3.08 gears.. is it enough for this build?

Okay first off let me start with what the engine has.
1971 buick 350-4, poston intake with 1" carb spacer, hei, 1 3/4x3" hooker supercomp headers, flowmaster 40 series dual exhaust, rhodes lifters, ta 284-88h cam, 460/460 lift, 223/230*@50, 110* lobe center, Cleaned up heads, 10.25:1 compression, th-350 with stage 2 shift kit, 2800stall, 3.08 gears. Are 3.08's enough to get me going? I was told "You will never be able to wind that engine out with 308 gears" Now i asked months ago about swapping to 3.42 gears and everyone said to stick with the 308s due to traction problems with the 342 gears.. What are thoughts about these gears with that engine?

 

First, I'm assuming that your 2800 stall converter actually stalls at 2800 rpm.
If that's the case then at 60 mph (with a 27" tall tire), your car will only be turning around 2400 rpm. You'll be slipping at cruising rpm. That's not a good situation as it builds heat and destroys transmissions. Even with a 26" tire, you'll still be slipping.

If you had a 26" tall tire with 3.42's, then you'd be just about right at 60 mph for your converter; ~2750 rpm.

You may want to check out an rpm calculator. The one I usually use is at www.ring-pinion.com
Just click on the calculator link and the rpm/gear/tire calculator. From there you can figure out what RPM you'll be turning at X MPH with X.XX gear ratio.

You'll be able to wind a 3.08, but it won't spin up as quickly, and you won't likely get close to topping out in Drive if yo'ure running the 1/4 mile with it. You'll be turning in the low to mid 4000 RPM range if it runs ~105 MPH at the track.

 

342

my sons car has almost the same motor you have .....he has a ta310 cam though and the heads are ported. The same converter and the car has 3.42....and i wish we had more. It had 3.08 before and it really makes adifference.....go for it

Mark

 

Well i used that calculater and at 75mph it put me over 3000rpm with the 3.08s. So the 2800stall would be to "big" and heat up the tranny from slipping? The wheels im going to use are a 15x8 with Mickey thompson indy profile SS tires in G60-15, 26" tire.

Torque converter i found on jegs and its a 12",2400-2700stall. Would that be okay? I dont really understand the differences so thats my main problem. Do i need a lower stall or higher stall like 3000+ so i dont heat up the tranny? I'd really like to keep the 3.08s for street use. Any help on picking out the right torque converter i need would help out greatly!

 

Jon,

Think of the converter as two fans - a small one blowing face-to-face into a bigger one. The smaller fan is the engine side, while the larger fan is the trans/output side. Now, turn on the small fan and see how fast it must go before the large fan is in sync with it. That's a way of thinking of your stall speed.

The larger the "small" fan, the less rpm's it will take to move the large fan at an equal speed. This would be a low stall converter. If the small fan is really small, it's going to have to really be working to move enough air to get the larger fan in sync. This would be a high stall converter. Although this is simplifying it, this is a way of thinking how a stall converter works. Instead of air, they're moving fluid and they're within a sealed case.

So basically, you're trying to figure out at what engine rpm's the trans is going to be at 1:1 with the engine. A 3000 stall converter means (theoretically) that the engine will have to be turning 3000 rpm's for the trans to be at 1:1. Any lower than that, and there's slippage between the two. This slippage builds heat. Heat is the enemy of transmissions (in addition to neutral-drops at 5000 rpm).

So if you're car is geared/tired so that your cruising rpm is below the converters stall rpm, then you're going to be constantly in a state of slip. That's bad as it will build up heat.

You'll have to also understand that a converter's "advertised" stall speed is not going to be the actual stall speed. In addition to the "two-fan" dynamics, it's also dependent on the torque being put out of the motor and the weight of the vehicle. This is more important to it's launch stall than it's cruising stall. With a heavy car, putting out lots of torque, think of that little fan as being turned on at high rpm's instead of working up the rpm's as in a part throttle acceleration. This will help determine it's launch stall.

