Mechanical Fuel pump question !

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steve cowan
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Re: Mechanical Fuel pump question !

Post by steve cowan » Tue Aug 01, 2017 2:05 pm

hi scott,
the pontiac is awesome,love the wheels up action on drag radial,curious as to what tire pressures you run
i did not realize that holley fuelpump was so so expensive,i purchased mine from summit about 3 years ago and cant remember the price tag.
are you running the standard fuel tank and does it draw fuel from the top of the tank meaning is the sender/pickup sitting on top of fuel tank?
i think this could be a problem if so,i believe fuel has to be able to gravity feed to the inlet side of the fuel pump as the pump really is a pusher not a fuel puller if that makes any sense.
that 170 pump should get it done but i hear what you are saying that none of us can afford just to keep bolting parts on which is usually known as the shotgun method of process of elimination.very interested how this turns out for you,please keep us informed,
steve c

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Re: Mechanical Fuel pump question !

Post by 427dart » Tue Aug 01, 2017 2:51 pm

I've been running a CV Products mechanical pump on my 427 SBF. This was the NASCAR pump they were using back in 2007 and fiqured if it was good enough for 750 HP engines all day it was good enough for my 550-600 HP which it has been.
I run a 1/2 inch line from bottom of tank thru a large screen pump at rear then up to the pump and then a filter right before the carbs.
6 psi going thru the traps at 6000 RPM/ 132 MPH.
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Re: Mechanical Fuel pump question !

Post by zums » Tue Aug 01, 2017 3:05 pm

I use the CV2502 with no issues
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Re: Mechanical Fuel pump question !

Post by SBC-68-FIREBIRD » Wed Aug 02, 2017 4:13 am

steve cowan wrote:hi scott,
the pontiac is awesome,love the wheels up action on drag radial,curious as to what tire pressures you run
i did not realize that holley fuelpump was so so expensive,i purchased mine from summit about 3 years ago and cant remember the price tag.
are you running the standard fuel tank and does it draw fuel from the top of the tank meaning is the sender/pickup sitting on top of fuel tank?
i think this could be a problem if so,i believe fuel has to be able to gravity feed to the inlet side of the fuel pump as the pump really is a pusher not a fuel puller if that makes any sense.
that 170 pump should get it done but i hear what you are saying that none of us can afford just to keep bolting parts on which is usually known as the shotgun method of process of elimination.very interested how this turns out for you,please keep us informed,
steve c
Hi Steve,
I have always had best luck running them between 17 & 17.5psi.
My car has the factory leaf springs in the rear & factory coils up front. When I go to the track I bolt in a set of Calvert Racing shocks front & rear & the Caltracks are set to 1/4 turn preload.
I have tried stalling the car up & it will generally spin the tyres, have always had best luck taking off from idle, always hooks well.
That fuel is expensive in the US so with the AU$ makes it worse.
I have the factory tank in the car but have a bulkhead about 3/4 of the way up the tank. When the line is disconnected it will syphon fuel out no problems but I wont get a gravity feed as the line has to run over the diff & the tank is obviously under the floor.
I am looking into a ProCam pump ATM, just waiting on some measurements to make sure it will fit otherwise will probably bite the bullet & buy that 170GPH Holley.
Took it for a run again last night with the guage fitted just after the pump & from a standstill it will drop to 3psi before hitting second.

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Re: Mechanical Fuel pump question !

Post by SBC-68-FIREBIRD » Wed Aug 02, 2017 4:46 am

427dart wrote:I've been running a CV Products mechanical pump on my 427 SBF. This was the NASCAR pump they were using back in 2007 and fiqured if it was good enough for 750 HP engines all day it was good enough for my 550-600 HP which it has been.
I run a 1/2 inch line from bottom of tank thru a large screen pump at rear then up to the pump and then a filter right before the carbs.
6 psi going thru the traps at 6000 RPM/ 132 MPH.
Thanks for the info.

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Re: Mechanical Fuel pump question !

Post by steve cowan » Wed Aug 02, 2017 6:12 am

hi scott,
thanks for the tip on the tyre pressures,i run 19psi but that gives me a bit to refine with if track prep is average.
this fuel pressure deal is a pain,are you running a return line,i re-read the thread and no mention of it,
did you have the same problem with the old engine?
is your regulator before or after carb lines,i read you have tried 2 x different regs now just throwing any ideas out
maybe try and run without the fuel filter fitted to eliminate that as a problem
i have run plenty of fuel systems that dead head over the years,but your engine is making some power,
its difficuilt to do a flow check with a mechanical system as i want to do that but still thinking about it,
damn sorry not much help at all........????

