BBC spark plug gap
Discussion
After selling the mid engined polo I have bought a 69 Camaro drag car runing a high compression 468 CI BBC.
It had its first outing at the weekend and alought I was just taking it very steady it ran very well.
After the first run I pulled on of the plugs and found it to be gapped to 75 thou ! I checked all the rest and they were all identical. After talking to the other racers , none had ever seen a gap that big before, so I set the gap to 36 thou. I ran fine for the rest of the day.
Anyone have any ideas why the gap would have been that big ?
It had its first outing at the weekend and alought I was just taking it very steady it ran very well.
After the first run I pulled on of the plugs and found it to be gapped to 75 thou ! I checked all the rest and they were all identical. After talking to the other racers , none had ever seen a gap that big before, so I set the gap to 36 thou. I ran fine for the rest of the day.
Anyone have any ideas why the gap would have been that big ?
Struth. Nearly 2mm? I imagine to fire a gap that big it must have some humungous ignition system and the aim was to try and minimise cycle to cycle combustion variances in the hope of an extra horsepower or two. It's rare to see a gap bigger than about 1.2mm though and back in the day most cars managed fine on half that.
I'll go with the theory that someone's either misread 1.2mm or can't use feelers properly.marT350T said:
After selling the mid engined polo I have bought a 69 Camaro drag car runing a high compression 468 CI BBC.
It had its first outing at the weekend and alought I was just taking it very steady it ran very well.
After the first run I pulled on of the plugs and found it to be gapped to 75 thou ! I checked all the rest and they were all identical. After talking to the other racers , none had ever seen a gap that big before, so I set the gap to 36 thou. I ran fine for the rest of the day.
Anyone have any ideas why the gap would have been that big ?
Are you sure you weren't using metric feeler blades?It had its first outing at the weekend and alought I was just taking it very steady it ran very well.
After the first run I pulled on of the plugs and found it to be gapped to 75 thou ! I checked all the rest and they were all identical. After talking to the other racers , none had ever seen a gap that big before, so I set the gap to 36 thou. I ran fine for the rest of the day.
Anyone have any ideas why the gap would have been that big ?
I'm asking because .75mm = about 30 thou.
I have a 460CI BBC with an HEI distributor & high powered coil & have mine set at 0.045 inch. I don't race it so for me I don't think it makes a great deal of difference. In the Haynes repair manual for Chevrolet pick-ups, the standard 454 BBC plug gap varies from 0.035 to 0.060 inch. So I guess it's not an exact science.
Edited by 109 Bob on Wednesday 14th October 01:12
oakdale said:
marT350T said:
After selling the mid engined polo I have bought a 69 Camaro drag car runing a high compression 468 CI BBC.
It had its first outing at the weekend and alought I was just taking it very steady it ran very well.
After the first run I pulled on of the plugs and found it to be gapped to 75 thou ! I checked all the rest and they were all identical. After talking to the other racers , none had ever seen a gap that big before, so I set the gap to 36 thou. I ran fine for the rest of the day.
Anyone have any ideas why the gap would have been that big ?
Are you sure you weren't using metric feeler blades?It had its first outing at the weekend and alought I was just taking it very steady it ran very well.
After the first run I pulled on of the plugs and found it to be gapped to 75 thou ! I checked all the rest and they were all identical. After talking to the other racers , none had ever seen a gap that big before, so I set the gap to 36 thou. I ran fine for the rest of the day.
Anyone have any ideas why the gap would have been that big ?
I'm asking because .75mm = about 30 thou.
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