's on the highway and the fuel mileage. It has all the get up and go that I need, but then I don't race it or care about performance. She's a cruiser.
 
Hughes 3200 IMHO is going to be a problem, I am not aware of a hughes that is built tight... its going to slip a lot w 3.23 and you will not like it, 3.55 is going to be on the edge of what is tolerable if you want to keep your performance level Step up to a dynamic or ptc 9 1/2" converter thats tight...the car will stall around 3800+ full power but moves the car at 2500rpm. There's other companies out there too, but those two companies I would recommend, I wouldn't get a 10" from anyone... i think the 9 1/2 is the best out there for what you are doing. You could run 3.23 then without much performance loss. 3.55s are a nice gear too. Just depends on how much 75mph driving down the interstate you intend to do.
 
I had 4:10 and now 3:23 and I am happy with them.
 
The way that car is built..... 3.55's.
 
I was kind of wondering about the torque converter. While it does feel like a fairly tight converter, I think a set of 3.55s will be a better fit.
 
davek said:
I had 4:10 and now 3:23 and I am happy with them.
Click to expand...
Same here Dave.
I just swapped out the 4.10 for my original GTX 3.23 gears in the A100.

From the small amount of seat-time so far, I can assure you that the swap has left me with a permanent smile.

I can feel the truck being even more aggressive, and launching harder, with almost frightening open road speed & acceleration. :D
 
The 512" motor will have no problems with a 3.23 gear if you are not asking for optimal drag strip performance. My Satellite has 4.10's with a 28" tire. I have no problem starting in 2nd gear. I don't know much about Hughes converters. I was very happy with the Turbo Action 10" (tight model) I had and am more happy with the Lupo Dynamic 91/2" I have now. The correct converter will make all the difference.
 
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