Yeah, that could be an issue. dummy
fuel pressure dropping over time
- Thread starter diymirage
- Start date
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Yeah, that could be an issue. dummy
TT5.9mag
Two atmospheres are better than one
diymirage
HP@idle > hondaHP@redline
well, in the light of full disclosure...this is what happened
when i redid the fuel system i replaced the stock sending unit with a 3/8 return style, the return was only 1/4 and i wanted it to be 5/16
so knocked the return barb out and put a 5/16th brass barb on
that leaked
so i got an Aluminum bulk head fitting and that leaked
put in copper washers on both sides and it still leaked...but only when the fuel level is higher then the return barb
at that point i said, screw it, so i bought a new sending unit, 3/8 with a 5/16 return from a member here
and wouldnt you know it...1/4 inch return
at that point i said some things i dutch i cant repeat here, and decided to keep the fuel level below the return barb
(untill i find a decent sending unit or figure out how to seal this one)
so...that may have had a little bit to due with my said "supply issue"
Do you have a return style regulator? That's what dictates return flow, not the size of the line. 1/4" is plenty big for a return line. Return orifices in the return port of return filters are normally like .060-.100", so 1/4" line is huge compared to that metered orifice.
diymirage
HP@idle > hondaHP@redline
yes, the mallory 4309
Mallory Ignition 4309 Mallory Fuel Pressure Regulators | Summit Racing
im not sure if you can compare a return style regulator with a return filter, because they generally are intended to be used with different pumps
according to the instructions, if the return line is too small, you get pressure creeping up (which actually sounds pretty good right now) so thats why i didnt want to have the step down in it
I'm late to the party but what about the isolator line to mechanical gauge being burped? Would air in that line cause this issue....
#shootingfromthehip
sounds like you have it figured with the supply issue.
#shootingfromthehip
sounds like you have it figured with the supply issue.
diymirage
HP@idle > hondaHP@redline
Oh, I see that now.
There are prices I pay for being really really ridiculously good looking yknow.
I don't think it will.....I'm no physicist, but it would be the same as having air in an oil pressure gauge line. The oil pressure gauge still reads correctly. The air in the line compresses some I am sure, but the gauge will read right since the air only compresses to a certain point. I imagine the fuel gauge is the same.
Your return line might be your issue. It should ALWAYS be as large or larger than the feed line. Stated on p. 2 of the 4309 instruction sheet.
I also use the 4309 reg, bypass mode, with an elec pump. I use a 3/8" feed line, 1/2" return line. Rock steady fuel pressure.
A bypass system is basically a 'full circle' system. Beginning at the tank & ending at the tank. The engine [ via the regulator port ] takes what fuel it needs.
I also use the 4309 reg, bypass mode, with an elec pump. I use a 3/8" feed line, 1/2" return line. Rock steady fuel pressure.
A bypass system is basically a 'full circle' system. Beginning at the tank & ending at the tank. The engine [ via the regulator port ] takes what fuel it needs.
That's just not true as a blanket statement. It totally depends on what pump you have, how many GPH it flows and at what PSI. Some manual pumps (which he's running) don't have enough flow to over come the loss from a large return, thereby starving the carburetor from sending too much back to the tank. That's exactly WHY the factory return filters used the metered orifice I spoke of earlier to regulate that return flow, so as not to make the pressure drop off too much going to the carburetor. There was just a guy the other day on the Facebook slant 6 page that was having a fuel starvation issue and that's exactly what happened to him. The solder in the return orifice fell apart and the return was totally unblocked and caused him fuel starvation issues at highway speed under load. He put another filter on and fixed the problem. Sure, for real performance mechanical pumps or electric pumps, you need a large return line. But even then, the correct way is to use the regulator in the return line for use as the return orifice, for the same reason. To regulate that return flow so the flow at the carburetor doesn't drop off.
