[Caballerokid]

Ok cool. That leads me to another question i guess... how do you decipher the denso plug numbers? Thanks!

[MouseFink]

Tapered seat Denso Platinum electrode spark plugs may not be available for your 350 CI V8 engine. It depends on which SBC heads you are using.

Tapered seat spark platinum spark plugs were introduced for 1971- up SBC heads. They are Denso PTF-16TT (hot) or PTF-20TT (cold).

Standard seat copper electrode spark plugs with a washer are for 1970 and earlier SBC heads. The standard spark plug is Denso W20PR-U (only one heat range).

I use PTF-20TT tapered seat spark plugs in my 1991 4.3L V6 for stop and go city traffic as well as high RPM road driving. I have only changed them once since the engine was built. The were like new (white) at 4,500 miles but i changed to the colder heat range anyway. I checked three of the plugs again about 6,000 miles and they are still prefect. I will change them at 25,000 miles even though they may still be in good condition. In a grocery-getter engine in good condition, they could last for 85,000 miles. I like spark plugs that last for modern crowded engine compartments because it is not fun changing them like it was in the '60's.

Google one of the Denso websites at www.globaldenso.com and bring up the appropriate chart for the engine that uses your heads. Then click on "details" in the RH column and it will give you the specifications of the spark plug.

[454 Made in Flint]

I live in Flint, I can vouch for AC Delco and much of GM manufacturing being reduced to a vast toxic field of rubble and a city in chaos. I cant really say if plugs made by outsourced plants and foreign workers are inferior or not, but my mildly cammed and built 454 still prefers OE plugs to the aftermarket Accell ones, I pulled them and went back to original because it just didnt feel right, once I got em out THEY WERE COMPLETELY CAKED IN TAN SOOT. Went back to OE Autolite plugs because thats all they had, I hope they last, but im a welder, not an engine guru. From the look of your pictures Id say youre fine for a few thousand miles.

[MouseFink]

Originally Posted by 454 Made in Flint

I live in Flint, I can vouch for AC Delco and much of GM manufacturing being reduced to a vast toxic field of rubble and a city in chaos. I cant really say if plugs made by outsourced plants and foreign workers are inferior or not, but my mildly cammed and built 454 still prefers OE plugs to the aftermarket Accell ones, I pulled them and went back to original because it just didnt feel right, once I got em out THEY WERE COMPLETELY CAKED IN TAN SOOT. Went back to OE Autolite plugs because thats all they had, I hope they last, but im a welder, not an engine guru. From the look of your pictures Id say youre fine for a few thousand miles.

Compare a current AC-Delco RapidFire spark plug with a older ACDelco RapidFire spark plug that was purchased after 2009. I was using AC-Delco Rapid Fire #1 spark plug until I purchased a set of the "new" RapidFire #1 spark plugs that were made in Mexico.

The difference is obvious and they did not even try to hide it. The current "offshore" ACDelco RapidFire #1 spark plugs appear to be nothing more than standard R43TS spark plugs that have been reboxed. The current versions do not have the clipped ground electrode and the center electrode is not a small wire electrode that is supposed to be the visual features of the AC-Delco RapidFire spark plugs. The AC-Delco Electronics Division that made AC-Delco batteries was salvaged when it was sold off to Johnson Controls in Plano, Texas and the battery manufacturing plants in Mexico were closed and moved into the United States.

I suspect the current "ACDelco RapidFire #1" spark plugs are nothing more than standard ACDelco R43TS spark plugs but with the premium platinum spark plug price.

In 1995, the GM AC-Delco Parts Division logo was changed to ACDelco (dropped the hyphen). That occurred after the sell-off of the GM AC-Delco Parts Division to Delphi Automotive, which has also went Chapter 11 bankrupt after the SEC filed suit for irregular accounting practices after investor lawsuits.

In 2006, Delphi closed 21 of the 29 parts manufacturing plants in the United States and Delphi was changed to DPH Holdings Corporation.

[454 Made in Flint]

I find all this new info on spark plugs enlightening, and thought provoking. I used to just ask for "stock big block OE replacements" The parts guy fiddles with their computer and comes back with 8 autolite, delco, or champions depending on the store. Gap em to.045 and snug em in with anti seize. I never really thought into it much, until now. Now Im thinking, "ok lets read the plugs and decide which way to go" How do you know when to go up or down with heat range or plug gap. Black is rich, tan is lean and thick crusty soot is plain bad, but theres gotta be way more to it.

[MouseFink]

IMO, in a older (pre-1995) GM engine, you should choose the ACDelco spark plug heat range recommended by the auto manufacturer but convert the ACDelco heat range to a another brand. I quit using the fake ACDelco Rapidfire #1 spark plugs and installed Denso PTF16TT platinum spark plugs. The Denso PTF16TT spark plugs have a similar heat range as the ACDelco RapidFire #2 platinum and ACDelco R45TS copper spark plugs. I used the Denso PTF16TT spark plugs but I felt that they were too hot, even for stop and go driving, because they were pure white when I checked them after the first 4,000 miles after the engine rebuild. I switched to Denso PTF20TT which the step colder. I have not checked those yet. My TBI engine seems to be running lean after the engine rebuild so that may be why the plugs were pure white after 4,000 miles.

Worn out engines, highly modified engines (such as mine) and engines used in the higher echelons of racing require the plugs to be checked and replaced more often.

I prefer platinum fine wire center electrode spark plugs because I want to change spark plugs as few times as possible in a congested engine compartment. I expect the Denso PTF20TT platinum spark plugs would last for 60,000 miles in a good engine but I will change them at 20,000 miles whether they need it or not. Another feature I like about Denso PTF20TT platinum/titanium tip spark plugs is the price...$3.00 each including shipping.

[cadillacdave1]

As far as half the porcelain showing, is it possible that the plug is not facing the exhaust valve? When installing the plugs change them around so the strap is open slightly toward the exhaust valve. If it is totally facing the intake you may get the symptom you are describing.

[steeny]

There is an excellent article titled "Tuning an Engine by the Spark Plug.
by Brian Odom", which states in part:

"When tuning a performance engine the spark plug is a important tuning tool. Being that there are many different tuning techniques, I will keep this article about the basics of spark plug reading on a Quarter-Mile Drag Strip (or wide-open-throttle tuning).
When tuning by the spark plug, you must always use a NEW plug to get an accurate reading.
To get a clean plug reading the engine should be shut down after the run and towed back to the pits.
Any running of the engine after that will skew the plug reading.
When tuning by the spark plug, you must always remember there are two major variables at play (air fuel ratio and ignition timing).
To make it easier to determine your on the right track when tuning, make small incremental changes and only 1 or 2 changes at a time."

To read more, go to http://honda-tech.com/showthread.php?t=3063102

Check it out, some good info here.

[cobalt327]

Originally Posted by Caballerokid

Hopefully these are larger pictures. Also... these were after 3 hard pulls on the dyno with a 160 degree thermostat. I want to go to a 180 thermostat. Would I need to go down to maybe an R43TS?

When you see one side of a plug colored much more than the other, chances are good that if you were to index the plug to tell what valve the colored side was pointing towards, it would be the exhaust valve.

You can mark the position of the colored half of the insulator on the outside of the plug w/a sharpie, then screw the plug back in the head (same plug/same hole it was in). Note the position of the witness mark you made, it'll be biased towards one of the two valves.

Reading spark plugs based on the Odom text, you can basically ignore the General spark plug info section below the info on reading plugs.