What's you carb. fuel delivery system?

[Phoenix]

As you may recall, over the past 1.5 yrs I've had my '73.5 CIS converted to PMO's which are incredible. (a bit low on mileage but I'm hoping that fine tuning will help bring this up.)

I've read all the posts concerning the need for PMOs and Webers to be fed clean go go juice consistently. Now that spring is on it's way and the weather is warming, I'd like to tackle this project and make sure I have the best reasonable set-up from tank to carb.

As part of my research, I'd love to see how you guys (the experts) have handled this and hopefully get a few hints as to what I could/ should do.

For reference, here are a few pics of the pump to carb. set-up. I'm assuming that from tank to pump is stock, as I can't find anything in the records showing that POs have changed anything.

[Phoenix]

any thoughts?

[TimT]

Id get rid of the facet fuel pump, get another pump and mount it near the fuel tank (on the front crossmember), its better to push the fuel to the carbs, rather than have the pump "pull" the fuel through the 6 or so feet of fuel line.

Not only does the facet pump have to pull fuel the 6 feet from the tank, It has to lift if up about 1 1/2' (dif in height of tank out to )pump in).

Also the glass fuel filter is more for looks than for its filtering capability. Fram makes a nice filter with a replaceable element that you could mount where the facet pump used to live

[RoninLB]

Don't know specificaly to what level of clean the routine Fram cleans. I'm going to go w/a 1 or 2 micron system.

[304065]

Oliver,

A couple suggestions, although it looks very good now, and to qualify my advice, when I decided to install my fuel cell I went with an aftermarket (Mallory) pump and regulator up front with Aeroquip -6AN stainless braided hose and anodized aluminum fittings, a route that I do NOT recommend for any but the most patient, safety-conscious and obsessive-compulsive (like me, and there are more than a few of us in the Porsche community. . . ) It is definitely overkill, rated to 1000 PSI and has taken me ten weekends to design and install.

I second Tim's opinion about the glass/pyrex fuel filter. In a rear-end collision (a possibility, considering that your brakes are more effective than 98% of the cars on the road) that glass tube could fracture and dump fuel onto the wiring harness where it passes through the engine tin, giving new meaning to the phrase "ignition points."

The Gates hose is probably fine, but I would consider replacing it with the factory, cloth braided stuff, not cheap at about $4 per foot, but it will perform like the original in terms of burst strength and abrasion resistance.

There are some extra hoses in there, look like the return lines for your CIS system. Where do they go, presumably they are not still connected to the tank up front?

What is your plan for the oil breather hose? When you converted to K&N's they probably didn't include a provision for the breather? I had a BMW 2002 that had the same issue, and I went with a filter mounted on the end of the hose, will allow the tank to breathe without introducing contamination into the system.

To Ron's point, I agree, those PMO's will want super-clean fuel. I would go with a relocated pump up front, on the crossmember like the later cars, with an inline filter between the tank and the pump, and then a second filter in the rear near the carbs. Overkill but probably worth it.

Good luck and congrats on coming back from the fire.

[Formerly Steve Wilkinson]

All you really need is a good Racor fuel filter (designed for diesel trucks) and two non-glass in-line filters downstream of it, where you have the current ones mounted. I'm not sure what all the fuss about fuel pumps is about. I use the stock one (modified 3.4-liter '83 SC) with the restrictor and fuel-pressure gauge that PMO supplies. Works fine road or track.

Stephan

[RoninLB]

I'm w/ Cramer on fire safety. Better overkill than killing yourself watching your 911 burn because you didn't have the patience to do a perfect install....good thread John..and I take anyone w/experience seriously, like Steve W.....R

[Formerly Steve Wilkinson]

Well, Steve W--by which I assume you mean Weiner, not Wilkinson--was my advisor on my fuel pump/filter/deliver/carbs installation as well as the rest of the engine. And do we assume from what you posted that a stock 911 is a fire risk, since I used the stock plumbing?

Stephan

[Early_S_Man]

Oliver,

I feel you have a very clean installation that has a couple of deficiencies in delivered fuel rate.

1. That Facet pump is intended for 4-cylinder applications only. I have used that same pump on several air-cooled VW's and lots of people have used them on 914's with carb. conversions, but there is a danger of insufficient delivery rate at high speeds in a 911 ... even a 2.4 'T' engine! A Bosch pump, installed near the tank would be preferable, but lower-cost American electric pumps, such as Holley, or Carter would work too ... since they are designed for American V-8 engines, and have excess capacity. The Facet will be working full-time to keep up with those PMO's, and may experience a shortened lifetime. One Facet per carb. is another possibility.

