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If you've followed my posts around here, I routinely complain about my truck's throttle/boost lag. I've often wondered (from early on) if the '07's had different cams that emphasized emissions reduction over power/performance. I've managed to tease out some hints that the exhaust valve timing could be MUCH improved, but no real definites.
The purpose is more for information/brainstorming than actually DOING anything about it.
2004 Model Year Changes:
The camshaft lobe separation angle, lobe lift, and duration changed to increase combustion efficiency characteristics (emissions).
Back in the dark ages, Matt Geouge (of Spartan Diesel) and I had a conversation relating to cam timing, and how it related to boost production.
We speculated that Navistar had the exhaust valve opening VERY late, (perhaps even well after BDC) and that's why it was so hard to get additional boost with additional fuel; the actual result is inky black clouds of soot instead of boost because the combustion event was well and truly gone before the exhaust valve opened. In addition, because of the late opening, any residual "oomph" from the hot gas was lost, and the only thing pushing the exhaust (and thus the turbo) was the exhaust stroke of the piston. Looking at engine geometry and math, the end of the Power stroke effectively ends around 135-145 degrees ATDC. There's still heat available, but the engine geometry can't take advantage of it; the math won't let it. Leaving the exhaust valve closed means the heat is dissipated to the cylinder walls and coolant -- completely wasted. Opening the valve much sooner allows the residual heat and pressure to spin the turbo just a little faster.
I've often wondered if making the simple and single change of opening the exhaust valve much sooner (at around 140-160 degrees ATDC-compression) would improve both boost production and throttle response.
I don't much want to fuss with the other cam specs; the engine otherwise runs too well to do much playing otherwise.
Of course, this was back when I actually had sufficient income to actually ponder playing with this... Nowadays it's just mind fodder to keep my mind occupied while going down the road day after day....
Originally Posted by navistarnut
Can one just simply install an early build cam in a later block?
I have no idea
On paper, there's no reason why you can't; I'm not aware of there being any differences year-to-year that would preclude it.
Those numbers are a start, but they don't tell you where any of the actual lift events begin, in relation to crank degrees (that I can tell).
Judging from Colt's website, IF I were doing this, I'd be looking at the Stage-1 or -2 lift numbers with the Stage-4 timings, especially if I could figure out the crank relation.
03-06-2017, 11:05 AM
