Gearing ?

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273

273

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I'm just playing around to see what my options are.

So I got a 65 cuda with a 318 when done I'm hoping it can do between 100-110 in the quarter mile. So let's say it does 105.
I hear you want to be 400 - 500 rpm past peak power so say I want to be 6500 rpm.

So that would be 4.56 gears with 25" tires, well it's mainly a street car don't really want to run that deep of a gear.

So would it be better to just run 3.55 gears and shift to where I gets the best time or say treat the 3 speed Auto as a 2 speed?

What I mean is a 2 speed powergilde with a 1st gear of 1.76 and final 1:1 if I times that by 4.56 would overall 8.05 1st and 4.56 final. Not the deepest 1st gear for a 318 but the cuda is lite.

Now I'm not gonna use a powerglide so say I ran a deep 1st and 2nd gears 904 with 2.94 rear gears. I'd get and overall gear ratio of 8.06 in 1st and 4.53 in 2nd/final. And 3rd wouldn't be used at the track so it would be somewhat like if a powerglide had a .65 overdrive gear.

So basically which would be better ?
The 3.55 option obviously is gonna be better out of the hole. But shifting into 3rd gonna idle across the finish line.
But going with the 2 speed idea with the shifting at 6500 and crossing the finish line at 6500 would be a little more dialed in and has the benefit of an overall lower cruising speed.
 
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273 said:
I'm just playing around to see what my options are.

So I got a 65 cuda with a 318 when done I'm hoping it can do between 100-110 in the quarter mile. So let's say it does 105.
I hear you want to be 400 - 500 rpm past peak power so say I want to be 6500 rpm.

So that would be 4.56 gears with 25" tires, well it's mainly a street car don't really want to run that deep of a gear.

So would it be better to just run 3.55 gears and shift to where I gets the best time or say treat the 3 speed Auto as a 2 speed with and overdrive kind of thing ?

What I mean is a 2 speed powergilde with a 1st gear of 1.76 and final 1:1 if I times that by 4.56 would overall 8.05 1st and 4.56 final. Not the deepest 1st gear for a 318 but the cuda is lite.

Now I'm not gonna use a powerglide so say I ran a deep 1st and 2nd gears 904 with 2.94 rear gears. I'd get and overall gear ratio of 8.06 in 1st and 4.53 in 2nd/final. And 3rd wouldn't be used at the track so it would be somewhat like if a powerglide had a .65 overdrive gear.

So basically which would be better ?
The 3.55 option obviously is gonna be better out of the hole. But shifting into 3rd gonna idle across the finish line.
But going with the 2 speed idea with the shifting at 6500 and crossing the finish line at 6500 would be a little more dialed in and has the benefit of an overall lower cruising speed.
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that's what, a 12-13 second car in 1/4? how much power are we talking out of this 318? how much does the car weigh, stock or are your running stripped down and fiberglass?
 
Here's an option. Get an OD tranny or a GVOD and run the 4.56 gears. Problem solved.

How much power out of the 318 currently?

Why such a short tire?

You don't want to be shifting right before the finish line.

Here is another thought. A 3.23 gear with 25" tires is about right for cruise RPM on the street. It would also go through the traps at 103MPH@6500RPM in 2nd gear.
 
dukeboy_318 said:
that's what, a 12-13 second car in 1/4? how much power are we talking out of this 318? how much does the car weigh, stock or are your running stripped down and fiberglass?
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Stock body car, from what I can find they weigh under 3000 lbs. I was just using 6500 as a reference but I might have juggle around with tires and gears if say 6000 is more likely concept is the same.

Trying to keep it very streetable it will be a daily driver for the 8 decent months we get up here.

It just seems the smart set up would to be treated it like a 2 speed overdrive.

From what I see 3.55 x 2.45 x .89 (27" tires) is the average setup which is a 7.74 overall 1st gear ratio. And mine seems a lot smaller with 2.94 gears but x 2.74 (lower 1st) x .96 (25" tires) would be the same overall 7.73.
You shift about 6500 and cross the line about 6500 and your done and cruise home at 2400.

