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  1. #1
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    Head Deckers -- I need some info!!! <---

    OK, so the original 3.5L in 1990s produced 10.4:1 compression, which has been reduced back to 9.9:1 in our engines. So does anyone have the calculations made already to deck the heads to get it back up to the 10.4 ratio? I believe even 10.6 should be possible for pump gas. How much timing can the knock sensor retard?

    Also, I think I have a solution for the cam timing retard issue with decked heads. Starting from the top going down, set the CAM at top dead center. Then work back down to the CRANK pulley and create a new slot in the crank pulley to re- TDC the pistons. That should do it, unless I'm missing something. Right?

    Also, has anyone found a set of light weight pulleys that are compatible?

    Love to hear some input...



  2. #2
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    I was under the impression ours were 10.1:1 ... i really think you are talking about minimal gains for the effort my friend, I wouldnt see why you couldnt just tune the PCM with HP tuners/diablo to adjust everything for the compression.
    2010 Challenger V6: Quickest N/A 3.5L 14.63 @ 95 mph
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  3. #3
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    Quote Originally Posted by DB3NTS View Post
    I was under the impression ours were 10.1:1 ... i really think you are talking about minimal gains for the effort my friend, I wouldnt see why you couldnt just tune the PCM with HP tuners/diablo to adjust everything for the compression.
    The 3.5 is 9.9:1 Compression. Dodge lowered it from 10.4 to 9.9. Basically to go to a single knock sensor, and make it more 87 Octane friendly.

    I'm adding the 4.0L Cam which provides 1 degree of advance with the added lift, and I don't want to just give the advance back by decking the heads. Messing with he PCM won't give the same results as increased compression. Especially if I can take advantage of having both.

    I also had the 10.4 engine, and trust me there was a difference.

    I'm not trying to build a 1320 car... LOL, but I would like to see how this combination comes together. Re-slotting the crank pulley shouldn't be that hard to do at all. It's only 3/16".

  4. #4
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    do you have the ptv clearance to deck the heads with the new cam?
    I would go to 11:1 if youre going to do it. Youll need to cc the chambers and then do the math to see how much to take out. Can you find thinner head gaskets ? Also keep in mind that you may need shorter pushrods.

  5. #5
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    Quote Originally Posted by DBL.DWN View Post
    do you have the ptv clearance to deck the heads with the new cam?
    I would go to 11:1 if youre going to do it. Youll need to cc the chambers and then do the math to see how much to take out. Can you find thinner head gaskets ? Also keep in mind that you may need shorter pushrods.
    Well the pushrods are no problem. It’s an overhead cam. LOL

    Haven’t found thinner gaskets. The 4.0L cams are supposed to be thinner, but it appears they would need to be AA gaskets, because Dodge superseded them, and the new ones are the same as 3.5 gaskets. I’ve only found AA gaskets for the left head.

    Yes, I will need to check for interference. That’s why I was hoping someone had already done the math when they decked their heads.

  6. #6
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    Quote Originally Posted by reefstar View Post
    Well the pushrods are no problem. It’s an overhead cam. LOL.
    LOLOLOLOLGood point haha.
    Overhead cams are not the first thing i think of.

  7. #7
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    I agree, I wouldn't think you would need to trick the ECM for timing. A custom tune should provide appropriate timing and take advantage of the cam swap and new found compression as well as running premium fuel. I wouldn't touch the timing setup from a mechanical perspective. Also you'd want it to still be able to knock retard if you actually develop detonation.
    Mopar11 Charger, MMX Cam, BBK Shorty Headers, Hemifever tune, Getrag 3.91 LSD

  8. #8
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    Quote Originally Posted by kb67mopar View Post
    I agree, I wouldn't think you would need to trick the ECM for timing. A custom tune should provide appropriate timing and take advantage of the cam swap and new found compression as well as running premium fuel. I wouldn't touch the timing setup from a mechanical perspective. Also you'd want it to still be able to knock retard if you actually develop detonation.
    Keep in mind, we are not talking about spark timing. We are talking about Cam timing. Theres NOTHING the ECU can do to advance Cam timing.

    Thats what I am refering to. Advancing the cam timing will move the power band forward in the RPM range. I'm not just looking for higher lift. 1 or 2 degrees of Cam timing makes a significant difference.

    If I had the 6 speed tranny, maybe it would not be an issue as much. But anyone with the 4 speed tranny will tell you that improving bottom end will be a significant driving advantage. The tranny resists down shifting, so grabbing more touque (via cam advance and piston compression) will make the 4 speed more enjoyable IMHO.
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  9. #9
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    Quote Originally Posted by DB3NTS View Post
    ... I wouldnt see why you couldnt just tune the PCM with HP tuners/diablo to adjust everything for the compression.
    Also keep in mind, I'm not referring to spark advance, I'm talking about Cam advance timing. The ECU cannot adjust Cam timing.

  10. #10
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    Cam timing for sure makes a big difference. But again, ptv will need to be watched for.
    Rather then shaving the heads. Have you thought about getting the chambers welded up? You'll be able to up the compression more accurately, and not have to worry about the cam timing as much. also will be able to shape the chamber to control the flame travel better.

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