911SC Turbo

[iamchappy]

Thanks for the test drive Sammy, It gave me a big smile, I will probably go back to the stock 901 gearing, I think the short gears 2nd, 3rd, 4th, are going to keep me very busy. especially 2nd and 3rd are so darn close right now that if your not accelerating into 3rd it feels like your downshifting. I cant imagine shifting through those gears on boost. I think 8lbs maybe my limit considering how light the car is, but you never know, Id love it to be scary.

[tsuter]

This week I'm finishing two revisons to the "modified" BAE".

1. I am relocating the Hobbs 3.0# pressure switch (for activating the enrichment CSV under boost) from the turbo outlet pipe (see earlier pictures) to the unused decel valve connection on the back of the throttle body below the butterfly.

2. I am relocating the enrichment CSV up in the turbo outlet pipe closer to the throttle body.

This exercise serves two purposes. 1. it allows the pressure switch to open faster on throttle closing or shifting thus shutting off enrichment fuel into the turbo outlet pipe faster, and 2. it allows room for a future BOV/DV in the turbo outlet pipe behind the enrichment CSV. Even an intercooler is possible as more room is now available.

I used the old BAE POP Valve flange and a blocking plate to install the enrichment CSV in the turbo outlet pipe.





Drilled and tapped 8-32 holes for machine bolts into the blocking plate for the CSV flange



Reinstalled the blocking plate onto the turbo outlet with the CSV.



The enrichment CSV will use the same fuel connection as before. A #4 cylinder fuel line to a T-fitting at the fuel filter. see earlier pictures.

[tsuter]

The Hobbs pressure switch is also relocated using a vacuum line to the decel connection on the back of the throttle body.

I used clamps and a small bracket attached to the thermo switch bracket on the back of the thottle body to support it.



It probably could be installed without the support bracket and just using a one inch piece of hose and two clamps right on the decel nipple. But I wanted better access for service if needed.




With the longer hose it sits right behind the turbo inlet pipe from the air intake bonnet.

[tsuter]

The last step was to reinstall the fuel line and reconnect the wiring between the pressure switch and the enrichment CSV.



And reinstall the turbo pipes. There is now much more room for a BOV/DV in the turbo outlet pipe as well as much better response on the pressure switch deactivation of enrichment with the pressure source from below the Throttle butterfly.

[tsuter]

Closer shot showing the positions of the enrichment CSV and the activation pressure switch.



I gave some consideration to relocating the enrichment CSV to the back of the air box right below the throttle body. See pictures a page or two back. Ultimately I did not do this for concerns over even fuel distribution to all six runners. It is the enrichment that reduces detonation under boost in excess of 3-4 lbs and you want that fuel in all six cylinders.

[tsuter]

And back together.

This ain't your Daddy's 911 !!!

[tsuter]

Ordered this Tial BOV today. It will be installed in the turbo outlet pipe where you see the red connecting hose and clamps in the above picture. Objective is to vent pressure on throttle closing to help keep the turbo speed up.





Test drives this past weekend detected no significant impact from relocation of the Hobbs pressure switch for triggering the enrichment to the old decel valve connection on the throttle body.
It may activate a bit later but I can't see there being much pressure drop between the old location on the turbo outlet pipe and the throttle body. Certainly it will close the entrichment CSV faster and not leave fuel in the turbo outlet.

[iamchappy]

Thad my Tial BOV came set at 11psi is this adjustable.

[tsuter]

David, I don't know if the Tialco is adjustbale. If it is, you just shim the spring or use a screw. However 11psi should be good to keep it closed at idle. That is the critical point... that it doesn't leak at idle and cause rough running or a rich mixture. It is vacuum activated. I'll use a vacuum line to the old decel conection on the throttle body below the butterfly where I also have the pressure switch for enrichment.
A Tial BOV this big should blow the excess boost off when the throttle valve is closed very efficiently. With the large pistons, it takes more vacuum to open them hence the 11 psi I guess, but they dump the boost better. This should significantly reduce lag between gear changes...and provide instant boost when modulating the trhrottle in corners.
Noise may make your neighbors happy!

[sammyg2]

Here's a BAE turbo question:
On my car if I nail it in second the car surges a little bit as boost comes on. Kind of a bucking but not violent. It just hits a little harder about two or three times before it smooths out. In third and fourth it doesn't do that at all.
Also if I roll on the throttle smoothly it isn't there.

