Let's talk squish - 1.8 vs 2.0

Discussion in '16-valve' started by Briankl, Aug 15, 2014.

  1. Briankl Forum Member

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    Hi guys.

    This one is really rattling my brain, and I need a sanity check - too much doesn't add up, and it seems to me that CGTI forum would be good place to consolidate some info, as well as get it qualified, discussed, etc.

    Background information:
    I am taking the 1.8 PL of my rally car apart, to overhaul it, since the oilpan was punctured => need for new bearings, etc.
    I had another no-oil-pressure-related incident with it a couple of years ago, due to other reasons that not really relevant. This called for yet another rebuild.

    Engine specs
    Engine is a PL. Stock deck, stock pistons, stock rods w. ARP bolts.
    G60 metal gasket (1.6 mm. compressed thickness).
    0.9 mm. skim of the head, to up the CR to get close to 11:1 or so (though I haven't cc'd it).
    Catcams 279/268 cams (http://www.catcams.com/products/camshafts/datasheet.aspx?ENGINE_id=85&CAMSETUP_id=1097).
    MegaSquirt ECU.
    I had the limiter at 7500 rpm, and it put out ~173 bhp at the crank @7300 rpm, with around 26 degrees max ignition advance.

    Problem
    By the time of the previous rebuild, I noticed erosion on top of two of the pistons, in the small area facing in the driving direction of the car.
    Some would call this the squish area - but I will be getting to that.
    This is often a sign of detonation - and I had - from videos - noticed pinging, and upon examination I decided that I had run too much ignition advance (30 degrees max or so IIRC).
    Thus I didn't do much else to counter the problem, than retard the ignition.

    After that rebuild, I decided to go conservative on the ignition advance - for a long time I ran with 22 degrees max advance. That should actually be below the factory advance, that according to my research should be around 24 degrees. I run high octane pump gas, and did not notice pinging, though that is by no means a guarantee.
    At the rollers added another 4 degrees of advance to the ignition, for around 3 bhp extra, landing me at the 26 or so degrees max advance.

    After this I only got to do one short race, and a freak accident punctured the oilpan and required me to take the engine apart again.
    This time I saw erosion again - and this time on all 4 pistons - so worse than last time, even though it had a lot less mileage.
    [​IMG]

    You will notice that the flat section is very clean compared to the main crown - and I have valve-to-piston contact as well.

    I have obviously set out to figure out the problem and solve it, once more, and this time I am going about it a bit more thoroughly.

    Initial thoughts
    My initial thoughts revolved around piston-to-head contact in the eroded area - though it was counter intuitive.

    In short: I see "everywhere" that squish gap should be in the 0,5-1,5 mm. range. Some claim that anything over 1,0 mm. won't have the desired effect, and the engine would be prone to pinging/detonation.

    One quite knowledgeable guy suggest from the picture, that the gap had been really small, basically causing a vapor lock in the area, which in turn could have caused the erosion. I.e. the erosion was possibly not due to detonation.
    A second theory was that the gap was too small, causing some of the mixture to be caught and not burned as part of the normal burn. This in turn could lead to a detonating mixture in that area.

    Some research suggested that the squish of the 16V is around 40 thou (1.0 mm.) static when stock.
    Once you factor in dynamic parameters like piston slap (around 0.3 mm. in my current case) and a rod stretch of maybe 0.09 mm. for each 1000 rpm., I could very well have, if not contact, then maybe a very close gap.

    Reality check
    So I had a million numbers from research, and no real evidence of at least some of the realities in my engine.
    So I measured what the gap in that area was with MY configuration.
    [​IMG]

    It came out to 1.35 mm. static, which is a bit on the open side of things. Some actually claim that above 1 mm. should be opened up to above 3 mm., since detonation can occur in the squish band if it is in a supposed danger zone of 1 to 3 mm.

    As mentioned, I use a G60 head gasket, which has a compressed thickness of 1.6 mm.
    My research shows that stock 16V gaskets are 1.75 - 1.8 mm. compressed - depending on the manufacturer.
    Thus stock gap should be more like 1.5-1.55 mm. with room for a bit of piston slap.

