Selection of Torque Converter and Rear Gears for Hot 340

[340inabbody]

I am curious as to what people are using and recommending. I have a hot 340 high rise intake, high lift cam and high compression engine. I don't have the build information on the motor unfortunately.

So if you are running a similar engine what gears are you using and what torque/stall converter?

 

[Garrett Ellison]

What is it going into and what is the overall intended purpose? What rear tire size are you planning on? Going to need your carburetor numbers (CFM), cam grind, and probably cold cranking compression. "Hot" is too relative of a term for any real specific recommendations, as it could really mean anything from 3.73 to 4.30 gears for a street car, depending on it's intended usage.

 

[rumblefish360]

I am curious as to what people are using and recommending. I have a hot 340 high rise intake, high lift cam and high compression engine. I don't have the build information on the motor unfortunately.

So if you are running a similar engine what gears are you using and what torque/stall converter?

Your description is pretty broad and vague so I will generalize a set up or two that will fit most anybody’s “Hot set up.” The one problem is the torque converter. You need to know a lot about the car and engine to get a decent one and know everything for a great one.

Basic level upgrade from Hwy. gears;
3.21 - 3.55 gears, 2200 - 2500 stall
(Generally up to [email protected] for a cam)

Mild hot street;
3.55 - 3.91 gears, 2500+ stall
(Generally a cam from [email protected] - [email protected])

Hot street;
4.10 - 4.30 gear, 3000 or better stall
(Generally a cam of [email protected] and better)

This is very general and highly flexible completely dependent on the build and intended useage. However, if your new at this, you can follow the above general parameters and have an excellent performer.

 

[340inabbody]

Your description is pretty broad and vague so I will generalize a set up or two that will fit most anybody’s “Hot set up.” The one problem is the torque converter. You need to know a lot about the car and engine to get a decent one and know everything for a great one.

Basic level upgrade from Hwy. gears;
3.21 - 3.55 gears, 2200 - 2500 stall
(Generally up to [email protected] for a cam)

Mild hot street;
3.55 - 3.91 gears, 2500+ stall
(Generally a cam from [email protected] - [email protected])

Hot street;
4.10 - 4.30 gear, 3000 or better stall
(Generally a cam of [email protected] and better)

This is very general and highly flexible completely dependent on the build and intended useage. However, if your new at this, you can follow the above general parameters and have an excellent performer.

Thanks Rumblefish this is what I am looking for. As mentioned I got an engine that I do not have the internal specifications for. Its in the car now with the stock rear maybe 273 and I believe a 2000-2500 stall converter and its a dog. I don’t plan for n cross country with it but more around town fun so I would rather error on the hot street side and fine tune with rear gears.

 

[340inabbody]

I guess dog is vague. I have almost no response just off idle.

 

[340inabbody]

What is it going into and what is the overall intended purpose? What rear tire size are you planning on? Going to need your carburetor numbers (CFM), cam grind, and probably cold cranking compression. "Hot" is too relative of a term for any real specific recommendations, as it could really mean anything from 3.73 to 4.30 gears for a street car, depending on it's intended usage.

In a B Body Roadrunner actually Sport Satellite. Intended usage around town fun. 15 inch rims.

 

[rumblefish360]

Well, in order to liven it up in a big way, with the consideration that you said it’s not a Hwy. car...
Go right to the 4.10’s and a min. of a 26 inch tire. That’s a 235/60/15. That is as small as I would go.
What year Sport Satellite?

 

[340inabbody]

Well, in order to liven it up in a big way, with the consideration that you said it’s not a Hwy. car...
Go right to the 4.10’s and a min. of a 26 inch tire. That’s a 235/60/15. That is as small as I would go.
What year Sport Satellite?

1970 so its the same body as the RR. Running Mickey Thompson 275x60x15 already.

 

[rumblefish360]

That would be the size tire I’d suggest for a B body since the rear of the car weight would just out a damper on the smaller tire. It wouldn’t grip as well unless you really have the weight distribution & suspension worked out.

I run did the same tire on my ‘79 Magnum. The extra width, as small as it is combined with tire height is a big difference.

