Ported Vacuum

G

gene

New member
Sep 29, 1999
2,215
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0
I am no expert on this but I am reading the literature and trying to get it
all straight
This reference

http://offroad-net.com/~ifsja/tech/motors/egrvacuum.html

says:
Port vacuum signal is generated via Burneulli's Principle in the carb's
venturi. The larger the volume of air flowing
through the carb., the stronger the vac. signal. At idle there is very
little air flowing through the carb and the vac. signal is very small.
Basically no vacuum. At wide-open throttle (WOT) and high RPM, the port
vacuum signal is strongest.
- ----------------

This reference

http://www.emsgas.com/vacuum1.htm

says:
PORTED VACUUM
Is obtained from a passage just above the closed throttle. At idle, no
vacuum is applied this port due to its location. As the throttle is
opened, this port is exposed to manifold vacuum, so vacuum at this port
begins to increase. Since ported vacuum is actually manifold vacuum applied
to a different passage it will also be near zero when wide open throttle.

- ------------

As Emery points out the GMC manual says the original equipment distributor
is connected to PORTED VACUUM when the engine is cold and MANIFOLD VACUUM
when the engine is hot using the TVS valve.

- ------------

When I installed my Holley 3210 TBI I tested the ports and found the two
outside ports facing the front of the engine were Manifold Vacuum. The
center port under the PCV port was ported vacuum and there was no vacuum
there until the butterfly were opened and then it went up to 20 lb. This
is just what Howell said was the configuration.

The Howell instructions say to remove the TVS valve and put the distributor
on the port nearest the passenger seat. This would be manifold Vacuum.

However when I talked to Tom at Howell last week, he said the distributor
should be connected to the ported Vacuum which would be the center port.
- --------

So I guess I will have to call Howell next week and see if they can resolve
this. My GMC bucked and backfired with the distributor was connected to
manifold vacuum.

gene

Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
 
Gene,
Your second reference is correct. Check the different vacuum connections on
your TBI with a vac gauge to verify which one is ported vacuum. That's the
one I would use for the distributor, so the timing advances as you
accelerate.
My 10 cents - everything is more expensive up here! -

Peter
77 Eleganza II
Colorado

- ----- Original Message -----
From: "gene"
To:
Sent: Friday, January 14, 2000 8:50 PM
Subject: GMC: Ported Vacuum

> I am no expert on this but I am reading the literature and trying to get
it
> all straight
> This reference
>
> http://offroad-net.com/~ifsja/tech/motors/egrvacuum.html
>
> says:
> Port vacuum signal is generated via Burneulli's Principle in the carb's
> venturi. The larger the volume of air flowing
> through the carb., the stronger the vac. signal. At idle there is very
> little air flowing through the carb and the vac. signal is very small.
> Basically no vacuum. At wide-open throttle (WOT) and high RPM, the port
> vacuum signal is strongest.
> ----------------
>
>
> This reference
>
> http://www.emsgas.com/vacuum1.htm
>
> says:
> PORTED VACUUM
> Is obtained from a passage just above the closed throttle. At idle, no
> vacuum is applied this port due to its location. As the throttle is
> opened, this port is exposed to manifold vacuum, so vacuum at this port
> begins to increase. Since ported vacuum is actually manifold vacuum
applied
> to a different passage it will also be near zero when wide open throttle.
>
> ------------
>
> As Emery points out the GMC manual says the original equipment distributor
> is connected to PORTED VACUUM when the engine is cold and MANIFOLD VACUUM
> when the engine is hot using the TVS valve.
>
> ------------
>
> When I installed my Holley 3210 TBI I tested the ports and found the two
> outside ports facing the front of the engine were Manifold Vacuum. The
> center port under the PCV port was ported vacuum and there was no vacuum
> there until the butterfly were opened and then it went up to 20 lb. This
> is just what Howell said was the configuration.
>
> The Howell instructions say to remove the TVS valve and put the
distributor
> on the port nearest the passenger seat. This would be manifold Vacuum.
>
> However when I talked to Tom at Howell last week, he said the distributor
> should be connected to the ported Vacuum which would be the center port.
> --------
>
> So I guess I will have to call Howell next week and see if they can
resolve
> this. My GMC bucked and backfired with the distributor was connected to
> manifold vacuum.
>
> gene
>
>
>
> Genef -- 77PB/ore/ca
> GMC MOTORHOME INFORMATION
> mr.erf
> http://www.california.com/~eagle/
>
 
Hi peter

Do you have the Holley TBI ?? I would like to keep track of how you like
your system.