    Theories
    First of all I noticed from a set of 6A pistons I have lying around, and various other pictures of 2.0 pistons, that the design of the 1.8 and the 2.0 pistons is different in the area in question.
    Basically the 2.0 pistons are entirely flat, with cut out only just for the valves.

    The 1.8 pistons have the area around 0.55-0.60 mm. lower than the main crown (I measured with a straight edge and feeler gauges)

    1.8:
    [​IMG]

    2.0:
    [​IMG]

    According to http://www.not2fast.com/vw/stuff/vw_engines.shtml the 2.0 has a lower compression height, which matches the value of the additional half stroke of the 2.0 over the 1.8.
    Thus the protusion of those two pistons over the deck (deck height), should be the same.

    If the compression height is the same on those two pistons, then the 2.0 will get slightly higher CR with the same head, which resonates with the apparent higher CR according to factory numbers.
    Also, the 2.0 would get better squish from the area in question, by around 0.6 mm.

    That would bring stock squish gap on a 2.0 down to 0.9-1 mm.
    That seems more usable :).

    Reverse calculation
    A reverse calculation can be done with these numbers:
    The protrusion of the pistons supposedly is around 0.6 mm. - that is calculated from the above link.
    On the cylinder head, the area in question is level with the sealing surface = 0.0 mm.
    The stock 1.8 16V head gasket is 1.75-1.8 mm. thick.

    The calculated gap of a 1.8 then comes to 1.75 mm. (gasket thickness) - 0.6 mm (protusion above deck) + 0.6 mm (difference in height from actual piston crown and supposed squish area) = 1.75 mm.

    I don't know if the height of the 9A/6A gasket is the same as the 1.8, but if it is, the squish should be around 1.75-0.6 = 1.15 mm.

    This all hinges on the 0.6 mm. protrusion to be true - I don't know if that is the case - please correct me if someone has an actual measurement, and I am wrong.

    What area provides the squish/quench in the 16V?
    That was a long way round to get to a supposed squish gap of around 0.9 to 1.15 mm. stock on a 2.0, and 1.35 to 1.75 mm. stock on a 1.8.
    But to me that seems to be reality - please correct me if I took a wrong turn somewhere.

    Going with that, I am seriously doubting that the area in question is actually what provides the squish-effect in the 1.8 version of the 16V engine - or at least that it has a sub-optimal gap.
    Going back to what I have heard a few places, that 1-3 mm. is a range to stay out of, it would seem that a tuned 1.8, could benefit from at bit of machining of the pistons in that area, opening the gap a couple of mm.

    A quote from a one guy on VWVortex:

    Given the stock CR and ignition advance, I would venture the guess that something IS providing proper squish in the engine - it has to with those numbers.

    I haven't examined this yet, but does the squish actually come from a "band" around the circumference of the piston, as it travels against the head?

    Given the bigger bore/same combustion chamber on at least 9A/6A, and the apparent same deck height, it would seem that the entire circumference is the squish - not only the flat area near the inlet valves.

    With the alternate piston crown design of the 1.8, it would even seem that the flat area near the inlet valve, is not really providing much squish, if at all.
    And that it actually may lead to detonation in that area, when running higher CR, due to the too open gap.

    The 1.8 also have a chamfer on the crown/side edge of the piston.
    I wonder what the effect of that is on the squish effect from the band along the actual crown circumference.

    It seems that the 2.0 does not have the chamfered edge, making the squish area much more effective.

    To-do
    I still have a few measurements and things I want to do.

    1. Verify gap in my current setup, with new bearings.
    2. Clay the piston circumference of my 1.8, to get a feel for what I suppose is the actual squish area, and what the chamfered edge means to the shape of that area.
    3. Measure actual piston protrusion.

    But given all this, I am prone to machining my next set of stock pistons (class regulations say that they have to be stock, but machining is allowed), and lower the height of my "problem area" by at least 1 mm. - possibly 2 - to get out of the supposedly hazardous 1-3 mm. range.

