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700R4+Gear Vendors= What rear gear to use?


ROMO

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So I have a 700r4 trans and jsut installed a gear vendors unit so now its like a close ratio 6-speed auto:) grin its mated to a 385 SBC Stroker! that will be street driven. my question is with the double over drive I will have now, How tall can I go with the rear gear before its too much to drive it around? I was looking at either 4.10 or 4.56! here is the graph they show: Thank you!

 

 

______________700R4/4L60E 4-SPEED AUTOMATIC OVERDRIVE

 

 

 

Axle Ratio___________4.88_____4.56____4.10___3.73___3.42__3.23

_____Trans Ratio____________Final Drive Ratio____________

1st_________3.06____14.93____13.95__12.55__11.41__10.47__9.88

Over________2.39____11.64____10.88__9.79___8.90___8.17___7.71

2nd_________1.63____7.95_____7.43___6.68___6.08___5.57___5.26

Over________1.27____6.20_____5.80___5.21___4.74___4.34___4.10

3rd_________1.00____4.88_____4.56___4.10___3.73___3.42___3.23

Over________0.78____3.81_____3.56___3.20___2.91___2.67___2.52

4th GM O/D__0.70____3.42_____3.19___2.87___2.61___2.39___2.26

Double OD___0.55____2.67_____2.49___2.24___2.04___1.86___1.76

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Actually you will have a close ratio 8 speed... wink

 

What is your convertor stall speed? I think you are looking in the wrong direction...I would say no more than a 3.42 but even more likely a 3.23. Here's why...your tranny already has a steep first and second gear, if you are looking at using the the overdrive between the gears you won't have much time between them to do the shifting if you have a 4.10 or 4.56...the purpose of the splitting will keep you from dropping out of your power band without having to use a steep rear gear.

 

I have a TH400 with a gear vendors overdrive and a 4.11 rear, even with my first gear of only 2.48 I barely have time to shift into 1st over...granted if I hit the button before i launch the car I can let it do it automatically at about 22 mph but even between second and third their isn't much time it is there...with your steeper tranny gears it will be even more difficult and I think unpractable.

 

I'm gonna get 3.42 gears when the time comes so I can use my GV more often.

 

A good tranny cooler with a fan will help if you have a high stall and you are driving around in a final drive of 1.86 or 1.76.

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Oh yes sorry you are correct Bill it would be an 8-speed. Here is the whole story I had the 700R4 way before I even thought about a GV unit but I found such a great deal on the unit that I couldnt pass it up. I have no money for this project any more (for now)so I cant replace the trans like I really want to. So in youre guys opinion what would be the best set up using the parts i have. Im running a 2500 stall and currently a 2.73 gear open rear end. I still havent even driven the car once in the 4 yrs that ive owend it frown But I'm so close now I can smell the exhaust fumes ;0 Thank you.

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What kind of cam do you have in your SBC? I think that would be one consideration. With a 3.42 in double over if you have a 27 inch tall tire at 70 you will be loafing along at less than 1500 RPM. With 4.10s at 70 you will be under 2000.

Just remember if you decide on a 4.10 or 4.56 you drive shaft will really get into some critical speeds. While your motor is turning less than 2000 at 70, the drive shaft is at 3600. 4.56s would put the shaft over 4000 at 70 mph. Make sure you have a good shaft. Like Bill mentioned, a good trans cooler is important!

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Just read your last post, I would put the gear vendors under the bench until you can afford the gears and the 3 or 4 series carrier. Enjoy the car for a while.

 

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just to give you some frame of reference... I have a 700r4 with 3.55:1 gears, and 27" tall rear tires (255/60-15) and I run 2250 rpm in 4th gear with the converter clutch engaged.

 

i wouldn't want to go much lower then that because trying to use o.d at say 55mph tends to push the rev's down to a point where the engine struggles...

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This is interesting. I think that if your plan is to be able to use all 8 gears in a quarter mile, it's not going to happen. You would need 4.88 or even shorter gears, and it would end up like driving a Jeep in the quarter mile starting out with the transfer case in low range.

 

Adding an overdrive makes a 3.70 or 4.10 gear liveable. It puts the rpms at cruise pretty close to what they were and gives you the extra oomph at lower speeds. Adding another overdrive on top of that will bring down your cruise rpms a bunch. You will need to do some math to find out what your cruise rpms will really be, and decide if the engine even likes to run at that speed. Some of the newer injected engines are happy at 2000 rpm, but our carbureted engines don't do well going that slow...and if you have an aftermarket cam, running the engine slow can be the worst thing for economy.

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Ok this is the cam I will be using.

 

:)Hydraulic roller, lopey idle. Great street machine cam! Likes upgraded intake carburetor and exhaust. Needs 9.5:1 or better compression and 2500 RPM stall speed converter and a 3.42 or better rear gear ratio.

