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Cam Selection

Discussion in '1994-2004 V6 Mustang Tech' started by V6procharged, Dec 26, 2012.

  1. V6procharged

    V6procharged Moderator Staff Member

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    my talk is about turbo cams. making a different thread JT. i was reading through some articles and saw this.

    Lift:
    How much lift should I get in my cam? Well that will depend on your heads' flow characteristics. To choose the correct turbo camshaft, you really need to know how your cylinder heads flow. Reason is if your cylinder head flows X amount of air at X amount of lift, choosing a cam that has a lift much greater then that will gain you nothing except extra heat and premature wear of the valve spring. Airflow through a head reaches a peak as the valve is opened, then starts to drop off as the valve is lifted beyond that peak. Most of this of this will hold true to definition, but with a forced induction motor, valve lift is not as critical since the incoming air is pressurized.

    A good rule of thumb is to select a cam that will lift the valve 20-25% past its peak flow point.

    So be the definition above if your head flows best at 0.500" of lift, use a cam that will lift the valve between 0.600" and 0.625". The reasoning behind this is, if you lift the valve only to its peak flow point, then the valve only flows best when it's wide open. The cycle is brief and would only happen once per stroke. So to benefit from you peak flow the most, you want to lift the valve past its peak. That way the valve will pass its peak flow twice in the cycle. The result is more flow during the opening and closing event of the valve. You do not want to raise the valve much past the peak flow though, or you lose total flow by going too high.
    Calculating the best lift:

    0.500 X 1.20 = 0.600
    0.500 X 1.25 = 0.625

    from here: http://teamzx2.com/archive/index.php/t-2603.html
     
  2. JTsStang

    JTsStang Boosted V6

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    It's all relative. Increasing compression will also move more air out the cyl on the exhaust stroke. Also 2:1 bp is ideal but 3:1 is acceptable for a street car. When I was running the comp 210/218 cam with the 6262 it felt real good, spooled the turbo fast, and pulled to redline. Wish I had got some bp data when that setup was running.

    I dont think you can go wrong with the 218/224 cam. Dave told me .580 is the most you can run with stock valves, so if you want more you'll have to go bigger. Curious to see what you end up with.
     
  3. JTsStang

    JTsStang Boosted V6

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    Brandon, what do stock heads flow? With or without intakes.
     
  4. V6procharged

    V6procharged Moderator Staff Member

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    yea, wish i knew what kind back pressure there was on my turbo setup as well so i could possibly run some overlap to give it a decent idle. it will probably be something a little smaller than the 218/224 actually, but even durations (dk what to call it when its not a split/ reverse split). i wonder why thats all you can run with stock valves. im anxious to get it all setup as well. gotta order a k member and wait for new heads, then spec cam. gotta find some stock untouched heads for a decent price as well.

    kirk posted this on v6p:

    Intake Stock
    0.100 61
    0.200 115
    0.300 165
    0.400 196
    0.500 210
    0.600 218
    0.650 219

    Exhaust
    0.100 44
    0.200 85
    0.300 104
    0.400 119
    0.500 125
    0.600 127

    damn it, it wont keep my spaces between the numbers!!
     

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    Last edited by a moderator: Dec 30, 2012
  5. JTsStang

    JTsStang Boosted V6

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    It may have something to do with seat pressure as to why he would only run .580 with stockers. I have heard 918's are enough to snap stock valves without machining the pockets. Thats why Tom Y says machining is required to run these springs.

    I think 218/218 would work well with your combo. 212/212 would be a little too small for a 4.2 imo. I dont think you need big valves if your goal is 500rwhp, especially if you go with a 218/224 cam. If boost is a concern you could always swap up to a billet 67 or 71mm paired with a 68, make more power with lower boost. My motor is 8.5:1 and would like to run at least 16psi on the street. Thats where this 62mm really screamed on my old motor.
     
  6. V6procharged

    V6procharged Moderator Staff Member

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    possibly so. on the heads i just sold, the pockets are machined down and the springs are installed at 1.76"

    yea, was thinking 216/216 but that will change with the new heads so we will see soon enough i hope. been trying to find somebody that has a decent price on making the valves for me. yea, i know i dont need the bigger valves but if im going all out, ima go all out ;)

    doing a bigger wheel, how does that lower boost and make more power? i figured it would support more boost which would be in turn more power.
     
  7. JTsStang

    JTsStang Boosted V6

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    Bigger turbo will support more volume. The harder you spin that 62mm the more heat it creates, same boost with a 67 will create less heat because it doesnt have to work as hard. The bigger the ex wheel the more volume of exhaust it will flow etc... You should check out squirrel turbo calc and read up on some compressor maps. The 6262 or 6266 is comparable to an s362 borg turbo if you wanted to punch some numers in on that site, it to flow about 70lb/min
     
  8. V6procharged

    V6procharged Moderator Staff Member

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    but with it flowing more volume, wouldnt that create more boost?
     
  9. JTsStang

    JTsStang Boosted V6

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    It will make what ever boost you wg is set to. Think of the smaller ex wheel as a restriction, boost is a measure of restriction, so if you're flowing more air out the exhaust there is less restriction and the compressor is flowing more volume at the same boost setting.

    Ever wonder why Casey made 660rwhp with the 6765, swapped to the s374 at same boost setting and made 826rwhp.