How to calculate engine compression ratio

Stories from our readers

“Fucking basin. "

Hi all! My name is Mikhail, now I’ll tell you a story about how I managed to exchange my two-wheeler for a 2010 Camry. It all started with the fact that I began to be wildly irritated by the breakdowns of the two-wheeler, it seemed like nothing serious was broken, but damn it, there were so many little things that really started to irritate me. This is where the idea arose that it was time to change the car to a foreign car. The choice fell on the melting Camry of the tenth years.

Yes, I had matured morally, but financially I just couldn’t handle it. I’ll say right away that I am against loans and taking a car, especially not a new one, on credit is unreasonable. My salary is 24k a month, so collecting 600-700 thousand is almost impossible for me. I started looking for different ways to make money on the Internet. You can’t imagine how many scams there are, what I haven’t tried: sports betting, network marketing, and even the volcano casino, where I successfully lost about 10 thousand ((The only direction in which it seemed to me that I could make money was currency trading on the stock exchange, they call it Forex. But when I started delving into it, I realized that it was very difficult for me. I continued to dig further and came across binary options. The essence is the same as in Forex, but it’s much easier to understand. I started reading forums, studying trading strategies. I tried it on a demo account, then opened a real account. To be honest, I didn’t manage to start earning money right away, until I understood all the mechanics of options, I lost about 3,000 rubles, but as it turned out, it was a precious experience. Now I earn 5-7 thousand rubles a day. I managed to get the car buy after half a year, but in my opinion this is a good result, and it’s not about the car, my life has changed, I naturally quit my job, I have more free time for myself and my family. You’ll laugh, but I work directly on the phone)) If If you want to change your life like me, then here’s what I advise you to do right now: 1. Register on the site 2. Practice on a Demo account (it’s free). 3. As soon as you get something on the Demo account, top up your REAL ACCOUNT and go to REAL MONEY! I also advise you to download the application to your phone, it’s much more convenient to work from your phone. Download here.

Table of approximate increase in engine power with increasing compression ratio:

Intermediate results are summed up, for example, raising the compression ratio from 8 to 14 will give an increase of 8.7%.

Table: compression ratio and octane number of gasoline. Approximate dependence.

Dependency table

Well, at the end, as promised, a small table of the relationship between octane number and compression ratio.

BUT I repeat once again, if you now fill in fuel with a higher or lower octane number on a modern engine, NOTHING HORRIBLE SHOULD HAPPEN. If the octane is lower, the power will drop slightly and consumption will increase. If it is higher, then on the contrary, consumption will drop and power will increase. BUT again, the error level is about 3 - 4% no more.

Now we are watching the video version

This is where I end, I think my article, table and video were useful to you. Sincerely yours, AUTOBLOGGER.

Similar news

• Fuel consumption at idle speed. How much per hour is considered normal...
• HBO 5th generation is different from 4th generation. I asked a question at the station...
• GAS to diesel (diesel engine). Operating principle and how many...

Add a comment Cancel reply

How to increase the compression ratio

The easiest way to increase the compression ratio is to reduce the volume of the compression chamber . To do this, grind the lower plane of the cylinder head (reducing its height).

A more effective way is to replace the pistons and bore the cylinders for them . This method increases the compression ratio and increases engine displacement.

The compression ratio is also affected by the installation of camshaft tuning, which allows you to improve the geometric indicators of the compression ratio by delaying the closing of the intake valves.

When to increase the compression ratio

Experts from ZaRulem magazine decided to check how increasing the compression ratio would affect the engine. The experiment involved a VAZ-2111 engine, which has a compression ratio of 9.8. Then the lower plane of the cylinder head was ground, first by 2 mm and then by 4 mm. We installed it on a bench motor and took the torque characteristics. The test results are presented in the table:

The increase in power in both cases was only 2–3%, and only in the low and medium speed zone. And at high levels there is no effect. The fact is that as the compression ratio increases, the pressure in the cylinder increases sharply. This increase provokes detonation, which is caught by the corresponding sensor and shifts the ignition timing back. Consequently, the power drops. And therefore the theoretical effect is significantly reduced.

But it is worth considering that after increasing the compression ratio, gasoline with a higher octane number should be used. Then the results would be a little better.

Octane number

The easiest way to increase power is to use higher octane fuel.

