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The Terminator
Engine/Tuning
Cam Question for 03 Cobra
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<blockquote data-quote="MalcolmV8" data-source="post: 15557242" data-attributes="member: 8854"><p>Having been down this road and through a couple sets of cams and multiple re-degreeing of my cams adjusting them I'll toss in my 2 cents.</p><p></p><p>Lopey idle sounds cool and that's where it ends. It drives like crap, it bleeds off boost in power, has reversion and higher IAT2s.</p><p>To define "drives like crap". Pulling off the car can be touchy. Ride the clutch out some. If the clutch grabs to soon it'll buck, hesitate and even back fire if real bad. You can spend some time in the tune playing with fueling and timing and smooth a lot out but you can't fix beyond the mechanical limitations of what the cams are doing.</p><p>To further compound the problem on our cars we have a boost bypass valve which as I've found needs at least 11" of vacuum or so to operate. Lopey cams with a "cool" idle have about 6 ~ 8" of vacuum at idle. That means your bypass valve is partially open or fluttering. This really aggravates the drivability issues as the bypass valve flaps in out and out of boost mode when trying to pull off or even part throttle driving. Heck even cruising down the highway at 70 mph and very lightly moving the gas pedal when you hit that sweet spot you'll see your vacuum/boost gauge fluttering along with your wideband and the jerkyness of the car can be felt by you and passengers. Mildly but you can feel it.</p><p>Your idle will be real sensitive too. Turn the a/c on and it may even stall. Again lots of adjustments in the tune to compensate but only so much can be done.</p><p></p><p>A low spring pressure bypass valve is a bandaid and has its own issues. It's operating at almost 0 vacuum and the rotors of the blower are filled with air when it activates so the car still jerks and shakes with the spike of "boost" as it operates. It's a bit better than stock but still sucks and is annoying.</p><p></p><p>Put a tiny bit of negative overlap in your cams. Doesn't take much, -8 to -10 degrees or so and it'll drive practically like stock. You'll have about 14" of vacuum at idle which is just enough to hold the bypass valve in place even when the engine loads up as the clutch is coming out and you're pulling off. The car will be 100 million times better to drive. You won't bleed off boost when in it hard either. It's a win win. You won't have the crazy lopey or choppy sounding idle but you can still hear the car has cams.</p><p></p><p>Or get the lopey idle that sounds cool and just live with the other stuff lol.</p></blockquote><p></p>
[QUOTE="MalcolmV8, post: 15557242, member: 8854"] Having been down this road and through a couple sets of cams and multiple re-degreeing of my cams adjusting them I'll toss in my 2 cents. Lopey idle sounds cool and that's where it ends. It drives like crap, it bleeds off boost in power, has reversion and higher IAT2s. To define "drives like crap". Pulling off the car can be touchy. Ride the clutch out some. If the clutch grabs to soon it'll buck, hesitate and even back fire if real bad. You can spend some time in the tune playing with fueling and timing and smooth a lot out but you can't fix beyond the mechanical limitations of what the cams are doing. To further compound the problem on our cars we have a boost bypass valve which as I've found needs at least 11" of vacuum or so to operate. Lopey cams with a "cool" idle have about 6 ~ 8" of vacuum at idle. That means your bypass valve is partially open or fluttering. This really aggravates the drivability issues as the bypass valve flaps in out and out of boost mode when trying to pull off or even part throttle driving. Heck even cruising down the highway at 70 mph and very lightly moving the gas pedal when you hit that sweet spot you'll see your vacuum/boost gauge fluttering along with your wideband and the jerkyness of the car can be felt by you and passengers. Mildly but you can feel it. Your idle will be real sensitive too. Turn the a/c on and it may even stall. Again lots of adjustments in the tune to compensate but only so much can be done. A low spring pressure bypass valve is a bandaid and has its own issues. It's operating at almost 0 vacuum and the rotors of the blower are filled with air when it activates so the car still jerks and shakes with the spike of "boost" as it operates. It's a bit better than stock but still sucks and is annoying. Put a tiny bit of negative overlap in your cams. Doesn't take much, -8 to -10 degrees or so and it'll drive practically like stock. You'll have about 14" of vacuum at idle which is just enough to hold the bypass valve in place even when the engine loads up as the clutch is coming out and you're pulling off. The car will be 100 million times better to drive. You won't bleed off boost when in it hard either. It's a win win. You won't have the crazy lopey or choppy sounding idle but you can still hear the car has cams. Or get the lopey idle that sounds cool and just live with the other stuff lol. [/QUOTE]
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