I got a upgraded 4L60e that we put a vac mod in about 3 years ago.

My 2-3 shift on spray hits the rev limiter of 6800, it will go bob, bob, bob, and then shift into 3rd. NA it shifts fine 2-3.

Thinking it was a Shift point and MPH think i took it back to the guy who tuned it and he looked at the files and I am calling for the shift at 6250 and the mph was 65. We tried leading it down to 6000 but it got worse with the bobs as I call it.

He called some gooru's for some information and they are saying since my vac mod shifts off of vaccum in the intake and we are putting all that nitro in the intake its loosing vaccum and thats why it's not shifting..

Just wanted to get someone elses take on it before I put it back to non vac mod.

 

No if anything lower vacume would raise the line pressure , the vaccume mod has nothing to do with shifts only line presure, Now however bear in mind that you will need to allow more time from command to shift on spray. Not just MPH but RPM too. You will either have to lower these or raise the limiter.
You see the time it takes to make the shift is a constant and where lets say 300 rpm may be enough N/A it may take 500 or 600 rpm on spray to do the same thing .

 

Thanks for the info... I wish I had some software I would try it.. I am starting to think the 3-4's are gone also.

I just went out and disconnected the vac mod and plugged both ports to see it it would shift on the bottle, still bobs pretty good. So it maybe time for new packs.

I was watching some vid from about a year ago and it held the shifts so this is the only reason I think the packs are not holding now.. It's been hit and miss all last season if I remember right.

http://s27.photobucket.com/albums/c1...lerCFR2007.flv

Same night...

http://s27.photobucket.com/albums/c1....80passCFR.flv

Next day..
http://s27.photobucket.com/albums/c1...runCFR2007.flv

 

Could be the 3-4 sets getting tired a good posibility