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Thread: Spark plugs for high compression large port

  1. #1
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    Spark plugs for high compression large port

    Does anyone know what te best spark plug would be for a high compression large port. I'm finding numbers for small port or large port. I'm just wondering which one of the two would be better for the combo set up. Thanks

  2. #2
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    hi-comp big port? Is this a thing? Smallport engine with big port manifold? Please to define your terms. Also, they're spark plugs. Use OEM or NGK.
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  3. #3
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    Sorry. Large port head on small port block. Different spark plugs are listed for the 2 different motors so I'm wondering which of the 2 I should run or something different all together. Also it burns some oil so I was warned to stay away from platinum plugs cause they foul too easily

  4. #4
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    Use the plugs listed for your head I would guess, Toyota/Denso or NGK. Don't bother with fancy multi-electrode plugs, they make no discernible difference. If you have a gap tool check the gap just in case but most plugs are ok out of the box. Just curious, why on earth would you want a bigport head? Or is it just the way it was when you got it or something? Free or cheap rebuilt head? I have always been given to understand that the smallport head is superior in every way. Some people apparently mistakenly (afaik) believe the bigport manifold flows better for forced induction, but my research indicates that this is not true. I may be wrong on this point, but I have never read any indications to the contrary from reliable sources. Again, no reflections intended on you, I am simply curious.
    Last edited by ae92man; 11-06-2014 at 05:30 PM.
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    That's the way I was when I bought it. Someone else built the motor that way I guess cause the bottom end is stronger and boosts the compression. I just plopped it into my car and have been trying to make it run better for a while now lol. Now my spark plugs are all messed so I want new ones just wondering what the best choice may be

  6. #6
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    Wouldn't it be like this?: If you're using bluetop electronics, use the ones that are listed for a bluetop; if you're using smallport electronics, use the ones listed for a smallport.

  7. #7
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    That makes sense. I think that possibly the high compression calls for a different plug tho. I am most likely wrong tho. I don't know very much about technical things like that

  8. #8
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    I think the main reason people do this is to up the compression and not have to change the intake or electronics. The small port is definitely better. I would agree about matching the electronics though, set it up like a blue top, because everything else is set for those plugs as far as injectors and wires go. It should just be a large port with higher compression. What was done about the oil drain hole in the block that the large port head doesn't connect to?

  9. #9
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    I have no idea. I just bought the car pulled the motor and put it in my car. I'm not even 100% sure it is a small port block cause I don't know any way to tell except for taking it apart. I did however compression test it and I was getting 200-210 psi. The guy actually told me it was a small port head on a large port block which it clearly isn't lol. I figured he just said it backwards. Other than that he told me it has colt cams which I compared to my stock ones and I could see a definite difference in the profile on them.

  10. #10
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    If it's a small port block, it would have 7 ribs, a hole in the flat spot at the back of the block on the passenger side for oil draining, and it will have a knock sensor under the intake on the passenger side. If those aren't there, it's probably not a small port. If it's running poorly, I'll take the cams! Haha!

  11. #11
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    I just found this ancient dusty old thread. http://www.dorikaze.net/showthread.p...k-plug-gapping . I will have to look for that knock sensor but I don't think there is one there. Maybe it was pulled and the hole plugged up by the previous owner. It is definitely a 7 rib block but As far as I know the later bluetops were 7 rib as well. Either way somehow the compression is higher than stock which is only 180 psi I think. It runs alright but has some hesitation at low rpm. Starts funny. I will have to investigate later after work. Again

  12. #12
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    I think you're making this way more complicated than it needs to be. Anything will work just fine.


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  13. #13
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    Cams will mess with your compression tester numbers, as will cam timing.

    As for plugs, anything that doesn't hit the piston is gonna work Allright.

  14. #14
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    tommy is offline Redneck engineer/machinist
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    Oh come on guys, electronics don't give a damn about spark plug. They are of the same type (thread and size) except that the smallport ones are one range colder and have slightly less gap... you know why? Because of added compression. So all you should care is what the bottom end is and how much compression you're pushing. Just get a set of NGK heat rance 6 and gap them accordingly.
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    lol yeah what Tommy said. what is all this gibber jabber.
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  16. #16
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    Cams will enduce a poor idle cory. I wonder how wild the cam duration and lift is.

    Someone feel free to chime in here, but would a larger I take cam open longer. Allow your compression to raise? I don't think it would. But I'm not sure I mean you'd be allowing more air Into the cylinder so technically perhaps.

    Also second the plug decision is more about proper Gap then anything. Stock plugs with a smaller gap is the answer.

    More compression = more heat. More heat = increased resistance.
    Increased resitance makes firing the spark harder. So you decrease the gap of the plug so the spark doesn't need to jump as far.
    Last edited by oldskoolcool; 11-07-2014 at 12:34 PM.
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  17. #17
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    Quote Originally Posted by jewbaka421 View Post
    It runs alright but has some hesitation at low rpm. Starts funny. I will have to investigate later after work. Again
    This sounds like your distributor is leaking oil, get a KBOX kit or get a reman from Rockauto. I had the same issue, I bought a KBOX kit and a spare distributor, got Greenie to rebuild it for me and viola. No more hesitation at low rpm and starts beautifully everytime. As for spark plugs, I think Space has hit the nail right on the head. Use the plugs that are supposed to go with whatever electronics you are using.
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  18. #18
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    I definitely have a leak in the dizzy. Bought a kbox kit and it stopped for a while. I've tried a few new inner seals and it still keeps leaking. I probly should get a reman from rock auto if they still have them. Also my throttle position sensor and timing are probly not quite set right. Is there anyone on the island that would like to go over some of these things. I can supply beer and munchies and smokables. I just wanna get it running mint so I can focus on other things like my crappy driveshaft and non functioning lsd and whiny, clunky rear end lol.

  19. #19
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    Meh. Put in K16TR-11 sparkplugs because it will cost $12 from Toyota.
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  20. #20
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    $12 for all of em or one? I found what appears to be a bolt plugging a hole where the knock sensor would be. So I'm pretty sure it is a small port block. Does anyone think I should switch to iridium over copper plugs?

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