what will my compression ratio be, maybe someone knows Options

[mightyohm]

I am putting 96mm KB's into a 2.0 liter motor, stock crank, stock rods, heads will only have slight flycut (just enough to get sealing surfaces back). Cylinders are stock 94's bored out to 96.

What will my compression ratio be?

I know this is a combo that many have looked at or built before. Maybe someone knows or has measured.

I want to get an idea of where I will be with no additional mods.

[Mark Henry]

So class, here is the math quiz of the day.

Engine cc formula:

Bore (mm) X bore X stroke (mm) X 0.0031416 = Engine cc

Example: 90.5mm X 90.5mm X 78mm X 0.0031416 = 2006.97cc


Deck volume cc formula:
Bore (mm) X bore X deck height (in.) X 0.01996 = deck volume cc

Example: 90.5mm X 90.5mm X 0.080" X 0.01996 = 13.07cc


Head cc is measured by using a Head cc kit

The CR formula:
Head cc + deck cc + (engine cc divided by 4) = CR
Head cc + deck cc (+ piston notch cc, if any)

Example:

54 cc + 13.07 cc + (2006.97 divided by 4) = 568.8125 = 8.48
54 cc + 13.07 cc = 67.07

568.8125 divided by 67.07 = 8.48 or 8.48:1 CR

[Mueller]

Jeff,

the problem is whether or not your heads have been cut or modified before you taking ownership of them. Your best bet is to measure them.

[Jake Raby]

Do NOT GUESS AT CHAMBER VOLUME! 1 cc means a whole lot to the CR calculation.

CC those chambers, measure your deck and go from there wth the math. CR cannot be guessed at.

[Mark Henry]

(IMG:style_emoticons/default/agree.gif)

Even stock uncut heads can be 2-4 cc different from each other, depending what day each head was made.

That's why I gave the math..no guesswork allowed here.

[mightyohm]

I was not looking for an exact number but wanted to know if someone had measured their CR for a 2056 combo and could give me a general number. I would like to know if I am going to be way off in either direction because of the KBs. From what you are telling me it sounds like anything is possible depending on the heads.

Mark, can I use a buy a head CC kit somewhere? Will a type I kit work or do I have to make my own?

Thank you Mike, Jake, and Mark for your responses.

If the factory was off by as much as 2 cc then does that mean the CR of stock engines varies wildly?

[Dave_Darling]

A head C kit is really complex, I don't know if you want to try to make it yourself.

You need:
* A round piece of plexiglass the same size as the cylinder "register" in the heads. With two holes, one to fill through and one for air to escape.
* A graduated cylinder or pipette from a chemistry supply store.
* Some liquid.

As you see, very complex and difficult to find parts.... (IMG:style_emoticons/default/rolleyes.gif)

--DD

[mightyohm]

Ok so who wants to cut a perfectly round piece of plexiglass for "i suck at using a hacksaw" Keyzer?

I assume the heads all have the same register size unless they have been opened up on purpose.

PS: I don't even have the heads back from the machine shop yet. I have time to figure this out.

[Mueller]

Jeff,

I have a CC kit, you can use it as long as you don't break it (IMG:style_emoticons/default/smile.gif)

I used Castrol Superclean for the liquid...........

[Mark Henry]

Dave's way is being a bit of a TW (IMG:style_emoticons/default/wink.gif)

Just go to a VW bug shop and get a head cc kit for 94mm cylinder. It might not fit perfect but it will work. About $20.

Put a smear of grease on the outer edge of the plate to make the seal, then just use water in the syringe that comes with the kit. When you clean up just make sure to blow out the water.

[Mueller]

no need to have a round piece.......you can place the plexiglass on the surface of the head and subtract the volume from bottom of head to the mating surface. (cylinder)

[mightyohm]

Mike, why superclean?

[Brett W]

Depending on deck height and chamber volumn you are looking at between 8.9-9.75:1. On engines with as big a bore as ours 1cc doesn't make that big of a difference, about a .10 of a point. Hit the site:

http://www.rbracing-rsr.com/compstaticcalc.html

The deck hieght will make a difference as well. If you want to measure your chamber volumn go to the vet and get the biggest syringe they have, take the needle out and get a piece of plexiglas to seal the top of the chamber. Fill the chamber and measure the amount from the ccs on the side of the syringe.

[TonyAKAVW]

The answer is 42:1...



but what is the question?

[mightyohm]

Depending on deck height and chamber volumn you are looking at between 8.9-9.75:1. On engines with as big a bore as ours 1cc doesn't make that big of a difference, about a .10 of a point. Hit the site:

That's pretty high for pump gas, isn't it?

[JWest]

Mike, why superclean?

Low surface tension so you don't have a big bulge of water at the exit hole.. At the very least put some detergent in the water if you use that. Soap breaks surface tension.

[MarkV]

You can get a kit here:

http://www.vwalley.com/

[cgnj]

I'd ask them for the chamber volume. I still check.

Carlos