How to Adapt LS Engine to 700R4 or Turbo 350 Transmissions
Can I use a TH350 or 700R4 behind my LS engine?
We get this question all the time, and the answer is very simple. We offer several kits that will help you make this happen. But first, why is it such an issue? The bellhousing bolt pattern is the same, give or take a couple bolts. What’s the difference? Well, the answer lies in the position of the crank flange relative to the bellhousing. On most LS engines, the crank is about .400” shorter, or further “in” relative to the flange where the bellhousing bolts on. This is taken into account on 4L60’s and the like that were made to bolt up behind these engines, but it means that on an earlier transmission, just bolting on a flat flexplate will pull the torque converter almost a half inch too far out on the input shaft.
The solution that we chose to mate the 5.3 and TH350 in our ‘68 C10 project is the dished flexplate and torque converter sleeve illustrated in the video. It even comes with hardware, making it an easy solution to this common problem. The dish in the flexplate will allow the torque converter to sit where it’s supposed to. The sleeve comes into play to make up the difference between the torque converter and the back of the crank. As you can see in the video, it couldn’t be simpler.
Notice that we say that this is a problem on “most” LS engines. It’s worth noting that there were a handful of early Gen III’s, mostly 6.0 truck engines, that had a “long” crank that protruded that extra .400” from the block and will not require the same adapters that a more common LS engine will use. Look out for those as you’re planning your swap.
LS swapping an older car can get expensive. Using the TH350, 700R4, 200-4R, or Powerglide transmission that you already have can really free up some room in your budget for more go-fast goodies!
