2G Limits of Line Pressure adjustment

[thiazole]

I was just wondering if anyone had any estimates to how far increasing the line pressure in an auto can take you by itself - ie, no valve body modifications, no internal transmission upgrades, just increasing line pressure. I've seen guys running 10s who it seems have done nothing more than increase the line pressure. I'm just curious if anyone has hit a point where the transmission became unreliable and actually needed internal modification to become reliable again, and if so, at what hp/torque level (or 1/4 performance level) did that occur?

 

[the_mork]

What you're saying is mostly correct about hitting 10s with just increased line pressure. The problem is that if you do not increase line pressure correctly you will have excessive line pressure at low throttle shifts and downshifts which will be uncomfortable, unnerving, and hard on transmission parts. Really I suspect that you need some more modification than line pressure to reach those goals such as upgraded end clutches and at some point you're going to shatter the stock diff with wheel hop but getting to the 11s on stock internals otherwise probably isn't too hard as long as you keep the flex plate bolts tight.

 

[thiazole]

My setup is a little complicated, but I probably only drive my car 500 miles on the street every year, anyway. Even so, I use the Road Surge box for full on drag racing and use the TCU with IPT's boost controller when I'm driving around town (I only use lower turbo boost when using the TCU - maybe something at the 300-350whp level). My question wasn't much about the streetability of running a lot of line pressure all the time - more along the line of how much torque will require more than just line pressure for the transmission to hold up. Based on my street logs, my car is easily in the mid 11s already and probably a little faster than that, so yes, I can guarantee that line pressure alone can handle 11s (and this is on a torquey stroker). Also, I roasted the tires pretty good launching at 20psi and didn't wheel hop at all. I used to wheel hop with the manual if I launched too hard (that is what ultimately broke my last manual), but it doesn't seem that my auto is as prone to hopping.

When comparing the logs, the speed sensor spikes very quickly with the manual when blowing the tires, but the auto is more gradual, like a clean bell curve, and I think it is the utter shock to the tires that causes wheel hop more than just spinning them. I should post a screen shot comparison of just the speed sensor log just to show what I'm talking about. I'll see if I can dig up that log that trashed my manual and compare it to a 20psi launch with the auto.

[Auto Merge] Here you go. I couldn't find my wheel hop log, but but you can see what I mean comparing a "good launch" with my old manual and a tire smoking launch with the auto. The auto still went 0-60 a full second faster than the "good launch" with the manual. You can see that the manual instantly shocks the tires loose, then grabs and bogs.

Manual Log (full 1/4 mile):

picture isn't posting, so just follow this link: http://www.dsmtuners.com/gallery/showimage.php?i=108462&c=506

Auto Log (0-80mph):

http://www.dsmtuners.com/gallery/showimage.php?i=108463&c=506

 

[the_mork]

That is a solid part of why the autos hold up better, besides the fact that they don't strip gears at high hp levels. Keep it from hopping and you'll keep the thing around for a while, but even then with enough power you're going to probably break the center diff. The front diff isn't as bad on an awd but if you were fwd you'd be sure to break that too. If you can get the center diff welded you'll be well on your way to a really solid driveline. Sounds like you've got a number of ways working well to control line pressure, personally now that I'm at the point of needing it (and not wanting to break a third transmission) I'm likely to go the route of a chipped tcu or a toggle switch for my line pressure, buying so many boxes seems prohibitively expensive for my budget and cluttered in the cabin.