Milton, I'm not going to try to convince anyone to like what I like. But I will share my experiences. In general the SWP doesn't seem to offer much to racing, since many of its attributes are irrelevant there. I'm not even that much in favor of automatics. But after all kinds of broken stick and auto transmissions, the 400 for my budget is by far the strongest and most reliable trans, beside being a simple bolt in.
27 Oct 06 "Infinite Space Systems, Inc." <[EMAIL PROTECTED]> writes: > Bruce, > > > So the > > 400/425 will easily outperform the old 4 speed hydramatic > > or a 3 speed manual, by providing a wider overall range > > of gear ratios. > Not in my experience. First, a B&M full manual TH400 and > a B&M HydroStick are fairly even. The 3.8 first gear, 2.5 > second gear, 1.5 third, and 1.0 direct drive of the HydroStick > will match up to a TH400 with its 2.2-2.5 stall ratio and 2.5 > first, 1.5 second, and 1.0 direct, assuming the respective > cars have engines and rear gears matched to the respective > transmissions. As mentioned, the engine/trans/axle need to be matched, and to the particular goal(s). If my 400 was 2.5 converter X 2.5 low gear X 2.41 axle = 15 torque multiplication, the HydroStick 3.8 would need about a 3.96 axle = 15 torque multiplication. Fine, an even race. Now we drive the cars on a trip. At 65 mph SWP engine is turning 2170 rpm, the HydroStick engine is wearing itself out and wasting gas at 3560 rpm. OK, lets turn it around. We optimize cruising for both at 2170 rpm, (both have 2.41 axle). The SWP still has 15 torque multiplication at launch, but the HydroStick has only 3.8 X 2.41 = 9.2. Race only cars don't care about this. > Second, that matching includes whether the engine likes > 4 gear runs or 3 gear runs through the quarter. There was > more that one pro-drag racer who won consistantly with a > 3 speed manual, not a 4 speed manual. There are very good > reasons for that. It's not a straight across the board comparison. Nothing wrong with using the right gears with the right spacing. My SWP does 0-60 in 1st. But when I drive home that 3 gear racer, I hope there is a 4th or 5th to cruise at 65 mph. > > The switch pitch (SWP) THM400 and 425 of 65-67 had > > a torque converter 3rd element (stator) with VARIABLE > > VANE angle, changeable between performance and > > economy (instead of a compromise) as you drive. This > > gave 2.5 times torque multiplication, a 25% increase. > The torque convert stall ratio was the same for either a > fixed pitch or variable pitch TH400, 2.2 to 1 or 2.5 to 1, > depending upon the application. The variable pitch simply > changed where the stall RPM was. I can believe there were some fixed converters at 2.5:1, esp in 1968. I also believe they aren't around any more, because they wasted too much gas. 2 experiences. My 68 Cutlass would move, got a consistant 10 mpg in the stop/go/slower speeds to work. Now I have a same weight car, faster, and does about 14 mpg to work (17-20 country). A 2.41 axle does most of it, but the SWP does the rest. Second, every vehicle I have converted to SWP measured faster 0-60 on my stop watch. Motorhome people report about a 7% better. Another thing about the GMC (Toro based) motorhomes. With big blocks pulling 5 tons, the many conversions seem to find the SWP converters just as durable as fixed. That is also my experience since 1985. > > It also gave a bit better mileage in the other mode. In > > a heavy vehicle this can provide a reduction of 0-60 > > time of up to 10%, and also give smoother shifts. > Unfortunately, I didn't see that in a stock variable pitch TH400. Lots of people report better times, there is a motorhome business built on this idea. This is most obvious when the engine must work hard to pull the weight. If you have a big engine in a light vehicle, you won't need the SWP to spin street tires. > > The switch pitch is most effective at getting engine rpm > > into the power range at low speeds. At maximum rpm > > all torque converters become 1:1 torque transmitters, > > so switch pitch makes no difference here. It is very > > effective at max throttle, low to medium rpms, with up > > to 25% more torque delivered. > > > More torque only at a lower RPM. > > > > The beauty of a SWP is ability to give a little more > > performance, a little more economy, and a little more > > smoothness in the strongest car trans ever made, for > > a dirt cheap price. Note that the stock 65-67 setup may > > not do all this. But a touch of technology used to control > > a SWP can considerably improve