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Torque converter question


ChrisM

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Hey everyone, it’s been a while since I’ve been on, I’ve been looking through a lot of treads in regards to converter size vs set up, but haven’t exactly come across my answer, so my question is what size stall SHOULD a set up like mine have. 
spec’s : 396 (0.30 over) 750cfm Holley double pumper edlebrok single plain, TH400 I believe right now has 2000-2200 stall, 12 bolt rear with 273 posi. Cam in the engine is comp cams xtreme energy duration 268/274 lift 553/568. 
Background info, when I drive the car it’s great, but when I get on it doesn’t feel like a big block, also from a dead stop, if you get all over it, it just bogs down, so times stalls, or I have to let off, ease into it and then mash it. I wondering if I don’t have enough stall, any ideas? 

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Definitely not enough stall if you have 2.73 gears. I'd go somewhere around 2700-3000 maybe higher. It could also be that double pump mechanical secondary carb. Those things like a steep gear and high stall or 4 speed. You might consider swapping to a vacuum secondary carb.

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Stall speed is fine. The issue you are describing is the gearing.  I would change the gearing to at least a 3.31 and if no posi, I would add a Detroit truetrac. 

I would also change the single plane intake for an Edelbrock RPM air gap. The single plane makes top end power as opposed to low end torque. The RPM is the best of both worlds for a street/ occasional strip car. I would also look at the carb adjustments. 

Start there, and then, and only then I would revisit the torque converter. 

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Mc1of80, would you say to at least start will changing the gearing before anything else? In the future Iam thinking of possibly going LS/4l80 (or possible 6spd) but that is far down the road, 3.31’s would still hold that? 

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What do you mean by will the 3.31s hold that? If you are definitely going 4spd overdrive or 6 speed, I would go with 3.73s. With the overdrive you have the best of both worlds. Highway capability and drag racing also. 

Definitely go with gearing first. You won't be sorry. It will make it a different car. 

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Sorry yes I meant would the 3.31s be a good fit for future ls swap, but I think I’ll look into the 3.73s 

appriciate the info, thank you 

 

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3 hours ago, ChrisM said:

Mc1of80, would you say to at least start will changing the gearing before anything else? In the future Iam thinking of possibly going LS/4l80 (or possible 6spd) but that is far down the road, 3.31’s would still hold that? 

2.73's are highway gears. Typically with a cam like that, you want a loose converter and a numerically higher gear ratio. The cam card will give you an idea of what works well. I have 4.10's and 3200 stall with a similar cam. It spins the tires just fine but forget about the highway. A good compromise would be a 3.73. It's aggressive, but not so aggressive you can't drive on the highway.   

Mc1of80 is right on the money, swap your gears first. It will make a world of difference.

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I'll agree with Tom, first choice would be gears. You should see an immediate difference. I think you have a 70 MC so if you do have a posi its probably a series 2 unit. Just saying when you order new ring and pinion. Also as Tom said, double check your carb. I do think your stall is a little low, but since I don't do highway driving and your future plans said I'll leave that discussion to the more experienced. 

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Thanks everyone for the reply’s and information! Yes my plan is to one day ls swap the car, that is one day haha. Yes I do highway cruise for meets etc, but even now I never really go over 100kms (roughly 60mph) so with the info you guys have given, sounds like the 3.73’s would be a gear that could really handle anything! 
 

so now my next question, I know there was I believe 3 different 12 bolts made, how would I go about ordering the right ring and pinion, and how would I know if the carrier I have would accept a 3.73 ring? 
 

Thank you everyone! 

 

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Order 3.73 12 bolt CAR gears from the manufacturer of your choice. I recommend the Detroit truetrac posi unit, for 30 spline axles. You may want to upgrade the axles while you are there to a little stronger units. 

Go on eBay, I believe quick time performance sells the posi unit, gears and bearings as a kit. I purchased it a few years ago and have recommended it on this site many times. One stop shopping. 

