fuel pressure dampeners

[Monkey Wrench]

I have an early 85, but it may also apply to the S2..
The fuel pressure dampener is a very expensive part and I'm wondering why it is needed or if an aftermarket one may help people that do not really want to spend something like 700 to $1000 for one.

I assume it is a piston with a spring behind it to dampen the vibrations in the fuel system. why the vibrations? are they from the pump or injectors? what happens if one is simply plugged off? why does my Porsche need one?, many cars do not from my understanding. is this correct?
this page points to an aftermarket in line fuel pressure dampener, as an example, maybe there are others.

I noted that the fuel pressure rating may be higher than the porsche, is it about 30 PSI?
=================
fuel pressure requirements:
- FPD-R base pressure requirement = 40 - 70psi (static)
- FPD-XR base pressure requirement = 40 - 120psi (static)
Base pressure is the fuel pressure measured when the fuel pump is running WITHOUT a vacuum line connected to the regulator.
=================

If one is needed at all , how would it work if the FPR is located ont he fuel line and not on the fuel rail? will it run as well like that?

https://subiesupplyco.ca/products/radium-engineering-fuel-rail-in-line-pulse-damper-6an

here is another one , its only about 50 bucks.
https://www.moreheadspeedworks.com/product/radium-fuel-pulse-damper-oem-style/

or this one
https://www.efihardware.com/products/3439/8-orb-fuel-pulsation-dampener

here is one that might mount on the fuel rail
https://www.gpsbrand.com/en/products/fuel-injection/fuel-injection-components/fuel-damper-assembly

my thinking is that the OEM part must be a bit scarce , hence the extremely high price, and it seems like going to a different brand of one might save considerable cost, perhaps without affecting performance adversely?
I did find a post on another forum about the subject and it may have been discussed here.

https://rennlist.com/forums/924-931-944-951-968-forum/1185250-944-na-cheap-options-for-replacing-fuel-pressure-damper.html

I tried to link to one from Pelican as a reference. It is nice to support this site because we enjoy the forum, but I don't see it in the listing, the page loads funny and I can enter a somewhat limited list of 944 parts fuel filters etc, but I'm not seeing a valid search option.

It may be possible for Pelican to carry aftermarket replacements and perhaps this is the case and I may just not be finding them. Its my understanding that parts are not shipped to Canada which means the only way I can see getting one is if I am able to establish a cross border account to forward my purchase to me

[walfreyydo]

A lot of people run aftermarket FPR's (which can be adjusted and set to a specific pressure). They would likely not be plug and play (requiring custom lines and mounting) and many folks mount them on the firewall. Fairly straightforward and a good reason to upgrade lines to AN or similar.

Here is an example from https://www.deancent.com/porsche-944-fuel-line-build-and-install/



Dampeners I am less sure of, but I think there are aftermarket options out there. Ive also read (but not confirmed myself) that you dont need a dampener. Further research would be warranted on both points, so take that with a grain of salt.

[Monkey Wrench]

I did note a comment o that other forum that said it can be removed and that the result is a bit more noise, and that the dampener might supply a bit more fuel when you hit the throttle because it is basically working a bit like a pressure accumulator, perhaps filling in a microsecond of lower pressure. Weather or not that holds true, or was just someone's theory I can't say for sure.

and sorry above I made a typo and was trying to refer to t he dampener and said FPR
I like that the one on the firewall has a gauge so you can monitor.

perhaps the gauge is a weak point and might rupture, I wondered about adding a petcock so you can read the gauge, otherwise might as well close it off and then if it fails it's not catastrophic. obviously no need for reading the gauge when normally driving, especially in that location.

I think my main concern was that of cost, if some can save 1K on this little part , that's a significant difference for some, perhaps with no real noticeable change in performance. Reliability of the part is another thing.

The Dampener was mentioned in the previous thread but that's an S2 and he seems to be throwing lots of OEM parts into it and the car is pristine enough for him to likely want to keep all OEM.

[djnolan]

Can you convert to a late N/A setup? There was a vendor at Hershey Porsche Swap Meet that had a crate full of old fuel rails complete with injectors and regulators. Selling them for around $50.

Also these parts can last forever, look for a used one:
check https://plyhammersparts.com/ or Just Joshin Porsche https://www.facebook.com/used944parts/ parts for a used one.

[Jfrahm]

Sequential injection reduces the need for a damper since the amount of fuel released in one go is reduced.
I suppose an aftermarket regulator with the return line capped plumbed into the system would also work just fine as a damper. It'd just be a spring-loaded fuel reservoir.

[v2rocket_aka944]

the dampener functions like a water hammer arrestor in household plumbing.
fuel rail pressure fluctuates and spikes with every opening of the injectors.

can make a little difference to engine running but does make a bit of noise too.

