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Quadrasteer 8.1L Suburban tow rig

2003 Suburban 2500 Quadrasteer camper towing 8.1L 6.0L swap 4L80-E
Overview Gallery Discussion
For transportation, I was thinking of just throwing an old tire in the trailer for the oil pan to sit in, but is an 8.1 pan too deep for that? I have a cradle for 3800s made from 4x4 posts and could whip something similar up if I had the dimensions.
 
Pics or it doesn’t exist


Said no one after 2000

where’s the pictures in this thread?
 
Way cool Luke. I have hp tuners if you need it. Changing pe and getting rid of torque management really wakes these trucks up. Not a crazy amount but enough to be noticed by the seat dyno. Good luck on the 8.1 hunt. Finding one complete with pcm would be the way I would go.
 
I've been debating whether it's best to start with the 8.1 PCM and change settings related to the vehicle or start with the PCM that's already running in this vehicle and change the few tables that are specific to the 8.1. They are the same PCM, after all and I can run the same MAF and some other stuff. I'm curious whether the shift tables are any different, but I haven't found an answer yet. There are bin repositories on the HPtuners website but you can't look at them until you register an MVPI serial.

Of course I'll need the 2nd PCM if the LQ4 finds it's way in another vehicle. Or I could sell it and recoup money since it might be a while before I go down that path.
 
Well, it's kind of crusty, but I'll see how it looks on the inside.

I'm not feeling confident in my engine stand, though. The sticker says 750lb. Rather than brace it up, I might just build a wooden holder.

20200215_142829.jpg

20200215_155741.jpg

At any rate, it's a build thread now.
 
Blue85 said:
Well, it's kind of crusty, but I'll see how it looks on the inside.

I'm not feeling confident in my engine stand, though. The sticker says 750lb. Rather than brace it up, I might just build a wooden holder.

View attachment 329842

View attachment 329843

At any rate, it's a build thread now.
Click to expand...
I used the same stand with my big block. It did hold it, but I braced the front with a 2x4 while transporting and storing it just for safely.
 
Blue85 said:
I've been debating whether it's best to start with the 8.1 PCM and change settings related to the vehicle or start with the PCM that's already running in this vehicle and change the few tables that are specific to the 8.1. They are the same PCM, after all and I can run the same MAF and some other stuff. I'm curious whether the shift tables are any different, but I haven't found an answer yet. There are bin repositories on the HPtuners website but you can't look at them until you register an MVPI serial.

Of course I'll need the 2nd PCM if the LQ4 finds it's way in another vehicle. Or I could sell it and recoup money since it might be a while before I go down that path.
Click to expand...


I’ll download the 8.1 and the 6.0 bins tomorrow if I have time and do a compare.
 
Yes, I was planning to just run it. Interestingly rated at 440ft-lbs, same as the 8.1L. Burb/Av/XL and some vans with 8.1 came with 4L85-E, which is rated for 460, but most seem to think these are all under-rated. 5-speed Allison sounds interesting, but requires body lift, floor mods, extra controller, etc. The advantage of the Allison is lower gears down low (Allison 3rd is the same as 4L8x 2nd), but won't be much different on the highway. Allison .71 OD is arguably worse for towing than 4L8x .75.
 
Should I consider running the factory radiator? It has the right fittings for the transmission lines, but the wrong ones for the radiator hoses. Raylar did this with one of their first conversions and said it works fine. There is some difference between the truck and SUV rads. I've read that the truck one only works with body lift. Anybody know if the shroud and or mounting brackets are different for SUV between BBC and SBC?

6.0L Suburban:
ACDELCO 21653 GM Original Equipment Info
Trans. code 4L80-E; 3.73R(GT4); CORE SIZE 34 IN X 18-1/2IN X 1-1/8IN, CODE AJW,AFA,ACY,ARY,APA,ATW, Transmission Oil Cooler; 4 speed Automatic trans.

8.1L Suburban:
ACDELCO 21729 {#21492, 89019168} GM Original Equipment Info
Trans. code 4L85-E; ENGINE OIL COOLING SYSTEM(KC4); CORE SIZE 19 13/32 X 37-3/4 X 1-3/8; 4 speed Automatic trans.

Silverado:
SPECTRA PREMIUM CU2948
4 speed trans.; w/ 37-13/16 in. x 19-7/16 in. x 1-1/4 in. Core; w/ Engine Oil Cooler; w/ Transmission Oil Cooler; w/ 3/8 Quick Connect Fittings

I suppose I should measure mine to be sure what it is. I have another radiator, but I think it came out of a 6.0L pickup. I've also heard that they went to bigger radiators in 1500s when they switched to e-fans in '04 or '05. Don't know if any change carried through to 2500s.
 
Here's the shift speeds from the 2001 Sub 8.1L and 2007 Sub 6.0L files @jekquistk5 sent me. Both have 3.73 gears in the files. At light and heavy throttle, the 8.1 is upshifted sooner, but there are mid-throttle points where it's shifted later.

shifting 6.0 vs 8.1.jpg

Down low, it doesn't look like a big deal, but it's definitely different for holding 4th gear. Let's say I'm cruising at 70MPH (the fastest I ever tow), in tow/haul. For the 6.0 table, I have to be down at about 32% throttle to get into 4th, but on the 8.1 table, it can be maybe 42%. Likewise, the 6.0 table will kick you out of 4th at 66%, vs. 82% or so on the 8.1. Both of these tables are for 4L80-E ratios.

That's the frustration - to climb even a slight grade it downshifts. Then you have to let way off the throttle to get back into 4th and in the process you lose speed. To try and get the speed back up risks another downshift.
 
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Just mentioned this in the gearing thread in the Garage, but I'd use the factory shift tables as a starting point. Most likely factory setup for the engine/trans you use. I.E. flash the entire 8.1 file in and start from there. Once you get it running/driving you will probable want to change some aspect of shift timing, which is super easy in HpTuners. Even stock they aren't perfect and could use improvement somewhere. Being able to tailor it to your driving/use style is great.
 
Sorry to bump with no real update - just a rant. I've been working on tearing everything down, cleaning stuff up and acquiring needed parts. It looks like a number of things were damaged in engine extraction, like the power steering pump reservoir, power steering dipstick, MAP sensor and EVAP purge solenoid. I've found or ordered replacements for all of that, but the exhaust manifold studs are killing me. Of the 8 on the passenger side, only 4 came out with a wrench. I got 2 more out with the welder, but I've wasted about 20 nuts trying to get the last 2 out. It looks like I'll be grinding flush and drilling. Since 8.1 exhaust manifolds have a split between each cylinder I don't dare run with any missing studs. On my 6.0 and 5.3 I was able to get broken exhaust studs out with the engine in the truck. It's probably a matter of aluminum heads vs. iron. (Yes, they've all been soaking in ATF/acetone for a week.)

The replacement exhaust hardware is either just standard bolts or like $18 each (you know, x 16) for stud and nuts to attach the heat shields. The heat shields I have are no prize. Do I really need them? I will be running the metal shields over the spark plug boots, but I read a lot of stories of 8.1's burning plug wires.
 
Change the oil pressure switch (I think that's what it's called), on the top part of engine, back center. Very tough to change when in the truck (first hand experience)…..
 
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