    In the meantime - please feel free to discuss. I think it is a bit weird to be honest, and all the info I have been able to gather from this and other forums, does not seem to hold up to the realities.
     
    Last edited: Aug 15, 2014
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  2. AjVR Forum Member

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    From what I have heard it is correct that there is a detonation "prone" gap can't remember what it is though - So at the moment you don't have any detonation marks at closest point of contact ?
     
  3. Briankl Forum Member

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    No det marks at the closest points - but the closest point are the very small protrusions at 3 and 9 o'clock in the head. I checked it out yesterday, and the width of that area where the piston meets, is less than a few mm. So I am guessing that it is without consequence.
    I held up a 2.0 piston as well, and the 1.5 mm. additional bore doesn't really do much - so I am kinda taking back the "squish is in the piston circumference"-thing. It is more like: 1.8 has really poor squish :).

    Since I can't change the piston, due to class rules (rally car), I have few options:

    - Decking the block to bring my problem area with 1 mm. or less of the head with a given gasket. Due to the difference in height of the squish pad of the piston, and the actual crown, I would need to either machine the crown a bit, or remove the 3 and 9 o'clock protrusions in the head. Otherwise they would be 0.55-0.6 mm. closer to the head, than the actual quench.
    -Thinner head gasket. Cometic makes them down to 0.76 mm. in a number of steps - need to do the math here. It is pricey compared to a stock item, but hey - this is motorsports :). This solution would require the same headwork/piston machining as decking the block.
    - Less ignition advance - pure and simple. But it may end up costing too much power for me to be comfortable width.
    - Less rpm. I am not sure if this helps, but I am figuring the shifting the powerband down 500 rpm or so could help.

    Right now I am very seriously considering the Cometic gasket-option.
     
  4. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Brian, good discussion by the way.

    Do not get hung up with squish or quench.
    It is there to help the end gases mix with the main tumble or swirl and improve FE.
    Also a hot spot generator if the end gas does not move outwards in the main mixture blurb and can lead to PI, dieseling and then det.

    Best performance result for the engine is, get it on a dyno and at WOT, use det cans to determine the BLD and MBT of the ignition settings at various AFRs no less than LBT of 13:1 AFR towards 12:1 AFR.

    My 2p
     
  5. fasteddie

    fasteddie Banned

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    Will read later when I'm firing on all cylinders :thumbup:
     
  6. Briankl Forum Member

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    With all due respect, I am going to get hung up on it. The 4 degrees extra ignition I added on the rollers, added 3 hp at 200 rpm or so lower.
    Al though I can't know for sure, I am pretty certain that safe levels of ignition advance will cost me too much power for me to be satisfied.

    So I'll be darned if I at least am not going to at least try to raise the level for what is a safe level of advance - at least when it is a matter of getting the right gasket, and modifying a piston that I am already going to modify (to solve the valve to piston contact issue).
     
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  7. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    What did tool did you use to determine 4 degrees was all that could be added and if the total advance was at BLD ( Boarder line Det) or MBT (Max Brake Torque timing). Also what fuel mixture was this test performed at.

    'Safe' levels of spark advance usually means either less than BLD or if not det limited, less than MBT. If this was not experimented with, you are loosing out on free torque for a given rpm/load site.
    Keeping the pistons cool with the optimum fuel mixture, ensures there will be no hotspots in the area prone to end gas accumulation. It is those hotspots that lead to local PI, which can contribute to det if the engine is already at the limit of spark timing.

    From what you wrote, it seems to me there is more robust performance to be had by looking at your calibration and the effect on torque per speed load.

    To put a spanner in the works to 'optimum' quench thickness, some of on here us run turbo ABF motors, with staked MLS gaskets ( just like the G60 but x 2) an increased squish area to more than 3 mm. At more than 270 bhp and 250lbft+, we have no det on our pistons, all kept in check with a well developed calibration. On a VR6T with a head spacer the same thing happens. Based on the internet's description of what is optimum, our engines should melt!
    On my stock ABF engine with 170 bhp and 163lbft, inspection of the pistons show no det in this area and this engine is calibrated to just short of det at 3 and 4k rpm and at MBT everywhere else. I do run it rich for component robustness though.

