Well, I know the converter plays a large role in the car's performance. But what is it actually doing for me? I have a '73 455 bored 0.030" over, out of the box TA aluminum Stage 1 heads, 1.6:1 roller rockers, 10.1:1 pistons, 800 cfm carb on an aluminum intake, 1.75" primary tube headers, cam is a TA 288-94H, street/strip HEI, tranny is a beefed up TH350. My exhaust is a 2.5" system with a 3" collector at the headers, Dynomax mufflers. Rear end is a Chevy 12 bolt positraction unit, at 3.31:1 ratio, I'm using a new one-piece driveshaft. Engine runs great, nice idle for such a big (for my taste) camshaft, and it still pulls 14" Hg I put in a 2000 rpm stall converter. The engine is running great, but power seems lacking. I do know that I'll need to re-do the carb and re-curve my distributer to reflect recent changes (cam and heads), and also I am going to check my cam degreeing again now that it's not snowing (don't ask) but if anything, the car seems a tad slower than it was with a TA RV12 cam, stock converter, and '73 smog heads. Off the line, it still moves, but after these changes, I should have been seeing a difference, I thought. On paper, I just put 70 hp into this engine, theoretically taking it from about 340 hp to 410 hp. My backside should have felt the seat hitting it harder and it just didn't happen. I think it's my converter choice, especially since it seems to make more power in the 50 mph range than it did before, but this could be cam, too, I suppose. But with the biggest change being the heads...my valves were burned, tack-headed things, and now I have a quality pair of heads with Stage 1 valves...I was disappointed in the performance. Obviously, It's how I've put the combo together The car is a true daily driver. It is heavy- 4,000 lbs. I use stock Buick steel rallyes with 235/60/15 rubber. I sit in this car in traffic to go to and from work. I didn't think I'd have to make a lot of compromises concerning performance versus driveability with this engine, and I still think I shouldn't have to. What's really happening with this 2000 rpm unit versus stock? What's happening in say a 3000 rpm unit versus mine? I thought I had figured this out and it's evident I haven't o No: What is the converter I should be considering for this car?
torque convertor Chris, My 72 stage 1 had a 12 in conv. 2200 rpm i believe , the same as a friend of mines LS 6 Chevelle and i think a stock GM one is 13 in. so if you put a 2000 in yours with all the changes your going backwards right off the line. I have since put in an 11 in. convertor with a switch pitch i bought from Jim Weise with 3.08 gears and thats the ultimate. 1.8 second 60 ft. time with ta street drag radials....Bill Arseneau
That's what I thought Bill. I bought an inexpensive one, since I wasn't 100% sure of the one I really needed, but I knew my stock one was probably 1500 rpm or so and that thing had to go. Since I only put 160 bucks into the converter, the hardest part of the swap will be the installation of the new unit The switch pitch tranny is out of the question for me...I'll be keeping my mild performance TH350 for the foreseeable future. It should handle the engine...for a while Your input is great, I appreciate it, but I have questions I need to discuss, like: What am I looking for in a converter? It's great to say "You need a 2500 rpm 13" unit" or something, but what does that mean? The diameter is obviously more rotating mass. What's the dynamics involved with playing around with diameter, and rpm speed? When I do something to the car, I like to understand what it does. Why am I looking for a particular diameter converter? What's the higher rpm stall actually doing for me, and what's the 2000 rpm doing to impede me?
Go with an 11". Get the distributer timing curve right and get the carb right. 800 cfm is small but it will do. You wont notice the "looser" converter unles you stab the throttle. As long as you take it easy you wont even notice the extra stall. 11" converters are still fairly cheep.
Rick- I don't understand. What do you mean, I won't notice the looser converter? Also, what do you mean by 'if I take it easy I won't notice the extra stall'? I do not know what you mean. It's great that you're helping, but what do you mean? I am not a tranny/converter guy, I don't know what you're saying here. Why an 11"? What stall should I be considering? I am still in the dark concerning this. This car is a daily driver, but I didn't build a 10:1 462 with high performance goodies so I could 'take it easy' :TU: . What would be the point? This car gets used like it should be used. Plenty of real street cars have more aggressive build-ups than this. Don't be fooled into thinking I drive like a grandma just because the car's a driver. I think that people are getting the wrong idea here. I'm the type of guy who drives his car to work and to the grocery store...and who also wrings the snot out of it hard enough to see the speedo needle down by the right turn signal I need to select a better converter for my car. Right now, the one it has won't do what i want. I'm sure the car's making plenty of power, but my converter is making the car behave as if it didn't. On a street car, I don't want to sacrifice low and midrange torque too much. i don't want to have to go to 3500 rpm just to make the car scat. It's my understanding that with some higher rpm converters, I'll need to 'load' the converter to accelerate from a stop quickly. No thanks, this is a street car, not a drag strip car. I want to punch it at idle and take off like a cat tossed into boiling water- but not because I brought my rpms up, looking at the lights. My cam starts it's power band at 2000 rpm, and I agonised over that. I don't want to sacrifice even more low end I need to know what's being discussed here What do the various diameter converters do for me? What's the stall speed really doing? What is the function of a 2000 rpm stall converter? What happens at that 2000 rpm? It means something, and I want to know what it means. I can't explain better than this. I want to know what this stuff means, and what it does for me, in addition to what you guys think my converter should be. I need to make a decision about which one to use, and to do that, I need info. I know that my stock one isn't right, and I know that my 2000 rpm one isn't right.
