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Quench advise needed

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    Senior Member H20MOFO's Avatar
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    Default Quench advise needed

    Soooo...I pulled my head to replace that lovely valve and have my heads looked at. I decided to take advantage of the borrowed dial gauge I have and check tdc and my quench. As near as I can tell my piston is .020 in the hole. Another awesome little detail from my old motor guy. I cant remember whats ideal with steel rods....seems like its in the .040 range. It looks like cometics get as skinny as .027 in the jegs I am staring at. And copper goes to .031. I have never tried copper on a non oringed deal...and I dont think my block is finished right for a cometic but I dont really know. I will edit in a pic...not sure if that will help or not. Not real sure what my options are....with my luck I will take it from .060 to .050 and it will make things worse than they already are. TIA
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    Edit; just noticed the cometics that go down to .027 in jegs are small block gaskets. =/
    Last edited by H20MOFO; 06-19-2011 at 09:51 AM.
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    Can't re-Member 28Eliminator's Avatar
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    My understanding is .050 or smaller is fine. .020 in the hole is gonna make it tough to get there..

    How thick was the gasket that came off of it? did you have any detonation problems before?
    I'd agree with you, but then we would both be wrong

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    Senior Member MACHINEHEAD1's Avatar
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    Looks like you have a 4.466+ bore with a -12cc dish. Is it N/A with a iron head? What comp ratio and what fuel?

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    Senior Member H20MOFO's Avatar
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    28 elim....I am fairly certain the one that came off of there was a std blue felpro...I think they are .040 I have never had a detonation issue. I run at 40* adv. I have had it as high as 43-44 but it didnt run any better there than it does at 40*. I just figured while these were off...I'd improve it some....if I could.
    Machinehead...they are aluminum heads...off memory I am 8.4 to 1 ish...bore is 4.5. I keep thinking someday I will be able to throw a little boost at this thing. Doesnt sound like I am gonna fix this with a gasket change. If not I will take her down this winter and get the blocked decked. Then my pushrods will be to long.lol
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    Can't re-Member 28Eliminator's Avatar
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    H2O...

    I can't imagine that running 8.5 to 1 with a "less than desireable" quench would be a problem, But I'm just a weekend engine builder (and even that's questionable). If you never had a problem before, I say put it back together and run it.. summer's gonna slip away before you know it

    When I went through my HP500 this winter, the pistons were .020 in the hole from Merc. I never had any detonation issues but I think the stock ignition only ran about 35 deg total.

    Hopefully one of the real engine builders will chime in with their opinion
    I'd agree with you, but then we would both be wrong

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    Quote Originally Posted by H20MOFO View Post
    Soooo...I pulled my head to replace that lovely valve and have my heads looked at. I decided to take advantage of the borrowed dial gauge I have and check tdc and my quench. As near as I can tell my piston is .020 in the hole. Another awesome little detail from my old motor guy. I cant remember whats ideal with steel rods....seems like its in the .040 range. It looks like cometics get as skinny as .027 in the jegs I am staring at. And copper goes to .031. I have never tried copper on a non oringed deal...and I dont think my block is finished right for a cometic but I dont really know. I will edit in a pic...not sure if that will help or not. Not real sure what my options are....with my luck I will take it from .060 to .050 and it will make things worse than they already are. TIA
    Click image for larger version. 

Name:	QUENCH.jpg 
Views:	52 
Size:	26.4 KB 
ID:	119721
    Edit; just noticed the cometics that go down to .027 in jegs are small block gaskets. =/
    I would like to ask about how many hours on that motor, do you idle alot, and what induction set-up and just for giggles what feul do you run? I am not being insulting in any way, just curious! M

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    gn7
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    Quote Originally Posted by H20MOFO View Post
    If not I will take her down this winter and get the blocked decked. Then my pushrods will be to long.lol
    Your pushrods are a longs ways from only being .020 short. A long ways!!!
    Your not going to find a gasket much thinner than .040 easily. The stock type shim gasket is about .022 but isn't recommended for alum heads. If you have any desire to get the quench down to something around .040, your going to have to deck the block. But I wouldn't worry about it until you decide to thow on a blower. You aren't going to find any HP from it at 8.5 to 1, and I seriously doubt it is going to have an effect on detonation.



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    I would like to ask about how you came up with your piston to deck and where you measured it at? did you try and rock the piston in the bore the only reason i ask is you may have more or less quench then you think. just asking here.

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    Senior Member H20MOFO's Avatar
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    Quote Originally Posted by havasubyou View Post
    I would like to ask about how you came up with your piston to deck and where you measured it at? did you try and rock the piston in the bore the only reason i ask is you may have more or less quench then you think. just asking here.
    When I posted that....I took the best meas I could. I found by build sheet a couple days ago and my ex motor guy had it in the hole .025. I didnt try to rock the piston till I just read your post...I cant move it. Old guy....my boat is running rich.. that and the fact my pistons came pre carboned.lol My block crank and rods are second hand....so to speak. They were in a blower motor.
    Another Hot Boat refugee

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    Quote Originally Posted by H20MOFO View Post
    When I posted that....I took the best meas I could. I found by build sheet a couple days ago and my ex motor guy had it in the hole .025. I didnt try to rock the piston till I just read your post...I cant move it. Old guy....my boat is running rich.. that and the fact my pistons came pre carboned.lol My block crank and rods are second hand....so to speak. They were in a blower motor.
    Well I was not trying to insult in any way but that engine is fatter than a thanks giving turkey from the piston pics. Lets just hope it cleans up after some run time! M

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    Quote Originally Posted by H20MOFO View Post
    My block crank and rods are second hand....so to speak. They were in a blower motor.
    Alot of people open up the quench distance when super/turbo charging. Especially the big boost app's.

  14. #12
    Senior Member MACHINEHEAD1's Avatar
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    Increasing quench area would be low on my list if you plan on supercharging. 8.4 to one is my safe limit for 6-8psi on 91 octane.
    I have done testing with same combos on blower engines with .035 piston to head and .060 piston to head, while still maintaining
    comp. ratio. They all made the same power. Not the case with N/A. Power differences of 5-10HP in quench alone in my testing on 540
    inch engines. Never tried to push the envelope of detonation resistance by putting in a couple extra degrees of timing. In your case I would not bother getting a .035-.040 PTH clearence, even if you stay N/A. Your increases probably wont be as much as what I have observed because I was in the 10.5-10.6 comp ratio range N/A. I never tried 8.4 N/A with good quench to see what would happen. Leave it alone and enjoy your summer

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