Boost problem/questions

[QWIKWE4]

Went to the track last weekend and noticed that my boost was falling off at the top end of each gear. For example my boost would jump up to 18-19psi and then as the rpm's increased it would fall to about 16-17psi and then jump back up to about 19 after the shift and drop as the rpm's increased again. It does this in every gear. Does anyone have any ideas on what causes this? It is a stock turbo but I cant imagine the stock turbo running out of air on a stock unopened motor especially at only 19psi.

Also I have a THDP on it and the DP does not seal against the DP flange face on the turbo. When you look at the turbo on the car in between the top two bolts on the DP the opening on the DP actually sits higher than the flange face on the turbo creating a gap big enough to put the tip of a pocket screwdriver in and its messing up my wideband readings. Has anyone else experienced this?

 

[RUQWKNF]

I'd bet that, that gap is causing your boost loss. Think about it like this. The wastegate puck is designed to sit flush against the turbine housing wastegate hole and seal this hole. If the pipe is tweaked enough that you have a gap that you can see, I can assure you that the puck is not sitting flush under WOT.
Gotta get that handled with a gasket from RJC and some high temp copper silicone. Also, check your headers and cross over pipe for leaks, as leaks under WOT can also cause a boost loss. Anything that takes away exhaust from the turbine wheel, will cause the boost loss. A wastegate puck that's not sealing properly and or a header/cross over pipe leak. I've also seen worn out or busted wastegate actuators cause similar symptoms as well.
HTH

Patrick

 

[QWIKWE4]

Thanks Patrick, will the RJC DP gasket work with an actuator style wastegate? Does the puck just seal up against the gasket? Or do I have to switch to an external WG? Before I went to the track I took off the headers to weld up some cracks that keep reoccurring. I didnt use any gaskets against the heads but I did use some high temp copper silicone and they seem to be sealing. I think I'll get the gaskets at the head and the down pipe gasket just to be safe. I have the gasket for the turbo/header flange from Full Throttle and was wondering if you have heard of anybody having problems with them sealing? It has the bead in it that seems to flatten out over time causing the turbo to have to be retightened.

I think I might order a new WG actuator as well because the car is running the original 20 year old actuator that is probably not working up to par ust because of age.

 

[RUQWKNF]

Welp, I might be mistaken in thinking it was RJC who had the internal style gasket. The one that he pictures on his site is for external wastegate use only. Someone has a gasket that will work with TH style downpipes. Currently, I do not run a gasket at the downpipe to turbo spot, just liberal use of High Temp Copper RTV and let it cure over night. Also, I run the embossed 3-bolt copper gasket between the turbo and header flange. I use the same High Temp Copper RTV on both sides of the gasket and let it cure over night before starting it up. It's the best way I've found to seal that spot when using the copper 3-bolt gasket and I've tried every gasket that's been made. Solid no fire ring copper, embossed fire ring copper, graphite no fire ring, graphite with fire ring.
It's not a bad idea to change the wastegate, you just need to make sure and tell whoever you order it from what turbo it is for and what compressor cover it has. As, unless the turbo is stock, the bolt pattern used on all the different compressor covers are different than stock.
HTH

Patrick

 

[QWIKWE4]

Thanks Patrick you've been very helpful. I'll try all new gaskets and a new actuator and see what happens.

Thanks