Spark plugs

Discussion in 'Street/strip 400/430/455' started by Kent Greenwood, Dec 31, 2018.

  1. Hi Guys
    I am running a stock 1972 455 with an after market HEI and AC44LTS plugs.
    Found out they should be AC44TS. I would therefore have the base of the plug protruding 6mm into the chamber.
    Is this going to cause detonation with the sharp edges of the exposed threads or ruin the swirl effects in the chamber?? Maybe the plugs get hotter...maybe beneficial as the tip is further into the chamber??
    Need some science on this one
    As per pics they are very clean
     

    Attached Files:

  2. CJay

    CJay Supercar owner Staff Member

    If it was a 72 455 with a points distributor, then yes, a R44TS would be the correct plug gapped at .035. But you have an HEI distributor so all spark plug specs go out the window. A 1975 455 came with an HEI. In that engine, they call for an R46TSX and they should be gapped at .060.

    As far as detonation, what's you total timing set at? How aggressive is the advance curve?
     
  3. I have just ordered a set of AC R44TS and a set of NGK UR55 plugs from Rock Autos
    Will try the AC44TS first
     
  4. CJay

    CJay Supercar owner Staff Member

    What are you going to gap those at?
     
  5. Probably .050
     
  6. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    Using the LTS plug was a trick we used years ago for more performance at the track. The protruded plug put the spark more into the chamber and took up 1 cc so increased compression .1. We found a slight gain in et, worth it, maybe at the track, but we felt good thinking it was.
     
  7. Bens99gtp

    Bens99gtp Well-Known Member

    the r44tsx is the lug made with the extra gap. it's the only difference between it and the r44ts.
    45s are a hotter plug than 44, I would think the 46 might be s touch hot
     
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Sharp edges inside the combustion chamber can be a trigger for abnormal combustion for sure. They can collect carbon as well making plug removal difficult (depending how long they are in there). Plug gap depends on cylinder pressure as well as the ignition system used. I think you made a good choice with both part #'s. A stock 72 455? You can probably get away with .060.
     
  9. Gotta love that science Gary. I had a good chuckle. Anything that made you feel like it was...WAS. I agree
     
  10. Hi Larry. Have been just working on efficiency rather than performance mods..so far. The squish should push the charge to where the spark plug should be, that is what had me thinking and the plug is more exposed so has less cooling.
    Not long after I bought the car we found the head gaskets were rotten and had a heck of a lot of leaks.
    Off came the heads. Tanked for 3 days to get the coke out of ports and off valves. Found that despite seals being hard, all parts were like new no wear.
    Under the right light you could just see the hone marks in the bore. Anyway to cut a long story short the heads were machined .020 and seats triple cut, all casting dags were removed. Just a tidy up.
    Cast iron intake came off, Aircon off, engine fan off, a weght and power saving
    On a slow trip 50-55mph it will achieve 20 mpg imp...16.8 mpg US not bad on our twisty lumpy terrain in NZ
    Miss Bessie will get some mods but the house reno has been a biggie for near 3 years so car is next.
     
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  12. Will do
    Thanks
    Will be interesting to see the difference in color if any
     
  13. Good article Larry
     
  14. Schurkey

    Schurkey Silver Level contributor

    Almost NONE of the specs go "out the window". He's still going to use a plug with the same
    Sealing type--gasket or taper
    Thread size--14mm in this case
    Thread reach
    Heat range that is correct for the application--which may or may not be the heat range spec'ed by GM

    In fact, the only thing(s) that might change is the gap (and potentially the length of the ground electrode to accommodate the change in gap.)

    Which is adequate for a low-compression, emissions-lean, EGR application breathing through a restrictive pellet-type catalytic converter. For any performance application, .060 is probably too wide, and certainly enough to stress the insulation of the entire secondary circuit. I'd also be concerned about the heat range.

    Unless you're prepared to do dyno or track testing--with precise measurements of test conditions and engine performance--anything over .045 gap is unlikely to achieve anything except occasional misfire and insulation problems.
     
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If you want the ground electrode to be perpendicular to the center electrode (as it should be), you are limited to how much you can adjust the gap. According to NGK, you can open/close the gap .008" Both the UR-55 and R44TSX are meant to be gapped at .060. If you close them down to .045, the ground electrode will noticeably be angled. The UR-55 comes gapped at .059, so you can close that down to .051. If you want a .045 gap, you are better off with the UR-5 which comes gapped at .039. I think with low compression, you might be fine with .060, but with the UR-55, I'd go with .051 to be safe.
     
  16. CJay

    CJay Supercar owner Staff Member

    What I was getting at was that you shouldn't gap it at .035. And the R44TS wasn't meant for HEI. The OP did say it was a stock engine meaning low compression. The OP also said it wasn't a performance application and his main concern was fuel economy. At least that's what I understood from his post about "efficiency". A R46TSX isn't that out of line to recommend. That's what Buick recommended isn't it for an HEI equipped, low compression engine? Naturally he would need to see how they're burning. A wideband O2 wouldn't be a bad thing to install either to see whats going on.
     
  17. BQUICK

    BQUICK Gold Level Contributor

    I would think you would go colder plug with HEI not hotter. Like R43TS....
     
  18. BQUICK

    BQUICK Gold Level Contributor

    Wow Gary....I was doing same thing using BN9Y Champion years ago. I did back to back testing at the track and it was worth .08 sec. Put spark in better spot and increased compression slightly.
     
  19. CJay

    CJay Supercar owner Staff Member

    I just looked up what a 455 with HEI came with from the factory. I figured it was a good baseline for the OP. Like any sort of tuning, you have to start with a baseline and see if the engine like it. Then make a change, if any. That's why they call it "test and tune" right?
     
  20. Schurkey

    Schurkey Silver Level contributor

    I don't know what that means.

    IF (big IF) the R44TS has all the right features to satisfy the application, spark plugs are stupid--they don't know what distributor is being used. For street use, it could very well be the "perfect" plug for him--or perfect except for gap width. I'd rather have too-small a gap than too-hot a heat range.

    The ignition system has almost nothing to do with heat range, just optimum plug gap. The engine--and the way it's used--are what determine best heat range.

    The baseline plug for his use is the SAME plug he'd be using successfully with the old ignition system. If the new ignition will fire a wider gap, you add some electrode length to the baseline plug. And without testing to VERIFY gains, I'd be very leery of going wider than .040--.045.
     

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