 

[AJ/FormS]

Like YR says; that combo need 4.56s and at least 275/60-15s. which are like 28 tall or so. With those and your current 2500TC and a 1.45 second gear, you can hit 60 mph at;
(60x 1056x4.56x1.45)/(28x3.1416)=4762 at zero slip. Figure 5000 minimum to 5250, with the TC slip; just about peak power with a [email protected] cam

BTW;
A stock 340 auto car should have come with 3.23s. With a 3.23x2.45=7.91 starter gear and a solid 10% in the TC ,yur looking at a starter gear of 8.7 to 1. At 2500 your "hi-compression" 340 should be putting out over 200ft lbs. So; 200x8.7=1740 into the rear axles. That's a pretty normal number and should be real peppy. Especially when you nail it on the line, at zero mph, cuz this could grow instantaneously to over 3000 ftlbs, which should be enough to break any street tires loose. After which the 1740 will climb to perhaps 350x8.7=3045ftlbs at say 3500rpm, enough to sustain the spin all the way to shift-rpm.
So, if your 340 is dead off idle and not doing that,then the first thing I recommend is to verify the rear end, and the second is a compression test.
Hyup 2.76s would kill it, but so would a 292/108 cam, and so would a smogger-340 in a rotten combo. So before you spend a wheelbarrow-full of doubloons, with only modest gains, I recommend you first check out what you have. If you already have 3.23s, then 3.55s are only 10% better so not a big change. And a 2800TC, altho I love those, is also only good to wake up say 10 or 15% more torque over the 2500.
But if your cylinder pressure is down to 130psi that combo is gonna be doggie no matter what you do. Arizona has elevation changes all over the map, and if you are stuck at high elevation, (mean elevation of Arizona is ~4100ft), you are gonna need some serious cylinder pressure to get Un-doggie.
Jus saying

 

[340inabbody]

Like YR says; that combo need 4.56s and at least 275/60-15s. which are like 28 tall or so. With those and your current 2500TC and a 1.45 second gear, you can hit 60 mph at;
(60x 1056x4.56x1.45)/(28x3.1416)=4762 at zero slip. Figure 5000 minimum to 5250, with the TC slip; just about peak power with a [email protected] cam

BTW;
A stock 340 auto car should have come with 3.23s. With a 3.23x2.45=7.91 starter gear and a solid 10% in the TC ,yur looking at a starter gear of 8.7 to 1. At 2500 your "hi-compression" 340 should be putting out over 200ft lbs. So; 200x8.7=1740 into the rear axles. That's a pretty normal number and should be real peppy. Especially when you nail it on the line, at zero mph, cuz this could grow instantaneously to over 3000 ftlbs, which should be enough to break any street tires loose. After which the 1740 will climb to perhaps 350x8.7=3045ftlbs at say 3500rpm, enough to sustain the spin all the way to shift-rpm.
So, if your 340 is dead off idle and not doing that,then the first thing I recommend is to verify the rear end, and the second is a compression test.
Hyup 2.76s would kill it, but so would a 292/108 cam, and so would a smogger-340 in a rotten combo. So before you spend a wheelbarrow-full of doubloons, with only modest gains, I recommend you first check out what you have. If you already have 3.23s, then 3.55s are only 10% better so not a big change. And a 2800TC, altho I love those, is also only good to wake up say 10 or 15% more torque over the 2500.
But if your cylinder pressure is down to 130psi that combo is gonna be doggie no matter what you do. Arizona has elevation changes all over the map, and if you are stuck at high elevation, (mean elevation of Arizona is ~4100ft), you are gonna need some serious cylinder pressure to get Un-doggie.
Jus saying

Ok lots to do here thanks! By the way not the original motor. Was a 318.....

 

[340inabbody]

Oh also its a peg leg that will need to be changed asap. Thats why thus info is very helpful. I am posting here rather than in the bbodies as I know the 340 is more prevalent here...I think.

 

[rumblefish360]

Ok lots to do here thanks! By the way not the original motor. Was a 318.....

Say hello to the windbag of information, AJ. (He’s a good guy really.) If your eyes don’t bleed from his responses of over informative babble, it’s a good read.

Considering you said. “Dog” as a description word, the Hwy. gears were a no brainer. Though I’d bet you could travel at 150+mph.
(Yea, guess how this non mathematical guy knows that chit!) If AJ would have told me this back then, I’d still have tried it out just because.....

 

[rumblefish360]

Well yes, the 340 is, but you got AJ!
And a few other good fellas as well.

