Best street and strip gear for a 1969 big block - Chevy Nova Forum
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Old 9th-February-2012, 11:13 PM   #1
jeep2001

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Best street and strip gear for a 1969 big block

I have a 1969 Nova with a 454 that is bored 60 over. I have a 280 magnum cam, 1970 open chamber heads, C 396 maniford, Holley 650 and a turbo 400 with a 2500 stall. The gear ratio is a 472 and I would like to install something a lot smaller. How small can I go with out hurting performace? The car is driven mostly on the street but I plan on going to the track a few times this year. The motor seems to stop pulling about 5200 RPMS so I think the 472 gear is too big for the 1/4 mile run. Any suggestions will be great?
Thanks Mike
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Old 9th-February-2012, 11:17 PM   #2
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From what I understand, big blocks don't require a lot of gear to get off the line quickly like a small block would. I would say 3.42-3.73 gear would be fine for your application.
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Old 9th-February-2012, 11:44 PM   #3
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3.73 is the way to go!!
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Old 10th-February-2012, 12:45 AM   #4
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Depends on tire diameter in most cases 3:42-3.73 are the most common. Like said above.

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Old 10th-February-2012, 01:42 AM   #5
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I have 255x60-15 street tires and also have 28x10.50-15 slicks.
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Old 10th-February-2012, 08:30 AM   #6
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If your combo is all done at 5200 your most likely to hit max rpm before the end of the 1/4 with 3.73 gears. That being said from what you describe of your combo the 650 carb is way to small. You should be running a 750 minimum maybe as big as a 850.That small carb might be whats holding you back. Id try a bigger carb even if you have to borrow one and see if it falls off still. If it picks up a couple hundred rpm you should be ok with a 3.73 gear. When it falls off does it just nose over or does it go into valve float? That cam should see 6k easy without falling off real badly.
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Old 10th-February-2012, 08:53 AM   #7
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Do you have a 12 bolt rear axle? If so, the 3.55 might be a nice choice. The back tires are on the tall side so you might be happy with 3.73. Just depends on how much highway driving you do.
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Old 10th-February-2012, 02:17 PM   #8
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The motor pulls good to 5200 RMP after that it pulls a lot slower. It will pull to about 5500 or 5600 before it stop pulling. I have a Ford 9'' in the car. With 373 gears what RPMs should I have to get down the 1/4 mile? Will rejetting the 650 carb help or is it just too small?
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Old 10th-February-2012, 02:27 PM   #9
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That is one steep gear for a big block! Even saying that, I'd first get a bigger carburetor, 650 is too small. Even with re-jetting you won't get the flow (CFM) you need to supply the air needed to support upper RPMs. Your combo needs air.

3.42 gear after the carb.
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Old 10th-February-2012, 02:28 PM   #10
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Quote:
Originally Posted by jeep2001 View Post
With 373 gears what RPMs should I have to get down the 1/4 mile?
It depends. What is your 1/4 mile speed right now with 28" tires?
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Old 10th-February-2012, 03:36 PM   #11
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swap the carb first 3.73 should be close to 5800 in the traps.
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Old 10th-February-2012, 03:41 PM   #12
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This calculator might give you an idea:

http://www.kabamus.com/garage/gears.html
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Old 10th-February-2012, 03:48 PM   #13
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I just changed my rear gear this year to a 373, and it's perfect for my 69 BB, it can reasonably drive an hour or 2 and still goes like a bat outta hell!!!

The fuel milage is still within reason too! My car is fairly mild with about 430-450hp .030 over 402 on pump gas.
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Old 10th-February-2012, 03:52 PM   #14
jeep2001

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I can get a Holley 750 vacuum secondary to try, if thats helps would I be better with a double pumper than the vacuum secondary carb with both carbs being the same cfm size?
Thanks Mike
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Old 10th-February-2012, 04:02 PM   #15
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That 750 vac secondary should be just fine just make sure the jetting is close.
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