Convert a 4 cyl tach to 6 cyl tach

[racinemg]

Hi all....looking for some help.  Seems like a while back that I found an article on here about how to convert a 4 cylinder tachometer to a 6 cylinder but I can't find it!  Can anyone help with this??

Thanks!
Dan

[Bill Young]

Dan, I've looked for that information for years and haven't seen it yet. I've found several sources for conversion to 8 cylinder operation, but the component values for a 6, I haven't found. The Midget is still running around showing 33% higher RPM on the tack than it's actually turning. I'm pretty sure I have saved files on my computer at home with the V8 information and I figure if you take the value of the 4 cylinder components and V8 components and find something half way between you should be pretty close for the 6 cylinder. I'll try to find them and pass them on.

[ex-tyke]

Dan,
       FWIW, I believe Rick Astley's book "MGB Electrical Systems" has a section on the different models of tachs used over the years in MGBs and some are better than others at lending themselves to a conversion using a potentiometer....not all tachs, it seems, are candidates for conversion for 6 or 8 cyl engines. There is some reference info in the book for the conversion process.
    Also, depending on the year of your car, an MGC tach might work.....come to think about it, somewhere in my parts bin, I have an old "C" tach but not sure whether or not it works!

[Moderator]

I know this isn't really what you asked... but it might be a little helpful as background info:

We discussed converting 4-cylinder to 8-cylinder in this message thread - http://forum.britishv8.org/read.php?2,1179,1496#msg-1496

[jimbb88]

Try a tach from a TR6 or GT6.

[Scott Costanzo]

Provided the mechanical side of your tach is in good shape, you can replace the circuit board with a unit from Theo Smit.

http://members.shaw.ca/tsmit/tachmod/tach_other.html#MG

It has facilities to be driven by a number of ignition systems. He modified the circuit to work with the GM DIS system on my v6.

-- Scott

[MGBV8]

The mod that Curtis links to will work for a late model MGB V6.

Use the same potentiometer (100K 10turn) & use something to reference it to. I have Sears engine analyzer/dwell meter (from long ago) that has a tach. function for 4-6-8 cylinder engines with a scale from 0-6000 rpm. If you can borrow something like that, it would be as simple as doing the mod & dialing in the trim pot to match the rpms.

[BlownMGB-V8]

I used Theo's board in my tach several years ago. It worked well and wasn't that difficult.

Jim

[racinemg]

Thanks for all the quick responses!  I think I've got all the information I need now.  I really appreciate everyone's help....I'm sending a donation to Curtis for the website!

Dan