Intake manifold vacuum fitting location

[boyt911sc]

I'm finishing the last part of an engine rebuild for a friend and need to install the individual manifold vacuum port/s to complete the project. The TWM intake manifold set-up shown in the pictures below does not have the individual port to connect the vacuum line/s. Before I start drilling the holes which I am not sure at this point, I wish to seek advise and help from those people who have done these before. Please see pictures below:







Where would be a good spot/location to install the individual intake vacuum port/fitting? Thanks.

Tony

[Eagledriver]

I could be wrong, but I suspect the nipple between two of the throttle bodies is the vacuum port. It appears to be below the throttle butterflies. Might be connected by the "tube" between throttle bodies below the butterflies. Don't know what else those nipples could be.

-Andy

[boyt911sc]

Originally Posted by Eagledriver

I could be wrong, but I suspect the nipple between two of the throttle bodies is the vacuum port. It appears to be below the throttle butterflies. Might be connected by the "tube" between throttle bodies below the butterflies. Don't know what else those nipples could be.

-Andy

Andy,

The copper tube between the 2 throttle bodies is the vacuum port for all three (3). The plan is to plug this vacuum tube and install individual vacuum connection for each of the stack (throttle body). According to some engine builders, you get more consistent vacuum reading with individual outlets than using one outlet for the 3 throttle bodies.

I'm building this 3.0 liter SC engine for a friend who wanted the following: CR from 8.5 to 10.3, single plug to twin-plug, crank fired using Tec-3R, TWM throttle bodies, individual fuel injection, etc. So my predicament is determining the 'sweet spot' where to drill the hole/s for the nipple/s to connect the six (6) vacuum lines. The TWM ITB I am using has one vacuum outlet for the whole side (3 throttle bodies) unlike those of the PMO's.

Picture of a PMO ITB:


This is how the 6 vacuum hoses would look like:


Would it be safe and prudent to drill the hole below the butterfly valve and in-line with existing vacuum hole/s? I've not done this kind of project before and my anxiety is at high level. So any advise is highly appreciated. Thanks.

Tony

[Flat6pac]

Tony, What do you use the vacuum for with crank fire?
If you were using a dietributor you would use vacuum from both sides, 1 and 4, T it and run it to the distributor.
Bruce

[brads911sc]

If he is using aftermarket EFI, vacuum will drive the ECU. I use vacuum and dont have it connected to the distributor at all. I have mechanical advance in the distributor set by Barry Hershon. Megasquirt is driven off the vacuum and TPS combo.

Originally Posted by Flat6pac

Tony, What do you use the vacuum for with crank fire?
If you were using a dietributor you would use vacuum from both sides, 1 and 4, T it and run it to the distributor.
Bruce

[boyt911sc]

Originally Posted by Flat6pac

Tony, What do you use the vacuum for with crank fire?
If you were using a dietributor you would use vacuum from both sides, 1 and 4, T it and run it to the distributor.
Bruce

Bruce,

I forgot to mention that the stock SC distributor for the ignition is omitted (deleted). The vacuum is needed for determining MAP (manifold absolute pressure) during tune-up (mapping). I'm computer challenge so don't ask me anything about 'mapping'.

I've done a few SC engines and this is the first time I got involve in a radical engine. I am doing all the mechanical assembly and adjustment during the rebuild as per spec or request by the engine owner who is a friend actually like a son to me. The ECU by Tec-3R technology would be the control and brain for the ignition with relation to the intake manifold pressure. This is my layman's understanding of the system for this particular project. Maybe someone knowledgeable would chime in and educate us.

One more question: What spark plugs (12) would be good for this engine? I have no idea at this point.

Tony

[Eagledriver]

I don't know much about programing engine managment systems but here are my thoughts. Unless you are going to program each cylinder separatly, I don't think individual vacuum connections help you. Each intake manifold will have wildly fluctuating pressure during the various strokes of the engine. I would think you could connect the two existing connections together and maybe add a small chamber to average out the pulses. I have a Subaru engine in my airplane that uses vacuum as an input to the ECU and it just reads the vacuum of the common intake plenum.

Will this just be for programing or will the vacuum be used to set the fuel mixture during normal operations. I would think that you'll be fine tuning with an O2 sensor in the end.

Sorry if this is of no use.

-Andy

[Eagledriver]

I would start with a fairly cold plug. I use NGK BPR8ES on my SC race motor. This is roughly the same as a Bosch WR4DC. I've used a hotter plug on street cars (Bosch WR6DC). NGK and Bosch numbers go opposite from each other.

My carb manifolds have vacuum ports on them about half way down and offset to the side so the port in the manifold is an oval. This would be a cheaper part to be drilling and plugging than the TBs.