FWIW i engine-swapped my car (not Porsche) and run batch injection and no dampener. it runs fine but the injector noise is noticeable.

this is a lower-cost option for replacement...
https://adaptmotorsport.com/products/classic-porsche-fuel-pressure-damper-944-944-turbo

[wwdwgs]

Originally Posted by v2rocket_aka944

this is a lower-cost option for replacement...
https://adaptmotorsport.com/products/classic-porsche-fuel-pressure-damper-944-944-turbo

It's also made by Bosch. Do you think, that any fuel pressure dampeners for any gasoline 4-cyl FI engines from late 70's, 80's and 90's could fit, given the fittings are the same and physical dims are similar?

[Monkey Wrench]

they will contain a spring and piston which is basically in equilibrium with fuel pressure. as pressure increases the volume increases and as pressure reduces the spring causes the volume to reduce, thus equalizing the pressure fluctuations.

Plumbing isn't too difficult to convert but the one you chose would need to be within spec for the fuel pressure of your vehicle. I think the 944 will have some differences depending on version and engine design.

the weight of the spring and the size of the piston are matched to the fuel presure your car runs. If the spring were too strong it would never move and it would do nothing. If the sppring were too weak then the spring could compress to it's limit and there would be no movement so that wouldn't work.
there may be adjustment , basically a bolt to adjust spring tension.
I think you can just look up your fuel pressure and set it or buy one that is within that spec in terms of bar or PSI rating.


rubber hoses may have some effect if they have elasticity, where as a hard line has very little ability to change in volume. I'm not too sure if the wire reinforced hoses used for pressurized fuel in the Porsche help equalize pressure fluctuations or to what extent.

it does not change overall pressure, it is acting very quickly and keeping the pressure equal , these are very short pulsations.

water hammer is when you have a volume of fluid and stop and start it abruptly . the mass ( weight) of water in a line is considerable so if you can stop it suddenly this inertia causes the plumbing to move and stress, perhaps break from fatigue. the device to stop water hammer can be a similar sort of thing with spring pressure or if you simply just plumb in an upright column that is capped off, what happens is that traps air and the trapped air acts as a spring.



If you picture an air compressor line,a short one will not cancel vibrations from the compressor head much, If the line is longer , lets say it is 200 feet of rubber hose, its basically an expandable pressure tank in itself, which is long and narrow, If you view it as such.

a pressure accumulator is sort of related, you can have a similar thing but with a large enough volume and more movement and that can store and supply pressure..

someone with a well and pump will often have a pressurized tank, sometimes with a bladder , that so that the pump can stop and have a rest. the larger it is the more time the pump has between charging cycles. similar idea but much larger in size.

the pump doesn't; actually create pressure, not without restriction. Nor does the dampener. the regulator applies restriction and that's where the pressure is set. Unused fuel is sent back to the fuel tank. that's not a high pressure line as there is no considerable restriction to it's flow.

in absence of the dampener, what is happening is there is vibration in the line, which is a very fast pressure fluctuation. since the line is a closed vessel it will cause fluid vibration all the way back to the pump. It is likely possible to relocate the damper after the pump and under the car. I doubt the location would make a lot of difference.

between the pump and the hard line there is a rubber line, this helps isolate physical vibrations from the pump itself from shaking the line physically. it would probably vibrate the outside of the line if it were a solid piping connection and that may also cause noise.

where there is this sort of vibration there is also fatigue so perhaps we'd possibly see a failure caused by vibration causing metal fatigue if the lines are caused to vibrate excessively over a long period of time.

the engine vibrates and also twists with torque so the lines need to be able to allow that movement without fatigue or a rupture could result.

if the dampener were located prior to the pump , there is no pressure there either and it would not help.

[v2rocket_aka944]

Originally Posted by wwdwgs

It's also made by Bosch. Do you think, that any fuel pressure dampeners for any gasoline 4-cyl FI engines from late 70's, 80's and 90's could fit, given the fittings are the same and physical dims are similar?

I looked for a while years ago to find such an interchangeable beast but did not succeed.

Plenty of Bosch EFI stuff in the 70s-90s didn’t use a damper, but had batch fire (Volvo, bmw, etc).

And plenty of cars with sequential injection still use a damper for noise reduction.

You could make any of those work with a custom housing. The Bosch unit in that part I linked to is from GM trucks and maybe the early C5 Corvette, I think.

[Bulldog9]

Originally Posted by djnolan

Can you convert to a late N/A setup? There was a vendor at Hershey Porsche Swap Meet that had a crate full of old fuel rails complete with injectors and regulators. Selling them for around $50.

Also these parts can last forever, look for a used one:
check https://plyhammersparts.com/ or Just Joshin Porsche https://www.facebook.com/used944parts/ parts for a used one.

Can't wait to be back on the East Coast and get back to Hershey. 2025!

[Bulldog9]

Originally Posted by v2rocket_aka944

the dampener functions like a water hammer arrestor in household plumbing.
fuel rail pressure fluctuates and spikes with every opening of the injectors.

can make a little difference to engine running but does make a bit of noise too.

