Spark plug heat range?

[ssanddemon]

Getting ready to put the 460 back in the old CVX soon, and I want to see if you guys can help with one of the annoying problems that caused me to take it out in the first place last fall. When reading the plugs after a full throttle chop, they were always real hot around the ground strap and insulator, dead black at the base ring. This leads me to believe that they are too hot a plug, and I ended up having a head gasket blow (most likely due to detonation), which caused me to yank the motor and do a full inspection. Some background: The motor was rebuilt by me with 10.5:1 forged TRW's, a Cam Research solid lifter with 10* centers, .500 lift and 230 duration both ends, run straight up as recommended. I did some minor porting on the D3 heads, mainly cleaning up the exhaust side, grinding down the air injection casting, matching the manifold to heads, and smoothing things out. It has wet logs, and I was running 32* total timing advance, all in at 2500 rpm on a Mallory Unilite with Petronix ignitor, no ignition box as yet. The motor pulled 5600 rpm on the AA impeller, but never really ran smooth in the upper rpms. I bought Adjust-a-jets for both ends of the Holley 1050 to ease the jetting nightmare, haven't tried it yet on the secondary side.
The specs call for an Autolite 25, and I worked down to a 23, which is the coolest of that series, but still real hot looking, with the color break right at the base of the ground strap. I know there are some cooler plugs out there, just wondering if you guys have run into this, and can give me some pointers and a starting point for plug selection.

[quiet riot]

Have you checked the actual comp ratio? Was the block decked? Are you running 91 oct fuel? I'm no 460 guru but you might be pushing the octane limit with the combination and iron heads if running pump gas. Does the cam have much overlap to ease the dynamic comp ratio?
You could always try to run a little av gas or race gas and then see if it moves the heat ring up to the bend on the ground strap.
Lastly, are you reading the plugs right after a wot run? If you take awhile to slow down or idle around much you might be getting a bad read for the plugs (could be lean at wot on the high speed circuit and rich on the low giving the darkened base ring.) It usually takes several passes after a jet change for me to see a diff in plug color.
Try and start your plug reading by only running low speed (no 4bbls open) and get the idle and primary mixtures to color the plug correctly first, then go into wot passes with immediately shutting down afterwards to get secondary jetting set up right.
With my combo (12.6:1 measured static comp ratio) I moved down 2 heat ranges in autolite plugs and it seems to be good for na and a 150 shot of n2o. Mines a sbf w/alum heads though, so its apples to oranges. And I have to run about 100 oct fuel also.
jd

[ssanddemon]

Things looked OK in the primary side, the color break still at the bottom of the strap, but more like a nice tan finish on the insulator. Way hot after a long WOT run and immediate shutdown (kinda exciting when the boat almost swamps). I was running super (92 octane) with a full can of octane booster on a 20 gal. tank. It would just about kill me to be stuck with race gas, and it really shouldn't need it if I can get the right combo of timing and heat range, I think. The pistons are TRW's designed to give 10.5:1 with D3 heads. Didn't deck the (D1) block, only a light surface deck on the heads. Never did a comp. check, my bad; gonna do that when I have the motor back together. BTW, the secondary mains were 97's, pretty big.

[ssanddemon]

Oh, and I did polish the piston faces and combustion chambers when building the motor.

[OkieDave]

5600 rpm on a AA impellor is pretty stout for a N.A. motor. should be pretty fast.

[steelcomp]

Things looked OK in the primary side, the color break still at the bottom of the strap, but more like a nice tan finish on the insulator. Way hot after a long WOT run and immediate shutdown (kinda exciting when the boat almost swamps). I was running super (92 octane) with a full can of octane booster on a 20 gal. tank. It would just about kill me to be stuck with race gas, and it really shouldn't need it if I can get the right combo of timing and heat range, I think. The pistons are TRW's designed to give 10.5:1 with D3 heads. Didn't deck the (D1) block, only a light surface deck on the heads. Never did a comp. check, my bad; gonna do that when I have the motor back together. BTW, the secondary mains were 97's, pretty big.
I'll say! I'd get that carb back to stock jetting and start from there. Which 1050 is it...I can tell you where to start. You could be burning raw fuel in the chamber which is going to heat things way up. You're about 10 deg. short on the ex duration for a BBF, as well. I would guess with your CR and cam, you're not burning near the amount of fuel you're dumping into that thing at WOT. Not at 32*. Did you ever try and bump up the timing?? I'm thinking you need a smaller carb or bigger cam. You also need to use new plugs every time you want to read them. You can't properly read used plugs...even with one run. :coffeycup

[ssanddemon]

I'll say! I'd get that carb back to stock jetting and start from there. Which 1050 is it...I can tell you where to start. You could be burning raw fuel in the chamber which is going to heat things way up. You're about 10 deg. short on the ex duration for a BBF, as well. I would guess with your CR and cam, you're not burning near the amount of fuel you're dumping into that thing at WOT. Not at 32*. Did you ever try and bump up the timing?? I'm thinking you need a smaller carb or bigger cam. You also need to use new plugs every time you want to read them. You can't properly read used plugs...even with one run. :coffeycup
Thanks for the reply Steelcomp. Yes, I'm doing pretty good for power on this motor, but as poor as it runs on top, I'm sure it will pick several hundred more rpm if I can ever get it dialed. Looking at the carb, I can't remember where the #'s are for identification, but on the primary air horn it sez:
SAEJ1223
80443
1224
Hopefully the right set of #'s is in there somewhere. I seem to remember the primaries at 88 and secondaries at 92. The stock 460 ran great with those jets. I kinda assumed the new build would need a big step up at both ends since power roughly doubled, so I went up in several steps, primaries smoothed out at like 92, secondaries have never cleaned up no matter what size. Since the motor only barely got broke in, I was always worried about running her lean, thus never experimented with smaller sizes much. I did adjust the throttle pump cams to the larger lobes (pink primary, red secondary) which helped some on takeoff. One other thing is that the shooters were factory at 31 on both ends, now they are 37 and 42. Haven't tried them yet, but it should take care of the minor full throttle bog. Never did play much with timing except to retard it, seemed like it wanted to ping on top even when dogged way down. Seemed pointless to try cranking it up, but my engine knowlege is pretty thin regarding this high performance stuff! I also wasn't aware of the need for clean plugs after every chop. It makes sense, tho. Guess I'll be buying one of those old-fashioned plug sandblasters to keep a clean set in the boat. Good news is that the motor looks great inside, won't have to worry about break in, and I can experiment with a little more confidence. So to get back to the original question, is a 25 to 23 plug in the ballpark, and I should concentrate of carb setup? It would be nice to narrow things down at least. Thanks again for replies, I'll be Ssanddemoning in Glamis dunes for the next week & 1/2, but will check back in asap.

[steelcomp]

80443 is a Holley 850 DP 4150, not a 1050. Pri jets 88, sec. 96, so you're in there. I thought this was a 1050 Dominator.