My theory is that the air flow sensor plate is over correcting a little, causing temporary swings to over-rich. Sound reasonable? Anyone BTDT?
I'm convinced it isn't ignition related at all. The only other time the car has acted like this was when I had the mixture set way too rich due to a vacuum leak at idle (pre-turbo, fixed now).
I know I'm still running rich right now but am waiting for additional measuring equipment before leaning it out.
Better to burn extra gas than a piston. Yes, I'm chicken but like to have hard data to make adjustments instead of going off a hunch.

It will prolly go away when I get the mixture set just right but wanted to know if anyone else has seen this.

[tsuter]

Sammy if you have the stock BAE pop valve in the turbo outlet pipe limiting the boost instead of a wastegate and MBC then what you are likely feeling in second gear is that valve opening and closing causing the surging/bucking you feel. Even a wastegate with no MBC will also not be so smooth. The MBC smooths things out quite well.
The best way to not get this is to not floor the throttle. Just ease it down more slowly. In second gear you're going to be at 6000RPM mighty fast anyway so no real need to floor it. Even third gear...just ease it down.

[sammyg2]

No BOV or pop valve, but I have the stock wastegate. Mechanical boost controller? Don't have one of those. I've seen em on e-bay and plan to get one, just haven't done it yet. Any tips or any secrets to install it right?

If it is just the waste gate bouncing that makes me feel better anywho, it aint something dangerous to the motor just annoying and a relatively easy fix. Thanks.

EDIT: just bought a MBC from e-bay, should be installed in a week or so.

[tsuter]

I think an MBC.... Turbo XS type will smooth out the boost rise at least it seems to on mine. My Tial wastegate has the .4 bar spring (6psi) and I have the MBC set maybe two psi over that for about 8 psi.

[iamchappy]

You guys are having all the fun, I just sent my turbo to turbo city for a rebuild, I want to take a test drive.
It's not fun anymore just looking around at all the parts I've assembled for the install.
I need to scratch the itch.

[rfng]

Originally posted by sammyg2
Here's a BAE turbo question:
On my car if I nail it in second the car surges a little bit as boost comes on. Kind of a bucking but not violent. It just hits a little harder about two or three times before it smooths out. In third and fourth it doesn't do that at all.
Also if I roll on the throttle smoothly it isn't there.

My theory is that the air flow sensor plate is over correcting a little, causing temporary swings to over-rich. Sound reasonable? Anyone BTDT?
I'm convinced it isn't ignition related at all. The only other time the car has acted like this was when I had the mixture set way too rich due to a vacuum leak at idle (pre-turbo, fixed now).
I know I'm still running rich right now but am waiting for additional measuring equipment before leaning it out.
Better to burn extra gas than a piston. Yes, I'm chicken but like to have hard data to make adjustments instead of going off a hunch.

It will prolly go away when I get the mixture set just right but wanted to know if anyone else has seen this.

I have experienced the same when I intitally installed my kit. Normally there are only two causes of the stumble:

1. Too big of gap on the plugs and the spark it getting blown out under pressure ( but usually more of a problem which running more than 9 psi or

2. There is a boost leak/vacuum leak at the injectors or the intake runners against the heads. This will cause the over-rich condition you speak off and cause the stumble.

Take some carb spray and shoot the injectors one at a time. It should stumble, you will need to replace the injector seals and sleeves. When you turn up the boost past 7 psi you will need to seal the injectors in as the pressure will gradually push them out of the sleeves.

[sammyg2]

Nope, no vacuum leaks, the injector seals are all new and tested. New intake runner sleeves installed two months ago, along with new gaskets. A great deal of time and effort was spent to make darn sure there were no vacuum leaks of any sort. I hate vacuum leaks.

After all that work the car ran almost too rich to idle as I had eliminated vacuum leaks that were there before but hadn't changed the mixture setting. I had to lean it out just to get it to run right.

The surging occurs at very low boost, usually as it first kicks in so I'd have to say around 2 to 4 psi. Aint gonna blow out the spark like that.