2. Those fuel filters do NOT have sufficient flow or filtering capacity, since they were first marketed to air-cooled VW applications with single-barrel Solexes in the 1960's! One of my current favorite filters is a Fram G3802A with 8 mm OD inlet/outlet. Engineered for Ford/Lincoln V-8 fuel injection systems, it is big, efficient, and cheap by Bosch standards! I really don't have a safety concern, because any rearend collision with SUV bumpers will crack the carbs' zinc-casting body before those rubber-cushioned filters break ... 911 engine fires after collisions are commonplace! Carry TWO fire extinguishers (one Halon, one dry powder ... to be used in that order) in the car within reach ... one for driver and passenger!

The Gates fuel hose is probably not rated for the high engine compartment temps of a 911 engine, though it might last a couple of years before cracking. OEM German fuel hose, though costly, is the best in the WORLD, IMHO! I have seen it last 10-15 years on Mercedes engines without leaking or cracking, though it was shrunken and hardened a bit after that time!

[Phoenix]

Thanks for the very helpful advice guys!!

Tim:
- I am planning to move the pump up front. I'm just not sure yet what the most reasonable pump is for my application (90% street/ 10% track for fun). Any ideas?

John:
- Your 1000 PSI systems sounds great but would be a little like using a sledghammer to drive a nail based on my needs.

- I understand your point about the braided hoses. I'll likely replace the Gates as I work through this project.

- I've relied on my mechanic for the switch to PMOs and wasn't aware of the return line issue. (That's what makes this board so terrific! Super high learning curves.). I'll ask him if they're open lines to the tank. If they are, I'm plugging them with a screw and a clamp anyway so this should not be an issue. (unless water/ condensation can get in?)

- I'm currently looking for a decent filter for the oil breather hose. Any suggestions?

Stephan - I'm currently thinking a Racor #110a which is a 10 micron filter. Then for final filtration I'm thinking a 2 micron Fram just before each carb as Ronin suggests (thanks Ronin).

Thanks again guys and keep it comin'. I'm juts a sponge continuously looking for something to absorb.

Stephan - I'm in Hoboken just on the other side of the river. I'd love to meet, pick your brain and check out your ride. Heading to Hershey?

[Oldporsche]

I believe that the hole in you upper K&N air filter cover is for the hose from you oil tank filler pipe. At least, sometime in the next two months that's where mine will terminate.

I think you should get rid of those glass things. Put them on the lawn mower. Wal-mart can supply you a couple of aluminum cased gas filters with universal ends. More capacity, and safer.

Mounting the fuel pump down by the gas tank would be a good move. It's easier for a fuel pump to push the fuel than to suck it up hill. I like the Holley red pump. If you experience a pressure loss then the next one up, blue I think, maybe not, with a regulator will be necessary.

You you could then put another, large fuel filter in the same position as the stock fuel pump, before the piping to the carbs.

I have often wondered about the placement of a fuel pressure regulator. From early experience, I have found that the carbs liked having a return line. Thus the carbs were sampling the fuel as it was going past them back to the tank. Wouldn't it make sense to place the pressure regulator in the return line? Just a thought.

Good luck,
David Duffield

[304065]

David,

Good point about fuel systems, here are my ideas:

A "return style" fuel system has a few advantages: it's better at responding to transient demands for increased fuel pressure and keeps the fuel cooler by continuously circulating it between the tank and the regulator. The "dead-head" style is just a restrictor in the line that starts and stops flow, which has difficulty changing state and bottlenecks the flow. It also causes the pump to run hotter, because it's trying to compress a fluid when the regulator is in the "closed" position.

This is the style that the fuel injected cars have, but guys with carbs can typically get away with a "dead-head" style because of the very low fuel pressure required, e.g. 3-5 psi.

If Oliver were going to convert to a return style system, it might make sense to put a fuel pressure regulator on the port-side wall of the engine compartment, with the "bypass" port connected to the CIS return line, and the "pressure" line connected to the carbs. Then hook the CIS return line back up to the factory tank and flip on the pump, then adjust the fuel pressure in the closed loop with the engine off to whatever the PMO spec calls for.

As far as the Holley pumps go, I've heard that carb guys go with the Red, FI guys use the Blue, and anything above that in their line or the other street-rod type pumps (Paxton, etc.) are overkill for a 2.7, and will draw a bunch of current (8-10 amps). The Holley pumps aren't that big, but there's not a bunch of room up front so I'd measure before buying one-- and if I were sticking with hose clamp connections would probably go with a Bosch.