    That is not to say that pistons with the same CR but maintaining the squish thickness, would not raise the BLD/MBT limit and allow more torque per speed load. I just think from your description, there is more performance to be had, finding out where BLD and MBT is before suggesting quench is limiting you.

    Hope what was written makes sense.
     
    Last edited: Aug 17, 2014
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  8. Briankl Forum Member

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    Just to mess up the quoting - I think I get most of it - and appreciate you taking the time :).

    MBT was not examined/considered in any way.
    BLD was very un-scientific - ears (no cans), and comparison to other peoples figures.

    As for the mixture, with the initial advance (22 degrees max), it is mapped to get fatter with more rpm. It was around 13:1 @ ~4500 rpm, 12.75:1 @ ~5700 rpm, just shy of 12.5:1 @ ~6700 rpm and up to the 7500 or so redline.

    After we added the 4 degrees, we retained the fuel map, and saw a cleaner burn basically all over the curve, but particularly from around 5700 rpm or so, and up. The mixture had gotten leaner by about 0.25 or so, which we/I interpret as a more efficient burn, obviously getting more power (which also showed at the curve).

    A couple of questions:
    - Does it sound too lean on the top end?
    - Does the strategy of fattening up with more rpm make sense, and am I at the right sites (i.e. should I have gotten fatter at an earlier point in the map)?

    Of that I am aware - it was just not in the books to get that optimized TBH :).

    Well, I don't quite agree on that interpretation. From what I gather, +3 mm. starts getting you in a safe, albeit less effecient zone. So that could be one explanation why it is working. At the same time you could argue that you are missing out on "free torque" at the same boost (well, not that free since it would require machine work and/or other pistons).

    Splitting hairs aside, I do think I get the point: one thing is theory, another is reality. I am just trying to take in whatever theory AND other people's practical experience at the same time, and make sense of it.

    I hear you...

    Actually, looking over the numbers, I have a feeling that I may - or may not - have issues in the top end... I could just as well have the detonation at the lower areas.

    Also, I have been toying around with a CR-calculator, to try and get a feel for the changes in CR and trapped CR, that would result from a 1-1.1 mm. thick Cometic gasket.
    The static CR will get HIGH, and I have an issue that I can't actually machine the pistons due to regulations (I know I wrote something else before - but I double-checked).

    So I may very well be back to my old recipe, and then optimizing that.
     
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  9. AjVR Forum Member

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    What does the roof of the PL cylinder head look like same as KR?

    Id be tempted to machine the piston so that you can close the gap of the area with det and then deck the block. Does ceramic coating the pistons help them to run cooler?
     
  10. Briankl Forum Member

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    PL and KR heads are the same.

    As for machining the piston, I am on the same page - except I discovered last night, that I am not allowed to :(.

    I could possibly go with a thinner gasket, but with my current 0.9 mm. skim, and a 1 mm. gasket, I would end up with somewhere along 12:1 CR. Too much for my cams and fuel.

    I could get a non-skimmed head, and combine it with a ~1 mm. gasket. I would need to take out a bit of the chamber in the head, to allow the piston a bit of space at 3 and 9 o'clock. But that isn't all that much.
    In that case I would probably get around 10.8:1 or so CR (would require a bit of cc'ing to be certain).

    I do have a couple of spare heads, but none that are P&P'd, and with new guides, so that would be more work, time and money to get up to par.
     
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  11. mr hillclimber Club GTI Supporter and Sponsor

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    KR pistons are 22 tho proud of the block deck in std form and have around 50-52 thou squish with a std gasket from memory.

    The clearance to aim for is 40 thou...the block can be decked 4-5 thou to achive 26 thou piston protrusion, which will an MLS head gasket will give the 40 thou clearance.

