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Leo,
When you get your JE's, check the CR - when I measured mine during rebuild, the actual CR was 13+:1, rather than the 11:1 it said on the box. Machined the crowns down to give (measured) 11.2:1. Initially retarded ignition by 2 deg, but after a day on the dyno, am back to standard settings (although now accurate, as timing marks on flywheel were out), with no pinking at all on pump gas.


Did you verify the CR with a compression test? I'm wondering what kind of pressure you got with 11: 1 vs. the oem 9.2:1.
 

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Measuring the actuall compression ratio achieved is a bit tricky. You need to be able to measure or calculate actual combustion chamber volume at TDC, and total cylinder + combustion chamber volume at BDC.

The most accurate way is the "beaker test". The high level overview is that we use a calibrated beaker full of liquid to first accurately measure combustion chamber volume with the piston at TDC, then drop the piston to BDC and measure the resultant combustion chamber volume + cylinder volume.

I use a little valve with a hose on it that I made that screws into the spark plug hole to control the flow of liquid into the chamber. The hose goes to a beaker with an outlet on the bottom of it, like an IV drip or something. I used the mondo turkey baster from hell for mine.

To do this, we need to assemble one cylinder, piston, and head to the motor. Leave the cam out of the head, but it needs the valves. Put some heavy grease on the rings so they seal the liquid that you will be filling things up with. I use ATF, but any oil will do.

The next part is easiest if the motor can be positioned with the spark plug hole up. Screw the valve into the spark plug hole, connect the hose, and hang the beaker. Fill the beaker enough that there is enough liquid to fill the whole cylinder, and then some. Write down the fluid level. With the piston at TDC, crack the valve and let it fill up. When it quits bubbling, and the fluid in the beaker settles to its new, lower level, the difference is your actual chamber volume. Write this down. The difference between the two measurements is the chamber volume.

From there, rotate the piston to BDC with the valve open, allowing the cylinder to fill. Take note of the volume of remaining fluid in the beaker. The difference between this lowest volume and the original volume in the beaker, the first number you wrote down before you filled the combustion chamber at TDC, is the combined volume. Write this down. A lot of guys get confused here, and use the difference from the second measured volume (after filling the chamber) - this is a mistake. This is the displacement, which we already know.

Combined volume / chamber volume = CR. And now you have one hell of a mess to clean up. It's easiest if the motor is on a stand that allows it to be rotated so the spark plug hole is down.
Is it really critical to know the measured CR accurately? I would think that a compression test would be sufficient, and as long as all the cylinders are reading the same, then their CR's are all the same also. I would think that having all the cylinders equal CR is more important than the absolute value of the CR.
 

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Thanks guys, pulled the trigger on a set of JE 92mm 11:5:1. $250 bucks.. not bad I'd say. Read some good things about the JE's, however most mentioned to retard timing a few degrees to offset for detonation.

I will think about adding an extra plug to the heads however, depending on the cost.
Did you get their heat barrier coating on the piston tops? I would if it was me.
 

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Great, thanks again, I will be doing most of the wrenching myself.

However, I'm concerned after talking to a local shop. They are recommending a replate of the cylinders even though they haven't seen them yet.

I have the standard drop in kit 92mm, and I'm no professional when it comes to assessing cylinder condition, but I was hoping to just do a hone and drop them in. What do you guys think? anything I should be concerned about. They look OK to me, still see cross hatching however there a few scores here and there. Keep in mind the motor did not smoke at all with previous pistons. The bike has 25k on it.
I don't think it's necessary, but I'm no expert either. That coating lasts a really long time.
 

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Discussion Starter #25
I did not get the heat barrier coating, didn't know it was available, and no I haven't checked the compression, the pistons will be in tomorrow actually.

I want to go ahead and get the cylinders sorted before I put it back together so I'm not ending up taking it apart again.

I guess in short I'm hoping to avoid a replate since I sprung for just the drop ins. I'm on somewhat of a budget. Do you guys recommend a hone regardless?
 

