Starting Point

I’ll wind it back a bit before we get to the most extreme modified state we got to on this vehicle, so, for now….

First, as usual when we get a new project in we start with a baseline Dyno Run to get our stock numbers and data. For the L5P these were very different to the usual data we get from the typical big American V8 Diesel’s. The L5P is pretty awesome stock.

After dialling in the Prohub dyno and getting some repeatable runs we a installed a Banks Cold Air Intake. The results were surprising for a cold air intake only, 7HP and 20Nm is pretty cheap power and torque – I need to mention that I wouldn’t recommend a Banks though. The L5P S&B Filters Cold Air Intake is a much better fit and quality, and if I did another L5P for myself – I’d use S&B for sure.

Banks Cold Air Intake L5P

Stage 1. ECU & TCM Remapping Results

There is so much misinformation on the internet about tuning these L5P Duramax’s. Still to this day, the only way of tuning these properly is to exchange the ECM and TCM with HPTuners Modified ones. I just buy new ones for customers because the cost difference is not that great and you don’t have a truck that wont run while the controllers are away getting modified.

The TCM is easy to replace. The ECM on the other hand is a little harder to get to. We found pulling it out from under the wheel arch is easier and quicker.

The gains shown in the graph below and on our L5P Tuning Page shows awesome gains from just tuning the ECM and TCM and leaving everything else stock. And if it were my truck again, in hindsight, I’d consider leaving it here. But it still sounds like a muffled 6 cylinder in this state. Pretty crazy gains of 174HP and 462Nm!

L5P Tuning With Emissions

Banks Intake L5P Chev Duramax
Banks Intake

Stage 2. Tuning With WCFab Turbo Back Downpipe & Dump Back P1 4″ Race Exhaust

Now this is where things start getting crazy with the L5P – the sound and jet turbine acceleration is worth every cent. More on that later.

We installed WCFab’s 3.5″ Intake Horn, 3.5″ Dump from the back of the factory turbo and hard piping both hot and cold side of the intercooler. The Kingsport Grey powder coating is just immaculate – we also did the top coolant pipe for aesthetic reasons only. But it kinda looks factory in a cool way. I’ve seen lime green etc but it just spells trouble during any sort of roadside “inspection”.

Without a topside crawler, which is kind of like an elevated work bench you lay on whilst working, this job would be nearly impossible. If you attempt this in the drive way and you have not done this type of thing before – I would seriously reconsider getting a workshop with experience in these trucks to do the job. Its full on, you will lose grams of skin from every joint, from your broken finger nails, to your shoulders. And without a heavy duty hoist I couldn’t imagine getting it done in a weekend. And you will need a GM diagnostic tool to relearn the immobiliser – you will actually need to do this for the previous stage also.

As you can see from the graphs, this is an awesome upgrade. It will spin the 33 x 12.5 tyres as it changes gears through the 6 speed Allison Transmission. But a word of warning, you will hurt the trans even with moderate abuse with this amount of torque and power. The TCM will detect slip and start to ask the ECM to begin to pull torque to protect itself.

The sound from the MBRP 4″ Full Exhaust is truly satisfying, quiet with just hint of turbo spool when lightly cruising, it wont grab the wrong attention. But let it rip and it will bark so loud people will shit themselves and look around in a panic to see where that sweet growl is coming from.

Fuel consumption is also so much less. It will easily cruise in single number territory, the best I saw in a 100km/hr zone was 7.8L/100k’s. Down from 14’s. But I drive it pretty hard all of the time so normal people would see better numbers.

Towing is just so easy with this upgrade. I mean it loved towing stock, but with 1724Nm now, it would pull a caravan past a tuned 200 or 70 series Toyota with nothing on the back of them.

L5P Tuned WCFab Downpipe

Stage 3. WCFab S369SXE Turbo Upgrade And 60+ Injectors

With our Stage 2 done, we did a 13.4 ET at the drags. If we didn’t have a full tank of juice, removed spare wheel and had the original smaller stock wheels in place, high 12’s would be achievable. But its not in my nature to stop modifying something.

So we went back in and installed WCFab’s S369SXE Turbo Upgrade and a set of their New Exergy 60% Injectors. Again, this isn’t something Id do in the driveway. There’s a lot of work and fiddling around to get the kit to fit up nicely – some aspects of our Right Hand Drive Conversion vehicle didn’t line up with the instructions so we had to be a little innovative to get around some road blocks.

On completion of the installation it was back on the hub dyno for tuning to suit the new set up. Our best numbers were 824HP and 1880Nm. A little rich down low but ran high 17 AFR’s throughout the pull.

Our first road test was pretty amusing, it just accelerates so fast for a truck of this size. Turning off Traction Control has it blazing the rears through 4th T/C locked!

But it wasn’t long before the stock transmission gave up…..

S369SXE Turbo Upgrade
S369SXE Turbo Upgrade

Stage 3. 1000HP Billet Allison Transmission Upgrade

We reached out to LinCo for their advice and we soon had a 1000HP rated new transmission on its way.

Fitting the transmission was a pretty straight forward exercise, we also installed an LDP bypass for the trans cooler which really helps keep the fluid temps down. The hardest part of all this is to make sure all of the left over debris from the old transmission is flushed out before connecting everything back up to the new trans.

While the trans was out we also installed a pair of WCFabs upgraded up-pipes which can withstand higher pressures, temps and flow better. The up-pipes are much easier to get to with the trans out of the vehicle

We installed a SoCal Flexplate and used ARP fasteners to fix it to the engine before fitting up the new trans.

After tuning the truck to suit the built trans, we test drove it again. And with the TCM sensing no slip we couldn’t keep the smiles from our faces. After further testing we weren’t happy with the Suncoast Billet High Stall converter, it was too tight. A quick call to LinCo and a new replacement T/C was on its way.

Now with a 1072 high stall correctly dialled in, this truck has minimal lag and launches easily from the line. We never got to test our new combination at the track but I would conservatively say it would pull mid 12’s.

We will miss this beast…

Thanks to Leon, the guys and LinCO and WCFab.

SoCal Flex Plate L5P
SoCal V Stock
L5P Suncoast Converter
L5P Suncoast Converter

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