Vacuum connections for SC turbo conversion

[gavinc69]

Hi everyone,

I'm part way though adding a turbo to my 3.0 SC and wanted to get some info/advice on the vacuum connections on the throttle body.

I've seen 'tsuter's' thread and got the BAE manual but my setup seems a little different maybe due to the model year, its a 1980 model.

Engine is out so I popped over to have a quick look on the way home from work
and look at the rear of the throttle body to get an idea of what vacuum connections
I need to cap off etc :




The Decel Valve has to be removed so I will cap off the two larger connections.
The Thermo Valve sits in between the Decel Valve and the Warm Up Regulator and
still needs to be connected, so I will disconnect it from the Decel Valve to plug it directly into the Throttle Body. This looks like the same others have done in there posts.

One of the two small vacuum ports next to each other is already capped off.
The other port runs down to the Distributor Cap so i'm thinking this needs to be left connected?

There are also two connections on the front of the Throttle Body :




The lower smaller port runs down to the Distributor Cap but it has been capped off and has been like this as long as I remember.

The larger port runs to the top of the Warm Up Regulator so again I'll leave this as it I guess?

I was also thinking of connecting a BOV to the throttle body and was wondering which port would be the best to use. Either the small port on the front or the small already capped off port on the rear?

If anyone has any info or other advice on these connections I would be very grateful, thanks

[copbait73]

Here is what I did on my 2.4L CIS conversion and all the various systems are happy on boost and off.
Go to NAPA and buy several vac one-way check valves.
Place one on each line so Vacuum works as normal (flow toward throttle body) and boost is closed off. Done.
I depend on my MSD with adjustable boost/advance to trim off spark advance. I adjusted my wastegate to run a safe 6PSI and set the MSD to trim 2 degree per 1PSI.

[Dr J]

^^^ that is a great suggestion!

[patkeefe]

I believe the bare minmum you need is WUR, distributor, wastegate and whatever you're using to regulate boost, such as an MSD Boost Timing Master. I ditched a lot of the stock SC CIS stuff when I built mine. I will look it over in the garage today to verify what I have. Do you have a turbo WUR?

Also, you need to consider if you are using a port upstream or downstream of the throttle butterfly. There are various threads regarding this.

[gavinc69]

Thanks for the reply's.

I had a very late night last night reading through various threads again and did find some info.
It appears the ports below the throttle butterfly are vacuum and the ports above would be under boost and that I should connect everything below the butterfly to just vacuum ports.

I will have connected :

BOV
Distributor
Boost gauge
Thermo valve - that then goes on to the WUR
And there is currently a connection from the top of the WUR to a front port on the throttle body, looks above the butterfly, so maybe I should relocate this to a port on the rear below the butterfly?

I will also be adding an MSD retard soon.
I was going to put a 'T' in the Thermo valve pipe and use that for the BOV.

Useful pic from other threads :

First on looks like my setup

[gavinc69]

My home made Bonnet for the Air Flow Meter has a 25mm port to connect the AAR. So that is taken care of, you can see it on the left of the pic.
The hole to the right of the black hose is a threaded hole for a bolt.

To the right I have removed the two larger connections for the decel valve.
I have also connected the Thermo valve to the lower right port (the black hose).
I will 'T' off this black hose for the BOV next week.

Silicone caps will be installed on the larger open ports next week.
The left lighter coloured hose goes to the distributor so I will just leave this I guess.

I will jubilee all connections just incase.

[Dr J]

Gavin those diagrams won't apply to you because those are for normally aspirated not for boosted cars. The lines below the throttle plate are vacuum when the throttle plate is closed or when you are not boosting. If the throttle plate is open and you are boosting then you have boost. In fact I use the decel valve port to connect to the pressure sensor and vac/boost gage. If I took the port above the throttle plate I would read boost only.

In your set up, under boost, the AAR is getting boost from the bottom of the manifold working its way out the bonnet to the air intake.

In my case I removed the AAR and AAV but now want to put it back which is why I got excited with the check valve idea suggested by copbait73.

[patkeefe]

Gavin:
Inlet Overrun Valve Modification? (BOV, lag) Attached is the original piping when my SC was n/a. Pretty much like the JW CIS diagrams.




My WUR is a Leask adjustable, so it requires a boost signal. There are certain schools of thought regarding the reactions of wastegates, boost overrun, and what the internals of the cylinders actually "see" depending on location of signal references, either before or after the throttle plate.

I get boost pressure signal to my gauge from one of the taps I have in the outlet tube from the turbo. I also have my pressure switch for the water injection system there. I get vacuum/boost signal for my Leask boost delay switch from the upstream port on the throttle body. I have the Forge diverter piped as in the referenced link. All of this becomes the tuning issues you will experience. Putting all of those parts together was the easy part. BTW, you have done a marvelous job of assembly, that engine looks great!

