Show full size 924Board.org
Discussion Forum of 924.org
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 Technical FAQ924 FAQ (Technical)   Technical924 Technical Section   Jump to 924.org924.org   Jump to PCA 924 Registry924 Registry

fuel pump

 
Post new topic   Reply to topic    924Board.org Forum Index -> 931 Tech.
View previous topic :: View next topic  
Author Message
Matias  
Guest





PostPosted: Wed Feb 06, 2002 10:59 am    Post subject: Reply with quote

My fuel pump, hasn´t been working so well, the last day´s. So I was thinking of replace both of them, (The in-tank and the other) with one mallory or holley fuel pump with a regulator. I know that I won´t have any increase in performance with these, but I plan to make some improvement´s in the future, like a boost control, an MSD, may be an intercooler, so I believe that a bigger fuel pump with a pressure regulator will make thing´s easier.
Now, Does anybody know wich is the fuel pressure that I need for a stock 1981 931?. Do you think, that changing the stock fuel lines with aeroquip bigger lines and fitting´s will benefit in someway?
Thank´s
Back to top
Rick MacLaren  
Guest





PostPosted: Thu May 09, 2002 2:52 am    Post subject: Reply with quote

Pressure doesn't matter; Volume per unit of time does.
Back to top
John Brown  
Guest





PostPosted: Thu May 09, 2002 11:26 pm    Post subject: Reply with quote

One of the distingishing features of the Bosch K-Tronic CIS is the relatively high pressure (compared to most other systems). Do not know the pressure from the pump but the spec at the pressure control relief valve in the fuel distributor is 75psi. (??)

So you need a pump that will not only supply sufficient volume of fuel but also at a pressure that will allow the various hydromechanical components to function. Most current systems and aftermarket systems and the pumps for them operate at lower pressures by about half.

I just ordered a Pierbug pump from AllEuro as suggested by Vaughan. When it gets here will report on its suitability.
Back to top
924RACR  



Joined: 29 Jul 2001
Posts: 8109
Location: Royal Oak, MI, USA

PostPosted: Thu May 09, 2002 11:58 pm    Post subject: Reply with quote

Ah, they managed to find it? Was it a different part number/application that I had listed for the 924? Please let me know how it turns out for the Turbo.

Heck, I replace the pumps on my turbo, can't remember what I even used for the external one. Maybe it was that Pierburg. I know I used a stock Bosch unit for the internal pump.

_________________
Vaughan Scott
Webmeister
'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Rick MacLaren  
Guest





PostPosted: Fri May 10, 2002 12:48 am    Post subject: Reply with quote

Ok I stand corrected. So you CAN have lower fuel pressure which can cause components not to kick on. Never thought of that. I guess I was answering with respect to how it affects the rate of flow of fuel from the injectors, the theory being in numerous cars that increasing fuel pressure increases flow from the injectors; with the 931 that increased pressure wouldn't change the flow markedly.
Back to top
John Brown  
Guest





PostPosted: Sat May 11, 2002 12:33 am    Post subject: Reply with quote

Both are correct. You need correct volume capability at the design pressure for the particular system. An oft stated generalization/simplification is that pumps don't supply pressure they supply a volume. Pressure is provided by the restictions in the system. Sort of a chicken and egg situation. Bottom line is that the pump must be capable of supplying sufficient volume but at same time at the corrrect pressure. So the full specification of a pump would include the volume AND pressure ratings. Usually we only see one or the other. Look in the hotrod catalogues and most times a gph rating is listed (cause carbuetors are essentially low pressure systems so pressure capability is secondary). Notice that the Bosch pumps we use talk about the pressure. The higher operating pressure dictates a beefier unit (read expensive too) and so pressure dominates the specification.

The minimum volume required is basically dictated by the power output of the engine. Any given power requires 'X' pounds of fuel per unit of time.

The Chevy small block (350ci) in my Porsche Support Vehicle needs more fuel volume (pounds of) towing down the interstate than my Porsche. But if it is an old carburator version the diaphram pump only puts out a few pounds of pressure as it fills the float bowl. And if a later throttle body injection the electric pump sligtly more to the soleniod style injectors. Neither pump would push fuel through the CIS of our 924s or 931s at a pressure sufficient for system operation.

The high pressure pump on our cars may or may not supply significant additional volume than the Chevy diaphram pump, but it is capable of continuous operation at the required higher pressure.

CIS uses the pressure of the fuel behind the metering piston against the airflow induced movement of the flapper to correctly meter fuel into the diaphram chambers. The diaphram in this case is a stainless steel so fairly stiff needing to operate at system pressure. The injectors have a valve built in also which only opens at 35psi (??? from memory).

I receiveed the Pierburg unit from AllEuro yesterday. Number as spec'd by Vaughan. Will install tonight. $139 plus shipping. If you have a 'connection' to wholesale prices this is almost identical to the Bosch unit price. I note that the application sheet with the pump covers two basic models differentiated by the pressure rating. This unit is rated at 6.5 bar the other at 3 bar. So our pump is just under 100psi.
Back to top
numbers  
Guest





PostPosted: Sat May 11, 2002 4:24 am    Post subject: Reply with quote

I believe that Haynes says the injectors open at 50 PSI, but I am just going from memory also. In any case you need a very high pressure (in fuel pump terms) pump for the CIS.
Back to top
924RACR  



Joined: 29 Jul 2001
Posts: 8109
Location: Royal Oak, MI, USA

PostPosted: Sun May 12, 2002 12:00 am    Post subject: Reply with quote

Hey there, finally got a moment to check, and sure enough that Pierburg pump is now residing in my 82 931. John, you should have no problems, I haven't seen any.

_________________
Vaughan Scott
Webmeister
'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
Back to top
View user's profile Send private message Send e-mail Visit poster's website
John Brown  
Guest





PostPosted: Sun May 12, 2002 3:37 pm    Post subject: Reply with quote

Yep. It's working. Got the 931 LJ Project running this afternoon!!!

Vaughan, you shoul post the Pierburg unit on the parts section.

BTW, even though the Peirburg cam with several fittings, needed the adapter off of the original pump to make the hookup.
Back to top
John H  
Guest





PostPosted: Mon May 13, 2002 11:10 am    Post subject: Reply with quote

I don't think anyone has answered MAthias question properly.

The holley or mallory units do not develop enough pressure to get the fuel injection system to work.
If you're stuck and getting parts seems to be real difficult in Argintina can then you can use the fuel pumps of some of the late model japanese fuel injected cars. These units flow about the same as the Bosch pumps and will develop pressures up to about 80 lbs. Should be easier to locate that a Bosch unit and probably cheaper.
Back to top
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> 931 Tech. All times are GMT + 11 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group