Gearing and shifting 4 speed at the track

-
68Dart500

68Dart500

Well-Known Member
Joined
Oct 24, 2017
Messages
364
Reaction score
273
Location
USA
Hey everyone,

I'm about to swap gears in my 68 Dart from 3.55 to either 3.91 or 4.10. I'm trying to decide which I should go with. This is going to be a 50/50 street/track car with minimal highway driving so I'm not concerned about my highway cruising rpm.

Engine is a 408 stroker
Tires are 28 inches tall.
Trans is an A833 with 2.47 1st, 1.77 2nd, 1.34 3rd, and 1:1 4th.
Max rpm I'm looking to spin the engine to is 6200

My two questions, what gearing and should I be planning to shift into 4th or leave it on the rev limiter in 3rd (I feel like that won't be a good idea but I've heard people say that so I wanted to ask).
 
Uh, with those big old tall 28" tires out back even 4.10's aren't bad at all. I mean at 3,500 rpm you're doing 72 mph. That's only a couple mph lower than what I was doing with 3.55's and 26" tall tires and I'm daily driving on a freeway.

You can run 4.30's, pull 67 mph @ 3,500 in 4th and still hit 120 mph @ 6,200.

Here's a decent calculator, it even has an 833 option with pretty close gearing to what you've got.
Gear Ratio Calculator

As far as whether or not to shift into 4th, we'd have to know what speed you're trapping at. If it's much above 90 you're gonna have to hit 4th if you go 4.10's or better.
 
I had 4.30s in my 65 Valiant with 28 11.50 15 ET Streets on the back and cruised 55 on the interstate at right around 2800 "or so". Wasn't bad at all. So I would certainly at least go with the 4.10s in your situation.
 
If the primary goal of the gear swap is quicker ET’s........ you’ll pretty much wanna run as much gear as you can stand.

What speed do you anticipate being able to run in the 1/4?
 
Last edited:
A 2.47 low and 4.10 only gives you a 10.127 first gear. That is awful tall.

A 4.10 gear with a 28 inch tall tire at 6200 through the lights is 126 MPH. 126 MPH in a 3400 pound car is about a 10.60 ET.

Can your car go that fast.
 
At speed, a 28" inch tire will usually grow to 29 inches, depending on the brand and type. I think 4.30's are probably going to be right on par with what a 408 stroker running to 6200 would work best with. If it keeps pulling to 6500 rpm or higher, as in going faster by raising the shift point then I would say 4.56. But at that point the emphasis becomes much more strip oriented and less street. If it stops pulling at 6200, 4.30 gears are all it would ever need.
 
Garrett Ellison said:
At speed, a 28" inch tire will usually grow to 29 inches, depending on the brand and type. I think 4.30's are probably going to be right on par with what a 408 stroker running to 6200 would work best with. If it keeps pulling to 6500 rpm or higher, as in going faster by raising the shift point then I would say 4.56. But at that point the emphasis becomes much more strip oriented and less street. If it stops pulling at 6200, 4.30 gears are all it would ever need.
Click to expand...



I agree. It would damn sure help his low gear. If his tire didn't grow, with a 4.30 at 6200 he'd still be about 120 MPH, and at 3400 pounds (I'm pulling that out of my hat) that's still an 11 flat'ish pass. Certainly doable if the engine is even close.

My car is 3400ish depending on my weight and I have a 14.09 first gear and that is almost not enough. I have to compromise on clutch tuning to keep from driving through the clutch.
 
Unfortunately...... if the car is driven in a manner that would yield the best ET’s...... there’s going to be a bunch of broken parts.

If it’s driven so you don’t break it, the ET is going to take a hit.
 
68Dart500 said:
Hey everyone,

I'm about to swap gears in my 68 Dart from 3.55 to either 3.91 or 4.10. I'm trying to decide which I should go with. This is going to be a 50/50 street/track car with minimal highway driving so I'm not concerned about my highway cruising rpm.

Engine is a 408 stroker
Tires are 28 inches tall.
Trans is an A833 with 2.47 1st, 1.77 2nd, 1.34 3rd, and 1:1 4th.
Max rpm I'm looking to spin the engine to is 6200

My two questions, what gearing and should I be planning to shift into 4th or leave it on the rev limiter in 3rd (I feel like that won't be a good idea but I've heard people say that so I wanted to ask).
Click to expand...
I have the same combination and drive on the street and drag race and just went from 4: 10's to 3: 54's.
I'd like to know your cam specs??
 
With the stroker I didn't see a major difference in E.T. between the two gears. I did feel a major difference in driveability. Although I found that as well with a cam change. The stroker doesn't need those 4: 10 gears for around town whatsoever.
I usually set my shift light to go off at 58 to 62 but it also depends on where the other person is. If it's a Ford in the other lane pulling on me f that damn blue light!
At that point I depend on the rev limiter to do its job... At 72...pop.pop.pop... SHIFT!!
 
j par said:
With the stroker I didn't see a major difference in E.T. between the two gears. I did feel a major difference in driveability. Although I found that as well with a cam change. The stroker doesn't need those 4: 10 gears for around town whatsoever.
I usually set my shift light to go off at 58 to 62 but it also depends on where the other person is. If it's a Ford in the other lane pulling on me f that damn blue light!
At that point I depend on the rev limiter to do its job... At 72...pop.pop.pop... SHIFT!!
Click to expand...


