HP limitations of stock RF fuel system

Mark Worthington · 03-30-06, 12:50 PM

I'm a little concerned about the size of some of the components and fittings in my RF's fuel system. The low pressure fittings are, I believe, 1/4" BSPT at the tanks with barbs for 5/16" ID fuel hose. Fair enough, I thought, as the low pressure system is constantly feeding the swirl pot and fuel consumption is at a maximum only for short periods of full-throttle operation. But my most recent (and probably last [img]/ubbthreads/images/graemlins/frown.gif[/img] ) shipment from RF contained the two solenoids that are supposed to be put in front of the LP pumps to prevent backflow through whichever pump is not selected. Now the fittings in these things are even smaller - the barbs are for 1/4" ID hose and the size of the solenoid fitting looks to be less than 1/4". So I need to step down from 5/16' hose from the tanks to 1/4" hose at the solenoids, then back up to 5/16" to the LP pumps. This leads me to wonder if these solenoids will be overly restrictive to fuel flow on the LP side of my system. Anyone have a source for larger solenoids I can use?

On the high-pressure side, the limiting factor seems to be the barb for 5/16" ID hose on the outlet of the pump - the ID of the outlet is more like 3/16". I wonder if that's enough to supply my 347 stroker. Also, the filter downstream of the HP pump takes 5/16" ID hose on both ends, and needs to transition to 1/2" at the bulkhead barb fitting.

So here's my question - what is a practical upper limit to horsepower that my stock RF fuel system (modified to include the solenoids) can handle? My 347 should make north of 425 hp at the crank, and I have a feeling that it wouldn't take much more engine to overwhelm the stock fuel system. I wonder if I should try to find solenoids with larger fittings and if I should look for a bigger HP pump.

Thank you in advance for your help.

Ian Anderson · 03-30-06, 02:09 PM

Mark

How about solenoids from the Jag XJ series - I believe they are 5/16 or 8mm.

I would also question a filter after the HP pump - more connections and more possibilities to leak under the pressure.

I am running 5/16 (8)mm) pretty well all the way with the return from the swirl back to tanks being 1/4 (6) - that is only due to the fittings on the Pollack valve.

BUT I am on a Rover 3.9Efi with 300 hp so no doubt yours will drink more.

Probably time for Paul Thompson to chime in

Ian

Mark Worthington · 03-30-06, 02:45 PM

I may look into the Jag solenoids - thinks.

I definitely want to keep the filter on the downstream side of the HP pump - gotta protect those injectors. But the fact that there are a bunch of barb fittings between the HP outlet and the fuel rails bugs me. I'm being real anal about my fuel system connections because the thought of a fire in a GT40 scares the crap out of me.

Ross Nicol · 03-31-06, 06:50 AM

Mark why don't you use AN fittings instead of barbs.Very expensive but the fittings allow much larger hose diameters.I used -6 sized all through my system with a little -8.No fuel problems with my car at 400hp.
Ross

Ian Anderson · 03-31-06, 09:42 AM

Mark

have a look at
http://www.gt40s.com/ubbthreads/showflat...=true#Post69873

Paul has a formula for the amount of fuel per hp per minute

If you can get the flow through the pipe diameters then you should be OK

BUT how to test it????

Perhaps

Ian

Mark Worthington · 03-31-06, 10:17 AM

Ross, if I go to AN fittings on the high-pressure side of the fuel system, I'll need a new fuel pump, filter, bulkhead fitting and associated lines. I may end up going that route but I'll probably try the stock system first. May require datalogging rail pressures on the dyno as I tune the engine.

Ian, thanks; I'll have a read through that thread.

Gordon · 03-31-06, 12:03 PM

Mark, the fuel system is suprising on how much power it will supply but I would concider larger for the 347. The thing I know you will need to do is go up on injector. We had to go up to 42# injectors to feed a 400hp 306. It was leaning out above 5000 revs with the ones that came with the manifold.

Ron Earp · 03-31-06, 01:33 PM

[ QUOTE ]
May require datalogging rail pressures on the dyno as I tune the engine.

[/ QUOTE ]

Don't get too involved - I've got a $20 pressure gauge I put on the schrader valve that you can simply watch on the dyno - works well and takes care of business.

R

Jim c · 04-08-06, 11:38 AM

Mark
One of the best tests is flow.
I have seen pressure but not a lot of volume.
When you are on the dyno put the fuel return into a container(return at fuel rail).
There will be enough fuel in the surge tank if you dont mess around.
Have the car hot start it & do a power run.

If the engine consumes more than the pumps will supply the fuel return will go down to a trickle.
I would expect a lt per minute or more at full noise from the return hose into your container.
Do it over 30sec & double it or 15 & X by 4 ect.

Keeping in mind the return I presume is returning to the surge tank on the std RF system this does help maintain fuel volume in the s/tank so dont hang around.

Doing it this way I find is good as it is a dynamic test with everything under full load & it leaves nothing to chance.

Jim

Paul Thompson 'Hooligan' · 04-09-06, 05:10 PM

Hi Jim
Good advice IMHO - We found that the flow rates from the facet Red-Top pumps varied incredibly when we tested them in a similar manner. Of course, we now use a Holley rotary pump as a lifter pump to the swirl pot. It flows about 70 gals per hour. The HP pump is fed by -8 but outputs via -6 to a twin rail arrangement. Quality fuel rails with a resonable capacity are also a good idea - 0.5 to 0.625 bore preferred.

We found we needed larger injectors when changing from batch to sequential injection (Accel to Motec). The sequential was running out of time for the injectors to flow enough and the motor would not rev past about 6200rpm. Changing to 59lb items immediately released additional rpm at the higher range, eg 7000 rpm. Engine unfortunately died shortly thereafter due to a water cooling problem that cracked the alloy block. [img]/ubbthreads/images/graemlins/frown.gif[/img]

Many people use two Bosch HP pumps for power over 4800BHP, although I think two flow too much, They should flow 240-280L/hr each in a well configured system, so a single pump should be good for at least 600BHP in my opinion.