ultimate lurker

cmnsnse, that's what screwed me up to begin with. Between the tensioner, the rotation, etc. I got all turned around. In reality, it doesn't really matter, reducing crank to cam distance will retard timing. I don't know about different ECU maps though, wouldn't surprise me.

Luis, thanks for the figures. I didn't realize that the only compression diff between USDM and JDM was the gasket. That makes it really easy to get more compression. I wonder if the JDM cam gears have different offsets in them to compensate for cam timing? If not, the natural retarding of the cam timing might provide some additional top end power on top of the compression gains.

UL

BTW, for those that didn't notice, 1.2mm is 0.047". Even compressed, that will be a little thicker than the nominal 0.030" I quoted (probably closer to 0.040", metal gaskets don't compress much). The JDM gasket, at 0.75mm is 0.030", which compressed will probably be in the 0.025"+ range. Luis, have you seen the gaskets? Does the USDM/ROW have another layer, or just a thicker center sheet?

cdelena

[QUOTE]Originally posted by ultimate lurker
[B] I wonder if the JDM cam gears have different offsets in them to compensate for cam timing?

cmnsnse

cam gears are brought closer to the crank, so there is less distance that is taken up by the chain.

Some engines have a cam gear that can be set to compensate for chain stretch(yes chains stretch because of wear)

Maybe this is the case - the main gear may have offset pin placements?

Also the mapping if different, (I think it should be) would give a slightly different power curve - compensating for higher compression at different rpm's.

mingster

what a beautiful, beautiful series of discussions.

i wonder how difficult it would be to replace the gaskets? maybe replacing it with JDM gaskets instead?

any thoughts? thanks to all.

cdelena

Sorry, this does not answer my question.. maybe I asked it wrong.

Of course chains stretch, and that is why there is a tensioner. But if the tensioner maintains the chain on the same cogs (which it probably does in a wide spec) doesn't the rotation of the crank and the cam gears remain the same?

I still don't see the issue.

marcucci

What you're arguing (thinking) is rotation- not distance. You have to remember that the chain is for timing, not just the rotational coupling. Yes, they still turn at the same rate. What throws off the timing is that by changing the vertical height of the cam gear (in relation to the chain drive), you remove distance in the chain (i.e. remove "links" or teeth). The problem comes from the fact that you are more than likley not removing a link at a time, but fractions of a link. So when you re-time the cams when you put the engine back together, you won't be able to get the timing exact. You might now be a half link off. Keep in mind that the cams and gears are keyed, you can't adjust them (they're not splined).

Now I'll throw my $.02 in the mix. I'm not familiar enough with the head to say for sure, but I'd be that with the coutinuously variable cam timing we have we *might* be able to adjust this, or the ECU might be able to figure it out. I don't think that with .020" off the head, or even .040" that the timing would be off too far. If we can't adjust it, maybe the ECU can/will do it itself.

Worst case you're looking at adjustable cam gears... with the chain, I'm not sure if this is possible. With as much as we share, though, with the new Civic and RSX it's only a matter of time until they are available.

cmnsnse

[QUOTE]Originally posted by cdelena

Quote:

Originally posted by cmnsnse

Sorry, this does not answer my question.. maybe I asked it wrong.

Of course chains stretch, and that is why there is a tensioner. But if the tensioner maintains the chain on the same cogs (which it probably does in a wide spec) doesn't the rotation of the crank and the cam gears remain the same?

I still don't see the issue.

point of rotation relative to crank changes = point in time when a vlave opens - duration and timing on the shaft remain the same

Nissan Z24 - pinned cam gear with 3 optional offsets to compensate between chain links
Subaru EA-82 - no adjustment straight pin=min adjustment is one tooth on a timing belt

Honda F20c = ??

Now they KNOW there will be chain stretch, did they design in an adjustable gear (not like the aftermarket stuff!)

PS our timing is NOT continuous, it is set mechanically between A and B parameters

ECU controlles spark and fuel maps only, well in a timing regard.

[Edited by cmnsnse on 05-25-2001 at 11:06 AM]

cdelena

Thanks for the explanation, I

Patch

Because of the JDM 11.68 - I'm curious if they are running a different FPR and slightly higher FP to compensate. I know honda dials in a margin of safety in the ECU for bad gas, etc to prevent detonation.

If the thinner gasket was added, the timing was advanced to spec and the FP was left at stock - I wonder if the ECU would pull the timing back because of detonation, if it saw any. That would erase all possible gains from the higher compression. I suppose to test - add in an EGR on the #3 runner and measure the temps with a stock headgasket in 4th gear at WOT and again with the thinner gasket [same tank of fuel and same weather conditions].

Patch

That gave me an idea
Theoretically - correct me if I am wrong - with a pinned cam gear, you could measure 2.5' of advance from the initial pin slot and (with a press} drill a new pin slot in the gear. Then you would line the chain, gears and cam on the orginal slot, make sure its to spec, slide the gear off the cam, advance the cam until the pin drops in to the newly drilled slot. Walla - 2.5' of advance.