But I'm a first time drag racer so seeing what you guys think ??
 
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roccodart440 said:
Here's an option. Get an OD tranny or a GVOD and run the 4.56 gears. Problem solved.

How much power out of the 318 currently?

Why such a short tire?

You don't want to be shifting right before the finish line.

Here is another thought. A 3.23 gear with 25" tires is about right for cruise RPM on the street. It would also go through the traps at 103MPH@6500RPM in 2nd gear.
Click to expand...

Can't afford overdrive plus don't want to cut up the Cuda to fit one and I already got the tranny with the deeper 1st and 2nd.

With 3.23 gears I get 6900 across the finish line.

The 25" is cause the car will be mainly set up for handling.

It's not gonna be a race car but want to go 6 or so times a year. But I like to have things set right with the least compromises.
 
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273 said:
Stock body car, from what I can find they weigh under 3000 lbs. I was just using 6500 as a reference but I might have juggle around with tires and gears if say 6000 is more likely concept is the same.

Trying to keep it very streetable it will be a daily driver for the 8 decent months we get up here.

It just seems the smart set up would to be treated it like a 2 speed overdrive.

From what I see 3.55 x 2.45 x .89 (27" tires) is the average setup which is a 7.74 overall 1st gear ratio. And mine seems a lot smaller with 2.94 gears but x 2.74 (lower 1st) x .96 (25" tires) would be the same overall 7.73.
You shift about 6500 and cross the line about 6500 and you done and cruise home at 2400.

But I'm a first time drag racer so seeing what you guys think ??
Click to expand...
according to Allpar, a 1965 Barracuda with a 273 (318 is gonna be pretty much the same weight), 3199 pounds. At that weight, to get to 105-110 mph, you're gonna need to crank that 318 up quite a bit or add some spray or boost to it. Doing the math using the formula HP=Weight * (MPH/234) ^ 3, you'll need 330 hp at the tires to pull that trap speed down. That's a pretty warm 318. Not impossible by any means, but a stocker or mild 318 ain't gonna pull it down.
 
dukeboy_318 said:
according to Allpar, a 1965 Barracuda with a 273 (318 is gonna be pretty much the same weight), 3199 pounds. At that weight, to get to 105-110 mph, you're gonna need to crank that 318 up quite a bit or add some spray or boost to it. Doing the math using the formula HP=Weight * (MPH/234) ^ 3, you'll need 330 hp at the tires to pull that trap speed down. That's a pretty warm 318. Not impossible by any means, but a stocker or mild 318 ain't gonna pull it down.
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OK so say I make peak power at 5500 so about 325 to 350 hp and add 50 - 75 hp shot of Nos for a 400 hp engine. So say now I got to shift and cross around 6000 rpm so replace everywhere I said 2.94 gears with 2.76 gears. So end result would be like a powerglide with 4.25 gears.
 
273 said:
OK so say I make peak power at 5500 so about 325 to 350 hp and add 50 - 75 hp shot of Nos for a 400 hp engine. So say now I got to shift and cross around 6000 rpm so replace everywhere I said 2.94 gears with 2.76 gears. So end result would be like a powerglide with 4.25 gears.
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i agree with rocco's sentiment above, shifting right before the finish line isn't gonna help you. Im curious, why are you so dedicated to shifting before the finish line?
 
dukeboy_318 said:
i agree with rocco's sentiment above, shifting right before the finish line isn't gonna help you. Im curious, why are you so dedicated to shifting before the finish line?
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I'm not, I want to use the 904 as a 2 speed only on the track use only first and second.
The deep first and second gear of the 904 with 2.76 rear gears would be exactly like a 2 speed powergilde with 4.25 rear gears with the same overall ratio with 1st and final gears.

So there would be only one shift at say 6000 rpm and it would cross the line in 2nd/final at 6000.

But as a bonus 3rd would act as an overdrive of sorts cause I'd be cruising with 2.76 gears instead of 4.25 like if I had a real powerglide.

