exactly what oil is it?
how many miles on the oil?
it doesn't have much zinc, so i would check to see how much zinc the oil has when it is new, and if it has around the same amount, i would consider using some other oil.
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2. Well, it can cause it to run hotter than it otherwise would, plus it will wear it out faster simply because it is turning over more than it otherwise would with numerically lower gears. I would definitely use a high quality oil.
If it has a posi, jack it up so both rear wheels are off the ground then spin 1 tire 1 full turn and count the driveshaft rotations.
If it has an open diff, jack 1 rear tire off the ground and spin it 2 full turns and count the driveshaft rotations.
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it would help if you told us what your goal is. if 1st gear is useless now, then installing numerically higher gears will make 1st even more useless, so if you want 1st to be more useful, you want numerically lower gears, not higher ones.
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since you have used copper gaskets and had good luck you could certainly try them again. as far as the "compressible" non metal gaskets go, remflex are by far the beast as others have mentioned.
you could also try the aluminum compressible gaskets if you want.
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I am too busy to read thru your 10 page thread although I'm sure there is some very good info there, so in short, did you have obnoxious drone and reduce it by a large amount by simply installing these insets?
Do the inserts come in different sizes?
unfortunately nobody can answer your problem completely because resonance is not always easy to cure in aftermarket systems, however, in general, i have experienced a lot less resonance with the magnaflows over any flowmaster.
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ferrea valves are overkill and not worth paying much more for in a mild street app, but if you are getting a deal on them or already have them then its a different story but you need to match the valve keepers with the retainer angle and the type of retainer groove the valve has.
titanium...