Launch stall is going to be important if you race a lot. The beauty of the stall converter is that it will allow you launch the car at an RPM where your car is putting out more torque. This is good to get the car moving down the track and get those 60-foot times down. If you have a car that puts out it's peak torque around 4000 rpm, then a stock converter won't have you launching in the sweet spot, if it'll only spin up to 1600 rpm for the launch. But if your converter will stall somewhere in the 3500 - 4000 rpm range, then you're getting the car moving when it's making the most pulling power. The trade-off is the potential slippage at the top end of the track.

So that 2400-2700 stall converter may stall at only 2000 if it's behind a 350-2bbl, yet it may spool up to the 2700 side behind a strong, torquey 455 motor.

When we got the scab motor into my Skylark a couple of years ago, we were driving with about 2800 stall in a car with 2.56 gears. On level ground, it would cruise at 65 around 1600 rpm or so. But if I started pulling a hill, it'd add 1000 rpm just to maintain that speed. It felt great if I drove on the highway in 2nd gear! Of course the scab got picked on it's second pass down the track and is now getting closer to being rebuilt. I expect the car to run in the 110-115 mph range down the track. I'm planning on using the same converter, which will likely stall closer to 3000 with the additional power. I'm planning a gear/tire combo that will put me across the finish line around 5500 rpm, while also keeping my rev's up for the drive to the track or around town. I'm looking at 4.10's with something around a 29"-30" tall tire or 3.73's with around a 27"-28" tall tire.

Another trick is to run a little more gear than you need for the street, while taming them with taller tires. Set it up for the track using a shorter tire, tame it on the street with a taller tire. It all depends on the use of your car.

So is it clear as mud now???

 

Stall speed changes depending on the engines torque output. What I think you should worry about is the size of the converter. Maybe an 11 inch? ( I might be off, I'm not used to Buicks yet) I would get someone elses opinion too, and see if they agree with me. With your engine probably being a little low on torque compared to, say a 455, actual stall speed would probably be around or lower than the stall speed rating though.

 

Heres an 11" 2400-2700 i found from postons. Would the 11" be better than jegs 12"? Im still lost on what torque converter to match with the motor. As for torque, it would be well over 400 ft lbs. Any torque converters that are 1 step up from stock and would improve my take off?

Street/Strip Converters Designed to bring engine speed into the power band for faster launches and better acceleration. All street/strip converters and furnace brazed to increase strength and have full needle bearings, front and rear, to insure reliability. Turbo 350 11" converter, 2400-2700 stall.

Product Code: PE20442-B

 

Oops another thing. this isnt a stock 350-2. read my very first post to get the info on it.

 

I know, I was just trying to give two ends of the spectrum to show that the same converter will act differently in two different vehicles with two different motors.

You could go nuts looking for "exactly" the right converter. There are high end converters that you can have customized specifically for your application. All 11" or 12" converters aren't the same. Some are tighter than others and may have a different pitch to the blades, which will affect the fluid flow within the converter. When buying an off-the-shelf part, there will always be a bit of a compromise, but custom can cost you.

There are also switch pitch converters that have the blades move to a different setting which gives two different stall speeds. Those are electrically controlled. Do some searches for the term switch pitch and you can find more information on them.

For a strong 350, you'd probably be fine using something that will stall in the mid 2000's with a 3.08 rear.

 

71gs455.. What torque converter stall would you recommend for my set up with 3.08 gears?

 

I installed a TCI Saturday Night Special stall convertor in my 350turbo. It's supposed to be a 2000 rpm stall. I bought a Comp Cam 268H-10 an the paperwork on car says it has 4.10's in it. But that hasn't been personally verified yet. If it was posi like it said then why in the heck is just 1 tire spinning. I will look into the rear later. But does this sound like a fairly decent convertor in a 455 with stockish compression?

 

Probably something that'll be in the low to mid 2000's. You may want to call some companies direct and tell them about your car. They may give you a better idea.