Moreover, now many petroleum product manufacturers are declaring that switching to A-98 will be the best and correct decision. Even if the engine is not designed for such fuel.

This is a somewhat dubious statement, since each motor has its own requirements and tolerances. So such transitions are entirely your responsibility. And only you are responsible for any consequences.

Tuesday, January 12, 2020

Choosing a tuning camshaft for the 2106 engine

Camshaft phase width

Narrow phase

Wide phase

In the version of the camshaft with a wide phase, the intake valve opens before the piston reaches TDC - this affects the valve overlap, which will be discussed below, and the intake valve closes when the piston, having passed BDC, goes far to the top. As you can see, the intake stroke took up part of the compression stroke, but let's see what result we can get.

At low speeds, we actually have a low actual compression ratio and, accordingly, low thermal efficiency, for two reasons. Firstly, due to the shortened compression stroke, and secondly, when the intake valves close late, the pistons go up after passing BDC, pushing the fuel mixture back into the intake until the intake valves close. It turns out that our engine, receiving a portion of the mixture on the intake stroke before the piston passes BDC, displaces part of the mixture back into the intake after passing BDC, that is, the engine ends up using only part of its volume. For example, a 1.6 liter engine, pushing even 0.3 liters back into the intake, actually becomes an engine with a displacement of 1.3 liters!

The math turns out to be interesting, but at partial loads this loss of displacement is not so noticeable, since it is not the reduced intake that limits the supply of mixture - but the throttle valve. But if you press the accelerator, the throttle is open, but the speed is low, here a significant drop in torque will be noticeable due to the correspondingly low inertia of the flow in the intake, as has already become clear due to the fact that the piston receives a portion of the fuel-air mixture at the end the intake stroke pushes some of the mixture back.

As a result, when using a wide-phase camshaft at low speeds, we lose torque, or in simple words, traction, as a result of shortened intake and compression strokes, resulting in low pressure in the cylinder. But not everything is so bad, the lack of pressure can be compensated by increasing the nominal compression ratio, and if in addition to this we use a camshaft with an increased expansion stroke (power stroke), we will get an engine operating on the Miller cycle, which can achieve greater thermal efficiency by reducing consumption fuel, unfortunately with some reduction in maximum power.

Now let’s increase the engine speed; the air flow speed in the intake pipe has increased and, consequently, inertia, which has made it possible to fill the cylinder even when the piston moves upward after BDC. Due to the amount of mixture entering the cylinder greater than the engine could receive when the piston moves only downwards, both the filling of the cylinders with the mixture and the pressure in the cylinder increase, therefore we obtain higher power.

Do not forget that the filling of the cylinders, in addition to the camshaft phases, is affected by the cross-section and profile of the channels, and the intake system as a whole. Small ports may provide efficient filling at mid-range speeds, but limit maximum filling at high speeds, thereby not utilizing the full potential of the wide-range camshaft. With large channels, it may become so that the entire speed range is lost, along with high ones, where part of the incoming mixture on the intake stroke will be sent not to the working process, but back into the intake pipe.

What will change if a camshaft 21213 is installed on a VAZ 2106 engine?

To make it clear to you about the characteristics of the phase width, I will explain it with an example, so to speak, using my fingers, trying on the RV 21213, which has a wider phase than the RV 2101 on the ICE 2106.

