Before I explain how our mods calculator can be used to design staged upgrades for your car, let me first start by explaining the basic premise behind 99.99% of all engine and performance modifications.

Modifications in general fall under 3 basic categories:

1- Raw Power

2- Engine Efficiency

3- Forced Induction

1- Raw power scales linearly with both rpm and displacement pretty much. Raise your peak power rpm by 20% and you’ve gained about 20% horsepower, increase your displacement by 20% and you’ve gained another 20% over that….

2- Engine efficiency has to do with making more power out of the same displacement at the exact same rpm. If you were making 300hp @ 6000 rpm from a 3.6 liter V6 and with bolt ons you are now making 330hp @ the same exact rpm point with the same exact displacement, then that means that your engine efficiency has increased by 10% over stock.

When it comes to making more power at the same rpm from the same displacement engine, one of the greatest tools to doing so is increasing your combustion pressure at that rpm point… this includes higher compression ratios, ported cylinder heads, later closing intake valve timing, ignition timing advance …etc

3- Forced induction is focused on significantly increasing the air charge density over what the engine would normally breathe. This includes turbochargers, superchargers, nitrous oxide, oxygenated fuels, and ram air intake systems on cars or bikes that will see speeds over 160 miles per hour.

I can spend hours detailing each of these three aspects of engine performance but the bottom line is this:

Most bolt on engine modifications grossly over-estimate the amount of power your engine can make. This is primarily a marketing ploy used by parts suppliers.

Here’s an example, let’s assume that for your car:

  • An intake makes a peak gain of 6 horsepower @ 3000 rpm and no hp gains at 4500 or 6000 rpm
  • An exhaust makes a peak gain of 6 horsepower @ 4500 rpm and no hp gain at 3000 or  6000 rpm
  • An aftermarket header makes a peak gain of 6 horsepower @ 6000 rpm but no hp gains @ 3000 or 4500 rpm

Some salesmen will happily sell you this combo package of intake, header and exhaust as an +18 hp package… when in fact what you will get after installing all 3 parts is only a 6 hp gain at peak.

The logic behind these modifications can be distilled down mathematically as follows:

1- OEM engine manufacturers do leave some engine efficiency untapped on the table because they have to comply with noise standards that require them to use quieter intake and exhaust systems. They also typically design their resonance tuning auxiliaries such as intake and exhaust manifolds to give the engine a volumetric efficiency boost near peak torque to improve engine drive-ability rather than near red-line (which would improve straight line acceleration).

The best you could hope for here is that the manufacturer has left some 10 to 15% volumetric efficiency untapped in the engine. What’s even worse, is that as time goes on, as emissions become more stringent, as manufacturers downsize engines more and more, while all the time trying to squeeze more and more power out of them, the amount of ‘margin’ they leave untapped on the table shrinks because they now need an engine which is both 20% smaller in displacement and produces the same horsepower as last year’s model… the result is an engine that is designed to be 20% more efficient from the get go with less tuning margin there.

2- There is some performance gain to be found by taking peak power from the rpm that it occurs in now, to red-line. The amount of gain here has to do with how big that gap is between current peak power and red-line.

To illustrate, let me give you an example …

My friend used to own a 1995 naturally aspirated Toyota Supra which produced about 220 horsepower at 6000 rpm from an in-line 6 cylinder that has a 6800 rpm red-line.

Dividing 6800 by 6000 we get 1.13 or a 13% potential increase in power if this engine were to make peak power at red-line rather than at 6000 rpm.

At the same time let’s assume that Toyota had done a horrible job of getting power out of its flagship sports car and had left 15% efficiency wasted in the engine that can be ‘harnessed’ back simply by applying the basic intake / header / exhaust …etc bolt ons

The expected bolt on power level for this car would then be:

Stock power * potential gain from raising peak power rpm * potential efficiency gain

Remember we are not changing the compression ratio on this engine, we are not porting the head, we are not increasing the displacement with a stroker kit or over bore pistons, and we are not using nitrous or turbos or superchargers… we are simply applying bolt on mods externally and tuning.

220 hp * 1.13  * 1.15 = 285 horsepower

That means the best you could hope to gain out of this engine, if you did all the external modifications possible including an intake, an intake manifold optimized for 6800 rpm, a header optimized for 6800 rpm, a camshaft with the proper duration for 6800 rpm and enough lift to support 285horsepower worth of air flow at that lift level with the current head …etc is going to be no more than 285 horsepower.

Not knowing this at the time (this is some 6 years in the past) and not having the mods calculator that we have today, he was somewhat tricked into buying a ’300 horsepower’ advertised bolt on package that included:

  • K&N replacement cone filter (on the stock intake pipe)
  • Aftermarket Shorty 6-1 header
  • Full header back exhaust
  • Apexi SAFC for fuel tuning
  • Lightweight accessory pulleys

Notice that this combination of modifications does not address two very important RPM targeting modifications which are the OEM intake manifold and the factory camshaft (which we already know runs out of duration at 6000 rpm which is why stock power occurs at 6000 rpm).

Furthermore, keep in mind that one of the main modifications towards increasing compression pressure (and thus volumetric efficiency) on a naturally aspirated car is going to come from a longer duration intake camshaft with a later IC (Intake valve Closing) event for better cylinder filling and higher compression pressures, is also missing from that list.

