I run NGK's. Not that I disagree with the German/Jap alignment of plugs, but for discussion sake, why is this? Setting the gap correctly and assuming that the plug fits correctly, what is the disfunction? Is it resistance, heat, core, tip, voltage ability, langauge (ha!)? In other words, if you have a platinum Bosch and NGK, what causes the German plug to foul in 10 minutes in Q engine? Would a NGK foul in a German V-8? I have heard this statement repeated over and over, but have never seen an explaination as to why?

Aus, I moved this to it's own thread for ya.

The only problem is that the +4 seem to break off electrodes [when subjected to mild knock] also the Q piston comes extremely close to the plug tips as the piston expand from heat.

We have replaced 19 +4 plugs with broken electrodes a few of which have damaged the cylinders by imbedding in the piston above the first ring.

High compression engine 10.2 to 1 with flat pistons have a tendency to build up crud on the piston tops raising the CR closer to 11 so the oem plug was what was used in the design test process..........they usually don't fail ever but need changing as the gap widens and to protect the head from galling the plug permanently in place.

The other problem with +4 is they only come in one heat range vs the oem's 4 separate temp range!

The larger gap is needed due to tightening emissions.What the manufactures are doing is leaning out the mixture, especially at idle, which means that there are fewer droplets of fuel per sq inch, & to light the mixture, the spark must come in contact with a fuel droplet (molecule) which starts the chain reaction. So, if you open up the plug gap, it's now 1.5mm in some cars today, you have a greater chance of lighting a fire.

We have the Holden Commodore & they changed from 1.3mm to 1.5mm without telling us, (an upgrade 1/2 way through a model run)& we started getting a bad idle. When we put in the larger gap plug (only .2mm bigger) the engine idled smoothly.

NB The larger the gap, the more load the ignition system is put under, & also the bigger chance of missing at high revs.

The Q uses the same 2.2-2.3-2.4 milliseconds injector open time at idle and 2000 rpm cruise.........talk about lean!

This is why I shout about the necessity of achieving a perfect idle as it yields a perfect cruise and the minimal use of gasoline on the highway.

If perfect is 2.2ms, 2.4ms means your highway milage drops by 9%.It is a constant battle between the O2, ecu, and injectors to average the least amount of gasoline that will maintain the rpm.

See the mixture steps go 4.5% lean, just right, then 4.5% [a 0.3 ms variance] rich......the average is suppossed to be 14.7 AF..........the ecu also tries out different ignition advance rates to narrow in on the best average [around 35-40 at light load cruise vs 15-20 at idle].

It is so much easier to think in gallons per running hour [6.1 pounds per hour] than to use mpg.

By the way the injector does NOT just snap on and off, the pintle is raised as a ramp up against the fuel rail pressure and it takes approximately 1.0000 ms before the fuel starts flowing so the usually rule of thumb is to multiply the open time by 0.66 to get the actual flow [2.2 x0.6666=1.4652] then the faster close has a minor bounch off the seat so subtract another 0.3 ms so net is approximately 1.1652 ms of rated flow [370cc/min = 6.1666 cc/sec {{or 4.4 grams per sec}} x 0.0011652 x [corrected for the lower cruise pressure 34/43.4=0.78341 take SQRT=0.8851] equals a tiny drop about 5 milligrams of gasoline per squirt x 4 cylinders x 2000 rpm..............~~~ 15.25 pounds[6908 grams] per hour and 60 mph [2000 rpm] no AC level road.

By the way the J30 uses smaller than 370 cc/min injectors and of course only 3 fire per rpm but the 60 mph rpm is higher by 13% [diff gear and smaller tires]............

Q45tech wrote:By the way the J30 uses smaller than 370 cc/min injectors and of course only 3 fire per rpm but the 60 mph rpm is higher by 13% [diff gear and smaller tires]............

during startup though, i think it's all injectors spray twice each revolution.(if i read the manual right) that's rich.

But this batch fire mode changes when the rpm reach 400, this is primarily to precoat the precats/cats with fuel to allow them to heat up fast and to make sure that there is enogh of the lighter fractions of gasoline available to burn in a 30F cylinder.

Smooth easy cranking [correct warmup cycle] is a much more difficult software design than any WOT or cruise operation.

The injector times I quoted were at the 176F coolant temperature say 10-15 minutes or so after cranking.

More modern designs actually measure the fuel rail temperature to correct for the fuel density changes as it warms up.

Thanks Mayhem! So the 4+'s break in the compression and heat. What about the conventional single tip Bosch platinums? What shape piston and clearence are found in the BMW and MB V-8's?