PMO install on 1980 SC

[Matt_West]

Well the carbs have been orderred and the CIS system has been removed. I have been searching the form and found some great photos and good advice.

I will be running a CIS fuel pump with the recirculating system.

As far as I am at this point my questions are:

1. What can / should I delete as regards wiring / vacuum lines etc.

2. What is the preferred solution for the hoses that went to the oil tank.

3. Passenger side of car on the far outboard side of the chain housing, there is a small sensor that took a single green wire from the top of the CIS air box... what is it and what should I do...

Detailed pictures and descriptions are appreciated.

Thanks,
Matt

[shbop]

You'll be left with one vacuum line for your power brake booster. Get the check valve from Richard , if you didn't order it. The wiring harness is up to you. I removed all the CIS stuff from mine. It's too bulky otherwise, and I know I'm not going back to CIS. Figure out your ignition. ie- re-curve, or whole new system. Good luck!

[Joe Bob]

Carb fuel pumps are cheap.....SC fuel pumps are WAY too high pressure even with a return line to the tank. Sell the SC pump and make a few bucks....you'll be money ahead EVEN with the lower pressure pump purchase.

[shbop]

Mikez, I'm curious. Richard recently told us to keep the SC pump and run it with his combination fuel manifold-regulator. Have you had a different experience?

[Joe Bob]

Having done carb conversions before.....I see what the recommendation is for fuel pressures....look at what the SC/CIS pump is rated at. Carbs run on 3-5 PSI.....then you make the decision.

Also fuel lines....FI fuel lines are 3 times what carb fuel lines are. An SC is what 25+ years old? Time to replace the lines....

[JP911]

Richard Parr (PMO) designed the regulator he sells to control the higher fuel injection pressures. It works well, and you can dial in 3.5 psi with the Bosch CIS pump. That said, Mike is right about the carb pumps being cheap. When my stock pump gave up the ghost I went with a Holley pump for about $100 and it's worked perfectly through several track days.

[Joe Bob]

Well, you CAN run a regulator after a high pressure pump....but IF the regulator goes, you have the high pressure running and the potential for fuel leaks.....just doesn't make sense to me.

[Matt_West]

Thanks. The ignition is going to be a re-curved distributor.

Any detailed write-ups on the wiring / vacuum deletes?

Also what is the sensor on the passenger side chain box. (Had single green wire coming from top of CIS? It is to the right of the oil presure sender.

[shbop]

Matt, Your wiring shouldn't be a big problem. If you want to retain the harness "as is", just wrap up the connectors for the CIS. Someone down the road might want to go back to it. If you search under MSD installs, you'll find some great write-ups with the wiring details. You didn't mention if you were installing MSD, but it's suggested as being very helpful. I started in that direction and then switched to Electromotive. Can't help with the green wire. Sorry. When you say "vacuum delete", are you going to remove the vacuum booster? There are a lot of smarter folks than me lurking here. Maybe they'll chime-in and answer your other questions. Hope this helps.

[JP911]

There's a sensor on the driver's side chain box (it's the cold start valve sensor), but I'm not sure about the passenger's side.

[jess p]

If you keep that cis pump and regulate it down to 5 psi,
YOU ARE asKING FOR PROBLEMS!!!

[2.7RACER]

The pressure regulator designed by Richard Parr of PMO is a great solution.
It is a simple bypass valve with no moving parts.
Set the pressure to 3.5 lbs and forget about it.
The original CIS pump works the same as it always has.
In fact it does less work, since it isn't pumping to injector spray pressures.
The bonus is the pressure gauge, you take one look at it and you know exactly what's happening.
Been running mine for over two years with no issues.
Richard at PMO knows what he is doing.