    Either the cam timing is wrong or the valve pockets are not deep enough to suit the cam lift @TDC.
     
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  12. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    No problem, that is why we are here and happy share some of our experiences.


    This is extremely critical so you can determine the capability of the engine hardware pending sensible mixture control.

    I like how you have tapered the top end fuel mixture a tad richer than LBT. Numbers you used look good! You can freeze that part of calibration work and then step the ignition advance, using det cans to determine BLD or MBT, monitoring torque rather than bhp to know if you are heading in the right direction..
    Not sure what you meant by 'fatter' though or 'cleaner burn', unless you have in cylinder monitoring equipment?

    Determining the detonation limits are standard practices when mapping any engine. Also no two engines are the same and so you can have one engine that would accept more spark advance than another and have different spark advance/ cylinder pressure raise ratios.

    What I described is not an interpretation, it is an implementation that we as Club GTIers and other dubers, have running on quite a few track and road cars, ABF/9A Turbo or Supercharged, VR6 Supercharged and Turbocharged. Mapping sensibly is what keeps there engines from destroying themselves due to hot spots, PI, DET or Megaknock. Where was the number of +3mm mentioned. For a VW or a V8?
    In big 600bhp+ non VW motors, with pentroof heads/pistons and in inevitably 2 squish zones on either side of the piston, if an engine has too much compression, determined by the BLD limit and a required level of torque cannot be achieved at certain RPMs, we use a thicker gasket to raise the BLD limit and achieve the desired level of torque. It would be uneconomical to replace the pistons to custom units, maintaining the squish bands and at the same time, reducing the compression to our requirements.
    At over twice the power and torque of the std NASP engine, us VW FI owners are less sensitive to the odd 2 or 3 torques here or there and can afford to run a bit 'inefficient' as it costs a couple hundreds at that entry level. Where the dynamic compression of the engine cannot be bled off with a cam profile alone an we are likely to lower the DET limit and torque due to running higher boost etc, stock pistons are junked and there is the justification to run uprated pistons with lower static CR. e.g lowering from 9:1 to 8.5:1 when updating from 300bhp to 520bhp.

    Depends on where the theory comes from and if there is supporting data to back up the theory. Lots of it on the internet can be myth.
    You might be well right with what you are saying but you cannot conclude this is your problem until other options are exhausted and in this case the calibration is simply not pushed hard enough.


    Check the calibration properly first and then you can see if and how those theories add up.
    Looks like you fuel control is already good IMO it s just the spark you really need properly experiment with, with before assessing the engine design.
     
    Last edited: Aug 18, 2014
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  13. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Jason, you are proper old Skool lol
    In 'new' money 022" piston protrusion = 0.56mm
    Your suggestion for minimum quench is 040" = 1mm
    Your observations on an stock engine is at 052" = 1.32mm, which sort of aligns with the 1.35mm Brain measured.
    If this direction is deemed necessary, I would also suggest decking the block and keep the gasket thickness std.

    I have measured the distance of the closed intake valve to the piston pocket@TDC on a stock ABF and KR engine, and it is just over 4mm of travel. The exhaust is not a problem that is over 10mm. The Cat Cam quoted is timed at 2.7mm open at TDC, so agree there could be an issue there.

    Thus making 2 problems to investigate before fettling the block deck.
     
    Last edited: Aug 18, 2014
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  14. HPR

    HPR Administrator Admin

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    I see your head is skimmed 0,9 mm that makes your inlet valves come closer to the pistons.
    Inlet valve is 2,7 mm open at TDC BUT thats not your closest point of valve to piston distance, as the valve opens faster than your piston moves away from TDC ...the first 15 degrees are the danger zone.... reckon 8- 9 degree ATDC as a typical figure were to valve is closest to the piston, You need minimum a 1 mm safety margin ( every cam manufacturer recommend this)

    0,9 mm Head skim + 2,7 Valve lift + 0,5 - 0,6 mm rod /piston stretch ...that makes up already 4,2 mm and then we havent counted a 1 mm safety margin....

