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Old 01-21-2010, 02:44 AM
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highway gear too tall?

Got a 56 panel truck that weighs about 3900 lbs w/driver. It will have a460 with about 500+ lbs torque. Will that torque make a 2.75 gear liveable or will it feel like a dog? It has a C6. I got the tall gear as a substitute for a costly overdrive...

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Old 01-21-2010, 04:54 AM
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If the cam not real big and the tires are not real tall. Should work fine.
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Old 01-21-2010, 08:06 AM
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I just helped a friend get his 73 impala running. it has a 402 bbc, th400, 2.73 gears, and weighs 4500 pounds (huge car). Cam is mild (208/212 at 0.050") 8.5:1 cr, no headers, and 26 inch tires.

It runs fairly well. spins the tires a little bit and pulls ok. feels like a 0-60 in 8 or 9 seconds (0-60 with only 1st gear). It has enough power to get out of it's own way.

3900 pounds and a 460 should run much stronger. should be ok if the cam is mild and the tires are less than 28 inches
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Old 01-21-2010, 04:27 PM
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Many years ago I had a '67 Pontiac Catalina with a High Cpmpression 400 2 Bbl., TH400 and 2.29 gears. It weighed right about 4,200 Lbs. dripping wet w/o driver. It would lay down a black stripe for 2 blocks, bury the speedometer in a little over a half mile and got an homest 20 MPG. Now time may have "fuzzied" the details a bit but if it has they aren't far from reality. You'll be fine.
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Old 01-22-2010, 01:35 AM
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Thanks. BTW,it has about 236/230 at .500, 9.5 compression, 28" tires,and about 2000 converter.
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Old 01-22-2010, 04:50 AM
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Sounds like.....

Sounds like your going to have some fun
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Old 01-22-2010, 05:28 AM
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Quote:
Originally Posted by Hwyhogg
Thanks. BTW,it has about 236/230 at .500, 9.5 compression, 28" tires,and about 2000 converter.
Just do the things that you know will help torque at the bottom like dual plane intake, good ignition w/a good advance curve, keep the header diameter moderate relative to the engine size, use a connector between the exhaust after the collector but before the muffs, keep the exhaust diameter =/< 2.5", size the carb correctly and in your case, I'd even suggest one of the annular booster-type carbs like the Truck Avenger.

Good luck.
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Old 01-22-2010, 07:57 AM
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cam is a little big for the gear but you need it that big for the compression.

the converter will help.

you are on the edge.
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Old 01-23-2010, 12:00 AM
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I did a 454 with a TH400 (similar ratios to the C6) with large (255/70-15) tires and it was pretty well matched. The cam was 218/224 with a stock stall in a 73 Impala S/W with 2.73 gears. It wouldn't roast tires, but there was plenty of torque to get you moving quickly and enough "leg" to make highway cruising nice and easy. Perfectly matched? No. 3.08 or 3.42 would have been perfect for that cam and tires, but it wasn't enough of an inconvenience for me to shell out the money for a new gearset for an obsolete axle that was only used for three years.
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Old 01-23-2010, 11:37 AM
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Will the highway rpm's be above 2000 with those tires and gears? I don't think so maybe someone can crunch the numbers.
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Old 01-23-2010, 12:17 PM
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A 28" tire has an actual loaded effective diameter of about 26.3" so you'd be turning a hair over 1900 assuming no converter slippage and there would be some. After reading your cam specs you may want to consider a little lower gear like a 3.08 or 3.23. Even in a 460 that might be a little "iffy" with 2.75's, not saying it wouldn't work but it does change the equation a bit.
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Old 01-24-2010, 08:38 AM
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I'm using the edlebrock rpm performer intake with a 770 street avenger. I double-checked the cam specs at .050; 224 int/234 exh. The lift is .544int and .569 exh. It has the older style CJ aluminum heads from Motorsports, valves 2.19 int/1.71 exh.. Maybe after truck is up and running, I'll look into a lower gear, (3.00 or 3.25). I understand I need to keep the cruising rpm above the stall speed for less slippage, is that correct? I'd like to take road trips and be able to cruise at 65-70 mph. If I win the lotto, I'd go gear vendors overdrive and maybe a 3.55 or steeper for stop light fun .....Thanks to all,
James
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