having an issue w/rear shocks on my crt.5

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I run the 13mm Ofna front buggy shocks on the back of my e-crt.5. The ones I have came stock with (2) 1.4mm holes in each piston. I went as light as 25wt oil and the rebound was good, but there was too much pack in the whoops causing the rear to bounce around. I bought a Kyosho 13mm piston kit (amain part# XRA358035) and now use the 1.5mm hole pistons with 30 wt oil. The rear is much better both in the bumps and on rebound.

What springs are you using? Do you know the rate?