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Great, thanks again, I will be doing most of the wrenching myself.

However, I'm concerned after talking to a local shop. They are recommending a replate of the cylinders even though they haven't seen them yet.

I have the standard drop in kit 92mm, and I'm no professional when it comes to assessing cylinder condition, but I was hoping to just do a hone and drop them in. What do you guys think? anything I should be concerned about. They look OK to me, still see cross hatching however there a few scores here and there. Keep in mind the motor did not smoke at all with previous pistons. The bike has 25k on it.
If they are within spec on out of roundness and taper, there is nothing to be gained in re-plating them. I'm of the opinion that re-plating is a last-ditch effort to save a bad set - I have never seen a re-plated set wear as well as the original plating. Just knock the glaze and ring ridge off and re-use 'em if they are good. You will want to do this so the new rings seat. There are special hones meant to do this on nickasil - don't use a standard hone.
 

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Is it really critical to know the measured CR accurately? I would think that a compression test would be sufficient, and as long as all the cylinders are reading the same, then their CR's are all the same also. I would think that having all the cylinders equal CR is more important than the absolute value of the CR.
And you would be dead wrong...

Absolute compression ratio is far, far more important than cranking PSI, or "compression" ("compression test" is really a missnomer, leading to all kinds of this confusion - we are not measuring compression ratio, but rather the cylinder's ability to hold pressure). Cranking PSI has nothing to do with C/R. We can get wildly varying PSI values from the same static compression ratio, depending on valve timing. Compression tests are only used as a check for wear on valve seats and piston rings, and even then are not as useful as some think. Leakdown tests are more revealing.

A long duration, narrow lobe center, long overlap cam profile will lower cylinder pressures at the cranking rpm's normal for a "compression" test. They are meant to increase dynamic compression ratio at high rpm. Our motors run some pretty aggressive cam timing, so they definitely fall into the "meaningless" catagory if trying to use a compression test to measure compression ratio.

Air-cooled, high rpm motors are particularly vulnerable to damage from unnoticed detonation at high rpm, making compression ever more critical. as they detonate, they build heat in the heads that is not as well dissapated as in a water-cooled motor. That heat continues to build, and detonation continues to get worse, until something has to give. Following are photos of some that "gave".

First, a 930 (911 turbo) piston ravaged by undetected detonation from too much boost (effectively raising compression). Second, a 3.0 liter 911 cylinder assembled with miss-marked pistons that had much higher compression than advertised (I trusted the manufacturer, and while I set deck height, I did not do the "beaker test" - never, ever, again...).
 

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And you would be dead wrong...

Absolute compression ratio is far, far more important than cranking PSI, or "compression" ("compression test" is really a missnomer, leading to all kinds of this confusion - we are not measuring compression ratio, but rather the cylinder's ability to hold pressure). Cranking PSI has nothing to do with C/R. We can get wildly varying PSI values from the same static compression ratio, depending on valve timing. Compression tests are only used as a check for wear on valve seats and piston rings, and even then are not as useful as some think. Leakdown tests are more revealing.

A long duration, narrow lobe center, long overlap cam profile will lower cylinder pressures at the cranking rpm's normal for a "compression" test. They are meant to increase dynamic compression ratio at high rpm. Our motors run some pretty aggressive cam timing, so they definitely fall into the "meaningless" catagory if trying to use a compression test to measure compression ratio.

Air-cooled, high rpm motors are particularly vulnerable to damage from unnoticed detonation at high rpm, making compression ever more critical. as they detonate, they build heat in the heads that is not as well dissapated as in a water-cooled motor. That heat continues to build, and detonation continues to get worse, until something has to give. Following are photos of some that "gave".
Man, I ask a simple question and you jump down my throat. What the hell is wrong with you? If a compression test was "useless" then why does Ducati specify an acceptable range for that test? A compression test is useful for verifying that all cylinders are generating equal pressure at cranking speed. That is valuable information to me. Obviously, going through extensive liquid measuring is probably better, but not many of us can do that?
 

