A to Z Posted June 22, 2022 Share Posted June 22, 2022 (edited) Since my car is a 1972 240Z with the Automatic transmission, I have developed a keen interest in how to increase performance using or rather keeping this transmission. The JATCO 3N71B. Used by both Datsun and Mazda in the early days.....early 1970's. While Datsun owners have done next to nothing with them, Mazda owners HAVE. In fact they are still used in Mazda Drag racing circles, and Australia seems to be the place where all levels of performance upgrades are to be found. Being a street car, I was interested in a shift kit to get rid of sloppy shifts and the possibility of a higher stall torque converter to get the car accelerating off the line comparable with a manual trans car fitted with 3:54 gears. So, the Automatic cars in 1972 came with 3:54 gears, and "drive" is a 1:1 ratio, so in Drive it is the same as a manual car in 4th on the interstate. "RB30X, a member on here I found, has been making and selling a "Stgae III shift kit" for these transmissions. You get a heaver duty spring to go inside the valve body and a CD with instructions on the modifications that are necessary to make it work like it really should. He does however note, that he also sells a Stage II kit with a tad bit weaker spring, for those who don't want it to shift "too hard". Hestates that teh modifications actually INCREASE the life of the transmission, as there is less drag! The next point in street car JATCO performance seemed to be Torque Converters. Even in Australia, that is a bit of a challenge. I found a shop, called TCE in Victoria, Australia that will custom make torque converters for our transmission. When I contacted them, they sent me a PDF file fo me to fill out and return to them, so they could look into what I would need for my individual setup. My thought process as of right now, is to use the 3:54 gears in the rear, because If I go with a lower gear set such as 3:90 or 4:11, the cruising RPM's in Drive are going to be awful. The one option is to find the rare 1984 year model only MAXIMA Automatic the "4"N71B. The trans is the same but has an overdrive for the highway. 1985 and onward, are electronic, not old school juice box controlled, and for an old Z car, you can't use the electronic ones, so, you have to find the trans, and also use the engine flex plate for that transmission and the crankshaft spacers. In short, A LOT of work and money. The 240Z at least is light enough, that 3:54's I believe will work, and acceleration with the shfit kit and torque converter may be the way to go. TCE asks for information on the car. One of the things they need are the came specs. Stock cam spec's? Welll they change from car to car 1970-1973 used a Nissan A cam. A google search got me this cool page that breaks it down and compares to aftermarket grinds: www.atlanticz.ca/zclub/techtips/cam/index.htm 1970-1973 "A" cam= .409 lift, 248 Duration, 109 degrees lobe separation, BTW. I will get a quote back from TCE I hope soon, and will add that to this writeup. You CAN make the auto work with the L series engine without going to a Chevy Turbo 350 with the adaptor kit! I will post a copy of the sheet I filled out which gives some of the critical info ont he car they ask for. Here is a link to get the shift kit if needed. If it doesn't work, go find him, "BR30X" on HybridZ. VL Turbo Commodore Nissan Datsun Jatco Automatic Shift Kit Servic | Engine, Engine Parts & Transmission | Gumtree Australia Gladstone City - Gladstone | 1021151782 Also, I have attached some relevant pics. The torque curves are useful in that TCE and the owner need to be able to see where is the optimum RPM for stall speeds etc. These are for my car, a stock L24 Automatic, in a 1972 240Z. To check your cars torque curve, if still stock, go to Google, type in your car, i.e. "1972 240Z Automatic Torque Curve" and the first site, it's the one to select ..."Automobile-Catalog". Cheers! TCE Hi Stall Specification sheet 2020.pdf Edited June 22, 2022 by A to Z Quote Link to comment Share on other sites More sharing options...
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