Looking for Info on TC head gaskets and head CC volumes

Discussion in 'Engine, Fuel and Exhaust' started by Rod Stewart, Aug 22, 2012.

  1. Rod Stewart

    Rod Stewart Active Member

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    I have read a few threads on the forum regarding static compression ratios for various engine diplacements, head volumes,etc..
    I still have a few lingering doubts, that I figured the experts on the forum could likley answer, so here goes:
    I see references to .030 and .045 head gaskets. Are all HD head gaskets .045"? Are there other aftermarket thicknesses besides .030"?
    I understand that original TC-88 heads are nominal 85cc volume, with actual values falling in the range of 83-87cc.
    When the TC-96 came out, did it use the same heads, or something different?
    The TC-103 and 110 engines use a 96cc head, correct?
    Are there any other common HD head volumes in use, other than milled heads?

    My 2004 FLHTCI has a big bore kit 95", SE 203 cams, V&H true dual exhaust, and K&N air cleaner. When measuring my compression I get 160/165 psi, which I thought seemed kind of high for a static 9.2 compression ratio. Does this sound about right? I used a standard compression tester and ran it through 5 or 6 compression strokes until the reading peaked. This is how I have always done a compression test.

    Thanks for any comments and feedback.
    Rod
     
  2. Jack Klarich

    Jack Klarich Expert Member

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    http://www.cometic.com/catalogs/harleydavidson.pdf Have a look here for the gaskets, keep in mind changing the thickness will alter your compression ratio, cc ing heads and milling may require compression releases
     
  3. dolt

    dolt Senior Member Contributor

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    I don't know what the factory is using now but the early gaskets were not MLS and actually measured about .050" but compressed to .042"-.045". The last set of H-D head gaskets I used was about six months back an they were MLS and measured .040".

    85cc-86 cc is typical. I haven't seen any smaller but have seen some that measured 89cc.

    The heads for the 96" are an upgrade with better flow. The floor was lowered on the exhaust side and the exhaust port is larger. 88 and 96 heads are interchangeable.

    No. The 96" and 103" heads are the same but the 110" heads are a completely different casting. They will interchange with the 96" and 103" heads but the chambers are much larger and unless other changes are made, the results will be less than satisfactory. A `103" is nothing more than a bored out 96"; like 88" to 95". The 110" uses a 4.00" bore cylinder with larger spigot and requires a case bore to use in 88"/96" cases.

    You did not mention the head gasket thickness but unless you are running the .030" thickness, your static CR is not 9.2 with a CCR of 162/165psi; more like 9.0 with a .045" gasket. In either case, CCR should be above 170; more like 175 with the thinner head gasket. Not that far off, the variance could be chamber volume and or deck height, which we don't know or it could also be related to your altitude; the above figures are based on sea level. So, not that far off and could be spot on when the unknowns are factored in.

    Did you hold the throttle open during the compression test? Did you perform the test on a hot or cold engine?
     
  4. Rod Stewart

    Rod Stewart Active Member

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    dolt:
    Thanks for all the info.
    I am reasonably certain that the head gaskets are stock HD .045", so the static CR is I guess more like 9.0 as you said. My spreadsheet shows that it should be 9.2 with a .045" gasket, .009" in the hole, and an 85CC chamber.
    Our elevation here is about 3200 ft ASL, so that may explain why my CCR's are a little on the low side.

    The heads are the original stock TC-88
    I did the test hot, and no, I did not have the throttle wide open.

    Rod
     
  5. dolt

    dolt Senior Member Contributor

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    Calculators are all a bit different but geometry is geometry; my calculator shows static should be 8.95 with the above data.

    Factor in altitude and your CCR calculates about 155psi but actual CCR measurements don't always reflect calculated CCR measurements; actuals are often times lower. Don't ask me why; I don't know.

    At any rate, your CCR looks good at your altitude and the pressures are very close; top end appears to be sealing up good. Take another reading but hold the throttle open if an EFI bike; if carburated, the CV carb slide won't open as it required engine vacuum so you will have to simply pull the carb out of the boot. You need to allow all the air availalbe into the cylinder for an accurate reading. Your CCR will measure higher.
     
  6. BUBBIE

    BUBBIE Well-Known Member

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    Just for information:

    My 09 96" pushes 200+ at 650 foot elevation in Wa.
    Down here at 4400 feet it is about 175-180.

    I am doing a build soon to 103 and Hoping I have it tightened enough to increase the CCcomp. to a Higher number but yet Not enough to be TOO much at close to sea level.

    Altitude Does make a big difference.
    Using the Big Boyz, you can plug in any elevation to see.
    Man, when I go to a spot that is close to sea level, from my 4400 feet, it feels like I have a Turbo installed:small3d031:

    signed....BUBBIE
     
  7. Rod Stewart

    Rod Stewart Active Member

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    Thanks again dolt and bubbie for all the info.

    I tried out the BigBoyz calculator. It seems to work very well, and I like the fact that you can select your cams and altitufe to find corrected CR and cranking compression.
    Using my parameters it looks like I should be getting cranking compression of around 158 psig, and I am seeing 160/165 psig. So I guess I can't complain.
    Actual compression likely depends on the barometric pressure on the particular day you do your test, so there are lots of variables.

    A few years back when I had the big bore kit and cams done my bike dynoed at 100 ft lbs and 82 hp, which I am happy with. It runs and drives well.

    Thanks again.
    Rod