Big cam idle & part throttle drivability

[ToddO]

First off be easy on me. I've read for 2 days straight. You know the rest.

05 GTO M6

Cam is 244/250 .631/.622 111+3. Heads TFS 225's Ported. Fast 90, 1 7/8 LT's, etc, etc, etc...

I'm working off an old tune from a shop. I since upgrades to the cam listed above and bumped the SCR to 12.0:1. These are the only changes.

I now have HP Tuners and do not have the WB installed yet. All I've done to the tune so far is bump the idle and change the speedo due to gears.

My issues are: Low rpm surging and hesitation. When cruising it seems like it loads up and misses. If I step on it a touch its fine. When slowing down and I push in the clutch, it will drop to about 400 rpm and stumble then returns to commanded idle.

Attached is a 14min log and the current tune. If you could in "laymans terms" point me in he right direction I would greatly appreciate it.

Todd

Attachment 12318

Attachment 12319

[Spectre]

Here's a good thread by 5_liter_eater you may want to read:

http://www.hptuners.com/forum/showthread.php?t=15564

[DSteck]

With 25º of overlap, you're not going to get rid of the bucking easily. There are threads in here about taming big cams with lots of overlap. What I've found works is lowering timing in the main spark advance table under 2000rpm and under 0.32 g/cyl air mass. My cam is 242/254 0.657/0.648 113+4 (so 23º overlap), and even though it's cleaned up a lot, it still has some shuddering/bucking once in a while.

[ToddO]

Anyone else?

[krambo]

So ToddO, how did you do with this? I will be tuning a similar cam and am reading up on all of the good tidbits on this site and would apreciate your input.

[edd1025]

Post your tune or email it to me and I'll take a look at it.

Ed

[NOS500]

The first scan needs some work in the ve table, it's too lean in some areas, is it an sd tune or maf? you can touch up the ve table using the narrow bands and copy - paste special - by 1/2 % in the ve table, this should get you close, most of the cams i've tuned have been in the 240's and this gets the best idle and light throttle trims. Also post your tune