If you were building a 1966 Dodge Dart for 1/4 mile racing only, no street use, what rear end gears would you use? Motor will be freshly bored .060 over, head milled .100, block milled .075. A cam (duration and lift yet to be determined) along with a 4 barrel carb and headers into single 2.25 exhaust system. Torque converter will be at least a 3500 stall.

Depending on factors, such as cam, carb, tire size, car weight, the gear would, most likely, be anywhere from 3.91 to 4.56

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

What Charlie said,I run 4.56s and can ALLMOST get into the 12s.Mark

You need to know camshaft duration @050", solid or hydraulic or roller and car weight. That and that alone determines final gear ratio and rear tire height.
Why?
because cam duration at 050 determines RPM for peak power. A solid needs more duration than a hydraulic or roller to achive the same RPM range.
peak power determines peak MPH in the quarter mile so it should be geared for that. Weight determines max MPH available for a given HP.
All this can be caculated before you turn a single wrench and is often very accurate. Sometimes we are with in 1/10th of a second for et and within 1 mph. Sometimes. several in fact we have been right on when all was dialed in.
Drag racing is science. NOTHING happens by chance.
When caculating be conservative. Especially when caculating HP. Also weigh the car with you in it. DO NOT guess or use published shipping weights as you will quickly discover they are meaningless.
As a rule of thumb 1 inch increase in tire height will equal 1 step in gear ratio more or less. IE 29 inch to 30 inch will have almost identical effect of going from 410s to 391s. Your question is a good one. Planning here will insure a successful and competitive car everytime.
Don

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Don

Mopar asked the same thing in late 1965 and came up with the D/Dart program. It did not include a /6 in the solution. Here is an excerpt from the flier they sent to the dealers concerning it.

Dodge Offers "D" Stock Dart

DETROIT -- A new 275-h.p. Dodge Dart GT that meets D Stock specifications of the NHRA, AHRA and NASCAR is now in production. The "D/Dart" has a shipping weight of 2,946 pounds.

The "D/Dart" features a modified 273-cubic inch engine with a special four-barrel Holley carburetor. Other features include:

A special Camcraft camshaft (284 degrees with .495 intake and .505 exhaust), Racer Brown valve springs, a modified, full-breathing intake manifold, a low-restriction air cleaner, and a Weber clutch. Other standard items are: a heavy-duty 4.86:1 Sure-Grip 8-3/4 inch rear axle, free-flow exhaust headers by Doug of California, a four-speed manual transmission, heavy-duty suspension, and 6.95x14 B.S.W. tires

Back in the day these would run in the low 13s to high 12s. Tire technology of today alone would provide a substantial improvement.

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You can't fix stupid. - Ron White

Here are the stats I have so far. 225 bored .060, head milled .100, block milled .075, cam duration .228/.228, lift .460/460, oversized valves most likely 188 intakes, clifford 3 into 1 headers, single 2 1/4" exhaust pipe going through a magnaflow muffler, offenhauser 4 bbl intake manifold and Edelbrock 4 bbl 650 carb. The tranny will be a NOS later model 904 with a 3500 stall convertor. Supposedly the later 904 had a lower first gear so I've been told. Proposed gears 3:91 posi (clutch type) in a 489 case. 14" tires on back.

What do you think?

Unless you have really short tires you'll need more gear.

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Check it out... www.symcoshakedown.com

Because?

I would buy Norm Fosters car it is a national champion and ready to run. Thanks Ron Parker











Bee Good Or Bee Gone

4.56.Mark

Well, I think you're on your way, but haven't got all the answers or maybe even all the questions.

Knowing how much you milled is interesting, but what's the actual compression ratio? That's too big an intake valve. You want something about 1.72-1.78". That's not much cam duration for a race car and too much carb unless it really is a race car. Trans will need work to live very long under race use. NOS just gets you new hard parts, not a race trans. Gears are a bit too low numerically for a drag car. 14" tires doesn't mean much other than the diameter of the rim they fit. Need to know the tire diameter to figure out the overall gearing.

If this is a race car I'd go ~11:1 compression, cam of about 240° duration at .050" tappet rise on the intake and 234° on the exhaust. Cam ground on 104-106° centerline advanced to 100-102° intake centerline. 2 1/2" exhaust with a straight through Magnaflow, welded Dynomax Ultra Flow or Hooker Aero Chamber muffler. 500 CFM Edelbrock if you want an AFB type carb. Talk directly with the torque converter builder. Expect to pay around $600 to get what the car really needs. You'll probably end up near 4.56 gears with a 28" tall tire. Shorter tires need numerically lower gears as the tires make more revolutions to cover the same distance.

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Joshua

Joshua, you spotted my typo. Yes, the valves I was looking at are 1.77. Proposed tire height is 28.5. I'm glad you commented about the cam as it was one I bought in a package deal with manifold and headers. As long as I have been turning wrenches, I have not taken the time to research cams and gear ratios. Thus my posting in this forum. Now, when I say a race car, I am defining it as for racing only. Not necessarily the fastest I can go. I'm not sure I want to get into the roll cage and all that. So for now, let's say I want to get as close to 14 seconds as possible.

If you have the budget for good head work and match it up with enough cam, compression, torque converter stall speed and the proper gear ratio 14s should be pretty easy.

I'd sell the current cam and get what the engine needs. Erson or Oregon Cam Grinding can get you something that works better. You might look at this thread. http://www.slantsix.org/forum/viewtopic.php?p=218586 $70 exchange plus shipping is all an Oregon cam will cost.

I'd probably do Oregon #346 at about 10.5:1 compression ratio. If you want to get a little wilder go with The #977 intake lobe with the #346 intake lobe on the exhaust side. Use lobe centerlines as described previously and bump the compression to 11:1 maybe 11.5.

So what's the budget?

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Joshua

No real budget concerns. The only part I am missing that will cost much is the torque convertor. Only other parts are replacement parts such as pistons, bearings, valves and such. Manifold, headers and carb are all onsite. I have read your carburator article and you might find it interesting that this will go into a 66 Dart GT.

If you have money to burn I'd get the K1 rods and Wiesco pistons. I'd probably also get a copper head gasket or two and spray some nitrous while I was at it, but that's just me.

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Joshua