[jess p]

That's incorrect. The cis fuel pump pressure pumps fuel
at a constant pressure. It is the job of the wur to regulate
it. The fuel filter and the accumulator tend to dissipate the
pressure. There is a pressure drop as the fuel leaves the
filter. Placing a fuel pressure regulator set down to 5 psi
from as high as 90 psi will cause the fuel pump to work
Harder. The pump will have to force fuel at a higher pressure
at 85 psi as opposed to a smaller and most importantly
changing pressure that the wur IMPOSES.
Where there is work, heat is involved in the equation. Thus
a shorter life on the pump. I would;nt want a constant fuel of
85 psi in any one of my cars, let alone a porsche.

At wot the most fuel that will flow downstream of the regulator is 5 psi if thats what it's set at. The fuel pressure
upstream of the regulator will be a constant of about 85 psi.
Provided that the csi pump puts out 90 psi. Some cis pumps have an even higher output.

[2.7RACER]

Sorry Jess,
Pressure is developed when there is a resistance.
The PMO regulator closes the circuit from the supply line to the return line sufficient to develop 3-1/2 lbs pressure.
Without this valve to restrict the fuel flow, the fuel simply goes from the supply line to the return line.
If the supply line is connected directly to the return line without any restriction pressure is not developed unless the line size is too small.
At that point the pressure is only developed at the entrance to the small line. At any point downstream from the pinch point you would see a lower pressure.
The Porsche fuel lines are not too small.
True the pump is capable of what 50/60 or more psi.
An analogy is your water faucet. Typical system is 40 psi. And it will flow and develop 40 psi if you put your thumb over the outlet of the faucet.
However when you just crack the faucet the flow is restricted and the pressure at the open, downstream, exit of the faucet is significantly lower.
Missing from this analogy is the fact that the water is running back to a tank. Without a restriction in the lines significant pressure does not develop.
Something like any pressure regulator in any fuel injection system. Take out the spring which holds the check valve in place and what happens to the system pressure?
What happens when the pressure relief valve opens on any pressurized system?
Take out the springs in your oil pressure system and see what happens.
The oil will take the path of least resistance. The pressure at your oil pressure gauge will drop like a rock.
I don't use an accumulator or WUR in my carb system. And there may be a slight pressure drop across my fuel filters. Very slight. More if they become plugged up.
The trick here is the fuel is recirculating. It doesn't deadhead at the carbs.
If it did in fact dead head at the carbs your premise would be correct.

[Matt_West]

On the vacuum delete I am seeing plumbing to the cruise control and some other stuff. I imagine that I end up with just an accumulator and one line to the brake booster, but am uncertain.

[jess p]

By recirculating the fuel back to the tank via a fuel pressure
regulator there is a sufficient fuel pressure drop. Again, I
wouldn't do it. The host of this site sells several electric fuel
pumps and regulators for carbs. The original and existing
PMO site recommends a holley electric fuel pump. Personally
I prefer a carter as they are quieter. Pressures exceding 15
psi is sufficient pressure to overcome the float seats. Why
risk an engine fire with a questionable setup.





76 911S
81 911 SC
66 912 V8
70 914 PROJECT CAR

[shbop]

Matt,

Here's a photo of a vacuum line with the check valve from an 81.'

[randywebb]

"The trick here is the fuel is recirculating."

- Exactly.

BTW, you may want to separate the fuel flow from the electrical wiring as much as possible - seems crazy that Porsche didn't do that when they designed the thing.

RoninLB has posted some pics of his setup before - even if you aren't into overkill they are fun to look at.

Also, think about what fuel filter to use -- Richard told me the 2 little things in his kit were all I needed. But, Steve W. likes the big Racor filters & I intend to switch someday when I have time. Search on Racor for pics.

[Matt_West]

Thanks Jon and Randy. I have seen Ronin's pictures and I am inspired. I am fond of overkill and liked his layout. I should make some progress this weekend and will post up some pictures.

[shbop]

Ronin's set-up is very nice. If you can find and use the Racor filter, it makes life much easier when it's time to change filters. Good luck Matt.