[Dr J]

Gavin, check the diagrams in these posts:

Distributor vacuum lines/smog removal

think I finally found my vacuum leak

These diagrams show the AAR connected between the intercooler and the bottom of the throttle plate.
You can connect the input to the AAR anywhere that is boosted. Here is the best one and includes pictures:

911SC Turbo

The only problem with this approach is that under boost the hoses to the AAR/AAV become pressurized. For me, the preferred way is to connect the AAR to unpressurized inlet as the factory location for the SC and put a check valve just before it connects to the bottom of the intake manifold near the cold start valve.

[gavinc69]

As you guys say the AAV would be under pressure from the bottom of the throttle body where to connects. I didnt think of that.
The SOK manual doesn't say anything about this which is strange because there air flow meter bonnet came with an AAV connection. I copied there design to make mine.
So I wonder how there setup worked correctly?
Also tsuter seemed to re-route his AAV to the upper Decel Valve connection, so surly this would also be boosted when the throttle butterfly is open?





Just a quick layout of how I thought I would go :





SOK air flow meter bonnet with connection for AAV :








Still not sure what to do with the WUR connection that goes to the front upper port on the throttle body and comes from the very top of the WUR. If I read correctly its a vent for the WUR, but not sure if its a good idea to have it under boost?

[gavinc69]

Taken from Tsuters tread :

This next image shows the AAR/AAV hose necking down to a smaller hose that is then routed to the upper throttle body air source instead of the boot which is gone. The air supply to the intake manifold from the AAR/AAV near the CSV is not changed.




Tsuters setup is taking air from the throttle body back to the throttle body, it will still be either vacuum or under boost depending on throttle position.

The setup I was thinking of using would be similar but I just won't be taking air from the throttle body, it just picks up from the standard location. If any boosted air goes back through the AAV it will end up in the air flow meter bonnet and taken back into the engine again, although I guess boosted air coming in there may disrupted the air flow or may even go against the airflow flap, as thats trying to come upwards and the boosted air would enter above it. But would there be enough boosted air to do that especially seeing as the 3" flow out of the bonnet it right next to the AAV port, maybe it would just get sucked straight back in!

[gavinc69]

After doing some more searching today it seems the top port on the WUR that goes to the top front port of the throttle body is indeed a vent to atmosphere.
On a 930 to connects to the large air box :



So I will disconnect the pipe from the WUR and leave it open (maybe put something on it to work as a filter so nothing goes in it). The throttle body end I will just cap off.

[patkeefe]

Yes, top port on the WUR is an atmospheric vent. Mine has a filter. I am assuming you have a 930 WUR? If not, you will find you get no boost enrichment from it.

[Ronnie's.930]

I'm not sure if you would call that a "vent", but what I do know, is that if the WUR diapram ruptures, fuel pours out of that opening . . .

There is no need for a filter on it as air is not drawn into it.

[gavinc69]

The WUR installed at present is a standard SC Euro 069, I also have a 930 WUR that I will install if needed (probably will need to).
Both look the same in terms of ports/connections but as you say the standard version will not enrich under boost.

I was thinking of just trying it with the standard WUR and monitor my AFR's then if it wont compensate enough installed the 930 WUR and if necessary also make it adjustable so I can tweak the pressures.

At present I just want to get all the vacuum connections at the rear of the engine done and correct so I can get the engine back in.

Really don't want to get it back in to then find something that is very hard to get to needs changing etc

Still not sure about the AAV.
BAE manual says connect it as Tsuter has done to the top Decel port because there bonnet did away with the original AAV connection.
But the SOK bonnet has the connection still there and there manual says nothing about it at all, so I assume there kit still used the original factory style setup.

[copbait73]

The standard WUR will function just as it does N.A. and probably enrich up to about 3 psi. then your A/F progressively goes lean. I bought a programmable "7th" injector for about $300 from Split Second and it does the job.

Many think it more elegant to use the factory 930 TURBO WUR because of perceived distribution issues however that concept is almost a joke. No two runners carry the same DRY airflow on any Porsche log manifold, turbo or N.A. , so the concept of equal fuel distribution assures equal A/F ratio is an elusion. Good enough is just that.

It will be hard to find a good used Turbo WUR so you will probably be back to a Leask adjustable and an RPM control to have the adjustabity you need.

Does your airbox have a pop-off valve? If yes what have you done with it?

[gavinc69]

I have a Turbo WUR and will most likely install it once I start tuning the car.

There is a pop-off valve installed and after reading other threads I've ordered a
plumbers pipe bung, used for pressure testing pipes.
A few people have had good success with these so I'll give it a go.
Still a little concerned about back fires, but I only get them under big climate changes., say the first start after winter storage.

[gavinc69]

This pic taken from another thread shows the 930 AAV connected to the intercooler and throttle body which I believe is the standard factory setup.
So assuming its connected below the throttle butterfly like on the SC it must also be taking boost.