TT5.9mag
Two atmospheres are better than one
In a perfect world the return line should be able to return ALL of the fuel back to the tank. Now, there are a lot of factors at play here. Most importantly the size and style of the fuel pump. An electric sized to flow enough fuel for 1000 hp will have drastically different requirements than a mechanical pump sized for 400hp. In @diymirage example his mechanical is sized about right for his combo and probably could get away with no return or regulator at all. Hell AJ said it’s what he uses, and his engine likely makes a little less power. The hardest the regulator and return will ever have to work is when the engine is idling so if your fuel pressure is stable at idle you don’t have a return problem.
A factory return system with a .060" metered orifice will return ALL of the fuel to the tank. It might take a while. lol
TT5.9mag
Two atmospheres are better than one
If it takes any longer than the combined amount of time it takes to get it there minus what the engine is using then it will create pressure rise and the .060 is too small. If it doesn’t, it’s not. It’s that simple.
I know, I'm just sayin the factories used that .060" "or whatever it was" orifice in those return filters, so they musta thought it was enough. I have a WIX return filter with the orificed return. I should go see how big it is.....or how "small". lol
TT5.9mag
Two atmospheres are better than one
They also do things like pulse width modulation on the electric fuel pumps. Which makes the fixed orifice return much less of a restriction. If you can reduce pump output when the engine doesn’t need it everything works better. Less heat in the pump and the fuel and a lot less return. The big manufacturers do a lot of testing and have narrowed it down pretty well.
Technology on a lot of things just keeps getting better and better.....but I think we've gone too far with computers.....but that's for another discussion. LOL
The return orifice in production filters is most likely there to smooth out the pulsating pressure at lower rpms that mech pumps generate.
The example in post #64 of the orifice suddenly becoming large[r] because of solder detaching & causing fuel starvation is different to the OPs set up. The OP has a bypass regulator where the carb takes the fuel it wants before the excess fuel is returned to the tank. In the example in post 64, the carb was getting fuel after the fuel was returned to the tank, which starved the engine of fuel; the carb was the last cab on the rank, not the first as in the OPs case. There is no such thing as a return line that is too big, only too small [ within reason ]. It is a small return line that causes the flow to back up & interfere with steady pressure. Which is why the Mallory 4309 instructions recommend a larger return line with increased length.
The example in post #64 of the orifice suddenly becoming large[r] because of solder detaching & causing fuel starvation is different to the OPs set up. The OP has a bypass regulator where the carb takes the fuel it wants before the excess fuel is returned to the tank. In the example in post 64, the carb was getting fuel after the fuel was returned to the tank, which starved the engine of fuel; the carb was the last cab on the rank, not the first as in the OPs case. There is no such thing as a return line that is too big, only too small [ within reason ]. It is a small return line that causes the flow to back up & interfere with steady pressure. Which is why the Mallory 4309 instructions recommend a larger return line with increased length.
I know that. He seems to be grasping for straws. Instead of being MR Asshole corrector all the time, why don't you try to help with the situation at hand? Or is that possible for you?
RRR, worried that someone may know more than you????
If I wanted to be an A-hole pal, there are PLENTY of your posts that I could comment on that are full of BS. Would you like some examples?
As far as helping the OP, I have stated that I believe his return line is too small, in numerous posts, another BS post of yours that I am not trying to solve the OPs problem.
If I wanted to be an A-hole pal, there are PLENTY of your posts that I could comment on that are full of BS. Would you like some examples?
As far as helping the OP, I have stated that I believe his return line is too small, in numerous posts, another BS post of yours that I am not trying to solve the OPs problem.
TT5.9mag
Two atmospheres are better than one
That’s a great filter. Expensive but worth it. And they are cleanable. I used two aeromotives very similar. One 100 micron on the inlet side of my electric pump and one 40 micron on the outlet side. That’s what aeromotive suggests. Holley I’m guessing would recommend something similar with an electric pump but with a mechanical pump I’m not sure. The sock in the tank may be enough. Just a 40m on the outlet.
Nope. Never been a problem for me. In fact, if you look through my posts, you'll see I disclaim what little knowledge I have all the time. What I know will fit on half the head of a pin, maybe less. I say it a lot.
As for the other, it's all a matter of opinion.
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