    Taking above into account skimming the block doesnt look wise .unless you put the valves deeper into the head to create more distance...

    On the 1 3 mm theory... take for instance performance pistons have there high dome close to the combustion chamber wall what forms also a squish zone and at the same time protecting the ringlands against detonation / extreme heat) or they leave a larger gap ( mostly 4 mm + )
     
  15. Jon Olds Forum Junkie

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    that 8 to 9 degrees figure is very useful, thanks
    Jon
     
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  16. TrackCab16v Forum Member

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    if your valves are hitting your pistons , not good , cam timing got to be out, , unless you have seriously machined things down .and all componants have not been equally machined

    ,so if your cam timing out your fuel air, and spark,are not going to work together , correctly , . its the incorrect timing of the burn that's eating your pistons , possibly the charge ignited to early in the combustion cycle
     
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  17. Briankl Forum Member

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    Judging from the marks they are just kissing them - well - maybe french kissing :).

    As for the timing being out, that is possible. I did spend a fair amount of time with dial gauges getting it settled, but I did have difficulties.
    The issue being that at least one of the adjustable chain sprockets seem to be ever so slightly off centre. That means that the tension of the chain is taut in one position of the cams, and a bit slack at a different.
    Unfortunately it is slack near TDC, and that allowed the inlet cam to move a bit when setting it - I couldn't really know for certain if it was going to be at one outer position or the other, that the cam would be at the point of timing. I spent quite a bit of time fiddling around with it. Obviously it is quite possible that something is a bit out, which is why I will be checking the sprockets again, determine which one is good (I hope at least one), and just go with that.

    One curious thing is that I have a CatCams adjustable belt pulley as well, and despite the 0.9 mm. skim, it ended up being adjusted at exactly 0.0 degrees. I could imagine that with a stock head, but that 0.9 mm. skim should give me somewhere around 0.7-0.9 degrees offset.
    It could just be circumstantial though - but I do find it curious.

    Yep - that is why I will be going through the process of meticulously measuring things and double checking once more, before I decide exactly what to do.

    And thank you for all the advice, info, experience, etc. - it is good to get a lot of input.
     
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  18. TrackCab16v Forum Member

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    may be first buy a brand new cam chain , its a must on tight tolerences ,
    if in dought remove them cam ajustable pullys and fit a pair of good standard cam cogs . you know they are wright .
    get a good quality cam belt vernier , , zero up every thing , , engine should turn all componants with no major cam chain slackness , correct tension on cam belt
    once every thing is working , turning , running , basic map , afr ok , bla bla .
    you can get enough cam movment from the vernier , power run , adjust in 1 degree incraments, advance,or retard some engines repond s accordingly . nothing should hit , don,t take much adjustment on that vernier .to gain hp.
    ive seen this procedure followed by all the old school 16v tuners with good proven safe results ,

    hope it helps
     
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  19. Briankl Forum Member

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    I have bought that already for the same reason. I actually just picked up the parcel on the way to work this morning.

    I was actually not going to consider that, but you do have a point. I originally bought the cogs because I went the dual exhaust cam route. But given that the CatCams set is made to just drop in, the inter-cam timing should be fine with the stock cogs. It is not likely that I am going to fiddle with the intercam timing anyway, so if it is correct with stock cogs, then that'll be fine for me.

    Generally I try to Keep It Simple (Stupid) for what I want to do, and not introduce too many changes and variables - and I think I am fairly good at that when planning ahead.
    But going back and reevaluating the relevance of past changes, is not a strong ability with me - so thanks for the reminder :).

    I have the vernier - nice CatCams one with indexed holes, allowing for 1 degree changes secured by a pin while adjusting. I was going to go for the zeroing of everything - particularly since I wanted to get rid of the chain slack issue, since I am fitting new pistons, etc. etc.

    Would anybody venture a guess on how much power it "should" make with the modifications listed in the initial post?

