You asked and we answered! As the final episode of LS vs Coyote 3 concluded, we got a lot of questions and thought it was a great opportunity to answer them all at once. This season of Horsepower Wars, presented by Summit Racing, has already surprised many thinking the LT’s cubic-inch advantage was going to seal the deal. So it’s only natural that many were left wondering what happened.

Q: How did you pick that size/configuration turbo?

A: At the beginning of the shootout – we established that we wanted to create a limited competition. We chose an HPT 76mm billet turbo to go along with E85 fuel for our targeted performance and output (1,300-1,400hp). The selected turbo was a mid-frame (T4) sized turbocharger. The target was primarily because we believe there was a power limitation of the stock aluminum LT block. As we dove farther in the competition, it became more clear that the size of the exhaust turbine was going to be a limiter, and during the dyno test, it became apparent that it was a larger issue than we all had thought regardless of the amazing power levels the engine made. After the dyno test competition was over, HPT built two new turbos for the trucks (large-frame billet 76mm with T6 flanges) for us that we will run at the drag strip that will address this limitation. We are expecting them to produce more power.

Q: What was the budget for each engine?

A: There was no set budget in the rules, but if you’d like a full rundown on what these engines cost you should check out this article. Both engines came in at around $22,000-23,000 in parts not including the core engine cost. With labor it was around $28,000 for both as well (not including core) but you should contact LME and FFRE if you are interested in building something similar for a quote for your exact combination.

Q: Why didn’t you run VCT on the Coyote?

A: We considered it. Ultimately, we wanted both engines and C10s to be controlled by the same EFI system. Because both engines are going into C10s that we will be racing, we felt having additional data and control in one streamlined EFI system (Holley EFI in this case) for things like boost control, shock travel, data logging, flex fuel, etc. made the most sense. Running two stock ECUs, or a stock ECU vs. an aftermarket ECU, or conversely, a different ECU/EFI in the dyno and then a different one in the trucks didn’t seem to make sense. That being said, VCT could have made a difference. At the same time, both engines have variable valve cam timing from the factory, and one could have also made the same argument about direct injection.

We asked Joe Irwin at FFRE on how he thinks it would have affected the dyno test: “The VCT allows you to move the centerlines of the camshafts, which in turn changes the cylinder pressure as well as overlap. The VCT would have allowed us to move the torque and horsepower curve to an area where the turbo was in its efficiency range. At some point we made over 1,200 lb-ft of torque, we just couldn’t turn that into horsepower because of the lack of RPM ability.”

Q: Why did FFRE get 40 dyno runs and LME less than that?

A: Both teams were given an effective “full day” to make power pulls. Each team got to use the dyno room, the dyno time, and dyno cadence of runs at their discretion. Both teams were also given access to CO₂ in order to control the wastegates, which they did. The CO₂ is used to control the wastegate spring (for boost pressure), not to control the atmosphere in the room. We did allow both teams to modify the exhaust systems, but it made no difference in power in either case.

Q: Why was John Mihovetz helping FFRE?

A: John Mihovetz is a well-known Modular racer and engine expert. We didn’t restrict any of the teams from calling anyone or asking anyone for help. At the end of the day, the Horsepower Wars team just wanted to see each engine make as much power as it could. Westech’s owner actually called John, who is just up the street, for some help troubleshooting.

Q: Why was the LT not allowed to run a larger displacement engine, or the Coyote not allowed to run a 5.2?

A: This year, we wanted to see what these engines could do with stock cubic inches. In years past, the LS has had a significant size advantage over the Coyote. We choose to set up the rules as a 5.0 Coyote vs. 5.3 LT combination with turbos from the beginning. Due to the turbo sizing, we are not sure it would have made any difference to the outcome to have allowed more engine displacement. In fact, it might have made the LT engine less efficient.

Q: What RPM did the engines make peak power, and was it what was projected in the builds?

A: Both engines peaked under 7,000rpm and were expected to go over 8,500 rpm by the builders. The T4/backpressure issue limited the dyno pulls. When the exhaust turbine is undersized, the turbo spools up quickly, but the exhaust backpressure is high, so it limits the engine’s ability to be efficient. (So basically, the exhaust is choking the cylinder head, crowding out the clean air as the RPM climbs, and it can’t make more power.)

Q: How much boost and backpressure did each engine make?

A: The Coyote made 28 psi of boost and the LT made 31 psi of boost. On backpressure, the Coyote made 93 pounds of back pressure. That’s a 3:1 ratio. “Anything under 2:1 is considered okay – meaning you have 30 psi of boost, and 60 psi of back pressure,” stated Rick Trunkett of Big 3 Racing who was on hand for the test. “I know it was high because the amount of pressure applied was over 100 psi to keep the wastegate closed.”

Q: What did Mihovetz do that led to such large gains on the Coyote?

A: After the wastegate dump extension didn’t yield any gains, Mihovetz and Joe started discussing the issue when he proposed an interesting theory. “It sounds like you’re losing control of your valvetrain, which is causing the turbo backpressure to spiral out of control.” His suggestion was to run a thinner oil to see if that allowed the hydraulic valvetrain to perform, well, like a hydraulic valvetrain again, and calm the turbo down. Ultimately, that was the call, with backpressure dropping significantly with 5W-30 oil, and again with 5W-20 oil. Once full control of the valvetrain was restored, the engine responded to boost, fuel, and timing changes like you would expect.