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Man, I ask a simple question and you jump down my throat. What the hell is wrong with you?
Dirk, you get this all wrong.
Higgy did nothing but bring up some very useful information, as always,
and in a very friendly, calm and adult manner.
thanks for the pics, the piston got his share of boost obivously.

:)
 

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Man, I ask a simple question and you jump down my throat. What the hell is wrong with you? If a compression test was "useless" then why does Ducati specify an acceptable range for that test? A compression test is useful for verifying that all cylinders are generating equal pressure at cranking speed. That is valuable information to me. Obviously, going through extensive liquid measuring is probably better, but not many of us can do that?
I'm sorry, I really did not mean it that way. I'm not here to upset anyone, or to "jump down (their) throat". I'm sorry I came off that way.

I didn't say a "compression" test is "useless". It is quite handy for determining whether a cylinder or cylinders are holding compression. Every motor out there will have a specified lower limit for the pressure generated when cranking. This number is easily derived from testing new ones, but it in no way represents their actual compression ratio.

I have seen very high compression (over 13:1) motors with the afore mentioned long duration, narrow lobe center, long overlap cams give as low as 130-140 PSI on a "compression" test. I have seen very low (7 to 8:1) compression motors with no overlap between the intake and exhaust show darn near 200 PSI under this test. This test is useless for determining compression ratio. It is only useful for determining leakage.

If you have no way of precisely measuring actual compressio ratio, you have no business building hot rod motors. Once we get away from a purely stock build and start using custom components, or start machining things, all bets are off. We need to be able to measure everything, including compression ratio.

That said, running certain aftermarket combinations may not require such care in assembly. A proven, off-the-shelf set-up, like the JE 92mm pistons under discussion, have been run - and therefore proven - by umpteen erstwhile engine builders. I would be confident in merely checking deck height with these and setting it to JE's recommendation. I would run the beaker test out of curiosity, having been burned in the past, but that's just me.

Anyway, no offense was meant. I'm just trying to help, and to save others the (sometimes expensive) grief I've suffered in the past. This stuff is a lot of fun, but it is not very forgiving of a slap-dash, hap-hazzard approach. "Good enough" hardly ever is, believe me...
 

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Discussion Starter #32
Been doing some research about Nikasil plating.

My next step would be to removed the "glaze" from the cylinder. Many people have used a green scotch brite with wd-40 and mimic the cross hatch pattern. I read that a stone hone can kill Nikasil.

What do you guys think? Anyone used this method for scuffing the cylinder prior to putting in new pistons?
 

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Thanks Higgy. Sorry for the misunderstanding on my part.
Hey, no problem. I know I come on kind of strong sometimes. My wife tells me it's a good thing I don't deal with the public in my line of work ;) - I'm an engineer, and they keep me all the way in the back, in a deep, dark corner of the office...

Anyway, at the risk of belaboring the point, I hope I was able to explain the difference between a "compression" test and checking compression ratio.

Been doing some research about Nikasil plating.

My next step would be to removed the "glaze" from the cylinder. Many people have used a green scotch brite with wd-40 and mimic the cross hatch pattern. I read that a stone hone can kill Nikasil.

What do you guys think? Anyone used this method for scuffing the cylinder prior to putting in new pistons?
You are correct. Do not hone nikasil with a standard hone. All you want to do is remove the ring ridge that builds up at the top and the glaze that covers the whole cylinder. Here are the ones we use:

The hone:
http://www.lislecorp.com/tool_detail.cfm?detail=106

The nikasil stones:
http://www.lislecorp.com/tool_detail.cfm?detail=124
 

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....I guess in short I'm hoping to avoid a replate since I sprung for just the drop ins. I'm on somewhat of a budget. Do you guys recommend a hone regardless?
No hone for sure on Nikasil. Regarding your exisiting barrels, you have a couple things to consider.

