930 Plug Gap for Bosch W4CS, CIS, Stock Ignition

[wcarson]

Hi everyone,

I'm getting my 1982 930 back on the road again. I will be running Bosch W4CS plugs. Do you all recommend I stick with the stock plug gap of 0.6mm- 0.7mm (.024- 0.027"")? These plugs are different electrode design than the original W3DPO and obviously slightly different heat.

My car specs:
3.3L stock displacement, running CIS with adjustable WUR, single plug stock original ignition, stock boost (0.8 bar), Kokeln IC, K27-7200 turbo, mildly ported heads, SC 330 cams. The car made 350 wheel HP on the dyno. It's a street car that I use for "canyon carving", no track use.

I'm assuming a plug gap of around 0.6 mm (.024") is best for these W4CS plugs? Thanks in advance from the experts on here!

Keith

[reclino]

One heat range colder than the stock plug. At 350 HP I wonder if you need a colder plug. Let us know how long it lasts before carbon fowling takes it out. I had planned on running BP8ES ngk plugs in mine instead of the W3DP0.

[gsxrken]

W4CS are a step hotter than the W3DP0. Bosch numbers: larger number is hotter.

Here’s a chart Speedy Squirrel shared (ridiculous- I have no idea what his real name is, lol) one time that I saved. I do my own homework but when Speedy talks, I tend to listen.

[/QUOTE]

[reclino]

I was mistaken, I thought the Bosch 3 crossed to a NGK 8. But it crosses to a 9. Looks like I can run my 8 heat range plugs for break in on low boost, but going to be shopping for some other plugs once I turn up the boost.
David

[wcarson]

Yes, the W4CS are hotter than the the original W3DPO. The electrode design is the more traditional design with the W4CS. But I'm assuming the plug gap set at stock is optimal?

[wcarson]

...............

[wcarson]

I'm planning on running 0.6mm gap (Unless anyone here thinks otherwise).

[reclino]

I don't think plug gap needs to change, more gap would just stress the insulation of the wires and coil without really providing any benefit. Your mods are pretty mild so you don't likely need more current to the plugs. I have no direct experience with this yet, I am still building a mildly modified turbo engine similar to yours.

[wcarson]

Originally Posted by reclino

I don't think plug gap needs to change, more gap would just stress the insulation of the wires and coil without really providing any benefit. Your mods are pretty mild so you don't likely need more current to the plugs. I have no direct experience with this yet, I am still building a mildly modified turbo engine similar to yours.

Thanks for the input. Indeed too large of a plug gap without a very strong ignition system in forced induction motors is bad because the high effective compression when on boost can basically snuff out the spark. If you use a larger gap, then you must have a correspondingly powerful ignition system to be able to support the larger gap. My ignition is the stock Bosch CDI.

I'll stick with the low end of stock range. The only reason I was going through this in my head is that the plugs I'll be using are of different electrode design and configuration that the originals. The original Bosch W3DPO have the central and ground electrodes oriented side by side, where as the Bosch W4CS plugs that I will be using now have the more traditional electrode orientation. My presumption is that the different orientation doesn't matter and the gap for the Bosch W4CS should be stock like my old W3PDO's. I was hoping that someone using one of the more traditional electrode designs (like the Bosch W4CS) could weigh in and confirm this.

[mark houghton]

I'm not a plug wizzard, just sharing that years ago I was running with NGK BP8ES (though I see not recommended in the chart Ken provided?), being slightly hotter than the stock W3DPO. I ran with a pretty healthy gap, don't remember exactly but seems around .040, because I was was using MSD ignition which could support the larger gap and it was their recommendation. Never had any issues with blowing out the spark that I could tell.

Probably of no value here, so just FYI.

[wcarson]

Thanks for the info Mark! That makes sense. I'm hoping to get my 930 up and running this coming week. Thanks again.

[spuggy]

I remember reading years ago that the factory, when they did the 930 as a homolgation special (so they could race in a Production class), worried they might not sell 500 cars - which they envisaged as being sold only for track use to hard-core drivers. So it was all basically setup for flat-out use in club racing or similar.

And they were astonished when it became an icon and dentists and accountants bought them....

The W3DPO is apparently very cold indeed for street use. That said, I've never had one foul since 2006, even with "stuck in stop-go traffic" use. They seem to Just Work for me. And the colder the plug, the better the throttle response. In theory (like mere mortals would ever notice).

Despite minor emissions changes (which apparently didn't require re-testing), factory never went through EPA testing again with the 930. Apparently changing something fundamental (like gearing, exhaust - and apparently plug) would have required this. In fact, factory changed precious little until going EFI with the 3.6 Turbo 2, I believe (and then they went for a hotter plug, which they also used in the 993 turbo and onwards).

As for changing the plug gap - yes, you should get a hotter/bigger spark. However, stock HT leads may then be marginal, meaning you may need to upgrade to prevent them breaking down & arcing out (known problem with at least one vehicle I own; Magnecore leads are the fix for that guy - and despite being notoriously lumpy stock, it does run better/cleaner with a bigger plug gap).

No idea what bigger gap/more energy might mean for the CDI box - if anything.

You may be surprised to know that many plug manufacturers now, if you read their blurb, do NOT recommend the user change the plug gap, as this changes the angle with the center electrode, may damage the central insulator. Or is simply impractical/impossible (as with multi-conductor plugs). Instead, they sell the same plug pre-gapped from the factory in different gap specifications...

[wcarson]

Very interesting info- thank you!