Deck height, compression ratio, and valve relief flat top pistons, In a 2.0 Options

[emerygt350]

I have the rings in but there is still quite a bit of free play. I have been generally measuring across the center of the pin, but I have not been paying attention. I bet it will make a difference if I pay better attention to that. I can use a micrometer to compare heights top to bottom as well.

[Jack Standz]

Did a real thorough job on the deck height today. Measured all the sleeves and tried to do some matching. I don't think it mattered much, it doesn't look like my case has ever been cut.

Bolted down nice and snug I got
.028
.031
.023
.028

So I guess I am pretty much stuck with a .03 shim. When I get ready to put it back together I will see if swapping cylinder/piston combo on the .031 with the .023 makes any difference. Looks like around 8.3 for compression ratio, which is what AA said for the combo.

Case hasn't been decked?

In a perfect world, send to the shop and get it machined. That way, you won't have any regrets (or hopefully leaks) later. But, then how many of us live in a perfect world??

[930cabman]

Did a real thorough job on the deck height today. Measured all the sleeves and tried to do some matching. I don't think it mattered much, it doesn't look like my case has ever been cut.

Bolted down nice and snug I got
.028
.031
.023
.028

So I guess I am pretty much stuck with a .03 shim. When I get ready to put it back together I will see if swapping cylinder/piston combo on the .031 with the .023 makes any difference. Looks like around 8.3 for compression ratio, which is what AA said for the combo.

Case hasn't been decked?

In a perfect world, send to the shop and get it machined. That way, you won't have any regrets (or hopefully leaks) later. But, then how many of us live in a perfect world??

Assuming the shop gets it right, easier said than done

What are the specs on your case now? very possible she's just fine

[emerygt350]

Everything seems nice and level on the case, no sag. I am going to remeasure again today being careful about the piston being level in the cylinder and measuring across the pin position.

[emerygt350]

Ok, redid them all using 4 bolts instead of two, extra careful to tighten equally and a little at a time. Made sure all measurements were taken at the same place along the midline of the pin. .028 all the way around. Much better. Surprised there was so little variation among cylinders.

[rfinegan]

Woohoo..great Job! Just need the 0.030 shims for 8.1 cr

[emerygt350]

That looks about right. Maybe while I wait for the shims to arrive I will try cc'ing the heads again.

[technicalninja]

.028 deck height on all four would make me want a base shim of .010-.014 with hypereutectic pistons (Keith Black).

With forged pistons I'd want a base shim of .015-.025 depending on the base material.
4032 would get .015-.018
2618 would get .020-.025

I'm a believer in NOT using anything between the cylinder and the cylinder head.

I prefer the hyper pistons OVER the forged pistons for a street car.

Want to scare yourself? Check deck height with a forged piston with no rings on it at 90 degrees from the pin bore.
Then rock the piston on the pin bore.
You will see a total range of .020 change in deck height between low and high.
Forged pistons can rock in the bore SO MUCH more than you expect...

Thank God that variation doesn't actually occur during operation.
There is so much resistance generated by the quench areas on the head that the pistons tend to stay flat during operation.

If they didn't, we'd need double the quench clearance that we use now, and the quench action would be greatly diminished.

I do have one question. Why do you need shims to check the combustion chamber CCs?
Figured it out! poor reading skills on my part...

How are you checking this now?

I've always used a plexiglass plate (round plate at the correct diameter for VW air-cooled stuff) with a couple of holes drilled in it and either a cattle syringe (60 cc) or a burette to measure volume.

The reason for two holes is it is a shitload easier to clear the bubbles with a vent hole.

I use Vaseline to form an airtight seal to the cylinder head.

[emerygt350]

These are hyper pistons. I am going with the .058 on the deck, flat tops with a relief, most people I have been reading (Wilson as well) say .04 at bare minimum. I don't want to take any chances and somewhere around 8.3 is good for me.

I was using veg oil and a piece of Plexi (two holes) but it was real thin Plexi and the Vaseline didn't seal well due to uneven pressure yada yada yada.

[emerygt350]

Decided to go about it differently. Play doh.
Shot a little oil spray into the chamber first. Worked pretty well. I think I am getting about 58 or 59. So pretty darn close to 60. Definitely not more.

[technicalninja]

I believe you are leaving 5-10 hp on the table with a quench distance that high.

.040 is what I use for customer engines where I'm being a bit more conservative.

Cast hyper from a reputable company on decent H-beams can often work at significantly lower distances.

One builder I know runs hyper-eutectic "claimer" SBCs at .029 without trouble.

Yes, I know this is not a T4 and is probably more dimensionally stable than a VW boxer but .029 is too tight in my book.

The tighter the quench the more detonation resistant the engine becomes.
It can run fuel with less anti-knock resistance and commonly requires 5-7 degrees less total timing to make MBT happen.
Compression increases slightly.
The piston crown and combustion chamber stay cleaner as well.
The only drawback IMO is you have to be far more careful during assembly and really nail the deck height measurements.
It's less forgiving for trash running through the engine as well but if you have foreign objects entering your intake track you deserve what happens...

The "quench" argument is a moot point if you're running a fuel that has extremely high detonation resistance. For a methanol or nitromethane application this distance is far less important.

