Spark Plug Gap

Bo's 55 · Jul 28, 2018

I've installed a basically stock GM crate 350 in my 55. I transferred the stock point distributor from the 327 that was in the car for about 46 years. The specs from GM say that the plug gap for the crate engine should be .045 but that is assuming that a HEi distributor is being used. The plug gap for a 350 from that era using a point distributor is .035.
I currently have the plugs gapped at .045 and the vacuum canister is connected to the ported outlet of the #1406 (600CFM) Edelbrock carb. Which plug gap do you think is correct? By the way, the motor is slow to get going on the low end. It either needs very light pedal or heavy pedal to get to about 2000 RPM.
Any ideas?

techman441 · Jul 28, 2018

I always gap plugs with a stock distributor at .032, so the plug life will be a little longer, doesn't seem to affect the way the engine runs...

Rick_L · Jul 28, 2018

HEI erodes the plugs a lot, opening the gap as they erode. As this happens, it becomes more difficult for the spark to jump the gap. Also the rounded corners that come from erosion don't help, the spark likes sharp corners. Because of this, gap the plugs when using HEI at about .035".

Tropturq · Jul 28, 2018

.035 for me.

57tim · Jul 29, 2018

My understanding is ported vacuum is for smog engines. I think you want non ported vacuum.:dontknow: Might be your sluggishness problem.

:bowtier:

Tropturq · Jul 29, 2018

My understanding is ported vacuum is for smog engines. I think you want non ported vacuum. Might be your sluggishness problem.

I agree, I think that you should be using full vacuum not ported.

billm55 · Jul 29, 2018

I went from 0.035” up to 0.045” when I changed my points distributor to electronic. I think it ran better with smaller gap so I have gone back to 0.035”. Not sure how this will affect plug lifespan but I would rather have my motor run better and replace plugs more often than have poor performance and longer plug life.

Bo's 55 · Jul 31, 2018

Thanks guys. It looks like I'll go with the .035.

Shadetree55 · Sep 28, 2024

spammers don't last long around here

angs1957 · Sep 29, 2024

Thanks great Tom, I've replied back to you to explain a little further with the report function.

Spark Plug Gap

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