Well, I finally got one, a DP...yeah! With 373 gears and 35" tires I have had turbo lag towing and was going to install a wicked wheel. I also can't get on it at all without hitting 25lbs of boost. I remember (Cris I think) saying something about a bigger turbo housing or something like that, that would take care of the lag and handle the pressures thus dropping your boost levels. I have been away for awhile but back now. I appreciate all your help and, as always, thank you.

 

A Wicked Wheel is for turbo surge issues, but it won't really help with turbo lag. The same goes for the ATS compressor housing, it's simply designed to eliminate surge, but it doesn't do anything in regards to real performance.

Also, dropping in a larger turbine housing on the stock turbo can actually increase turbo lag on the bottom end, making your problem worse, not better. As for the 25 psi, I wouldn't worry too much about it. If you were going over 25 psi constantly, then you might eventually run into problems. But the turbo should be ok at 25 psi or less (this is me speaking conservatively, some people have ragged the stock turbo well over 25 psi over and over again. Some have blown the turbo, others just keep on going).

I bought my truck used in 2003. The only mod the previous owner did to the truck was put a lift and bigger tires on it. When I bought it, I lived at lower elevations, so having large tires and the stock 3.73 gearing really wasn't a big deal. I could even tow moderately decent. Sure there was a difference in lag compared to a truck with stock sized tires, but it wasn't anything that was causing a major issue.

Jump to a few years later when I moved to Colorado. I learned that altitude severely increases turbo lag, and just driving my truck around empty was a huge chore. I eventually had to regear and throw in a set of 4.30's in order to give the truck some pep on the bottom end. It was expensive to do, but now my truck is a towing monster.

There is a little bit that Jody can do with tuning to help with lag issues, but the rest of it simply comes from having the gear/tire combo you have that keeps the truck at lower RPM's. You need RPM's to get the turbo to spool up, you simply can't make a whole lot of boost below 1500 RPM's.

Other people have simply adjusted their driving style and learned how to work the throttle on the bottom end. Joe (CSIPSD) runs 37's with 3.73 gearing and does just fine with it. In that respect, it comes down more to personal preference and driving style.

 

I am glad I hit the refresh button before I typed a response. Curtis covered it very well (as he always does). I am running 315"s (35's) with stock gearing and am having no issues other than surging like a big dog when moderately towing, but I am at sea level which as Curtis pointed out, makes a big difference.

 

Curtis your reply is great except now I'm confused about surge and lag. My truck, towing up a grade at low speed (curvey road) will make noises and jerk a little before I shift auto tranny to 2nd. The noise sounds like the turbo is clattering. I have checked the wheel and no slop. This is lag right? A wicked wheel isn't for that? Your comment about keeping above 1500 RPMs makes a lot of sense. I'll work on my style, apparently I let my RPMs drop to much before downshifting. Thanks again for your ecellent reply...I love this forum.

 

well if your hearing "chattering", this is more likely turbo surge. An ATS housing or wicked wheel will cure this.

 

That chatter is surge. On a stock turbo, surge typically happens below or at 1800 RPM's, and when loaded down and/or going uphill. Over time, continued surge can destroy the turbo. Since yours checks out fine, yours isn't damaged yet. But it is best to get rid of the surge, or at least downshift and get out of the surge range. Also since you have larger tires on stock gearing, you are naturally running at lower RPM's than usual. This of course puts you in the surge range more frequently and for a longer duration. So turbo surge is typically worse.

Lag is the amount of time it takes for the turbo to spool up and make boost. Turbos of course are driven by exhaust, and at very low RPM's, you simply don't have enough exhaust gas to power the turbo. Superchargers are another type of forced induction, but they are belt driven. Because they are belt driven, superchargers typically exhibit zero lag, or at least not enough lag to notice on most vehicles. So lag is simply the amount of time it takes to spool the turbo and to see boost.

 

Excellent! I had lag and surge mixed up. Curtis I thank you again and everyone else who piped in with good info. So which do I go with, wicked wheel or ATS housing. You'll probably come back with ATS and is it a relatively easy install?

 

WW is cheaper and the install isn't too bad- WW runs around $100 while an ATS ported shroud housing runs over $400.

 

OK, one more question, sorry to be a pain but I can't help it. Do I open up the waste gate, which way do I turn it and how many 360* turns. Some one had pics of this but I can't find them, thanks.

 

Adjusting the wastegate won't affect surge or lag... but to increase the holding pressure on the wastegate you take the actuator off the arm on the turbo and turn it clockwise to shorten it up. It's easiest to just pull the wastegate solenoid off to do this. Mine was sticky and I had to clamp it in a vice and work end piece back and forth to free it up and get it to spin.

