What Heat Range Plugs Should I Use?
 

Some of you may have read my recent thread on my start and run problems, which seem to have been successfully solved by installing a newly refurbished WUR.

On my engine I have always used Bosch heat range 7. Originally an 80 3.0, it is a 3.2 w/ 10.1:1 CR. It is set up for twin plug but I am only using a single plug, points style dizzy.

A mechanic who I recently went to in order to confirm my fuel pressure tests noticed the black plugs and went to range 8, which is one hotter, to better burn off the carbon buildup.

I am not sure that the carbon buildup is from the plug not burning cleanly or from the fact that I had the mixture set rich in order to help "cure" the starting and warmup issues I had prior to fitting the new WUR.

I have an MSD CD and the plugs are gapped @ .045"

I've read in Bentley that 78/79 engines (no lambda, like mine w/ vac assist WUR) use WR8DC, whereas 080-83 (w/lambda) use WR5DC. I am using a 78 WUR.

What tests can I now do in order to verify which plug to use? I read in another thread that I should redline the engine and pull the plug, and look for a color change in the ground to occur @ the bend.

Most of my driving is done not @ WOT but some in town 3rd gear 3000 rpm, and some highway @ 3500.

I've always heard that if you do an engine mod, like raising compression or increasing displacement you should go 1 heat range cooler. Anyone else ever hear this?

Also, why the switch from 8 range in 78/9 to 5 range in 80? The Lambda system?

He was correct in doing so by his reading of the plugs which he pulled out. You are correct also in your statement. Have you checked these plugs since? What do they look like?

The test you are referring to is for reading your ignition advance. For the optimal total ignition you would want the ground strap on a new plug after the redline pull under full load and a clean shut off to be at the middle of the 90* curve.

This does not tell you that this is the right heat range for your engine or that you have the optimal a/f ratio. For the right heat range you need to look at the first two threads of the plug for color change.

The color of the porcelin will tell you the enrichment of your engine. You also have to look at the porcelin base inside the plug.

This type of testing is to find the optimum settings ie. total ignition, air/fuel ratio and plug heat range for your engine under full load for best performance. These settings will work under any conditions but are for all out best performance from your engine

There are several places on the internet about plug reading to obtain the optimum settings for performance. Reading plugs can tell you a lot about your engine and what it wants. Every engine is different and will want different settings for optimum power.

If your just looking for the best plug heat range for every day driving with your engine then simply read the plug for color on the porcelin. You ideally want a light tan color.

This is assuming that your tune is in good order ie. your a/f is right and your timing is right.

You can mask problems, ie. over rich setting, with plug changes. That is not the best situation for optimal operation but it will work.

If you pull these plugs and they are white then go to a colder plug if they are still black then check your a/f ratio. If it is correct then go to a hotter plug. It won't matter much if you are not right on if you are just looking for an every day plug and not worried about optimal tune.

Just another note when you go to dual plugs you will have to find the optimal heat range for that set up again. I doubt that it will be just a matter of putting in 6 extra plugs the same as you have now.

Most engines have been tuned with too much advance, too rich a mixture and too cold a plug. Dedicate some time and an assortment of plugs in several heat ranges to get started. A dyno is helpful if you don't have a long stretch of highway lightly enforced by the local constabulary.

Work out the heat range and timing (they move together) and finalize with adjustments on mixture.

See the site:

http://www.dragstuff.com/techarticles/how-to-read-plugs.html

great job gary!
there is a lot of good info on "reading plugs" out there. some sites contradict each other though. i have read that the threads tell the heat range and also that the overall color of the porcelin tells the heat range. i think the NGK site says to look at the porcelin color for heat range, i will have to go back and look.

i agree in that most have too much advance. i dont think you can really tell what the proper advance is without a dyno. as for heat range, i think most have too hot a plug.
i use to think hot meant better.

paul, with the problems you were having, he should not have changed the heat range until all was fixed and new plugs were put in and checked again.
with the compretion you have, i would start with a set of W4's or NGK 8's. if you sre going to track the car, i would definately use the W4's for the track and maybe a W5 for the street.

