Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Monty Takes A Deep Breath

Dave,

It must become a case of deminishing returns on £'s spend as you chase the extra BHP. The real acid test is the performance and enjoyment of the car on the road and it seems you have been extremely successfull.

I've always beleived that straight thru exhausts whilst they can increase high range BHP, they can reduce mid range torque. So I asked AI and it came up with this.

A straight-through exhaust will generally not improve low-end or mid-range torque on a naturally aspirated 2L Duratec engine, and it can actually cause a noticeable loss in low-speed torque and drivability.While a straight-through exhaust or "straight pipe" design decreases restriction to help peak high-RPM horsepower, naturally aspirated engines heavily rely on exhaust gas velocity and scavenging to pull exhaust gases out of the cylinder during valve overlap.

)How It Affects the 2L Duratec Powerband:Low-to-Mid RPM Torque Loss:

When you remove the catalytic converter, resonators, or mufflers and replace them with a wide, unrestricted straight pipe, the exhaust gas velocity drops significantly. The slower-moving exhaust gases fail to create the negative-pressure "scavenging pulse" needed to help empty the cylinder at low engine speeds, leading to weaker acceleration and a loss in daily driveabilty.

High-RPM Horsepower Gains:

If the vehicle is driven at a sustained high-RPM range (such as on a racetrack), the massive volume of moving gas will benefit from the reduced restriction, yielding a minor 2–5% increase in peak horsepower at the very top of the rev range.

How to Actually Improve Torque on a 2L Duratec

:If you want to maximize torque rather than just making the car louder, focus on an engineered exhaust setup:4-2-1 Exhaust Manifold: Upgrading to a quality, matched-length 4-2-1 header design (such as specialized kits from performance retailers like Retroford) merges the primary tubes in pairs to maximize mid-range scavenging pulses, which preserves and increases torque. : Avoid oversized 3-inch exhaust pipes unless the engine is turbocharged or a highly modified, high-compression build. A 2.5-inch system with straight-through mufflers strikes the optimal balance between high flow and high gas velocity. [ECU Remapping: Modifying the exhaust changes the air-to-fuel ratio and cylinder filling efficiency. Pairing hardware upgrades with a tailored ECU tune is essential to lock in performance gains.