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| Looking at Taller Gear Options https://slantsix.org/forum/viewtopic.php?t=33286 |
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| Author: | wjajr [ Mon Jan 12, 2009 11:51 am ] |
| Post subject: | Looking at Taller Gear Options |
Presently I have an 8 3/4" Suregrip with 3.55:1 ratio, 205/70R14 tires that makes for approximately 3000 rpm at 60 MPH. Engine is 225 ci. with Clifford headers & intake, Holley 8007 4 bl., unknown Erson cam, and duels, she likes to spin up. This combination generates too much thrashing for a cruiser where most rides to a show are 100 miles one way. A little math tells me the following ratios will result in rpm @ 60 mph. 3.23 = 2730 rpm 9% reduction 2.94 = 2460 rpm 18% reduction 2.76 = 2310 rpm 23% reduction What I would like is an idea how the performance is with these different axel ratios based on seat of the pants experience of folks on the board. |
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| Author: | Reed [ Mon Jan 12, 2009 12:18 pm ] |
| Post subject: | |
I would go for the 2.94, unless your motor can make decent low RPM torque. Then I would go for the 2.76. If your goal is to lower the RPM and get better mileage and longevity, 2.76 is about as low as you can go. You will notice a big difference in launch times as well as acceleration, and not for the better |
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| Author: | wjajr [ Mon Jan 12, 2009 1:23 pm ] |
| Post subject: | |
Thanks Reed. Presently I have a Manual Reverse Valvebody soon to be jettisoned for a conventional M/AB if the weather ever warms up around here. The car may as well be a two speed the way is set up now as first gear runs out quickly, and of course no passing gear. My thought was to go with either the 2.94 or taller 2.76 to take advantage of the new valvebody's passing gear capability. I may lose a little punch off the line, but once she is spooled up I would have three useful gears. Quote: I would go for the 2.94, unless your motor can make decent low RPM torque.
As for low end torque, she will not spin the tires on bare asphalt from a stop. Add a pinch of sand under the tires, and she will spin'em. So not a lot of low end grunt I'm guessing. This lack of off the line spunk may be due to a too low stall torque converter. I don't know the stall point of my present unit. Any shade tree methods of ball parking stall speed with out using a wrench? More input welcomed. |
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| Author: | Doc [ Mon Jan 12, 2009 3:05 pm ] |
| Post subject: | |
As far as "real world" driving goes... I can pretty well set my freeway driving speed by rear end gear ratio selection. Seeing how most of my 1 to 1 final drive SL6 powered cars seem to like the 2800 to 3000 RPM engine speed range, (the RPM "sweat spot") here is how it works for me: 3.55 = 55 to 60 mph 3.23 = 60 to 65 mph 3.07 = 65 to 70 mph 2.94 = 70 to 75 mph 2.76 = 75 + I pick the ratio to support the speed I want to cruse at. Currently, I am running 3.23s in our 66 Dart wagon, that does a lot of towing and the 3.07 is in my "Dacuda", used mostly for mixed city and short freeway "commute" driving trips. Our 64 Dart sedan and the 65 Dart convert are both using the 2.94 ratio with a shorter (24.5 inch) tire size. DD |
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| Author: | tlrol [ Mon Jan 12, 2009 5:07 pm ] |
| Post subject: | |
I appreciate Doc's input and totally agree with his numbers. I have little to add except to say that in a A833 O/D with a 3.56 rear end that the O/D is worthless until you hit about 70 plus mph. Conversely I find that 3rd gear (1 to 1 or 3.56) is easy enough to slide into around 35 mph and is down right sporting at 60 mph or so... Nice to see that my experience mirrors Doc's... Tire sizes make some difference, Google rear end ratio calculators, many of them are around online... |
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| Author: | DusterIdiot [ Mon Jan 12, 2009 6:02 pm ] |
| Post subject: | Weight is a factor too... |
Quote: I have little to add except to say that in a A833 O/D with a 3.56 rear end that the O/D is worthless until you hit about 70 plus mph.
But you have a 'truck'...I have that combo in my duster and it's great on the flats of I-5, and it'll keep running up through the rpms...I only have to downshift to 3rd if I have to a) go up a 'steep hill' , or b) need to go from cruise at 2300 rpm to 3200 rpm and get around that idiot talking on the cell phone making involuntary lane changes...Power to weight ratio/driving style/driving terrain does factor somewhat in where the vehicle is comfortable. -D.Idiot |
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| Author: | SV162 [ Mon Jan 12, 2009 8:05 pm ] |
| Post subject: | |
I went from 3.7 gears to 2.92 (not 2.94 but close enough) and I did lose some performance. To give you some "real world" figures I lost 7 tenths on the 1/4 mile. But as far as seat of the pants difference there wasn't much in it. I notice it, but friends who have been in the car say it feels the same as before. Where you will notice the difference will be out on the highway. Sitting on 2500rpm at 60mph is very cruisey.  And at those revs you can drop back a gear and hold on. 
