External Wastegate on Turbine Housing

[nightrain]

I am looking for advice on external wastegates to avoid boost spikes. My combo is in my sig below and my specific issue is a 4-5lb boost spike since installing the FMIC and having to rewhack the actuator mounting to clear the reclocked turbo outlet and the external wastegate port on the turbine side. The CPT66-BB I bought a few years back came with the external wastegate port on the turbine and the stock style actuator rod barely clears the flanged port. I’m using a stock style actuator with a bit heavier spring and a modified bracket.
I’d like to switch to a Tial external wastegate. I used a Deltagate years ago with less hp and smaller turbo, but it locked dead on 19lbs boost; no spike, no creep. So, I figured an external WG would be the way to go. But, I’ve read, and Cotton’s confirmed, that mounting it directly on the turbine housing doesn’t give adequate control. And Cotton’s no longer sells a 3” DP with external WG.
So, does anyone have an experienced opinion on the external wastegate connected directly to the turbine housing as to controllability (spikes, creep)? I’m using an AEM Tru-Boost electronic controller.

As an alternative, I was told that the DP’s (with external WGs) sold these days don’t fit well. Any opinions there?
Thanks!

 

[bison]

It depends on the mass flow potential of the engine. If the engine is swallowing the air the spikes won't be as bad. Mounting on the housing is not ideal and won't be as effective as moving to a different location. I've never had a problem getting a cast wheel 66 turbo with a smaller than gtq turbine under control. All engines I used them on made at least 550whp and trapped in the high 120's at least and had stock wastegates with smaller than 1.1" bypass holes. In some instances I had the opposite problem where the boost dropped as rpm climbed because of the turbo being out of steam


Posted from the TurboBuick.Com mobile app

 

[nightrain]

Thanks for the response, Bison. The only thing I changed, though, from pre to post-FMIC (pre was a Dutt extended SLIC) was the actautor location and, of course, the inlet pipes; now 3". Could it have been very restricted on the inlet side with the Dutt before? I understand there's not much difference between a Dutt extended and an FMIC. Before I only hade 1-2lb spikes running 27-28lbs boost (track). Now I spike to 19-20 before settling at 13-14 on the street. I need it to stay at 19-20 on the street. Same actuator spring, but mounted at a slight angle now. Perhaps it's a geometry thing on the actuator location.

 

[bison]

Thanks for the response, Bison. The only thing I changed, though, from pre to post-FMIC (pre was a Dutt extended SLIC) was the actautor location and, of course, the inlet pipes; now 3". Could it have been very restricted on the inlet side with the Dutt before? I understand there's not much difference between a Dutt extended and an FMIC. Before I only hade 1-2lb spikes running 27-28lbs boost (track). Now I spike to 19-20 before settling at 13-14 on the street. I need it to stay at 19-20 on the street. Same actuator spring, but mounted at a slight angle now. Perhaps it's a geometry thing on the actuator location.

The mass flow is too low at that low boost that's why you see the spikes. You are asking a lot of any wastegate that doesn't have an external pressure source and an increase/decrease controller.


Posted from the TurboBuick.Com mobile app

 

[nightrain]

"External pressure source" being boost signal on the back of an external wastegate (which I don't have) and "increase/decrease controller" being an electronic boost controller (which I have)? Sorry for the slight ignorance here. I just haven't seen this severe of a spike sitution and I've used the AEM controller in both street and track (A and B) settings all last season and had predictable boost levels and only slight spiking. Just trying to figure out what I need to do to get back to that point. Since I changed the actuator location I had to reset the rod length. I just can't recall how much preload I had on it before I made the change (1/8" maybe). I know I had to pull it on to the post with a pair of pliers, so maybe 3/16"-1/4". Could it be as basic as the preload?