Cam surging question
Thread Starter
Safety Car
Joined: Aug 2004
Posts: 3,745
Likes: 5
From: Lakewood WA
Cam surging question
I have a RR Stalker cam in my supercharged C6 ZO6 and haven't been able to tune out the low rpm surging in 1st, 2nd, 3rd and 4th gear in the rpm range of 1500 to about 2200. I've increased the timing in that area and increased the minimum idle airflow in that range which has improved the situation, but I haven't eliminated it. Any suggestions?
Instructor
Joined: Apr 2009
Posts: 145
Likes: 0
What are your cam specs?
How much did you increase your timing below 2000 RPM in your main spark table?
How much did you increase your timing below 2000 RPM in your idle spark table?
How much did you increase your timing below 2000 RPM in your coastdown spark table?
What percentage above stock is your minimum airflow?
Everyone's setup is different, but my LS3 with a 242 duration 115 LSA going through 1 7/8 headers and no cats needed about 5 degrees more timing in those cells and below (on average) due to the EGR effect of the cam overlap. Idle minimum airflow needed to be increased almost 40%.
Those changes, and getting the VE and MAF dialed in, got the low end torque and MPG back to right were they were with the stock cam, and removed the surging.
I can not see the supercharger being much of a factor at those lower RPM, but I have never tuned one, so other will know more than I do.
If the cam was similar to mine, combined with the larger stock cam, and larger displacement, a good starting point may be 3 degrees across the whole range in all 3 tables, and 20-30% more idle minimum airflow.
How much did you increase your timing below 2000 RPM in your main spark table?
How much did you increase your timing below 2000 RPM in your idle spark table?
How much did you increase your timing below 2000 RPM in your coastdown spark table?
What percentage above stock is your minimum airflow?
Everyone's setup is different, but my LS3 with a 242 duration 115 LSA going through 1 7/8 headers and no cats needed about 5 degrees more timing in those cells and below (on average) due to the EGR effect of the cam overlap. Idle minimum airflow needed to be increased almost 40%.
Those changes, and getting the VE and MAF dialed in, got the low end torque and MPG back to right were they were with the stock cam, and removed the surging.
I can not see the supercharger being much of a factor at those lower RPM, but I have never tuned one, so other will know more than I do.
If the cam was similar to mine, combined with the larger stock cam, and larger displacement, a good starting point may be 3 degrees across the whole range in all 3 tables, and 20-30% more idle minimum airflow.
Last edited by Amric; Aug 18, 2009 at 04:48 PM.
Burning Brakes
Joined: Mar 2008
Posts: 949
Likes: 0
From: Williamsburg Virginia
Are you sure it is your cam and not your MAF?
After I installed my SC and had it tuned I decided to cut out my radiator shroud for some cooler air and now get the same surge in the RPM range you mention. The LS3 is known to have problems with the MAF with CAI's and I am assuming the Z06 has the same MAF.
After I installed my SC and had it tuned I decided to cut out my radiator shroud for some cooler air and now get the same surge in the RPM range you mention. The LS3 is known to have problems with the MAF with CAI's and I am assuming the Z06 has the same MAF.
Thread Starter
Safety Car
Joined: Aug 2004
Posts: 3,745
Likes: 5
From: Lakewood WA
Pro
Joined: Oct 2005
Posts: 626
Likes: 0
From: UAE / DUBAI
try to search the hptuners forum... there is alot of info about this ..i just order the same cam due it size ( smallish) so i dont get into those problmes ...
and i have to agree ..i have read that both adding timing or subtracting it is one way of solving the problme .....
and i have to agree ..i have read that both adding timing or subtracting it is one way of solving the problme .....
4th Gear
Joined: Aug 2009
Posts: 4
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Former Vendor
Joined: Sep 2009
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It's a combination of many factors, but what you're trying to do when you tune for this is reduce the effects of intake reversion. By reducing timing, you reduce engine torque and that helps somewhat. So does driving in a higher gear (taller ratio). When you increase timing advance, generally the engine will produce more torque and have slightly higher manifold vacuum for a given throttle opening at that engine speed. The effects of intake reversion due to cam timing are generally compounded by the springs in the clutch disc on manuals, and reduced or damped somewhat in auto trans cars by a higher stall converter. Unfortunatley there's no easy answer...you have to tune for the components in your car. Trans type, rear axle ratio, MAF size, head port area and length all affect reversion, so each car is a little different. Tune for maximum refinement for how you drive the car and what parts you've put in it.
Pro
Joined: Apr 2008
Posts: 525
Likes: 1
From: Vancouver BC
It's a combination of many factors, but what you're trying to do when you tune for this is reduce the effects of intake reversion. By reducing timing, you reduce engine torque and that helps somewhat. So does driving in a higher gear (taller ratio). When you increase timing advance, generally the engine will produce more torque and have slightly higher manifold vacuum for a given throttle opening at that engine speed. The effects of intake reversion due to cam timing are generally compounded by the springs in the clutch disc on manuals, and reduced or damped somewhat in auto trans cars by a higher stall converter. Unfortunatley there's no easy answer...you have to tune for the components in your car. Trans type, rear axle ratio, MAF size, head port area and length all affect reversion, so each car is a little different. Tune for maximum refinement for how you drive the car and what parts you've put in it.
Former Vendor
Joined: Sep 2009
Posts: 48
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Not directly, but it does influence it. The tighter the LSA, the worse the reversion becomes. If you have a wider lobe separation, you'll have higher intake vacuum (lower kpa on your data log) and thus a more stable idle. The intake duration and timing greatly affects reversion, for if you close the intake valve later (higher up on the compression stroke), reversion increases as the piston pushes some of the intake air back up through the intake manifold. Cams are a compromise for the performance you wish to achieve from the engine, which is why infinitely-variable valve timing and lift is so desirable. You can have your cake and eat it too.