I had checked the ports and found the front, lower, center port to be the
ported vacuum.

That is the one I am currently connected to. When I used the Manifold
vacuum, the advance was too soon and caused a lot of back fires at start
up. The ported vacuum worked better. I am not sure why the confusion
from Howell, but I will find out.

Thanks
gene

>Gene,
>Your second reference is correct. Check the different vacuum connections on
>your TBI with a vac gauge to verify which one is ported vacuum. That's the
>one I would use for the distributor, so the timing advances as you
>accelerate.
>My 10 cents - everything is more expensive up here! -
>
>Peter
>77 Eleganza II
>Colorado
>
>----- Original Message -----
>From: "gene"
>To:
>Sent: Friday, January 14, 2000 8:50 PM
>Subject: GMC: Ported Vacuum
>
>
>> I am no expert on this but I am reading the literature and trying to get
>it
>> all straight
>> This reference
>>
>> http://offroad-net.com/~ifsja/tech/motors/egrvacuum.html
>>
>> says:
>> Port vacuum signal is generated via Burneulli's Principle in the carb's
>> venturi. The larger the volume of air flowing
>> through the carb., the stronger the vac. signal. At idle there is very
>> little air flowing through the carb and the vac. signal is very small.
>> Basically no vacuum. At wide-open throttle (WOT) and high RPM, the port
>> vacuum signal is strongest.
>> ----------------
>>
>>
>> This reference
>>
>> http://www.emsgas.com/vacuum1.htm
>>
>> says:
>> PORTED VACUUM
>> Is obtained from a passage just above the closed throttle. At idle, no
>> vacuum is applied this port due to its location. As the throttle is
>> opened, this port is exposed to manifold vacuum, so vacuum at this port
>> begins to increase. Since ported vacuum is actually manifold vacuum
>applied
>> to a different passage it will also be near zero when wide open throttle.
>>
>> ------------
>>
>> As Emery points out the GMC manual says the original equipment distributor
>> is connected to PORTED VACUUM when the engine is cold and MANIFOLD VACUUM
>> when the engine is hot using the TVS valve.
>>
>> ------------
>>
>> When I installed my Holley 3210 TBI I tested the ports and found the two
>> outside ports facing the front of the engine were Manifold Vacuum. The
>> center port under the PCV port was ported vacuum and there was no vacuum
>> there until the butterfly were opened and then it went up to 20 lb. This
>> is just what Howell said was the configuration.
>>
>> The Howell instructions say to remove the TVS valve and put the
>distributor
>> on the port nearest the passenger seat. This would be manifold Vacuum.
>>
>> However when I talked to Tom at Howell last week, he said the distributor
>> should be connected to the ported Vacuum which would be the center port.
>> --------
>>
>> So I guess I will have to call Howell next week and see if they can
>resolve
>> this. My GMC bucked and backfired with the distributor was connected to
>> manifold vacuum.
>>
>> gene
>>
>>
>>
>> Genef -- 77PB/ore/ca
>> GMC MOTORHOME INFORMATION
>> mr.erf
>> http://www.california.com/~eagle/
>>
>
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
 
Gene,
No, I don't have TBI on my coach, I have the stock Q-Jet. The vac advance
shoud work the same way, though - Steve Ferguson pretty much said it all in
his excellent post.

Peter
77 Eleganza II
Colorado

- ----- Original Message -----
From: "gene"
To:
Sent: Saturday, January 15, 2000 4:10 AM
Subject: Re: GMC: Ported Vacuum

> Hi peter
>
> Do you have the Holley TBI ?? I would like to keep track of how you like
> your system.
>
> I had checked the ports and found the front, lower, center port to be the
> ported vacuum.
>
> That is the one I am currently connected to. When I used the Manifold
> vacuum, the advance was too soon and caused a lot of back fires at start
> up. The ported vacuum worked better. I am not sure why the confusion
> from Howell, but I will find out.
>
> Thanks
> gene
>

