So I rounded up an 18.5cm housing after my super-duper intercooler install, figuring it would open up the top end on the truck and that the I/C would absorb the extra heat down low when the 18 wasn't spooling. Wrong I port matched the 18.5 and it actually spooled quite nicely. Problem is I couldn't control boost. Even with lots of timing, I was hitting the peg on my 40psi gauge...too much since I don't have a backup vehicle if (when) the HG takes a dump Soooooo, back to the 12cm w/g I went and, after about 4 hours with the die grinder and a lung or two full of cast iron filings, I think I've got something. I had already drilled through the center divider, so I decided to open up the hole that the wastegate flap covers. Sorry, no pics of that, but the hole is within 1/16'' the diameter of the flap, or almost 1/8'' diameter larger than when I started I also removed some material from the flapper mechanism itself, as well as some material from the backing plate to allow the gate to open farther. I'd say I gained 10-15 degrees of opening with those mods. Combined with the larger hole, I think the overall wastegate flow capacity is up by 20-25%. Again, sorry for no pics, my digi cam was giving me fits. As for the famed 'drilled divider', well I took it to another level after seeing, I think, 'Northslope' do something similar when using a 35/12 for a secondary in twins. The idea was/is to not force the flow through the small divider hole, but rather to encourage a smooth trasition to the gate at the appropriate pressure and to be able to maintain that pressure for the paltry fuel my truck is capable of delivering FWIW, I had just a drilled divider before and could overcome the 'gate and boost beyond the gated setting at WOT. Here's a side-by-side of a port matched 18.5 and the hogged out 12:



And here's a somewhat blurry view of the 'hopefully' better path to the wastegate:



Testing this afternoon has been promising--my insta-spool is still there and even with a maxed pump, ground AFC and a heavy foot, the 12cm will hold me to 25psi without trouble. The 3rd gen IC laughs at my power level. With temps in the mid 30's, the winter front on, flaps open and truck to operating temp, I can give it all she's got in 4th, stay gated at 25psi (rolling smoke pretty good, gonna set the gate to 30psi) and not see the high side of 800* pre turbo

Real world #'s are likely not much over 300rwhp, maybe 650-700tq, but I can use it indefinitely, which is awesome to me. I've got some weight to pull in the coming days/weeks, so I'll keep everyone posted as to how it deals with a load. Cruise @70 mph today was 14psi, 325* pre turbo compared to 600* with the 18

 

That sounds great, but... those numbers sound too low. I know the 3rd gen IC is big and should be very efficient, but with the fuel you've got, you should be getting over 800 pre-turbo IMO. I've got almost all the fuel the pump will give me (with stock non-IC injectors) and I can get 1300* with either the 12cm or 18cm housing. Maybe you could find a different pyrometer probe and swap to confirm the numbers?

If those numbers are correct, however, I'm envious. I'd love to be able to run the truck hard without worrying about EGT's (and I'm NOT turning it down ).

 

I could get 1300 with the 12 in drilled divider form. And, to be fair, the roads were wet today, I couldn't stay in the throttle as long as usual. Plus, my timing is excessive, so I'm paying the price with cylinder pressure to the tune of water running down the front of the head already

 

Interesting, exciting, fun, thanks!

 

When I said the far side of 800 in my original post, I should have been more clear and said approaching 900. Given that was in 4th gear, 1100-ish in 5th shouldn't be too much trouble. I would be suspicious of my pyro (and I do give it a constant 100* benefit of the doubt when towing) but I could easily hit 1500 on a hard run before the I/C.

 

I missed the part about being in 4th.

In that case, it sounds like the truck's running great

I may put my 12cm back on if I can work out a different way to mount the wastegate (I love the sound of the 12), and I'll probably do something like this if I do.

 

...to change feet...I had a pyro wire ever so slightly grounding to the firewall, skewing my readings. It was worse at cruise, which now reads 500 @60mph, much more realistic. Still, pulling my test grade (3/4 mile, 12%-ish) I accelerated from 55 to 70 in 5th and could not hit 900 holding 23psi. What's interesting is that I can't build the same boost as I used to be able to. For those not familiar, the Turbo-Master boost controller works off of exhaust pressure pushing against the wastegate flapper. There's a spring and a threaded rod with a locknut. The tighter the locknut, the more preload on the spring, and thus the more exhaust pressure pushing on the 'gate flap it takes to overcome the spring and open the gate. Anyway, before, about 1/2 of the threads with the locknut would give me 35psi. Now, I'm just about out of threads and am still at 26-27psi, leading me to guess that maybe because the path to the 'gate is smoother, the spring can't hold in the way it was intended. Those with a traditional boost-referenced controller can pretty much disregard this. I've looked for boost leaks, but given good temps, low smoke and excellent power, I'm inclined to think the TM spring won't hold the extra flow. I plan to block the 'gate closed tomorrow to rule out leaks.

 

When you made the port larger you gave the exhaust more surface area to push on.

 

Makes sense...probably why northslope went with the Bank$ big hoss controller. Maybe I'll go spring shopping tomorrow...

 

Yup. Blocked the gate and now have all the boost I need (and more). Gonna look for different springs for the TM, but otherwise, I guess I'm looking for a Bank$ controller....

 

Why not a ball and spring type MBC, with a stock type actuator?

You can adjust the preload on the stock actuator to keep it from opening.

 

I thought most of the stock actuators had the threads crimped? In any event, I don't have one, but will keep my eyes open.