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| What's the lowest you can go ---- rpm? https://www.slantsix.org/forum/viewtopic.php?t=15826 |
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| Author: | slantophile [ Thu Jan 19, 2006 12:22 pm ] |
| Post subject: | What's the lowest you can go ---- rpm? |
I am piecing together the drivetrain for my 65 Valiant wagon. Engine will be a fresh stock early 70's 225 I had on hand with a supersix set up and 2 1/4 single exhaust. This will be backed up by a 833 OD four speed. Behind that is an 8 1/4. The 8 1/4 I have has 2.45 gears --- ouch! Does anyone have opinion if I will ever be able to shift to overdrive? Just how low can a 225 turn and produce decent torque? With the overdrive, this is like putting something like a 1.8 axle behind a straight 833. At this time, I plan to try it since it costs me nothing other than time and frustration if I have to put a steeper gear into it. My goal is highway cruising/fuel economy. |
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| Author: | zedpapa [ Thu Jan 19, 2006 12:30 pm ] |
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those are going to be very hard on the clutch as you will have to slip it forever to get moving in first. my dart has a similar setup with 3.21 gears and first is still a little low for it. if the car is a highway cruiser, then get 3.21 gears or if you like a little more spunk in your engine get 3.55. i turn about 2200 rpm at 65 with the 3.23 gears. the 3.55's will be around 2500 rpm at 65. zedpapa |
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| Author: | mcnoople [ Thu Jan 19, 2006 1:11 pm ] |
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I could be mistaken, but I remember reading that carrier/housing was different for the 2.45 equipped cars. I maybe remembering a 9.25 or maybe something else, but the pinion gear for 2.45 gears is fairly large requiring the ring gear to move to offset it. |
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| Author: | slantophile [ Thu Jan 19, 2006 2:05 pm ] |
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Yeah, the 2.45 is a different carrier, so I would need to change that to swap up to a numerically higher ratio. As far as first goes, my trans has a 3.09 first. So, the way I see it, a straight ratio 833 has a 2.47 or so first which is about the same as my differential. That means the first gear final drive ratio with my set up is the same as a 3.09 differential behind a straight ratio trans. That doesn't sound too, too bad. |
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| Author: | DusterIdiot [ Thu Jan 19, 2006 2:46 pm ] |
| Post subject: | Tall gear... |
Quote: As far as first goes, my trans has a 3.09 first. So, the way I see it, a straight ratio 833 has a 2.47 or so first which is about the same as my differential. That means the first gear final drive ratio with my set up is the same as a 3.09 differential behind a straight ratio trans. That doesn't sound too, too bad.
One thing you have to remember though is: some of the early A-body slant six 4 speed boxes had the 3.09 first gear (and I hear some of the late run 318 4 speed boxes too)... The -non- heavy duty 4 speed had a 2.66 ratio also... I have run the A-230 in my '74 with 3.21, 2.94, and 2.76 gear ratios (tranny ratios are 3.08,1.70,1)...the 2.76:1 was nice at 70 mph...just putted along...getting it off the line was not easy and required slipping the clutch about 3 times to get it to clear an intersection with any kind of speed....once over 30 mph in 2nd it was OK(which usually meant running it up to 20 in 1st gear...). 2.45 is an ok ratio if you have some nice low end V-8 torque to motivate it.... Assuming that you follow through and shift at 2500 rpm for a little extra Zoom and using a 'stock' type tire your shift pattern will be something like: 1st gear run it up to 25 mph shift to second run it up to 45 mph (OD box and 3.55's and I'm already in OD by now and running up the powerband)....shift to 3rd gear will happen at 75 mph.... In overdrive you may have some problems at 1500 you'll be at 62 mph and it may lug in the transfer section of the carb or 2000 at 81 mph and then you'll be in the main metering area... comparing leaving ratios would be: 2.45 Feather Duster 2.94 1st 7.57 9.08 2nd 4.09 4.91 3rd 2.45 2.94 OD 1.79 2.15 Cruising Fuel Economy would be aided by using an EGR to lower your cylinder volume using spent exhaust gas like the Feather Duster...the thing that kills the A-833OD is that rpm dropping wide ratio shifting... let us know how you turn out (you might invest in a 10" clutch over the 9.25"...) -D.idiot |
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| Author: | Jeb [ Thu Jan 19, 2006 5:39 pm ] |
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How can EGR help gas mileage? |
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| Author: | sandy in BC [ Thu Jan 19, 2006 6:37 pm ] |
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Jeeze thats a high ratio!...I find my 3.23 rear gears a little high now that we have a bigger cam...I might be happier with 3.55 gears. We do nothing but unregulated highway driving and shifting into OD at 70 is a bit much. I would get a lower gear and make that OD gear useful....and 1st useful |
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| Author: | Reed [ Thu Jan 19, 2006 6:43 pm ] |
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The lowest I have ever gotten a slant to idle was about 250 RPM. It didn't stall out, I just couldn't get it to go any lower. |
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| Author: | SlantSixDan [ Thu Jan 19, 2006 9:35 pm ] |
| Post subject: | Re: Tall gear... |
Quote: Cruising Fuel Economy would be aided by using an EGR to lower your cylinder volume using spent exhaust gas like the Feather Duster
I disagree. EGR doesn't increase fuel economy by reducing (effective) cylinder volume. That, in fact, is the mechanism by which EGR reduces fuel economy. The Feather Duster/Dart Lite had EGR for the same reason almost every other '76 car had EGR: To reduce peak combustion chamber temperatures by introducing inert exhaust gas into the intake tract, thereby reducing the formation and ultimate emission of NOx. You can neutralise and with very carefully balanced calibration slightly reverse the fuel economy/efficiency reduction caused by EGR, by increasing the spark advance. Because EGR is reducing peak combustion chamber temperatures, there is less tendency to ping. Therefore, more ignition advance can be used. That's why the Feather Duster/Dart Lite had such an enormous long throw on the vacuum advance (still available as Standard-BlueStreak VC208): So that under cruise conditions, you were running a whackload of spark advance for max economy. |
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| Author: | slantophile [ Fri Jan 20, 2006 7:28 am ] |
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Interesting feedback about the EGR. I had never even thought of keeping it, but if I could get a bit better fuel economy, I will experiment with it. I agree, completely, that the 2:45 is way to low, I wish I would have noticed the ratio when I bought the axle. I understand that I need to change the carrier and gear set and I'm good to go. Might as well switch to a sure-grip when I am at it. 3.23 or 3.55? I suppose 3.55 since with the OD, it's more like a 2.7 |
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| Author: | kesteb [ Mon Jan 23, 2006 10:19 pm ] |
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I run a 2.45s, with the 8.25 axle. I have a 4 speed (a '64 3.09 first gear tranny) and 26" tires (p235x60x15"). I don't have the problems that DusterIdiot refers too when starting out. Freeway travel is nice and effortless, steep hills can be a problem, when starting out. I can keep up with normal stop and go traffic just fine. When I am below 25 mph I need to run 3rd gear, otherwise I can pull 4th around town. It is really intersting to let the car wind out in 1st gear when the car next to you has sifted 3 times. |
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| Author: | slantophile [ Wed Jan 25, 2006 9:08 am ] |
| Post subject: | |
Your set is very much like mine, kesteb. Thanks for the feedback. It doesn't cost anything to try it with the 2.45, so I might as well do it. I will try to get some feedback on this issue back to the board when it's up and running (summer?) |
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