Fuel pressure @ wot
06-25-2015, 07:25 AM
#11
Registered
Yikes. I've always used the rule of thumb that if pressure fell more than 1-2 psi OR dropped to 5 psi at WOT, you need more pump. Granddad drilled that one into me.
Are you positive the guage isn't acting up due to vibration, etc? At 1 psi, I would expect stumbling and missing. Basically running like crap.
Are you positive the guage isn't acting up due to vibration, etc? At 1 psi, I would expect stumbling and missing. Basically running like crap.
06-25-2015, 07:46 AM
#12
Registered
iTrader: (1)
^^^^Agree.
They say 5psi is minimum. As much as I've tested in my life, I can't say if 5psi is good or bad.
I don't like - so this is my opinion - more than 9psi at idle, nor less than 7psi at WFO.
=======================
And yeh, I've seen plenty of carbs on the dyno (with glass sight bowls) that end up with a fuel bowl full of 'froth' (extremly aerated) fuel under say 3-4psi. Most run, but you better watch your balls when standing next to it at WOT. You can see and hear the engine wanting to give up life. You shood have seen me next to the one approaching 18:1 AF. Youch !
They say 5psi is minimum. As much as I've tested in my life, I can't say if 5psi is good or bad.
I don't like - so this is my opinion - more than 9psi at idle, nor less than 7psi at WFO.
=======================
And yeh, I've seen plenty of carbs on the dyno (with glass sight bowls) that end up with a fuel bowl full of 'froth' (extremly aerated) fuel under say 3-4psi. Most run, but you better watch your balls when standing next to it at WOT. You can see and hear the engine wanting to give up life. You shood have seen me next to the one approaching 18:1 AF. Youch !
06-25-2015, 08:45 AM
#13
^^^^Agree.
They say 5psi is minimum. As much as I've tested in my life, I can't say if 5psi is good or bad.
I don't like - so this is my opinion - more than 9psi at idle, nor less than 7psi at WFO.
=======================
And yeh, I've seen plenty of carbs on the dyno (with glass sight bowls) that end up with a fuel bowl full of 'froth' (extremly aerated) fuel under say 3-4psi. Most run, but you better watch your balls when standing next to it at WOT. You can see and hear the engine wanting to give up life. You shood have seen me next to the one approaching 18:1 AF. Youch !
They say 5psi is minimum. As much as I've tested in my life, I can't say if 5psi is good or bad.
I don't like - so this is my opinion - more than 9psi at idle, nor less than 7psi at WFO.
=======================
And yeh, I've seen plenty of carbs on the dyno (with glass sight bowls) that end up with a fuel bowl full of 'froth' (extremly aerated) fuel under say 3-4psi. Most run, but you better watch your balls when standing next to it at WOT. You can see and hear the engine wanting to give up life. You shood have seen me next to the one approaching 18:1 AF. Youch !
06-25-2015, 09:07 AM
#14
Registered
iTrader: (1)
We where pumping water thru them at that time.
Believe it or not, faster ways to make headers glow:
Not enough initial timing. Can't tell you how many times I've been drooped over the hood of a decent cammed engine while it's idling doing some tuning or what have you and the header primaries start to glow.
Too much fuel, like way too much. The fuel that doesn't burn in the combustion chamber, that then ignities in the 'hot header.' This can happen at low speeds too.
Pssst: If you can't tell....I've done many things in the dark....lol. I'm sure many people have 'glowing headers' but don't see it.
Believe it or not, faster ways to make headers glow:
Not enough initial timing. Can't tell you how many times I've been drooped over the hood of a decent cammed engine while it's idling doing some tuning or what have you and the header primaries start to glow.
Too much fuel, like way too much. The fuel that doesn't burn in the combustion chamber, that then ignities in the 'hot header.' This can happen at low speeds too.
Pssst: If you can't tell....I've done many things in the dark....lol. I'm sure many people have 'glowing headers' but don't see it.
06-26-2015, 01:07 PM
#16
Banned
iTrader: (9)
Not set in stone but stock OEm apps say 4 to 7 and ideal would be 5.5 psi to 7 psi for low performance stock apps.
I have never even seen a stock V-6 - 175 hp run or even stay running on 1 psi fuel pressure.
Has to be a gauge problem and or a leak / air problem at the fuel pressure gauge as he states 1 psi at WOT. No way that motor especially a big block will run and like I said it will fall all over its face trying to at 1 psi especially anything above 2500 / 3000 rpms.
I have never even seen a stock V-6 - 175 hp run or even stay running on 1 psi fuel pressure.
Has to be a gauge problem and or a leak / air problem at the fuel pressure gauge as he states 1 psi at WOT. No way that motor especially a big block will run and like I said it will fall all over its face trying to at 1 psi especially anything above 2500 / 3000 rpms.
08-03-2015, 09:19 PM
#17
Registered
iTrader: (1)
So my motor still tops out at 4800 regardless of prop and after some kicking around the internet the stock Merc pump may be inadequate for for 502/500hp. I saw that a trick is to bolt the bottom of a Holley onto the Merc top, but do you replace the diaphragm as well? That seemed impossible.
130gph with regulator.
https://www.holley.com/products/fuel...rts/712-454-13
Also I noticed a plastic bushing on sea pump shaft spinning freely so hopefully that's the way it outa be. It otherwise seems to work fine.
It looks like I've got a 3/8" line coming from the tank and also noticed the fuel separator is plumbed with 1/4" nip fittings. Adequate? The 850 QF carb only has a 3/8" barb so that should be adequate for 500hp, no?
My apologies for such newbie questions. Just trying to go faster.
The boat in question is a Baja Islander 272 originally with the 454 Mag MPI.
Last edited by Baja Rooster; 08-03-2015 at 09:32 PM.
08-04-2015, 12:34 PM
#19
Gold Member
Gold Member
130gph with regulator.
www.holley.com/products /fuel pumps /carbureted_mechanical_pumps part # 712-454-13
I have run 2 of the above part # Holley mechanical fuel pumps for years with my regulators at 6 to 6 1/2 psi, they flow 130 gph, I have 5/8 fuel lines from the tanks feeding Perma Cool #81000 high flow filters, to use these filters you will need the Perma Cool Filter Kit.
www.holley.com/products /fuel pumps /carbureted_mechanical_pumps part # 712-454-13
I have run 2 of the above part # Holley mechanical fuel pumps for years with my regulators at 6 to 6 1/2 psi, they flow 130 gph, I have 5/8 fuel lines from the tanks feeding Perma Cool #81000 high flow filters, to use these filters you will need the Perma Cool Filter Kit.
