19 replies to this topic

[LC-GTR-1969]

Gday everyone,

 

I am playing with plug gaps at the moment in my 202, and thought it might help to bounce some ideas round here...

 

I have a 'crane cams, fireball HI6' ignition system with the matching fireball, lx92 coil...

 

Car is heavily worked 202, about 11.1 comp, triple webers etc...

 

Crane specify 45 though for spark plug gap, however I figure that I can open up the plug gaps for the larger ignition system... I have tried 60 thou and the car seemed to have better low end throttle response and marginally improved idle, however I am not sure if this is just my mind playing tricks on me... With 60thou I didnt really notice any missing at high rpm, but that doesnt mean it isnt happening...

 

Advice???

[Rockoz]

Mind playing tricks

[LC-GTR-1969]

Mind playing tricks

Very possibly...

 

45 thou still seems fairly narrow gap though considering the strength of the ignition system... however my guess is that the crane engineers know a lot more than me...

[LC-GTR-1969]

Larger gaps will certainly clean up the idle and light throttle sharpness if you have the spark energy to support them, though it doesn't affect peak power. The only downside is that the higher voltage will tend to find any weakness in the cap/rotor/leads. But if everything is in good shape 60 thou will be fine and a good choice for a street car that spends a lot of time at very small throttle openings.

 

While we're at it, you definitely should run a projected tip plug if at all possible. They improve the light throttle sharpness noticeably as well. Also avoid the old wives tale that says any modified engine needs super-cold plugs. Cold plugs are a pain in the arse, especially on the street. The actual heat range required is a function of how much power the engine makes and how long it spends at full load. Realistically, even a very strong street and strip Holden six is unlikely to need anything colder than a 7 (and if it only get short bursts of WOT I'd even go so far as to run a 6).

Thanks for your reply ol' johnno...

 

Currently running a #6 plug- projected tip.

 

Engine is a fairly "hot" six. Camtech 629b cam- 266 duration at 50thou with all the other 'stuff'...

 

Seat of the bumb feel was better with 60 thou plug gap when compared to 45 thou- full throttle no difference but lower rpm throttle response was better (from what I observed).

 

However, as said, I am 100% aware that this may be simply my mind convincing me of something that isn't really happening...

 

I may try 60 thou again and try to take notes on drive-ability etc to compare and will post back the results

[LC-GTR-1969]

It's not just in your mind, it really does make a difference and works well provided you don't try to take it too far - 50 to 60 thou seems a good compromise.

 

Here's something else to do with ignitions that I discovered recently (the rest of the world probably knew about it years ago, but meh..) that I found interesting: a certain amount of resistance in the secondary circuit is a good thing - not just for reducing interference but also for spark quality.

 

I'd been playing with a programmable ignition and having typical EMI problems. The leads I was using were fairly low resistance spirals (270ohm/ft) with non-resistor plugs. I'd tried some other things that helped a bit but eventually put some resistor plugs in. It didn't completely solve the interference problem (which turned out to be coming from somewhere else) but I noticed that the engine ran as if it had wider gaps and the plugs seemed to lose all tendency to foul, something that had previously been a problem. I thought that was odd so did back to back tests using the same brand and heat range but with and without the resistor, and sure enough the engine wanted the resistor every time. I tried various leads too, and it seems that the engine doesn't care whether the resistance is in the plug or the wire or both, but about 5k total seems to be the sweet spot.

 

Now, I wouldn't try to run these plugs with a SuperMag44 but the ignition I was using was pretty strong (160-180mj from memory) and the plugs lasted fine. So anything I play with now I always try to use leads and/or plugs that'll give me something close to 5k resistance. It looks like the coil of solid core wire will stay hanging on the wall.

Thanks again for your reply - a few things to think about!

 

I may look into the overall resistance in my circuit and work out what levels I am running...

 

Also, do you think 60 thou spark clearance could cause high rpm mis-fire with the Crane Fireball system? I havent noticed any, however I dont spend much time at 7500rpm to find out (albeit, whilst not spending much time up there, I still want it running as clean as possible right through the rev range).

[LC-GTR-1969]

I doubt it. A hot n/a six is about as undemanding as it gets, ignition-wise.

I have just re-gapped the plugs to 60 thou and will report back.

 

Regards

[LC-GTR-1969]

I have just re-gapped the plugs to 60 thou and will report back.

 

Regards

 

So I adjusted the plug gap to 60 thou, and it does seem to improve the low end response, as well as idle.

 

The car also appears to have a better resistance to stall, which is good.

 

My car is quite 'angry/grumpy' due to the cam, hence it has very lumpy (read poor) idle, which in many respects may make the plug gap change more noticeable in my car.

 

I will be leaving it at 60 thou and make observations over the next few months.

 

Thanks for all the help.. Regards

[Dave6179]

I'm about to fit a Summit Racing CDI. The instructions say to use the recommended gap, with the Bosch HEI it's 1.5mm, then open the gaps by .005 for testing to achieve the best result.

[LXCHEV]

What are the V8 boys running as far as plug gaps go? I found this thread very interesting...

When we first built my 383 SBC my tuner used to use a tiny 0.028" and whilst this sounds tiny it always netted great results - particularly at the strip. Ignition system is ICE but using a Bosch transformer style coil. NGK plugs BP6FS.

Some of my mates with similar V8's used to just run with the 'out of the box' gap for their NGK plugs which is around 0.032" or thereabouts. Still small.

If racing is no longer a priority, I'm thinking maybe it's time I tried much bigger gaps? 90% of the time these days I'm just cruising and idling at low revs and low throttle openings. Thoughts? My car definitely gets fuelie and carbons up due to the double pumper 750 HP Ultra on it.

[EunUCh]

That makes sense,the heavy load of fuel/air will tend to drown out the spark hence the need for a closer gap to overcome the load depending on the 

system used.

[LXCHEV]

Great reading.

 

oldjohnno - yeah I should clarify - I shouldn't blame my carb for running rich and carbon build-up - the tune itself certainly needs some attention. I'm very keen to look at it. It's interesting you mention the vac advance, as my dizzy is locked out. I wonder if that has a huge impact or not on low speed cruising. I wouldn't call my combo wild by any stretch of the imagination - 383, 10.5:1 comp, cam approx 240 @ 0.050. Hopefully some clever play time can neaten it up a bit. I never have any issues with fouling, it's just running rich.

 

I'm still running plug gaps of .032" these days, might open them up a bit for street duties just to see.

 

AED262 - very interesting results indeed. It seems fairly consistent that the race engines like a conservative gap. Just curious - what do you term a race engine? ie. greater than 11:1 comp, cams over say 260 or 280 duration? Or more wild than that?

[TerrA LX]

I wonder if that has a huge impact or not on low speed cruising.

 

Not sure what you call huge but any motor not cruising on max vacuum (created by ignition advance) will suffer throttle response and economy.