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Turbo Slant Six

Gill Welding & Fabrication's Dodge D-150 Turbo Slant Six
PBT-D150 Prototype For Power Nation

Turbo Slant Six engines are a dream for many, but they are difficult to plan, build, and create, without proper study. When we started Project Lab Rat we always intended to end up with a forced induction system but hadn't decided which route to go (turbo or supercharger?). Our goals with Lab Rat have always been to test our products and to test new concepts so that the Slant Six could continually develop, and be modernized with new technologies. We've had great success over the years with developing a range of bolt on EFI fuel systems due to Gill Welding & Fabrication's Mark series intakes and Gill Welding & Fabrication's Direct Modified Aussiespeed line of intakes. We decided to move towards turbo kits.

Our reason for choosing turbo kits were numerous, but the highlights were efficiency, A/C, power steering, and TorqStorm. We felt that TorqStorm's unit fit its needs and goals to the point that the supercharger "wheel" didn't need to be reinvented. This is why we started carrying and selling their products. They sell an excellent product that serves our customer's needs well. We decided to move towards our PBT turbo kit, because we knew that there wasn't bolt on options for Slant Six enthusiasts who wanted a turbo system. We stepped into fill this role.

When we built the PBT we had a couple goals in mind. We wanted this turbo kit to be compact. We wanted it to work with a wide range of manifolds. We wanted it to work with RV2 A/C systems (and soon Sanden "Style" 508 systems). We wanted it to work with power steering. We achieved these goals using Lab Rat as a test bed.

Lab Rat's engine was built in a way to show the impacts of a turbo system on a lower budget 225 Slant Six engine build. There aren't special pistons, rods, crank, head, or camshaft. All most everything was purchased from Clegg engines. The point was to get as close to a stock engine rebuild as possible with very minor changes. These changes don't require special parts, but rather take labor and time. These changes were mainly oil system, cylinder head milling, ARP head studs, ARP main studs, and ring gap. The compression ratio is 9.0-9.5:1 (depending on head gasket). The rest of the parts in the engine are stock rebuild components. You will be able to read more about the engine in a separate post.

Lab Rat's engine doesn't have special components, but rather it has stock style components that have been carefully clearance checked, with the exception of the camshaft, which was set, "dot to dot", and not degreed. Lab Rat's engine is not designed for a 400 HP build. Lab Rat's engine is designed to show what you can do with common parts, careful planning, and proper engine control. Lab Rat's first turbo setup is in no way an extreme engine.

Turbo Mockup
Inital PBT-AC Prototype Mockup on Lab Rat using a broken turbo.

Lab Rat always has something changing under the hood.

When it comes to turbo engines there is a lot of variables to think about. Lab Rat is an example of taking stock components and properly controlling them with computerized control. There are many parts used in this build that we would recommend upgrading for longevity and power limits. This build isn't to show you what should be done, but rather what can be done as a test. We do recommend talking to an engine builder about your specific build.

We aren't sure of Lab Rat's safe max HP level yet, as of now our goals were for 230 HP without intercooler and 290 HP with intercooler. Due to the transmission and differential, we won't be shooting for 300 HP+ on Lab Rat. We do have a few upcoming projects that will be in this range, but Lab Rat is about testing the reliability of new applied technologies. Lab Rat is a smooth full featured car that will be continually evolving. The suspension, handling, and ride of Lab Rat have all been radically changed to perform more like a modern vehicle.

For this turbo test we are using a Holset HX35 off of a Dodge Ram, this in an oil cooled turbo that hasn't been modified in any way. This HX35 is bolted to our T3 flange on our PBT system. This turbo isn't the best option efficiency wise for our setup, but it is impressive nonetheless. We chose a HX35 due to its vast availability, cost, and reliability. This HX35 has a wastegate mounted on it, and boosts around 2300 RPM up.

