Spark Plug Brand and Gap w/ MSD coils

[tbrell]

I run demo derby, and pretty heavy in the W body builds. I run a 3100 that's been fooled into never going into limp mode, other than that it's stock (for now). I'm upgrading to MSD coils, and universal 8.5mm plug wires.

What would be the best bet as far as spark plugs go? Should I run a cooler plug since I often run the engine hard and usually do not run a cooling fan or will sometimes lose a radiator? Since I have a (supposedly) stronger spark w/ the MSD coils, would it be beneficial to have a larger gap?

I've read a few spark plug threads on here, but they list different suggestions for different applications...thanks for any input.

[3400-95-Modified]

I think others will agree... I don't feel that the MSD coils are an upgrade in any way. Stick with stock or go to the D576 coil which is guaranteed to be better than the D555 you may be running.

Check this thread for info regarding that.

http://60degreev6.com/forum/showthread.php/52030-Coil-Dwell-Time-ACDelco-D576-and-D555?highlight=coils

[tbrell]

Thanks for the input. If I am using the 3100 PCM and the ICM that came with said 3100, will the dwell time be too long for the other coils and burn them out? I have only scratched the surface on tuning, I have read up on MS-II, but have not made any purchases, so I'm a bit in the dark on this, even with my electrical background.

I have not yet purchased the MSD coils, they're just sitting in my shopping cart on Jegs...was waiting to get some input on spark plugs before picking some out and finalizing the purchase...

[tbrell]

I did a little more research and came across this comparison. This thread claims that Summit Racing coils are the best bet. Anyone have or hear of any experience with them?

http://www.grandprix.net/forum/ubbthreads.php?ubb=showflat&Number=96807

[robertisaar]

the ICM self-adjusts for different dwell times when necessary. I don't know if there is a limit to how much it will add/subtract, but other delco coils should be fine on it.

when you mention limp-mode, I don't believe any PCM that has ever run a 3100 has a limp mode outside of the 94-95 A-body unit. the 93-95 flash unit doesn't have any limp-home hardware in it that I can tell and I don't believe GM bothered with it for the OBD2 PCMs either. if the processor(s) quit executing instructions correctly for either of those, they go into BAD OPCODE loops and not a whole lot gets done. spark events would still happen via the PCM dropping the EST bypass circuit, but injection events should cease.

for the plugs..... perhaps a range or two colder wouldn't be a bad idea. the factory specified units are designed to compromise between short trips and WOT, moving towards the cold side may help keep the plug from getting hot enough to cause pre-ignition/detonation when the stock spec would have. I don't believe a range or two colder plugs would save the engine in the event of radiator loss though.... they may give you a few more seconds before they heat up to the point of self-ignition, but the heads are already going to be in poor shape by that point anyways.

[geoffinbc]

Even with stock ignition, if your not concerned with plug life then you should be able to run a .070" gap no problem. The more gap the more the arc will be exposed to fuel and it will be hotter. You can experiment too by opening the gap until you experience a misfire.

[robertisaar]

gap also has a noticeable change to coil and wire life as well... larger gaps require a larger voltage to build up on the secondary side of the coil before an arc can begin.

[tbrell]

All great information, thanks guys.

Whether it's the PCM or the trans, W platforms most definitely have some sort of limp mode, many people that run these vehicles have experienced it. It may not be in the engine PCM per say, but a lot of people talk about it that run these engines in demo derby. I believe what they are experiencing is the transmission overheating, and I believe there is a temp switch in the W platform-common 4t60e transmission that forces it into 2nd gear on take off. Most guys (including myself) will hotwire the transmission solenoids so that it is constantly in 1st gear, so the overtemp occurrence does not effect which gear is used.

I know that a lot of guys that run these engines will do one of two things to avoid "limp mode" (whether it or something similar exists). Both ways include the water temp sensor. 1 way is that the builder purchases a second water temp sensor and zip ties it in open air and plugs the PCM wiring into it, or (as I do) unplug the water temp sensor and put a 220-330 ohm resistor across the pins so that the PCM thinks the engine is at 180-210 degrees at all times.

So, in the other article I put a link to, is there any truth to the Summit Racing coils being my best bet (other than quality of product, which I'm also interested in) and what brand would be a good suggestion for the plugs? Maybe the 60 degree V6 is not, but I have heard some engines designs like some brand of plugs over others.

[geoffinbc]

Delco plugs are your best bet. NGK would be my second choice. I have never used anything with a Summit label. Some things they sell are re branded quality parts others are China sourced parts they spec.

[robertisaar]

the PCM does have a "hot mode" function that modifies shift points, along with a few circumstances where the PCM will command 3rd gear at all times(though that is defeatable to 2nd gear via the shift lever). the transmission temp sensor indicating high temps can cause hot mode as well, perhaps another sensor you could considering emulating should you run into other odd operation.

[tbrell]

Thanks for the input on the Delco plugs.

As stated before, some of us hotwire the trans to be in first no matter what (other than reverse), but I did not state that almost everyone shifts straight to 1st, we do not use the "Drive" shifter position. Also, I pretty much cut all the wires going to the trans so there is no feedback to the PCM.