Do you need to upgrade the bottom ends (differential) for the 9lbs boost? or will the stock rear end can handle the boosts?

 

Stock rearend is fine as long as you don't dump the clutch too often.

 

you can also check on ebay. i found mine used through a member here.

 

is 550cc rc injectors sufficent enough handle the 9lbs boost? or is it better just to go with the 650 cc?

 

Personally I would go with 650cc injectors - in my opinion it is better to have extra than not enough.

On my last tune with the 3.25" Pulley my tuner saw 9.75psi - he said due to weather conditions I should see another 1-1.5psi under cooler conditions. With a fuel pressure setting at 57psi he said that if I gained that extra 1psi I would have been around 84% duty cycle on the 650cc's. So I honestly think 550's would be too small for 9psi.

Again, this is just my opinion - hopefully a tuner can confirm/deny this!

 

I have an 00' with 78k miles - 4k of which were on a Tech2 7psi Pulley, 2k were on a 9.75psi Pulley. No launching the car, but many many hard gear changes. When we took my differential apart not too long ago everything looked fine - however my axles weren't in the same condition, they went bad.

Non-the-less, I still chose to send out my differential internals to www.percryo.com (Performance Cryogenics) for cryo-treatment!