Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
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What plugs are you running in your ZZ4? My Discount Auto Parts only had Autolites and I think they are too long (thread wise). I compared it to a RapidFire I had in my cast iron L98 heads. The thread end of the Rapid Fire is about 1/2 inch long. The autolites are about 3/4 of an inch long where the threads are. Is this because of the aluminum heads? I seem to keep fouling out plugs with these autolites and I have an MSD6AL, new O2 sensor and adjFPR set at about 38lbs due to #24 injectors.
Let me know.
tks
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"Beware he who would deny you access to information, for in his heart, he dreams himself your master"
'84 Black Camaro ZZ4 M5 (V-6 in a former life) -- street beast
'91 Medium Blue Metallic Z28 A4 (UB-HSTRY's old ride) -- currently broken
'99 Navy Blue Metallic Firehawk #120 M6 (99.44% stock) -- daily driver
My ZZ4 data sheet calls for AC MR43LTS. I'm a little worried about the length of a standard plug (porcelin part) and my 1 5/8 SLP headers. Anyone running the ZZ4 with SLP 1 5/8s?
The ZZ4 motors came with the A/C MR43LTS plugs installed (yours should have come that way from the supplier).
The ZZ4 L98 aluminum heads on the ZZ4 use a 14mm thread pitch by 3/4" thread length spark plug. (tapered seat plug).
You should be able to go to any parts store, and ask to look at their spark plug book, and find the cross-reference section in order to see if your desired brand cross-references with the A/C MR43LTS plug or not. Be prepaired for the parts counter guy to look at you dumbfounded when he tries to figure out what you need by asking your year/make/model, and you tell him it's an "Aftermarket" engine. DON'T LET HIM TELL YOU WHAT YOU NEED. Just ask to see the spark plug books, and then find what you need for yourself and ask for it. If they don't have it, go somewhere else. I've had so many problems with auto parts guys lately if you couldn't tell.
As far as the Autolites, they're an inferior plug with very low quality, and that goes for the Splitfires too which are made by Autolite.
On to your headers. The stocker plugs will probably fit with your headers, but it will be a tight fit. That's unfortunately the way it is with all headers. Just make sure your plug boots don't touch your headers. A good rule of thumb is that they stay at least 3/8" away from the headers. If they're too close, look into getting 90° boots since they give you more room.
From the seat to the end boot tip of a standard plugs is about 2". If you need even less length to clear your headers, stop by a speed shop and have them cross-reference your stock plug for the Accel Shorty style plug. the shorty plugs are about a half inch shorter at the porcelain, and Accel plugs are made by Nippondenso/Denso for Accel. Definately a very high quality plug, that only represents Accel by name.
With your ignition setup, you can open up your plug gap. Try .045 and see how that works, as I'm thinking you are running a standard gap right now correct? Another way to keep from fouling is to bump up your heat range of your new plug selection by one point. You may be running too cool of a plug which will tend to foul out if it doesnt retain enough heat. The speed shop guys can help you out in selecting one heat range hotter. Keep in mind, if you go too high in the heat range, you will risk detonation, especially with the 10 to 1 CR of the ZZ4. You should be fine bumping up one or two ranges, but that's about it. If you're a little weary, just stick with a cross-referenced plug, and open up the gap. If that doesn't help, THEN try a hotter plug.
Hope this helped,
Steve
------------------ 86 Trans Am WS6 Black with tinted windows, shaved door handles
ZZ4, Mini-ram, true duals ***Too many other mods to mention***
"In the future, cities will become deserts,
roads will become battlefields, and the hope of mankind
will appear as a stranger"The Road Warrior
Steve,
Thanks. I found my old plugs, the ACs and they are comparable to the autolites in length. I've always heard autolites were pretty good. I switched cause DAP and Autozone were out of the ACs (hmmm wonder why). I already have the 90deg boots and wirelooms so no burnt wires yet. I have been having IAC problems so perhaps that, helped foul the plugs. Getting some ACs to put in plus I have my Datamaster software and laptop cable, so I can scan away!!!
Cool deal. I was going to ask if you had a scanner or software of some sort, but I figured I wouldn't type a book in my previous post.
If you're still fouling after the plug change and IAC correction, kick up to a hotter plug maybe, and look for the ECM knock counts. Diagnostic software is a godsend for us, as I'm sure you already now.
The ZZ4 engine uses the same heads as the L98 Corvette. I tell the parts store I need spark plugs for a 1991 Corvette (Non-ZR1). I use Bosch Platinums.
Well, no one here in Jax carries MR43LTS plugs. Not even the dealer. NAPA said that R42LTS is the new plug, however, thats one step colder then the 43, not what I want. I called ACDELCO and confirmed that RapidFire#8s cross to the MR43LTS plugs. However, after installing them and running the car trying to get my Datamaster Software to work the car is running rich again and fouling the new plugs I just installed. Man I am baffled. And to add insult to injury I think I orderd the wrong software. The cars about this close to a trip to the dealership for diagnosis.
Plugs for aluminum heads always seem to have more threads. I am assuming that is so it would be harder to strip out the hole, since aluminum is much softer.
I want to respond the autolite comment. I'm not a professional mechanic or racer, so take my advice with a grain of salt. My uncle however races both dirt track stock cars and does some drag racing and is very successful, and he swears by Autolite even though he is a die-hard chevy guy. I have them in my '92 RS and have never been happier with a set of plugs. Just my $.02.
I have had bad experiences with Autolite plugs in GM's. Just to be sure, I run AC Delco's in GM, Champion in Chrysler, Motorcraft, or Autolite in Fords, and NGK, or Bosch in Imports. I do enough tune-ups tho be able to say that the plugs that were designed into the car works best.
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Working on:
'84 Z28 LG4 305 with 200,000 original miles!
Added dual elec fans.
145 MPH IROC Speedo
Building 430 HP 350 (ZZ430)
using primarily GMPP parts.
Short block sitting on a stand. (Man, those Fast-Burn heads sitting on it look good!)
