superloaf

So apparently Bosch discontinued the fuel pressure damper in 9/17 so they are very difficult to find now. Many sites still list them for sale and then after i order, they take 2 days to tell me they are out of stock.

Anyway, being the impatient person that i am, i routed the fuel line directly into the fuel rail and deleted the damper. I've read a bunch of opinions on this but nothing definitive.

So, just wondering about those who have run without a damper on a street car and any problems or success you might have had. I plan to install a damper when i can find one but I am about to embark on a drive from Nashville to LA so I don't want do that if i'm going to kill my fuel pump or regulator.

It sure is a neater install than using the damper and the short line and much less fuel line to fail or leak.

Thanks.

Humboldtgrin

I highly recommend a LR billet fuel rail kit with an adjustable FPR and the dampener as well as the aftermarket fuel lines. I have had two stock fuel rails leak at the mounting tabs and I felt it’s just not worth loosing my car to a fire. I also picked up an 89 944 auto many moons ago that’s i got for cheap due to the fuel lines failing. Just go with aftermarket on this one. 30+ year old parts and design just isn’t as good as today’s available replacement parts from our vendors. It’s one of the first items I recommend replacing every time if you don’t have new or upgraded parts already installed. Yes it’s pricey but so is loosing your car and watching it burn.

H.F.B.

I never run my engine without the fuel pressure damper. So here no real experience. But basically the Porsche engineers installed on their engines only things, that were technically essential. As a result of the sequential fuel injection principle in the Porsche 968 and the low pulsations in the ring line, a pressure damper had been eliminated. In the case of the 944 "batch fire" system, this generates much bigger pulsations so the damper is needed for a constant fuel flow to the injectors. The damper acts also as a sort of accumulator. So when you slam the throttle open, without the damper the fuel rail pressure regulator won't keep up with the manifold pressure changes and can’t keep the required fuel pressure. So your engine could run lean under acceleration.

Tom M'Guinn

You might also get some fuel line "hammering" -- i.e., a knocking sound from under the car...

Droops83

This is 100% spot on.

Here is a another take on the subject from an aftermarket (perhaps advertising-driven) perspective, but from a source that I respect and trust:

https://www.hpacademy.com/blog/tech-...m-engineering/

The bottom line is that your engine will run OK without the pulsation damper, but I wouldn't trust it if you have any kind of aggressive tune, or plan to drive in any other conditions than low-load cruise!

superloaf

Fuel lines were long ago switched to braided SS. In fact I'm on my second set which is what caused my damper to fail; I lightly clamped it in the vise to tighten the short line and I guess I damaged the seam where the two halves join.
One thing no one mentions when switching to aftermarket lines is that they are not a permanent solution. The manufacturers of these lines say their lifespan is about 5-7 years with fuel. Also, unless your using Teflon PTFE, the rubber in SS lines will weep and smell like gas, right from the start. I've been told this is not a fire hazard but I'm honestly not sure about that. If I had to do it again, I would use metric adaptors to switch to -6 AN and use PTFE hoses. I still might switch just for peace of mind and losing the gas smell. The smell is usually only apparent when bending down and sniffing right near the hose.

Thanks for the HP Academy link, I love those guys! And some strong evidence for not running without a damper.

So, the part is NLA and no one has it in stock even when their website says they do. Really annoying how i keep having this problem with certain sellers, (I'm talking to you, Pelican!)

But the 928 damper is still available, i think. Never know until actually oredering but it appears that it is. It looks the same except for dual fuel outlets. I imagine using this with a cap on one of the outlets would be the same? Anyone have other ideas? From what i've read, most dampers are not application specific other than the attachment points. I'm sure a major difference in working fuel pressure could cause problems. Does anyone know the 928's fuel pressure? Is it the same as our cars?

Hmmm, just now reading about the 928 fuel system and it is quite different than our's. There a fuel cooler! Seems like that would benefit a turbo engine. And the regulator seems to limit pressure on the way into the injectors rather than at the return line as our cars do. Not sure if any of this matters. And the 928 has 2 dampers so again, not sure if this matters.

Anyone out there with fluid dynamic experience? I don't know what to do here. Adapt the 928 damper or go with a used 944 damper.....

V2Rocket

go to your local auto parts store and try to order one.
they have a parallel supply chain...

Tom M'Guinn

Lart must have used ones by the dozen, no? Not sure which 928 damper you are looking at, but be aware that the 928 used the CIS injection system for years, so I'm guessing those dampers are very different.

Droops83

To your point about the aftermarket SS fuel lines, I agree. I simply replace the factory fuel hoses with high-quality rubber hose every few years, reinstall the factory heat sleeves, and all is well. They can easily be re-inspected every time the hood is opened.

As for the 951-specific damper, I second Tom's advice to contact Lart to see if he has a good used one. The damper can be bench-tested by applying a hand vacuum pump and checking if it holds vacuum. That way you will have a functional damper while you research a permanent aftermarket/NOS solution.

Voith

I you don't find it I have few but am on vacation till 1st.

Humboldtgrin

Dave951

Wow, nothing like a 4X+ price inflation for the OEM units vs. what these things used to cost.

Alex89

So did you just cut the collars off the original crimped lines and use fuel-injection hose clamps now? And what pressure rating does the hose need to be? I'm also not sold on cutting the original hard line and using compression fittings, its just another point to leak.

Dave951

Aeroquip FCV04 and FCN06 are often used which are rated for 250psi.

Long ago Rennbay used to make the style that didn't not require the hard line fittings but I think there was some issue with a track car blowing off the line, fire..etc and they switched to selling only the compression fitting style.

Droops83

Yes, cut the crimps and use high-quality fuel injection hose of the type used by OE German carmakers. The factory 8x13MM BMW hose is best for the 8MM ID return hose, while the larger feed hose is 9 or 10MM ID. Use screw-type hose clamps such as these and you will be fine:


I don't understand the issue of a 944 "track car" having the fuel hose "blow off." A track car is not going to be running much higher fuel pressures than a street car if at all, nor should the engine move enough to cause such an issue, so it must have been either an installation issue or inferior quality of the hose and/or clamps. There are millions of cars on the road that use fuel injection-rated hose and hose clamps in the engine compartment from the factory. The key is proper maintenance at reasonable intervals and installation of quality replacement parts.

I am not bashing the idea of stainless braided fuel hoses, but like brake hoses of the same, the rubber portion cannot be inspected without disassembly. I replace stainless hoses after 5-6 years as a preventative measure. I work at a Porsche/BMW shop, so it is super cheap and easy to replace my 951's engine compartment fuel hoses and clamps every few years with high-quality parts.