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1973 distributor advance curve

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willholmania Avatar
willholmania Will Holman
Peterborough, Cambs, UK   GBR
Hi all. I've just got a 123 Tune + dizzy for my 75 B, and want to add a 1973 advance curve t it. So I need the data for both the mechanical and vacuum advance. Does anyone know where I might find this?

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Steve64B Avatar
Steve64B Steve Opitz
Phoenix, AZ, USA   USA
1966 MG MGB
ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
Road tune the curve
The 73 curve is far


from optimal



"I'm a long way gone down this wild road I'm on
It's gonna take me where I'm bound
It's a long way around"



"These are the days that must happen to you"

RD2 Radar/ Electronic Warfare Technician
Vietnam 1969-1972



Edited 1 time(s). Last edit at 2017-07-03 01:02 PM by ohlord.

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tvrgeek Avatar
tvrgeek Silver Member Scott S
Bowie, Maryland, USA   USA
1965 MG MGB
Another source is:
http://www.teglerizer.com/mgstuff/advance_curves.htm

You might ask Jeff for advice. I run 18 @850, 32 @ 3800 base. Of course, it stays below 10 below 500, and vac is ignored until over 1000. I actually don't bring in my vac until 1200, and go 8 degrees.



Cogito ergo sum periculoso

gooser Avatar
gooser Drake Myers
Danville Va, USA   USA
In reply to # 3544490 by ohlord Road tune the curve
The 73 curve is far


from optimal

i totally agree. in 1973 the advance curve was set up up not to improve driveability but to reduce emissions.

willholmania Avatar
willholmania Will Holman
Peterborough, Cambs, UK   GBR
Thanks guys. Mine's a UK car and I'm reliably informed that 73, 74 represented the best UK spec dizzy. My 75 car, in the other hand, takes its vacuum feed from the manifold instead of a carb. This was an emissions thing.

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Will With the 123T the vacuum advance will be fine with manifold vacuum as you can programme it to what ever you want. I use 8* vacuum advance starting at over 1500 revs and about 4hg - 8hg vacuum. Your mechanical advance timing with the static set at zero (green light showing and engine stationary) then 10* @ 500 about 15 @ 1500 and 32 @ 3000. No more after that. On my engine I like to set the 500 and then 1000 the same ( in my case 17* for a supercharged engine) 10* in your case, as it gives a rock steady idle at 800 revs. The 123T is so easy to use you can try a couple degrees more low down later on but very few make anything extra after 32* total. That should give you a good starting point. Denis



68 B roadster, Daffodil yellow, Moss supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine early in the year with high comp pistons and a few other nice but not too wild bits. Have completed the firewall and steering mods but it is a complete resto and will take time. I am however really enjoying this new project.

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ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
A 1967 and prior had reliably the best curve 40897
Someone reliably sent you in the wrong direction

73 pales in comparison with manifold ported vacuum etc
Start with the good curve as a base point and road load tune it ftom there



"I'm a long way gone down this wild road I'm on
It's gonna take me where I'm bound
It's a long way around"



"These are the days that must happen to you"

RD2 Radar/ Electronic Warfare Technician
Vietnam 1969-1972

willholmania Avatar
willholmania Will Holman
Peterborough, Cambs, UK   GBR
Denis – the reason I'm doing this is to get a baseline power figure on the rolling road with the engine as it is. Once that's done I'll be fitting a Moss supercharger so the curve will need modifying, which is why I chose the 123 in the first place. After that I'll be fitting a modified head and a different cam so again, the curve will need tweaking.

I'm just unsure how to get started with the 123 Tune +. The instructions are pretty basic. I was hoping it would come pre-loaded with an MGB curve, but but it doesn't. So I need to be able to quickly get a working curve on it as soon as I fit it (can't do it before as it has to be on the car before you can load anything on to it).

Can you talk me through how I do this? You say 10˚ at 500 and 1000rpm, 15˚ at 1500rpm and 32˚ at 3000rpm: what about the points in between? Do I just draw a straight line between these settings?

Vacuum advance – can I just set a maximum figure?

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tvrgeek Avatar
tvrgeek Silver Member Scott S
Bowie, Maryland, USA   USA
1965 MG MGB
The mechanical unit did draw a strait line between points. You could ignore vac for now if you wish. It won't effect your WOT dyno power much if any.
Procedure is to get the base correct and then add the vac and boost retard. 123 instructions are to use the built in RPM to RPM timer to set the optimal advance by testing, or use a professional with a dyno.

So using the 123 LED, you get the 10 degree baseline for below 500 RPM.
Then set the first point to the spec idle.

By the Bentley book, 41288 HC dizzy
7 to 11 @ 900 This is for were it starts to move, slop out etc. More a check value than one to set.
13 to 17 @ 1600 This is where the second spring starts to take effect
18 to 22 @ 2200 This is where the cam hits the post
This is without the 10 degree base. so 32@ 2200

41290 LC dizzy
6 to 10 @ 800
7-11 @ 1000
16 to 20 @ 3000
22 to 26 @ 4400
Again, with 10 more static. How the have 4 values when with two springs they can only have three points I don't know. I assume the 1000 point is more of a reference.

If you believe the professional engineers and Burgess, the curve should pretty much follow the torque curve shape, with the max @ peak torque. So, the HC dizzy comes in too early and the LC dizzy comes in too late. I wound up with idle @ 18, I put the knee @ 2400, full in of 32 @ 3000. Not perfect, and that was with a different carb whose AFR was not as good as the HIFs, so I get to do it again. I added 8 vac. Pretty close to Dennis.



Cogito ergo sum periculoso

willholmania Avatar
willholmania Will Holman
Peterborough, Cambs, UK   GBR
Thanks guys. So I set the engine at TDC on number one pot, fit the 123 and turn it until the green LED comes on. And this gives me a basic 10˚BTDC setting?

tvrgeek Avatar
tvrgeek Silver Member Scott S
Bowie, Maryland, USA   USA
1965 MG MGB
Correct, TDC on compression. It should be correct on the crank mark.



Cogito ergo sum periculoso

willholmania Avatar
willholmania Will Holman
Peterborough, Cambs, UK   GBR
Thanks. I'll give it a shot when I get a minute.

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
In reply to # 3544708 by ohlord A 1967 and prior had reliably the best curve 40897
Someone reliably sent you in the wrong direction

73 pales in comparison with manifold ported vacuum etc
Start with the good curve as a base point and road load tune it ftom there

Are you sure the UK had the same distributor specifications as the USA?

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
It isn't but it still isn't near optimal for the home market engine and modern fuel.

In reply to # 3545128 by pinkyponk
In reply to # 3544708 by ohlord A 1967 and prior had reliably the best curve 40897
Someone reliably sent you in the wrong direction

73 pales in comparison with manifold ported vacuum etc
Start with the good curve as a base point and road load tune it ftom there

Are you sure the UK had the same distributor specifications as the USA?

Adrian



"I'm a long way gone down this wild road I'm on
It's gonna take me where I'm bound
It's a long way around"



"These are the days that must happen to you"

RD2 Radar/ Electronic Warfare Technician
Vietnam 1969-1972

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