The HX35 is coming in strongly. We performed this test on 93 octane, but less could be used, or greater compression. The turbo is impacting our dynamic compression ratio allowing us to shape an ignition curve that is responsive on the low end and cruise, but that pulls back in higher throttle/ higher RPM areas. We are running between (1.5* : 1) and (1* : 1) ratio of ignition timing reduction to PSI gain. This engine is not intercooled yet and is not currently using a PTP turbo blanket. We found that pulls above 12 PSI resulted in Inlet Air Temperatures that were in the 160F-200F range, which greatly increases the risk of detonation, with our saving grace being our conservative timing. We limited our boost below 12 PSI, and our IAT's stay below 160F, and also implemented the use of timing reduction according to IAT temperatures, which allowed us to increase our timing at the higher boost range and let the Megasquirt pull timing as it sees too much heat.

Our data log above shows our IATs are holding us back from higher power. This is especially relevant to the second panel where you can see the reference ignition timing table in red, and the actual ignition timing in white. With an intercooler we could be more aggressive with our timing and boost pressure, and we would have the added benefit of higher molecular density of a cooler air charge. According to our data logs, we have 90-105 LPH of fuel usage at 4500 RPM, which, puts us very close to our 230 HP goal without intercooler. We will be putting Lab Rat on a dyno in the future.

Our down the road cruising is able to achieve a safe lean burn while attaining higher volumetric efficiency from the wasted combustion energy. The key to fuel economy here is to achieve exactly the HP you need to overcome parasitic drags without producing excess wasted energy. Several factors are at play here such as intake charge density (directly impacted by IAT temps), combustion turbulence, timing control, and much more. There is not a "one size fits all" solution that works best in this scenario, but its best to look at your situation from an efficiency point of few. Where is the energy from the fuel going? Burning fuel creates heat this heat energy drives your pistons, but how much of this energy is wasted? There is an estimated 35-40% of heat energy that moves your pistons through pressure, but what about the rest of the energy? A majority of this heat energy exits through the exhaust and the rest is absorbed through the cooling system. This is largely where turbos come into play, they use part of the wasted heat energy to turn the turbine creating a denser intake air charge on the compressor side. This is similar to a supercharger, but superchargers use some of that original 35-40% heat energy to turn off of the crankshaft making them parasitic. The density of the force inducted charge can allow for higher volumetric efficiency than a naturally aspirated engine under the same load demands. Thus, higher HP/greater efficiency from the RPM. Your fuel economy may not benefit from this however, horsepower requires BTUs which means you need fuel. Though you are producing more HP per RPM by having a higher VE, you now need the fuel to support it. When thinking about fuel economy, your engine and turbo should be sized properly, for the work you intend to do. Talk with your engine builder, and study your turbo compressor maps, well before purchasing, and building parts for your engine.

Lab Rat is seeing cruising timing of 45-50 degrees at 1500-2800 RPM below 65 Kpa. Where your engine will operate best will depend on your combination. Lab Rat is using 14.8-15.5 AFR in this same cruising area. The goal at cruise is torque efficiency, we found with Lab Rat that AFR's above 15.5 typically reduced our torque and required more throttle to maintain the same speeds causing an increase in RPM and fuel consumption. Lab Rat's fuel economy hasn't been fully dialed in yet, but we are seeing averages at 23 MPG with valley floors and flat highways seeing 25-28 MPG. Our best efficiency is typically above 45 MPH and below 70 MPH, which is mostly due to our Camshaft and our Aerodynamics. Lab Rat still has no trunk floor and has no other aero modifications. We will be addressing MPG tests and furtherment in a separate post.


What's next?

What's next for Lab Rat? Lab Rat has plenty of upgrades and experiments on its road map. Here is a short list of things to look forward too:

Lab Rat dyno numbers and videos

Air to liquid intercooler

MPG optimization through aerodynamics

MPG optimization through tuning

MS3X upgrade

Full sequential fuel upgrade

Coil on plug upgrade

Traction control

We also have some other non-Lab Rat, but still Slant Six projects coming up to look for:

Project Warhammer

A race/street Dodge D-150 with a Truck Only PBT. This series will be showing step by step MPFI EFI setup and turbo install. With a goal of a 10 sec or less 1/4 mile.

**Unnamed Torqstorm EFI Project**

This series will show a built high compression Torqstorm Slant Six with EFI and Dyno Numbers.

**Unnamed MPG Project**

This series will be about achieving the best MPG possible in various set circumstances.


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