 

 

Advertised Duration (Int/Exh): 282/290

Duration @ .050 (Int/Exh): 231/239

Gross Valve Lift (Int/Exh): .535/.550

LSA/ICL: 110/106

Valve Lash (Int/Exh): Hyd/Hyd

RPM Range: 1600-6200

Part # 60112

 

Part Number: 60112

 

And it is carbureted. It has a ProSystems carb 4150

 

I will have the money for the rear end but not for both the rear end and a new trans. Thats why I want to get it right the first time. What would you guys do. Its looking more and more like I should be going to something like a 3.42-3.73! Yes/No??? crazy

 

 

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that cam is NOT going to like running at low rpm.

 

my cam is only 214/224 @ .050 and it doesn't like pulling below 2000 rpm

 

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Ok...wow. I ran the numbers.

First, your camshaft is going to be in it's sweet spot between 2500 to 3000 rpm. You will want your cruise rpm to be in that range. If you want to have a slower cruise rpm, you should go smaller on the cam.

 

Here are the numbers I ran through this on-line calculator gear calculator

 

:edit...I had bad info here.

 

 

I really think the best plan is to choose one overdrive or the other, but don't use both.

 

 

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Wow those numbers really suck! How about this if I just dont engage the last OD on the GV unit, I just use the 700R4 OD? Changing my cam is really not an option at this time. Should I just get rid of either the 700 or the GV unit?

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Mark, I think you need to revisit your math. I think the double overdrive would work out to .55.

With a 4.88 and a 27 inch tall tire I get 2004 rpm at 60 mph

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Here's some quick calculations I came up with using a 27" tire

 

3.73 gear

6000 RPM 233.96 MPH

5500 RPM 214.46 MPH

5000 RPM 194.96 MPH

4500 RPM 175.47 MPH

4000 RPM 155.97 MPH

3500 RPM 136.47 MPH

3000 RPM 116.98 MPH

2500 RPM 97.48 MPH

2000 RPM 77.99 MPH

1500 RPM 58.49 MPH

 

3.42 gear

6000 RPM 259.11 MPH

5500 RPM 237.52 MPH

5000 RPM 215.93 MPH

4500 RPM 194.33 MPH

4000 RPM 172.74 MPH

3500 RPM 151.15 MPH

3000 RPM 129.56 MPH

2500 RPM 107.96 MPH

2000 RPM 86.37 MPH

1500 RPM 64.78 MPH

 

 

Obviously you would not use the double overdrive until you were cruising at higher speeds on the highway.

 

 

 

 

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Mark, I think you need to revisit your math. I think the double overdrive would work out to .55.

With a 4.88 and a 27 inch tall tire I get 2004 rpm at 60 mph

I must of used the same calculations as you because when I punched in 4.88 gears that is exactly what I got.

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I stand corrected. I grabbed the wrong number from his chart.

The correct number is .55 for double OD output.

 

With those numbers I agree:

4.88 gear is 2000 rpm @ 60

5.38 gear is 2200 rpm @ 60

5.86 gear is 2500 rpm @ 60, and shaft speed would be 4500.

 

With the 5.86, if you take it up to 100 mph, driveshaft rpm is 7500.

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use one or the other pretty much.

 

What Bill said. With a 700 & GV I would be curious to

see what a 3:08 would give you.

 

I retract that statement because it would be ridiculously low

rpm's at cruising speed.

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What trans would benefit me? I kinda dont want to get rid of the GV.I think I would rather change my trans when the time presents itself! What would be the ideal all around set-up for a car that will be driven alot?

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The strongest setup would be a TH400 with the gear vendors.

2nd would be a TH350 with the gear vendors.

The gear vendors website has some good info. They consider the 700r4/480LE trans to be less sturdy than even the TH350.

They do push the advantage of using the GV unit for gear splitting with a 4-speed auto trans, because the giant steps the 700R4 takes from one gear to the next is the reason they lack strength.

They recommend using the GV to split the gears, and then cruise using the trans OD, with the GV unit turned off.

 

I don't know about whether the GV unit will shift on its' own...I think you have to push a button to turn it on & off. That might be kinda tricky to try to engage/disengage it between the normal trans shifts, especially if you are going thru the gears quickly. It would make sense if you were towing a heavy trailer up a grade though...

I would prefer to have the trans do all its normal shifting through the gears, and then engage the OD as a last step if needed. This is how it would work with the TH350/400.

 

here is a link to the GV site: GV LINKY

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  • 2 weeks later...

Just started installing the GV unit! What a pain its a super tight fit the worst part is the biggest part of the unit is right where the floor support is at! Alot of cutting and hammer swinging!

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i had to make room for my 700r4 too..

 

note.. the trans fits w/o this modification, but you can't remove the govenor from the side of the case w/o dropping the crossmember...

 

before

 

The hole I cut

 

The final product

 

side note: don't use flux core welder for sheet metal...

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I assume your tranny is longer than a TH400 as I didn't have any floor support in the way, just a the soft smooth tranny tunnel metal that I hammered away on.

 

Make sure you spend the time getting it up and in there to achieve the proper angle you had before...you don't want the GV unit angling down and messing up the driveshaft angle... wink

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