I have a ton of shift lag between 1 and 2 especially when the cut outs are open. When they are closed, it doesn't have near as much lag. Is this a result of to much loss of backpressure? A lot of people talk that dual 2.5 is to much loss of backpressure. But no-one seems to come up with any facts to back it up. I show top end dyno gains when the cutouts are open, which make me think I am not having a B/P problem.

 

That's interesting. When I got my truck the other day I found that the previous owner had true dual exhaust put on.

I wonder if that has anything to do with the trans. lagging into the next gear. It almost feels like its slipping but, it still shifts hard. I think there might be a Hypertech on there with the shift firmness turned up.

It seems like everyday I find something else with the truck. That's why I bought a used truck though, because I plan on upgrading everything eventually. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Maybe I could weld some block off plates, with 1.5" holes in them, into the exhaust tips to get some more backpressure to test out your theory. <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />

Have you checked the computer with and without the cutouts open? Maybe its a tuning problem when going from open to closed.

John

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Fast4.8:
<strong>I have a ton of shift lag between 1 and 2 especially when the cut outs are open. When they are closed, it doesn't have near as much lag. Is this a result of to much loss of backpressure? A lot of people talk that dual 2.5 is to much loss of backpressure. But no-one seems to come up with any facts to back it up. I show top end dyno gains when the cutouts are open, which make me think I am not having a B/P problem.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I thought not enough back pressure made you lose torque and doesnt really affect upper rpm HP.

 

tq management maybe <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
thats my guess, mine lags bad, and if i drive with tow/haul on it shifts better but still not like i want it to.
my old buick jumped forward on shifts(tci street fighter 400)and usally kicked sideways <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />
now i dont expect it to rip sideways but cant stand the way it shifts now, feels like it falls flat on its face
also kida weary of putinng a shift kit in it being electronic

 

Mine does and it really sux! After atapping it I found that I am getting the max amt of tqm in every shift -10*. <img border="0" title="" alt="[Mad]" src="gr_images/icons/mad.gif" /> Also in one of the logs I had the gear displayed. On the 2-3 shift it showed the change to 3rd then 6 frames later the rpms drop noting a true shift. Tell me that isn't wack! <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Fast4.8:
<strong>I have a ton of shift lag between 1 and 2 especially when the cut outs are open. When they are closed, it doesn't have near as much lag. Is this a result of to much loss of backpressure? A lot of people talk that dual 2.5 is to much loss of backpressure. But no-one seems to come up with any facts to back it up. I show top end dyno gains when the cutouts are open, which make me think I am not having a B/P problem.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">maybe dual 2.5in is too much, especially for a 4.8.when i went up to the muffler shop he highly recommended 2.25in diameter pipes. maybe you should switch to that instead of a single 3".

 

Greg, look no further then the Torque Managment.

Tell me if this makes any sense to you... Torque Managment is a function of the programming that reduces timing for a few tenths of a second, before, during and after the shift. On the fullsize trucks it also pulls timing at low speeds in first gear. (This is why most of you may feel your trucks are faster from a roll.)

This being the case anything that is done to speed up or firm up the shift will make this momentary power reduction more noticable. (Increased line pressure, corvette servos, shift kits..)

Now on to your particular situation... An increased loss of power with the cutout open.

Assume two trucks both operating with 25 degrees total advance. The first truck makes 300hp but during the shift timing drops to 4 degrees total timing. The second truck produces 325hp and drops to the same 4 degrees during the shift. The more powerfull truck is going to lose more power and will therfore have what feels like a slower, softer shift.

We have had great success in reducing the torque managment on the trucks through custom tuning. MTI offers the custom tuning @ $500. This a one-time charge and any future changes will be done at no cost.
<img border="0" alt="[Truck]" title="" src="graemlins/gr_truck.gif" />

<small>[ July 18, 2002, 03:50 PM: Message edited by: MTI Sport Trucks ]</small>

 

I agree with the above since they did mine, but will offer this on the cutouts - yes, you can lose low end torque even with the damned TM neutered with the cutouts open or too open an exhaust, of course you gain at the tail end of the run. One of the advantages to the QTEC fast switch is that the cutouts open in the first 5 seconds of the run, ideally you would connect them with a Hurst line locker for launch - that is if anybody could figure out how to get a Hurst unit mated with the brake system on an '02 truck. <img border="0" title="" alt="[Mad]" src="gr_images/icons/mad.gif" />