Chevy High Performance
Click here to find out more!

Spark plug gap?

  
Chevy High Performance
Item Posts    Sort Order

Spark plug gap?

 
chevyvanfan chevyvanfan
New User | Posts: 4 | Joined: 08/11
Posted: 08/02/11
07:40 PM

I am installing stock 1968 chevy 307 heads  on a 1974 350 that has been bored .040 with truck style pistons.   It will have an HEI dist.  Just curious about what to gap my plugs at.  

idrivejunk idrivejunk
Addict | Posts: 5117 | Joined: 12/09
Posted: 08/02/11
08:12 PM

.045 works.  
idrivejunk

WRIGHTRACING WRIGHTRACING
Enthusiast | Posts: 437 | Joined: 03/10
Posted: 08/02/11
11:00 PM

Why put the smaller heads?
What are truck style pistons?
Are these different than car style pistons?  
WRIGHTRACING


www.outlawracing.com
www.dragraceplace.com
www.ndrra.com

chevyvanfan chevyvanfan
New User | Posts: 4 | Joined: 08/11
Posted: 08/03/11
06:40 PM

Had the heads laying around and someone once told me stock car racers used them on their cars.  And I should have said dished pistons, just seemed like every chevy truck engine  that I have seen torn apart had those in them.  Sorry for the confusion.  Not an expert here!!!  

chevyvanfan chevyvanfan
New User | Posts: 4 | Joined: 08/11
Posted: 08/03/11
06:43 PM

Thanks, at the auto parts store I heard everything from .035 which I thought was for point style to .060  

tuffnuff tuffnuff
Moderator | Posts: 7828 | Joined: 12/09
Posted: 08/03/11
06:49 PM

Use the .045" Junkman suggested.,. gap increases as the electrode/bridge wears and increases gap, over time.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

chevyvanfan chevyvanfan
New User | Posts: 4 | Joined: 08/11
Posted: 08/03/11
06:55 PM

.045 it is  then!  Thank's for the info.  

tuffnuff tuffnuff
Moderator | Posts: 7828 | Joined: 12/09
Posted: 08/03/11
07:02 PM

You welcome

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 08/04/11
09:29 PM

sticking it in a Van where the plugs are hard to reach..

spark plug selection may be important..

there are special thick center and thick side electrode spark plugs by Delco for van and heavy duty applications..

with 14MM threads and a tapered seat, 5/8 wrench..

5048

ac delco   CR43TS, CR44TS, CR45TS   are the numbers..

just a thought..

the reason NOT to go over 0.045"  

with distributer type ignitions.. there are TWO gaps to jump.. and two resistors to go through.. and a larger gap needs a higher voltage spike to start the arc...

from the coil...     to the center of the cap terminal..   through the carbon button.( resistance)  across the rotor and jumps the gap to the outer terminals inside the cap..    down the resistor spark plug wire..   through the resistor in the spark plug and across the spark plug gap..

the wider gap at the spark plug pushes the voltage required to jump the gap  along with all the other resistance in the system..  to the break down point of the insulation of the rotor.. and of the exterior of the ignition coil..  sometimes the carbon buttons actually melt the cap they get so hot..

0.060 gaps pushed the ignition system over the edge...

hope this helps...  

Pontiacman2 Pontiacman2
Moderator | Posts: 8956 | Joined: 09/08
Posted: 08/05/11
07:43 AM

I would set them at .040-.045.  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

greg_moreira greg_moreira
User | Posts: 226 | Joined: 07/11
Posted: 08/05/11
10:31 AM

as described above....its pretty taxing on an ignition system to try and jump a large gap.  And just as everybody else mentioned, .045 is the max I'll go.  Tighter will not hurt just as long as you have enough current jumping that gap, and enough of the spark "exposed" to light the mix.  .040 is usually where I gap.