My own system is a Mallory 60FI pump that will flow 60GPH connected to a bypass-style pressure regulator, with a VDO sender mounted in a 1/8" NPT pipe to 3/8" NPT pipe adapter in one of the pressure ports of the regulator and electric fuel pressure gauge in the cockpit. Defying convention I mounted the regulator with a 3/8 NPT pipe nipple directly to the output of the pump instead of placing it in the engine compartment: it's easier to adjust up there and the pressure drop back to the MFI filter console is pretty minimal.

Lots of fun, now lets see if it wins races.

[RoninLB]

John/David,,, I have been thinking about a fuel system for carbs. for awhile. I have loved the full loop theory, but have not read about a full loop system even mentioned anywhere. I agree w/everything that you guys have wrote. I'm not clear on the fuel regulator bypass port being hooked up to return line. My understanding is that it would create 2 dead head lines instead of a full loop?? Also using the regulator on the return line may create a regulation problem, I don't know?? It may work if the regulator "out" was flipped to "in", I don't know. I think a full loop would start at a non-bypass regulator and have 2 "T" fittings, one to each carb. The loop would end at the somewhat restricted return line. I think a 45deg. "Y" fitting would be more efficent than a 90deg. "T" fitting. I have no experience with this loop system or know of, or read about anybody who has this experience...What makes this topic interesting is the logic behind the theory and that the fuel loop system is never discussed, IMHO.

[si2t3m]

Hi,

For some suggestions:

Concerning the fuel pump, i would also put it up front. I'd ditch the facet pump and find a bendix style pump. Purolator makes a nice bendix style pump. I found the info doing a search a while back. Don't forget to put some rubber mounts on it for quiet operation.

I'd also change the fuel hoses and those nasty clamps. I'd find some nice fuel hose clamps with rounded edges.

I'd take the advice regarding the fuel filters. I have a fuel filter just before the pump, but i have those clear filters before each carbs. I'll be looking for something else when the car comes out of storage.

I'd also install a fuel pressure regulator just before the carbs. I've read somewhere that the purolator one (the chrome one with the dial) is'nt really accurate, and that it could starve the carbs at high rpm. I have this setup for now, with a fuel pressure gauge juste after the regulator, going to a T. Each lines after the T (going to the carbs) have equal lenghts. The dial on the regulator and what is on the gauge show 2 different numbers! (gauge is set a 3.5 psi)

I'll be replacing the regulator with a holley fuel pressure regulator that will act as a T with gauges installed after the regulator.

I already have the stuff so why not!

HTH

[TimT]

Since your car had cis injection, you already have a return line in your car, so you can plumb the fuel to the carbs, install a regulator after the carbs, and return the excess fuell to the tank,
holley makes a low pressure fuel regulator that is perfect for this

[RoninLB]

TimT...if you install the reg. after the carbs what regulates the psi to the carbs??..........R

[TimT]

I like to install the regulator after the carbs because it is mimiking (sp) the fuel circuits of injected cars.

install the regulator in the fuel circuit after the carbs, use a gauge on the carb/pump side of the circuit, and adjust the regulator to the required pressure, the regulator will bleed excess fuel back to the tank via the return line. This way when demand for fuel rises the fuel pump is still active in the circuit.
Think of the fuel pump always working against the regulator, when the floats open the and it (the pump) is in the circuit between the regulator and the carbs the float bowls will fill more quickly.

if the regulator is before the carbs all you will ever see is a given pressure/volume. the fuel pump cant give any more than the amount you have adjusted the regulator to. The floats will open but there isnt anything the pump can do to fill them more quickly.

Take our mutual friend Billies 700+ hp monster... the regulator is on the return side of the fuel circuit on that car..


If Im on a track like watkins glen where it is pure flat out all the time ( in my car anyway) I dont want to worry about a float bowl going dry

It may be overkill but it works



tgif LOL

[RoninLB]

TimT---perfect story..I have to think on a different circut other than the carb being the dead end. This is my first taste of the return line that has full digestion instead of a burp. I love hydraulics. I usually use two 45's instead of one 90. It saves a touch in friction loss, neurotically speaking/writing.......Thanks..R

[Phoenix]

Thanks again guys...

I'm out of town for 2 weeks and I just brought Phoenix to her primary care physician. He'll give her a nice 1,300 post rebuild maintenance along with a Bosch fuel pump mounted up front (on rubber bushings - thx). As I don't have a lift, space or proper tools (yet), I'll have to pay to get that part done

Once the pump is in the front, I'm going for the Racor #110a filter (located where the Facit pump sits now) plus one 2 micron Fram for each carb. I'm not racing the car and have yet to get to my first driver ed (will be soon now that the motors worn in a bit) so this should suffice for now. I'll add on & evolve if necessary.

BTW..the day I pick her up I'm heading to Hershey. I hope to see some of you there!