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Username Post: Spark Plug Gap On Race Motor        (Topic#136978)
Badss350 
Senior Member
Posts: 693
Badss350
Loc: Lumberton,Texas
Reg: 01-01-01
07-28-06 03:34 PM - Post#976436    

468 BBC, alcohol injected, .722 lift cam, MSD7AL3, 8MM plug wires, NGK plugs...they came gapped at .030...seems a tad low on gap to me?
Distant Thunder Cold As Stone A V-8 Screams Down From Its Throne One By One Each Car Succumbs When Something CHEVY This Way Comes


 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15643

Loc: Colorado Springs, CO
Reg: 08-08-04
Re: Spark Plug Gap On Race Motor
07-28-06 07:09 PM - Post#976437    
    In response to Badss350

Usually the widest gap you can consistently and reliably fire with your ignition system. .050 is usually a good starting point.

 
IgnitionMan 
Valued Contributor
Posts: 2713

Reg: 04-15-05
Re: Spark Plug Gap On Race Motor
07-29-06 05:35 PM - Post#976438    
    In response to Vaughn

Obviously a high compression engine package.

The higher the comp ratio and cylinder pressuyres, the TIGHTER the plug gap needs to be, even with an MSD box helping the thing.

I'd try the .030 to start with, and if it sputters on the top end, drop the gap. .018 is about the practicle limit on a blown alchohol engine, .022 is getting right down there on a normally aspired one, and if the tighter gap doesn't help, fix the injectors.

 
Badss350 
Senior Member
Posts: 693
Badss350
Loc: Lumberton,Texas
Reg: 01-01-01
Re: Spark Plug Gap On Race Motor
07-29-06 08:44 PM - Post#976439    
    In response to IgnitionMan

Thanks, we set them at .030 tonight, ran 8.42 all night, very consistant...and yes, very high compression engine, JE 13:1 slugs..the injectors are brand new, we bought the Rons Terminator set up for alky....I think with a little tuning like going to 36 on the injectors instead of 35, playing with returnpills to get correct EGT, we can run some 7`s in the 1/4..but we ran 5 runs at 8.42x..first run was 8.54 but the first run is always slow for us...I read where NGK comes pre gapped at 30, just have to pick the correct heat range..As always, THANKS for the info!
Distant Thunder Cold As Stone A V-8 Screams Down From Its Throne One By One Each Car Succumbs When Something CHEVY This Way Comes


 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15643

Loc: Colorado Springs, CO
Reg: 08-08-04
Re: Spark Plug Gap On Race Motor
07-30-06 06:55 AM - Post#976440    
    In response to Badss350

Dave, wouldn't running more voltage to his ignition system help him to run more gap in this situation? Bigger gap usually means better flame front in gas motors - but alcohol may be different (I have limited experience with pure alcohol motors).

 
IgnitionMan 
Valued Contributor
Posts: 2713

Reg: 04-15-05
Re: Spark Plug Gap On Race Motor
07-30-06 05:20 PM - Post#976441    
    In response to Vaughn

It's called ignition system compression resistance, or, the ability of the added cylinder pressure to blow the flame out.

Remedy, tighten the plug gap.

 
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