I keep hearing all this talk of drive pressures and have found out what is meant by that. Now how would i use these numbers as far as tweaking twins. People talk about setting the primary wastegate at certian pressures and so on. What guide lines should i use for adjusting the wastegates? I would like to learn what all this means and how to use these numbers.

 

Normally, the primary turbo isn't waste-gated.

 

K-31 has an internal wastegate, its around the 74mm inducer size. That a decent size for a primary. I was gonna hook-up the wastegate to be open for the first 10psi of boost so there is no exhaust back pressure/restriction so it doesn't hurt spool-up.

I think that your thinking about the secondary. The trick is to have the exhaust bypass the secondary and put more load onto the primary turbo. Larger wastegate in the secondary allows the primary to load more and push in more air. Depending on the truck, that will regulate the wastegate size. Bigger HP trucks like bigger wastegate sizes. Most street twins run a smaller secondary(turbine A/R sizing is important) for decent spool-up, which choke exhaust/air flow depending on the truck/turbo sizing.

 

I prefer to set the secondary's WG tight, so that all of the available drive HP works on the small compressor first for better spool-up & street manners... when the WG opens, ideally it would bypass all excess drive HP to the primary turbine.

 

Agree with XLR8R.... and so do most turbo engineers.

Get your top turbo spooling to suggested max boost for that turbo and let the bottom catch up when it can. Ideally, you want 50% of the total boost from the Primary.... IMO.

But the amazing thing, to me, about twins on a CTD is that just about any combo of setups and turbos seems to work. Hard to screw it up.

RJ

 

You might have to adjust the length of the lever on the wastegate so that it can open at 25psi and still be tight. I find that once you drop the opening pressure on the wastegate down to 24psi on some turbos, the wastegate is no longer tightly closed, of course this depends on which turbo you use.

As for the K-31 (primary turbo), I was gonna hook-up the wastegate to be open for firstly and then be fully closed at 10psi tightly. This way you'll still have nearly same spool-up as using the turbo in a single application but after 10psi, you'll have fully lite twins.

I have found beniefts in putting in a larger wastegate flapper (drilling out the wastegate turbine hole larger). The primary seems to lite harder and egt's are lower than stock.