Understanding the Performance Differences: 16V vs 8V Engines

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Discussion Overview

The discussion centers on the performance differences between 16-valve (16V) and 8-valve (8V) engines, specifically focusing on horsepower production and torque characteristics at different RPMs. Participants explore the underlying mechanics, design considerations, and practical implications of engine valve configurations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant seeks a detailed explanation of why 16V engines typically produce more horsepower compared to 8V engines, and why 8V engines tend to produce more torque at lower RPMs.
  • Another participant references an external article to provide additional context on the differences between single overhead cam (SOHC) and double overhead cam (DOHC) valvetrains.
  • A participant highlights the LSx series engine from GM as an example of a two-valve-per-cylinder engine that achieves high power output, suggesting that good performance can be achieved with fewer valves.
  • One participant proposes that the choice between valve configurations is a practical matter related to manufacturability and flow area, explaining how smaller valves can fit more flow area into the available cylinder head space, particularly at high RPMs.
  • Another participant discusses the impact of inlet geometry on torque production, noting that the positioning of the valve can create swirl in the cylinder, enhancing mixture and combustion efficiency at lower RPMs.
  • Variable valve systems are mentioned, with a suggestion that they can optimize flow characteristics by shutting off one inlet at low RPM to induce swirl.

Areas of Agreement / Disagreement

Participants express differing views on the advantages of 16V versus 8V engines, with some supporting the idea that more valves improve performance while others argue for the effectiveness of fewer valves in certain designs. The discussion remains unresolved with multiple competing perspectives on the topic.

Contextual Notes

Participants do not reach a consensus on the exact reasons for performance differences, and the discussion includes various assumptions about engine design and performance characteristics that remain unverified.

karabiner98k
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I want to know exactly why 16V engines produce more HP?
Please explain in detail.
What is the exact reason?
Why usually 8 Valve engines produce more torque lower down the rev range?
 
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Look at the LSx series engine from GM. Two valves per cylinder and they make good power. 400 HPs from 5.7 liters.
 
I thinnk it's a practical matter - manufacturability.

The flow area through which the engine "breathes" would be the circumference of the valve, not its area, times valve lift.

flow area of valve = pi X diameter X height
cylinder head real estate occupied by valve = pi X (diameter/2)^2

Make it simple - look at one 2" valve vs two 1" valves, all having 1/2 " lift..

The two inch valve requires pi square inches of cylinder head real estate, and provides pi square inches of flow area.

The smaller valves provide the same flow area in half the cylinder head real estate.

So, when valve flow area becomes the limit on breathing, which would be at high RPM, switch to more and smaller valves . That way you can fit more flow area into available real estate.

Sound logical?
 
Last edited:
2milehi said:
Look at the LSx series engine from GM. Two valves per cylinder and they make good power. 400 HPs from 5.7 liters.

So what?
The reason for 2 valves per cylinder creating better low down torque, is partially inlet geometry. Typically the valve is off to the side, so when the cylinder fills swirl is generated, allowing for a better mixture and combustion. At high rpm tumble is the dominant flow in cylinder.

Variable valve systems with 4 valves, now shut off 1 inlet at low rpm to induce swirl in cylinder.
 

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