The car runs flawlessly at all times, never even a hiccup except for when I stomp on the throttle in second. If I roll on the throttle it climbs smoothly. It starts right up hot or cold, it runs smooth and steady no matter the condition except for this case.
If I stomp on it in third it pulls smoothly, it only surges in second. It would prolly do it in 1st but I aint gonna try it and over-rev the engine.
That leads me to believe it has to do with the engine revving up quickly as well as boost hitting at the same time. That creates a very large increase in air flow past the air flow sensor. I think the sudden increase causes it to move too far, then over-correct. The flutter results in the surging and is compounded by the wastegate bouncing. I consider that a distinct possibility anyway.

As previously stated the mixture is set a little rich on purpose for now, it is possible the surging will go away if when I lean it out some more.
We'll see after I install the MBC.

I have some new solid engine mounts, maybe I should install them to make sure the engine aint jumping around and causing the throttle to bounce open and closed a bit.
One thing at a time.

[sammyg2]

My car is officially running perfectly now! knock on wood.

I pulled a couple plugs after a run on boost to read them, then leaned it out a little, the stumble was gone and it ran smooth without hesitation.

Then...... I replaced the spark plugs. Made a world of difference.
The PO installed split-fire POS crap junk snake oil plugs in the car, I'd checked thenm a couple times and they looked fine, I was gonna replace them one of these days but as far as I could tell them were working fine.
Shame on me. At least I wasn't dumb enough to pay money for split-fires, I was just dumb enough to leave em in the car.

Anywho, the engine now pulls silky smooth all the way past redline no matter how I drive it and what gear it's in.
cool. Next is to start creeping the pressure up a little after I get more air/fuel data.
Yes, I have the disease.

[tsuter]

Well Sammy, Here is your next step.
Chop a big hole in the turbo outlet pipe for a big Tial BOV flange.
I'm locating mine where the red silicone hose is in the above pictures. Used to have the enrichment injector there before I relocated it.



The BOV uses a clamp to attach and it will be sitting adjacent the coil on the outlet pipe. Vacuum source will be the old EGR nipple or a T to the decel connection on the throttle body which is currently used to control the enrichment switch.



I gotta clean up these pipes this weekend and I think I'm going to break down and have both pipes powder painted on Monday next week.

Then I'll get my Fuchs polished ....... NOT!!

[sammyg2]

Next step for me is to install the MPC I bought a few days ago and hopefully is on it's way, they an air/fuel ratio meter, then a little more boost up to around 7 psi. My exhaust system doesn't have an O2 bung so I need to take it off to drill the hole and weld on the bung. I don't want to have metal shavings going through the turbo.
I wonder if it makes any difference if the O2 sensor is before or after the turbo? the muffler is much easier to R&R than the header is. Heck I could prolly drill and weld the bung on the muffler pipe with it still in the car.

After that I need to look for a simple and inexpensive intercooler set up. I may have to go hit the pick-a-part junkyards and see what's out there.
Either that or try and find a deal on a factory intercooler for a late 70's 930.
It never ends.

On the BOV I have a question:
If the air sensor meters fuel based on how much air is passed by it, wouldn't it add fuel for the air that is discharged to atmosphere causing a short period of over-rich mixture?
maybe it is so quick it doesn't matter. Any thoughts?

Has anyone looked into installing a rising rate fuel pressure regulator on a turbocharged CIS system? I know this is a common trick on other types of turbocharged cars.

The injectors in a CIS system work off of differential pressure i.e. when there is more pressure in the fuel lines than is in the intake they squirt. The more differential pressure the more fuel they squirt.
If the intake pressure goes up the differential pressure goes down, the amount of fuel delivered will go down too unless the fuel distributor makes up for it because of the additional air.
If a pressure regulator increases pressure at say a 3 to one ratio, it would increase the fuel delivered as boost rises, eliminating the need for extra injectors. At least that's how my feeble mind sees it.

I'm not sure if a riding rate regulator is available for this pressure range but I would think it would be.
I need to do some more homework on this one.

[tbitz]

Guys,

I've been following this thread and it is interesting to read about all the issues with CIS. Don't know if you guys have seen my CIS to EFI thread? It would be perfect solution for all the fuel needs of a turbo and would clean up the engine bay.

With the EFI setup fuel pressure automatically goes up when manifold pressure goes up due to the vacuum/boost port on the fuel pressure regulator. No need for any external enrichement injectors either. Just program the enrichement in the VE table. You simply set how much enrichement you want for a given manifold pressure and rpm. You can also log boost, rpm, O2, manifold air temp, etc...

I'm working on turbocharging my car which is already running EFI.