- A Corvette Forum: Link:https://www.corvetteforum.com/forums/c6-scan-and-tune/2545251-stock-c6-z06-dyno-tune-gains.html

Building Horsepower Part:1

1y ago

6K

We all have seen those people on here who haven’t touched an engine in their life but are full of opinions of torque VS horsepower and what is good for making horsepower and all that bullshit they talk. I’m going to take my experience of building engines and modifying them, studying mechanical engineering (I’m specifically referencing Thermodynamics here) coupled with plenty of hours watching Engine Masters and Roadkill to give some tips over a couple of articles. There will be links below to see the actual physical parts I am talking about.

Copyright: Pearltrees, Link: http://www.pearltrees.com/georgelittlewood/engine-configuration/id12625550/item125674438

For this article, I will be talking about any normally aspirated engine since that is all I’ve worked on and the rules apply to all of them. They are also the easiest way to learn about the normal combustion engine. I will be mentioning components and telling you about their function and how to modify them or replace them with aftermarket parts to make more power. Engine nerd warning, I might sound like James May and talk in extreme depth.

Firstly, what is an engine? Thanks to my Thermodynamics lecturer, in its basic definition an engine is an air-pump. The more air you put in, the more fuel you can burn, the more power you make. Easy right? If you have a shitload of money, yes very.

Component 1: Cylinder Head(s) and valvetrain (they have the same purpose).

The Heads:

The power of an engine lies within the cylinder head or heads. That is a fact and if someone tells you different, they are lying to you ladies and gents. Like I said above, an engine is an air pump and therefore, the components which control the airflow into it are the most crucial to the power capability of the engine. The cylinder head has so many variables to it that can make or break it. Port size and shape, runner length and straightness, combustion chamber size and design, placement of spark plug, water channel size, valve size, etc. All of this affects the amount of air that can be moved into the engine and how efficiently it will burn the air-fuel mixture. I will now discuss the main issues about those listed variables.

Ports and Runners: When it comes to port size bigger is not always better. Classic example is the BOSS 429 Mustangs. That engine was designed with racing in mind. So when they dropped the compression ratio a bit, put a smaller camshaft and pulled some timing out of it for the street car, it wasn’t as impressive as it should have been due to its gigantic ports. The air molecules were on trip through Disney Land doing site-seeing and stuff before they reached the intake valve. It is by no means underpowered or slow, but it would be more torqy pretty much everywhere and make more power with a slightly smaller port. The only way you are going to change the runner distance or straighten it is to buy a different cylinder head.

Combustion Chambers: That thing I know only the very basics of. Firstly, some engines will have the combustion chamber in the cylinder head and have a flat piston while others will have a flathead with a dish piston (combustion chamber in the piston itself). The size of the combustion chamber determines the final volume of what the air-fuel mixture will be compressed to. The smaller the combustion chamber, the higher the compression ratio (because the same volume is being compressed into a smaller space than before) (also, the expansion ratio is equal to the compression ratio). The higher the compression ratio, the higher the efficiency due to a cleaner and more complete combustion process inside the cylinders which increases the power output of the engine. As per usual, there is a negative side. When you get to really high compression ratios in non-diesel cars the air-fuel mixture starts to combust before the spark plug fires which is bad trust me. This is due to the increase in temperature at elevated pressures and is called “knock” or “pinging”. The combusted gasses will try to force the piston down while it’s trying to move up, which not only causes a loss in power but if it gets severe enough, also a loss of conrods, cash, patience and sanity. This can be controlled/minimized by using higher octane fuels which are more resistant to “knock”. Different shapes of combustion chambers also affect where the combustion process starts and has a great influence on power output. I don’t know anything about which design/shape is best.

The Cam shit:

Now the valvetrain (camshaft and all its trinkets that opens the valves) is a bit cheaper to modify with the same end goal as modifying the cylinder head: Move more air and make more power. A camshaft usually has three major variables called lift, duration and lobe separation angle.

