odonnell

Has anyone significantly weeded out a lot of their vacuum components? I know that they are all there for a purpose, but I really like the idea of minimal/barebones for simplicity and reliability reasons...less to go wrong and leak.

This guy only has 3 lines: brake booster, damper, and FPR:


I think a good compromise would be a car that idles on it's own (obviously) which means keeping the auxiliary air valve and the idle stabilization valve.

Then there's the other stuff you see in the diagram, and to be honest I'm not sure what half of it does. I have researched some parts and they appear to be for vapor venting from the charcoal canister. I would be on board with deleting this part of the vacuum system and routing the canister to the airbox or something if that eliminates clutter under the manifold. Has anyone done anything like this?

Dougs951S

Michael, first off you might want to read through here real fast, some decent info regarding the emissions control vacuum stuff there. https://rennlist.com/forums/944-turb...ve-delete.html

I've deleted a very large number of vac lines and as you know, I'm not running an ISV, a fuel pressure damper, or a factory boost recirculating valve. Here is a diagram of my vac lines. This is a COMPLETE diagram, all the heater control vac lines and stuff behind the dash has been deleted too. What you see in this pic is every piece of vacuum hose on my car. My car idles just fine on its own, even on a dead cold start. Pulls 20" vacuum.

odonnell

I found an old pic I took from my car's engine bay:



I'm a little confused by the "Control Valve I/II" components. At first I thought Control Valve II uses the pressure in the J-boot as the input to determine how much air is allowed to flow through it (there are two other lines coming out of it) but usually control valves get an electrical input and a motor or heated valve opens or closes the pathway.

The venturi, control valves, and thermostat valve are the main parts which I am unsure about with regard for what they do. One of the two control valves is probably the ISV, but I can't tell from the diagram.

What can safely be deleted without any real drawbacks? The car has no AC so I believe the AC airvalve is gone already. Ideally it will just be brake booster, damper/regulator, and whatever idle stabilization I need.

Dougs951S

Michael, control valve I&II are emissions control stuff, they can be gutted safely. Let me try to find a pic.




Basically all emissions stuff is a loop running from the gas tank, to those valves, and then to the charcoal canister under the driver side front fender well. It feeds fumes into that little J-hook shaped fitting underneath and attached to the throttle body, and is powered by vacuum from this little bunny ears looking fitting under the intake.

Dougs951S

Michael give this a read, it will explain a lot of your questions. Hell..give me a call


https://rennlist.com/forums/944-turb...ve-delete.html


I only have 7 vacuum lines in my car, 3 of which are specifically turbo related stuff. 1 is for the BOV, 1 is for the wastegate, and 1 to my boost/vac gauge in the cabin. The other 4 are MAP sensor, FPR, the big vacuum line from the manifold to the brake booster, and then a line tee-ed off the brake booster hose to the vacuum canister near the firewall. That's it. You dont actually need the vacuum canister either, so long as you feel comfortable stopping the car at speed if the engine stopped and left you with no vacuum assist, you can delete that too without effecting anything.

Will Feather

Doug, any issues without running the dampner? Running an aftermarket fuel rail with regulator?

Dougs951S

Will, no issues to speak of, just a cleaner engine bay Running a stock rail for now with a bosch 3 BAR FPR, 80 lb/hr high Z injectors, and rebuilt stock fuel lines that use E85 rated hose.

Will Feather

Any particular reason you deleted it? I know some people who have done so have experienced some lean conditions. Running Megasquirt that would be easy for you to tune out...

Dougs951S

I've never noticed any air/fuel issues related to me removing it. The AFR's are always dead on. I ran without it even before I went to megasquirt and still didn't notice any issues. I deleted it because I knew it was a non vital component and like Michael, I strive to make my car as simple and reliable as possible. Compared to a stock 951, my engine bay is shockingly bare and easy to navigate/investigate/work on, which is how I like it.

Will Feather

Good info, I couldn't agree more, the less lines and the cleaner the bay the better!

odonnell

Thanks for the info. One thing I still don't fully get - the ISV. The early 944 has the auxiliary air valve where the late car has a DME-controlled unit. Video. Looking at the DME pins on a late car versus an early car it looks like pins 33 and 34 on the late DME are for that, I may be mistaken. It has a ground pin and two power pins, each of which spin the motor a different way, I am assuming these are from the two DME pins.

So does the early car only have the aux. air valve and no "true" ISV? I don't see anything else in the schematic except the AC air valve, which I guess increases idle when the compressor is on which isn't relevant in my case.

Dougs951S

You are correct michael, the cold start valve operates differently than the ISV on late cars. The late car's ISV is controlled digitally by a darlington transistor pair which actually controls how far the valve is open between 0-100% via pulse width modulation. The DME varies how long it pulses the ground to the ISV, but it is a closed loop function intended to target 850 rpm on a stock car, and is always "on." In an ideal situation though, once the car is up to temp it is intended that the car will already be at it's correct idle speed and so the valve will not really be doing anything unless you kick on the A/C or say, cut the wheel to lock with power steering and load up the motor.


Here is some more info on the late car's ISV operation >>> https://rennlist.com/forums/944-turb...the-dme-2.html

Will Feather

When deleting your ISV Doug, did you have to play with the idle screw? I know some people do.

Dougs951S

No I did not, my idle screw is all the way closed and sealed with an O ring, no air is bypassed with it. When I deleted it and I was still running a DME tune, I had to open the idle screw some and it was a compromise between getting it so I only had to give the car minimal gas on a cold start, and still have a warm idle that wasnt racing. Now with megasquirt, I have the car tuned to provide as much idle torque as the motor is physically capable of, and this is enough to provide a nice 1000 rpm idle once warmed up and to allow the motor to idle on its own, albeit a bit low on cold starts. Once the car is warmed up, I can nearly take off from a stop with just the clutch, its definitely has a lot more low end torque than before, and I'm still stock displacement and stock 8:1 compression.


Michael, with respect to the venturi, this may help you. It's not commonly messed with on N/A cars, but deleting the venturi is really common on turbo cars and actually the factory did it themselves in 89' on the turbo S. \/\/\/\/\/\/\/\/\/\/\/

https://rennlist.com/forums/944-turb...te-thread.html


This might be helpful too, a cleaner image of the early vacuum system that makes it easier to see the little lines where all the components connect.

V2Rocket

Doug,
Would you be able to share your fuel/timing values for the "idle torque" adjustment?
That is a very attractive mod for me. The only downside of the 951 gearbox is there is not enough gear to get a decent slow takeoff...