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Opinions vary on the improvements seen with a LS6 manifold swap on a stock 2000, but a highly-respected Dallas tuner indicated about 7-8 HP.
I did it, but made some other mods also, so can't document the improvement.
But, if you compare the 2000 to the 2001, the latter has 25 ft/lbs more torque. That's significant.
The changes to the '01 were:
1. Smaller cam with 0.025" less lift.
2. Slightly better air filter lid.
3. larger MAF sensor.
4. Better exhaust manifolds, but 2 additional Pre-cat-converters.
4. LS6 intake manifold.
The lS6 intake had to be a major part of that big torque improvement.
If you did choose the LS2 manifold, also realize you will need the mating 90mm throttle body, the adapter wiring harness to make it work with your stock wire connectors, and finally, some PCM tuning changes. Possibly the fuel rail too (not sure if LS1 rail fits over a LS2 manifold).
In short, definitely not worth the cost or effort.
The LS6 manifold would be a relatively inexpensive and worthwhile upgrade, without any of the adapting work needed. (other than the small coolant lines under the manifold that would needed to be updated to the 01/later style to clear the underside of the manifold)
Opinions vary on the improvements seen with a LS6 manifold swap on a stock 2000, but a highly-respected Dallas tuner indicated about 7-8 HP.
I did it, but made some other mods also, so can't document the improvement.
But, if you compare the 2000 to the 2001, the latter has 25 ft/lbs more torque. That's significant.
The changes to the '01 were:
1. Smaller cam with 0.025" less lift.
2. Slightly better air filter lid.
3. larger MAF sensor.
4. Better exhaust manifolds, but 2 additional Pre-cat-converters.
4. LS6 intake manifold.
The lS6 intake had to be a major part of that big torque improvement.
DG
In addition to increase in torque, and perhaps 7-10hp, you'll also see better throttle response with the LS6 intake on your 2000 C5. The 2000 LS1 engine has the largest camshaft, and therefore stands to gain the most performance of the '97-'00 C5s in an LS1 to LS6 intake manifold swap.