For folks running pump gas it is the single most important "blue-print" distance to get right IMO.

This measurement for me is "the smallest clearance possible that has the ability to turn at 110% redline without the piston crown touching the head."

If this ends up placing the piston crown too close to the opening/closing valves then the valve pocket in the crown needs to be deepened/modified.

It is possible to build a 10.5-1 flat top Datsun Z motor that can run regular with less chance of detonation than the stock 8.3-1 motor has.
It also requires a much larger duration cam profile (has to with the compression) and makes 40% more power than the stocker.

I believe the quench phenomena starts about .065" and only gets better right up to the point of contact.
At which point it all comes apart.

I've built multiple engines (not T4s) with a quench of .035-.040 and had no failures.
I'm also beyond anal regarding engine clearances...

One thing to remember. Changing deck height on a T4 is EASY!!!
Doing it on almost anything else requires adjusting rod length, offset grinding the rod journals, decking the block: significant machine shop processes and if you go too low...
It sometimes requires a new/different block.

Being able to place shims between the cylinders and the block is a very welcome change for me.
Gives me options I've never had before...

[emerygt350]

You are tempting me to go with .02 but since I am not touching the bottom end I suspect I should be pretty conservative right?

[930cabman]

"Leaving horsepower on the table" nobody wants this.

[emerygt350]

I mean, if I go with .02 that puts me at .048, that's almost .05

..

[technicalninja]

.048 wouldn't bother me with forged but...

If I had it out, down as far as you have gone, it would go all the way.
I'd know exactly how much bearing clearances I had, and the basic condition of all the lower end parts.
I would NOT put a stock camshaft, stock rods, or stock compression height pistons back in.
I'd do a bunch of little things that you are not doing.
I'd change quench, rod length, compression height, cam profile, pushrods, bore size.
If the crank requires grinding, I'll have it offset ground. (I think it's good to go as is)
I did a bit of weight reduction measurements a month back and found 3 1/2 lbs. of reciprocating weight to dispose of (without going to exotic parts). That's a BUNCH.
I'd drill extra holes for rear main seal drain back.
I'd try to find a reverse lip rear main seal.
I'd smooth the combustion chamber and port profile the head (mild porting).
I'd have the heads heavily fly cut.
I'd lap the cylinders into the heads.
I'd ceramic coat the piston crown and combustion chamber. I might use a heat dispersing coating on the outside of the cylinders and heads. (Still researching this)
I'd do all of the oil system mods.

I purchased a nice core 2.0 from 914sixer and am currently entertaining re-using the stock 2.0 crank with the above mods. I may re-use the Mahle cylinders and have them bored out to 96mm. It's a actually more expensive than buying new cylinders but I've seen way too many complaints on the forum regarding the quality of currently available new parts.
You, yourself, wanted to re-use pushrod tubes and I agree with you.

Jake Raby killed a new flywheel for me just recently. His machining .300 material of a brand-new German flywheel was an eye opener for me.
His advice- find used real VW stuff from the 70s. I have four...

What I'd prefer to do is find a good 78mm crank but the costs associated with the stroker build quickly escalate to greater than the price of a used conversion engine.

I haven't built a performance engine with greater than .042 quench in 20 years.
All my stuff is streetcar (and crappy fuel) based and quench is paramount to me.

If you're shooting for 8.3-1 you are fairly detonation resistant just because of low compression and it is far less important.

A water pumper below 9.5-1 is an appliance motor to me (not worth going hard) but this is not normal in the air-cooled world.

It appears that the T4s most of you are running have bigger cams and lower compression (a full point) than water cooled stuff.

So, I'm a builder and have to rip it all the way down. I cannot resist the urge...
You should do you, if you want conservative, stay conservative. It's cheaper.

I'd have no issues running your combo down to .040 but I wouldn't actually do it.
I'd do more!

I'd expect a proper 2055 build, with the above mods to generate 125 HP at the flywheel using normal supporting pieces (dual 40s or stock FI / 123 distributor / premium fuel / conservative tune).

My two liter will have 9.5-1 (or higher) and a cam profile nearing 300 degrees of duration.
I will run LESS than .040 quench on this motor but it will be blue-printed, balanced and assembled by an OCD pin-headed bitch.
With a modern sequential COP FI system and E/85 fuel I want to hit 125 at the wheels which is getting close to doubling the stock power

My first 914 was a stock 1.7l with a big bore kit in it (1911?). It was assembled by me when I was 16/17. I didn't know what I was doing back then but it still was great fun and was one of the early builds that started my automotive career.
I didn't even know about quench back then...

[emerygt350]

All good points, but I exceeded my budget on this (time and money) long ago. In a couple years I will do it again and get the bottom end.

I think I will add .02s to my order and make a decision at install. I will start with the .02 and measure it up and see how I feel about it.

[emerygt350]

Engine is going back together now. Ended up with a .02 shim that put me at .043 for my deck height. A little tighter than I wanted but the 8.6ish compression is right around what I want. Checked the valve clearance on the pistons with some clay, no issues there. Exhaust didn't even touch the clay and .960 depth of clay on the intake. Tomorrow I will check the valve geometry and it's just engine tin and reinstall....

[emerygt350]

[emerygt350]

[930cabman]

Exciting stuff

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