 

[crackedback]

JMO, get the tune up at idle correct before delving in much further. Disconnect hose at vacuum advance can and plug it if it has Vac Adv. Get a vacuum gauge and timing light. Hook up vacuum gauge and get a reading now. Set the timing and find the point where the engine kicks back or cranks very hard on the starter when warmed up. That's your idle timing limit. Then set the timing a little below 2-4*, reset idle speed, mixture screws and check vacuum reading. The vacuum reading and initial timing will likely help determine the camshaft in the engine. You want to get this correct because EVERYTHING above idle is a band aid if the foundation (idle) is poor.

Check total number and make sure it's not to high with vacuum advance disconnected and plugged. DO NOT pick an RPM to stop, rev it up until it stops advancing. See "hillbilly timing tape" if your balancer isn't marked. Usually total #'s fall in the 34-38 on a SB with iron heads. If it's too high you need to bust open the distributor and limit the advance.

It takes work to get this right. Some distributors are easier to work on then others. MSD are simple and I have bushings that make this process easier.

Converters are the KEY to a auto trans car. 340's like flash speed! 3.55 and high #'s are good too!

Don't feel bad, I have a car just like yours. Someone else built a 340 with a 508 cam, 3.21 gears and a stockish converter. A granny in a walker can outrun that thing to 30mph. Sounds like tarzan, runs like a crippled Jane. LOL

 

[AJ/FormS]

150 in an A-body must be freaky fast.
My barracuda used to cruise real nice at 100 for hours,120 for shorter hops on the interstate following faster cars. But when I crank it up to give chase, I try 140 briefly, then lose my nerve. 140 is an awful lot faster than 120. And ohlordy the wind-noise!
I can't imagine 150 in an A-body.
OP
If you are higher than 4000 ft, you got some thinking to do. That difference in elevation, on a true10.5 engine, is over 20psi, compared to sealevel, and basically makes your 340 feel like a smogger-318@ sealevel, until the Rs get up..
So, if an original 318 car ,then just go straight to the compression test, then check your local elevation; these two go hand in hand.

 

[rumblefish360]

Oh AJ, FWIW, in a ‘73 Cuda 4spd, 2.76 gears, 255/60/15’s, rpm held at 6700.

 

[AJ/FormS]

Oh AJ, FWIW,in a ‘73 Cuda 4spd, 2.76 gears, 255/60/15’s, rpm held at 6700.

Hey; (6700x85)/(1056x2.76)= 195mph... Ima thinkin' you meant 3.55s=152 mph cuz 23% clutch-slip sounds a lil excessive.lol

FWIW; 120mph with 3.55s, a clutch, and 27s is ~5300 in Direct; ~4130 in .78overdrive; ~3000 in .71x.78 double-O. Altho that 367 made fierce power down low, I don't recall if the Hughes 223cam was able to do 120 in double-over .
I know in second-over,she cruised 65~1600,and 75~1830.
Three years earlier, this combo went 105 in the Qtr with the 750DP.

Same combo,600VS carb now; on a trip to attend the 2004 Car-Craft National show, made ~32mpgUS, point to point at mostly 75mph stateside, and 62 in the Homeland. This was over about 10 hours and ~550 miles, from just North of Wallhalla ND (where I live) to Shakopee MN, via St Cloud. On the way back we deviated from 65/75 a tad...........
That was a trip to remember!

 

[rumblefish360]

Hey; (6700x85)/(1056x2.76)= 195mph... Ima thinkin' you meant 3.55s=152 mph cuz 23% clutch-slip sounds a lil excessive.lol

195? Naaaaaaaa can’t be.

 

[str12-340]

If this is really a street car, I can't imagine 4.30 gears. Cruisin around town would be great if you never had to spend any serious time at say 40 - 45 mph. I hope you would never have to get out on a highway and actually go anywhere...

 

[AJ/FormS]

Mild hot street;
3.55 - 3.91 gears, 2500+ stall
(Generally a cam from [email protected] - [email protected])

On the money; the cam puts the rpm where you want it; the TC launches it to the power curve pronto; and the gears keep her on the pipe.

 

[rumblefish360]

If this is really a street car, I can't imagine 4.30 gears. Cruisin around town would be great if you never had to spend any serious time at say 40 - 45 mph. I hope you would never have to get out on a highway and actually go anywhere...

