Spark plug gap with HKS twin power DLI

[Chris@Rvengeperformance]

The real answer to this is to run the largest gap you can without blowout, but in your experience what is a good gap to use for a NGK BCP7es plug and ~20PSI on 19Ts with a DLI?

Without the DLI I'd probably gap down to .026 or .028 or even .024. but I was thinking of trying .032 with it. Will that gap be too large?

[UTRacerX9]

I don't have any firsthand experience with the unit, but I've seen tests where a supercharged mustang has run .50 and even .70 without experiencing blowout. I honestly think you could get away with .36 at 20psi, and probably a bit higher.

[mb7050]

for what its worth .i run stock gap @ 15psi (9bs) without issues with the dli .

[bboyalan]

I am also in the process of discovering the largest gap possible. As of now, we have managed to push MHI 16G's to 20psi with the HKS DLI and BKR7E @0.032" This is on Pump-91+Meth. I will be tuning for another 2-4psi all else equal [hopefully this weekend].

[Chris@Rvengeperformance]

I am also in the process of discovering the largest gap possible. As of now, we have managed to push MHI 16G's to 20psi with the HKS DLI and BKR7E @0.032" This is on Pump-91+Meth. I will be tuning for another 2-4psi all else equal [hopefully this weekend].

good to know, there's no reason I can't try .032 then. Thanks!

[green-lantern]

I need to pull my plugs back out and regap them. I always run about .029-.028 but for some reason I put them at .034 this time. I do have some sort of boost a spark at the house (I can’t remember the name at the moment), I could put that thing on and see if I get any blow out. I doubt I’ll get over 15 psi very soon though. I just want to drive the damn car around for a while before going for any big power.

[BaadVR4]

I've built two engines with TD04 19Ts and two with Evo 3 16Gs. All had AEM standalone and all supporting mods on fully built motors. All of them had MSD Coils/Taylor wires/HKS DLI units. Every engine experienced blow out about 19-20 psi with plug gap above .026".

Every engine/car is different. Your car may not experience blow out at .032 gap. But I wouldn't bet on it. Of course, the larger the gap, the greater the energy from the spark. Until the voltage difference to create the spark exceeds the voltage available from the ignition system. On the other side of the issue, smaller gaps need less voltage to create spark under WOT, high boost conditions.

Unfortunately, those smaller gaps may result in spark at idle/low power conditions which is insufficient to ignite the air/fuel mixture, so the engine misses. That's why ignition amplifiers (like the HKS DLI) were made. They increase the voltage available to spark across the plug gap, which, in turn, allows larger gaps at WOT/high boost and keeps the spark energy high enough to prevent missing at idle/low power conditions.

So the issue is how much energy the ignition system can generate. It takes more energy to fire plugs at WOT/high boost than at idle. The amount of energy available from the ignition system is a function of several factors, including the coils/wires/trigger system/amplifiers/etc. The plug gap issue relates to how much voltage difference is required create the initial spark. The larger the gap, the higher the voltage required and the greater the energy created by the spark. Blow out occurs when the ignition system can't produce enough voltage to create spark at WOT/high boost. So you close the gap until blow out doesn't happen. Sometimes you can't close the gap enough to prevent blow out and sometimes the gap to prevent blow out results in misfire at idle/cruise.

Full race ignitions, like the MSD DIS-4 HO, typically provide MUCH greater spark energy to fire the plugs at WOT/Very high boost (or NOS or very high C.R.) and use "multi-spark" technology to fire the plugs repeatedly at idle/low power operation. The multiple sparks increase the probability the plug will fire at idle, even with very large plug gaps. Of course, most full race ignitions aren't designed to run continuously under "street" conditions and you might have to supply extra cooling to them to run them on the street.

Summary: run the largest gap you can without plug blowout. If you can't find a plug gap that works at both WOT/high boost and idle/cruise mode: change/add ignition system components until you have enough spark energy to satisfy the engine's needs.

[J. Fast]

Time for new plugs and I think I'm going to try some new plugs this time and crank up the boost. What's a good plug and gap to run in conjunction with DLI and E-85 boosting 20-25 psi?

Copper 7, gapped to .032" or is that going to be problematic with ethanol? I'm currently gapped to .027"

Thanks for the suggestions ahead of time.

[mb7050]

though I would share.
This is what I did to get rid of my high load missfire so I did this and noticed there is no need to gap down the plugs .(I got some voltage drop at Coil+ when WOT)

HKS.GIF

[J. Fast]

Sweet! (I'll pass some rep your way when I can hand more out!)

Where did you buy the relay from? Do you have any manufacture or model #'s? Any installed pics?