2375 Water Boxer Tear Down

[Piledriver]

When I run the calculator on the motor you have described... and tweak the static CR (as you spec) to 10.5...
the DCR is ~9:1, which is high, but probably just manageable on pump premium gas with Heron heads and a tight deck.

This is based on the 35 degree IC timing mentioned + 15 degrees for the ramps.

To have the static and dynamic cr be the ~same would require a cam with zero actual overlap, which is A) unlikely and B)nowhere near what you are talking about.

I'm not sure what you are calculating DCR with.

[fastback]

i'm just curious about that cam's base diameter for the lobes?
IF it has a larger diameter there is a small chance that the lifters will block the oil return from the heads.
This has happend to me when using type 1 lifters and bushings for the lifters, filling the valvecovers and sucking oil through the valveguides

[jberger]

When I run the calculator on the motor you have described... and tweak the static CR (as you spec) to 10.5...
the DCR is ~9:1, which is high, but probably just manageable on pump premium gas with Heron heads and a tight deck.

This is based on the 35 degree IC timing mentioned + 15 degrees for the ramps.

To have the static and dynamic cr be the ~same would require a cam with zero actual overlap, which is A) unlikely and B)nowhere near what you are talking about.

I'm not sure what you are calculating DCR with.

I don't know how many different ways I can say it. My engine calcs out at 10.5:1 static compression. Using the not2fast compression ratio calculator using a 34° Intake valve closing event it has 9.93:1, give or take... Not 9.0:1

[syncrogreg]

That's what I get too.

ENTER YOUR DATA

CALCULATED DATA

Cylinder Head Volume (cc)17 Cylinder Head Vol (cubic in.) 1.037
Piston Head Volume (cc)39 Piston Head Vol (cubic in.) 2.379
Gasket Thickness (in.).040 Swept Volume (cubic in.) 36.219
Gasket Bore (in.)3.7795 T.D.C. Volume (cubic in.) 3.809
Cylinder Bore Diameter (in.)3.7795 Gasket Volume (cubic in.) 0.449
Deck Clearance (in.)-.005 Deck Volume (cubic in.) -0.056
Stroke (in.)3.2283 STATIC COMPRESSION RATIO 10.509

OPTIONAL DATA

Rod Length (in.)5.3937 Adjusted Stroke (in.) 3.028
Intake Closing Point (degrees) 34 DYNAMIC EFFECTIVE COMPRESSION RATIO 9.919

[Piledriver]

Ah, now I see the error...

If the not2fast calculator defaults are based on a stock late 8v VW motor, IC @ 50 ATDC would seem to indicate that is not .050" timing but ZERO LASH timing, so add 15-20 degrees worth of ramp to your .050" numbers.(or measure at .006 or so, the hydros have to move a tiny bit to close the check valve, an exact value would be very hard to measure)

Even a stock 1600 DP cam (with negative overlap at .050) will NOT provide 10:1 dynamic CE is the static is 10.5:1.

[syncrogreg]

Right you are. Did not add ramps. That brings it down to : DYNAMIC EFFECTIVE COMPRESSION RATIO 9.283

[Steve Arndt]

It is all an estimate since each brand of cams has a different opening ramp.

[Piledriver]

It is all an estimate since each brand of cams has a different opening ramp.

Right, and real hydraulic cams use different ramps than solids.

[syncrogreg]

Yes, which is why I thought I would offer my real world experience with this exact build. The only difference is the step cut in the head. Soooo jberger what did your head cc at? Did you have zero deck? I assume you had around 38-39cc in the pistons?

[jberger]

Yes, which is why I thought I would offer my real world experience with this exact build. The only difference is the step cut in the head. Soooo jberger what did your head cc at? Did you have zero deck? I assume you had around 38-39cc in the pistons?

My heads measured out at 16cc, milling .020" step only yeilded .5cc. Perhaps, depending on how accurate the measuring. I used a piece of glass cut to 104mm with a hole in the center and a graduated cylinder filled with dyed isopropyl alcohol. A spark plug installed without grounding electrode... I actually think head numbers can be off as the intake valve kisses the glass plate, holding it SLIGHTLY aloft. Pistons at 39cc if I remember correctly and yes I turned to zero deck. .040" copper head gaskets

I don't understand what ramps have to do with it. If I measure the degrees of the cam via a degree wheel on the crank, intake close at .050" (accepted height for measurable flow).... Then why would we need to add degrees for the "ramp".

To really blow your mind... How about figuring in the .040" of carbon build up on 86ish percent of the combustion chamber surfaces..... That has an actual impact on real time numbers. This is why my build went from no detonation to pinging within several weeks/months.

[syncrogreg]

Because .050 is not properly open, especially at high rpm. Its all about when the flow starts and stops.
You bring up a good point about the carbon build up. This situation has told you how close you are to over doing it. So I say fix your rings and install the same cam or one that closes the inlet latter and you won't have an issue. Then get some big rubber on that syncro and get it dirty!