Fuel Volume to Webers question

[tom pritchett]

I had the GT40 at a dyno a few weeks ago. It really leaned out badly above 4250 rpm. I didn't have my extra jets thinking that I needed larger jets. A thought came to mind which was that maybe I didn't have enough fuel flow to the carbs. I just tested the regulator and it was set to 2 lbs for each tank/fuel pump/regulator. At least they were consistant to eachother. I just changed that to 3.5 lbs and then checked the fuel flow. I am getting 1/2 gallon per hour. I read that I need 60 gallons per hour for a 500 hp engine.

I guess the question is: Do I need to install a fuel pump that has more volume? This is a stock set in a CAV and the pumps are made from FACET. I don't have any more information for these pumps yet without taking them out.

The engine is a SBF B&S to 382ci.

Thanks in advance for the help. I just don't want to run too lean and hurt the engine.

 

[tom pritchett]

I just found my fuel pumps online and they are 36gph. They seem to be a little light.

 

[Kevin Box]

In the past I have used Holley Red pump to run just uunder 500 HP and found it worked quite well with four 48mm IDAs
They only have an internal pressure regulator so I added the external regulator and ran it at 3.5 psi.

I also ran an oil filled pressure gauge on the end or the fuel rail to tell us what was goiung on during the race. - you may find this handy while tuning on the dyno.

On the next boat I built I used the Holley Blue pump, not because of the volume capabilty (110 GPH) but becaue of external pressure regulator.

part number as below

97 GPH “RED” Electric Fuel Pump PART #: 12-801-1

Only thing about these pumps is you have to be careful where you mount them as they are noisy. Also make sure you have the feed in and out come upwards from the pump so the seals are always wet.

Regards Kevin B

 

[Kevin Box]

Recomendations from Holley

 

[Frank Catt]

TOM, Depending on your engine specificatios you will no doubt need substantially better volume flows to your webber system if you intend to run long duration high revs. ( long duration is more than a few minutes ) I know the CAV system, and it definatley has issues, particularly with the fuel flow from the tanks and the low volume delivery ability. If you are running IDAS I suggest that you need at least 110 GPH pumps ( I like Mallorys) and -8 lines, with a full return flow fuel pressure regulator ( not a "dead head" ) As written on other threads here, Webers do suffer from various problems, the most critical is from heat soak from the engine, especially when the engine is first stopped after a hot run. Fuel in the float chambers can boil, expanding to sit on the top of the butterflys, just ready for a fire. This is then compounded by residual pressure in the fuel lines to the carbs, pushing even more fuel into the carbs, excarbating the problem. I always fit a fuel pressure dump valve into the fuel lines to the carbs, which automatically dumps fuel pressure back to the tanks as soon as you switch off the ignition. ( pilots seeing a switch marked " fuel dump valve" on the dash immediately get a hard on ! ) Make sure the fuel return lines are switched to return to whichever tank is being used, use a solenoid valve which is normally closed but opens with the feed to the fuel pump to whichever side you are useing. If you are useing rotary pumps rather that solenoid pumps ( like the Facet ) make sure you have non return valves in the delivery lines also. Fuel flows can be calculated fairly accuratly, but you need all the data, we have one engine that will be capable of emptying BOTH tanks in 9 minutes at full revs/maximum power, which is extreme ! Frank

 

[David Briggs]

The Facet pumps that came on my CAV would not flow enough to operate the Webers, and did not even register on the fuel pressure gauge.
I installed Carter rotary vane pumps that are preset for about 3-3.5 lbs of fuel pressure.
The Carter pumps come with a small pipe fiiting on the housing for the fuel lines, I disassembled the pumps and drilled and tapped the inlet and outlet holes to accept -6 fittings.
Webers need high volume of fuel but at about 1/2 the pressure that a Holley works with.
Dave

 

[tom pritchett]

What an eye opener. I am glad that I spent some time with the dyno and this showed it's ugly head. Thanks everyone for your input and experience. This forum is the best!

The chart plainly shows that 36 gph for 48 IDA's are just too light. I'll look closer to the 110 gpm as mentioned above and continue to study out the best way to fix this problem. I like the idea of the high volume with the return, however will take alot more work to fix. ( running fuel lines back to the tanks, solenoids, etc...)

 

[Frank Catt]

Tom, you also need to have a min 3 litre fuel swirl pot to supply the pump feeding the fuel rail, the ( early ) CAVs had issues with being able to feed the pumps from the tanks while going downhill/heavy braking, the swirl pot will always have sufficient capacity to supply the engine in these conditions. Pictures available if required. Sorry , forgot to add that earlier, Frank

 

[Cliff Beer]

Tom, not sure if you said you were running EFI, webers or a Holley...? No doubt the twin Facets are a little light for that kind of hp. The lines in my CAV were quite small in diameter - roughly 1/4 - so I re-plumbed it with the next size up and that improved the flow meaningfully. I know because I had installed an external float bowl level indicator, basically a clear plastic tube, and under WOT/full load the bowl was going dry. No doubt, changing the fuel pumps to larger capacity would further improve flow but for my meager 350hp engine the Facets work OK.

I haven't had any problems with my CAV drawing air on steep inclines/braking but perhaps others have.

Ditto the reco on the Holley Reds - nice pumps that look about right in a vintage car.

ps. you might want to install a pressure gauge on the fuel inlet line just to make sure you're in the right pressure range.

 

[tom pritchett]

Cliff, I am running the 48 IDA weber set up. I ran a pressure guage and found that my pressure was light (2 lbs). I raised them to 3.5 lbs. Running the 382ci stroker, I ran 350 hp until the pumps ran out on the dyno at 4000rpm. I am hoping that I will be able to have 450 bhp on the dyno with the new pumps. Boy, it sure is thirsty.

I also havn't run out of gas as of yet on decell or heavy cornering. My car is #61, so it is an early CAV. I am learning alot from the members of this forum.

Neil and I missed you at the Redmond Town Center for a great car get together today. The GT40's were well represented.

 

[Kevin Box]

Tom

I agreee with frank the Mallory pumps are much better than the Holleys.
Go for 110 GPH if you want to reach your peak power.
IDAs or IDFs manage 3.5 pound just fine and it ensures good delivery.
I never had problems with flooding.
Just remeber "Fuel Is Cheap" when compared to a leaned out melted engine.
There is probably heaps of other exotic pumps around but in reality the Mallory or Holley pumps work!!
Dont get tied up in "what might have beens"
All the people with ideas about small pumps seem to be absent when you've got a melted piston and aluminium all through your engine.
The bottom line is you need a pump that is big enough to supply fuel for when you give a bit of a thrashing for an extended burst.
Good luck with your project

KB

 

[John Fitzpatrick]

Anyone know if the dual SW pump configuration was used to provide higher flow or was it for redundancy in the event one pump failed?

 

[Jim Rosenthal]

I think both. The pumps are ganged together and operate in tandem as parallel units. The Mark II cars had a THIRD SW pump, which may have been the backup unit; Jay or Jimmy would know. (at least this is what I recall from the wiring diagram that we had up recently for view). I've seen at least two cars (Marriott and Armstrong cars) with one SW pump, so evidently that's enough for at least some uses.