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Yikes! I bought a '74 Super!!
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VW_Jimbo Premium Member
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PostPosted: Wed May 12, 2021 9:16 pm    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Here is what I got!

Looks like .30 of deck height to add!

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PostPosted: Thu May 13, 2021 12:08 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Thanks Jimbo. How did you come about that .30 number? Help me understand. And is adding deck height mean shims to the cylinder head? I want to measure it a couple more times again before I pull the trigger on anything.

Also - this still doesn't account for the valve adjustment "problem."

VW_Jimbo wrote:
Here is what I got!

Looks like .30 of deck height to add!

Image may have been reduced in size. Click image to view fullscreen.

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'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
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PostPosted: Thu May 13, 2021 8:35 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

vamram wrote:
Thanks Jimbo. How did you come about that .30 number? Help me understand. And is adding deck height mean shims to the cylinder head? I want to measure it a couple more times again before I pull the trigger on anything.

Also - this still doesn't account for the valve adjustment "problem."

VW_Jimbo wrote:
Here is what I got!

Looks like .30 of deck height to add!

Image may have been reduced in size. Click image to view fullscreen.


I inputted the numbers you had into the calculator. I do not, or I did not go back to look at, what your design compression ratio was, so I plugged in that 8.1. That way, the calculator could do its job! If you want it higher or lower, then type that in.

The camshaft is what dictates the compression ratio more than anything else. Also, the fuel type. I figured you are using pump gas, want a reliable engine for years to come, that it will have a stock camshaft and most of the other parts are stock or aftermarket stock copies. SO, I SET THE BAR LOW! 8.1 is fairly low on the compression ratio. So, if you think you have a better understanding of it, bump it where you want to. My 2127 was designed for 8.7, but that is a lot of extra stress on parts. I was not willing to screw with the engine again (ha ha ha)! So, I set the ratio at 8.3 when I did the calculations. Ended up at 8.37 when I got all done.

I always add shims under the barrels, between the case and cylinder jugs. I squeeze Copper Red RTV between each one, the case and the barrel. Just a small 1/16” bead is all that is needed. No wiping up, no mess. Be sure to clean all of those sealing surfaces with brake cleaner, leaving no oil behind. Be carful, the shims are razor sharp!

If you add shims to the barrels, the combustion chamber has only one seam in it. Each shim one adds into the head is a seam in the combustion chamber. Make sense?

Also, adding shims, will increase the distance from the case the rocker arm sits from the case. This automatically changes the rocker arm geometry, (so you will need to check that) which makes the push rods protrude out of the head less, which allows the rocker arms to come off the valves more!!!! Which is what your engine desperately needs!!!!

Make sense?
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PostPosted: Thu May 13, 2021 9:09 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Thanks Jimbo I think I get it now...closer anyway. Pump gas, daily driver is the goal, nothing more. What was the factory compression back in the day?
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'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
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PostPosted: Thu May 13, 2021 9:12 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

vamram wrote:
Thanks Jimbo I think I get it now...closer anyway. Pump gas, daily driver is the goal, nothing more. What was the factory compression back in the day?


I know it but cannot think of it right now. Damn it! I do know it was higher, because the fuel was way better! WAY BETTER!!!!! Well for combustion’s sake, not human health!
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PostPosted: Thu May 13, 2021 9:29 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

One more question - where do the 41ml I measured in the head chamber come into play in the CB chart? It seems like the only measure that mattered was the piston top to cylinder top.
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'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
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PostPosted: Thu May 13, 2021 1:22 pm    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

vamram wrote:
One more question - where do the 41ml I measured in the head chamber come into play in the CB chart? It seems like the only measure that mattered was the piston top to cylinder top.


In the combustion chamber cc's.

I was wondering what that 12.8 was. Never had a number that low, but I am not there. 41mm sounds WAY BETTER! I have had to carve more out of the chamber to get the compression I wanted on a few motors back in the day.

So, I inputted the new numbers for you. On a stock cam with regular fuel 87 RON, you could run with 9.3 to 1 compression, but the engine will not last as long. So, I used to tune them down, to the 8.4 area. In your case that makes for a .10 shim under the barrel!

Really nice! So much better!

I say build it!
Image may have been reduced in size. Click image to view fullscreen.


What do you think?
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PostPosted: Thu May 13, 2021 1:35 pm    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

12.8 was the volume of the cylinder that makes up the area of the piston head times the height/depth. The 41ml was how much oil went into the cylinder space between the CD and the valves. You can see in the picture I posted of the cylinder/piston that the piston is *very* close to the top of the cylinder edge. I measured this distance at 2.12mm.