i have been using a used set of bosch W4 plugs for about 2 months now. i have not had any more fouling than when i had the W7's in. sometimes when i do a hot start it may run on 5 cylinders for about 15-20 seconds, no big deal, it always clears up. driving around town the porcelin was on the dark side, the center electrode was clean as was the ground strap, but i need a W5 for daily driving. after driving 600 miles to nashville, the porcelin was clean ( back to what it looked like when i put them in. they came out of a 930). so just from the test i have been doing, the main reason you would need a hotter plug is for the idle circuit. it runs much richer increasing the chance for fouling.
the one thing i did notice that may or may not of had anything to do the the colder plug was my car seemed to run a tad hotter??? i dont know if the extra heat the plug is dissapating into the head is making the head temp go up. any ideas on this? i never went over 210, but still it seemed to run a little hotter. my temps coming back from nashville crept up to 205, about 70 deg. out and cruising at about 80 mph.

Thanks, guys. That's the type of feedback I was looking for. I've always just looked for light gray/tan deposits.

I've run W7DCs in this engine for about 75,000 mi w/o any problems I know of. The temp went down about 10 degrees to about 190 w/ the 8s, although as you know there are other factors that can contribute to this and temps can vary quite a bit on my engine.

I think I've got to now make sure my A/F is good first and then do some driving and do a plug check. Since I'm concerned the 8s may be too hot and lead to detonation on a long run, I think I may put clean 7s back in first.

Gary,

Should the first 2 threads be the same color as the porcelain, or should they be dark?

db,

Why the comment on most engines having too cold a plug? Are you referring to 911s or engines in general?

T77,

You say the center electrode was clean. No deposits at all? Was this w/ the 4s, indicating to you that you should go w/ the 5s?
I'll check the NGK site you mentioned.

yes, the center was clean and had a grey color, no deposits. and that was after 600 miles at 80 mph. that was the same color they were when i put them in, its going to run leaner at that speed versus driving around town where i would frequently idle and cause the carbon build up, but still no fouling. before the trip the center porcelin was black, but the electorde itself was still clean. i am going to put in a set of W5's and that is what i probably will stay with, although i may change over to the NGK's.
if you are going to put new plugs in, i would go ahead and put in at least a W5

thats interesting that your temp went down with the hotter plug. i guess the heat is staying in the plug instead of going to the head.

db,

Why the comment on most engines having too cold a plug? Are you referring to 911s or engines in general?
Answer:
In general. The specs for 911's were pretty good from Germany. Some refinement could be done because we don't have the same quality fuel Porsche used in the R+D. The junk we must use in our cars is very poor compared to the lab at Porsche.

Most tuning must be reversed. Timing first, starting with spec and backing it up a few degrees. Plug heat range, most likely up a range warmer from stock then mixture, set for best performance.

Then go back to the timing, check for any signs of detonation. Adjust if necessary.
Spark Plugs, confirm heat range, adjust if necessary
Mixture, confirm and adjust if necessary.

Keep the quality of fuel consistent, same vendor and be conservative with the engine specs. The quality of fuel will only decline. If you use "octane booster" your plugs will be discolored. Keep some around for emergency use only.

T77911s,

This temp change is in line w/ yours. In your example, temps went up when you went to a colder plug.

Your trip to Nashville was w/ the 5s, right?

db_cooper,

How to test for detonation w/o melting my engine down?

Paulporsche

I should clarify a few things.

Finding the optimum settings for all out performance may not mean that you can run this on your daily driver. Your A/F ratio and ignition advance and total ignition settings should be ok but you may find that you have to go to a hotter plug for the daily driving as you will probably foul the ultimate performance plugs. I think that T77911s is finding this out.

This is due to the fact that these settings are for all out engine under load at full throttle or there abouts. Under daily driving conditions you are at part throttle most of the time and lugging the engine at times. This puts a different requirment on your settings.

As I said earlier reading daily driver plugs is quite difficult as you have to know under what conditions the vehicle was driven prior to pulling the plugs and reading them. Here is a good link to reading daily driver plugs. As you will notice there is a wide range of a good or acceptable reading. Some of which I do not agree with but that's just me. http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

you will see that 14 and 15 are the best looking plugs and is what you should be striving for if this was out of a vehicle which was driven daily in the city with some highway miles and with a lot of miles on the plugs. I disagree with 14 as bieng shown as THE best and would look for 15 as The best under those conditions.

If you have a lot of highway miles and little city driving then I would look towards a plug as shown in 18 or 19.

Here is a good link to reading plugs for optimum performance. http://www.wallaceracing.com/plug-reading-lm.html

On your question on how to check for detonation. I wouldn't suggest that you try and test for this ( I mean purposely set your car up to detonate) but if want to test if you have detonation under your present set up then it is very simple. With your present set up find a slight inclined area where you can put the car in a gear that will lug the engine ie. climb in 3rd or 4th gear rather than 1st or 2nd and listen to your engine. If you hear any rattling or knocking then you have detonation. You will need to back your timing off.

The whole thing with reading plugs is that it is all dependent upon the type of fuel used and the combustion characteristics of your engine. Your engine will tell you what it wants if you look and listen to it. As db said Porsche and the other mfgs have done a pretty good job of specifing a generic plug for their engines but you can improve on that by reading your plugs and adjusting things for the optimum settings under the conditions which you are running. This will be different for different conditions.

There are a lot of different things to look at when reading plugs and they will tell you a lot about what the condition of your engine is as well as to what the engine wants under varying conditions. For my style of driving and under the conditions of where I drive I look to get a plug that looks like 23 as shown in the first link. This is on a fairly fresh set of plugs. That plug shows the right heat range, the right timing, and the right A/F ratio for the conditions it is bieng driven in.

Hope this helps.

Thanks, Gary. I had a look @ that chart. I agree that I would rather see something akin to number 15, which seems just slightly richer, for my daily driver, since typically there would be some warmup, some stoplight idling, some cruising, some highway, and some stop and go in the mix.

Funny, your detonation test is exactly what I have always done. In fact, while I was chasing my recent WUR problem, I found I was doing this on several hills I have near my house. My engine is loud, and I sometimes wondered if that was masking any knocking.

Heat range is what I'm concerned about now. Looks like there should be some black on the first 2 turns of thread for correct range. Is that right? Or is there something else to look for?

db_cooper,

How to test for detonation w/o melting my engine down?

Answer: The spark plug will tell you. Pepper on the ceramic is not good to see. Worse is tiny balls of aluminum, coming off the pistons. You may hear "pinging" under load too. All these indicate too much advance and / or poor quality fuel.

Back up the timing and check the plugs, no pepper, no ping. Use high octane fuel.

Once the plugs look good, you may need to correct the heat range, look at the grounding electrode, it should be clean almost all the way to the base. Ceramic should be almost like new, with some darking around the base. Use a lamp and magnifier to good a good look.

db_cooper,

I think I have the timing nailed down OK. I've been using the same for about 18 years w/ this engine. As for fuel, I've always used Sunoco 94 which is the highest octane here (except @ the track and airports).

It's the heat range change that has me concerned. I just don't want to test the 8 range plugs by burning my engine to the ground. I've always used 7s. I like the slightly lower temp that seems to come w/ the 8s, but I'm worried on a long highway run they'll just be too hot and I don't want to find out the hard way.

To play it safe, I might as well go back to the 7s and observe their condition.

Sure this is a basic question for many , but please help! Purchased WR8DC+ plugs as recommended for my new '78 3.0. The ones with yttrium.
Thing is, the old cold platinum W6DPO ones installed in Japan at some point in the past are shorter - the tip points toward the centre electrode whereas the WR8DC overlies it and thus is longer. Thread length is identical.

Please explain & guide; am I safe installing these zundkerze as recommended - not sure of the clearance.
Engine was totally rebuilt in Japan (have a pile of photos, but that's all the provenance I have) and as far as I am aware , a stock standard job.

Motor is running fine, starts fine with no smoke , hesitation or backfires at all . Probably a bit rich given the plug condition; "cold or rich" according to http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
I'm just doing the ground zero tuneup given the unknown history. Plus the other 911sc necessaries...

http://forums.pelicanparts.com/uploa...1263804771.jpg
http://forums.pelicanparts.com/uploa...1263804797.jpg
Thanks!