[Dr J]

Hello Gavin

The above diagrams are good. I just want to correct a few things to keep the value of the thread, since it will be useful to others in the future.

Tsuters setup is taking air from the throttle body back to the throttle body, it will still be either vacuum or under boost depending on throttle position.

Tsuters setup takes the air from the top of the throttle body so that part only sees boost (the lowest pressure it sees is atmospheric and the highest is boost pressure- no vacuum).

The setup I was thinking of using would be similar but I just won't be taking air from the throttle body, it just picks up from the standard location. If any boosted air goes back through the AAV it will end up in the air flow meter bonnet and taken back into the engine again, although I guess boosted air coming in there may disrupted the air flow or may even go against the airflow flap, as thats trying to come upwards and the boosted air would enter above it. But would there be enough boosted air to do that especially seeing as the 3" flow out of the bonnet it right next to the AAV port, maybe it would just get sucked straight back in!

If you take the input to the AAR from the Porsche location in the bonnet, boosted air can come in backwards through the AAR to the bonnet (as you noted above.) However, the pressure at the bonnet is atmospheric pressure. In other words, you will lose your boost as it will vent out the air filter. When the AAR closes, then this will be somewhat sealed, but others have indicated that it is not a perfect seal so you will have a boost leak.

The reason Tsuters' setup and those of the diagram above work is because the input to the AAR always has pressure greater than or equal to the bottom of the manifold. In the stock configuration, the inlet to the AAR is atmospheric pressure, while the manifold is anywhere between vacuum and near atmospheric because it is not boosted. So in the stock configuration the pressure at the inlet to the AAR is always greater than or equal to the bottom of the manifold. The only thing that might be a concern is that these hoses are now pressurized when there is boost and originally they never saw pressure above atmospheric.

The SOK manual doesn't say anything about this which is strange because there air flow meter bonnet came with an AAV connection. I copied there design to make mine.

This is a good point on what seems to be the AAR connection on the bonnet. I looked at a SOK manual for autorotor and another for a Paxton on a 3.0L. The Paxton one had no details. The autorotor one said to connect the "oil breather hose" to it. I assume they mean the line from next to the oil tank cap that normally goes to the airbox. Interestingly the Paxton manual says to put a small filter and not connect it to the airbox.

In my case, I just plugged that part of the bonnet; however, now that I am considering reinstalling the AAR, I am looking at options.

[Dr J]

Hello Gavin

The above diagrams are good. I just want to correct a few things to keep the value of the thread, since it will be useful to others in the future.

Tsuters setup is taking air from the throttle body back to the throttle body, it will still be either vacuum or under boost depending on throttle position.

Tsuters setup takes the air from the top of the throttle body so that part only sees boost (the lowest pressure it sees is atmospheric and the highest is boost pressure- no vacuum).

The setup I was thinking of using would be similar but I just won't be taking air from the throttle body, it just picks up from the standard location. If any boosted air goes back through the AAV it will end up in the air flow meter bonnet and taken back into the engine again, although I guess boosted air coming in there may disrupted the air flow or may even go against the airflow flap, as thats trying to come upwards and the boosted air would enter above it. But would there be enough boosted air to do that especially seeing as the 3" flow out of the bonnet it right next to the AAV port, maybe it would just get sucked straight back in!

If you take the input to the AAR from the Porsche location in the bonnet, boosted air can come in backwards through the AAR to the bonnet (as you noted above.) However, the pressure at the bonnet is atmospheric pressure. In other words, you will lose your boost as it will vent out the air filter. When the AAR closes, then this will be somewhat sealed, but others have indicated that it is not a perfect seal so you will have a boost leak.

The reason Tsuters' setup and those of the diagram above work is because the input to the AAR always has pressure greater than or equal to the bottom of the manifold. In the stock configuration, the inlet to the AAR is atmospheric pressure, while the manifold is anywhere between vacuum and near atmospheric because it is not boosted. So in the stock configuration the pressure at the inlet to the AAR is always greater than or equal to the bottom of the manifold. The only thing that might be a concern is that these hoses are now pressurized when there is boost and originally they never saw pressure above atmospheric.

The SOK manual doesn't say anything about this which is strange because there air flow meter bonnet came with an AAV connection. I copied there design to make mine.

This is a good point on what seems to be the AAR connection on the bonnet. I looked at a SOK manual for autorotor and another for a Paxton on a 3.0L. The Paxton one had no details. The autorotor one said to connect the "oil breather hose" to it. I assume they mean the line from next to the oil tank cap that normally goes to the airbox. Interestingly the Paxton manual says to put a small filter near the oil cap and not connect it to the airbox. They don't say wha to do with the port in the bonnet.

In my case, I just plugged that part of the bonnet; however, now that I am considering reinstalling the AAR, I am looking at options such as the check valve I mentioned.