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05-24-2004 02:41 PM #1
I had a similar problem with my TH350 when I went to 3.42's. I ended up going to a local tranny shop, and talked to the owner, and expereniced trans guy, told him my problem, And he got me a gear with more teeth to slow it down. It wasn't new, but it was in good shape and it worked. my speedo was 40mph over, and now it's 10, so it's and improvement. seeing how yours is only 20 over to begin with you might be able to get it dead nuts with the right gear.
Also the parts guy at your local GM dealer can be helpful, as they deal with that stuff more than most. try bringing them your old gear, they can probably get you the right one.
worst case scenerio is you live with a 10 over speedo, as long as you know how much over it is, you'll be alright.
Welcome to CHR. I think that you need to hook up your vacuum advance. At part throttle when cruising you have less air and fuel in each cylinder, and the air-fuel mixture is not as densely packed...
MSD 8360 distributor vacuum advance