> >Gene,
> >Your second reference is correct. Check the different vacuum connections
on
> >your TBI with a vac gauge to verify which one is ported vacuum. That's
the
> >one I would use for the distributor, so the timing advances as you
> >accelerate.
> >My 10 cents - everything is more expensive up here! -
> >
> >Peter
> >77 Eleganza II
> >Colorado
> >
> >----- Original Message -----
> >From: "gene"
> >To:
> >Sent: Friday, January 14, 2000 8:50 PM
> >Subject: GMC: Ported Vacuum
> >
> >
> >> I am no expert on this but I am reading the literature and trying to
get
> >it
> >> all straight
> >> This reference
> >>
> >> http://offroad-net.com/~ifsja/tech/motors/egrvacuum.html
> >>
> >> says:
> >> Port vacuum signal is generated via Burneulli's Principle in the carb's
> >> venturi. The larger the volume of air flowing
> >> through the carb., the stronger the vac. signal. At idle there is very
> >> little air flowing through the carb and the vac. signal is very small.
> >> Basically no vacuum. At wide-open throttle (WOT) and high RPM, the port
> >> vacuum signal is strongest.
> >> ----------------
> >>
> >>
> >> This reference
> >>
> >> http://www.emsgas.com/vacuum1.htm
> >>
> >> says:
> >> PORTED VACUUM
> >> Is obtained from a passage just above the closed throttle. At idle,
no
> >> vacuum is applied this port due to its location. As the throttle is
> >> opened, this port is exposed to manifold vacuum, so vacuum at this port
> >> begins to increase. Since ported vacuum is actually manifold vacuum
> >applied
> >> to a different passage it will also be near zero when wide open
throttle.
> >>
> >> ------------
> >>
> >> As Emery points out the GMC manual says the original equipment
distributor
> >> is connected to PORTED VACUUM when the engine is cold and MANIFOLD
VACUUM
> >> when the engine is hot using the TVS valve.
> >>
> >> ------------
> >>
> >> When I installed my Holley 3210 TBI I tested the ports and found the
two
> >> outside ports facing the front of the engine were Manifold Vacuum. The
> >> center port under the PCV port was ported vacuum and there was no
vacuum
> >> there until the butterfly were opened and then it went up to 20 lb.
This
> >> is just what Howell said was the configuration.
> >>
> >> The Howell instructions say to remove the TVS valve and put the
> >distributor
> >> on the port nearest the passenger seat. This would be manifold Vacuum.
> >>
> >> However when I talked to Tom at Howell last week, he said the
distributor
> >> should be connected to the ported Vacuum which would be the center
port.
> >> --------
> >>
> >> So I guess I will have to call Howell next week and see if they can
> >resolve
> >> this. My GMC bucked and backfired with the distributor was connected
to
> >> manifold vacuum.
> >>
> >> gene
> >>
> >>
> >>
> >> Genef -- 77PB/ore/ca
> >> GMC MOTORHOME INFORMATION
> >> mr.erf
> >> http://www.california.com/~eagle/
> >>
> >
> >
> Genef -- 77PB/ore/ca
> GMC MOTORHOME INFORMATION
> mr.erf
> http://www.california.com/~eagle/
>
 
Ok thanks
May be in your future ??

gene

>Gene,
>No, I don't have TBI on my coach, I have the stock Q-Jet. The vac advance
>shoud work the same way, though - Steve Ferguson pretty much said it all in
>his excellent post.
>
>Peter
>77 Eleganza II
>Colorado
>
>----- Original Message -----
>From: "gene"
>To:
>Sent: Saturday, January 15, 2000 4:10 AM
>Subject: Re: GMC: Ported Vacuum
>
>
>> Hi peter
>>
>> Do you have the Holley TBI ?? I would like to keep track of how you like
>> your system.
>>
>> I had checked the ports and found the front, lower, center port to be the
>> ported vacuum.
>>
>> That is the one I am currently connected to. When I used the Manifold
>> vacuum, the advance was too soon and caused a lot of back fires at start
>> up. The ported vacuum worked better. I am not sure why the confusion
>> from Howell, but I will find out.
>>
>> Thanks
>> gene
>>

