MG Sports Cars

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

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PaulV8
Paul Avery
England
(18 posts)

Registered:
11/13/2007 03:57PM

Main British Car:
'78 B Roadster V8 , '96 RV8 , '75 MGB GT Jubilee '77 B Roadster , '71 B Roadster , + others

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MGB to V8 Tach
Posted by: PaulV8
Date: January 10, 2008 02:14PM

Hello all.

I'm running the stock MGB tach on my V8, mine's a later electronic tach and i'm running Mallory dual point Dizzy.

Is there anything i can do myself or any simple mods to change the 4 cylinder tach to run with the V8?

Really appreciate some tips guys.

Thanks in advance.

Paul


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: MGB to V8 Tach
Posted by: V6 Midget
Date: January 10, 2008 02:27PM

Paul, the information on modifying the tach to work is on the web, I just can't remember where right now. I'll take a look at my home computer tonight and see if I can find the link in my favorites there.


Moderator
Curtis Jacobson
Portland Oregon
(4478 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

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Re: MGB to V8 Tach
Posted by: Moderator
Date: January 10, 2008 02:45PM

I'm no expert on this because I've always used an aftermarket tach... but from what I've read, the first thing to do is determine exactly which tach you have. There were three different electronic MGB tachs, called "RVC 1410/00", "RVC 1410/00AF", and "RVC 2432" respectively.

The first one (RVC 1410/00) is easiest to convert because it already has an adjustment potentiometer inside it. You simply add a 150 ohm resistor in series with either of the wires going to the meter movement, and then you use the existing potentiometer to re-tune the calibration.

The later two tachs don't have tuning potentiometers, so you need to add that too. Specifically, glue a 1000 Ohm (i.e. 1 k Ohm) pot to the circuit board (connected to the red wire, because that's the one that's easiest to access).

All this is second hand though. I think there was an article on this in one of the very old MG V-8 Newsletters, but it hasn't been digitized and uploaded yet. (Except for Pete, our vendor sponsors apparently haven't recognized the value of adverts on back-issue articles yet. In most cases, we don't get a penny for time spent digitizing back issues or supplementing them with new photography and it takes much more time than you'd think!) Those newsletters didn't have color photography... If anyone can provide me with good photos of the tach modification(s), I'd be very pleased.


PaulV8
Paul Avery
England
(18 posts)

Registered:
11/13/2007 03:57PM

Main British Car:
'78 B Roadster V8 , '96 RV8 , '75 MGB GT Jubilee '77 B Roadster , '71 B Roadster , + others

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Re: MGB to V8 Tach
Posted by: PaulV8
Date: January 10, 2008 05:22PM

Thanks guys, i will remove it and take alook.

Simon Austin mentions a tach converter fitted to his car, off the shelf or custom?


kstevusa
kelly stevenson
Southern Middle Tennessee
(945 posts)

Registered:
10/25/2007 09:37AM

Main British Car:
2003 Jaguar XK8 Coupe 4.2L DOHC/ VVT / 6sp. AT

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Re: MGB to V8 Tach
Posted by: kstevusa
Date: January 11, 2008 09:04AM

my 1978 tach was an easy conversion using my old issue of V8 Mag and Leon Zak's web-site. (google it). The V8 issue is
VIII Vol. 1 on page 11. rather than place the pot. inside the tach case, i drilled a hole and insulated the wires from the board to the pot on the outside where i glued it (hot melt) to the case. The pot can be accessed easily for adjustment. hooked up the MGB & a known good (S/W) tach and made the calibration. this operation requires very small gauge wire, may be difficult to locate. i believe the pot is a 10 turn, 100K. if memory is correct. the web sites list the correct one.
Safety Faster!



Edited 1 time(s). Last edit at 01/12/2008 08:29AM by kstevusa.


Simon Austin
Simon Austin
Surrey, British Columbia
(107 posts)

Registered:
10/23/2007 01:44AM

Main British Car:
1977 MGB V8 / 1970 MGB GT V8 project Rover 3.5 / Rover 3.5

Re: MGB to V8 Tach
Posted by: Simon Austin
Date: January 11, 2008 08:57PM

I had my tach modified for the V8 by an avionics technician. I can ask him what he does to convert them if you like. The tach adapter was for the MSD ignition (provided by MSD) I installed in the car. Might be what you're thinking of, Paul.


MGBV8
Carl Floyd
Kingsport, TN
(3980 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

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Re: MGB to V8 Tach
Posted by: MGBV8
Date: January 12, 2008 11:26AM

Way back in 1998, I was spending many hours scouring the 'net for MG V8 info. This was before Google had become the dominant search engine, so I was using metacrawler. I found some very helpful sites. Moneypenny was a good one, but has long since disappeared. Leon Zak's site was exciting 'cause it contained an easy solution for my tachometer obstacle. I had stumbled across this only a week or so before attending my first MG V8 Meet in Annapolis, MD. While at the meet, I used the hotel's computer to show Kurt Schley Leon Zak's tach conversion info.

[www.zaks.com]

Bernie Posey & Jeff Foote went home, did a tach conversion, documented & photographed it. Then Kurt put together the excellent article for the MG V8 Newsletter (January 2000) that Kelly mentions above.

The potentiometer is 100K ohm, as Kelly states. Although, I asked someone (can't remember who) to measure the value after the tach was calibrated. I decided that a 47K ohm 1/4 watt fixed resistor was close enough & that is what I used. My tach is off about 200 rpm at 3 grand. So, starting with the potentiometer in the middle of it's range will get it in the ball park.

PLEASE NOTE:Leon's website instructions says that the potentiometer is soldered across pins 4 & 7 of the IC chip. This wrong and this mistake was carried over to Kurt's article. Solder the potentiometer. across pins 3 & 8. Kurt printed a correction in the next issue. I used white-out & corrected my original article. I sent an email to Leon years ago, but he still has the wrong pins on his website



Edited 1 time(s). Last edit at 01/12/2008 11:28AM by MGBV8.



PaulV8
Paul Avery
England
(18 posts)

Registered:
11/13/2007 03:57PM

Main British Car:
'78 B Roadster V8 , '96 RV8 , '75 MGB GT Jubilee '77 B Roadster , '71 B Roadster , + others

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Re: MGB to V8 Tach
Posted by: PaulV8
Date: February 06, 2008 03:48PM

Sorry for the late reply i've been on Holiday.

Thanks for the info i'll try it this weekend and see how i get on. Cars almost finished!


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