Image may have been reduced in size. Click image to view fullscreen.



VW_Jimbo wrote:
vamram wrote:
One more question - where do the 41ml I measured in the head chamber come into play in the CB chart? It seems like the only measure that mattered was the piston top to cylinder top.


In the combustion chamber cc's.

I was wondering what that 12.8 was. Never had a number that low, but I am not there. 41mm sounds WAY BETTER! I have had to carve more out of the chamber to get the compression I wanted on a few motors back in the day.

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'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
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PostPosted: Thu May 13, 2021 1:37 pm    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Ah. So do we need to add 12.8 to the 41 to get the full combustion chamber area, or is there more somewhere?

Anyways, with the new info, the combustion chamber goes up to 53.8cc. Inputted into the calculator gives you 0, yes zero shims for a 8.8 compression ratio. Not too bad!

Image may have been reduced in size. Click image to view fullscreen.


I know that there are several that may disagree with me, but you could afford to machine down the barrels to get closer to 9.3:1 compression ratio. But that would mean cutting down your pushrods. I think you may have to anyways, though. Or you can add shims to under the rocker arm base points (where they rest on the head).

What ever you do, you will need to double check you rocker arm geometry, now.

So, install the barrels without any shims, based on the calculations from inputting the variables. Then set up to measure for push rod length.
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TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


67rustavenger wrote:
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PostPosted: Fri May 14, 2021 6:22 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Jimbo - i re-input the numbers into the calculator and I think my compression ratio is actually lower at 7.3, which from what I've been reading should be fine for a non-wild engine. To get this I input the 1st four numbers I actually got from my measurements then hit the Compression calculation button = 7.3. Based on this, I think I only need rocker shims and to check the rods. Hopefully I don't need to do any cutting...

Image may have been reduced in size. Click image to view fullscreen.

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Eventually, "we are what we pretend to be.’”
Give peace a chance - Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
Save the Supers!!
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PostPosted: Fri May 14, 2021 8:24 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Like I stated up above. I was not sure of all of it, as I am not there, so if you have more to add into the equation, do so. I am only able to assist with your understanding. I cannot do the actual measuring or decision making, those are on you!!!!

7.3 seems a little low. If you get to low, the engine works to hard for what you expect from it. The swing side is to high and it all can go BOOM! So, there is a line somewhere in the sand. I currently run 8.4 on the 2127. Had I to go back and do it a third time, I would raise it up. I run mid grade gasoline.

Again 7.3 seems low, but that is all you. You really need to figure out that valve geometry before committing to the stock length pushrods. It is always good to double check, everything!

Good luck and let’s see some more progress!
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TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


67rustavenger wrote:
GFY's Xevin and VW_Jimbo! Smile


Last edited by VW_Jimbo on Sun May 16, 2021 8:51 am; edited 1 time in total
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PostPosted: Fri May 14, 2021 8:26 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Yep, I'll be trying my hand at checking the valve geometry when I return to VA!
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Give peace a chance - Stop Russian-Soviet Aggression!!

'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
Click to view image
Save the Supers!!
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PostPosted: Sun May 16, 2021 1:19 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Quote:
I got 41 ml of Smart Balance under the modified CD... And I got 12.8CCs of volume for the piston top/cylinder top space. I measured 87.95mm & 2.12mm depth from the top of the cylinder to the piston head

Hold on- vamram wrote that his DH is 2.12 mm, and the chamber volume is 41 cc. The 12.8 cc VOLUME of the DECK does not matter for the CB calculator, because it automatically calculates the volume based on the linear 2.12 mm DH. So inputting those # into the calculator, you get 8.8 as the CR.

Jimbo- from one of your calculator inputs, 0.3 inch DH is nearly 1/3 inch- way too much.
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PostPosted: Sun May 16, 2021 3:33 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

vamram wrote:
... What was the factory compression back in the day?

FWIW...

Image may have been reduced in size. Click image to view fullscreen.

