Engine "over-cammed"?

[BronzeOnSteelies]

My car has a really lumpy idle so I am assuming one of the previous owners put a high performance cam in it. The car is not far from factory otherwise.

If I take timing out the car hesitates from a stop unless I hit the gas hard, If I put timing in it pings on 93 Octane. Right now I am living with the hesitation.

My mechanic tells me to replace the cam to one with "factory" specs, that the motor wants to run on more vacuum and the cam in it is robbing it of vacuum. The stock cam should have better low end performance vs the mid-range performance of the one that is in the car and that is fine with me. He said the cam in it would really wake up if my car had headers, a higher rpm stall converter, etc. but that is not the route for me.

Do you guys think a cam switch would rid me of the hesitation?

Mark

[firefighter3931]

Mark, if you can outline the whole combination ; stall speed, rear gears etc...

The trick to making engines run properly is tuning. Big cams with more duration and overlap allways respond well to incresed base timing...which you've discovered. 

When you advance the timing at idle you are also advancing the total timing which can create the detonation problems you experience with the added timing at idle. What you need to do is to shorten the mechanical advance in the distributor and possibly adjust the rate of advance....by use of springs on the advance weights. The idea is to get enough timing in at idle to keep it happy but not too much at wide open throttle to send it into detonation.

Generally speaking that means ~36* total timing "all in" by 2800-3000 rpm maximum. 


When you advance the distributor to the point that the engine is happy, how much total advance are you putting into it ? Get a timing light and map out the advance curve in 500 rpm increments starting at idle. What we need to see is how much it is advancing, how fast it's advancing and at what rpm it stops advancing.



Ron

[BronzeOnSteelies]

  Obi-Wan   

  I will work on getting you the data you request.

  It will be a few days.

  Seriously, thanks Ron

  Mark