No offense but the author of that was very loose with the facts. He makes it sound like a switch-pitch TH400 is the greatest thing since sliced bread. Gosh,I wonder if the fact that he sells them might have something to do with it? Oh,that's right,I see those things used all the time out there.<g> Clint Hooper H&H Custom,owner 1969 El Camino ProTourer 2001 H-D FLHR custom bagger http://dalesplace.com/misc/friends/clint/clint_hooper.htm ----- Original Message ----- From: "mike f" <[EMAIL PROTECTED]>
> The Switch Pitch TH-400 > Summary: > The reasoning behind installing an overdrive > transmission is running a low rear gearing to get off > the line, but still retain manageable RPMs at freeway > cruising speeds. This seems like the best of both > worlds, but this article will examine some reasons why > an overdrive transmission is not always be the best > solution. > > Traditionally GM overdrive transmissions such as the > 700-r4 and the 200-4r were viewed as anemic pieces for > gas sipping transportation appliances. The last > several years have revealed that these transmissions > can be modified to handle significantly more power > then in base configurations. A well-built and properly > adjusted overdrive transmission should be able to > handle around 450 ft/lbs of torque. Is that enough for > the engine combinations that people run in their hot > rods? In many cases the answer is no and I for one, > have been through enough "built" 700-r4s for a > lifetime. > > So what then is the solution? > The solution is the tried and true TH-400, more > specifically the variable-pitch version of the TH-400. > > The variable-pitch, or switch-pitch TH-400 is nothing > new as it has been around since 1965. Originally found > in Buick, Olds, and Cadillac the switch-pitch offers > two stall speeds, a low stall and a high stall. > Applying a positive 12-volt signal to the appropriate > terminal on the transmission case makes the selection > of low or high stall. The high stall gives you the > advantages of torque multiplication to get off the > line with a taller rearend gear and the low stall > decreases slippage for cruising or on the big end of > the track. > > The variable-pitch stator is not the only advantage > that the TH-400 holds over its more modern overdrive > counterparts. A TH-400 will generally cost less then > an overdrive and it can be built to handle some > serious horsepower numbers. The TH-700 and TH-200 also > require a T.V. cable to be installed and adjusted > correctly or serious damage and shifting problems will > result, and getting it correct is often harder then it > seems at first glance. Another advantage of the TH-400 > is a small spread between gears. First lets put some > gearing numbers out there for reference: > > Gear Ratio Comparisons: > > 1st 2nd 3rd 4th > TH 400 2.48 1.48 1.00 > TH 700 3.06 1.63 1.00 0.70 > TH 200 2.74 1.57 1.0 0.67 > > It is clear that the two overdrive transmissions in > the comparison chart have lower first gear ratios as > well as have the advantage of overdrive, but let us > look at the numbers that are hidden between these > ratios. > > Between Gear Gap Comparisons: > > 1st-2nd 2nd-3rd 3rd-4th > TH 400 1.00 0.48 > TH 700 1.43 0.63 0.30 > TH 200 1.17 0.57 0.33 > > Notice the large gaps between gear ratios. The TH-700 > has a particularly nasty gap between 1st and 2nd. In > fact if you combine the 1st-2nd and 2nd-3rd gaps on > the TH-400 you get roughly the same gap as the 1st-2nd > on the 700-r4. The result of this is that your first > gear in the TH-700 may launch you like a rocket, but > the huge gap is going to lug your engine and drop > RPMs, hurting performance. The TH-200 has a more > favorable gear separation then the TH-700, but the > TH-400 still has a slight edge. > > Now to address the flaw in my argument that I am sure > many of you are thinking about. The TH-400 does not > have an overdrive gear and if you don't run an > overdrive then how can you possibly expect to have a > respectable freeway cruising RPM? > > The solution to this is easy, run a taller rearend > gear. I argue that the many hotrods rarely, if ever, > see the drag strip and spend a lot more of their time > on the road. So why then do we put in a low rearend > gear that makes freeway driving unpleasant and limits > out terminal velocity to 115 miles per hour. An > overdrive transmission will make up for our low rear > gearing, but this introduces several problems. > > Overdrive was never intended to be an acceleration > gear, which it is being forced to become if you are > running a deep rearend. > High drive shaft speeds > Running a 4.11 gear with a TH-700 sounds like a good > idea until you consider that with a 275/40R17 tire at > 100 mph your drive shaft is spinning at somewhere in > the neighborhood of 5383 RPM for comparison a TH-400 > with the same tire and a 3.08 rearend gearing will > turn 4034 RPM. The same comparison at 150 mph yields > 8075 for the overdrive versus 6051 for the TH-400. > Spinning the drive shaft that fast takes horsepower > and can have other problems like magnifying the > effects of driveline alignment problems, drive shaft > imbalance, and driveline component wear. > > With the right setup, a switch-pitch TH-400 provides a > viable alternative to the modern overdrive. > > Controlling the converter: > There is a multitude of possible methods for > controlling when and how the converter changes from > high to low stall. Use a delay box to have the > converter go to low stall after you leave the starting > line. An RPM switch could have the converter lock up > once your car is into its power band. Wiring a relay > to the brake switch would allow you to put the > converter in high stall for stoplights in a car with a > radical camshaft. A simple switch can be used to allow > full driver control of the system. For most those who > want to have the most control of their driving > experience this probably the best option. [article on > wiring a switch pitch transmission] > > Where do I get my hands on a switch pitch TH-400? > I bough mine from PAE Enterprises in Texas. They offer > both Chevy and BOP cases for a resonable price. PAE > also sells conversion kits so those of you that > already have a TH-400 are in luck. PAE's contact > information can be found in the sources section of > this article. > > Sources: > How to Work with and Modify the Turbo Hydra-Matic 400 > Transmission > by Ron Sessions > ISBN: 0-87938-267-8 > > P.A.E Enterprises, Inc. > 4401 Turf Rd. Bldg E > El Paso, TX. 79938 > 915.855.6009 > 915.857.4727 -> Tech Line 8-10am and 4-5pm MST M-F > www.paeenterprises.com > > > --- Dan Mascheck <[EMAIL PROTECTED]> wrote: > > > > > > __________________________________ > Start your day with Yahoo! - Make it your home page! > http://www.yahoo.com/r/hs >