One is the condition of the bore. In my opinion, if you can still see the cross hatch and the vertical lines in the bore are not too deep (ie can't catch finger nail) you are probably OK.

You should have both the piston & bore measured to verify piston to bore clearance. It's not hard or expensive and you may as well know now in case it's off. Any auto machine shop can measure for you. The target is to have about .0015" to 002" clearance on installation. Every make of piston is different so check with JE on this one for acceptable installation tolerances, it could be less. Service limit is around .004". I am assuming BTW that these are new pistons. All pistons will shrink some so if it is a used piston (pre-shrunk as it were) you could install with up to .003". If you've got issues, a replate and hone to precise size is in order. Send the plater the piston to be sure. Of course at that point, you may as well go to the 944cc 94mm piston since your are plating anyway. Be like the rest of us and spend more money than you planned :)
 

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OK, I did some reading and found this article:
http://www.chevyhiperformance.com/techarticles/81679_tuning_engine_compression/index.html
It appears that it is the intake valve duration and not the valve overlap that can lead to lower compression tester readings. A late closing intake valve spills the cylinder mixture up the intake at low speeds. On another site I read that the effects of valve overlap during a compression test can be overcome by making sure the throttle plates are wide open. In the above article, they advise that a long duration camshaft combined with a lower static compression ratio will lead to lower compression tester numbers and result in an engine that does not respond well to the throttle at lower engine speeds. They suggested that getting the reading up to around 175-180 would provide better lower engine speed throttle response and a more enjoyable engine. Since our 2 valve engines seem to read about 140-150 psi, it appears that increasing the static CR would be a good idea unless we want to change camshafts to shorter intake duration versions. I looked up the data, and for the 900 IE engine, the intake duration is 280 degrees. This is higher than almost all stock Ducati 900cc engines, but I don't know if that is considered "long".
http://www.bikeboy.org/duccamspec.html
I found this:
"Camshafts with up to 220 degrees of duration (at 0.050 in cam lift) are considered best for stock unmodified engines and those with computerized engine controls. Once you go beyond 220 degrees of duration, intake vacuum starts to drop appreciably which upsets idle quality and affects the operation of computerized engine control systems."
So it looks like we are well into the "race" type of camshaft, hence the low compression tester readings.
The static CR on this engine is supposed to be 9.2:1. I would be curious to know what compression tester readings others have obtained with higher static CR pistons.
 

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Old school American pushrod V-8's are a whole different animal with regards to compression ratios and camshafts than our Ducati motors. The common plenum style intake and relatively low rpm operation changes everything.

Those guys are looking for street driveability in the 1,500 to maybe 3,000 rpm range. I don't know anyone who would continually lug a motorcycle engine in that range (except for a Harley, which is an awful lot like a pushrod V-8 anyway). Yes, a pushrod V-8 can reliably rev to 6,000 - 7,000 rpm or even much higher, but no one just cruises around spinning one up around 4,000 or more. They want linear power off idle to redline. We don't. We are happy when our power comes in much higher.

The common plenum intake really does not like long duration, narrow lobe center, long overlap cams. These cams can cause a great deal of reversion into the intake tract at low rpm's, as the piston starts to come up on compression when the intake valve is still open. This causes all kinds of tricky high and low pressure waves through the intake tract, and if it's shared with other cylinders, it "confuses" them by significantly altering the vacuum they are drawing on their intake stroke. It makes for a pretty darn rough idle, and a lot of coughing and spitting in the intake. We used to "idle" our big block MOPAR drag motors at over 2,000 rpm to mitigate this a bit.

Keeping the intake valve open past BDC on the intake stroke intuitively makes no sense. Why would we want this, if the piston simply pushes part of the charge back out when it starts to come up? Well, because at some point in the rpm range, it quits doing that. At higher rpm's, the momentum of that incoming intake charge takes over, and it continues to fill the cylinder even though the piston is coming up. That's the beauty of it - it actually "super charges", or "super fills" the cylinder. But it needs high rpm's to do that.

