Koenig-Specials 928

I'm running without the in-tank and a Bosch 044 pump. Last week I drove to Key West from Orlando (460 miles) but went through downtown Miami traffic in high 80s temp and A/C. I experienced no problems. I refilled once at 1/3 tank. Car was also driven to Florida from Canada (1200 miles)

I've been running with this setup for about 5 years now.

jcorenman

The 044 pumps more fuel, which means more pressure drop on the inlet side, and lower pressures within the pump. I am pretty sure that the "noise" from a noisy fuel-pump is cavitation within the actual pump itself, right at the inlet side of the rollers.

That's the point of lowest pressure, and bubbles of fuel-vapor form and then collapse, making noise. The bubbles are unstable because the pump can't pump vapor, so as bubbles form the flow drops, and reduced flow means higher inlet pressure which collapses bubbles. The same effect is what eats boat props.

The solution is a liquid with a higher vapor pressure (see Greg's post above) or maintaining a higher inlet pressure at the main pump-- in other words, force-feed the main pump.

Sure, worked fine even over the 11,000 foot pass.

That's the difference between what engineers do, and what many folks here do. I don't mean that unkindly, it's just a different mindset. Porsche (at least when engineers made the decisions) wants all of the cars to work all the time for everyone, no matter what the situation. That requires a "worst-case" design, with a margin for the unexpected. Some people call this "over-engineering", and for most situations it is fine to cut corners. But a large part of what attracts us all to these cars is the very thing we seem willing to compromise-- their ability to perform flawlessly in a wide variety of situations and last darn near forever doing it.

What Porsche did not anticipate was the "amazing" things that have been added to fuel. And because the engineers apparently no longer make the decisions at Porsche, they didn't make any changes.

The single downside to the in-tank pump is the stupid little molded hose, still made of old-school rubber that gets eaten by the ethanol in modern fuel blends. But that's easily fixed, a 27mm-long piece of Greg's cosmic fuel hose and done. The turbine pump itself seems to last a very long time, so replacing the connector hose makes a lot of sense.



(Yes, that's a new pump from late last year before the price-raise, but machined rather than cast-- which explains a lot of the new higher price).

SteveG

I think I understand Porsche's reasoning and why, and I appreciate people taking the time to explain one of the less sophisticated but puzzling mysteries of this car. Thank you Greg, Fred, Jim et al. But bottom line for me -- When I hear a loud whoooosh at the gas cap, is that air going in or out? and should I be concerned about it? I have had a noisy pump at 1/4 (and then bought a spare in-tank) and know not to do that.

FredR

Steve,

If you are hearing a "whoosh" when opening the fuel filler cap I rather suspect that will be internal pressure in the fuel tank and if so suggest you check that the breather valve on the front of the engine is operating correctly. I dare say there will be a thread on this somewhere.

Rgds

Fred

jtrygstad

Now I am curious. I just put a new "057" on mine sans the in-tank pump which the PO removed.

What is the difference between 057 and 044?

jcorenman

The Bosch "057" (0 580 464 057) is the stock pump for '89-95 cars. It was intended for use with the in-tank pump but should work OK with all the caveats above.
The Bosch 0 580 464 045 for '83-88 would be a better choice without the in-tank pump, as Greg mentioned above it is designed to suck.

The Bosch "044" (0 580 254 044) is a Bosch Motorsports pump, same case size but different inlet, pumps more fuel and needs more amps. It is commonly fitted for modified motors (strokers, boosted) but is not useful for stock motors.

the flyin' scotsman

Fantastic statement Jim..........there is no substitute

dfrhodes

is it possible to repurpose a smog pump as an internal fuel pump?

i'm assuming that since the air pump has similar flow to a stage 3 murf, it might also work well for fuel

jtrygstad

Thanks Jim for the differences in pumps info.

hacker-pschorr

The first time I heard anyone talking about an 044 pump making odd noises were Tim Murphy and Turbo Todd with their supercharged cars. In their case it was cavitation, but only in the higher end of the power range.

With regards to the 044 pump this is not necessarily the best answer.

One solution that's been around for a few years:
https://rennlist.com/forums/928-foru...ml#post8516374
https://rennlist.com/forums/928-foru...iner-kits.html

Todd did a lot of research and was a bit surprised to find out the specifications for the 044 pump call for a specific inlet / outlet size from the tank and the 928 is too small. He was surprised because we could not find where anyone had ever attempted to address this with the 928. When he shared this information with me I went to work with him designing the above pieces and while Tim Murphy handled the production and distribution.


