compression calculation for advanced people...??
Turbo Mini Forums

hy. so i know standard way to calc compresion ( cilinder +head =... etc)

but know there is a methode to calculate it where you need to calc in the camshaft ( eg when a cam has big overlap timing there will be some of the compression lost there)

can any one please explain this methode to me? explaining and maybe example would be nice....

you can do anything if you set your mind to it...
i rather blow it up winning than keep it together losing.

finish date set for project 1... march 2018

this is what i used

http://www.wallaceracing.com/dynamic-cr.php

Hello, this is one
http://members.uia.net/pkelley2/DynamicCR.html

Racecar spelled backwards is Racecar

Superb info. Thnx

you can do anything if you set your mind to it...
i rather blow it up winning than keep it together losing.

finish date set for project 1... march 2018

Wich of the 2( dynamic or static) would be the safest to look at when building a turbo engine?

Edited by Rammie2000 on 22nd Sep, 2015.

you can do anything if you set your mind to it...
i rather blow it up winning than keep it together losing.

finish date set for project 1... march 2018

im not experienced enough to say what you should do but i will say it how i see it

dynamic is as close as you will get to what the engine is getting when running how ever its still a calculation and cant account for air speed and that sort of thing

the idea of dynamic compression ratio is to find as close as you can the cylinder pressure before adding the spark and burning your air fuel mix

the air fuel mix can only take so much pressure and temperature before getting unstable we all know that

so if we can get the air fuel mix compressed nearly to where its unstable compressing air makes heat so take that into account after its burn has started it takes time to compleat its burn and its has a peak presure rise from the burn you want that peak pressure quite early after tdc theres a degrase where your useing that pressure to do the most work it can

its getting that peek pressure after tdc at that angle that makes good power manny things determin it like how the air fuel mix burns and how long it takes to burn

I used this one for my k1100 race engine
from the corvette forum look at post # 28 and download it onto your computer. i know it sounds risky but it is a real calculator and it adjusts per your rod length and bore. you can also add numbers for valve opening if they are not low enough
http://www.corvetteforum.com/forums/c6-tec...#post1567653356

Racecar spelled backwards is Racecar

Bringing up an old thread.
What are people's thoughts on a maximum dynamic compression ratio? Obviously the later the inlet valve closes after BDC the lower it will be, but what about VE ? The calculators assume 100% VE. The cylinder isn't 100% full all of the time if ever ? So assuming the fairly low VE (80-85% ?) of most of our A-series 5porters what would be a safe target ?

Phil.

WWW.TURBO-MINI.COM

Sure I've read somewhere about desired maximum cylinder pressures calculated using dynamic CR on here Phil. I can't think who's thread it was though.

If something is worth doing, it's worth doing half of.

It's a step in the right direction to consider the inlet valve closing in determining the optimum compression ratio. However, it is just one of many factors that determine the temperature in the cylinder at the point of ignition and the potential for detonation. Big subject, many factors involved.

I produced this years ago:


Still seems relavent.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

somthing that confuses a lot of people is that Dynamic comp ratio numbers are different to Static ones, and not may people have much idea what dynamic compression they need,

as an example, i stuffed some figures into the wallace calculator based on K1100 cam timing, and got this out.


Static compression ratio of 8.5:1.
Effective stroke is 2.69 inches.
Your dynamic compression ratio is 7.30:1 .
Your dynamic cranking pressure is 140.84 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 20 PSI is 17.14 :1.
V/P (Volume to Pressure Index) is 30

Quit a difference indeed. But what is the safe one to follow then?

you can do anything if you set your mind to it...
i rather blow it up winning than keep it together losing.

finish date set for project 1... march 2018