Tuning NASP (Naturally Aspirated) engines.

When it comes to petrol engines you have 2 option, Naturally aspirated or a forced induction unit (Turbocharged or Supercharged). Different people prefer one over the other and can give a cohoerent and passionate answer as to why one is superior. Rather than get into this age old and unresolved argument we will just present tuning tips for each engine type in separate articles. This article is for fans of NASP engines and will look at the tuning options on them.

As a piston moves down the cylinder it creates a vacuum and air is pulled into the engine. The larger the cylinder the greater the volume of air moved and the more power is obtained.  A NASP engine rewards with a smooth power delivery and Torque is available from low revs right through the rev range.

Primarily your aim in tuning a NASP engine is to get more air into the cylinder, this is done by removing restrictions to the air flow in the head and increasing the suck duration of the engine. Duration is handled by the camshaft and a fast road cam will open the valves for longer.

Inside the head you need to focus on polishing and porting, as this allows more air into the cylinder, a 3 angle valve job substantially increases the air flow into the engine and actually improves economy and power.

The air intake in many cars can be restrictive so opening this up and fitting a wider air intake MAF sensor is often the answer. In a carb fed engine the fitting of twin larger throat carbs will also increase the power providing you match the fuel and air to the correct ratio.

When increasing your engines power you will also need to increase the fuelling to match the air flow. Most standard setups can cope with 20% power gains but over this it may start running lean and you will need to look at injectors and uprated fuel pumps.

Balancing and blueprinting will allow you to hit higher rpm limits and this will widen your power band. Honda are masters at creating high revving engines with plenty of power.

There is a practical limit of around 100bhp per Litre when it comes to NASP engines although advances in technology are allowing car makers to exceed this.

Advancing the timing can also be beneficial but care must be taken to avoid pre ignition. Modern ECU controlled fuel injection engines benefit from remaps and you can tighten up the fuel delivery and ignition characteristics over a wide range of load conditions.

Raising the compression ratio of the engine will also allow more power to be extracted but will restrict you to using high octane fuel. This will typically mean higher compression pistons are used but it could be combined with a rebore and stroker kit.

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