-Andy

[brads911sc]

has nothing to do with tuning. has everything to do with it running properly on an ongoing basis. the MAP signal runs the EFI... the need for more than one port is directly related to how aggressive the cam is and the itb set up. this has been done many times before and a single vacuum port is less than optimal.

Originally Posted by Eagledriver

I don't know much about programing engine managment systems but here are my thoughts. Unless you are going to program each cylinder separatly, I don't think individual vacuum connections help you. Each intake manifold will have wildly fluctuating pressure during the various strokes of the engine. I would think you could connect the two existing connections together and maybe add a small chamber to average out the pulses. I have a Subaru engine in my airplane that uses vacuum as an input to the ECU and it just reads the vacuum of the common intake plenum.

Will this just be for programing or will the vacuum be used to set the fuel mixture during normal operations. I would think that you'll be fine tuning with an O2 sensor in the end.

Sorry if this is of no use.

-Andy

[HawgRyder]

If you are going to drill each runner...make sure you drill at the correct angle ( I believe it's on a slight down angle).
Bernoulli's principle comes into play here (air rushing past open tube..etc) so the angle is important enough to research it with people who know (engineers...of which I am not...LOL).
Bob

[brads911sc]

+1

The PMO's are tapered.

Originally Posted by HawgRyder

If you are going to drill each runner...make sure you drill at the correct angle ( I believe it's on a slight down angle).
Bernoulli's principle comes into play here (air rushing past open tube..etc) so the angle is important enough to research it with people who know (engineers...of which I am not...LOL).
Bob

[jpnovak]

From experience.

Drill the vacuum ports in the manfilods, not the ITBs. On stock weber manifolds there is a small flat on the outside surface that makes a great mount. Drill and tap for NPT threads and mount a threaded hose barbed end there. Use the brass NPT/hose fittings. Solder them closed at the end and drill the smallest hole you can find. This should give you a good vacuum signal to the ECU.

The single vacuum port on the TWM is crap. I took mine off and closed up the connection channel under the trottle with epoxy. Just a poor design from a pressure wave point of view when using decent cams.

After you have your 6 lines, run them into a manifold and then send a single line to the ECU. I was using a Mod_S cam and had to also fill the manifold with open cell foam and install a carb jet in the single outlet to quiet down the MAP signals due to cam reversion pulses. These problems are all multiplied in an ITB system and you will have serious issues tuning unless you take them out properly. The manifold will average the MAP signal nicely.

btw, the angle of the vacuum port does not matter in this application. You are looking for instantaneous pressure changes based on throttle position, not trying to suck fuel through a jet.

[LJ851]

Install the vacuum ports in the manifolds. Anywhere below the butterfly is ok.

[boyt911sc]

Originally Posted by jpnovak

From experience.

Drill the vacuum ports in the manfilods, not the ITBs. On stock weber manifolds there is a small flat on the outside surface that makes a great mount. Drill and tap for NPT threads and mount a threaded hose barbed end there. Use the brass NPT/hose fittings. Solder them closed at the end and drill the smallest hole you can find. This should give you a good vacuum signal to the ECU.

The single vacuum port on the TWM is crap. I took mine off and closed up the connection channel under the trottle with epoxy. Just a poor design from a pressure wave point of view when using decent cams.

After you have your 6 lines, run them into a manifold and then send a single line to the ECU. I was using a Mod_S cam and had to also fill the manifold with open cell foam and install a carb jet in the single outlet to quiet down the MAP signals due to cam reversion pulses. These problems are all multiplied in an ITB system and you will have serious issues tuning unless you take them out properly. The manifold will average the MAP signal nicely.

btw, the angle of the vacuum port does not matter in this application. You are looking for instantaneous pressure changes based on throttle position, not trying to suck fuel through a jet.

JP,

I completely agree with your assessment about vacuum port orientation. The vacuum/pressure reading would be the same at a given plane (axis) regardless of angle of installation. The owner of the engine has spoken to Richard from Clewett Engineering and gave us the go ahead to drill the hole/s on the intake manifolds at same level and make sure the vacuum line won't get in the way of the throttle linkage.

BTW, do I need to apply epoxy (JB Weld) around the installed vacuum nipples? Would the teflon tape on NPT thread not sufficient to seal it? Thanks.

Tony

[boyt911sc]

Originally Posted by LJ851

Install the vacuum ports in the manifolds. Anywhere below the butterfly is ok.

LJ,

Where could I tap the vacuum supply for the brake booster? After installing the six (6) vacuum ports on the intake manifolds, the plan is to plug the original vacuum port for each bank. There are 2 existing vacuum ports, one on each bank of ITB. Could these vacuum ports be utilized for the brake booster? Thanks.

Tony