Fuel System Damper, why not? Options

[yarin]

I couldn't find that much info on here.... Pelican lists a damper in the FI system.

http://www.pelicanparts.com/914/Parts/Fuel...system1_big.htm

Which years and which systems include this? Why leave it out?

I'm building a MS system, do i need a damper in the system? Thanks

[ClayPerrine]

I have worked on 914s for 20 years, and I have yet to see a fuel system damper. It may be a VW diagram that is reused for a 914.


Cap'n, you have any input on this???

[TimT]

if you are batch firing the injectors a damper is supposed to help out, dont think you need it with sequential.

Dampers

My 911 is batch fired EFI, and I have no damper plumbed in that system, and it seems to run fine, which makes me wonder if they are really needed

[Cap'n Krusty]

That's a VW Type 3 diagram, which MOSTLY applies to the T4/914 engines. The Cap'n

[ClayPerrine]

Thanks Cap'n.


You have just confirmed that my memory is not completely gone........

[lapuwali]

From personal experience, if you omit the damper on the Type 3, you get a whining noise just after startup. I've noticed no other effects from removing that damper (redid all the fuel lines, and didn't want yet another pair of connections).

[wwhalenc]

Looks to be the same as the "accumulator" used a la VW CIS cars to help maintain the fuel system pressurization. Might help for starting??

[lapuwali]

QUOTE (wwhalenc @ Feb 6 2006, 03:14 PM)

Looks to be the same as the "accumulator" used a la VW CIS cars to help maintain the fuel system pressurization. Might help for starting??

Nope, it's not an accumulator. No check valve on the damper. CIS needs 100psi of fuel pressure to operate, and it takes the fuel pump a bit of time to work up that pressure from zero w/o an accumulator. D-Jet (which the Type 3 also uses) only uses 29psi, and 1-2 secs of fuel pump operation on key on is enough to generate that pressure. The VW system mounts all of the relays under the dash, so you go key on, click, fuel pump whirrs, click, fuel pump goes off, twist key to start, vroom. The 914 also does all of this, but you can't hear it as clearly as the relays (and often the fuel pump) are mounted in the engine bay.

[wwhalenc]

So it's just helping maintain a stable pressure behind the injectors...so there's not a pressure drop for a long duration/high volume injector squirt? I guess that'd be somewhat consistent with TimT's statement

[lapuwali]

QUOTE (wwhalenc @ Feb 6 2006, 04:04 PM)

So it's just helping maintain a stable pressure behind the injectors...so there's not a pressure drop for a long duration/high volume injector squirt? I guess that'd be somewhat consistent with TimT's statement

Honestly, I think it's there only to prevent the odd resonant noise the system makes. Most EFI systems get away w/o a damper and are otherwise very similar to D-Jet in operation, esp. wrt possible pulsations in the fuel system caused by the injectors operating. Remember that D-Jet was the very first production EFI system available, so they were still learning how to make it all work. The 914 version of the D-Jet doesn't have the damper. The two L-Jet systems I've worked on didn't have one, either.

The damper was also up by the fuel pump in the nose of the car, not back by the fuel rails, and with all of the rubber lines involved in the Type 3 injection system, I'd say they would provide as much damping as you'd need for reducing any pulses in the fuel lines caused by the injectors.

Note, btw, that the noise goes away by the time the injectors are running. It's only there while the injectors are NOT running and the pump is operating. It's just as likely it's some characteristic of the pump.

MAYBE if you're running EFI with lots and lots of hard line running fuel, you'd see some benefit from such a damper. On a 914 with a stock or near stock system, it's clearly not needed.

[Air_Cooled_Nut]

QUOTE (lapuwali @ Feb 6 2006, 01:00 PM)

From personal experience, if you omit the damper on the Type 3, you get a whining noise just after startup. I've noticed no other effects from removing that damper (redid all the fuel lines, and didn't want yet another pair of connections).

There was a discussion about the fuel damper on the T3 email list (400+ members worldwide) and nobody noticed a single difference with/without it. No power loss/gain, no mileage loss/gain, and nobody mentioned anything about noise differences.

I had one on my late model automatic T3 and took it off. Saw/heard/felt no differences whatsoever. It's a real stumper because not all vehicles got them. ???

Take it off. If you suddenly feel/hear a difference then put it back on. You won't damage anything.

[Twystd1]

Cut and pasted from the net. Cause I don't know shit bout this.

1:
Whenever multiple high-flow injectors are installed on a fuel rail, hydraulic pulsations from the injectors opening and closing cause the fuel to “hammer” back and forth. This creates pressure and flow variations within the rail and can lead to large inconsistencies in fuel delivery from cylinder to cylinder. A damper is used to absorb these pressure fluctuations and allow each injector to receive the proper amount of fuel pressure and flow, eliminating rich or lean cylinders, etc.

2: NOTE: Some factory cars have fuel dampers from the factory. Toyota, Nissan, Mazda RX-7 etc.

3: Dampers are placed specific to each combination. Some are a simple diaphragm located after the in tank fuel pump and before the fuel filter. Some are at the fuel rail. It depends on the specific application.

4: According to a couple of ricer guys. Several BIG Racers (eech) use large dampers at the end of their fuel rails.

5: Some dampers are spring loaded to help dampen. Some are simple cannisters with a foam interior. And some are air cushioned.

Thats all I know from Google.

Obviously they have some use. As so many factory cars have them.

Twystd1

Note: If any of this data is incorrect. Blame it on Slits.. Just because...

[lapuwali]

The two Mazda RX-7s I had (both with EFI) didn't have dampers on them. I can't remember if the only Nissan I owned had a damper or not. The Mazda Miata I had DID have a damper on the rail.

Putting them on the ends of the fuel rails I can see as maybe being useful. The idea is that the pressure in the rail will fluctuate substantially as each injector opens and closes. This could cause some surging in the rail that may affect fuel mixtures from injector to injector and injection event to injection event. It would likely be more useful if you were running BIG injectors, as the pressure changes will be more substantial. Drag guys, who not only run giant injectors, but also tune their engines to within a squeak of blowing up, very likely may see a difference with dampers on the rails.

There are also stories about people claiming to see differences between having a fuel rail fed at one end v. having it fed in the center (esp. true on inline fours or sixes). No hard data, just stories. Also, no evidence that the pressure variations seen in the rails actually made any difference to how the engine ran.

None of this makes any difference on a 914, or a Type 3, since they have so much rubber in the fuel system, and they run at fairly low pressure to start with.