What about MPH when you went to the taller gears? Did it go up or down? Surely you had to cross at a much lower RPM with the 3.54 gear.
 
The one and only time I made it last year it was trapping 110-111. It was my first time with the car after finishing the build and first time drag racing a rwd car. I was foolishly short shifting it at 5400 rpm thinking it was better to keep it in the peak hp band... I realize now after calculating torque tables with my dyno sheet it's better to shift st 6200 and not short shift. I also was blowing the tires off it getting 1.9 to 2.0 60 foot times because i wasn't heating up my Mickey thompsons enough.

My cam is a 248@ 050. 565/578 lift with 108lsa. Timing is 17 initial and 39 total (need to swap the bushing in my msd distributor so it only goes to 37 total).
 
Bottom line I didn't mind giving up a very small amount of et for a lot of driveability...
 
j par said:
Bottom line I didn't mind giving up a very small amount of et for a lot of driveability...
Click to expand...
I agree. IF you had only changed the gear, you'd saw a small difference with your set up. But you did a massive change to the entire car.

I did a swap with a mild 360 I went from 4.30's down to 3.91's. My E.T. and MPH stayed exactly the same.
 
318willrun said:
I agree. IF you had only changed the gear, you'd saw a small difference with your set up. But you did a massive change to the entire car.

I did a swap with a mild 360 I went from 4.30's down to 3.91's. My E.T. and MPH stayed exactly the same.
Click to expand...


Then the RPM at crossing went down and you had too much gear to begin with. It's a math calculation. Stroke length has nothing to do with it. It's RPM, tire diameter and gear ratio.
 
318willrun said:
I agree. IF you had only changed the gear, you'd saw a small difference with your set up. But you did a massive change to the entire car.

I did a swap with a mild 360 I went from 4.30's down to 3.91's. My E.T. and MPH stayed exactly the same.
Click to expand...
My old cam was nowhere near a street cam. The 4.10's helped on the street with the old cam. On the new grind we reeled in the duration and got rid of a little under used lift.
The funny part here is the op's cam is right in the middle of where I was and where I'm at now LOL. I'm very curious how its manners are on the street with the 3.55's now? Should I go back the other way with my cam? LOL....
 
j par said:
My old cam was nowhere near a street cam. The 4.10's helped on the street with the old cam. On the new grind we reeled in the duration and got rid of a little under used lift.
The funny part here is the op's cam is right in the middle of where I was and where I'm at now LOL. I'm very curious how its manners are on the street with the 3.55's now? Should I go back the other way with my cam? LOL....
Click to expand...


Yes. Always the bigger cam. Always. Don't let Kenny convince you that other cam was too big. The engine was just to small. Get a longer crank.
 
fishmens67 said:
I think you are backtracking, your new Trickflow heads are gonna want the old cam, gear and bigger tire. lol
Click to expand...
Well I don't regret the duration I had on my last cam I'm not looking forward to going back to it and staying on the street. I'd probably end up looking at more lift if I had the four grand to put the heads on and new headers and the new cam... I'm positive that's not where I would spend four Grand right now though..
 
Ok, now garbage is starting fall out of the truck ….. LOL!
You HAVE to get the combo to work for YOUR particular project!!!!
  • Yes, cams can be too big.
  • Yes, you can have too much gear
  • Yes, you can have too much converter..
  • etc, etc, etc.
If I installed a 260@050 cam with .557 lift in either of my Duster's now, they would both slow up. I'd have to "match" all the components around the cam, which would include alot more gear, alot more converter, should have better heads and better compression. And then I'd have the exact car I would hate to drive on the street.
 
yellow rose said:
Then the RPM at crossing went down and you had too much gear to begin with. It's a math calculation. Stroke length has nothing to do with it. It's RPM, tire diameter and gear ratio.
Click to expand...
I shifted that 360 at 5700 rpms, and I didn't reach 5700 rpms with the 3.91's crossing the lines.
Here comes the disagrees, but sometimes you have to let the torque "push you".
 
318willrun said:
I shifted that 360 at 5700 rpms, and I didn't reach 5700 rpms with the 3.91's crossing the lines.
Here comes the disagrees, but sometimes you have to let the torque "push you".
Click to expand...
That's the Stroker motor there's a lot of push LOL can you imagine the gear that it wouldn't roast the tires with a 4-speed? For a car that sees a bit of street/highway action the 3.54's have been great!!
Easley Drive the freeway 20-30 miles to the Dragstrip and take passes that are easily Within a second of full Kill trailer car... Load up the chairs and coolers and drive back home...
 
So to summarize it sounds like people are saying put as high (numerically) of a gear as I can tolerate or did I misunderstand?
 
You must log in or register to reply here.
-

Back
Top