1. We take a standard VAZ 2106 engine with a 2101 camshaft which has a GCR (geometric compression ratio) of 8.5
   and an intake valve closing of 55 degrees.
   — after BDC, intake phase 265
   degrees, compression phase
   95
   degrees.
   Now we measure the compression and it will be within 12
   kgf/cm2.
2. On this engine we replace the RV with a camshaft 21213, which has a wider phase of the intake valve, which opens in the same way as the RV 2101, but closes at 73 degrees. — after BDC, as a result, the intake phase is 283
   degrees, the compression phase
   is 77
   degrees.
   Now we measure the compression and it will be within 11
   kgf/cm2.
3. Now let's see how the characteristics of the 2106 engine with RV 21213 have changed. So, at low speeds the thrust has worsened, at medium speeds it is about the same, at high speeds it has become a little better. If you measure fuel consumption, the consumption will increase throughout the entire range; I will note in advance that the greater lift of the RV 21213 valve has nothing to do with it. It is not difficult to guess the whole reason for the failure at low speeds, decreased pressure in the cylinder, which reduces efficiency. At high speeds, more mixture enters the cylinder than with RV 2101, this gives an improvement, and although the incoming increased dose of the fuel mixture increases the pressure, ultimately raising the efficiency close to the result of RV 2101, but in the end the consumption is still a little higher.
4. To make it clear why the ICE 2106 with RV 21213 lost its bottom, let’s supplement our “debriefing” with one more data, the characteristics of the VAZ 21213 engine which has a GSG 9.3
   , the intake valve closes at 73 degrees.
   — after BDC, as a result, the intake phase is 283
   degrees, the compression phase
   is 77
   degrees, when measuring compression you can see the result within
   12
   kgf/cm2. Paying attention to the numbers, everything becomes clear.
5. To summarize, based on the results of 4 points, it is clear. Engines 2106 and 21213 have different GSG 8.5 and 9.3, different intake valve phases, but the same pressure in the cylinder at low speeds is the actual
   compression ratio, compression measurements confirm this. From which it follows that when installing a 21213 camshaft on a 2106 engine, at low speeds, it will turn out to be deformed and can easily digest 76 gasoline. At high speeds, thanks to the increased intake valve phase, the power will increase slightly compared to the RV 2101, but at the same time with increased fuel consumption due to lower pressure in the cylinder, which gives a lower degree of expansion - accordingly, a decrease in efficiency, however, such an engine can be safely fueled with a mixture of 76 and 92 gasoline. It is logical if in the 2106 engine we increase the GSG to 9.3 and install RV 21213, we will get the bottom end at the level of RV 2101, an increase in power at high speeds and lower fuel consumption.

Engine compression ratio calculator

Geometric compression ratio (GC) is the ratio of the total volume of space above the piston when it is at BDC (bottom dead center) to the volume of the combustion chamber.
The total volume of the combustion chamber (CC) consists of: the volume of the CV in the cylinder head, the volume of the CV in the piston, the volume of the cylinder hole in the cylinder head gasket (in its compressed state), the volume formed due to the piston not reaching the plane of the cylinder block at TDC . If the piston has a displacer, its volume is included in the calculations with a minus sign (similarly, if the piston exits the block at TDC, which is acceptable in some cases). Don't confuse compression ratio with compression.

Do not confuse geometric compression ratio with dynamic compression ratio.

Calculation of the compression ratio is necessary when changing the volume in the combustion chamber of the cylinder head. In my case, the cylinder head was milled, the combustion chamber in the cylinder head was changed, plus the Prior gasket. And since I’m already cutting the cylinder head, why not find a couple more horses by increasing the compression ratio. First, you need to find out the degree in the stock configuration, the piston's shortfall to the upper plane of the cylinder block, the volume of samples (forgings) in the piston, the net volume in the cylinder head. I googled the characteristics of the VAZ 21083 engine, and almost every site has its own special data on this engine. Therefore, it was necessary to recalculate Art. szh. and check the data. As a result: Volume of samples (puddles) in the piston = 11.8 cm^3

: piston pool volume 21083

Piston shortfall in VAZ 21083 block = 0.4 mm

:

Thickness of the VAZ 21083 gasket in the compressed state = 1.05 mm

: gasket thickness 21083

Thickness of the PRIORA gasket in the compressed state = 0.45 mm

: PRIORA gasket thickness

Calculation Art. szh. for drain with Prior gasket:

I increased the compression ratio to 10, this is the extreme limit for 92 gasoline, and I need to make the net volume in the cylinder head = 25 cm^3.

Dependency graphs Art. szh. from octane number:

Calculation Art. szh. for cylinder head 25 cm^3 and prioro gaskets:

The volume of the cylinder head was measured with a syringe with testing; it was necessary to obtain 25 cubes. In photos 1 and 4 the camera needs to be sharpened a little more:

The working volume of the cylinder is the volume located between the extreme positions of the piston movement.

The formula for calculating a cylinder has been known since school curriculum - the volume is equal to the product of the area of ​​the base and the height. And in order to calculate the engine volume of a car or motorcycle, you also need to use these multipliers. The working volume of any engine cylinder is calculated as follows:

h - piston stroke length mm in the cylinder from TDC to BDC (Top and Bottom Dead Centers)