8 3/4 Sure Grip ratio change

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brodphish

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I have a resto-modded 67 Barracuda with a built small block in it. The car currently has a built 727 with a 8 3/4 Sure-Grip with 3.23 gears. I'd like to do a 4-speed swap but that's out of question as she loves the car as it is. So I am thinking about a lower gear ratio (she will never know Ha Ha).

The car is used for local car shows and going out to dinner, etc. A few shows might be 30 miles away, most are 10 or so here in Northern WI. What would be a good swap for harder acceleration and keeping the small block revving?
 
I was thinking 4.10 but that seems like too much based on the responses? Also any recommendations on good gear sets?

Thanks
 
I guess what I am really asking - would the 4.10 ears compromise driveabiliity the way use the car? I've never driven anything with that much gear in it.
 
-- 3.55 is plenty --
-- 3.55 is a good street gear, and available as a OEM Mopar gear. (salvage yards etc.) -- 3.73s are available , for Mopars, in The Aftermarket. As a OEM gear, they are GM.
 
personally I like 3.91 put them in most of my mopars, 3.73 is a great gear better highway and still fun around town. 3.55 is to close to 3.23
 
jokes aside i agree with 3.91s, a lot of punch but still reasonable, especially if you run a 28 inch tall tire, i think if you go much smaller than 3.73s its not gonna be noticeable, in other words not really worth the time and money
 
In my old 69 Charger R/T SE I ran 3.54 gears in a Dana behind a 440 and 18 spline 4spd. trans with 275 15 tires and at 60mph I could nail it and break my tires loose. I would have no problems running 3.55's in my small block Barracuda at all and that's what I am going to run soon as I get the 7 1/4 out lol
 
3.91s chief! I have 3.55 in my 8 1/4 & seem ok. Have another fresh 8 1/4 ready to go in! Can't wait!:steering:
 
3.91s chief! I have 3.55 in my 8 1/4 & seem ok. Have another fresh 8 1/4 ready to go in! Can't wait!:steering:
I bought a unfinished 68 barracuda, installed the 8 3/4 rear end which came with the purchase, I switched the 3.91 chunk out for a 3.23 before I installed it, no bottom end with 3.23 gears, a 340 does not have that much torque to begin with, big mistake.
 
Great point 68. I have a 417 stroker it is pretty tourqey. However it shifts around 3400 rpm or so even under full throttle. I want to make sure:

1. the 3.91 gears are compatible with a 417 stroker and

2. the 3.91 will hold revs longer into the upper end of the rev range.

NOt sure if it's relevant but I have a 2800 RPM stall converter. If the responses to the above are are affirmative the I'll go with the 3.91.
 
Great point 68. I have a 417 stroker it is pretty tourqey. However it shifts around 3400 rpm or so even under full throttle. I want to make sure:

1. the 3.91 gears are compatible with a 417 stroker and

2. the 3.91 will hold revs longer into the upper end of the rev range.

NOt sure if it's relevant but I have a 2800 RPM stall converter. If the responses to the above are are affirmative the I'll go with the 3.91.
I think you are spot on, I have a 2500 stall, lesson learned
 
Great point 68. I have a 417 stroker it is pretty tourqey. However it shifts around 3400 rpm or so even under full throttle. I want to make sure:

1. the 3.91 gears are compatible with a 417 stroker and

2. the 3.91 will hold revs longer into the upper end of the rev range.

NOt sure if it's relevant but I have a 2800 RPM stall converter. If the responses to the above are are affirmative the I'll go with the 3.91.
Rear gear ratio has nothing to do with your WOT up shift speed, your going about this all wrong, fix your shift issue FIRST
 
Rear gear ratio has nothing to do with your WOT up shift speed, your going about this all wrong, fix your shift issue FIRST

I second this.

All changing the rear gear will do is change what MPH you change gear at. Not what RPM. 727's came from the factory setup for that car. The governor/linkage/line pressure in them was setup to change gears at certain MPH. Here is the factory chart:
upload_2017-3-12_20-55-53.png


Obviously with some cars having a higher or lower gear set, they would need to change at different RPM's in order to change at the same MPH. You probably just have a transmission that was setup with a high gearset (2.71 or something) so it shifted at LOWER RPM which was HIGHER MPH than you have now. If you need to up your full throttle shift point. Then you need to:

Check line pressure
Check shift linkage/kickdown linkage/throttle linkage
Change governor

Low line pressure or incorrectly set linkage can cause the transmission to "short shift" at full throttle. So make sure those are good first. If that is all set properly. Then you need to change out the governor. Check - Home - A&A Transmissions. They sell governors for 727s that will help you pick what it shifts at. BUT please MAKE SURE that line pressure/linkage is set properly before. Low line pressure is a main reason for low RPM shifts in 727's. And it will COOK your transmission if you aren't careful. Here's an article that goes a little more into detail. Increasing Shift Speeds On The 727 Torqueflite - Mopar Muscle Magazine

And no. Changing the torque converter won't increase WOT shift RPM. A shift kit, or new valve body might, but only because they are increasing the line pressure.
 
That HR article is awesome - the solution lies in there. I'll sort that out first and then worry about the gearing. It does get good rubber and / or accelerate well with the 3.23 gears
 
Sounds like your happy with what you got?
Unless you do any type of street racing, Save on gas,and engine rev.LOL
 
I was thinking 4.10 but that seems like too much based on the responses? Also any recommendations on good gear sets?

Thanks

I have 4.10's right now and I have to spin it up to 3,500 RPM just to keep up with traffic. I have about a 28" tire in the rear.
 
wait a minute .... You have a 417 stroker... and its not snappy enough ???
... if you go to 3.91 or 4.10 you will notice it and she will freak because the engine is racing ! and unless you are racing it I dont see much advantage for you. I would tune engine and fix shift point issue 1st.

30 miles is a LOOOONG way to drive with 4.10s...lol especially if you are not used to it !
 
wait a minute .... You have a 417 stroker... and its not snappy enough ???
... if you go to 3.91 or 4.10 you will notice it and she will freak because the engine is racing ! and unless you are racing it I dont see much advantage for you. I would tune engine and fix shift point issue 1st.

30 miles is a LOOOONG way to drive with 4.10s...lol especially if you are not used to it !

I've done it. It sucks! LOL
 
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