3.91 or 4.10?

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haybag

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Have a 69 Dart, currently stock 5.9 with fuel injection, 833 4spd , 8.75 3.23 sg.. Best time so far is 14.3,would like to get into the 13's and think I can with some lower gears.Eventually going to do a cam, tune and a few other engine upgrades. Only go to the track a couple times a year, otherwise just an around town cruiser, doesn't see the highway. I have a spare chuck with 3.23 for street use. What gears would be best for my setup 3.91 or 4.10 or would I even notice a difference between the two?
 
haybag said:
Have a 69 Dart, currently stock 5.9 with fuel injection, 833 4spd , 8.75 3.23 sg.. Best time so far is 14.3,would like to get into the 13's and think I can with some lower gears.Eventually going to do a cam, tune and a few other engine upgrades. Only go to the track a couple times a year, otherwise just an around town cruiser, doesn't see the highway. I have a spare chuck with 3.23 for street use. What gears would be best for my setup 3.91 or 4.10 or would I even notice a difference between the two?
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Probably not much of a difference there.
Maybe a couple hundred rpm at the stripe.
If & when you go with a bigger cam the 4.10 will probably help more.
I have a small roller in a 5.9 with 3.92 gears In a Dakota r/t that gear at highway speed in od is annoying but that's probably more my loud exhaust.
 
440, I would have recommended 3.91. That's what I have.
For your 5.9, IF you truly only drive it around town, 4.10s
I had a big block car with 4.10s, freeway driven to work, every day. 3700 rpm gets old.
 
haybag said:
Have a 69 Dart, currently stock 5.9 with fuel injection, 833 4spd , 8.75 3.23 sg.. Best time so far is 14.3,would like to get into the 13's and think I can with some lower gears.Eventually going to do a cam, tune and a few other engine upgrades. Only go to the track a couple times a year, otherwise just an around town cruiser, doesn't see the highway. I have a spare chuck with 3.23 for street use. What gears would be best for my setup 3.91 or 4.10 or would I even notice a difference between the two?
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Sounds to Me You just need better skins out back, w/3.23's & a 4-gear, that thing should be runnin' 13's already. Count out-loud "One Thousand"......, if it spins that long, You should be running 13.50's easy.....ET Street radials...ask Santy Claus for Christmas.....
 
If you got a 26" tire probably 3.91 if 28-29" maybe 4.10s, what rpm does it do now at finish line at what mph ?
 
fishmens67 said:
That was my first choice with a 14X32.
Anything would be better than the 3.23's with a 4spd.
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I tried 5.38s with 14x32s. It was quicker and faster with 4.57s (?)
Gonna try 4.10s in my other big block car with 315 60 15 drag radials, but it's a light car.

IMG_20231216_184617.jpg


IMG_20231216_184639.jpg
 
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Get rid of the wussy Magnum cam first, or at least retime it. I mean, from the Factory, they were installed on a 119 Installed Centerline for truckes to bleed off cylinder pressure, to prevent detonation under load.
They run a whole bunch stronger at about 107. So by the math, they are 12* retarded!!

Fix the cam timing, it costs you a gasket and I bet it goes 13s even with the 3.23s which, with a 4 speed should get you 98 in Third gear at 5500 .......
Four series gears will force a shift into 4th, and I guarantee you, neither of the two options are gunna be correct.
3.91s will hit 98 at near 4770, and 4.10 at 5000. whereas the factory cam is done around 4500
At 3400 pounds, 98mph is already a 13.9
At 3600 to go 98 requires 278 hp, and that might get you to 13.68, with a SS chassis. With a street chassis you can expect to be about a second slower;
partly from the crappy 60ft, and partly from trapping off the cam.

But yur stock 5.9, even with the cam in correctly, might never make 278 hp, so, at 3600 pounds, she'd never make 98 mph. jus saying.


And honestly, as a city car, yur already making more power than either your tires or the cassis can handle, and 3.23s are already the right gear to downshift back into first, at 35 mph. which should hit 3750 just before tirespin.
3.91s will get you 35=4540, massive tire-smoke, and bam, time to shift into Second, that's gunna suck.
 
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Interesting.

Are the tires spinning, or do they grab and the car bogs?
 
I’d go with 3.91 with what you run now it would turn 4700 rpm but if you gain mph be closer to 5000 rpm, plus once you add a cam and gain more mph and rpm, 4.10 might be slightly too much.
 
Revised recommendation.
With tires that short, 3.91s
With REAL drag slicks (very much recommended for stick cars, over drag radials) 28" tall: then 4.10s

I'm gonna be running 4.10s with a big block...... but my tires are 31 inches tall.
 
For a 93 mph pass, a 14.3 is pretty good. 2.2, not so much. You could work on the launch, maybe improve for little to no bucks.
I realize you're handicapped by gears and a stick.
 
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haybag said:
Forgot to mention I am running 26" drag radicals. 2.2 60' times,93mph 1/4
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A 275/60/15 (28") will fit under a 69 Dart with some work (springs and offset).

With 26" Hoosier drag radial my 69 Darts best was a 1.889 60' 4 spd 3.91:1. And the car is crossing the line at 54-5500. I believe the set up is struggling to get the weight transfer, so I tried a set of gears...

Compare 4.30:1 with the same set up, and the car was out of breath at 1000' of track.

Save your $ and work on getting the weight to transfer, and your fuel system to keep up with the load a launch.
 
If you’re gearing for the track you need gears that will have you at max HP about 150-200 feet before the stripe. If you’re having problems with your 60’ with the proper gears then you need tire and suspension.

I run 4.86 gears, 30x10.5W slicks and 1.37-1.39 60’ times on my street driven Plymouth.
 

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