CR Struggles

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Re: CR Struggles

Post by Amskeptic » Mon Nov 11, 2013 1:52 pm

Bleyseng wrote:Ok, I'll try but its devolved since trying to learn Dutch grammar for the last 4 years.
In English this would be a Dutch sentence: "Ok, I next to nothing try have".

Go slow with the grinding as it doesn't take much to remove too much quickly.
Your point taken is but very well. :cyclopsani:

Yes on the grinding, it is best to spread out your operation and kiss all the recommended spots before going back over them. While it is scary to consider that you are trying to blast away 1,000 cubic millimeters, just grinding back the combustion chamber exhaust area wall 1mm at the center striped area and 2mm on the upper and lower curves should do it nicely. You want a smooth surface finish and sharp transitions to the quench area near the plug area, not so important across from the plug where you can see that the combustion chamber ceiling is just scooped on out of there.

We are not allowed to touch the areas where the machinist has already ground down (up?) your ceiling.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: CR Struggles

Post by cegammel » Fri Jul 11, 2014 4:42 am

Will one of you experienced guys please check my numbers? I'm having trouble wrapping my head around this deck height thing...

Type iv engine, going in a 1980 Vanagon, 94mm pistons, 71mm stroke. I am putting an AMC head on one side, and a rebuilt VW on the other (don't judge, I can only afford one at a time).

The AMC head has a step of .028. The volume of the head without adding that step is 50 CCs. Am I correct to think that I should either calculate the .028 or the extra 5 CCs, but not both? (Note: If I calculate both , my CR drops to 7.1).

Not including the AMC .028, but including the .008 base shim, my deck height is .033.

The CBPerformance.com calculator puts my CR at 7.5 using the above numbers (94, 71, 65CC, .061 total deck height).

Is it worth it to remove my .008 and add a .020 shim to the base to get my CR down to 7.3?

That's one side. I'm still waiting on my VW head to come in, so I have no info on the other side. But, for the sake of math, let's assume that my deck height will be the same, and that there will be no step cut into the head. Let's also assume the same CC's...I would then need a .028 shim to get my deck height up to .061. Would I be better off using the .028 seal ring that comes in the gasket set (between cylinder top and cylinder head), or purchasing a shim for the cylinder base? In the latter case, I assume I would eliminate the .008 shim and purchase a .040 to make up the .008 + .028 (unless .036 are available...I haven't seen fractional shims).

Thanks for all your help; I would be sunk without this forum!

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Re: CR Struggles

Post by Amskeptic » Fri Jul 11, 2014 10:50 am

cegammel wrote:Will one of you experienced guys please check my numbers? I'm having trouble wrapping my head around this deck height thing...

Type iv engine, going in a 1980 Vanagon, 94mm pistons, 71mm stroke. I am putting an AMC head on one side, and a rebuilt VW on the other (don't judge, I can only afford one at a time).

The AMC head has a step of .028. The volume of the head without adding that step is 50 CCs. Am I correct to think that I should either calculate the .028 or the extra 5 CCs, but not both? (Note: If I calculate both , my CR drops to 7.1).

Not including the AMC .028, but including the .008 base shim, my deck height is .033.

The CBPerformance.com calculator puts my CR at 7.5 using the above numbers (94, 71, 65CC, .061 total deck height).

Is it worth it to remove my .008 and add a .020 shim to the base to get my CR down to 7.3?

That's one side. I'm still waiting on my VW head to come in, so I have no info on the other side. But, for the sake of math, let's assume that my deck height will be the same, and that there will be no step cut into the head. Let's also assume the same CC's...I would then need a .028 shim to get my deck height up to .061. Would I be better off using the .028 seal ring that comes in the gasket set (between cylinder top and cylinder head), or purchasing a shim for the cylinder base? In the latter case, I assume I would eliminate the .008 shim and purchase a .040 to make up the .008 + .028 (unless .036 are available...I haven't seen fractional shims).

Thanks for all your help; I would be sunk without this forum!
I hope Bleyseng reads this . . . :cherry:

If your cylinder barrels fit to the head spigots with a little clearance, do NOT use head sealing rings on a Vanagon 2.0 if you can help it.

Establish your deck height using base shims. I recommend that you be conservative and shoot for the 7.3 compression ratio. If you have a ledge on one head and no ledge on the other head, yes, use head sealing rings on ledgeless head to make them equivalent. Add the ledge to the deck height number, and measure cc's only to the quench area, like you would for the ledge-free head.
Am I perfectly clear?
Colin :scratch:
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: CR Struggles

Post by cegammel » Fri Jul 11, 2014 1:31 pm

Got it...but just to be sure...buy .020 shims for AMC side. My current deck height on side 2 is .023. So, I will use .028 sealing rings, which brings my deck height to .051. That means I also need .030 shims (and remove .008 gaskets) under the cylinder to equalize the two sides, assuming the volumes are the same. Right? Which part would Bleyseng not like?