>> >Gene,
>> >Your second reference is correct. Check the different vacuum connections
>on
>> >your TBI with a vac gauge to verify which one is ported vacuum. That's
>the
>> >one I would use for the distributor, so the timing advances as you
>> >accelerate.
>> >My 10 cents - everything is more expensive up here! -
>> >
>> >Peter
>> >77 Eleganza II
>> >Colorado
>> >
>> >----- Original Message -----
>> >From: "gene"
>> >To:
>> >Sent: Friday, January 14, 2000 8:50 PM
>> >Subject: GMC: Ported Vacuum
>> >
>> >
>> >> I am no expert on this but I am reading the literature and trying to
>get
>> >it
>> >> all straight
>> >> This reference
>> >>
>> >> http://offroad-net.com/~ifsja/tech/motors/egrvacuum.html
>> >>
>> >> says:
>> >> Port vacuum signal is generated via Burneulli's Principle in the carb's
>> >> venturi. The larger the volume of air flowing
>> >> through the carb., the stronger the vac. signal. At idle there is very
>> >> little air flowing through the carb and the vac. signal is very small.
>> >> Basically no vacuum. At wide-open throttle (WOT) and high RPM, the port
>> >> vacuum signal is strongest.
>> >> ----------------
>> >>
>> >>
>> >> This reference
>> >>
>> >> http://www.emsgas.com/vacuum1.htm
>> >>
>> >> says:
>> >> PORTED VACUUM
>> >> Is obtained from a passage just above the closed throttle. At idle,
>no
>> >> vacuum is applied this port due to its location. As the throttle is
>> >> opened, this port is exposed to manifold vacuum, so vacuum at this port
>> >> begins to increase. Since ported vacuum is actually manifold vacuum
>> >applied
>> >> to a different passage it will also be near zero when wide open
>throttle.
>> >>
>> >> ------------
>> >>
>> >> As Emery points out the GMC manual says the original equipment
>distributor
>> >> is connected to PORTED VACUUM when the engine is cold and MANIFOLD
>VACUUM
>> >> when the engine is hot using the TVS valve.
>> >>
>> >> ------------
>> >>
>> >> When I installed my Holley 3210 TBI I tested the ports and found the
>two
>> >> outside ports facing the front of the engine were Manifold Vacuum. The
>> >> center port under the PCV port was ported vacuum and there was no
>vacuum
>> >> there until the butterfly were opened and then it went up to 20 lb.
>This
>> >> is just what Howell said was the configuration.
>> >>
>> >> The Howell instructions say to remove the TVS valve and put the
>> >distributor
>> >> on the port nearest the passenger seat. This would be manifold Vacuum.
>> >>
>> >> However when I talked to Tom at Howell last week, he said the
>distributor
>> >> should be connected to the ported Vacuum which would be the center
>port.
>> >> --------
>> >>
>> >> So I guess I will have to call Howell next week and see if they can
>> >resolve
>> >> this. My GMC bucked and backfired with the distributor was connected
>to
>> >> manifold vacuum.
>> >>
>> >> gene
>> >>
>> >>
>> >>
>> >> Genef -- 77PB/ore/ca
>> >> GMC MOTORHOME INFORMATION
>> >> mr.erf
>> >> http://www.california.com/~eagle/
>> >>
>> >
>> >
>> Genef -- 77PB/ore/ca
>> GMC MOTORHOME INFORMATION
>> mr.erf
>> http://www.california.com/~eagle/
>>
>
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
 
You bet - I think it's the way to go!

Peter
- ----- Original Message -----
From: "gene"
To:
Sent: Saturday, January 15, 2000 12:14 PM
Subject: Re: GMC: Ported Vacuum

>
> Ok thanks
> May be in your future ??
>
> gene
>

> >Gene,
> >No, I don't have TBI on my coach, I have the stock Q-Jet. The vac advance
> >shoud work the same way, though - Steve Ferguson pretty much said it all
in
> >his excellent post.
> >
> >Peter
> >77 Eleganza II
> >Colorado
> >
> >----- Original Message -----
> >From: "gene"
> >To:
> >Sent: Saturday, January 15, 2000 4:10 AM
> >Subject: Re: GMC: Ported Vacuum
> >
> >
> >> Hi peter
> >>
> >> Do you have the Holley TBI ?? I would like to keep track of how you
like
> >> your system.
> >>
> >> I had checked the ports and found the front, lower, center port to be
the
> >> ported vacuum.
> >>
> >> That is the one I am currently connected to. When I used the Manifold
> >> vacuum, the advance was too soon and caused a lot of back fires at
start
> >> up. The ported vacuum worked better. I am not sure why the confusion
> >> from Howell, but I will find out.
> >>
> >> Thanks
> >> gene
> >>

