350 HP Potential for CIS

[JShadzi at aol.com]

In a message dated 10/5/00 10:00:24 AM Pacific Daylight Time, 
tquattroguy at yahoo.com writes:

<< Can you explain Why you dont want more push out the exhaust valve?  
Wouldn't this decrease lag.  Are you thinking that above 4k RPM at full boost 
it will be to hard on the Turbo?  
 
     I'm pretty sure that Chad Clark ran a 272  (err, wait,  now I seem to 
remember it was a Piper 268 cam).   What is the duration on the Stock MC cam, 
do you remember?  Also, do you mean Elgin is also doing a 272 for you?    
Will you try that in the MC for a bit and see what it does?
  >>

    It is as I explained in that original email, the longer the exh. valve is 
open, the longer the turbo is not pressurizing the combustion chamber.  That 
is why turbo cams typically have less duration, and less overlap, to minimize 
that effect.  
    Granted, at higher RPM's when the turbo is moving a lot of volume thru 
the motor, the cam can tend to be more aggresive at high RPM by sacrificing 
the low RPM response and pressure within the combustion chamber.  It can be 
decieving too, while your boost guage is still saying X amount of boost, the 
actual pressure in the comb. chamber will be much lower with big overlap and 
duration cams.  
    Frankly, a 270+ degree cam can work if it is designed properly by 
increasing the offset and decreasing duration.  The 264/260 cam that I am 
doing for my motor will be a great mid/high range cam, still maintaining the 
strong bottom end of the stock cam, but opening things up vastly at higher 
RPM's.  With my 8.5:1 compression, I have very little lag from 2500 RPM and 
up, the car really drives like a V8 more than a wheasy turboed small 
displacement motor.  But, I miss the high RPM clawing and screaming of my 
272'd coupe GT, so in goes the cam  =)
    I really do not know what a stock MC cam is rated at, but I would guess 
it have very little overlap and a duration of less than 250 degrees.  I may 
try the 272, but I have a feeling I will be very happy with the more turbo 
specific 264/260.  I will let you know though.
Javad