cfc928gt

I've been thinking of going with PorKens GTS recommendation and put in Bosch WR5DC plugs in my GT. I don't know that I have any knock or pinging but then again between my X-pipe, no cats and an RMB combined with my lousey hearing I wouldn't know anyhow. Since there's no way that I know of to tell if the EZK is retarding timing or not, other than seat of the pants, I figure it's worth a try. NAPA is getting eight of them in this afternoon for a whooping $10.01 including tax. What's the downside to using a colder plug? Fouling, hard starts or just what should I look for or be aware of?

PorKen

Check for carbon clogging the tip, but it's really unlikely to, unless you have an oil or mixture problem. (Any plug is cold at startup.)

I can't think of a situation where you'd need the stock, hotter plug with 4-V and LH injection. Maybe in a cold climate, with a stock exhaust system.

cfc928gt

Thanks PorKen, I think I'm going to retard the GT cams using your tool and following Louie Otts specs and finish it off with the colder plugs and a battery disconnect to reset the computers. I'm running a GTS chip in the EZK that's supposed to give me 2 more degrees advance at higher rpms so I don't want to invite trouble with detonation if I can avoid it - and the colder plugs seem like a bit of insurance.

GlenL

I think you're doing the wrong thing for the wrong reason.

The spark plug heat range is about having the plug run at the right temperature. The mods you've made aren't that severe and don't warrant a plug change. This is a street driven car? Then no way is it needed. Check the spark plugs for the right color and otherwise forget it. At two heat ranges down you'll need to check them for not cleaning and getting carbon deposits.

The reason this is the wrong approach is that a hot spark plug doesn't cause knock. "Knock" is pre-detonation where the whole charge (or most of it) pops off simultaneously. This is like a diesel. The sudden rise in pressure damages things.

Knocking is caused by several factors. These include hot charge temps and high pressures. High pressures are from a higher compression ratio and forced induction. High temps are from hot engines and hot cylinder walls.

A very hot plug will give "pre-ignition." So will other hot spots like carbon deposits. This makes the car run rough but the result is a normal burn. It is just earlier than expected. It is not a diesel detonation. Cylinder pressures will be higher but it is nothing compared to true knocking.

2 degrees extra spark advance and some cam tuning on a street car will not result change the cylinder temps.

If you're worried about your engine add some octane booster or a few gallons of race gas to a tankful. That will prevent detonation. Changing the plug heat range will not.

dr bob

What GlenL said.

Tune the engine for max power, then use plugs that will survive well. Deposits on plugs cause hard starting and poor cold performance, which then causes more deposits ad nausea until the car won't run righ without 'clearing its throat' every once in a while.

Plugs are selected for the amount of heat that can be dissipated out through the shell, while keeping the tips just warm enough to stay clean. You aren't changing that. Unless you are adding a lot of chamber heating (lots of power), stay with the original plug recommendation. If you notice plugs that are very white, damage the ground electrode, or erode the tip of the center electrode prematurely, you might then consider a plug one range colder.

cfc928gt

GlenL and Bob, thanks for your input guys, that's exactly what I was hoping for.

Mrmerlin

Hey man i see your in Denver try adding some marvel mystery oil to your fuel the Ethanol we have to drive on isnt good for the fuel system,the marvel will keep the injectors and the fuel pump lubricated keep the plugs you have, changing the cam timing will only work the best if you know for sure that the cams have been indexed to the pulleys.

PorKen

Try it! Plugs are cheap. Start with the 5's (coldest available in this plug). If the insulator doesn't stay white, move up to 6's.

Which way are you trying to move the powerband? Up or down? Retard is up. Retard will also reduce cylinder pressures, so you have even less chance of pinging.

I was surprised that on the dyno with my '86 (similar to GT cams), 4-5° crank retard lost 20ish HP, and strangely, the exhaust AFR was leaner. 1-2° retard made the most power. I'm running straight up at the moment, and I miss having some advance for around town. 4-5° advance is nice for more grunt at low rpms. More advance requires better gas, and plugs to combat pinging!

928ntslow

Yea...what they said, 'CEPT the race gas You are asking for big trouble if you are running with a catalytic converter. Stick to the basics.,,,and the old saying, if it ain't broke, don't fix it. The only time you need to tweak is to compensate for a known condition. You will KNOW if your engine is knocking. At that point, I would use a colder plug or just use your good ol' single electrode copper Bosch...the best cheapest plug for the 928 (the one you're supposed to use ).

Good Luck!

Larry Velk

In the 60's Ford had a publication for techs ('mechanics', at that time!) which had temp graphs for plug temps and cylinder temps. Ignition advance cooled the charge and heated the plugs. At this time, of course, you turned the distributor to change timing and replaced advance weights on a distributor machine. On Chevy mouse motors you could "advance" timing by going to an extended nose as this brought the spark further into the chamber (the original AC 44's were very short nosed). The bike guys would do a 'plug chop' at the strip and shut off so they could read the plugs after a run. In this moderen era I think this avenue is optimisied and I no longer give it any thought.

hacker-pschorr

I disagree.

We've seen 100% stock 928's shwoing knock on the shark tuner that none of us could hear. Even on the dyno.
So either we could not hear it or the shark tuner was wrong. The plugs during these runs were 100% clean & free of any "damage" normally associated with knock.
Maybe these knocks were very minor, but IMO a knock is a knock - something I don't want my engine to do.

Drive the car to Green Bay & have Tim shark tune it.

I should really check with Tim before making offers like this

cfc928gt

Exactly my point. If the engine detects knocks, it's going to retard the timing. I've also read of many who never heard knocks but the sharktuner did. I assume at some point based on # of knocks the EZK will retard the timing. My point is that if running a colder plug would help reduce the possibility of this and assuming there isn't a downside, why not do it?

John Speake

The EZK will trigger the retard if there are more than about 30 knocks per 10,000 engine firings IIRC.

The knocks indicated by the SharkTuner are those actually recognised by the uC in the EZK ECU as valid knocks, and not noise.

Brett928S2

Hi

For my Nitrous I usually run one heat range colder/harder ...thats moving from standard NGK BP6ES to NGK BP7ES...although I have runs NGKBP8ES if needed...

Then engine runs fine on 7s ...the heat range spread on NGKs is pretty wide...so you wont have a problem running one range colder....2 might be pushing it a bit

All the best Brett

928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS,
KICKDOWN SWITCH - K&N FILTER - WIZARDS OF NOS - NITROUS KIT 150 HP - 505 HP/500 FT LBS TORQUE -
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Tony

came across this recenlty...good cross reference.

http://www.spark-plugs.co.uk/pages/t...chw5a-y6dc.htm