Colder Plugs?

[SRD art]

For my 2500 mile drive to Georgia I want run smooth and cool. Engine is .030 400 small block Chevy, 9:1 compression, pocket ported factory 400 heads, XE268 cam, Proform air gap dual plane intake, 600 carb, Hooker 1 5/8" headers, 2.5 head pipes into 3" single exhaust, electric fan on 3 core radiator. I will be using a tow dolly to tow my 73 Nova along. I plan on cruising between 65 and 75 mph, about 8-10 hours at a time (besides stopping for potty breaks ;) ).



I've mostly run an ac delco R45TS in my motors, but noticed that this 400 tends to run a little warm (about 190-200) when I'm into the throttle, normally about 170-180 on a 160 thermostat. I'm a bit heat concerned about the fact that I'm towing.

If I bump down to R44TS that's a step colder correct? This will help me avoid excessive heat and detonation correct?

Been a long time since I was in the plug game, just wanted to double check my memory...

[TheJDMan]

If you are running a 160deg tstat and engine temps are 170-180 and spike up to 200, that tells me your cooling system is just barely able to keep up with the engine cooling load. Spark plugs have to transfer all their heat to the head eventually. Cooler plugs just transfer heat to the heads faster so the plug tip runs cooler.

[SRD art]

Probably so. It's a 400, not sure how much that really makes a difference but I've never had a 400 run at 160 with a 160 t-stat, and I've had 400s in 4 different vehicles.

I also need to get a fan shroud on there, right now it's just got the electric fan attached to a bare radiator.

Mostly I just need to know if going a step down on plugs is colder or hotter, I can't remember.

[TheJDMan]

Heat range markings depend on the manufacturer. Some the higher the number the hotter the plug some are just the opposite. Go to the plug MFG's web site and see if you can find a heat range chart. The R45TS and R44TS sound like AC Delco plug numbers, if that is the case the 45 is the hotter plug. Changing spark plug heat range will have absolutley no effect on engine coolant temps.

[SRD art]

As far as engine temps go, I don't expect the plugs to make a difference, rather the concern is the temp that the motor runs affecting the plug's performance. My theory is that a warmer running motor will cause the plug to run hotter and potential for detonation may occur. It may not happen in my case, but I just wanted to play things safe. I'm already nerve racked enough about towing a car across the country alone in a car that just barely got put together, lol!

I checked AC Delco's site and there wasn't any useful info. A little searching on a couple forums confirmed my thoughts that the 45 is hotter than the 44. Funny how some people added their opinions and were backwards, you really gotta be careful what you believe from the net. I looked up a 71 Impala and a 76 1500 4x4 truck with a 400 on Oreily's site and it recommended the 44 for both. Since I'm looking for a good plug to stay cool at sustained rpms for a long distance I'll stick with those for the trip and tune the carb and ignition system for racing when I get to GA.

[BulldawgMusclecars]

Sounds like a good plan, Ben! You may want to fab up a simple, flat aluminum radiator shroud for that fan before making the trip, and reduce the amount of coolant in the system to 30%, or less. Add a bottle of Water Wetter, and you should be good.

[TheJDMan]

IMO, 160deg tstat is too cold. You would be better off running a 180 which is where the engine wants to run anyway. Ignition timing will have more effect on detonation than plug heat range. I would not run more than 35deg total advance.

[rrelco]

plugs will do nothing for keeping the engine cooler....do what Steve says

[SRD art]

O.k., I'd better clarify what I meant in my first post. I'm not so worried about the heat of the engine coolant. I think I can resolve that with a fan shroud and better fan system. Here's where my worry comes from...

My first serious 406 motor I put together for my Nova had flat top pistons, the block deck shaved .010, and 64cc heads that were shaved .030. I'm not sure what compression ratio it was but it ran fine on the street as a daily driver on 93 octane and ran high 11's at the track with 105 octane. Then after about 6 months of daily driving, it started pinging on pump gas at full throttle. I figured it was simply carbon build up, but messing with timing didn't change anything. The only way to make the pinging go away was to use 105. Well, I did a lot of light to light impromptu street racing back then and eventually it took it's toll. One day a piston blew a small chunk of itself out the exhaust, bending the valve. Luckily the cylinder and the head survived. After pulling the heads we found skirt to skirt cracks in 5 other pistons. This motor was a time bomb ready to go off.

Maybe 6 months or so ago I read somewhere that a hotter plug can cause detonation in the right situation, and possibly a little extra heat in the combustion chamber. Looking back I realized that I changed the plugs on the Nova's 406 just before all the pinging started. I'm thinking in my ignorance I put in a hotter plug.

My biggest concern here is that a hotter plug, (meaning plug temperature, not engine temperature,) may cause pinging in the wagon while I'm towing my Nova uphill towards Denver. I'm just tying to make sure I get the right plugs for the job.

Typically I set the motor advanced at about 16 degrees idle and 36 degrees at rpm. Really I suppose I have nothing to worry about since the motor is only about 9:1 compression, I'd just rather not have a broken motor half way to Georgia.