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G5X3 PTV 243 and 853

This is a discussion on G5X3 PTV 243 and 853 within the Internal Engine forums, part of the LSx Technical Help Section category; Here are the numbers i have with the 243 Exhaust BTDC 15 deg .150 10 deg .109 5 deg .085 ...

  1. #1
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    G5X3 PTV 243 and 853

    Here are the numbers i have with the 243

    Exhaust BTDC
    15 deg .150
    10 deg .109
    5 deg .085
    0 deg .078

    Intake ATDC
    0 deg .049
    5 deg .057
    10 deg .080
    15 deg .129


    With the 853 heads

    Exhaust
    15 deg .202
    10 deg .155
    5 deg .130
    0 deg .121

    Intake
    0 deg .069
    5 deg .076
    10 deg .103
    15 deg .146

    I beleive the tolerance for the intake is suppose to be .080 and for the exhause .100. According to my readings i cannot use either head on with this g5x3 112lsa.

    Does anyone have any opinions on the numbers i have come up with.

    I am using the stock lifter, so maybe this is the issue. I am going to the dealer tomorrow to buy one and make it solid.

    Any opinions??????

  2. #2
    Moderator Firebirdjones's Avatar
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    Are you rotating the engine and using the valvetrain with a dial indicator on the rocker??

    If so you'll need a solid lifter or a dummy lifter to accomplish that. Even a hydraulic lifter full of oil will still compress and give false readings.

    You can take a hydraulic lifter apart and stack washers inside to make it solid if need be.

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    Ok i went and purchased the lifters and made them solid. With the 853 heads at TDC i have .011'' on the intake. With the 243 heads i can not get past tdc, the valve hits the piston. While doing this i am using light check springs.

    I called LG motorsports regarding what my readings and they told me to put number 1 cylinder at tdc and measure the valve drop for the intake and exhaust.
    This is what i found
    243 head
    intake=.202
    Exhaust=.219

    853 heads
    intake=.207
    Exhaust=.223

    They told me that anything under .200'' will not work.

    I am thinking about just buying the AFR 205 with the 64cc chambers. I already have comp 921 springs i can use and 7.4 push rods.

    Any opinions on what you are reading?

    I also check my degree wheel to make sure it was reading TDC at 0 and its right on.

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    Member Jay37's Avatar
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    What is the installed intake center?

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    Member Jay37's Avatar
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    232-240-600-610 114 LSA=your cam=alot of lift=alot of duration=

    some motha fuckin piston to valve action is going on...

    A couple options

    1. get new pistons with larger valve reliefs

    2. get the pistons fly cut

    3. get different heads

    4. get a smaller cam

    also just kind of curious, what is the details of your engine?

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    Member Jay37's Avatar
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    just my 2 cents

    Guys on the interenet, and local burger king parking lot will go all day on what you should do. I understand I am in the "guy on the interenet" category. But I recommend you find yourself, a good reliable local machinist with ls experiance.

    Reason being-
    People can recommend, rotating assemblys, cams, pistons, heads or just what ever all day long. Tell you what works for them, but In the end, your the one spending the money. I along with my other internet buddys, lol have nothing really to loose if YOU get the wrong parts...
    but your local machinist has a reputation to uphold... (if he doesn't, don't go to him), so therefore he will make sure your parts properly match up, so that means you will be saving money.

    I will gladly give you my experiance and try to help. Nothing is better than face to face though.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by 1slowbusa View Post
    Ok i went and purchased the lifters and made them solid. With the 853 heads at TDC i have .011'' on the intake. With the 243 heads i can not get past tdc, the valve hits the piston. While doing this i am using light check springs.

    I called LG motorsports regarding what my readings and they told me to put number 1 cylinder at tdc and measure the valve drop for the intake and exhaust.
    This is what i found
    243 head
    intake=.202
    Exhaust=.219

    853 heads
    intake=.207
    Exhaust=.223

    They told me that anything under .200'' will not work.

    I am thinking about just buying the AFR 205 with the 64cc chambers. I already have comp 921 springs i can use and 7.4 push rods.

    Any opinions on what you are reading?

    I also check my degree wheel to make sure it was reading TDC at 0 and its right on.
    Wow, you are more than close on the intake valves according to LG.

    I take it both sets of these heads have been milled extensively??

    Edit: I forgot to mention, are you figuring in head gasket thickness? Since you are probably doing as I do,,,and set the heads on without a gasket and a couple of bolts.
    If that's the case you need to take the compressed thickness of the head gasket you plan to use and add to those measurements you are getting.
    Last edited by Firebirdjones; 04-28-2011 at 05:08 PM.

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    Quote Originally Posted by Firebirdjones View Post
    Wow, you are more than close on the intake valves according to LG.

    I take it both sets of these heads have been milled extensively??

    Edit: I forgot to mention, are you figuring in head gasket thickness? Since you are probably doing as I do,,,and set the heads on without a gasket and a couple of bolts.
    If that's the case you need to take the compressed thickness of the head gasket you plan to use and add to those measurements you are getting.
    I know the 853 heads have not been milled because i just took them off the car and it has never been apart. As for the 243 i dont know because i purchased them from a member off another forum. I have read on forums that you do and dont have to fly cut with the 112 but here is proof. Im sure its ok to run the 853 heads with this cam but its to close for comfort for me. I am going to purchase a set of afr 205 with 62cc.

    I was checking with the gasket installed. i measured the gasket and its .062. I just snugged the head bolts down when i put the head on.

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    Moderator Firebirdjones's Avatar
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    Very good then. I agree, that's too close for comfort. It would take expensive high end valve train, lightweight valves, good springs etc....to control everything. Because the slightest hint of valve float could spell disaster.
    Besides,,,I think you'll like the AFR 205's better after it's done

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    Quote Originally Posted by Firebirdjones View Post
    Very good then. I agree, that's too close for comfort. It would take expensive high end valve train, lightweight valves, good springs etc....to control everything. Because the slightest hint of valve float could spell disaster.
    Besides,,,I think you'll like the AFR 205's better after it's done
    I think so to, I ordered them today, and cant wait to get everything back together.

  11. #11
    TunedbyFrost.com Tuner Frost's Avatar
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    Generally, with stock bottom end/pistons, that grind on a 114LSA will clear and a 112LSA will not.

    The BEST bet is to further mill the heads and fly-cut. That's what the fast cars do. The 243s will make the same or very close up top as the AFR 205s. Fly cutting is not the big deal that it's often portrayed as being, and the setups that go that route are consistent performers on the track and the dyno.

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    Quote Originally Posted by Frost View Post
    Generally, with stock bottom end/pistons, that grind on a 114LSA will clear and a 112LSA will not.

    The BEST bet is to further mill the heads and fly-cut. That's what the fast cars do. The 243s will make the same or very close up top as the AFR 205s. Fly cutting is not the big deal that it's often portrayed as being, and the setups that go that route are consistent performers on the track and the dyno.
    Thanks Frost for your input, what tool do you recommend for flycutting? I spoke with LG and they will rent it for $500 dollars and thats with a deposit, but if i can buy the tooling for that price i would rather do that.
    Thanks again.


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