My 1640 runs smooth with a compression of 8.6 and a precision-balanced stock crankshaft since 1990.
Gasoline: RON 95, 5% ethanol (Germany).
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PostPosted: Sun May 16, 2021 7:54 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Thanks Maddel. Is that page from the small orange technical data book? I forgot that I have that one at home. To get to the factory 7.5 I'd have to have the heads machined to remove more material from the head to get the CCCCs to 52...is it worth the hassle for a .2 increase?
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'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
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PostPosted: Sun May 16, 2021 8:59 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Rome wrote:
Quote:
I got 41 ml of Smart Balance under the modified CD... And I got 12.8CCs of volume for the piston top/cylinder top space. I measured 87.95mm & 2.12mm depth from the top of the cylinder to the piston head

Hold on- vamram wrote that his DH is 2.12 mm, and the chamber volume is 41 cc. The 12.8 cc VOLUME of the DECK does not matter for the CB calculator, because it automatically calculates the volume based on the linear 2.12 mm DH. So inputting those # into the calculator, you get 8.8 as the CR.

Jimbo- from one of your calculator inputs, 0.3 inch DH is nearly 1/3 inch- way too much.


That sounds correct. I inputted that value twice, didn’t I! This is why it always takes a village! (You know the saying?)

Victor - time to recalculate. You may need to carve the heads out or shim the barrels after all! I am busy today, I will attempt to recalculate it later, if you have not already completed it.
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PostPosted: Sun May 16, 2021 9:46 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Ahhhhhh.....I completely missed Rome's post while viewing this on the phone. What you guys are now saying is that I double-counted the deck height....
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'74 Super 9/16 - present, in refurb process.
'73 Super - 6/18 - Present - Daily Driver!
'75 Super Le Grande...waiting it's turn in line behind '74.
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PostPosted: Sun May 16, 2021 9:54 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Here's an article about "Dynamic Compression Ratio" that explains how the intake valve closing point affects things.

http://cochise.uia.net/pkelley2/DynamicCR.html

Static compression ratio comparisons are really apples and oranges on engines with different intake valve closing specs.
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PostPosted: Sun May 16, 2021 10:19 am    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Adding the below comments for anyone following this thread trying to calculate their compression ratio. Found this pic to help with understanding the variables involved with compression ratio calculations. On ACVWs the one variable you normally don’t need to worry about is the head gasket as the cylinders mate with the heads directly, but if you are running a copper shim between the head and the top of the cylinder its thickness should be treated as the head gasket or added as increased deck height.
Image may have been reduced in size. Click image to view fullscreen.


The CB Performance calculator uses the different measurements to calculate the different volumes in the cylinder, then uses those volumes to determine the compression ratio. The combustion chamber volume is the only thing measured in CCs. All other measurements are dimensional in mm or inches. The calculator calculates the volumes from these dimensions making it easier for you.
    Compression ratio = (Piston displacement + Deck height volume + Combustion chamber volume) / (Deck height volum + Combustion chamber volume)


vamram wrote:
I tried my hand at the deck height and such calculation.

I got 41 ml of Smart Balance under the modified CD, which is tight flush up against the ....what's it called...step? Anyway, it's flush against the sides and tight down against the edge/top of the chamber.
Image may have been reduced in size. Click image to view fullscreen.

It wasn’t clear from your descriptions but the CD should sit “on top of” any step inside the head opening when measuring combustion chamber volume. This step is where the top of the cylinder rests and where a copper shim (if used) would also sit.. If the CD pictured was resting “inside” this step instead of on top of the step you are not measuring the correct combustion chamber volume. Also, if there was any air still trapped under the CD when you filled it with oil then the volume will appear to be smaller than the actual chamber volume.
The one variable which is easily controlled when assembling an ACVW engine is the deck height. By adding steel spacers between the cylinder and the case you increase the deck height by a controlled amount; reducing the compression ratio.
Note: Any increase in the engine displacement without making any other changes to the dimensions always results in increased compression ratio. This is why you must always check compression ration when assembling an engine with new parts.

vamram wrote:
And I got 12.8CCs of volume for the piston top/cylinder top space. I measured 87.95mm & 2.12mm depth from the top of the cylinder to the piston head.
Image may have been reduced in size. Click image to view fullscreen.

Seems like initially you were trying to measure the deck height “volume”. This is not needed as the calculator will calculate the volume based on the measured deck height (top of piston to top of cylinder) and the diameter of the piston. Instead of the 12.8cc you only needed to enter the 2.12mm as the measured deck height.

You last calculation seems much closer to the norm.
vamram wrote:
Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Sun May 16, 2021 1:01 pm    Post subject: Re: Yikes! I bought a '74 Super!! Reply with quote

Rome wrote:
Jimbo- from one of your calculator inputs, 0.3 inch DH is nearly 1/3 inch- way too much.


DAMN! That is not good. Should of had a zero in front of the three, after the decimal point. Nice catch!

Thanks Rome!
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TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


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