Some claim running a pre-pump to an 044 will actually restrict the flow. Fuel pressure will be just fine but the pump will not be able to offer the correct volume of fuel.
For the VW / Audi setups where removing the in-take pump is not as easy as our cars, they offer a surge tank for the stock pump to fill which will keep the 044 properly fed:
http://store.034motorsport.com/fully...urge-tank.html


In my opinion, the in-take pump is too unreliable and until someone comes up with a real solution I'll never run one in my 928's.
I agree the stock dual pump setup has benefits and I would absolutely keep my 87 with that configuration if I had any confidence in that system not prematurely fail.
Since I plan to supercharge my 87 some day, I'm preemptively installing an 044 pump with the above adapter and a relayed power source using the stock wires as a trigger.

Honestly, even if I were keeping my 87 stock I would still upgrade to the 044 configuration. It has been proven to work and I have no doubts about the reliability.


As for the stock wiring, the harness for the fuel pump in my 81 had the connections for a second, in-tank pump. They both shared the same wires running to the fuel pump relay. Does anyone know offhand if the 87+ cars are the same way or do they have separate wires for each pump? If they are the same, curious to test if the dual stock setup draws more / less / about the same as a single 044. My gut tells me the 044 will be greater, just general curiosity.......

jcorenman

Interesting. The fuel flow (and associated pressure drops) should have been constant, independent of horsepower, as long as the pump can keep up with demand. How much horsepower?

Certainly the stock strainer and inlet hose is not adequate-- it doesn't even fit, the 044 has a M18 threaded inlet. When you change one component then you need to consider the other components in the system. There is no argument that a larger strainer is a good solution, and I think keeping the intank pump is also a good solution-- it accomplishes the same thing for the 044 that it does for the stock pump. My personal preference is for the in-tank pump because of the marginal vapor pressure-- I think maintaining positive pressure is better than trying to minimize negative pressure, but that does involve another moving part. It's a choice, not a religion.

That's nonsense. Have you ever flow-tested an in-tank pump? It's scary (at least with gasoline), even with a couple feet of head.

Have there been any failures other than the stupid rubber hose? That's an honest question, everything I've heard or read about is about pumps getting tossed because the hose is broken. Our GT has 250K miles, the last 100k are ours. The PO had an intank pump failure, stock rubber hose. We had the same thing two years later, stock rubber hose. Our 88 S4 has NO in-tank pump and left me stranded in Seattle traffic (toasted main-pump brushes). Small sample.

Look, if posting alternate solutions here is a problem, then I'll delete my post and refrain in the future. This thread started with an obituary for the in-tank pump, the only points I was trying to make were (a) it does serve a useful purpose, and (b) is easily made reliable.

The '044 is a side-discussion, as are the fueling requirements for high-horsepower engines. Hopefully it is obvious that if you drop in a stroker or bolt on a supercharger, then you need to take a look at everything that is connected: Fuel delivery, tuning, clutch, brakes, tire budget, etc. The 044 does draw more current, and most folks fit a separate relay whatever is connected to the inlet.

Randy V

Yes, you should be concerned about this condition.

That sound of air indicates the gas tank vent line is clogged or kinked, resulting in a vacuum condition within the tank.

This common condition results in the plastic tank imploding under vacuum.

Another indication of an imploded tank is revealed when filling the tank at the gas station and it never takes 18+ gallons to fill from an empty state.

Rectify this condition immediately. Search here for 'imploded gas tank' for many threads discussing the condition.

The Forgotten On

I think they just killed their stock of pumps entirely. Have you seen the price for one on Porsche Classic
http://www.classicshop.porsche.com/p...060811300.html

Petza914

So what are the part #s for both the in-tank fuel pump and main fuel pump for my On my '79 K-Jet 5-speed I'm running the OEM setup with the dual fuel pumps (one in the tank) even though I have one of Carl's Stage 2 Supercharger Kits. AFR is exactly where he wants it under all conditions, including full boost. Living in SC where it can get hot in the summer and taking this car on some longer drives, I'm a bit concerned about eliminating the in-tank pump. I experienced fuel vapor lock in the summer in my 914 before relocating the fuel pump to the front of the car near the tank so don't want to create the possibility for that to occur again on my 928.

So what are the part #s for both the in-tank fuel pump and main fuel pump for my car? Is a 928.608.013.00 the right # for the in-tank pump as I can still find one of these around $440. If I wanted to keep a spare set of pumps, should I buy a new in-tank pump before they're all gone and what pump should I pair with that for the main pump, an 044 or something else? Is this the right # for an 044 pump (0.580.254.044)?

Thanks for the help.

soontobered84

Jim,
My GTS did actually have an internal pump that had seized. The external pump was giving all she had to suck fuel around the seized components of the internal pump. I replaced it with a strainer and haven't had any apparent issues.