    I haven't mentioned that the head has had a mild P&P. It was done by myself though, so who knows what the quality is like.
    Since I did go conservative on the inlet I tried to trade potential performance for insurance against messing things up :). I was not really going for actual reshaping, more like cleaning up.
    As for the exhaust I tried a bit more reshaping, going for a proper taper (measured by some inserts I made), etc.
     
  20. Briankl Forum Member

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    Denmark
    Ok, I guess I should come back with an update. I spent a lot of time in the shop yesterday into the night (as in: I went to bed at 3:00 AM - I wanted to get all the measuring done so I can lay down the plan, and order the remaining parts).

    I mounted up the new used crankshaft, cleaned up one of the new used pistons, and mounted that as well.
    Just for giggles I put in a piece of solder on top of the piston - just to see what the worst case would be while zeroing everything in.
    I then proceeded to put on the cylinder head loosely, and then lift out the cams. I examined the adjustable cogs for runout, but couldn't measure any more than about 0.2 mm. with calipers. It was very unscientific though, and just to see if I could easily determine if one or both cogs were askew, or what.

    I took of the adjustable cogs, and dug out a pair of stock ones from the parts pile, and mounted these. Then the cams went into the head again, and everything bolted down with the old head gasket.

    First off I obviously timed the exhaust - and this time the stock/zero setting of the vernier was WAY out. I don't remember the exact number, but using the "timing at 1 mm. lift"-method, I was off by something like 10 degrees at the crank. Pretty significant to be frank.

    After timing the exhaust, I moved to the intake, and right off the bat, it was evident that using the stock cogs on the CatCams, did NOT work. The timing was out by more than 10 degrees. Obviously I double checked the timing marks and so on, but everything here was spot on (hard to get wrong TBH).

    I then took to determine more precisely which of my adjustable cogs had the most runout. I own an old lathe, so I turned down an adapter that had a tight fit with the cog, then put the cog on it, and measured the runout of the cog while mounted in the chuck. Somehow this was pretty good. The other cog was checked in the same way, and didn't seem too bad either, but was worse than the first.

    I then took out the cams, pulled the stock cog off the intake cam, and mounted the adjustable one, and then refitted everything again.

    I was now able to get the intake timing spot on, and the chain didn't have any slack in any positions, and thus it didn't lash back and forward when adjusting.

    After that, I took the head off once more, and examined the solder. It had been squeezed significantly, but it was well within the limits.
    This was worst case measurements, since I had been fiddling with cam timing.
    So I proceeded to put in a new fresh piece of solder, lay down the head once more, remount cam belt, time it up, go through a couple of revolutions, and then disassembled once more and measured the solder.

    Finally I measured the protrusion of the piston above deck, as determined the thickness of the gasket (stamped on it, and I measured as well to verify).

    All of the above netted me the following results:

    Protrusion 1.0 mm - maybe a bit more (I used feeler gauges, and I don't have any thicker than 1.0 mm., and that did feel a bit loose. I think 1.05 or maybe even 1.1 could have fit).
    Squish: 1.35 mm. as before. The new used pistons are about the same as the old ones with regards to compression height as well as the difference in height of the squish pad and the actual piston crown.
    Valve to piston clearance: One valve was 1.5 mm. The other was 2.0 mm. Clearance of the side of the valve to the piston was around 1.5 mm.. I attribute the difference in height to either difference in seat height, or a lifter that isn't as "pumped".
    Gasket thickness: 1.7 mm.

    The protrusion surprises me a bit. It is a fair amount above the 0.6 that the standard measurements promise. I have no evidence, but I would be surprised if the block has been decked in the past, so maybe the protrusion is more like 1.0 mm.?
    I was also a bit surprised by the gasket thickness. I can't remember seeing regular/stock G60 MLS gaskets in 1.7 mm. thickness - and I am very certain that it was just a stock OEM part.

    I am very tempted to go for a 1.5 mm. gasket. It would bring the squish down easily, and the valve clearance would still be ok according to conventional wisdom.
    A part of me is a bit vary though - what if some of the valves have bit less clearance - I have to make up my mind whether to take that chance.
     
    erreesse and tshirt2k like this.

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