Page 1 of 3 123 LastLast
Results 1 to 10 of 22

Thread: For All You Olds 455 Guys...

  1. #1
    I'm in the process of building an Olds 455 and was curious...
    I know which spark plugs were originally designated to run in this motor, but this motor isn't exactly being built stock, on top of the fact that it's a marine motor now so it's gonna run a lot colder.
    What I'm wondering is how do I know which heat range of plugs I should run in it? Here are the specs:
    455 Olds punched .020 over
    Elgin Pro Stock Cams -
    .328/.328 SAE Duration (Int/Exh)
    .244/.244 050 Duration (Int/Exh)
    .475/.475 Valve Lift (Int/Exh)
    .297/.297 Cam Lift (Int/Exh)
    110/110 Lobe Centers (Int/Exh)
    Holley 4150 750cfm Marine Carb w/mechanical secondaries
    Edelbrock Torker 455 Manifold
    Naturally Aspirated

  2. #2
    try asking here as well..
    Olds powered Jetboats:

  3. #3
    If all else fails- most plug manufacturers have a heat range chart available. Look up the OEM, for your marine application, then compare to the chart, and choose how far you want to go, then pick the plug you want. 2 steps should be sufficient to start with in the direction you want to go. But take into consideration- since a marine engine is running on the colder side, you may want to go to a bit hotter plug, to burn off deposits, rather than a colder plug, which could foul easier.

  4. #4
    Thats a pretty stock motor by my definition, no offence. I'd go with a little larger cam. I run NGK R5670-5 plugs. 4 is the stock heat range so the 5 is one heat range colder. I'd say if you are running higher compression or a larger cam you would need colder plugs but the -5 should be ok. I've even run -6 and did not notice a difference.

  5. #5
    Heat range
    The term spark plug heat range refers to the speed with which the plug can transfer heat from the combustion chamber to the engine head. Whether the plug is to be installed in a boat, lawnmower or racecar, it has been found the optimum combustion chamber temperature for gasoline engines is between 500°C–850°C. When it is within that range it is cool enough to avoid pre-ignition and plug tip overheating (which can cause engine damage), while still hot enough to burn off combustion deposits which cause fouling.
    The spark plug can help maintain the optimum combustion chamber temperature. The primary method used to do this is by altering the internal length of the core nose, in addition, the alloy compositions in the electrodes can be changed. This means you may not be able to visually tell a difference between heat ranges. When a spark plug is referred to as a “cold plug”, it is one that transfers heat rapidly from the firing tip into the engine head, which keeps the firing tip cooler. A “hot plug” has a much slower rate of heat transfer, which keeps the firing tip hotter.
    An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as a turbo, supercharger, increase compression, timing changes, use of alternate racing fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature and may necessitate a colder plug. A rule of thumb is, one heat range colder per modification or one heat range colder for every 75–100hp you increase. In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70°C to 100°C from the combustion chamber.
    The heat range numbers used by spark plug manufacturers are not universal, by that we mean, a 10 heat range in Champion is not the same as a 10 heat range in NGK nor the same in Autolite. Some manufacturers numbering systems are opposite the other, for domestic manufacturers (Champion, Autolite, Splitfire), the higher the number, the hotter the plug. For Japanese manufacturers (NGK, Denso), the higher the number, the colder the plug.
    Do not make spark plug changes at the same time as another engine modification such as injection, carburetion or timing changes as in the event of poor results, it can lead to misleading and inaccurate conclusions (an exception would be when the alternate plugs came as part of a single precalibrated upgrade kit). When making spark plug heat range changes, it is better to err on the side of too cold a plug. The worst thing that can happen from too cold a plug is a fouled spark plug, too hot a spark plug can cause severe engine damage

  6. #6
    Same here, I'm running NGKs one range colder than stock.

  7. #7
    Hey Malcolm hows your 455 running? You did any head porting or are they stock?

  8. #8
    El Prosecutor
    Heat range
    The term spark plug heat range refers to the speed with which the plug can transfer heat . . . . .
    Good post, thanks for taking the time. I learned something already this morning.

  9. #9
    It's already put away for the winter, it was still running good though.
    No porting, just big valves (2.07/1.71).

  10. #10
    I used to run autolite racing plugs in mine back in the day. The plug numbers were AR74

Page 1 of 3 123 LastLast

Similar Threads

  1. Paging Olds Guys
    By hickz3 in forum Jet Boats
    Replies: 11
    Last Post: 04-13-2006, 05:11 AM
  2. Olds guys!
    By n8dawg in forum Jet Boats
    Replies: 2
    Last Post: 03-29-2006, 07:52 PM
  3. Attention Olds Guys... I need help!
    By n8dawg in forum Jet Boats
    Replies: 25
    Last Post: 07-12-2005, 06:16 PM
  4. Olds guys???
    By 1HOTGMCJET in forum Jet Boats
    Replies: 8
    Last Post: 05-11-2005, 08:57 PM
  5. Olds guys.
    By Back Forty in forum Jet Boats
    Replies: 16
    Last Post: 05-16-2004, 08:24 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts