1987 e350 Motorhome, desmogged+EFI, low boost turbo?
TLDR further down**
Ive got a 460 in an e350 1-ton motorhome manufactured 03-1987. GWVR is 11,400 and 4200 lb towing capacity and im running 10,000 lb wet with me and my stuff + 3500 lb car and dolley. Came as non-cat because "heavy duty", carb and smog stuff with a secondary motor oil and trans oil cooler. Running 3.54 gears in dana 70u, c6 trans, and slightly oversized E range tires makes it run 2400-2500 rpm @ 58-64ish mph. The take away is that I'm running well within factory recommendations, highway rpms aren't hateful, and it does well for a big ol' boy. So now I've got the irresistible urge to mess with it.
So far, i have de-smogged, re-timed cam to 0 deg, replaced stock rusted out muffler with 2, 4-inch bullet mufflers stacked together in series, and installed an msd atomic efi with return kit that can supply 530hp. Currently getting 8.5-9mpg on highway at 60mph, which im pretty pleased with considering its shoving a 14000lb shoe box with a 3 speed non OD. The way I drive, it rarely sees >3000 rpm or >65% throttle position.
Runs great at sea level, never wanted for power. But it struggles through the 6000-10000 ft steep roads in the mtns, as would nearly any NA gasser towing with those gears but id like more power. With my ready-for-boost EFI, 3-5psi seems like the most effective and easiest route for me since Ive got some experience with turbos and dont wanna raise RPMs with high flow stuff like a lot of you guys. I believe it should have a low CR based what ive found.
Plan: blow through 5psi (efi is set for it), low mount my non-wastegated Holset HC1 turbo off a 12v 5.9 cummins (500hp flow capacity) and add a big external wastegate, and a scavenger pump for oiling it. I want the wastegate to be big enough so that i can shut turbo down to <2psi if i want.
Nobody can chassis dyno it near me, obviously too big for a car dyno, and the semi and rv dynos near me log data from ecm and need drive-by-wire. But working backwards from injector duty cycle (rough I know) it cruises at 60mph at 15-25% injector duty cycle and 80% IDC is the max recommended before you throw a fault. 80% inj duty = 530 hp i guess, so i suppose it takes roughly (15%-25%/80%*530hp) = 99-165 hp worth of fuel to keep her rolling. What I noticed is that in high altitude, injector duty cycle stays constant vs low altitude (same amount of fuel burnt), but throttle position has to go waaay up which causes the kick down lever to activate and send revs to the moon. AF ratio is held constant thanks to the wide-band o2 sensor, so this tells me its just the thin air. So just force a little air down her throat eh?
**TLDR: "heavy duty" '87 460 previously carbed engine, low rpm towing duty, desmogged and efi'd and I want to sling 5psi of turbo on and here's my questions :
Would EGTs, pistons, exh valves, etc be a concern with everything stock at 5psi? I believe id be under boost most of the time based on my turbo size, and EGTs will go up no matter what with the extra turbo restriction and definitely with more power, but HP output will be pretty flat 95% of the time.
Anyone know if my exh valves are sodium filled or can handle the heat? I can take off valve cover and check stem dia... but i haven't yet.
I can mess with ignition timing, fuel ratios, or a little squirt of alcy/water in intake as needed, but with 5psi and low CR i don't anticipate many problems... or should i? lol
Anything else i should be worried about or should i just do the dang thing?
Any feedback is appreciated, thanks.