over the original. > > > I have a real problem with the economy part with increased > performance. You can't get something for nothing. When > the variable pitch throws more torque to a lower RPM, it must > be paid for. The engine must give some more power to the > transmission through the torque converter. The Law of > Conservation of Energy demands it. No problem with Conservation of Energy. My 2.41 axle held my engine to pretty low rpms for 0-20, not much horsepower produced. The SWP (like a a higher stall converter) let the engine run 500 rpm higher in that range, which translates to more horsepower. Yes, it used a lot more gasoline to produce that extra power, energy conserved. But the gas wasn't all wasted, cause I got done sooner. > > My first SWP project was a 4000 lb Delta 88. That low > > compression 350 would cruise all day so nicely at 60 > > mph and 2000 rpm. But the 2.41 axle felt like starting > > in the wrong gear, 0-60 in 10 seconds. The SWP > > brought it down to 9 seconds, what an improvement > > (no other change)! Performance at no cost. > There had to be a cost. Increased performance demands > more power. It's that bad Law of Conservation of Energy > again. Energy in must equal energy out. Right. By getting my engine into its power range more quickly, I have more power in and more power out. > There's no way around it, unless one wants a perpetual motion > machine. > > At idle and high stall mode, the SWP put less drag on > > the engine. So I used less gas idling, and the car had > > less creep. For part throttle through the gears, the > > high stall gave up to 25% more torque off the line, and > > was generally more snappy below 2500 rpm. And the > > shifts were MUCH smoother. > I did not see that in a stock variable pitch of any type. That in large part is because the stock SWP control only works at idle and near maximum throttle. That's why I use a simple electronic control that works over all rpm and torque situations. The trans is still a stock SWP. > > Cruising in high gear and low stall mode, the SWP is > > tigher than a fixed converter, so I pick up a couple > > points on gas mileage. > Both a fixed pitch and a variable pitch will be in 1 to 1 > stall at that time. How? Converters still slip some, even at "1:1". That's why the economy guys put in lock up converters, to get that last several percent mileage out of the converter. A SWP in low stall gets part, but not all of that advantage by being a little tighter than a compromise (fixed) conv. Its more important when teamed with a tall gas savng axle ratio. Hard to measure, but my SWP is tight enough overall that I can see the extra 50 rpm slip of hot oil vs cold oil. > > Cruising at 60 mph I want to move ahead a little. > > Touching the gas causes a manifold vacuum drop, > > the SWP goes to high stall and pulls the car ahead. > > Engine rpm may increase by 500, without a gear > > change, and then back, smooth as silk. > And that will eat into gas mileage. Engine power is > required for a torque increase. Correct. So if you keep the SWP in high stall all the time, you would get terrible gas mileage. If its only there 2 % of the time, and the overall setup (tall axle) is saving lots of gas, you are way ahead of a fixed pitch using a less economical ratio axle. > > Going into a corner you might brake, and the SWP goes > > into high stall. Pulling out, you get extra torque to recover > > speed. A few seconds later, you are smoothly back in > > economical low stall. > Braking causes high vacuum, for the foot comes off > the accelerator. The varible pitch would go into high > stall when the accelerator is depressed, dropping > vacuum, coming out of the backside of the curve. Right, with the crude stock control. That's why my electronic control goes to high stall as soon as you hit the brake, then stays there just long enough to get back to speed. > > The original mechanical control won't do it all, I use > > electronics to sense torque and add time delays. > That's the only conceivable way anyone could get > improved performance with a variable pitch. No argument there. > Sorry, but I must stick with fixed pitch converters. You > haven't convinced me. > > Milton Schick > 1964 442 Cutlass > [EMAIL PROTECTED] And then there are smooth SWP shifts at part throttle and high stall. I have received so many comments on this from people riding in my cars. The latest cars do the same thing, using a computer to control engine torque for shifts. In a racer nobody cares. Bruce (hearing Byron Dragway down the road) Roe
