Coil resistance?

alien8 Wolfsburg Wizard

521 posts · joined Sep 2008 · 12 Jan 2010, 10:32 pm

#757303

I scratching my head a little over this one.
I have three 12V Bosch coils with different ohm readings from the center terminal to 1 and 15. The readings just dont add up.

First coil is a old Australian GT40 with a reading of 10 000 ohms across center terminal and 1 or 15.

Second is a Black Label Bosch, four months old reading 14000 ohms across the center terminal and 1 or 15

Third is a brand new Gt40 which I bought today which has a resistance of 16 000 ohms across the center terminal and 1 or 15

All three show 3.5 ohms across terminal 1 to 15

From what I have been reading a coil resistance above 11 000 ohms is not desirable from the center terminal to either terminal 1 or 15 and should be thrown in the bin.
My oldest coil has the lowest reading and the brand new one has the highest reading???
I am trying to sort out a running problem so if anyone has some insight to coil resistance it would be much appreciated.
Shouldn't the newer coil be somwhere in the ballpark of 9000 ohms?

clinker42 Officially Full-On Dubber

381 posts · joined Aug 2008 · 12 Jan 2010, 10:46 pm

#757305

Alien

They increase the primary and secondary windings in higher output coils. Im pretty sure they do. Given that, the resistance will be higher due to the extra windings. That would explain why your brand new GT40 is at 16 and then the 4 month old black label at 14 and then the really old GT40 at 10. I have a MSD pro mag and a few different HVC coils here so will drag em out in the morning and test em for you and see what I come up with.

alien8 Wolfsburg Wizard

521 posts · joined Sep 2008 · 12 Jan 2010, 11:47 pm

#757314

Thanks Clinks. I be really intrested to find out what your coils measure.
Anyone else with a gt40.I like to know what they measure.

The info I was getting for coil resistance was Johns writings from Aircooled.net and Bob Hoover. Both insist that coil resistance should be 9 to 10 000 ohms from center to either terminals.
Maybe I am overthinking this but I would like to rule out coil problems.