Spark plug gap for a blown 440

[67charger383]

Hey yall,

I’m trying to figure out what I should gap the spark plugs on my 440 (ported iron heads, forged pistons, 8-71 BDS blower running 15psi of boost)

I haven’t raced it yet and have only cruised it around at a few fairgrounds/cruise week events and I previously had the plugs set at .035 but I’ve had some problems with it popping at low throttle and when starting up. I’ve heard 2 different camps saying open it up or close it up.

What are y’all’s recommendations?

 

[pnora]

Gap is fine at .035. What brand and heat range? Carbs or EFI? You had better have an AFR gauge or you will make quick work out of that motor.

 

[RemCharger]

If anything on boost, close it up. I'd go 28- 30.

 

[67charger383]

Gap is fine at .035. What brand and heat range? Carbs or EFI? You had better have an AFR gauge or you will make quick work out of that motor.

NGK V plugs R5670-5 2298

Yea I have a AFR gauge it’s good on that front

Dual boost referenced 750dps

 

[67charger383]

If anything on boost, close it up. I'd go 28- 30.

Would there be any side affects of closing it up or should I be fine? New to forced induction stuff.

 

[RemCharger]

No ill side effects. I would start with a colder plug like a R5670-7 / -8.
15 lbs sounds pretty heavy duty on a roots deal to start out with. Haven't run a blown deal personally, but there's a few out at our track

 

[pnora]

What are your AFR readings? Pops in the exhaust or in the intake?

 

[RJRENTON]

Hey yall,

I’m trying to figure out what I should gap the spark plugs on my 440 (ported iron heads, forged pistons, 8-71 BDS blower running 15psi of boost)

I haven’t raced it yet and have only cruised it around at a few fairgrounds/cruise week events and I previously had the plugs set at .035 but I’ve had some problems with it popping at low throttle and when starting up. I’ve heard 2 different camps saying open it up or close it up.

What are y’all’s recommendations?

IMO......USUALLY, the higher cylinder pressure require a smaller gap to be easier for the spark to jump the gap and perhaps consider a side gap plug (exposes more spark area to ignite the mixture easier) or one with s cut back ground electrode and a colder heat range. Since you're using iron heads (906?) a 3/8" reach plug, a Champion J-7J or a J-6J ....both non projected insulator and are cut back ground electrodes. Heat rsnge depends on operating duty and compression ratio and cam profile and intended fuel........just a thought......
BOB RENTON

 

[R413]

Call BDS and ask them they should have an idea what the hot setup is.

 

[dvw]

We always run small gaps on boosted stuff. Doesn't hurt anything being small. But it may missfire if it's to large. You better not have more than about 25 degeres total timing and some good fuel with a 906 head at 15psi. Try me I learned the hard way. 3 sets of piston later
Doug

 

[RemCharger]

We always run small gaps on boosted stuff. Doesn't hurt anything being small. But it may missfire if it's to large. You better not have more than about 25 degeres total timing and some good fuel with a 906 head at 15psi. Try me I learned the hard way. 3 sets of piston later
Doug

I learned that from Monte Smith, if going to run something serious at least knock it back to 28 *.