[Scott65]

The external regulator would seem the better, and easier long term plan. You could conceivably stretch the horsepower rating of the Sniper to almost 800 with the appropriate pump, that being closer to what you have now, rather than going to the smaller pump. Thing is, unless you have another pump on hand to verify whether the regulator is overpowered, or bad, you may change the pump and still have a bad regulator...

[JLMounce]

Most people don’t know this, but it is in fact possible to change the injectors on these things. There’s a bit of pigtail trimming that needs done, but the option is there to do so if you need extra headroom.

That’s outside of this discussion though. One thing that hasn’t been touched on here is the PWM settings in the software. That GPA5 pump should be pwm ready. There’s no need to set the pump to run at 100% all the time.

I don’t know what Holley recommends, but for the FiTech systems you generally want to set the pump at around 70-75%. The fuel pump driver will ramp additional fuel as needed.

That may also help as you’re not trying to bypass as much fuel.

[Scott65]

I was talking about the 100# injectors. At 58 psi and 85% duty cycle they oughta support close to 800 on gasoline N/A. Just by the numbers, I'm sure Holley doesn't advise cutting it that close. But supplied with enough fuel it's doable. That wasn't really the point of my earlier post, which was overall, in the OP situation a different pump without verification of the regulator would be a step backwards overall.

[Formulajones]

Originally Posted by Scott65

I was talking about the 100# injectors. At 58 psi and 85% duty cycle they oughta support close to 800 on gasoline N/A. Just by the numbers, I'm sure Holley doesn't advise cutting it that close. But supplied with enough fuel it's doable. That wasn't really the point of my earlier post, which was overall, in the OP situation a different pump without verification of the regulator would be a step backwards overall.

That's what I found as well Scott. Holley's HP ratings on these units are primarily based on the injectors, and they are extremely conservative in that regard.

I agree, I wouldn't bother changing the pump and would rather get a capable regulator on there. That to me, seems like a better long term idea.

[gman005]

Thanks guys. I have the new regulator so I will try it. If it doesnt work I will get a external one.

[Formulajones]

Did it work? I'm curious to know if what I had read has any merit.

They never did mention in the discussion what pump would be okay with those internal regulators. If this is in fact the case, I'm guessing a 255 should work just based of the HP rating of the EFI unit itself. Since it's 600hp it would stand to reason it should handle a 600hp capable fuel pump, hence the 255 LPH.

[gman005]

Sorry guys been busy doing family stuff hopefully today after work I can get out to the garage.

[gman005]

So I changed the regulator and the pressure was at 62 psi running it into the gas can. I hooked up the return line back to the tank and started it. It held at 60 psi for about 5 minutes and then it went back up to 70 psi and I still have other issues. I am going to bring the car to someone hopefully get it figured out. If not I will put the 850 back on so I can drive it.

[Scott65]

From your description, it sounds like the regulator is being overpowered/ blown out by the higher capacity pump. If the someone your taking it to is charging, you'd be money ahead to put a bypass regulator on it and the block off for the Holley and get fuel pressure correct and reliable before hand. If you use the Aeromotive that comes with low and high pressure springs, you can also use it with your carb if you end up needing to.

[Formulajones]

Yep like Scott said, sounds like the stock internal regulators just aren't capable of holding a decent pump. Pretty much what I read on the holley forum.

I agree with Scott, get yourself an Aeromotive 13301 regulator, (or what ever your regulator of choice is) mount it somewhere convenient near the throttle body, and run a full return line back to the tank. That'll cure the issue and much cheaper than paying someone to do it. I'd rather do that and keep the bigger pump in the car.

I'm running the Aeromotive 13301 on both cars. Actually they've been on there for 20+ years. I just changed them to the EFI spring they come with when I put Snipers on both cars. Both cars run 450 LPH pumps in the tank.

[JLMounce]

Agreed, but I actually think you have two issues going on.

62 psi with fuel emptying into an open gas can, then pressure creep to 70 psi with the system back at the tank. The system would have been able to cope with the 62psi pressure, but who knows how long the regulator would have lasted.

You likely have a venting issue at the tank as well. the pressure creep up to 70psi pretty much confirms that.

Solutions will be to either drop the pump size (I'd go 255 walbro) or change to an external bypass regulator. You also need to address the venting of the tank.

[Formulajones]

Is it venting and/or maybe the size of the return line??

I don't remember if return line has been discussed but a line too small will cause this issue as well.

I have a formula around here somewhere I'll have to dig up. It takes the length of the return and the pump output, as well as coefficient of drag, and tells you what diameter return line should be run.

I usually error on the side of bigger because too big doesn't hurt anything. Too small creates problems. General rule of thumb is the return should be "at least" the same size as the feed line but most will recommend one size bigger.

The shorter the length the less you can get away with.

[JSchmitz]

Seems like line or regulator size wouldn't take five minutes to creep up. Should be immediately apparent. Seems like venting, filter clog, or something. Should be increased flow, increased resistance to flow, or bad pressure reading. Has the pressure been verified?

[JLMounce]

That's my thinking as well. An improperly sized sized return line or kink/upstruction should show up almost right away.

The caveat to that is if the sizing is just right on the edge. A cold engine will pass less fuel at idle as it require more consumption, but as temperature increases and fuel demand drops, you could start building pressure in the line.

I believe gman stated he was running 3/8 line for both supply and return.

[Scott65]

Maybe the 340 is really a mismarked 400 or 450... Maybe a flow test to verify that. -6 line I don't believe will handle the 400 or especially the 450 on the return side anyway.
ETA: I ordered my tank with a 400lph, that showed up not putting out the correct flow (significantly low), I'm sure mistakes get made....

[Formulajones]

Oh 3/8?? Personally I'm a bigger line guy myself.

Is this a lower HP application? I assumed it was fairly stout since he opted for the 340 pump.

[Scott65]

I believe somewhere in this thread he stated -6 feed and return.

[JSchmitz]

Oversized lines can be a problem as well. Especially in a deadhead system. Fuel inertia can cause wild swings in pressure. I saw this with a 1/2" deadhead carb fuel system. Changed it to return and rock steady. Also heated fuel because of high residence time from slow moving fuel.

I went with !/2" supply and 3/8" return on my LS conversion. Overkill for now. But planning for serious upgrade. What a PITA those were to install!

[JLMounce]

A -6 line (3/8 ID) with a pusher pump is sufficient for around 800 hp on a naturally aspirated setup, assuming the pump is properly sized, but you'd typically have to increase your pressure quite a bit to get there. It's more appropriate up to about 600hp.

gman's combination is somewhat similar to mine. I run -6 line for the feed and return, but utilize the tanks ink GPA-4 pump, which is a walbro 255. Between injectors, lines and pump, I have enough to support about 630hp. Based on my car's weight and trap speeds, I actually make about 420hp at my altitude, roughly 360 to the tire.

[Formulajones]

Yeah I never run a deadhead system, even with a carb.