What I mean is that under normal driving conditions when you don't have it to the floor, you won't really notice that it is a looser converter. If you want the best benefit out of your car put a 3000 stall 10". I drove mine on the street with a 9" to the store and work. It stalled to about 3600 with slicks on the drag strip but I couldn't hold it on the brakes past 2800 and normal light driving rpm was between 2500-2800 rpm. What I'm trying to say is just because a converter is a 3000 stall doesn't mean the car wont move until 3000 rpm. It takes alot of power and load to get it to stall that high. Every car is different. I can stall my converter at the track to 4800 on the nitrous but the same converter in your car wouldn't stall past 2800. SO don't be scared to put a good stall converter in a street car. If your not going to spend $500 for a decent 10" your taking at it being "sloppy". I ran a 11"TCI in my th350 behind a 350 SBB and was pretty happy with it. Also with rpm the converter "tightens up". Just because you have a 3000 stall converter doen't mean it slips that much the whole time. With rpm it tightens up. By the time you shift the converter is probably only slipping 5%. Size is everything. Each size has an effective operating range compared to HP and vehicle weight. If you had a 12" that was any looser than what yours is it would slip all the way up the rpm range since the converter works off fluid flowing thru it. The larger the converter the more surface area it has and leverage. To make a large converter "stall" they have to make it real inefficient to get it to "slip"/stall. There are angled vanes inside a converter that directs the fluid. They take away the angle to make it stall on say a 12" converter. On a smaller converter they can keep and sharp angle on the vanes inside to keep it efficient at higher rpms but because it is a smaller converter it will slip"/stall at lower rpm. A small converter needs to spins faster(needs rpm) to get enough fluid moving thru it to "lock up"/tighten up. I put a very tight 9" in another street car that drove around fine on the street and was plenty "snappy" at the street lights. It was about $700 shipped to the door though. A ATI 10" is @ $500 shipped last I checked. A TCI Street Fighter 10" is $349 @3000stall, There Break-Away 11" is $229 @2500stall. On a budget, they work fine. Does that help???
I have converter questions too. Does the high stall, say 3000, do anything for performance after launch? How much can you trim from your 1/4 mile ET by changing to a 3000 stall from stock on 235mm tires? a 2000 stall? Can you slow yourself down by going to a higher stall if you don't have the traction to handle the torque at 3000 at a standstill? Do some converters accelerate better than others regardless of stall speed? anyone?
No, unless during the shift it drops out of the power range of the motor. A 3000 stall will help you launch but only if you don't spin. Those 235's will spin easy with a little power not to mention stall. Yes you can slow down if you spin. Some converter do accelerate off the launch better since they have better torque multiplication. It depends on how the internals are setup. Some allow a little more slip after the shift to help keep the motor rpms up and in the power band. If you were to switch to a 3000 stall or a 2000 you should be able to pick AT LEAST a little. If you are mostly stock I would stay with a 11" 2500 stall.
Just to clarify- the 3000 rpm 'stall' is simply the point at which I can't bring the engine rpms up any more when loading the converter, correct? Or am I mistaken? Also, the only way I've ever removed a converter is by removing the engine. Can I slide the tranny back and get the converter out from underneath? Removing the engine is a mild pain, but a well-practiced one
Chris, Yes, you can slide the tranny back to change converters. This is the easiest way. I have a 3700 (10") converter in my GS that I drive almost daily. I can't tell the difference between it and a stock converter just driving around town. No, you don't have to "load" the converter for an aggressive take-off. I just mat it unless I'm at the track. Tom Jenkins
Hey Chris i have the same build as you with even 3.31 gears also i have a 850 Q-jet good iron heads 290-204 same cam i have my cam at 6adv i set timing at 20 and 33 total.JW did alot of testing he found that the cam works great at 6-8 adv brings low end down my motor is very reponsive.you should check cam first.I have a jw sp converter 11 inch it is in at about at 2800 on high side when i go from a 5mph roll it blows the tires away you have to let off. i would start with the cam before you do anything if the cam is in wrong you won't have good low end hope this helps
If the converter is setup for the torque of the engine and 3000 is were the converter would "flash" at, you would probably only be able to hold it on the brakes until 2600 rpm. You can on hold the car with the brakes only with so much power but with slicks on a sticky track you can "plant it" to the floor so with the added power the converter will stall a little higher to say 3000. So you are correct, the 3000 would be the point were you couldn't bring the rpms up any more without car/tires moving. Depending on your engine torque and vehicle weight can cause a converter to stall a little higher or lower than advertised. Nitrous is usually good for another 500 rpm's worth of stall even up to a 1000rpm+.
I'll chime in here, because I've got some questions too. Mainly with Lock up torque converters. Are there any for our Buicks? Would there be any benefits? Does anybody run with one? Price and difficulty of installation?
Lock up torque converters are used on the 200R4, and 700R4, as well as all late model transmissions. The THM350C also used one, Greg Gessler runs one in his FAST 72 GS Stage1. I believe I read about a lock up torque converter conversion for the THM 400 in one of the GS Extras. BTW, there's nothing really unique about Buick Transmissions except the bolt pattern (BOP). Anything that works in a Chebbie trans will work in ours.
Trevor I am running a lockup converter in front of my homebuilt 700R4 and have not had a minutes problem. I lock it up manually with a switch on the dash. This is the second car I have done this way and it works fine.- Mike D.
