Mechanical Fuel pump question !

[SBC-68-FIREBIRD]

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

Hi Steve,
I have never checked the bead so cant say if its ever moved.
I bought one of the Holley 170GPH mechanical pumps which has 1/2" inlet & outlets so now it has 1/2" from the pickup all the way to the reg which is 6" from the carby. It does still drop a bit which I expected to happen but very hard to tell while driving on the road. Need to video the guage while having a run at the track.
Was thinking about even fitting a 1/2" check valve near the fuel tank to stop any fuel that is in the line from draining back towards the tank on take off but not sure if I would be just wasting time.

[steve cowan]

Hi Scott,
Yep, extremely difficult to test on the street especially when our cars get to 100 mph in 7 seconds
I personally think the check ball deal will be a hinderence more than a help, really don't want any restrictions at all,
What I did notice on your car is the air cleaner is through the bonnet and so is mine on my hq Holden Ute, when I first got mine going again with this new motor I was having trouble with carby going lean and finally found that by putting a deflection plate inside the air filter made my air fuel ratio stable, I am not saying that you have the same problem but I found with the air cleaner off the engine the air fuel was going way lean at even low speed so the air must of been shearing off top of carb
I wonder if the bowl vents could have a problem that may cause a fuel pressure problem, only thinking out loud here but anything is possible, I will put a photo up tomorrow of what I did on my own airfilter

[steve cowan]

deflector plate hq ute 002.JPG

scott,
air filter though the bonnet and deflector plate inside airfilter

deflector plate hq ute 001.JPG

deflector plate hq ute 003.JPG

deflector plate hq ute 004.JPG

deflector plate hq ute 005.JPG

deflector plate hq ute 006.JPG

as previously stated i had issues early on this year with carb going lean
the fuel pressure was not effected,but i am using a return bypass and a bigger mechanical pump
your engine is making 50 + more horsepower than mine
the deflector plate is only an idea that worked for me,it made sense with air shearing across the carb
scott,on your first post you said the engine ran on the dyno with the 130gph pump and all looks ok
is this a complete new combo or freshen up with upgrades,it bums when we spend all this hard earnt coin for little return but unfortunatly thats the game we play.
have you pulled a spark plug after a run and had a look?
my next suggestion is a return line and bypass reg,line should be near same size on the return,i thinkyou need to get rid of the dead head system
summer is round the corner
hope this helps in some way
steve c

[steve cowan]

scott,
one of the best things i have done is bought and fitted autometer air/fuel guages
yes its more gizmos to confuse us but it can get you in the right paddock to start with as long as we dont get transfixed by the numbers we will be ok

[MadBill]

A couple of points:
o A check valve can't help, it can only restrict. The fuel can't ever be back-flowing in the feed line without the engine dying.
o K&N XStream® filter tops often lose power if the cylindrical filter area is adequate. I suspect it's due to turbulence from the horizontal and vertical flows interfering.
o I hope that hex nut got retrieved before you bolted up the aircleaner assembly..

[steve cowan]

Hey bill,
Would you try a hard lid on the airfilter and remove the deflection plate
Kinda makes sense what you are saying as far the air crashing together
Like I have said, I tried to drive car on the street without air filter and air fuel guages went lean at 30 mph hence the deflection plate brain storm, that cured that problem but might be bandaid solution, open to suggestions and duly noted
Yep, air filter nut not in a compromising position, thanks anyway
Steve C

[MadBill]

I'd try both ways: no plate, then no deflector, then neither.
Of course a chassis dyno would cut to the chase for you, if stationary AFR was good but moving wasn't. (Our road race SBF with ram air for some reason goes the other way; at 120 MPH plus it runs richer than on the dyno.)

[77cruiser]

Try the deflector on the back too.

[F-BIRD'88]

I'd be wanting to now look into some kind of forward facing carb scoop/hood scoop
than may integrate a air cleaner and air flow management too.
Can be attached to the hood or can be pokin up thru the hood as like a "shaker carb scoop"
Don't be afraid to get creative to make it functional.

A Sealed ducted cowl induction system is another path.

Another path is to just have the "power bulge" "shaker" carb hat pokin up a bit thru the hood
yet it is ducted to front of the car for air pickup in the high pressure zone, thru air cleaner(s)
to smooth and clean air flow.

maybe something like this li mini Areo scoop attached to a carb box.

[SBC-68-FIREBIRD]

Thanks guys.

I have previously read stuff about having the air cleaner through the bonnet without a scoop over it so I had previously been thing about setting something up but have not got around to it yet
I was thinking something very similar to what you have Steve. I have a 15x8" oval filter which is 4" high with a solid top. Was going to make up a shield that goes inside the air cleaner that wraps just around the end curve so I can swap it from front to back just by spinning the filter. This is a no cost thing but just gotta get some time to do it.

[PbFlinger]

Hello, long shot here but a couple of things I have seen cause problems with mechanical pumps:
1. More than once I have seen a composite pump drive rod worn badly at the cam end, thus not fully stroking the pump. Provided plenty of fuel & normal pressure at low speed, failed miserably on the track. Got thrown off on troubleshooting as we installed a new pump without taking the rod out. Hair puller there.
2. Similarly had a steel rod that was all gnarfed up from an overly long bolt having been installed in the hole in the front of the block that runs into the rod bore. It was causing the rod to hang up & not stroke the pump fully.
3. Mud from track (or helpful mud dobbers) had plugged the vent hole for the top of the pump diaphragm chamber.

Good luck & hope you get it figured out

[SBC-68-FIREBIRD]

Hello, long shot here but a couple of things I have seen cause problems with mechanical pumps:
1. More than once I have seen a composite pump drive rod worn badly at the cam end, thus not fully stroking the pump. Provided plenty of fuel & normal pressure at low speed, failed miserably on the track. Got thrown off on troubleshooting as we installed a new pump without taking the rod out. Hair puller there.
2. Similarly had a steel rod that was all gnarfed up from an overly long bolt having been installed in the hole in the front of the block that runs into the rod bore. It was causing the rod to hang up & not stroke the pump fully.
3. Mud from track (or helpful mud dobbers) had plugged the vent hole for the top of the pump diaphragm chamber.

Good luck & hope you get it figured out

Thanks for the idea's but all good on all of the above.