Spark plugs for Bosch HEI

[Dave_EH]

I have been working hard on getting a commodore Bosch HEI dizzy to perform on a Red six.

I have finally overcome the problem of a substandard advance curve for a modified engine (even after having a recurve at an igntition specialist) by using an exchange shaft from the 720 model dizzy that was available only on the VK EFI Black motor - a friend put me onto this idea and fitted it.  This differs significantly from the more common 700 and 702 advance curves.

My final obstacle are the spark plugs.  The factory gap for a properly functioning HEI dizzy (running a full 12 volts with 30 amp cable) is 1.5mm, or around 59 thou.

My head is a modified 179.  I currently run NGK BP6ES.  The issue is that you cannot set a gap of 59thou on this plug and still have the ground electrode parrallell with the spark electrode.  This starts to diminish at 40thou.

Therefore I need a different plug to reach optimal running performance.

Has anyone else ovecome this problem?

I believe a Champion RN12YX6 (or slightly cooler), or NGK BPR5ES13 could suit?

The main problem is that the 179/186 head has a gasket 3/4" reach plug, and the 202 that most HEIs come from have a 1/2" tapered seat plug.

I guess its just an issue of going to a shop an putting the feeler gauge through a few different plug types?

Any help appreciated!

[craiga]

Hi Dave,

Always good to see your interesting posts :-)

A couple of things - I purchased a 'Pro Comp' dizzy from eBay.

http://preview.tinyurl.com/27vftg



This distributor is much better than the stock Holden unit and has a built in adjustable rev limiter. I paid $195.00 for mine so this one is cheap - until someone else bids!!

This dizzy, out of the box, runs 36 Deg overall advance (initial is at 12 deg on my car).

Coil currently is a 50KV Bosch but I have a 70KV unit ready to be fitted.

I run a 1.0mm gap and everything is fine on pump fuel, engine revs to 7000 RPM limiter no problem. I am suprised at such a wide gap - I would think you would need a better coil than the standard one to achieve a strong spark this gap at high revs.

You can purchase a special racing plug with a centre electrode - this basically gives three spark locations.



Hope this helps.

Cheers,

Craig.

[Dave_EH]

Hi Craig

Always good to get a helpful response

I'm just running a Bosch HEC716 epoxy filled coil.  The specified gap does seem large, but is stated as such in the workshop manuals.

Regarding the ProComp dizzy - I must admit I have heard several negative reviews of these units, although I'm not sure how a referee check would go with some of the individuals complaining...  

At least you can report back with some good qualified advice.

Do these units have vac advance?

Of most interest is the total advance you are running.

Dr Terry and the early holden workshop manuals prescribe an optimum total of 34-38 degrees.

A book I read on modifying ignition systems prescribed somewhere around 28 - 30 on a wedge shaped combustion chamber.

The Bosch HEI 720 has approx 20 degrees of mechanical advance, so with my static timing set at 12 degrees, a total of 32.  Advance starts at approx 1200rpm on this unit.

Does your Harmonic balancer have degree markings?  Would you be able to plot a graph through the rev range and show your curve?

I'd assume the Bathurst model XU-1s would have had an advance curve to suit the cam.  Any idea if such graphs would be available?

Look forward to hearing your thoughts

Cheers
Dave

[craiga]

Hi Dave,

I have a Snap-On timing light with digital advance display so could do the advance graph for you. The balancer I use is a Romac unit and has degree markings so this job would be quite straightforward, albeit bloody noisy!!!

The ProComp dizzy seems fine to me, not sure what problems people would have experienced? Any further info? The ProComp doesn't have vac advance, highly suited to my application.

I have a copy of Fiv Antonio's XU1 book so I'll have a look when I get home from Brisbane. Won't be till next week though :-(

Other guys would surely have some more info on modified reds - Leon? Jockster?

Cheers,

Craig.

[2door350]

Gday all,

if you want to run the same heat range all you need is ngk bp5es11 or bp5es13´s

the 11 or 13 at the end of plug number relates to the plug gap ie 11 = 1.1 gap 13 = 1.3 gap

you can buy these of the shelf for the same price

If you really want a 1.5 gap you can open up a set of 13´s although I found a 1.1 gap works best.

i use ngk6es11´s in my 186 that pumps out 250hp and pulls hard to 7500rpm


hope this helps - any probs let me know

[craiga]

2door350, what dizzy do you run?

And what initial and total advance do you use?

Cheers,

Craig

[2door350]

I use a blue electronic distriubutor and am running a monster solid cam (310 degrees duration!!) so my dizzy is locked and runs at around 28 degrees.

[Dave_EH]

Hi Guys,

Thanks for the most helpful replys and sorry it has taken so long for me to respond.

Craig, the negative feedback on the procomp units was on the GMH-Torana forum:

http://www.gmh-torana.com/forums/index.php?showtopic=15455&st=0

I'm not sure what the problems are - possibly module failing, which could be a problem with the silicon grease?

After giving the spark gap issue more thought, I guess a stock blue motor would only rev to approx 4500, or 5000rpm tops, and not all that often.

Considering we run our engines higher up the rev range, it makes sense to use a smaller gap.  I'll try both the 1.1mm plug and the 1.3mm plug and see how I go.

Craig, if you ever get the time to draw up an advance curve that would be great and then at least I can compare apples with apples.  I've held off on buying any XU1 books, as I was told at the Speed on the Tweed event last year that Harry Firth is presently writing his own, and this will be the difinitive book.

Would still love to get a firm answer as to what the ideal total advance is for a red six?

I'm looking forward to getting the ignition right so I can fit my tripples

2door350, when you say "locked" - is your staic and total advance the same (28)?  Do you crank at 28 degrees?

Cheers
Dave

[craiga]

Hi Dave,

Interesting feedback about the Procomp dizzy  

Seems to be the V8 ones though, but will keep an eye on it and retain the VK unit as a spare.

Checked the well known Fiv Antoniou XU1 book and factory specs for the 73 Bathurst XU1 is as follows:

Initial Timing - 10 BTDC
Centrifugal Advance -
0 @ 1100 rpm
13/17 @ 2000 rpm
22/26 @ 5600 rpm

Total is max 36 Degrees (initial + centrifugal) @ 5600 rpm

A vacuum advance reading is listed, 11/15 degrees @ 8.5/10.5" HG.

Spark plugs were C44NS with a gap of 40 thou (1mm).  

Factory, dealer sold/road going XU1's used a 10.3:1 compression ratio.

Interestingly the late '71 model (186 powered) used a total advance of 28 degrees.

2door350, this book lists the '72 202 powered car as using a 304 degrees rotation camshaft, and a factory recommended idle speed of 900 rpm. The late '73 cars used an even longer duration camshaft, many of them were raced with Webers and allegedly made over 250HP. Good power for a factory produced 6 cyl powered car back then - well thats if you ignore the 280-300HP E38/49 Chargers ;-)

Dave, over Easter I will try to find somewhere away from everyone to do the advance curve on my car.

I know Mark (Blown_FC) had an XU1 replica engine built for his FC - he may have more info on advance curves - better still Dr Terry would be the one to ask as his business regraphs dizzies.


Cheers,

Craig.