Ahhhhhhh, throw away the fear away and enjoy the happiness of mad dog acceleration and the brutality of creating panic for your opponent as his fear of loosing becomes reality while they grow smaller in the rear view mirror. There wasn’t anything more enjoyable than to bury a few big block rivals back in the day. There look clearly stating “WFT!” is worth every last red line rpm clutch dumping tire chirping gear slamming change.

(Now add in a comic relief Dr. Evil laugh)

I’ve lived with 4.10’s and a 26 inch tire for many years. Hwy. traveling is a slow go. But available & do-able. On this Island I live on, the countries high Hwy. speeds are traveled at (even though the posted limit is 55) and exceeded BUT the right lanes min. speed is 45. There are also Alternatives in roadway travel where the interstate can be by passed for more rpm friendly roadways.

The current Duster sports 4.88’s. There isn’t a place I cannot travel to here. They only consideration is the time it takes to get there at the reduced speed. That gear with 255/60/15’s has temporarily proven almost a bit much. I need a larger tire.

 

[340inabbody]

Ahhhhhhh, throw away the fear away and enjoy the happiness of mad dog acceleration and the brutality of creating panic for your opponent as his fear of loosing becomes reality while they grow smaller in the rear view mirror. There wasn’t anything more enjoyable than to bury a few big block rivals back in the day. There look clearly stating “WFT!” is worth every last red line rpm clutch dumping tire chirping gear slamming change.

(Now add in a comic relief Dr. Evil laugh)

I’ve lived with 4.10’s and a 26 inch tire for many years. Hwy. traveling is a slow go. But available & do-able. On this Island I live on, the countries high Hwy. speeds are traveled at (even though the posted limit is 55) and exceeded BUT the right lanes min. speed is 45. There are also Alternatives in roadway travel where the interstate can be by passed for more rpm friendly roadways.

The current Duster sports 4.88’s. There isn’t a place I cannot travel to here. They only consideration is the time it takes to get there at the reduced speed. That gear with 255/60/15’s has temporarily proven almost a bit much. I need a larger tire.

Yes yes yes lol I know the big block would have given me more low end torque but I thought a 340 would be cool with the right set (which I certainly don’t have yet). I don’t plan on autocross just digging around town to shows and meet ups etc.

 

[rumblefish360]

Hey whoa hold on, I’m not stating what you said nor am I advocating it. I just left a post showing my love for my small blocks and happily relived burying a few big block way back when I was a young gun killing it.

By the way, ‘70 is my favorite year. Honestly the only year RR I’d own. If the car is not a car to worry about worth or modification to, lighten the nose up as you see fit and as far as to want to go. More the merry and help it will be in weight transfer as well as a small advantage on the time slip.

 

[AJ/FormS]

Ahhhhhhh, throw away the fear away and enjoy the happiness of mad dog acceleration and the brutality of creating panic for your opponent as his fear of loosing becomes reality while they grow smaller in the rear view mirror. There wasn’t anything more enjoyable than to bury a few big block rivals back in the day. There look clearly stating “WFT!” is worth every last red line rpm clutch dumping tire chirping gear slamming change.

(Now add in a comic relief Dr. Evil laugh)

I’ve lived with 4.10’s and a 26 inch tire for many years. Hwy. traveling is a slow go. But available & do-able. On this Island I live on, the countries high Hwy. speeds are traveled at (even though the posted limit is 55) and exceeded BUT the right lanes min. speed is 45. There are also Alternatives in roadway travel where the interstate can be by passed for more rpm friendly roadways.

The current Duster sports 4.88’s. There isn’t a place I cannot travel to here. They only consideration is the time it takes to get there at the reduced speed. That gear with 255/60/15’s has temporarily proven almost a bit much. I need a larger tire.

I totally get that;
I got me a GVOD so I could run any rear gear I wanted to, and I had a shed full of accumulated pumpkins.
My 367;blew up some ex race-gear 5.38s; and zinged off a couple of teeth on some used 3.91s; I traded the 4.10s for 3.55s,sold the nearly new 4.30s;and no takers yet on the 4.88s; so I totally get you,lol.
Finally I got the Commando box with the 3.09 low, and re-installed the 3.55s. Then it was , bye-bye to the byway blues, with a 2.77 equivalent overdrive gear.