Rearend Gears |
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Scott
Senior Member Joined: 31-January-2012 Location: Versailles,Ohio Status: Offline Points: 216 |
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Posted: 31-July-2013 at 7:29AM |
I have a S&H car with a mildly built 1969 351W and a CJ trans. The torque conv.from the CJ c-6 was no good so instead of the factory orig small converter it has a normal size conv. in it.The rear gear is a 2:79 - 3:00 I think it has been a while since I done it.The rear tires are 255/60/15 and my question is the car will not burn tires from a dead stop why? I don't know if it is a combination of the gears and the big tires or if it would be the fact I have a stock regular size torque conv. in it?The car will break the tires when it shifts into 2nd gear but from dead stop forget it.Anyone have any thoughts on this?
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Rockatansky
Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6059 |
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all 3 factors are playing a role, it's what we call a 'combo', short for combination as you hit on in your post IIRC the 10" CJ converter is rated @ 2600 rpm vs around 1600 rpm for the standard 12" converter, BIG difference! the engine is producing significantly more torque @ 2600 rpm than it is at 1600 rpm, so it was able to overcome the tires with the old CJ converter where as now it's not able to with the standard 12" donut. pizza cutter tires will reduce available traction, maybe enough to allow the new combo to break the tires loose? a higher numerical gear will provide more torque multiplication and more power cycles from the engine for the same number of tire revolutions... again more power @ the rear tires when the trans hits 2nd gear what rpm is the motor turning? again, lots more torque at that rpm than @ 1600 the stall speed converter allows the engine to get a little 'head start' on things before the converter couples the engine to the trans, like revving up the engine a wee bit before letting out the clutch on a manual shift car |
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72 GT Ute
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unlovedford
Senior Member Joined: 17-December-2010 Location: Tennessee Status: Offline Points: 10142 |
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Back when I was driving it, my 1976 would roast the tires (and grab a ridiculous 2nd gear) with a junkyard rear of unknown ratio, 245/60-15 tires, rebuilt C5 transmission, and a thoroughly worn out, smoking 351W 2bbl engine. No power-braking needed, just stab it and go. I have no idea what rpm's that poor windsor was turning when it hit 2nd gear, but I do know it was running 50 mph. Engine was so loose that it could (and did) take that abuse many, many times, would just not rev or pull any harder - just leveled off before I would manually shift to 2nd.
The 1975 GTS I bought last year has a Jasper rebuilt Windsor (stock, 2 bbl)and a rebuilt C4, runs 3.00 gears, has 235/70-15 tires on it and it will smoke the tires as well. Have not tried to grab a 2nd, lol, since it might break the car in half. My point is that yours should be able to at least turn the tires over, I would think. There seems to be something else at work here (timing, carb issues, perhaps an even worse ratio rear, HP losses somewhere) in addition to the convertor change. |
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Joe
1972 Mom's Squire Wagon 1972 Torino Wagon 1976 Torino 1968 Cougar XR7-First batch 1972 Torino 460 1989 BroncoII/Jeeps/Titanimous Popeye and Brutus (Rams) |
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Scott
Senior Member Joined: 31-January-2012 Location: Versailles,Ohio Status: Offline Points: 216 |
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When the car shifts into 2nd gear when really nailing it, it shift's out at 5500 RPM's.Motor is punched .030 over around a 492 lift cam and a 600 holley carb.
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