> >> >Gene,
> >> >Your second reference is correct. Check the different vacuum
connections
> >on
> >> >your TBI with a vac gauge to verify which one is ported vacuum. That's
> >the
> >> >one I would use for the distributor, so the timing advances as you
> >> >accelerate.
> >> >My 10 cents - everything is more expensive up here! -
> >> >
> >> >Peter
> >> >77 Eleganza II
> >> >Colorado
> >> >
> >> >----- Original Message -----
> >> >From: "gene"
> >> >To:
> >> >Sent: Friday, January 14, 2000 8:50 PM
> >> >Subject: GMC: Ported Vacuum
> >> >
> >> >
> >> >> I am no expert on this but I am reading the literature and trying to
> >get
> >> >it
> >> >> all straight
> >> >> This reference
> >> >>
> >> >> http://offroad-net.com/~ifsja/tech/motors/egrvacuum.html
> >> >>
> >> >> says:
> >> >> Port vacuum signal is generated via Burneulli's Principle in the
carb's
> >> >> venturi. The larger the volume of air flowing
> >> >> through the carb., the stronger the vac. signal. At idle there is
very
> >> >> little air flowing through the carb and the vac. signal is very
small.
> >> >> Basically no vacuum. At wide-open throttle (WOT) and high RPM, the
port
> >> >> vacuum signal is strongest.
> >> >> ----------------
> >> >>
> >> >>
> >> >> This reference
> >> >>
> >> >> http://www.emsgas.com/vacuum1.htm
> >> >>
> >> >> says:
> >> >> PORTED VACUUM
> >> >> Is obtained from a passage just above the closed throttle. At
idle,
> >no
> >> >> vacuum is applied this port due to its location. As the throttle
is
> >> >> opened, this port is exposed to manifold vacuum, so vacuum at this
port
> >> >> begins to increase. Since ported vacuum is actually manifold vacuum
> >> >applied
> >> >> to a different passage it will also be near zero when wide open
> >throttle.
> >> >>
> >> >> ------------
> >> >>
> >> >> As Emery points out the GMC manual says the original equipment
> >distributor
> >> >> is connected to PORTED VACUUM when the engine is cold and MANIFOLD
> >VACUUM
> >> >> when the engine is hot using the TVS valve.
> >> >>
> >> >> ------------
> >> >>
> >> >> When I installed my Holley 3210 TBI I tested the ports and found the
> >two
> >> >> outside ports facing the front of the engine were Manifold Vacuum.
The
> >> >> center port under the PCV port was ported vacuum and there was no
> >vacuum
> >> >> there until the butterfly were opened and then it went up to 20 lb.
> >This
> >> >> is just what Howell said was the configuration.
> >> >>
> >> >> The Howell instructions say to remove the TVS valve and put the
> >> >distributor
> >> >> on the port nearest the passenger seat. This would be manifold
Vacuum.
> >> >>
> >> >> However when I talked to Tom at Howell last week, he said the
> >distributor
> >> >> should be connected to the ported Vacuum which would be the center
> >port.
> >> >> --------
> >> >>
> >> >> So I guess I will have to call Howell next week and see if they can
> >> >resolve
> >> >> this. My GMC bucked and backfired with the distributor was
connected
> >to
> >> >> manifold vacuum.
> >> >>
> >> >> gene
> >> >>
> >> >>
> >> >>
> >> >> Genef -- 77PB/ore/ca
> >> >> GMC MOTORHOME INFORMATION
> >> >> mr.erf
> >> >> http://www.california.com/~eagle/
> >> >>
> >> >
> >> >
> >> Genef -- 77PB/ore/ca
> >> GMC MOTORHOME INFORMATION
> >> mr.erf
> >> http://www.california.com/~eagle/
> >>
> >
> >
> Genef -- 77PB/ore/ca
> GMC MOTORHOME INFORMATION
> mr.erf
> http://www.california.com/~eagle/
>
 
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