Combustion Chamber Measurement

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misszora
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Combustion Chamber Measurement

Post by misszora » Fri Jan 06, 2012 12:36 pm

I need to get clarification on what I'm measuring on the heads. See photo below.
And when you have dished pistons, do you add or subtract that number into the total cc number?

thank you.
- paige

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Miss Zora - '77 VW Riviera Hard Top Campmobile
Dharma Bug - '69 VW Bug
The Vandejo - '74 VW Westfalia Poptop (former mom)

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hambone
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Re: Combustion Chamber Measurement

Post by hambone » Fri Jan 06, 2012 1:13 pm

Here's a Hoover write up on the process:
http://bobhooversblog.blogspot.com/2006 ... heads.html

I think #2 is what you're going for. How would you seal off #1? It's not a machined surface.
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vdubyah73
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Re: Combustion Chamber Measurement

Post by vdubyah73 » Fri Jan 06, 2012 1:17 pm

it's #2 the cylinder to head sealing surface.

i believe you add it, wait for more informed sources to answer.
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Westy78
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Re: Combustion Chamber Measurement

Post by Westy78 » Fri Jan 06, 2012 1:45 pm

The piston dish must be added to the head cc for a total cc figure.
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misszora
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Re: Combustion Chamber Measurement

Post by misszora » Fri Jan 06, 2012 1:55 pm

thanks..I'm going back over and redoing the process again.
Miss Zora - '77 VW Riviera Hard Top Campmobile
Dharma Bug - '69 VW Bug
The Vandejo - '74 VW Westfalia Poptop (former mom)

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Gypsie
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Re: Combustion Chamber Measurement

Post by Gypsie » Fri Jan 06, 2012 2:42 pm

put a thin even coat of...wait for it....vaseline around the outer edge of the disk you are using to sit in the head. push it down and the grease will make a seal.

You can cc the dishes by doing the same thing (vaseline seal around the edge and seal it on) and then measure the dish (from the top of the piston not the top of the cylinder. this will be dish cc's

Here's the area of my rebuild where I did this math. (halfway down pg 36)
viewtopic.php?f=3&t=6244&hilit=ratio&start=510

Your dishes will likely be around 14 cc's. (I'll wager that you will be near to 68 total cc's)
Use the step cut ring to set your plastic disk on and spark plug fully seated. Measure cc's, the total HEAD and Dish CC's will be added to come up with chamber cc's.

Your deck height measurement will tell you how thick your base (cylinder to case) ring should be for optimal CR.

It was suggested that I subtract the step cut in the head from the final cc's and add it to DH in the calculator but either way it worked out the same.

My step measured .030" (which converts to approximately 6cc's). If you are not able to get a good measurement on the step cut, don't fret because you can just use the cc measurement you get from the head with the disk sitting on the step cut.

If you plan on using head side sealing rings this will get added into the equation as well. But let's not get ahead of ourselves...
So it all started when I wanted to get better gas mileage....

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Amskeptic
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Re: Combustion Chamber Measurement

Post by Amskeptic » Fri Jan 06, 2012 3:44 pm

Place the plastic disc (I use a CD ground down to correct diameter, preferably John Denver hits or Olivia Newton John Sings Christmas Carols) on the step with aforementioned vaseline or grease. The step does not change your math, it is the math, no subtraction necessary. Deep dish pistons are usually 15cc's the shallow dishes are easy to spot because they have such a gentle wall and minimal depth, they are 7cc's.

Do not add sealing ring depth to any equation but deck height.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 104,650 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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misszora
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Re: Combustion Chamber Measurement

Post by misszora » Sat Jan 07, 2012 9:13 am

For MY peace of mind, I packed up the cylinder heads & went to Bearing Service (Troy at A-1 smashed a finger and had to have surgery) in NW Portland to have them cc'd. I wasn't feeling confident that I was getting the right measurements and it was eating up valuable work time. They did it immediately at no charge and were very nice about it.

So at the end of today here are the measurements:
52cc for heads
15cc for piston dish
.016 deck height (mock-up) #3 & #4
.015 for #1 & #2

I'm shooting for a deck height of around .045
With that in mind, these are the calculations using Aircooled.net:

Image

After I posted this on the Miss Zora Get a New Heart thread, I found this information on http://www.tunacan.net/t4/reference/case.htm regarding engine identification:

2.0 series (1971cc or 120.2 cu.inches)
GD 1976-77 VW Transporter
Compression Ratio: 7.3:1
Horsepower: 67hp@4200rpm
Torque: 101ft-lb@3000rpm
Notes/Comments: L-Jetronic f.i., solid lifter 

So does that mean I need the deck height to be a little higher to adjust the CR?
Miss Zora - '77 VW Riviera Hard Top Campmobile
Dharma Bug - '69 VW Bug
The Vandejo - '74 VW Westfalia Poptop (former mom)

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Westy78
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Re: Combustion Chamber Measurement

Post by Westy78 » Sat Jan 07, 2012 11:39 am

No you're good at 7.6. 7.3 was factory and a bit inefficient. You want to shoot for 7.5-~8.0. At 7.6 you should get a little more power and better mileage while still not having to worry about running high octane fuel. In other words no pre- detonation.
Chorizo, it's what's for breakfast.

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Amskeptic
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Re: Combustion Chamber Measurement

Post by Amskeptic » Sat Jan 07, 2012 1:09 pm

Westy78 wrote:No you're good at 7.6. 7.3 was factory and a bit inefficient. You want to shoot for 7.5-~8.0. At 7.6 you should get a little more power and better mileage while still not having to worry about running high octane fuel. In other words no pre- detonation.
Careful here ... :cyclopsani:

Volkswagenwerk dropped the compression ratio as they tried to maintain the reliability of their reputation. They discovered that lower compression creates less heat as they upped the displacement.
In 1973, the compression ratio was dropped from 7.7:1 down to 7.3:1 for several damn good reasons. A STOCK rebuild has no field justification behind bringing it back up back up. A Raby rebuild, of course, can.