Lift: Lift is how far the valves will open. There are two types of lift named cam lift and valve lift (also known as total lift). Cam lift is how far the camshaft will push up/down to open the valves. Sometimes the camshaft pushes against something called a rocker or rocker-arm which acts as a multiplier of the cam lift. If you have a 1.5 rocker (1.5 rocker ratio) the total lift is then equal to 1.5 times the cam lift. So for example if you have 10mm of lift from the camshaft, the valve will open by approximately 15mm. Higher lift, more airflow, more power. To increase lift, you will probably have to install new camshafts (this is usually the case for overhead cam engines where the cams rides directly above the valves on little flat lifters called “shims”). In older cam in block engines or in an overhead cam engine that also uses rockers (like the Ford Pinto 4 cylinder for example), a higher lift camshaft can be installed or you can install new rockers with a higher rocker ratio. For example if you take the same system above and change the 1.5 rocker to a 1.65 rocker, you will now have an extra 1.65mm of lift with the stock/same camshaft as before. You will also then skip the hassle of running in a new camshaft which is a bitch sometimes.

Duration: This is what makes a car idle lumpy and rough. Duration is how long the valve will be open for. There are two ways to modify this and that is to either change the camshaft or regrind your current camshaft. When you regrind your camshaft, you will lose a bit of lift but will have massive gain in duration which improves the power output and you won’t have to run in a new camshaft. I don’t really like that method. Just spend some money on the new camshaft and be done with it.

Lobe Separation Angle (LSA): I cannot explain how or why this works or has such a massive influence on engine performance but it does so again, trust me on this. Lobe separation angle is the angle (in degrees of camshaft rotation) between the exhaust valve closing and the intake valve opening. There will always be an overlap region. Right before the exhaust valve closes fully the intake valve will start to open. The tighter/smaller the LSA the more overlap there will be and this will cause the exhaust gas to go into the intake at low revs. The small LSA (below 110 degrees is regarded as small) camshafts are for racing and love high rpm usage. The wider/bigger the LSA the less overlap there will be. The big LSA (bigger than 110 degrees is regarded as big) camshafts are more for less insane performance cars like Cadillac CTS-V and has good idle quality and low down torque. In conventional cam in block engines like the Chevy LS, you will have to replace the camshaft if you want to change the Lobe Seperation Angle. But, in the non ancient more modern Ford Coyote (and any Over Head Cam engine that has a seperate cam or cams for the intake and exhaust valves) the Lobe Seperation Angle can be adjusted to any angle you please by removing the timing chain / belt and whatever rocker or valve covers are in the way and turning them in which ever direction you think will make more power.

I have seen plenty of times on Engine Masters that buying the amazing cylinder head and opting for a smaller camshaft (although much more expensive) is better than installing the gigantic camshaft with the shitty cylinder head that can’t flow the air needed to make big power.

Ford did most of these modifications for the Gen 2 Coyote V8 update (from 2015 onwards). They made new casts after they designed a cylinder head with a straighter path of airflow (runner). They cut new camshafts with 1mm extra lift on the intake and exhaust side. All these breathing improvements are the main reason for the power increase over the 2014 Gen 1 Coyote engine.

Camshaft Specs Explained:

www.youtube.com/watch?v=9LTDHiUftlU&index=7&list=PLGvTvFzdMg_O2T3UdUEt5dIHutSOu7srE

How to gain 92hp by porting your cylinder heads and intake to perfection:

www.youtube.com/watch?v=aijyLKCvbU8&index=5&list=PLGvTvFzdMg_O2T3UdUEt5dIHutSOu7srE

CNC ported cylinder heads VS as cast cylinders:

www.youtube.com/watch?v=Fbd33oEyCbU&index=20&list=PLGvTvFzdMg_O2T3UdUEt5dIHutSOu7srE

I hope you enjoyed or learned something from this. Comment below what you think or what you would like me to address in a future article. If you have questions, ask away. #engineering

Cheers, Brian.

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