The downside of this is that it underfills the cylinder at low rpm's, where reversion is the dominant factor. To make up for this, we run high static, or mechanical compression ratios. This helps keep the motor from feeling "flat" at low rpm. A low compression motor with a long duration cam is a real dog at low rpm's, but we sure feel it come up "on cam" when it's spinning fast enough for this supercharging affect to start working.

Anyway, our motors mitigate many of the problems inherent in pushrod V-8's by both reving higher and having dedicated intake tracts. We can run a lot more duration and still have an acceptable idle, and no noticable "flat spot" at low rpm's, because our "low" rpm's are much higher than that pushrod V-8. And we don't have that low rpm reversion messing with the intake charge in the other cylinder, another reason we can run a lot more cam before running into low rpm problems.

The long and the short of it is that we are not constrained in the same manner as a pushrod V-8 with regards to camshaft choices. Their operating parameters are far different than ours, and demand compromises our's do not. Their "race" cams are our "street" cams.

Dynamic, or running compression ratio is a whole 'nother can of worms. Long duration cams, with their high rpm "supercharging" affect, are intended to raise dynamic compression at high rpm's. The bugaboo here is that, in an attempt to not completely kill low rpm power, we raise static compression ratio to help out down low. It can reach the point where a high static compression ratio, paired with long duration cams, can raise high rpm dynamic compression to an unacceptable level and we start seeing high rpm detonation. In the old days, we fattened it up and backed off timing, making low and mid range even worse. Today, we can map in a high rpm retard on the timing and richen up high rpm's on the fuel map to eliminate this detonation.

Anyway, I've rambled on enough. Cams/compression/intake must work as a package in the desired rpm range. Operating parameters for different engine types are, well, different...
 

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Dual plugs shine in applications where the original single plug is well offset from center and the piston dome blocks off the far side of the combustion chamber. It allows the flame front to start from two sides and meet in the middle, which allows the timing to be backed way off while still achieving complete combustion. Think old style hemi head, with big valves that almost touch, with the plug way off to one side in the crotch formed by those valves, like these:
Like in my Guzzis.

Dual plugging improved fuel economy 20%.

They are high-domed hemi-heads as you described.

Tom
 

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The downside of this is that it underfills the cylinder at low rpm's, where reversion is the dominant factor. To make up for this, we run high static, or mechanical compression ratios. This helps keep the motor from feeling "flat" at low rpm. A low compression motor with a long duration cam is a real dog at low rpm's, but we sure feel it come up "on cam" when it's spinning fast enough for this supercharging affect to start working.

Anyway, our motors mitigate many of the problems inherent in pushrod V-8's by both reving higher and having dedicated intake tracts. We can run a lot more duration and still have an acceptable idle, and no noticable "flat spot" at low rpm's, because our "low" rpm's are much higher than that pushrod V-8. And we don't have that low rpm reversion messing with the intake charge in the other cylinder, another reason we can run a lot more cam before running into low rpm problems.

The long and the short of it is that we are not constrained in the same manner as a pushrod V-8 with regards to camshaft choices. Their operating parameters are far different than ours, and demand compromises our's do not. Their "race" cams are our "street" cams.

Dynamic, or running compression ratio is a whole 'nother can of worms. Long duration cams, with their high rpm "supercharging" affect, are intended to raise dynamic compression at high rpm's. The bugaboo here is that, in an attempt to not completely kill low rpm power, we raise static compression ratio to help out down low. It can reach the point where a high static compression ratio, paired with long duration cams, can raise high rpm dynamic compression to an unacceptable level and we start seeing high rpm detonation. .
You make a lot of good points, as always. I wasn't aware of the constraints on cam duration caused by the common plenum. I just wanted to say that my motor has basically very little power below 4,000 rpm or so. I suppose this is normal, but I wonder if a higher static CR piston would help with this, and if so, how much is too much? Would a higher static CR increase low rpm power? I don't consider a static CR of 9.2:1 to be "high", but maybe I'm wrong about that. It seems to me that this Ducati motor has the combination of a long duration cam with relative low static CR, leading to not much power at lower rpm.

