Guest zfan Posted December 16, 2002 Share Posted December 16, 2002 I have a 355 sbc and a built 700r4 tranny with the toggle lock up/non lock up switch. Should I be locked up when racing/launching etc.. I really do not know to much about the overdrive trannies obviously! Oh and I'm running a 2300 B/M stall. Mike Quote Link to comment Share on other sites More sharing options...
Mike C Posted December 16, 2002 Share Posted December 16, 2002 The only time you want to lock up the converter is in top gear (overdrive). With that said, however, you may experiment and find that your car is faster if you lock it up in 2nd and 3rd gear when drag racing unless you have a converter that is so large that when you shift your RPM drops to below the stall point. Or conversely it may run better if you just leave it unlocked. Once you run through the stall speed of the converter you are no longer getting torque multiplication through the converter and the slippage may cost you some horsepower and as a result, MPH. I'm not sure how detrimental that could be to the converter, however. Most TH700 swaps use a converter that is only locked in OD, but I'm sure the 4l60E the computer makes other determinations when considering locking the conveter or not. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted December 16, 2002 Share Posted December 16, 2002 I can give you my experience from a GN/TH200-4R perspective. The Buick Turbo version is controlled by the ECM and locks up in OD at about 45+mph. The ECM does not lock up the converter at WOT so you need a manual switch. I lock mine 2 secs after the 2-3 shift so I can get the maximum MPH in 3rd. Lots of Buicks hit the switch manually at the line and the converter locks up after the 1-2 (it does not lock in 1st). A strong running Buick will gain .2 and 2mph locking up at the line. The engine gets bogged down when it locks up in 2nd but the massive torque pulls it through. Its a catch-22. Locking up the converter does take its toll unless you have an expensive multi-disk converter. It helps that our cars are so light. If you do not lock up you are giving up a little ET/MPH. If you run out of RPMs in 3rd and do not lock up, shifting to OD is also hard on the tranny and results in a massive drop in RPMs. If you are not running out of RPMs in 3rd at the traps, try locking at the line a couple of times then try after 2-3. Evaluate the results and make a decision. Quote Link to comment Share on other sites More sharing options...
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