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Cam timing under boost

Discussion in 'Technical Q&A' started by smg2, Jul 21, 2007.

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  1. smg2

    smg2 F1 World Champ
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    #1 smg2, Jul 21, 2007
    Let's make this a thread on the effects of adjusting the cam timing when under boost. Turbo & Supercharger, bear in mind there are a few flavors of each so it would be helpful to state which one you're running. I.e. centrifugal or lysholm.

    Ok, I spent this morning adjusting the cams via those great adjustable pulleys everybody is raving about :D I took out the A/C last night as the compressor needs to be rebuilt. without the A/C and not rushing I can adjust the cams in less than 1hr, that's all 4 and that includes the getting it in the air and back down!

    so the results from the butt dyno are:

    Vortech 9F supercharger, pullied for 20psi @ 8k rpm

    Stock timing events;
    IO 16*
    IC 48*
    EO 50*
    EC 14*
    LSA 107*

    decent range of power 4~8k rpm, picks up around 4k and pulls hard. Idle very lopey and rough, low vacuum. under 4k it feels NA stock. falls flat when engaging 1st from a stop, needs more throttle to keep from stalling.

    Extreem adjustment;
    IO -2*
    IC 56*
    EO 64*
    EC 0*
    LSA 123*
    narrow power window, idle to 3k. purrs at idle, very high vacuum and steady. pulls hard off idle then falls flat @ 3k. not a good setting. pulls GREAT from a stop with no throttle input.

    Aggressive adjustment;
    IO 8*
    IC 56*
    EO 56*
    EC 8*
    LSA 114*

    Best so far, wide power range from idle to 7k rpm. starts to pull hard from 2500 rpm. idle is smoother but has a bit of a fast lope, good vacuum. does not fall flat when engaging 1st from a stop, helps for starting on hills.

    Ignition map is the same for all settings,I'll play around with it some, but will dial it in on the dyno in the next few weeks.
     
  2. snj5

    snj5 F1 World Champ

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    #2 snj5, Jul 21, 2007
    Mark and I had gone through a similar drill in discussion and computer simulation. Naturally as you widen the angle and lessen the overlap there will be less blow down and certainly more low end. As you can tell, your low/moderate overlap at 16 degrees gave the most subjective improvement. With the blower, you are not as worried with the more subtle dynamics of intake pulsing as in a NA car (that ought to set Mark off :) )

    Like you, the question I am facing is what is the best compromise.I think the stock 107 is good for the NA car and what it was designed to do needing a bit better breathing up high - in fact, according to author Allen Bishop in his Ferrari Performance guide he clearly states classic Ferraris were well known for their narrow lobe angles.

    In your application, I would think somewhere around 112 would be good as it is showing in your tests and I am thinking 110 in my NA application in a heavier car needing a bit more robust low end. It's all in where you want to place your power band, and how you ultimately use the car.

    Looking forward to other results!
     
  3. mk e

    mk e F1 World Champ

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    #3 mk e, Jul 22, 2007
    On my first set-up, I found I had to spin the blower way I than I should have to get 10psi. The cams were at the stock US 107 so I try rolling them to the stock Euro 109 but saw no measureable change in boost. I never dyno'd the 107, but at 109 the torque peak was at the euro 5000 not not us 5500 so I left it. If there is any way you can get a boost gauge plumbed into the plenum that would be really interesting pre-dyno data.

    I think the "best" cam timing will depend on what outcome is sought. Peak hp will probably still be with the cams in the 107-110 range as long as the compressor is big enough to deal with the blow-down and still make the target boost.

    I think the widest, most usable power curve will be with the cams in the 112-116 range. I think this is going to be the majic setting for blower/turbo motors with my screw-type liking 112-114 best since it works well down low anyway and your centrifugal/turbo liking 114-116 to help pull up the bottom end up a little more.

    As an aside, I think my new blower will be a 2.8 liter kenne-bell, which is basically a hot-rodded autorotor I guess. I think the re-flowed heads will also help with the blow-down as will re-timing the cams, but I don't want to take any chances of the blower being too small........for the 3rd time.....
     
  4. smg2

    smg2 F1 World Champ
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    #4 smg2, Oct 6, 2007
    bump for now.. more info to come later
     
  5. Artvonne

    Artvonne F1 Veteran

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    Paul
    #5 Artvonne, Oct 9, 2007
    Scott, you have a PM
     
  6. mk e

    mk e F1 World Champ

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    #6 mk e, Oct 10, 2007
    Paul, you aren't going to the dark side(boost) now are you? You're the one who talking me back into the light (natural aspiration)!
     
  7. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
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    #7 Artvonne, Oct 10, 2007
    Nooooooo, I just was going to ask him a question. I will keep an eye on this thread though as its all very interesting.
     

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