Also, isn't it true that for individual runners with carburetors, you're limited in intake valve duration because the carburetor needs to see a good steady vacuum? I guess this is not a problem with fuel injection.
 

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You make a lot of good points, as always. I wasn't aware of the constraints on cam duration caused by the common plenum. I just wanted to say that my motor has basically very little power below 4,000 rpm or so. I suppose this is normal, but I wonder if a higher static CR piston would help with this, and if so, how much is too much? Would a higher static CR increase low rpm power? I don't consider a static CR of 9.2:1 to be "high", but maybe I'm wrong about that. It seems to me that this Ducati motor has the combination of a long duration cam with relative low static CR, leading to not much power at lower rpm.
Yup, you're right on all counts. 9.2:1 is a relatively low static number, and that's part of why our motors feel sluggish below about 4,000 rpm or so. A higher static ratio would certainly help that.

The trouble we run into, though, is that the cams are not well suited to a much higher static ratio. We read above where guys have had to back off the timing to keep them from pinging, and possibly even richen the mixture. This is because our cams are the classic long duration, narrow lobe center, long overlap design. They are meant to provide this "supercharging" affect at high rpm. This provides for a good deal of dynamic compression, and the power gains comensurate with that high compression.

Motor design is always a compromise. To achieve notable specific output (hp per liter, hp per cubic inch) we need to spin them up faster, and tailor them to high rpm operation. Low rpm power suffers as a result. In trucks and family cars, we want low rpm power and driveability, so we sacrifice specific output.

Our carbies are "dumb" motors. We cannot progam an ECU to retard timing and richen the mix at high rpm. As a result, we need to tune for the "worst case scenario" of maximum dynamic compression. To do this, we lower static compression. Modern cars and bikes with programable ECU's change all of this.

The ultimate expression of this is modern variable valve timing couple with modern ECU's. We see new cars with very high static compression numbers that "fill in" low rpm power. We see low rpm cam timing set relatively "mild" to avoid reversion, and provide good low rpm cylinder filling and scavenging. Then, as rpm's rise, we see cam timing getting more aggressive to increase dynamic compression, all the while timing and mix being adjusted on the fly to eliminate detonation.

But, alas, our "dumb" old carbies aren't smart enough to do that themselves. So we have to protect them with wise choices in cams, compression, timing, and mix. It's all a trade-off, based on desired specific output (lots) at desired rpm (high). Harleys are at the other end of this spectrum - mild valve timing and higher static compression to provide low specific output at low rpm. You pays your money and makes your choices...
 

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The trouble we run into, though, is that the cams are not well suited to a much higher static ratio. We read above where guys have had to back off the timing to keep them from pinging, and possibly even richen the mixture. This is because our cams are the classic long duration, narrow lobe center, long overlap design. They are meant to provide this "supercharging" affect at high rpm. This provides for a good deal of dynamic compression, and the power gains comensurate with that high compression.
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Thanks again Higgy. I appreciate you sharing your knowledge.

So, if we install higher compression pistons and run into detonation, is it practical to change the deck height by changing the cylinder base gaskets instead of figuring out how to retard the ignition and/or richen the fuel mixture? I don't think the oem ECU allows the latter. I looked at the parts manual and they only list one size, which is 0.4mm thick. I realize increasing deck height will reduce power, but it's better than blowing up the engine. I thought I read somewhere that Ducati makes these gaskets in different thickness? Is there a known formula for the relationship between the gasket thickness and the static CR on our engines? What's the best method to measure deck height in these engines? I should check that before I put the engine back together.
 
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