I figure this is the best way just wanted some experienced input. Cause other way of saying going with 3.23 I'd have to shift into 3rd at some point. So out of the hole would be good but a dog at the end.
 
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Here is a good calculator for the RPM, gear and tire sizing. Speed/Tire/RPM calculator

You need to know what's up with your engine before making too many more decisions. If it is a street/strip car like people tend to title their cars, including myself, they spend way more time on the street than at the strip. Strip time is won by consistency. Forget the ET, that **** is bragging rights and most people lie or their cars don't work on the street. Most guy make "500hp" and run 10's 11's or 12's. Yeah.. whatever...

Me personally I'd set it up to run the RPM you want on the street. There is a little subjectiveness here but general rule of thumb you want to be in the ball park of 2500RPM at 60mph give or take. Let the 1/4 mile nonsense fall where it may. When in doubt go one step taller than you think you want. I.e. in hindsight 4.56's were perfect on paper. 4.30's would have been perfect in real life. You aren't looking to be competitive, you are looking for a timeslip. I can tell just by reading what you wrote.

And FYI you don't cut anything up to install a GVOD. Well, with exception to your wallet, lol. I'd never own another car without an OD of some sort.
 
roccodart440 said:
I'd never own another car without an OD of some sort.
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Amen. I haven't raced in years but I'm gonna try to make a few passes this year in my street car. I have 3.23 gears and a 27.5" tall rear tire, that's about as steep as I can 'personally' tolerate on the street and highway, around 2600 at 65mph.
I know the 3.23's aren't optimal for the track but the stroked big block will certainly help.
My next car will have a Gearvendors and 3.73 or 3.91 gears.
 
A Gear vender (GVOD) would make my 4.56s worth driving on the street again!
It's a LOT OF MONEY FOR ONE. But simple maintenance and it will out live your 904 many time over. The GVOD will pay for itself many time over.
I do like your 2 speed/3 speed concept:thumbsup:
Just do it, run it, and then build power into the teen as you can afford it. The most fun, affordable time, i have had at at the track was when my car ran low 14s:)
 
Run a taller tire and split the difference with the gear, say a 3.91.
 
What Rusty sez! Fact is, Taller tire gets you a much better footprint at the drag strip.
Or maybe, build a second, much lighter car, for drag race use and leave the street/ road racer as is?
 
sst3193 said:
What Rusty sez! Fact is, Taller tire gets you a much better footprint at the drag strip.
Or maybe, build a second, much lighter car, for drag race use and leave the street/ road racer as is?
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I'm not building a race car it's to be a daily driver but I'd like to go to a few drag and autox races a year. Obviously it's ability to do either well will be hampered by taken street as a preference. If I get bitten by the racing bug I'll probably build a race only car but first I'm focusing on this car.

But I'm not one to just throw in 3.23 or 3.55 and called it a day I believe drivetrain should be designed to work as a whole even at this level.

It seems to be getting lost what I'm asking.

If I was building 327 Chevy with a 2 speed powergilde and 4.25 gears. Which would shift and cross the line at optimal rpm or would 3.23 and a 3 speed be better and try to find compromised shift points?

But using the 904 as a 2 speed it's like I'm getting an OD in 3rd cause I'll be running at 2.76 instead of 4.25 or even 3.23 if I go that way.
 
i get what your thinking and it can work, might not be the path most taking! ive been hypothesizing similer thoughts with a 3 speed od 833 with 4:10 or 3:73, race like a 3 speed topping out 3rds 1 to 1,..and od for livable rpm's cruising home, but i lack the mathematical skills to crunch them numbers...DWB
 
dirty white boy said:
i get what your thinking and it can work, might not be the path most taking! ive been hypothesizing similer thoughts with a 3 speed od 833 with 4:10 or 3:73, race like a 3 speed topping out 3rds 1 to 1,..and od for livable rpm's cruising home, but i lack the mathematical skills to crunch them numbers...DWB
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The problem with the 3 speed OD is the 1st so deep it's hard to go too deep rear gear. If you ran 3.23 with the 3 speed OD and compare the ratios with a regular geared 904 it would be like 4.10 in 1st 3.73 in 2nd and 3rd would obviously be 3.23 plus some thing like 2.45 in OD.
 