Knowing all of this, I was not surprised to see that although the car was faster and more responsive … it still struggled to make power above 6000 rpm, and the claim of 300 horsepower, let alone our calculated conservative figure of 285 horsepower were both mirages that were never going to be seen with this list of modifications.

The mods calculator built into our horsepower calculator is a conservative calculator that helps you understand weather or not these manufacturers and part supplier claims are true or a hoax.

I have designed the horsepower calculator to tell you two very important figures:

1- Your stock volumetric efficiency is _ _ . _ %  (for example 85% for the Supra 2jzge engine which is on the upper range for engines of that era).

2- The maximum bolt-ons power you can expect from your engine (by taking power from the current peak out to red-line, and assuming no gain in VE) is going to be _ _ _ hp (248 horsepower in the Supra’s example).

Having these two figures let’s you know that:

1- My engine efficiency is already high for the technology that comes in that era of engines and that there is no way I’m going to gain 17% volumetric efficiency without radically revising the engine design (including head design, and combustion chamber design).

2- If the maximum bolt on power I can expect without a serious boost in VE is going to 248 hp, and if that horsepower is going to require a new intake manifold , exhaust manifold, and camshaft all targeting 6800 rpm… then there is no way this kit offered to me right here is going to make it’s claimed 300 hp…

Before you start attacking me and flooding my email box…

I’m not saying that you can’t build a 300 horsepower naturally aspirated 2jzge. However, I am saying that it will NOT happen at 3.0 liters of displacement, with a stock 9.6:1 compression ratio, at a stock 6000 rpm…

Build a 3.4 liter stroker with a 12:1 compression ratio breathing happily to 7500 rpm and you can have a cool 350 horsepower naturally aspirated engine…

Which brings us back full circle to the concept of  staged upgrades and how the mods calculator works…

Using the mods calculator you can design a staged upgrade approach:

Stage 1: A little bit of fun

Stage 2: Maxing out what you currently have to work with

Stage 3: Shoot for the moon

Stage 1:

When running a stage 1 calculation, you are basically telling the calculator that you will not be investing in a camshaft or intake manifold upgrade. In this stage, the calculator will basically help you to identify bottle necks in your intake & exhaust system at your current power level.

The question it answers:

At my current power level, what can I do to maximize the response and fun of my engine?

Going back to the Supra example with 220hp at 6000 rpm. At that power level and at that rpm, the horsepower calculator can tell you what the ideal intake, throttle body, header, and exhaust system dimensions should be.

By comparing these dimensions to what is factory equipped on the car, you can easily identify and unlock the most ‘bang for the buck’ modifications on the platform.

Power gains in this stage are modest but also cheap… and since we’re identifying and unlocking bottle necks in the system we usually get back our investment in the form of increased mileage and peppier response.

Stage 2: For a stage 2 calculation you are basically telling the horsepower calculator that you are willing to invest in a camshaft or new intake manifold. That you are willing to make more power and tune for that power …

The question it answers at this stage is basically:

How do I maximize the potential of this engine by taking power out to red-line … using only bolt ons (ie with out raising my compression ratio or changing my displacement).

This is the kind of modification stage that most enthusiasts are willing to go to. In this stage you can gain a health 10 to 13% in power over stock figures depending on how big the gap is between your current peak power RPM and your engine’s red-line.

The calculator in this case will come back with a complete list of recommended parts including:

  • Intake & Exhaust manifold dimensions supporting your power goal (worth of flow) and with resonance tuning targeting your red-line (which will become your new peak power rpm).
  • Camshaft lift & duration specifications to match your new target rpm and power levels
  • Cylinder head port flow levels (in CFM) that will be required to your target power level and flow that much air
  • Valve sizes to support your power goal (which may be larger than stock…)
  • Supporting intake and exhaust dimension’s
  • Fuel supply capable of supporting your power goals
  • …etc

Notice that in this stage your engine bottom end need not be touched. You need not change your pistons, raise your compression, or alter your bore and stroke… and this is where most enthusiasts end their modifications path.

Stage 3: Stages 1 and 2 are meant for working with what you already have to work with. Stage 3 is for people that have a specific power target in mind (that is definitely higher than the expected bolt – ons power level that the calculator is estimating. Since this power level is unreachable with simple bolt-ons then we definitely know that we’re going to need more raw power, much more efficiency, or even forced induction to get to our power goal and are willing to undertake significant engine modifications to get there.

The question the calculator answers for you here is:

I want this Supra to make 300 horsepower, how do I get here using (All motor / nitrous / a turbocharger / a supercharger).

Once you choose what kind of buildup you are planning on undertaking, the calculator will tell you exactly how to reach that power goal including but not limited to :

  • Everything mentioned in stage 2 plus the following…
  • New bottom end dimensions (Bore X Stroke changes)
  • New static compression ratio
  • Required boost level or nitrous spray level… and much more

To summarize:

Our horsepower calculator and the mods calculator … not only help you to design your staged upgrade path for your car or motorcycle. But also, they help you sniff out when someone is trying to rip you off by selling you a ’50 horsepower guaranteed’ camshaft when you’re already making your peak power 500 rpm short of red-line…

By having this information you will be a more educated engine builder and a more educated a shopper.

Use the mods calculator to design your staged upgrade path



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