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Last year I went from 3.31s to 3.73s and a true trac at the recommendation of 1of80 and I definitely drive it over 60 often, it woke the car up quite a bit and mines just a near stock 402. The deeper gearing makes the car much more responsive everywhere in the rpm range, and with 275/60/15s on the back 60 Is only like 25-2600 so still manageable for mileage, when im just cruising and not making pulls I can eek out a little over 12.3 mpg. 

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My 350 bored 20 over and a roller cam and rockers has a 700r4 with 3:73 gears and I am quite happy with the performance. 2700 RPM at 75 MPH down the highway and if I hammer it it will bark the tires when it hits second

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Thank you everyone for the reply’s and knowledge! 
I am going to look into changing these gears, hopefully in the next few weeks!! 
 

again thank you!! 

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1 minute ago, Leghome said:

My 350 bored 20 over and a roller cam and rockers has a 700r4 with 3:73 gears and I am quite happy with the performance. 2700 RPM at 75 MPH down the highway and if I hammer it it will bark the tires when it hits second

Awesome!! I just want more power out of this thing, spent a lot of time building the engine/trans and it just doesn’t feel like a big block power car!! 

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I don’t know what you’re used to driving but there’s a lot of weight to these cars. For street use don’t expect funny car type of speed. Although you’re on the right path to get the most out of your car. There’s always room for improvement. 

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41 minutes ago, Dtret said:

I don’t know what you’re used to driving but there’s a lot of weight to these cars. For street use don’t expect funny car type of speed. Although you’re on the right path to get the most out of your car. There’s always room for improvement. 

The total lack of power in this car just bothers me, I know there is so much more it can give, and tons of fun to be had, just trying to do exactly what you said and get the most out of what I’ve done so far!!! 

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Once you get these things together you have to, sorry to say, science these things out. A single plane intake and highway friendly gears do not make good friends. Especially in a heavy car. You want to make torque to move the mass. 

Horsepower is how fast you hit the wall, Torque is how far you push it. 🤔

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10 hours ago, ChrisM said:

Thanks everyone for the reply’s and information! Yes my plan is to one day ls swap the car, that is one day haha. Yes I do highway cruise for meets etc, but even now I never really go over 100kms (roughly 60mph) so with the info you guys have given, sounds like the 3.73’s would be a gear that could really handle anything! 
 

so now my next question, I know there was I believe 3 different 12 bolts made, how would I go about ordering the right ring and pinion, and how would I know if the carrier I have would accept a 3.73 ring? 
 

Thank you everyone! 

 

Type 1 carrier is good to 2.54 gear ratio. Type 2 is 2.73 to 3.08, Type 3 is 3.24 to 3.73, and Type 4 is everything above 3.80 to about 5.00..... 

The differential you're looking for, (casing) is unique to '70-'72 Chevelles, El Caminos, and Montes... Unless you find a "BOP" differential, which is for Buick, Olds, and Pontiac "A/G" bodies. 

Hope that helps. :)

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I know it seems like we enjoy spending your money, well we do lol. And I'll agree with Tom, while your at it do the axels. I went with 355 gears because that's what my buddy had "in stock", and this how I learned about the series 2 vs others, my buddy also has a series 3 "in stock" for those gears. I went with Strange axels. As you can tell lots of experience here for your choices. 

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3 series Detroit truetrac, 3.31 gears and strange street axles. Same set up in "Big Red" and "Barn Find". 

IMG_20200712_130524.jpg

IMG_20200719_125355.jpg

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Awesome, love the pictures!!! I appreciate all info!! This car is a great driver, I know the intake isn’t the best for what Iam looking for, but I have to say it has done a great job this far. I know the rear gears are an issue, and it’s something that needs to be addressed for sure, I think I’ll start with rebuilding that, and then go further, you never know, maybe this will keep me away from go ls!!! 

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The LS makes power but they are UGLY!!!! Lol. No, seriously! UGLY!!!  And now a days, they are like belly buttons..... Everyone has one! Lol

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12 minutes ago, MC1of80 said:

The LS makes power but they are UGLY!!!! Lol. No, seriously! UGLY!!!  And now a days, they are like belly buttons..... Everyone has one! Lol

Lol I hear that, honestly 

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