Wes said:
Hmm, having kind of the same problem on my friend's truck. We took the wastegate off and pressurized it with an air compressor. It did open right around 18psi. However the base boost we're getting is 10psi!! What base psi are you getting with the 18psi spring?
Also I've read that it's tricky to get that wastegate back together, are you going to do it yourself? I'd like to know what results you get with the 20 spring.
FWIW.. Ive learned from ppl on here and my own experience tinkering with my ext WG that the spring rating isnt gonna always give you the same base boost. As in a 18lb spring might give you 10 psi on one build up vs getting 15+ on another.
Seems that exh back pressure has a lot to do with it if I understand it right. The more back pressure you have (say stock manifolds/xover vs headers/dump) the more force thre is trying to push the WG open along with the psi from the intake that is pushing against the diaphram inside the WG actuator.
On my external it came with a 9lb spring. I could get 9psi base boost but could only make a max of 20psi due to the back pressure in the exhaust blowing the WG open according to the ppl I talked to. I switched to a 14lb (might be 15. Id hafta check) spring but only got 13psi base boost. This was due to the back pressure in the manifolds/exh housing/etc getting too high at the upper RPM range and forcing the WG open a couple of psi early. Least thats the way it was splained to me or at least the way I understood it.
IMO if you only get say 14psi on a 18psi spring (base boost) then you may actually have to run a even heavier spring to achieve that 18psi with a particular combos exh restriction.
Reduce or take the exhaust restriction(s) out with that same "higher" spring and sweeeet daddy mommy britches!!! Look the hell out cause you'll end up with more boost than you know what to do with.
Correct me if Im wrong but thats the way I hear'ed it. :wink: