I run an MSD 6A ignition and I have been using Bosch W5CC plugs with a .050 gap. This time I couldn't find that plug so we substituted an NGK R5671A-7 with the same gap. I ran it for about 20 miles and the car runs great. Cylinder head temperatures are the same but when I checked the plugs they sure are lighter in color than I am used to. How long does it take to get an idea of the way the spark plug burns? Do I need more miles or is this plug hotter?

Thanks for your help,
Dave

That plug is hotter. It should only take a few minutes.

We typically run a W7DC in all of our cars (street and track)


B

That's what we just put in my car, right?

Correct.


B

Should I be worried? Here is a picture of the two plugs out of #1. The Bosch is on the right and the NGK is on the left. Granted the Bosch is old but it doesn't look as bad as the picture. It has dark grey electrodes and some soot at the outer ring. It was in the car when I converted to the Megasquirt ECU and saw some rich mixtures averaging around 12.5/1.

The NGK is certainly seeing leaner conditions with the system now running in closed loop correcting to 13.8/1 for a target AFR.

Thanks,
Dave

Sorry forgot the picture, doh!!

I'm surprised by the difference in the size of the plug north of the threads. The NGK is much smaller (skinnier) than the Bosch.
Does that affect performance?

That's kind of misleading. Everything looks the same to me except the size of the hex on the Bosch is 13/16 and the NGK is 5/8. Also, the NGK sports a v groove in the electrode which they have all over their box. Gimmick?

Dave

The NGK looks lean to me. The V groove works.. not sure what we gain.. but we tested some AC Delco's with the groove and they showed better flame propagation than a non grooved plug.

Hum.. the Bosch is/was toast. I'm surprised it ran on all 4 cyl's.

B

Hi Brad -
What are you gapping your plugs at? I am getting ready to change my plugs and can't find the MSD paperwork (you know, that paper I made sure to put in a place where I wouldn't lose it!?)

I am using the 6AL, with a comp-u-fire and the stock 2.0 distributer with the vaccum hooked up to the passenger side 40 Weber.

Thanks!
Scott S

Guess I'll richen the mix just a little. I was trying to get it as lean as I could, but with the hotter plug I may be too lean. The software with the megasquirt allows you to richen or lean the whole fuel table by a changing a fueling constant they call Reg Fuel.
I'll try a few percent and see what it looks like.

Dave

45 thou.

B

How about this one, Brad?

Geoff

G*d D**m buttons

Scotch tape dispenser with a spark plug!

What the F$&^!!!!

That was so I could take a picture of it ya nitwit! Atleast I don't have my effin' shoes in the picture!
Geoff

It looks pretty damn good to me. A tad lean.. but no reason to change anything. What I dont want to see: WHITE. Tan with a light grey = good.


B

What?
Did I post something with my feet in the pic?

Sean, that's a standing joke on the BBS's. People take pictures of parts and always have their feet in the shot. duh!
Geoff

Geoff,

what spark kind of plug is that in the picture? Looks like the one I use in my VW Golf 1.8i, the Bosch N7BYC, and NOT a 914 (type 4 engine) plug.

Please tell me if such a multiple electrode plug can be used in a 914 (with standard ignition). Why else did you show the picture?

The spark is directed differently with such a multiple electrode plug, so combustion is more uniform. On the other hand, it would not surprise me if this only works with electronic spark units (MSD or whatever).

Anton

How about pics of dog paws?

You need a dog to hold your camera?

Yes... only my German Shepherd can photograph my Porsche parts!

Why?... doesn't everyone have a picture-taking dog?

Here he is protecting the "stash" of parts...

Nice dog. Nice stash of parts too with the GT flares and other goodies.

I can see the dog has assumed the typical stable photographer's position so that the camera doesn't move... LOL

13.8:1 is definitely too lean for full power application. It may be close to peak power at that AFR, but too hard on the valves/pistons. Exhaust temps could be as high as 1450F running that lean

12.8-13:1 would be a better ratio. A bit rich of peak is much safer at WOT.

I thought the factory WOT was close to 12.5 to 1 A/F mix if I remember right.

Karl, I have seen pics of dog bones before but thats a first, dog paws. Kewl

Oh, that is a spark plug out of my 76. Of course you can run the Bosch W7DTC in a 914. They run pretty good too.
Brad, do you have any dyno numbers for the different plugs?? Might be fun to do when the old dyno is running.


Geoff

Now I am confused. Are we talking about the Bosch W7DC or W7DTC?

The pic is of a W7DTC that was in my 76 2.1 914.

Geoff,

Thanks for the reply. I will try this spark plug. Your suggestion about dyno testing with different spark plugs sounds challenging.

Does converting to an electronic (or even multiple spark) ignition yield a gain in HP as compared to the stock ignition set up? I have never had problems with cold or hot starting, and my revised 1.8 L-jet engine (with new Euro pistons) runs strong up to about 6,000 RPM.

Anton

I installed an MSD unit and didn't see much of an improvement. Others have. HP gains woud be maybe 1 hp.
I liked the triple tip plug but would be interested in seeing some dyno work done with it. I am going next week with DHunt so maybe I will bring a set to toss in if theres time.

Btw. On the type 4 the peak of the hp/torque curve is about 4500rpms so reving to 6000 your hp has dropped off 20+hp. On a stock 1.8 Euro version hp is 85 so you only have 65 hp at 6000 rpms. Shift earlier and you'll get there quicker

Geoff

Why would you ever need a mixture richer than stoichiomtetric? Isn't the relevant chemical equation balanced when there is 14:1 air-fuel ratio? With less air wouldn't there be less combustion and therefore less power? BTW, page 1 of this thread was pretty funny!

Jeff,

The main reason we run on the richer side of stoich is for cooling. Running an air cooled engine at stoich probably woud lead to valve and piston damage. Most of what I have read indicates AFR should be around 13.7 and still richer at WOT.

My first post showed a plug run at 13.8 and Brad thought it was too lean.

Dave

Yes, the air cooler cars run a richer charge for cooling, about 13.7to1 for partload mix and 12.5 to 1 WOT. This keeps the head temps down so you don't drop a valve seat.
Geoff

Dave, here are the chassis dyno results for a Rennlist member's (basically) stock 2.0 motor. I was very impressed to see how the old d-jet could keep the air-fuel mixture close to 14:1 throughout much of the rev range. Please post the results of your dyno testing as soon as you get them.

83hp is pretty good but I think he is running a tad lean if that is at WOT which most pulls are. Should have checked the fuel pressure
Geoff

ah so i guess 4500 rpm is the magic number to shift at <_<

No, about 5000 so when you shift (the engine rpms drop) you are hopefully hitting the peak of the power curve at 4500 when you complete the shift. Try it out sometime.
Geoff

Somebody answered that question pretty well in a previous thread.

Would different tire sizes produce different chassis dyno results? For example, would a smaller circumference tire produces greater torque and therefore hp at the rear wheels? I guess because of the law of conservation of energy the curves would just be shifted, right?