Myles_SR20 0 Posted March 20, 2017 Hey guys, recently took my car to the tuner after my rebuild. The cars a s14 sr20det 9.0 comp with a t28 on 14psi. He started to tune it but realised it wasnt coming on full boost until 4000rpm and it should be there by 3250-3500rpm. Any ideas what would make it lag this much? He mentioned it may be the vtc gear stuck or the cat being blocked. Seems really odd Share this post Link to post Share on other sites
Scotties15 14 Posted March 20, 2017 Vct stuck ? Cas properly timed or aligned? Blocked cat or restrictive exhaust yes possible. Could also be split cooler pipe work. Anything really. Including the tune. Share this post Link to post Share on other sites
pmod 261 Posted March 20, 2017 Are you sure the wastegate isn't stuck open to some degree? That will kill response. Share this post Link to post Share on other sites
chris_c30 3 Posted March 21, 2017 Pull the exhaust off before the cat, that would rule one problem out Share this post Link to post Share on other sites
Myles_SR20 0 Posted March 21, 2017 (edited) Vct stuck ? Cas properly timed or aligned? Blocked cat or restrictive exhaust yes possible. Could also be split cooler pipe work. Anything really. Including the tune. Yeah Ive heard of a vct gear wearing out and ticking but never stuck in the retarded position... Ive aligned the cas correctly, checked multiple times before fitting the rocker cover. I will have to try putting the back pressure gauge on or removing the exhaust. But was told it wouldnt even make 14psi boost if it was blocked? Just made a boost leak tester, will have to try it out this arvo. There was a crack in the turbine housing where the wastegate flapper sealed but didnt think it would make that much of a difference?? Edited March 21, 2017 by Myles_SR20 Share this post Link to post Share on other sites
wrmdma 0 Posted March 21, 2017 (edited) Can confirm wastegate leak will lead to a very bad time. Fixed my t28bb's kowabunga actuator preload by a couple mm and went from 16psi at 4500rpm to 16psi at 3500rpm plus way better transient response. Prior to finding that I checked for boost leaks, dead vtc, collapsed cat, knock sensor etc. If that crack has enlarged near your wastegate then there's a chance it could be replicating the same effect. Edited March 21, 2017 by wrmdma Share this post Link to post Share on other sites
Scotties15 14 Posted March 21, 2017 Yeah exhaust leak and actuator problems will cause issues. And same with the crack if its big enuf. I have a fucked VCT and still in by 4000 with gtx2876 and 260/12 cams. Wouldn't think it's the issue. Vct won't retard anything. Just make down low a bit sluggish if worn out. And rattle like mofo. Also check for bolt tightness on turbo, manifold, dump pipe etc etc. Share this post Link to post Share on other sites
Scotties15 14 Posted March 21, 2017 Manual boost controller? Share this post Link to post Share on other sites
blingcommander 278 Posted March 21, 2017 Yep. Cracked housing is the issue. Had one that did the same. Was shit as Share this post Link to post Share on other sites
Myles_SR20 0 Posted March 22, 2017 Yeah I have a manual boost controller. The crack is only about 5mm long, so not very big. Share this post Link to post Share on other sites
