[Supras] Whipping noise, throttle control, stock fuel piping

[berniek at technicaldevelop.com]

Jim: 

   
    Thanks again for writing back.  Since I'm not going over 18 PSI 
boost, I believe I'll leave the fuel system as-is, with the possible 
exception of adjusting the damper for minimum "hammer" in the fuel 
rail.  It is in the stock position now, and I will carefully count screw 
turns to restore it to stock position if need be. 


    The FPR is in good condition, with rock steady static fuel pressure 
set to 45 PSI (engine off).  I have a Schrader fitting in the rail which 
allows me to use a push-on temporary gauge.  At first I did have a gauge 
permanently installed, but realized that it would not last long without 
any damping.  45 PSI static and the stock Lex screw halfway out seems 
optimum, although I have not measured Vf.  Interestingly the TSRM states 
that static fuel pressure can span the range of about 36 to almost  60 
PSI if my memory is not too far gone.  If I ever have reason to replace 
the starter (not likely; rebuilt it with new contacts and contact 
plunger; brushes were OK), I'll get rid of the crazy fuel feed fitting 
at the crankcase. 


    Bernie


Jim Jobe wrote:
> I removed the FPD on my car but about the only original piece left
> on my fuel system is the fuel rail itself.  Others have drilled/enlarged
> the holes which you may look in to if you want to retain it.  You might
> look at the lines between the tank, filter, and hard line.  Seems to me
> one of those was a restriction too.
>
> Just to give you an example, we've made over 500rwhp with most
> of the above mods along with 550's, aeromotive afpr, and a walbro
> pump.
>
> Also, are you sure your fpr is working properly?  The diaphrams
> have been known to break down esp with higher pressures.
>
> On Tue, Feb 05, 2008 at 12:24:34PM -0500, berniek at technicaldevelop.com wrote:
>   
>> Jim:
>>
>> Thanks for the information.  I've understood that bad things happen if the
>> pulsation damper is removed, including unequal fuel delivery between
>> cylinders, presumably due to standing waves in the fuel rail at certain
>> speeds.  That is not surprising when considering similar situations
>> arising from water hammer in plumbing systems.
>>
>> The question is how to set the pulsation damper on the premise it is
>> retained.  At idle and slightly higher I can feel light hammering in the
>> (modified stock) FPR, apparently from effects of nearby injectors.
>>
>> When assembling the engine I was surprised by the restrictive size of some
>> of the fuel feed fittings.  Thankfully that is more easily rectified than
>> changing the fuel line from the rear of the car.
>>
>> Thanks
>>
>> Bernie
>>
>>
>>     
>>> The stock fuel line under the car is large enough, but
>>> there are other restrictions in the circuit such as the
>>> fuel pulsation dampener, FPR, and various other banjo
>>> fittings that can be opened up or eliminated.
>>>
>>> On Tue, Feb 05, 2008 at 02:36:41AM -0500, berniek at technicaldevelop.com
>>> wrote:
>>>       
>>>> Jim and group:
>>>>
>>>>
>>>>    In summary, I'm just beginning to see a very small amount of
>>>>    fuel mixture leaning at 18 PSI boost.  It could be the boost
>>>> extrapolation mapping of the stock ECU, but as you pass 350-375
>>>> flywheel HP (just a guess at this point) with low compression
>>>> ratio, fuel requirements start to climb to about 3/4 GPM or
>>>> slightly more if you run really rich.
>>>>
>>>>         
>
>
>