I have a 71 Skylark, and the original 350 in is the machine shop getting a fresh rebuild. I'll be increasing the compression from 8.5 to somewhere around 9.5, and a mild cam, bigger than stock, TA Intake, TA headers. My TH350 is rebuilt with B&M shift kit, and stock 2.56 gears. Should I stick with a stock torque converter or larger. I don;t quite understand exactly what stall speed is/means?? Can some please xplain stall speed, and torque converter advice????? Thanks Jay
Jay, Your torque converter should be matched to your cam. With a mild cam, the stock converter is often sufficient. Find out what cam you are running, and the duration at .050 figures, and then we can make a recommendation. There are 3 parts to a torque converter. Turbine, impeller, and stator. The impeller is driven by the engine, and in turn drives the turbine. The stator is in between the impeller and turbine. It redirects fluid to increase the efficiency of the converter. Without the stator, a torque converter would simply be a fluid coupling, and incapable of multiplying engine torque. Stall speed is defined as the highest RPM the engine can turn the impeller, with the turbine held stationary. When the impeller is turning faster than the turbine, engine torque is multiplied by 2:1 or more. Think of a ten speed bicycle. When you want to climb a hill, you use a lower gear. This enables you to pedal faster so the drive wheel develops more torque, and you have better mechanical advantage, to climb a steep grade. Think of a torque converter as an infinite number of different gear ratios to vary the mechanical advantage available to the engine. At some RPM, the torque converter impeller and turbine approach the same speed. This is the coupling speed. Above this speed the converter transfers power 1:1, and nop longer multiplies torque. The impeller and turbine never reach the same speed unless the converter has a mechanical clutch (lockup converter). The actual speed a converter stalls at has alot to do with engine load, vehicle weight, and engine torque. That is why no cxonverter will stall exactly the same in different vehicles. The reason this is important has to do with the engine power range. A stock cam will start to make power at RPM's as low as 800 RPM. When you increase the duration (how long the intake valve is open), it moves the power range up. Some cams don't come on untill 2000 RPM, or more. A stock converter may stall as low as 1400 RPM. See the problem? Try to take off from a dead stop with a cam that begins to make good power at 2000 RPM, with a stock converter, and the car is a pig until the revs come up. Now put a converter with a stall speed of 2500 in the car. From a dead stop, hit the gas, and the engine can rev into it's power range, as the car starts to move. With a higher stall converter, the converter will slip more once the car gets moving, which creates more heat, and wastes gas. That is why it is so important to match your converter to the cam. Most of the above is simplified. There is alot more to it, I tried to give you a basic understanding. Hope that helps.
Thanks for the explanation, it does help. I was leaning toward the TA RV-12 cam, which is known for strong low end torque, the duration at .50 is 205 intake, and 215 exhaust, or the TA 112 with 210/215. Each have a power range of 1000 - 5500. I am staying away from larger cams because I only have 2.56 gears
Stall Larry sure knows his stuff, huh! :TU: He's answered questions in the past for me too. I'm curious, has your tranny been switched at any point over the years to a 350-c (lockup)? If not, like Larry said use the stock converter. If it is, Summit carries a 2500 stall lock-up converter (forgot which brand, a buddy of mine bought one a couple of years ago) that will really wake the car up off the line and cruises better than a stock non lock-up. Best of both worlds! :Brow:
Larry what should I do my 70 350-4 I put a mild cam in duration.050 intake 211 exhaust 217 would a 2000 stall be ok? I have 3.42 pos
2000 would be more than enough. The stock converter would probably be OK too. I like this chart I got from the Sumitt Racing Catalog.
Did you degree the cam? I would also check your timing, initial and mechanical. Have you read this? http://www.v8buick.com/showthread.php?t=63475
larry help me out... i have a 70 350 that has been rebuilt with a ta 212 cam. the paper works says the duration is 280 intake and 285 exhust..these numbers seem alittle high from everyone else is this a type o.... i am new to engine work and cars for that fact....any way i want to pull more power out of the motor... i and think i need to swap out my converter as well..the shell has a th350 and the rear gears i have been told are 3.24, posi.... tell me what you think jeff
Jeff, Those are advertised duration numbers. No one compares cams using those specs. Instead they use duration at .050 lifter rise. The Advertised specs for the TA212 are 265*Intake, and 280* Exhaust. At .050, they are 218*Int., 230* Exh, 110* Lobe Center(350 CID), with .459"Intake Lift, .470" Exhaust Lift(1.55 rocker ratio) Power Range is 1500-5500 RPM. TA says stock converter is OK, but a 2000 stall would probably be OK for maximum performance.
Power Band/Curve I was at a swap meet last year, and i bought a camshaft for a SBC. It was kind of an extreme one from Cran Cams, and it blew the last engine cuz the engine wasnt strong enough. My question is, when the duration is increased, ur Power range moves to higher RPMs. I was looking at graphs of this, where it showed you which cams produced peak torque/hp at which rpms. The bigger the duration, the higher along you need to go on ur rpms to get peak power (generally speaking). But if i put an extreme cam into a regular street/strip car, i may not be producing peak power at 2000 rpm, but wont this power be alot more than cam with a power band of say 1500-6000 rpm? The cam i got is part number 111431 from Crane. Has 260*/268* duration at .050 lift, and has a power range of 4400-7400. Suggested applications are bracket racing, and pro street applications. Im basically curious what would happen if i put this into a "mildly tuned engine". I realize its chevy, but its more of a general cam question. Thanks
Everything is combination. If you put mismatched parts together, you won't get the intended results. Putting a big cam into an engine that has untouched heads, for instance, will give you more power at much higher RPM's, but not as much as if the heads could flow the larger amount of air that the cam could supply. In other words, the heads or the intake, or the exhaust would be the restriction, or the bottleneck to producing optimum power from that bigger cam. To get any kind of decent results out of that engine, you'd need a 4500 stall converter, and 4.10 gears so the engine would get up to it's power range on launch. Lots of guys make the mistake of throwing a big cam in a motor without considering what they really intend to use the engine for. The results are always disappointing. Always match your parts for the intended use, street,street/strip,full race, whatever.
Thanks thats a big help Thats the answer ive been searching for for a while now. I know that the right combination can do wonders for a motor, rather than extreme parts on only some of the motor. So i guess i might be looking to trade that cam for a cam thats more in my range. Cheers.
