MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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racinemg
Dan Root
Leawood, KS
(14 posts)

Registered:
02/05/2008 12:37PM

Main British Car:
The Racine

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Convert a 4 cyl tach to 6 cyl tach
Posted by: racinemg
Date: June 05, 2008 01:52PM

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


V6 Midget
Bill Young
Kansas City, MO
(1337 posts)

Registered:
10/23/2007 09:23AM

Main British Car:
'73 MG Midget V6 , '59 MGA I6 2.8 GM, 4.0 Jeep

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Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: V6 Midget
Date: June 06, 2008 03:12PM

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
Graham Creswick
Chatham, Ontario, Canada
(1165 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

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Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: ex-tyke
Date: June 06, 2008 04:55PM

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!
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Moderator
Curtis Jacobson
Portland Oregon
(4577 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

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Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: Moderator
Date: June 06, 2008 05:33PM

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 - [forum.britishv8.org]


jimbb88
Jim Stuart
Maryland, USA
(47 posts)

Registered:
10/23/2007 07:43PM

Main British Car:
1966 MGB V8 conversion Rover 4.0 fuel injected

Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: jimbb88
Date: June 06, 2008 08:07PM

Try a tach from a TR6 or GT6.


Scott68B
Scott Costanzo
Columbus, Ohio
(562 posts)

Registered:
10/25/2007 11:30AM

Main British Car:
1968 MGB GM 5.3 LS4 V8

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Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: Scott68B
Date: June 06, 2008 08:12PM

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

[members.shaw.ca]

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
Carl Floyd
Kingsport, TN
(4514 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

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Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: MGBV8
Date: June 07, 2008 12:52AM

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
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6470 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: BlownMGB-V8
Date: June 08, 2008 06:47PM

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

Jim


racinemg
Dan Root
Leawood, KS
(14 posts)

Registered:
02/05/2008 12:37PM

Main British Car:
The Racine

authors avatar
Re: Convert a 4 cyl tach to 6 cyl tach
Posted by: racinemg
Date: June 09, 2008 11:56AM

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


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