Fuel pressure

356 Porsche-related discussions and questions.
Post Reply
Message
Author
User avatar
Alex Goodhart
356 Fan
Posts: 212
Joined: Wed Apr 09, 2008 11:21 pm

Fuel pressure

#1 Post by Alex Goodhart » Tue Sep 11, 2018 5:08 pm

I do
Last edited by Alex Goodhart on Sat Oct 13, 2018 4:11 pm, edited 1 time in total.
 

Hugo Karasawa
356 Fan
Posts: 196
Joined: Fri Sep 09, 2016 10:40 pm

Re: Fuel pressure question for engineers t: Is setup raising

#2 Post by Hugo Karasawa » Tue Sep 11, 2018 5:33 pm

Why two pumps ?
One pump is enough.

Use a pressure gauge just before the carbs and you will know if you have the required pressure.

Alan Hall
356 Fan
Posts: 1046
Joined: Wed Mar 26, 2008 12:06 pm
Location: Orinda, CA

Re: Fuel pressure question for engineers t: Is setup raising

#3 Post by Alan Hall » Tue Sep 11, 2018 5:39 pm

At first look it does not seem to make much sense unless there is a check valve in the bypass line around the second pump. If there was a check valve, the second pump would increase the pressure, but in the event of a failure of the second pump the output of the first pump would go direct to the carbs through the bypass line. If no check valve it seems that the second pump is running but just dumping any increase in pressure back to the input of the pump via the bypass line.

Hugo Karasawa
356 Fan
Posts: 196
Joined: Fri Sep 09, 2016 10:40 pm

Re: Fuel pressure question for engineers t: Is setup raising

#4 Post by Hugo Karasawa » Tue Sep 11, 2018 5:43 pm

At what altitude are you using the engine ?
If they tuned the engine at sea level and you are at higher altitude you are running rich.

Martin Benade
356 Fan
Posts: 3588
Joined: Wed Nov 23, 2011 10:52 am
Location: Cleveland, Ohio

Re: Fuel pressure question for engineers t: Is setup raising

#5 Post by Martin Benade » Tue Sep 11, 2018 9:01 pm

Can you ask your mechanic how and why it is hooked up this way? I doubt if any of us have ever seen it done that way. One healthy pump should be more than adequate.

User avatar
Alex Goodhart
356 Fan
Posts: 212
Joined: Wed Apr 09, 2008 11:21 pm

Re: Fuel pressure

#6 Post by Alex Goodhart » Tue Sep 11, 2018 11:51 pm

I did
Last edited by Alex Goodhart on Sat Oct 13, 2018 4:12 pm, edited 1 time in total.
 

User avatar
Alex Goodhart
356 Fan
Posts: 212
Joined: Wed Apr 09, 2008 11:21 pm

setup raising

#7 Post by Alex Goodhart » Tue Sep 11, 2018 11:52 pm

Facet sent
Last edited by Alex Goodhart on Sat Oct 13, 2018 4:12 pm, edited 1 time in total.
 

User avatar
Thomas Sottile
356 Fan
Posts: 905
Joined: Wed Mar 26, 2008 3:02 pm
Location: Stamford CT
Contact:

Re: Fuel pressure question for engineers t: Is setup raising

#8 Post by Thomas Sottile » Wed Sep 12, 2018 12:24 pm

I would put back the mechanical pump. mine is been in the car and working for 32 years.

User avatar
Alex Goodhart
356 Fan
Posts: 212
Joined: Wed Apr 09, 2008 11:21 pm

Re: Fuel pressure question for engineers t: Is setup raising

#9 Post by Alex Goodhart » Wed Sep 12, 2018 2:55 pm

Thanks for all the suggestions.
 

User avatar
Wes Bender
356 Fan
Posts: 2267
Joined: Wed Aug 27, 2008 10:54 am
Location: Alpine AZ, Green Valley AZ

Re: Fuel pressure question for engineers t: Is setup raising

#10 Post by Wes Bender » Wed Sep 12, 2018 3:04 pm

I'm with Tom. Put the mechanical pump back on and then mount one electric pump up near the fuel petcock. The mechanical pump will do the job and you will have the electric pump to prime the carbs or act as a backup in case the mechanical pump quits.

Because those electric pumps are not positive displacement pumps, I don't see how they could increase the pressure much by hooking the two of them up in series..... Parallel would increase the potential volume, but I can't imagine needing it.
Some days it just isn’t worth the hassle of chewing through the restraints......

User avatar
Alex Goodhart
356 Fan
Posts: 212
Joined: Wed Apr 09, 2008 11:21 pm

Re: Fuel pressure

#11 Post by Alex Goodhart » Wed Sep 12, 2018 3:44 pm

The reliable mechanical fuel pump
Last edited by Alex Goodhart on Sat Oct 13, 2018 4:13 pm, edited 1 time in total.
 

Hugo Karasawa
356 Fan
Posts: 196
Joined: Fri Sep 09, 2016 10:40 pm

Re: Fuel pressure question for engineers t: Is setup raising

#12 Post by Hugo Karasawa » Wed Sep 12, 2018 6:01 pm

Ok, I understand what you want.
You should use a switch SPDT to chose one or the other pump , if one fails you switch to the other. And your actual connection should be changed to parallel connection. What I do not know is if you will need a check valve in each pump. Do not know if those pumps have a check valve.

Or follow Wes Bender suggestion.

User avatar
Alex Goodhart
356 Fan
Posts: 212
Joined: Wed Apr 09, 2008 11:21 pm

Re: Fuel pressure

#13 Post by Alex Goodhart » Thu Sep 13, 2018 3:05 am

I am
Last edited by Alex Goodhart on Sat Oct 13, 2018 4:13 pm, edited 1 time in total.
 

User avatar
Wes Bender
356 Fan
Posts: 2267
Joined: Wed Aug 27, 2008 10:54 am
Location: Alpine AZ, Green Valley AZ

Re: Fuel pressure question for engineers t: Is setup raising

#14 Post by Wes Bender » Thu Sep 13, 2018 12:13 pm

Understanding that you cannot use the mechanical pump, I would place the two electric pumps in series up near the fuel petcock. Use Hugo's suggestion of a STDP switch to control them. Either pump will pull/push fuel through the other. The reason for placing them near the tank is that pumps are better at pushing fuel than sucking fuel. The mechanical pump would have had built in check valves, so you might want to mount one check valve at the outlet of the second electric pump.

(Now I guess you've got far more info than you were seeking when you first asked.........)
Some days it just isn’t worth the hassle of chewing through the restraints......

User avatar
Alex Goodhart
356 Fan
Posts: 212
Joined: Wed Apr 09, 2008 11:21 pm

Re: Fuel pressure question for engineers t: Is setup raising

#15 Post by Alex Goodhart » Thu Sep 13, 2018 3:41 pm

Thanks for the ideas, pumps are already mounded under the tank in a good location. I have ordered the check valve . The only question now is how to do the electrical wiring to a switch neatly. I have to pull the floor board to see how it was wired. Looks like each pump is on its own circuit but not sure. The fuel regulator will mount in the back near the transmission and bolt to the place were the flexible hangers are that support lines.
 

Post Reply