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Discussion Starter #1
I am considering two things:

1. Get a 4.11 posi or mini spool third member to install prior to going drag racing or...

2. Switch my 3.50 gears to 3.73 or 3.89 gears permanently in my third member and not bother switching third members prior to drag racing.

I had 4.11s in a 66 GTA Fairlane years ago and it was unpleasant driving around town especially on the freeway spinning a big block that high while only doing 60 mph. I suppose there isn't much of a difference between 3.89s and 4.11s. Maybe settling for 3.73 permanently wouldn't be too bad. Needless to say, these small blocks like to rev!
 

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I've got 4.11s and with my stroker and wishing I had 3.73s for freeway crusing. I'm turning just over 2500 RPM at 75 which isn't that bad with OD, but I'd rather be using my torque and cruise around 2100-2200 RPM instead.

There isn't that much difference between 3.50s and 3.73, so I don't know if I'd want to go through the effort to swap over. You'd see a very noticable change with the 3.89s however. Might be a good compromise gear for you. Those online calculators are helpful, type in your gear sets and see what the RPM difference is between them.
 

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If you go racing frequently then it would be worth it to switch to the 3.73 as a compromise for street driving so you're not always swapping out the center, but if it's only a once in a while thing then I would leave the street gears in it and have a spare center chunk set up for racing that you can switch for the street gears when needed. Then again, you can always swap out the C4 for a built AOD, then you can put 4.11's in the rear permantly and still an effective highway gear ratio of 2.79 ::
 

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Hey... I really loved your article on the 5-speed swap 2bav8. This will help me a lot in the future (TKO swap). With this 408w stroker and 4.11's, I would still like to cruise. So I think the TKO is right for me.

Anyone know how much different it is to install in a 68?
Still gotta do some research.
 

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2. Switch my 3.50 gears to 3.73 or 3.89 gears permanently in my third member and not bother switching third members prior to drag racing.
I've had both 3.50s and 3.73s, and could not tell a difference between them. I vote for 3.89s ::

Paul
 

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I find the best way to determine your 'acceptable' rpm limits is to put your tire/rear combo on a graph like the one here and determine what RPM range you're looking for.
http://www.smokemup.com/auto_math/mph_range2.php
Choose your transmission ratios, rearend gear ratio, and tire diameter and it will plot every RPM in every gear for you. If you want to be under 2000RPM at 70MPH you won't be able to finish 4th gear at the 1/4mi drag strip, it's a trade off. When I first built my engine I regularly put it in 5th driving around the streets and freeway and with my high 2.79 gears it would putput around in 5th under 2k and get outstanding mileage, then the 3.50's made a HUGE noticable difference in acceleration but my cruise RPM's also went up, now with 4.11's I will be runnin near 3000RPM to keep up with freeway traffic but I will be able to redline 4th gear 1:1 through the traps in the 1/4mi. Changing 3rd members is a PITA, if you really want to have two and be able to change it then you might want to look into a floater housing or DANA60 rearend with quickchange cover. I vote for a 4.11 street geared posi 3rd member, and 4.56 geared minispool 3rd member for the strip.
 

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Discussion Starter #7
Thanks...i'll check out the calculator. Its pretty straightforward to detemine rpm differences. Going from 3.50s to 3.89s is going to be about an 11% difference. Its never as good though as hearing from someone who has first hand experience and actually has 3.73s or 3.89s in their car. Anyone out there have this setup and care to comment?
 

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I believe you will see a difference with either gear set although obviously the 3.89's will be more dramatic. I am running 3.89's in my cougar right now and I had 3.73's before. Although I am now going to go back the other way after I swap out the cam or motor. I will probably go with a 3.25 or 3.50 gear. Right now I am running a dart sr headed 351w with a large cam and an AOD. The car would lug from being at the bottom of the torque curve with the 3.73's when I drove in the 55-60 mph range. The 3.89's solved that problem but this combo would prefer 4.11's and a looser convertor.
John
wvcat
 

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You didn;t ask but here's what I'd do....

Build a 4:30 for "fun"

Build another punkin',... a 3:50 for when you're not havin' fun!

C'mon guys, 4000 rpm is no big deal on a properly built and balanced smallblock! You have a whole nother' 2500 rpm top go before you have to shift! ::

I cruise around with a 4:30 gear all the time! :: (although I wouldn't drive it Florida!) ::
 

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I went from 3.50's to 3.70's in my 9 inch behind the 427. I cant tell much if any difference. It does fine on the highway up to about 75 then its buzzy.

If I were you, I'd go 3.89 in a small block, they dont nearly sound as buzzy as your old FE. They like the RPM
 

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C'mon guys, 4000 rpm is no big deal on a properly built and balanced smallblock!
It is when you're cruisin 400 miles to the Knotts Show in CA and paying $2.50 a gallon it is!

Crusing at 2600 RPM in 5th with a 347 is like crusin in 4th gear on city streets, so much torque and no legal place to use it, lol
I've had enough tickets to last me a life time ::
 

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I've got 4.11 gears in my 67 GT350 (215/65-15 tires) and 3.89 gears in my 73 vert (255/60-15 tires with a C6 auto and loose converter).

The GT350 is screaming (about 3500) at 70 mph. I would not want to drive it very far at that RPM level. The vert has bigger tires and 5% less rear gear, but because of the loose converter it is turning about 3300 at 70.

I personally consider 3.50 to be about the limit for freeway driving if you have a 1:1 high gear. Anything higher and you're turning too many RPMs.

Something you might consider is getting radically shorter tires for drag racing (maybe go to a 14" wheel with a 40 or 45 series tire). You can easily get a 10% difference in effective gear ratio by changing tires. I've considered bolting light truck tires on the back of the GT350 for road trips. They would just fit into the wheel wells and would lower my RPMs by about 10%.
 

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low pro tires make a HUGE difference in your overall cruising rpm's. i have 15" rims with 50 series tires along with my 3.55 gears. the car spins 3000 rpm's at around 50 mph or so. on the freeway, trying to keep up with traffic around here, FORGET IT, its about 4000 RPM's. its a complete nightmare, and i dont like at all driving around like that for a long period of time
 

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4.11 has more pinion surface contact with the ring gear. I feel it's stronger. Roughly 2.5 touching at one time. The 3.89 only has 1.5. But they both work.
 
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