Long crank - hot start

[11GS]

Ok, I'm throwing in the towel on this one and hoping the guru's here can help! I've searched the forum and tried some things that have been suggested, such as reducing the "Cranking VE" table from 100 to 80. My "Idle Startup Airflow" for some reason was set to all 138 by the tuner. I tried dropping in factory values and tweaking them but didn't have any noticeable difference so I put the 138's back. It also does not seem to matter if it's 1 minute from shutdown to restart or 15-20 minutes. Car will usually fire right away if I tap the gas while cranking, otherwise it will crank for 5-10 seconds before firing. Cold starts not a problem, starts in 1-2 seconds. Battery is good, starter is strong, grounds are all 100%.

Car is a 2011 C6 GS, manual trans, cam/headers CAI. Cam specs are 113* +3, 235/243, 0.621" intake / 0.624 exhaust. Kooks 1 7/8" LT.

Happy to post a log file of a hot start, please let me know what parameters would be helpful!

[jsllc]

Go back to stock for all values that you do not have to have.

Post your stock tune here as well so people can help.

[11GS]

Go back to stock for all values that you do not have to have.

Post your stock tune here as well so people can help.

Hi jsllc, great point, thanks! Edited my original post with the stock tune. I think I may have already deleted the rear O2's in the stock file but that's it, the rest is factory.

[kevin87turbot]

You'll usually have to increase the cranking airflow on the first couple of columns substantially over stock values. I've never seen one populated with the same value on each cell. I would go back to the stock table and increase the first couple columns by at least a factor of 2. You may still need a little more in the lower cells, but it'll get you in the ballpark.

[jsllc]

This is just math. IF you did not change the displacement then it should run with the same air. The only way it does not is if there is an issue. As for the cam, the overlap creates and issue. Never seen on on the street yet that needed double or could not idle at 750-800. Many times people do this to create choppy idle but it is not required. Usually means bad tune or mechanical issue. Return to stock. Minimize the tuning. It will work

[11GS]

This is just math. IF you did not change the displacement then it should run with the same air. The only way it does not is if there is an issue. As for the cam, the overlap creates and issue. Never seen on on the street yet that needed double or could not idle at 750-800. Many times people do this to create choppy idle but it is not required. Usually means bad tune or mechanical issue. Return to stock. Minimize the tuning. It will work

Thanks again! I went looking for my fuel pressure gauge to see if something is leaking down but I can't seem to find it, must have "lent" it to someone before I moved a couple years ago. Such is life...

It's a built short block (car was cam only, then S/C, then back to cam only) but still stock displacement, save for 0.010" over, and still stock compression ratio.

You're right about the idle RPM etc. Earlier today I changed the spark tables in the lower RPM ranges to 20* across the board, really helped with part throttle drivability and surging. Most of the current tune is actually leftover artifacts from when I first did the cam but new absolutely nothing about tuning, so I had the cam MFR send me a "startup tune" so I could get the car to a tuner, then had it street tuned by a local tuner. So a few hands in this tune. I think I will follow your advice and just tune from the ground up when I get the time. Thanks again!

[kevin87turbot]

This is just math. IF you did not change the displacement then it should run with the same air. The only way it does not is if there is an issue. As for the cam, the overlap creates and issue. Never seen on on the street yet that needed double or could not idle at 750-800. Many times people do this to create choppy idle but it is not required. Usually means bad tune or mechanical issue. Return to stock. Minimize the tuning. It will work

I've found that all stroker combinations need additional cranking airflow, as well as engines that have much larger than stock cams. A cam that has a lot of overlap will drop the cranking compression drastically. They always need more cranking airflow than stock, more idle speed than stock, more idle airflow and usually a little more spark advance during cranking as well.

[jsllc]

I believe stroking changes the displacement unless you have some magic LOL. So you are making my point. Then the math kicks in again. If you changed the volume of the engine by 30% you would change air by the same. Then add for loss in idle rpm overlap. 25% usually covers it. 50% dang sure will. But never had one on the street need that much. Track is different. Those engines only know WOT.

[kevin87turbot]

I was 100% agreeing with you on the need for additional cranking and idle airflow for larger displacement engines.

I was also disagreeing with you needing stock cranking airflow tables on engines with significantly larger than stock cams.

[07GTS]

what i found with mine was less crank timing worked best, the earlier u advance it the less compression it has at that point so if u wait closer to TDC u get a potential better environment to ignite especially when cold, but its also just what your engine likes so try different things