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Re: Mechanical Fuel pump question !

Post by F-BIRD'88 » Wed Aug 02, 2017 11:09 am

If the diaphram return spring and or the pump lever arm spring is broken or lost its tension ( heat) the pump will float at high rpm and not move (much) fuel.
Something to check if its a two piece bolt together pump housing.

G-Force:
By the time you get to the top of first gear the highest G-force of acceleration
is long past. That G-force at that point is much LESS than the G-Force at and near the start line.
At high rpm, high carb fuel demand when flow is high the pressure will be lower.
It is fuel flow that matters, not fuel pressure. As long as the fuel bowl(s) is staying full
at max high rpm power demand you don't need more pressure.

A AFR gauge will tell you more than a fuel pressure gauge.
That AFR gauge/O2 sensor need not be a WideBand type. A simple low cost Narrow band type will tell you all you need re: fuel flow consistency . If its not flowing enough fuel VOLUME to meet engine max demand for fuel the AFR gauge will drift lean(er) as you progress thru the run.

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Re: Mechanical Fuel pump question !

Post by F-BIRD'88 » Wed Aug 02, 2017 11:36 am

That little short length of fuel line hose that connects the feed side fuel line hard line to
the engine mounted fuel pump is CRITICAL.
Heat and the lack of pressure at that point combined cause that connecting hose to collapse
and the fuel in it to bubble too (vapourize). This action is most pronounced at Highest fuel DEMAND ( high rpm max power).
Even the pretty /and expensive braided hoses can collapse and kink shut when subjected to heat and partial vacuum.
Check that lil hose. it gets soft and tends to kink and or collapse the hotter it gets and the higher the fuel draw of the pump at high demand.
The fix is get a better feed side flex hose and add ///or a "Pusher pump" at the back near the tank to pressurize the feed side fuel line and push vapourized bubbled fuel (vapour lock) thru so the mechanical pump can work.
This "Pusher pump" need not be high pressure. A 5psi Carter (72GPH free flow rated) P4070 electric pump is plenty for a 650HP engine. No regulator is needed.
Supplying fuel to a carbed engine is all about VOLUME, not pressure.

The correct fuel line hose for this is specifically designed to not collapse or kink or restrict when subjected to engine heat and a partial vacuum. The pretty out braid of a braided line says nothing of the quality or suitability of the hose for this purpose.

DRAG Cars with hot cramped engine compartments and headers are famous for this:
Camaro, Firebird, Corvette, Chevy II etc. The radiated heat you pick up off the hot pavement when sitting waiting in the staging lanes ("Hotsoak") is enough to cook the under car fuel line and create vapourlock. On a drag car that lil $50 carter P4070 "pusher pump" does wonders for the perf of a Mechanical fuel pump, on a drag car.

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Re: Mechanical Fuel pump question !

Post by SBC-68-FIREBIRD » Thu Aug 03, 2017 4:17 am

steve cowan wrote:hi scott,
thanks for the tip on the tyre pressures,i run 19psi but that gives me a bit to refine with if track prep is average.
this fuel pressure deal is a pain,are you running a return line,i re-read the thread and no mention of it,
did you have the same problem with the old engine?
is your regulator before or after carb lines,i read you have tried 2 x different regs now just throwing any ideas out
maybe try and run without the fuel filter fitted to eliminate that as a problem
i have run plenty of fuel systems that dead head over the years,but your engine is making some power,
its difficuilt to do a flow check with a mechanical system as i want to do that but still thinking about it,
damn sorry not much help at all........????
Hi Steve,
I never checked with my old engine but what got me checking was the new engine has an extra 50HP & ran exactly the same ET & MPH.
No return line, from tank it is 1/2" hardline to about 6" from the pump, then into a Mallory filter, then into the reg which is right next to carby.
I have put a new element in the filter.

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Re: Mechanical Fuel pump question !