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| Author: | VG-265 [ Tue Jan 13, 2009 3:19 am ] |
| Post subject: | |
I agree with Doc and find 3.23 suits me fine. (speed limit 100 KMH or 62 MPH) |
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| Author: | wjajr [ Tue Jan 13, 2009 3:27 am ] |
| Post subject: | |
SV162: Quote: Where you will notice the difference will be out on the highway. Sitting on 2500rpm at 60mph is very cruisey. And at those revs you can drop back a gear and hold on.
What size tires are you running?
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| Author: | SV162 [ Tue Jan 13, 2009 6:02 pm ] |
| Post subject: | |
Quote: SV162:
I'm using 205/60/15 which is around 24.5 inch diameter.
What size tires are you running? |
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| Author: | tlrol [ Tue Jan 13, 2009 7:34 pm ] |
| Post subject: | |
DI--true, a car will be better with lower numerical gears than a truck will. The link below takes one to Currie Enterprises gear ratio calculators--handy tools... http://www.currieenterprises.com/cestor ... ors.aspx#? |
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| Author: | wjajr [ Thu Jan 15, 2009 5:06 am ] |
| Post subject: | |
Spied this from Dan in a nearby post this morning: Quote: Post subject: (Sun Dec 28, 2008 9:48 am)
There is some "slop with a clunk" in my current set up that needs to be shimmed out so I think I will make the change to a less busy 2.94 while in there. Also with just two traffic lights in a county half the size of Connecticut here there is not a lot of "in town" driving to be had. -------------------------------------------------------------------------------- If you drive on the highway, with stock sized tires and an automatic your ears will get tired of listening to the engine rev on account of those 3.55s in a big hurry (and so will your wallet when it comes time to gas up the car). Putting this rear axle back together with a broken tooth is almost certain to wind up being a large waste of time, effort, and money. If you're into swapping ring and pinion sets, and you want a slightly snappier pickup around town, look for a set of 3.21/3.23 gears. They should be easy to find, as they were used in 8¼" rear axles right on up through '97 or so in Dakota pickups. But really, the 2.93/2.94 set is a good all-around choice. There's probably other stuff preventing the car being as snappy as you'd like it to be. What are the details of the car? Thanks everyone. |
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| Author: | Aggressive Ted [ Fri Jan 16, 2009 6:24 pm ] |
| Post subject: | |
wjajr, For real world numbers with a 2.76 8 3/4 posi I am right at 2500 rpm for 60 mph which nets me in the 24 to 25 mpg range. I drive 120 miles a day so the numbers are pretty consistent. My tire size per the book is 24.7" P225 60R 14 x 7" wheels. They are BF Goodrich T/A Radials. Cruising is nice at 50 on up to 65. It will hit 90 mph in a heart beat if you need to pass. So seat of the pants spunk is great, but my motor is built for torque per Doc's formula. Doc says this build is about 160HP with the little 1920 Economaster. From a dead stop it is very spunky and will break loose in a heart beat with the old P235 Grand Am's. I just bought the T/A's to use in the snow and ice and had them sipped, so it takes a little more effort to bust them loose with the posi at 28#'s air pressure. This spring I will putting on the Weiand four barrel manifold and trying two barrel and four barrel carbs. Reference my build in the signature block. |
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| Author: | wjajr [ Sat Jan 17, 2009 5:27 am ] |
| Post subject: | |
Ted, there is evidence that my car's transmission was recently worked on out of the car. Where there was four owners two of which were car lots in seven months befor I purchased her, I have no way of knowing what was done. When replacing floor pan metal I noticed abundant deposits of rubber fragments attached to the wheel wells, and points south to the rear bumper. This tells me this car at one time would brake'em loose with out much trouble. I suspect that someone recently installed a standard stall torque converter, replacing a higher stall unit. This car likes to idle in "N" with steady vacuum of 13 Hg. at about 1000 rpm, in "First" with 8 Hg. at about 800+ rpm, and when in gear she will creep at 1200 rpm. Any rpm under 800 there is a pronounced lope with this engine which combined with low vacuum suggests that the cam has a good bit of over lap. The unknown cam grind is killing me, and I don't have a dial indicator to help solve the mystery My questions are; what stall speed is your converter, and using SWAG** analyses what would be a good choice for my car? **For those of you not familiar with engineering lingo; SWAG = scientific wild as guess. |
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| Author: | rock [ Sat Jan 17, 2009 6:11 am ] |
| Post subject: | wjajar, regardless of convertor, those vacuums suck |
WJ, I use a 2500 stall convertor from midwest, and a 3.91 in a truck. Now using a slant six bell 727, but ran the 833OD for a while. Regardless of tranny or convertor, that vacuum you repoert is a long way from acceptable. For instance I idle in P at about 1,000 at 18 - 19 inches, and in D at 600 at 15. My experience would show you are losing power righ there..valves not right, induction system leak,timing, idle mix,..I would get my c\vac where it should be before pulling and repulling a tranny adn achanging convertors. Is your vac gage correct? have you8 checked it against another? and where is that gage tapped in? Just thinking, not criticizing. rock '64d100 |
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