[MySallyMI]

Im browsing Vt engines, site and gettin ready to buy a stroker kit but what is the difference in the piston sizes? The cheap one has 28cc. Then theres a billit stroker kit stating 5cc .020. Is the second one i list for Bored out applications? This is one thing i never paid any attention to in auto shop or had any experiance with during my 3 years in the army, what do you guys suggest? I need forged internals, and its gunna be a stroker which kit you guys think?

[MySallyMI]

ALso i just found a place in Waco, TX that will install 21cc pistons and bore my block for 2g's this sound bout right? Normally i do my own work but im having surgury on my torn rotator cuff soon so cant do it.

[acmillr]

Need more info.............

You going blower or staying NA?

[MySallyMI]

Blower when i can afford it.

[acmillr]

Originally Posted by MySallyMI Blower when i can afford it.

You need to get with the people you plan on ordering from and try to get the correct compression worked out based on compression chamber volume. As far as compresson goes, you will have to dtermine how much boost you plan on running. I would think that at low boost levels you could go as high as 9:1, and the higher the boost the lower you want to stay. I thought you were going to say naturally aspirated, which is something I would know more about. I'm sure some of these other guys, like chrisj, will chime in on this subject. Don't forget camshaft lift and duration so you can get valve reliefs if needed.

[02steedagt]

mysally weren't you selling your car a few weeks ago???

-sorry I don't have any input on this topic, but I am interested in this myself. How does the volume of the piston chamber affect compression? (sorry I don't know a thing about this)
-will bigger volume give you more compression?

[acmillr]

Originally Posted by 02steedagt mysally weren't you selling your car a few weeks ago??? -sorry I don't have any input on this topic, but I am interested in this myself. How does the volume of the piston chamber affect compression? (sorry I don't know a thing about this) -will bigger volume give you more compression?

OK, this is a dished piston. Dished pistons are used to lower compression. They come in sizes such as -4cc's, -12cc's,etc. Those are only a couple of examples. Dished pistons create a higher net chamber volume resulting in lower compression.


Now, this is a domed piston (note the raised top). This piston is designed to create a lower net chamber volume resulting in higher compression- that is, forcing the same amount of air and fuel as before into a smaller space. These pistons are measured in +cc's or in inch measurements (i.e. +.150" domes, +.250" domes, etc.)



Here is a flat top piston (very common in hot rod motors). Flat top pistons are somewhere between domes and dishes. Think of these as the starting point.


This is a good look at valve reliefs. Valve reliefs are cut into pistons to help avoid valve to piston contact. Camshaft duration and lift (mainly duration) should always be taken into account to determine proper valve relief depth.


How do pistons and cylinder head volume relate?
You must determine what cylinder head volume you will be using to determine which piston type will yield your wanted compression ratio. As the cylinder head volume gets larger, the piston dome or lack of dish can increase and vice versa. Here is a good look at a typical cylinder head combustion chamber.

[02steedagt]

ok so i higher compression would give you more hp correct? why would you ever want to get dish pistons and decrease your compression? is it because other components can't handle the higher pressure?

[acmillr]

Originally Posted by 02steedagt ok so i higher compression would give you more hp correct? why would you ever want to get dish pistons and decrease your compression? is it because other components can't handle the higher pressure?

The answer to that question can be summed up in one word- DETONATION.
Detonation occurs when your air/fuel mixture ignites before it is suppose to. Several things can cause detonation- heat, low octane fuel, to much advanced timing, too high compression, etc.. Since, typically, we can only get 93 octane fuel for street use, we must limit our compression to around 10.5:1 (that number is opinionated as some people feel like compression should be run lower or slightly higher on pump gas).
As boost goes up, two things occur- heat becomes an issue, and boost raises compression resulting frequently in detonation (commonly referred to as knock).

[MySallyMI]

I was going to sell it then i broke it lol. Im awesome! I Haaaaad to have that one last thrill before i got rid of it, now it mine forever lol THE WORLD IS MINE!