Build it for the street, then do things afterwards that won't hurt bottom end. like header 4b dual plane intake and a 600 cfm carb.
When i first bought my E-body i had 2.76 gear in the rear, 318 bone stock up front. took it to the track and got high 18 and 19s et's. Put a sets of 22" tall tires and pull my et down some(yes it look dorking with them little tire out back.) but it work. found a 340 stock and put it in got better. 3.23 poss and got even better. build a warmed over 340, 3.91 poss. 10" slick, Now we're having fun!!!!!
For me that was the tipping point. was running truck tires on the back that were 27" tall to get me at the track' but freeway driving sucked. always in the slow lane to the track.
now with my 408 3500 stall and 4.56 gears.............never leaves the garage unless it's going an a trailer
 
That sure would be nice..........and it's going to happen someday,year,.... century:D
 
I felt the same way about an AlterKation. Then I bought one.. with big ticket items you have to keep stuffing small amounts away and leave it away. Under the bed, in the freezer, a safe, etc.. Then bite the bullet and order.

If the wife is a issue mail the money to them. That's what I did instead of using my CC with Bill.
 
I did 13.92 at 98.**mph, 318, 3.55 gears, 225/70x14 tires, 65 Barracuda, after that run tried to tune it up to go faster......went slower!! Never did any further development on THAT combination.......different 318(sorta) went 12.54 @ 107.61mph, 4.88 gears, M/T 275/60x15 drag radials.

I don't think your idea of using your 904 as a 2 spd is gonna make it..........I tried it once in the 1/8th and hit the rev limiter at 7000 in second
 
Y
JBurch said:
I did 13.92 at 98.**mph, 318, 3.55 gears, 225/70x14 tires, 65 Barracuda, after that run tried to tune it up to go faster......went slower!! Never did any further development on THAT combination.......different 318(sorta) went 12.54 @ 107.61mph, 4.88 gears, M/T 275/60x15 drag radials.

I don't think your idea of using your 904 as a 2 spd is gonna make it..........I tried it once in the 1/8th and hit the rev limiter at 7000 in second
Click to expand...

Yes if he was only racing 1/8 mile it would work pretty well. About 5 years ago I broke the 5.14's I was running and stuck some 3.55's in so I could race the next weekend and I only lost a half a tenth. I crossed the finish line in 2nd and ran 6.39 @ 109 mph. It also gained 1 mph. I also run a 315/60 Drag Radial it is 30 inches tall.
 
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with a 3.55 gear you are not crossing the finish line "at an idle" in drive=more like 5000 at 105 mph. a quick quarter mile is about leaving the line hard-not happening with a 2.76 rear gear! I do not care about how radical you think your first gear ratio is. I have been 1/4 mile drag racing for decades-with 3.21, 4.10, 4.30, and 5.13 rear gears, and driving them on the street. with 2.45, and 2.66 and 3.09 first gears. and 1.0 and .7 high gears. I have driven to the strip 105 miles, ran 12.5, and back with 5.13 gears and 1.0 4th gear. run as much rear gear as possible, and use all 3 trans gears
 
I believe, and will be testing it out this year.......You can make a quicker ET (1/8) with running your engs top rpm in 2 gear then a lower gear ratio that require 3 gear but no where near you top rpm.
I'm mainly doing it so that i don't over revving my eng on a 1/4 mile tracks. But i do most of my racing on 1/8...so we will see.(Loosing my 4.56 for some 3.91s)

This is basicly what 273(op) is trying to do.(I'm Just coming at it from the opposite direction)
You should run it as it sit right now and then start the experiment. You real don't know what its going to run....until you run it. I guarantee your 276 rear end car will be much faster then my 18 sec 2.76 geared car:p
 
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