FWIW i engine-swapped my car (not Porsche) and run batch injection and no dampener. it runs fine but the injector noise is noticeable.

this is a lower-cost option for replacement...
https://adaptmotorsport.com/products/classic-porsche-fuel-pressure-damper-944-944-turbo

The Damper works to keep fuel pressure across the injectors consistent and absorbs the pulsing from injectors opening and closing. What I don't understand is why Porsche saw fit to attach a vacuum hose and apply vacuum when in 'theory' a springed expansion chamber (which is all it really is) should work.

After sitting for 10 years, my FPD leaks gas, creates hard starts, has strong gas fumes and occasionally gas in the vacuum line. I did a thorough search. Most Porsche dealers have them in stock and some shopping around brings decent (relative) pricing. I found mine for $503 delivered. The only other I found was from Auto Atlanta who offer an aftermarket unit in the $300 range. I'm trying to keep my 44K mile survivor as OEM and stock as possible. Thankfully, the FPR is good, but I am going to source one for when it fails.

****UPDATE: With the FPD being replaced, the FPR also failed and after one drive was pumping gas through the vacuum port. I have one on order from 944 Online.

[Monkey Wrench]

this page explains a lot about what we are discussing , it also mentions a type that is connected to vacuum, I count' take the annoying music in the video so I bypassed that.

"The smaller FPD-R is a compact version designed to fit into tight spaces. The only compromise being that it is calibrated for use with 40 to 70 psi base (static) fuel pressure only. If your base fuel pressure is higher than 70 psi, then the larger FPD-XR should be used, which permits base pressures between 40 and 120 psi."

https://www.radiumauto.com/Blog/Post/Radium-Fuel-Pulse-Dampers-90


this page has a list of the fuel pressure of various cars, but omits the early 944 like mine, it looks like the 88 mazdas might be approximately compatible so far ads fuel rail pressure for example but you can see which cars of the era are out of comparable range.
https://www.laspositascollege.edu/auto/assets/resources/Fuel_Pressure_Specifications.pdf




- it doesn't cover the earlier 944 and mine is early 88


here it says 29 PSI
https://www.pca.org/tech/1984-944-fuel-pressure-1225047536

"With the relay jumped the fuel pump should start. With the engine stopped and relay jumped you should have 2.5 bar of pressure +/- 0.2 bar on all 8-valve 944 and 944 turbo motors (red arrow); 16-valve motors should have 3.8 bar +/- 0.2 bar (yellow arrow). "

( 2.5 bar is 36 PSI)
- https://www.pelicanparts.com/techarticles/Porsche_944_Turbo/04-FUEL-Fuel_System_Pressure_Tests/04-FUEL-Fuel_System_%20Pressure_Tests.htm

https://www.pelicanparts.com/techarticles/Porsche_944_Turbo/04-FUEL-Fuel_System_Pressure_Tests/04-FUEL-Fuel_System_%20Pressure_Tests.htm


The problem as I see it is that the 8 valve porsche 944 has a lower than 40 PSI fuel pressure rating which is below the spec. Therefore I'm thinking the spring might be too strong to work properly ? for the S2's with 2.5 Bar, they may work


It seems like there are a lot of them and it might take more research to find out which other ones are designed for compatible fuel pressure, but maybe one suited to a mazda of about the same age would work fine. a lot of the parts sources are showing them in the $50-$100 dollar range and not crazy prices like $500 to $1000 like the Porsche.

The pressure can vary a lot from one engine to the next so it might be important to make sure the fuel pressure of any substitute is within range. also there are some terms I dont fully understand well in there , deadhead pressure, residual pressure, rest pressure, pressure at idle..

if people can run their cars without the thing but hear noise, I dont think it would be damaging to try to substitute some other brand and see if it's effective, but care must be taken to make sure any replacement is within the correct pressure range otherwise it's just not going to work out right.

[Monkey Wrench]

Originally Posted by walfreyydo

A lot of people run aftermarket FPR's (which can be adjusted and set to a specific pressure). They would likely not be plug and play (requiring custom lines and mounting) and many folks mount them on the firewall. Fairly straightforward and a good reason to upgrade lines to AN or similar.

Here is an example from https://www.deancent.com/porsche-944-fuel-line-build-and-install/



Dampeners I am less sure of, but I think there are aftermarket options out there. Ive also read (but not confirmed myself) that you dont need a dampener. Further research would be warranted on both points, so take that with a grain of salt.

I followed the link to the fuel pressure regulator from that page, it went here:
https://www.amazon.ca/dp/B000CFQNWW?tag=deancent02-20&geniuslink=true

- on that page it says Base pressure adjustable from 40-75 PSI.

for the 16 Valve motors , it should be
3.8 bar, that's 55 PSI so it would be within range if it is an S2

I'm questioning if it is within a suitable range for the 8 valve 944 because it is lower than 40 PSI..

the parts list might be very handy, I'm thinking of just trying to obtain all the fittings I need or my early 85 944 and just convert it to this style of fittings. but dont want to end up buying a whole bunch of wrong parts. Many will be the same, some differences..

Im wondering if some of the FPR's incoporate the dampener, it stands to reason they may be built into a combined unit.