Post by SBC-68-FIREBIRD » Thu Aug 03, 2017 4:23 am

F-BIRD'88 wrote:That little short length of fuel line hose that connects the feed side fuel line hard line to
the engine mounted fuel pump is CRITICAL.
Heat and the lack of pressure at that point combined cause that connecting hose to collapse
and the fuel in it to bubble too (vapourize). This action is most pronounced at Highest fuel DEMAND ( high rpm max power).
Even the pretty /and expensive braided hoses can collapse and kink shut when subjected to heat and partial vacuum.
Check that lil hose. it gets soft and tends to kink and or collapse the hotter it gets and the higher the fuel draw of the pump at high demand.
The fix is get a better feed side flex hose and add ///or a "Pusher pump" at the back near the tank to pressurize the feed side fuel line and push vapourized bubbled fuel (vapour lock) thru so the mechanical pump can work.
This "Pusher pump" need not be high pressure. A 5psi Carter (72GPH free flow rated) P4070 electric pump is plenty for a 650HP engine. No regulator is needed.
Supplying fuel to a carbed engine is all about VOLUME, not pressure.

The correct fuel line hose for this is specifically designed to not collapse or kink or restrict when subjected to engine heat and a partial vacuum. The pretty out braid of a braided line says nothing of the quality or suitability of the hose for this purpose.

DRAG Cars with hot cramped engine compartments and headers are famous for this:
Camaro, Firebird, Corvette, Chevy II etc. The radiated heat you pick up off the hot pavement when sitting waiting in the staging lanes ("Hotsoak") is enough to cook the under car fuel line and create vapourlock. On a drag car that lil $50 carter P4070 "pusher pump" does wonders for the perf of a Mechanical fuel pump, on a drag car.
Thanks for the info.
I think if I was going to fit an electric pump I would just do away with the mechanical.
I am hearing what you are saying regarding the pressure not being as important as the volume but am thinking that's why I would like to step up to a pump that has 1/2" inlet & outlet instead of 3/8" like the current pump I have.
Might invest in one of them AFR gauges.

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Re: Mechanical Fuel pump question !

Post by Geoff2 » Sun Aug 06, 2017 6:06 am

It is NOT all about volume. Without pressure, there would be no volume.... You need both, in the right amounts, for the job.
600 hp will consume about 50 gph [ or proportion thereof ] , assuming correct A/F ratio. Doesn't matter how it makes 600 hp, if it is turboed, blown, NA, still needs 50 gph.

For a carbed engine, that means 50 gph delivered by the needles & seats. That means a minimum size n/s AND a minimum pressure will be reqd to provide that 50 gph. You also want a 50% safety margin, so now you are at about 75 gph. That would require TWO Holley 0.101" n/s @ 6psi to deliver enough fuel. It pressure fell, to say 4 psi, you would be on the edge. Hence why pressure is important.
You can increase n/s size to the next size, 0.110", but it is better to use the smallest n/s size that gets the job done, with reasonable pressure, because a smaller n/s seat maintains better control of fuel level in the bowl. A big mistake is fitting a pump that is too big, as it will be bypassing & possibly aerating the fuel. Fuel pumps seem to fall into the 'big ports' category. If big is good, bigger must be better............

The Carter 4600 series electric pumps can supply 900 hp. They are reliable, last forever; one is internally regulated, one requires a reg. Best arrangement is to use the unreg pump with a bypass reg; bypass reg gives much more stable fuel pressure than a dead head set up, which is continually 'fighting' pulsations in the fuel system. Use a 1/2" line from the tank to the pump & a spin on fuel filter from a small truck for minimum pressure/flow loss.1/2" line from pump to filter. I have this deal, filter is at the back of the car near the pump. Use 3/8" line from filter to reg. 1/2"return line [ NOT 3/8']. This set up will deliver 90 gph to the carb.

Scott, check your valve springs...

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Re: Mechanical Fuel pump question !

Post by pamotorman » Sun Aug 06, 2017 9:25 am

make sure the tank vent is big enough as air has to get in for the fuel to get out

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Re: Mechanical Fuel pump question !

Post by greg » Sun Aug 06, 2017 12:37 pm

i run stock 55 chevy gas tank ,took out the stock pickup ofcourse put half inch pickup tube in ran aluminum half inch all way to my 950 carb an thru the fram gas filter in the back,i run 10.40,s 127,bakersfield,neva any problems,the car weighs 3500 me in it....i run a big holley manuel 130 gallon a minute.. :D

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Re: Mechanical Fuel pump question !

Post by F-BIRD'88 » Sun Aug 06, 2017 1:40 pm

I'm sure there is a $800 solution to a $50 problem.

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Re: Mechanical Fuel pump question !

Post by steve cowan » Tue Aug 08, 2017 10:54 pm

Hey Scott,
Did you come up with any solutions on fuel pressure deal
I raced on Saturday night, run my radials on 18 psi
Passengers rear has turned about 10 mm on the bead
Have you ever had the same thing on yours

Steve c

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