10 Best Upgrades to Improve Low-End Torque

Upon delivery of the AC Cobra 427, the 427 Side Oiler was paired with a competition camshaft designed for high-rev operation. Given the ever-present law enforcement, the idea of constantly pushing the tachometer is no longer realistic. Pleasure is no longer found in pure top speed, but in acceleration.

The camshaft installed by Danbury Competition is therefore replaced with a Comp Cams 274H Extreme Energy, in order to favor low-end torque rather than mid-range power.

Here are some complementary solutions to further optimize thrust as low in the rev range as possible:

Solution 1: Install a carburetor spacer

✅ Cost: ~€20–100

✅ Effect: Increases low-end torque by optimizing air/fuel distribution

✅ Easy installation: A few bolts to remove, no need to open the engine

Why is a carburetor spacer one of the best upgrades?

• It increases the height of the intake manifold, improving air/fuel mixture distribution.

• Certain spacers improve cylinder filling at low and mid RPM, delivering more torque from 2,000–3,000 rpm.

• Very effective on a 4-barrel carbureted engine like your Holley 750 double pumper.

Which spacer type to favor low-end torque?

1️⃣ Phenolic spacer (wood, nylon, Bakelite) – ✅ Ideal for your goal

• Reduces heat transfer to the carb → better low-RPM efficiency

• Denser intake charge → stronger throttle response

• Ideal thickness: ½ inch (12 mm) or 1 inch (25 mm)

• Cost: €20–50

2️⃣ Divided spacer – Best compromise for your engine

• Separates primary and secondary circuits, improving low- and mid-range torque

• Ideal for dual-plane intake manifolds (such as an FE Medium Riser)

• Cost: €30–70

3️⃣ Aluminum spacer – Not ideal for low-end torque

• Favors high RPM by increasing plenum volume

• Can increase intake temperature → less low-end torque

Simple installation

1. Remove the carburetor (4 bolts)

2. Install the spacer with new gaskets

3. Reinstall the carburetor and slightly adjust idle speed and mixture

✅ Why this is the best torque-per-euro upgrade

• Very effective from ~1,500–3,500 rpm

• Low cost

• Installs in about 30 minutes

• Fully reversible

Conclusion

For maximum low-end torque at minimal cost, a ½-inch phenolic spacer (divided if possible) is the best investment.

Solution #2: Increase side-pipe backpressure

✅ Cost: €0–50

✅ Effect: Significantly increases torque below 3,000 rpm

✅ Installation: Often reversible

Why it works

• Side pipes are very open, favoring high RPM but reducing low-end torque

• Too little backpressure = poor cylinder filling at low RPM

• A mild restriction improves low-end torque without hurting peak power

How to test for free

1. Temporary restriction (DIY): mesh or perforated disc in the side pipes

2. Removable baffles (~€30–50)

3. Reducer discs (0.5–1 inch) depending on pipe diameter

✅ Why this upgrade makes sense after the spacer

• Low cost

• Immediate effect

• Fully reversible

• No engine teardown

Verdict

Lightly restricting the side pipes is one of the best low-cost ways to gain low-end torque.

Solution #3: Optimize primary throttle blade position (Idle Transfer Slot tuning)

✅ Cost: €0

✅ Effect: Better transition from idle to throttle → more torque at 1,000–2,500 rpm

✅ Installation: Carburetor adjustment

Why it works

• The Holley 750 uses an idle transfer slot

• Incorrect exposure causes hesitation or torque loss

Adjustment

• Transfer slot should appear as a small square (~1 mm)

• Too exposed → rich, torque loss

• Too closed → hesitation

Verdict

Free, effective, and immediately noticeable.

Solution #4: Optimize throttle linkage and pedal travel

✅ Cost: €0

✅ Effect: Faster throttle response, more perceived torque

✅ Installation: Mechanical adjustment

Why it works

• Improper linkage geometry limits throttle opening

• Ensure full throttle at full pedal travel

• Optimize pedal travel and linkage angle (~80–90°)

Verdict

Better throttle control = stronger low-end response.

Solution #5: Modify mechanical ignition advance (MSD 8594)

(See dedicated detailed pages for values.)

Solution #6: Optimize spark plug heat range

✅ Cost: €0–30

✅ Effect: Improved low-RPM combustion and torque

Why it works

• Plugs that are too cold (NGK B8ES) reduce low-RPM efficiency

• One step hotter (NGK B7ES) can improve response

Checks

• Plug color: light brown is ideal

• Gap adjustment (0.8 mm instead of 1 mm) improves low-RPM ignition

Verdict

A simple and effective way to improve low-end torque.

Solution #7: Improve carburetor air supply (cooler air / ram air)

✅ Cost: €0–50

✅ Effect: Denser air = more torque

Why it works

• Cooler air contains more oxygen

• Engine bay air is often hot

Tests

• Temporary run without air filter

• Improve thermal isolation

• DIY fresh-air ducting

Verdict

Cooler air directly improves combustion and torque.

Solution #8: Verify and optimize fuel pressure

✅ Cost: €0–50

✅ Effect: Better air/fuel mixture, more torque

Ideal pressure: 6–7 psi (≈6.5 psi optimal)

Checks

• Regulator adjustment

• Fuel pressure measurement

• Clean or replace fuel filters

Verdict

Correct fuel pressure unlocks the engine’s torque potential.

Solution #9: Check and optimize valve lash

✅ Cost: €0–50

✅ Effect: Improved cylinder filling and low-end torque

Why it works

• Incorrect lash reduces valve lift or compression

Checks

• Measure lash cold

• Typical values:
  
  

  • Intake: 0.018”–0.022”

  • Exhaust: 0.020”–0.024”

• 
  

• Slightly tighter lash can improve low-RPM torque

Verdict

Proper valve adjustment has a major impact on drivability.

Solution #10: Check and optimize intake manifold sealing

✅ Cost: €0–50

✅ Effect: Eliminates torque loss caused by air leaks

Why it works

• Intake leaks cause lean mixtures and hesitation

Tests

• Spray brake cleaner or starter fluid around gasket areas

• Retorque bolts (~25–30 lb-ft in a cross pattern)

• Replace gaskets if needed

Verdict

A perfectly sealed intake ensures maximum low-end torque and smooth operation.