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Re: CR Struggles

Post by Amskeptic » Fri Jul 11, 2014 6:45 pm

cegammel wrote:Got it...but just to be sure...buy .020 shims for AMC side. My current deck height on side 2 is .023. So, I will use .028 sealing rings, which brings my deck height to .051. That means I also need .030 shims (and remove .008 gaskets) under the cylinder to equalize the two sides, assuming the volumes are the same. Right? Which part would Bleyseng not like?
Bleyseng would not believe that I recommended not using head sealing rings on 2.0 engines . . .

NOW THEN, back to work!

You CAN gain all necessary deck height with base shims for the VW head side of the engine, but you must ascertain that the cylinder barrel edges are contacting the ledge (AMC) / cylinder head contact area (VW), and that the fin casting portion of the barrel is not contacting the head fin casting. This happens all the time! People over flycut! If your VW combustion chamber bowl has been hit with the flycut and is now smaller in perimeter than the AMC head, please go get the VW bowls scooped out carefully to match the bowl cc's of the AMC heads if possible. THEN you can add deck height on the VW side to match the ledge on the AMC side. Eventually, you will have similar quench area, same CR, and a smooth professional engine . . . yes, you will.
Colin

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http://www.thesamba.com/vw/forum/viewto ... highlight=
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: CR Struggles

Post by ruckman101 » Fri Jul 11, 2014 10:26 pm

The heads I used were reconditioned. And my machinist did take material off the cooling fins a tad to ensure the cooling fins weren't obstructing the ability of the heads to mate and torque to the tops of my cylinders. You don't want to torque to the cooling fin, but head to cylinder.

I had to use shims at the base of my cylinders to even things up from side to side, in addition to getting my CR down out of "high" compression zones. But mine is an upright type 1 engine. First time I've used shims on a rebuild. Ah youth.


neal
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Re: CR Struggles

Post by Bleyseng » Sat Jul 12, 2014 7:22 am

Amskeptic wrote:
cegammel wrote:Got it...but just to be sure...buy .020 shims for AMC side. My current deck height on side 2 is .023. So, I will use .028 sealing rings, which brings my deck height to .051. That means I also need .030 shims (and remove .008 gaskets) under the cylinder to equalize the two sides, assuming the volumes are the same. Right? Which part would Bleyseng not like?
Bleyseng would not believe that I recommended not using head sealing rings on 2.0 engines . . .

NOW THEN, back to work!

You CAN gain all necessary deck height with base shims for the VW head side of the engine, but you must ascertain that the cylinder barrel edges are contacting the ledge (AMC) / cylinder head contact area (VW), and that the fin casting portion of the barrel is not contacting the head fin casting. This happens all the time! People over flycut! If your VW combustion chamber bowl has been hit with the flycut and is now smaller in perimeter than the AMC head, please go get the VW bowls scooped out carefully to match the bowl cc's of the AMC heads if possible. THEN you can add deck height on the VW side to match the ledge on the AMC side. Eventually, you will have similar quench area, same CR, and a smooth professional engine . . . yes, you will.
Colin

Yes You Can
by Amskeptic
June 24, 2006

http://www.thesamba.com/vw/forum/viewto ... highlight=
Matching the Combustion Chambers size is important as Colin states. Using mismatched heads does create problems so try to match them as much as possible. Leaving out the head gaskets means you should "Lap" in the cylinders to the heads to get the best seal. 7.3 to 7.5 CR is fine but I am not afraid of going a little higher on CR. A tighter deck height can help with efficiency of the motor and I don't like to go above .060.

I do miss the days when you could just go buy OEM VW parts and just assemble them and it was good to go without problems....Ah, youth.
I can hardly wait to pull apart my Ghia to see wait BS is in the engine as the rest of the car was worked on by Ham Fisted Howler Monkeys.
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

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Re: CR Struggles

Post by Amskeptic » Sat Jul 12, 2014 10:08 am

Bleyseng wrote: I do miss the days when you could just go buy OEM VW parts and just assemble them and it was good to go without problems .... Ah, youth.
If I had known that the future would be this current state of cynical cheapness . . . I would have bought a used Datsun F-10 in college and just driven in between the lines for the rest of my life. Then I would not have had to endure being seduced by the quality of Volkswagens only to see it get strangled slowly by the indifference and greed of the current parts purveyors.
Bleyseng wrote: I can hardly wait to pull apart my Ghia to see wait BS is in the engine as the rest of the car was worked on by Ham-Fisted Howler Monkeys.
An image that I now cannot shake . . .
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: CR Struggles

Post by cegammel » Sat Jul 12, 2014 2:40 pm

"A tighter deck height can help with efficiency of the motor and I don't like to go above .060."