My untouched factory build engine in the BobD is as sprightly as any and has given me decent fuel economy. I did find the detonation point, however, as I was fooling with the AFM last summer, and I can easily guess that higher compression would have forced me to run it richer/more retarded than I am currently able to get away with. What am I able to get away with? Pretty much boxed-in at factory spec. Phooey.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 104,650 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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misszora
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Re: Combustion Chamber Measurement

Post by misszora » Sat Jan 07, 2012 5:21 pm

A Jake Raby rebuild, she's not.
Everything is in place. My deck height is .055. CR should be right between 7.3 & 7.4 now. I am happy and am going to create a celebratory cocktail from the stuff I have at the house. :drunken:
Miss Zora - '77 VW Riviera Hard Top Campmobile
Dharma Bug - '69 VW Bug
The Vandejo - '74 VW Westfalia Poptop (former mom)

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MountainPrana
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Re: Combustion Chamber Measurement

Post by MountainPrana » Fri Dec 07, 2018 9:35 am

Amskeptic wrote:
Sat Jan 07, 2012 1:09 pm
Volkswagenwerk dropped the compression ratio as they tried to maintain the reliability of their reputation. They discovered that lower compression creates less heat as they upped the displacement.
In 1973, the compression ratio was dropped from 7.7:1 down to 7.3:1 for several damn good reasons. A STOCK rebuild has no field justification behind bringing it back up back up. A Raby rebuild, of course, can.

Colin
Colin, this raises a question for me as Molly and I are doing a Raby Rebuild. I read and understand that we “can” take the compression ratio up to 7.7:1. My question is what is optimum for a Raby rebuild? We are at the stage of figuring deck height and wanting to get it right.

TimlivinginoursubaruforesterinsteadodourvanisMorechallengingthanwethoughtduringThesouthernutahwinter

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Amskeptic
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Re: Combustion Chamber Measurement

Post by Amskeptic » Fri Dec 07, 2018 11:16 am

MountainPrana wrote:
Fri Dec 07, 2018 9:35 am
Colin, this raises a question for me as Molly and I are doing a Raby Rebuild. I read and understand that we “can” take the compression ratio up to 7.7:1. My question is what is optimum for a Raby rebuild? We are at the stage of figuring deck height and wanting to get it right.

TimlivinginoursubaruforesterinsteadodourvanisMorechallengingthanwethoughtduringThesouthernutahwinter

It all revolves around the camshaft profile, Tim. What is your camshaft profile?

Did I mention that these electric lights and a real built-in gas furnace are the cat's meow in this 2,300 sq ft HOUSE? Off to the coffee maker, oh, and I think I will tick the thermostat up to a cozy 69*, life is grand.
Colin :sunny:
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 104,650 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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MountainPrana
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Re: Combustion Chamber Measurement

Post by MountainPrana » Fri Dec 07, 2018 11:54 am

Amskeptic wrote:
Fri Dec 07, 2018 11:16 am

It all revolves around the camshaft profile, Tim. What is your camshaft profile?

Did I mention that these electric lights and a real built-in gas furnace are the cat's meow in this 2,300 sq ft HOUSE? Off to the coffee maker, oh, and I think I will tick the thermostat up to a cozy 69*, life is grand.
Colin :sunny:
A)
Web Cam 9590
Intake / Exhaust
Lift .426 / .426
Duration 262* / 273*
Duration@.050 224* / 233*
Lobe center 108* / 108*


B) Thank you for your sunny disposition, you brought both of us a needed laugh!

TimgoingtoclosethestorageunitdoorToblockoutthegreycoldday :compress:

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Amskeptic
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Re: Combustion Chamber Measurement

Post by Amskeptic » Sat Dec 08, 2018 11:25 am

MountainPrana wrote:
Fri Dec 07, 2018 11:54 am

Web Cam 9590
Intake / Exhaust
Lift .426 / .426
Duration 262* / 273*
Duration@.050 224* / 233*
Lobe center 108* / 108*

TimgoingtoclosethestorageunitdoorToblockoutthegreycoldday :compress:
Here is a stock camshaft profile:

Intake / Exhaust
Lift .333 / .313
Duration 224* / 230*
Duration@.050 196* / 196*
Lobe center 108* / 108*

You camshaft will diminish vacuum at low speeds/idle.
Fuel injection does not like that. Cold idle does not like that. Take off from stop lights does not like that. Emissions tests do not like that. High elevation engines do not like that.
A loaded Vanagon at high elevation NEEDS TORQUE low down so you can launch from a stop light or start on a hill at 7,700 feet.

If that is your chosen camshaft, you will need a little more compression than stock, like 8.0:1.
You will need higher idle timing, but you cannot have more upper end advance, so you need a distributor that can hit you with 12-14* centrifugal at IDLE but not exceed 28*-32* centrifugal at 3,400 rpm (the 28* is the limit at sea level, 32* the limit at 7,000 ft)

You will get lots of advice and recommendations and suggestions from the performance community. It is up to you to state and restate your requirements and heck, ask them if they have ever done actual cross-country drives in the winter above 8,000 feet. "No, but really, this combinations works, I have had this in MY car for three years and ..." "But have you ever started it at 15* in Jackson Hole?" " No, but really, this combination works, I have had this in MY car for three years and stuff."

Am I done?
Yes.
Colin :blackeye:
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 104,650 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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