 

Won't adjusting the waste gate help with high boost.

 

You don't want to "open up" the wastegate. Instead you tighten the rod by screwing it in to shorten it. This holds the wastegate closed longer. Think of a wastegate as a designed exhaust leak.

 

No, it only helps to control when the wastegate opens. It crank it down tight.

 

If I use the two letter abbreviation for Pressure Ratio the text gets all chopped up???

You're definitely getting turbo surge and I'll explain why it occurs and how to avoid it. Below is a turbo compressor map which is a graph of a number of parameters including Pressure Ratio on the vertical axis and VAF=Volume Air Flow ft^3/min=cfm on the horizontal axis. The additional overlay of engine RPM lines on this map indicate it's for a gasser application because the maximum VE occurs at 5,000 RPM and for a PSD the VE peaks at about 2,000 RPM, but this is the best map I've found to explain turbo surge.

Note that there's an operating point indicated on this map at Pressure Ratio=2, cfm =570, TCE=60%, and a compressor wheel rpm=105,500. This point is the maximum cfm rating for this compressor. Note that at Pressure Ratio=2 if you reduce the cfm from 570 to 400 you're now operating with a TCE=76% which is a more efficient use of the turbo.

Look along the green line for engine RPM=5,000 at the point where Pressure Ratio=1.8, cfm=200, BP=10 psi and compressor wheel rpm=80,000 rpm. Now assume you start up an increasing grade hill which requires progressively more and more throttle to maintain 5,000 RPM.

As you move up the line for engine RPM=5,000 to the point Pressure Ratio=2.2, cfm=250, BP=15 psi, and compressor wheel rpm=95,000 you're now making more HP to climb the steeper grade at the same 5,000 RPM, but now you've hit the dotted surge limit line and if you press harder on the throttle you'll start hearing the rattling, banging, etc... noise due to compressor stall which is not unlike what a jet engine gets under similar operating conditions. If you allow your turbo to do this it'll eventually wind up in the Hudson river just like the jet did!

If you downshift to the yellow line for engine RPM=6,000 you get more HP due to the increased RPM and you can also move up the RPM=6,000 line to a BP=20 psi for even more HP before once again encountering the dotted surge limit line.



Keep the above compressor map in mind when you look at this graph which is for a OEM GT38 7.3L turbo with a OEM (L99.5) compressor wheel and with a WW (E99) compressor wheel. A Turbonetics T61 is also shown.

Assume you're towing a grade as before and applying more throttle to move along the lavender line for engine RPM=1,800 to increase your HP as required by the increasing grade. When you get to the point Pressure Ratio=2.15 at BP=15 psi you get surge with the stock L99.5 compressor wheel. If you install a WW (E99) compressor wheel you can keep moving up the RPM=1,800 line to a Pressure Ratio=2.5 at a BP=19 psi before encountering surge!



The first graph is for an altitude of 315 ft, but the real grades are out west and the second graph below is for an altitude of 6,000 ft. Note that in this graph the BP scale vs the Pressure Ratio scale is different than in the first graph because at altitude the turbo produces less BP for a given Pressure Ratio.

Considering the same RPM=1,800 example as above, you now hit the surge line at Pressure Ratio=2.1 at BP=11 psi with the stock L99.5 compressor wheel, and at Pressure Ratio=2.5 at BP=15.5 psi with a WW (E99) compressor wheel.



You can also use these graphs to see why you can encounter surge if you apply too much throttle when accelerating from a stop. The lowest RPM curve is the green 1600 line, but if you imagine the other lower RPM lines to the left of that you'll see that it doesn't take much BP to drive the turbo into surge at lower RPM. Even though this surge when starting up too aggressively is a momentary condition the wear and tear on the turbo bearing accumulates.

You can have a little bit of surge and not even realize it. It takes significant surge to make the noises that people report, and for sure this is the most damaging surge condition, but surge comes on gradually in the vicinity of these surge lines, and if you keep pushing it then surge announces itself with the tell tale noises that indicate a higher level of more immediate damage.

 

Ernesteugene, that's an incredable and worthwhile post you spent some time and energy on. You also explained it so any layman (me) can understand. I'm going to try and send you rep points, never have and I'm limited on my computer use. Thanks for the answers and It looks like a WW is in my future, not to mention keeping RPMs up and the right gear. I'm printing this out to keep in my PSD folder, COOL.