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Manifold Vac Advance vs Ported on the street

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GeorgeOhr Nonya Business
Yes, confused, USA   USA
For guys like me with DCOEs, is it possible to run manifold vac advance on the street? I've read conflicting things over the year. I'd especially like to here what Jeff has to say.

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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"
No



"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

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
In reply to # 3660846 by GeorgeOhr For guys like me with DCOEs, is it possible to run manifold vac advance on the street? I've read conflicting things over the year. I'd especially like to here what Jeff has to say.

You must have a manifold... with vacuum in it. What would the stumbling block be?

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.

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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"
The stumbling block is the dcoe
Ported or manifold the vacuum signal is erratic
That's the reason you cant run vacuum advance with a dcoe on an mg



"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

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
In reply to # 3661047 by ohlord The stumbling block is the dcoe
Ported or manifold the vacuum signal is erratic
That's the reason you cant run vacuum advance with a dcoe on an mg

Why is the signal erratic?

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"
Alternating intake pulses
Unstable signal



"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

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
Balance tube.

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.

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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"
Been tried
The balsnce tube doesnt balance the vacuum signal

Common knowledge when running the sidedraft DCOE and the reason you need to run it with a mechanical advance only distributor.



"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

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
Interesting. The engine has the same "intake pulses"(unless I'm missing something) with twin SU's in place and it isn't an issue. Do you have any idea why the Weber doesn't react the same way? In plan form it looks like 2 tubes with butterfly valves just like 2 SU's. Or does "it just does" satisfy everyone?

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.

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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"
Dual su has vacuum from one carb only or manifold
The dcoe has alternating vacuum pulses even if you used the balance tube.
and ported from just one barrel
Is worse



"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

converse212 Avatar
converse212 Eric Morgan
Tucker, Georgia, USA   USA
1958 MG MGA
1970 MG MGB "Daily Driver"
1970 MG MGB GT "Rusty"
1971 MG MGB GT    & more
couldn’t a small reservoir be used to smooth out the vacuum signal some? It seems like a film canister sized container and pulling vacuum from both runners would produce a reasonably smooth signal...

I guess the way to test this would be to hook a vacuum gauge up to both runners and look at the needle under running conditions.

Rob, don’t you run a dcoe?



Daily driving a '71 MGB

Resurrecting a '58 MGA

GeorgeOhr Nonya Business
Yes, confused, USA   USA
I failed to specify single DCOE.

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
In reply to # 3661216 by ohlord Dual su has vacuum from one carb only or manifold
The dcoe has alternating vacuum pulses even if you used the balance tube.
and ported from just one barrel
Is worse

I'm seriously intrigued by this. How does the Weber do this while dual SU's do not? (manifold vacuum)

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"
Look at the manifold designs



"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

converse212 Avatar
converse212 Eric Morgan
Tucker, Georgia, USA   USA
1958 MG MGA
1970 MG MGB "Daily Driver"
1970 MG MGB GT "Rusty"
1971 MG MGB GT    & more
In reply to # 3661315 by ohlord Look at the manifold designs

What’s the difference? Lacking a balance tube on the dcoe manifold? Well sure, so pull from both runners.

Otherwise, what’s the difference?



Daily driving a '71 MGB

Resurrecting a '58 MGA

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