Reading the discussion of the possible difference between the measurements of the DR vs LS from piston top to top of cylinder.  I did get a spec from Wiseco on that the distance from the top of the pin to the deck is 0.0607", and from the center of the pin to the deck is 1.128".  However I'm  not so sure that I got everything correct.  Why ?  Because I was wondering about how this is useful when it occurred to me that I can compare a DR piston, of which I have a several, to a LS piston.  So I did.  Now these measurements are not exact because I could not find my digital caliper but did find a manual one.  The crude findings are:
Measured from top of piston pin to base level of the piston top.
DR:  17.2mm
LS:  16.6mm

Different from what I got from Wiseco.
Even if this is not absolutely accurate, in relation to each other the difference remained at about 1/2mm over the course of 8-10 measurements.  So there is a difference in the two pistons.  It would seem that the DR piston sits higher in the cylinder than the LS.  However this does not take into account of whether the piston pins in both sit at the same level  in the cylinder.

I found some parts and put a stock piston on a bottom end and a cylinder.  At TDC the distance from top of piston to top of cylinder is 5/32", measured roughly with a small metal machinist rule with a stop.

Does anyone have a DR engine handy ?

Let’s focus on the things we know, and see what we can figure out from them.

Dave reported a 195 psi compression pressure with a Wiseco 95mm and a stage 1 cam.  The stage 1 has an intake closing point of 40 degrees ABDC @ .050” lift.  The 95mm bore is 3.740”.  The 94mm stroke is 3.700”.

I reported a 155 psi compression pressure with a completely stock engine and a little over 1000 miles.  The stock engine has an intake closing point of 40 degrees ABDC @ .050” lift.  The stock 94mm bore is 3.700”.  The stock 94 mm stroke is 3.700”.

The stock combustion chamber volume is 57cc.

The stock head gasket is .026” thick (I measured with micrometer).  That works out to 4.7 cc.

The 5/32” negative deck reading Lancer took is very much appreciated.  It proves without doubt that there isn’t sufficient quench clearance to support ideal combustion.  At .156” its way too big.  It needs to be .040”.

Dave & Fast650 provided some rod length data, and its approximately 6.535” from the centerline of the gudgeon pin to the centerline of the wrist pin.

Regarding the compression height (vertical centerline of wrist pin to top of piston).  The value Wiseco gave to Lancer is correct.  I measured a new Wiseco at 1.123”.  That’s close enough to the 1.128” that Wiseco provided.  

The measurement Lancer provided for the LS piston (16.6 mm) works out to a compression height of 1.107”, so the LS piston is about .016” shorter.

That’s a lot of information to work with.  If we plug some of it into the RB Racing Compression Calculator and fiddle around with it, we can get some really valuable info.  All the calculations assume zero boost pressure and 500 feet elevation.  If I'm off a bit on the elevation it shouldn't be too big of an error.

Now, let’s use Dave’s numbers to estimate what the actual Wiseco compression ratio is.  You can do this by simply repeating the calculations using different compression ratios until you get a cranking pressure around 195 psi.  Using the following data, I got 195 psi cranking pressure.  Bore 3.740” (95mm), stroke 3.700” (94 mm), rod length 6.535”, static compression ratio 10.3:1, intake closes 40 degrees ABDC, boost 0, elevation 500 feet above sea level.  So the 95mm Wiseco results in a static compression ratio of 10.3:1.  I think that’s high enough.

I personally feel that anything over 10:1 is too high for a street application.  Pump gas is pretty sketchy, with 93 octane about the best available.  Over here 92 is the best you will find.  We can’t do much with ignition timing, and the bore is large.  I know the spark plug is centrally located, but the bore is very large, and its air cooled.  I wouldn’t advocate running much over 10:1, unless you can find a cam that closes the intake at 50 or more ABDC. Dave’s engine has slightly more displacement than a stock engine.  That results in a tiny bit more static compression.  A stock bore will probably come in a bit lower, like maybe 10.1:1.  That looks OK.

It looks to me like the cat’s meow would be to relieve the top of a flat top piston about 6 or 7cc.  You could do that by cutting valve reliefs or possibly machining a small depression in the top equal to 7cc, leave a nice wide band around the circumference to generate the quench.  That way, you would end up with around 10:1 static compression (relatively safe), maintain a quench clearance of .040”, and keep the combustion chamber wide open for flame travel.  To accomplish this, you need a piston with a compression height about 5/32” greater than stock.

By moving the crank sprocket on the crank one spline, and the chain on the sprocket one tooth in the other direction, minor changes in timing are possible. Looking at how stretched some of the cam chains are (pics posted on the forum), people using the modified tensioner are getting away with some really stretched out chains and really extended tensioners. Maybe the extended tensioner and a new chain would be enough to make up for the additional slack created by cutting the cylinder down?

Armen, it's a thing of beauty.  Indexing the drive gear to advance and retard cam timing is so cool.  So, if you achieve a 2.583 degree change by moving the chain one-tooth and the spline one-tooth, wouldn't you achieve a 5.166 degree change by moving the chain two teeth and the spline two-teeth?  And couldn't you go either direction, advance or retard.   Sounds like it's pretty adjustable.

Lancer my man, you are the test bed.  You lobbed material off the head and cylinder so you have intimate knowledge regarding the effect on cam chain tension.  What can you tell us about your real life experience with the chain after removing a total of .040" from the total height?  How much looser did the chain become?  How close did the slack side get to the drive side after the head & cylinder were shaved?  In your opinion, do you feel the system is forgiving enough to remove around .124" from the underside of the cylinder.  That's about 3 times more than you removed.

For example, the head gasket is .026" thick.  We want .040" quench, so we should shoot for .014" negative deck height.  If we achieved .014" negative deck, the result would be .040" quench (.026" gasket + .014" negative deck = .040" quench).  The Wiseco piston has a compression height that is about .016 to .021" greater than stock and the stock negative deck is 5/32" (.156").  With a Wiseco installed the negative deck would be reduced .016" to .021" (mid point about .018").  So just installing the Wiseco gets us to about .138" negative deck (.156" - .018" = .138"), and we want .014" negative deck.  So to achieve .014" negative deck, we need to shave the cylinder base .124".

Shave .040" from the head/cylinder interface is basically the same as .080" chain stretch.
At .03" chain stretch, you have about 18mm plunger projection.
At .08", you probably needed the second hole on the verslavy and were near the end of travel.