One like the 11" ATI Pro Streetmaster may work alright for you:

http://www.atiperformanceproducts.com/products/tc/smtcprices.htm

Their phone number is at the bottom too. For comparison, you could call some of the other converter manufacturers and see about where they put you.

Here's another thread discussing converters, including some of the higher end manufacturers: http://www.v8buick.com/showthread.php?t=110720

 

what if i were to give in and bump it up to 3.42's? then what would be a good torque converter stall?

 

Probably about the same one. It wouldn't be worth it to increase a few hundred rpm stall, especially if this is primarily a street car.

I went from a 3.08 open rear to a 3.42 posi rear in my 71 GS455. It was a good all-around gear for me. I didn't drive the car much - mostly to the track for racing or just to take it for a drive on the weekend. It did have a stock converter in it though. It ran mid 13's at around 98-100 mph. 60 foot times were around 1.9.

If you can do the gears/posi cheaply, then you may want to go for it. But if you're looking at spending another $1000, it wouldn't be worth the cost, I don't think. I wouldn't bother doing it and not going to a posi though - waste of time. I don't know that you'd have a lot of traction problems with the 3.42's and a posi. My GS was fine on the street with the 3.42's and 26" tall tires. I could break them loose if I wanted to, but it was pretty tame leaving from a stop. Rain is another story though. Plus, you're at a pretty high altitude, so that will kill a lot of power anyhow. I remember visiting a friend in Albuquerque and he let me make some passes in his 93 Cobra. Due to the altitude, the car was running mid 14's before the correction for altitude. I had a low 14 second Mustang, and it was weird driving a car that was technically much quicker (by about 1 second), yet was slower.

You've also got to realize that I don't know exactly what your converter will stall at. Those numbers are only ballpark figures. A converter company could probably estimate pretty well, if they know exactly the power figures for your motor, weight of vehicle, etc... but they're still likely to be of +/- a couple hundred rpm.

 

Maybe I missed it, but I don't see you mention how you are going to use the car. Is this a street cruiser? A daily driver? A lot of highway miles? Track-only?

If this will be a track-only car, then your answer is 3.42 or 3.73. But I get the impression that your primary concern is highway driving, so 3.08 will be fine. If your car will be a daily driver with lots of 70-80MPH driving, then 2.56 is the way to go (with a lower-stall convertor).

Please give some more detail on how you plan to use the car.

-Bob C.

 

Steve, that's the best, by far, explaination of how a converter works I've ever read!!

Jon I'm not sure of the charactristics of that cam but you really need to know what your torque curve is before you pick either a gear ratio or a converter. That's just an uneducated guess so take it for what it's worth. Good luck!!

 

it will mainly be a weekend car to take on short trips and possibly a trip to the local drag strip " 2 hours away" I'd much rather keep the 3.08's if i can find a torque converter that would be a step up from stock. I guess i'll just keep the stock torque converter and gears untill i find something to use. I just wanted to get a head start and start planning on what to use later on. i dont want to use steep 3.73+ gears due to my cam limiting me to 5500rpm.

 

Thanks Dave,

Now did you go round up all of the fans in your house to see what kind of stall you could get out of them? :Brow:

 

Th350-C

What you want is a 350-C. It's a 350 with a lock-up converter. They were common in the late 70's and early 80's. Hughes makes a nice 2500 stall that a buddy of mine has been running for a few years now with a 406 and a hundred shot of juice. If you drop to 2000 stall you'll definately loose some of the fun factor of your car. With the lock-up you get the benefits of the extra stall and 0 slip cruising.

 

Very good advice

Final drive ratio's assume a 26" tire. So, if you're running 3.42's and 26" tire, your final drive ratio IS 3.42 which is a decent gear for the track but a bit high for extended 70+mph highway cruises - BUT - bolt on a set of 28"-30" tire and you essentially knock that gear down 3.08-3.23

Also good advice was to keep you converter stall at least 2-300 rpms below your cruise rpms to limit slippage and heat buildup when cruising at highway speeds.