So...Should I not push to .073? I still don't have the VW head, so this is a bit premature, but here is the current outlook:

AMC side: Deck Height .025 + Shim .020 + built-in head seal step .028 = .073. I can keep my CR at 7.5 by eliminating the .020 and adding .008 (which is actually what I have done now, so it would be great to leave it alone...). I could even go ahead and button up that side if I don't have to order more shims.

VW side (assuming volumes are the same = 65cc): Deck Height .015 + Shim .030 + additional head seal step .028 = .073. Again CR remains 7.5 if I add .010 to the .008 in place of the .030.

In each case, I can easily lower deck height to .061. The head should be in by the end of next week, and then reassembly can begin in earnest! I'm running out of pieces to scrub and paint.

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Re: CR Struggles

Post by Amskeptic » Mon Jul 14, 2014 8:53 pm

cegammel wrote:"A tighter deck height can help with efficiency of the motor and I don't like to go above .060."


So...Should I not push to .073?
Nobody has given you anything but an off-the-cuff opinion above. No rationale but "the efficiency of the motor (engine)."

You DO what you have to do to meet your parameters. We have discussed them. Do you want 7.5 or do you want 7.3? I don't see a whole lot of difference and I do see a whole lot of thinking.

Please imagine that you are on the road. Can you feel the quarter-second faster time to 60 with a higher compression ratio, or can you see the happier CHT gauge at 7.3?
I am brushing in broad strokes here, don't over-analyze it.
Colin :blackeye:
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: CR Struggles

Post by Bleyseng » Tue Jul 15, 2014 7:25 am

The piston top is basically flat and the combustion chamber is in the center of the circle, a kind of pocket that contains the valves and spark plug. Beyond is the flat area of the head where the cylinder meets the head to form a seal.
You want the explosion contained in the combustion chamber not off to the sides so the "push" is in center. Too much deck ht and the explosion is pushing across the whole piston/head area vs contained in the small combustion chamber. Engineers try to keep the head combustion chamber shape small, just big enough for the valves and the spark plug. When the plug ignites the fuel mix the flame front travels across the combustion chamber. If the deck ht is too big the fuel mix/flame front travels outwards instead of pushing as hard as it can downwards. The engineers control the combustion ratio with domes or dishes in the piston top usually about the size of the combustion chamber not across the whole piston. Again this is to contain the explosion in a smaller area which I think helps keep CHT's down.
So try to keep the deck ht below .060 so the flat area of the piston to head are fairly close together but not less than .040 so they can't touch with expansion. This helps with the "efficiency' of the motor burning the fuel mix pushing the piston down in the center not spread out across it. We are trying to get the most "push" and complete "burn" of the fuel mix before the exhaust valve opens.

In my engine I am using the 1800 style heads with a 55cc chamber so I matched them with the 94mm 914 pistons that have a 10cc dish. I kept the deck ht to just below .060 and the Combustion Ratio worked out to 7.7 to 1. Yes, I tried some flat topped pistons after a friend drove my Westy and broke the top rings lugging it in my first set of 914 pistons. I had to set the deck ht to .075 with a CR of 8 to 1. The engine was a dog compared to the set up with the 914 10cc dished pistons and ran hotter. I ran this setup for about a year until I had time to find a set of 914 10cc dished pistons to install. Now when friends want to borrow my Westy, I say "No" as I already have enough headaches.
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

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Re: CR Struggles

Post by cegammel » Wed Jul 16, 2014 3:53 am

Excellent explanation. Now I need one of those about oil circulation, ignition switch function, timing, and the list goes on...

I think I will purchase a CHT sensorto prevent another meltdown. My main concern is longevity, not speed...

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Re: CR Struggles

Post by Amskeptic » Thu Jul 17, 2014 8:55 pm

Bleyseng wrote:I am using the 1800 style heads with a 55cc chamber so I matched them with the 94mm 914 pistons that have a 10cc dish. I kept the deck ht to just below .060 and the Combustion Ratio worked out to 7.7 to 1.
Did you know that the Road Warrior's VW dealer-rebuilt 1700 engine had 90mm Porsche domed pistons? I wonder what compression ratio I lived with in those early years . . . it was never particularly quick.
The pistons I used henceforth were lightly dished (7.5cc) 93mm.
Colin
(I have a set of domed 1700 Cofap pistons new in their boxes)
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: CR Struggles

Post by Bleyseng » Thu Jul 17, 2014 10:41 pm

Stock domed pistons gave a 8.2 to 1 CR which with good set are fine in a bus. A 1700 head can take more heat as it was way thicker thoughout its cross section. The cam also plays into the CR setting. Static and dynamic CR is important to engine set up. That is why I can set up my 914 with 9 to 1 and it runs really cool CHT's.
I am traveling now in search of camper parts in the Nederlands so no more detailed explanations from me!
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

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