I figure because I have personally done it all the ways listed above (albeit with an HX-35, but same turbine wheel).
One other mod I forgot to mention, is that the backing plate stock is in the way, an only allows the wastegate flapper to open partially. There are aftermarket backing plates, or you can just to a little cutting and welding.
Response is still better with just drilling through then carving out the divide, or going to an open housing of similar size. As long as the manifold before it is still divided. The amount of extra flow through the turbine, in my opinion was not worth the loss of time it took to light, and the amount of boost lost in between shifts.
To give you some actual figures. On my truck, a stock HX-35 would light at 1450rpm, even with the wastegate actuator disconnected so the wastegate was essentially open, it would still slowly climbed to a max of 47psi. With the wastegate wired shut, it would climb to a maximum of 52psi. Both with drive pressures in the 80psi + range.
With the single volute drilled to 15/16th's, and the wastegate set to open at 35psi, it would maintain that with in about 2psi in 1st-3rd, in 4th it would creep to about 40psi, and in 5th, would hit about 42psi. It would still light at 1450rpm. Drive pressures in 1st-3rd were about 37-40psi, in 4th and 5th would skyrocket to 70psi+
With the divide drilled right though, boost would maintain solid at 35-37psi, in all gears, as long as I stayed near that 35-37psi drive pressures stayed close to 1:1 or 37-42psi range, but as soon as I tried for more they took off. It would light at ~1475rpm.
With the divide augured out, and cleaned up, it wouldn't light till 1575rpm, I could push it to ~38psi before drive took off, and it felt lazy between shifts.
I have never seen an open housing internal gate for a Holset of that size before, if you know of one I would gladly purchase it and test it and add it too the list.
Now I have never done this, but I have seen it on the internet
of it being opened up to 40mm, now it took a fair bit of machining to accomplish, and I really don't know if it was worth it.
For the actual time and effort of each step, this is what I would suggest. Modify the back plate, and drill out the single volute and run it. If that is not enough, drill the hole into the second volute. If still not enough, get an external gate.
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Topic: HX40 wastegate (Read 13764 times)