[Formulajones]

Originally Posted by 78w72

right, but only the early year cars had that EEC standpipe on the rear seat, my 72 had that but i eliminated it.

charcoal canisters on most or all 73/74 or so & up years were up front in the engine bay & used a separate line than the vapor return line off the pump.

Charcoal actually started in 70 for California built and sold cars. My Formula has one. I realize where they are, but that wasn't what I was talking about as the return line doesn't go there.

Like mentioned, it's just dependent on year, where the car was built and sold. But my point was to check the return and make sure it terminates in the tank as some vary, and you don't want to just blatantly pump fuel through it not knowing, or you may end up in a not so pleasant situation. That's what I wanted the OP to understand.

[PunchT37]

Originally Posted by 78w72

yes thats the idea & some have issues with it... but myself & many others on here & out there in the world dont have any problems with todays "piss gas". i normally run 91 premium with no ethanol in my higher compression stroker motor but it will run fine on mid grade 89 with 10% ethanol too... i have huge super comp headers & the fuel line passes within 1" or so as it passes by that area of the engine, never any vapor lock or fuel heat related issues in any street driving situation or at the drag strip. same for other pontiacs i own/owned with ~400 or more HP, all stock fuel systems. yet some need to add all kinds of crazy mods & tons of heat wrap just to get down the road to the dairy queen. guess im just lucky.

You might have problems down here. Even though I don`t have problems with mine, the weather can aggravate issues. Running 87 to 89 octane where you are ain`t gonna be the same as here. Especially in the summer. High heat AND high dew points.

Like today. All you have to do is stand outside doing nothing. You will sweat your balls off.

[78w72]

Originally Posted by PunchT37

You might have problems down here. Even though I don`t have problems with mine, the weather can aggravate issues. Running 87 to 89 octane where you are ain`t gonna be the same as here. Especially in the summer. High heat AND high dew points.

Like today. All you have to do is stand outside doing nothing. You will sweat your balls off.

have you been to the central midwest or plains lately? was 95-97f & very high humidity last week & this week is lower 90's all week, & its only mid june... july & aug we can get almost as bad as FL & LA etc with just about as bad humidity, granted thats not normal or everyday but upper 80s & mid 90s are regular temps all summer long.

in iowa & surrounding states we get just as bad of humidity as southern states, stand outside in the shade on even a upper 80f day with 75-80% humidity & lower to mid 70s dew points & youre wet & sticky doing nothing.

im not saying iowa temps are as bad as southern fl or la etc, but there are plenty of days that are almost just as bad as central & northern fl/la/tx etc.

[Formulajones]

Summers were like that in SW Ohio. Temps in the 90's, dew point 70 degrees and humidity 90% BLECK!!! Couldn't be outside 10 minutes and you needed another shower. Then of course afternoon pop up thunderstorms from all that humidity was also pretty much a daily norm.

I never had vapor lock or fuel issues, as long as they were running the proper grade of fuel for the season.

What gave me fits was that damn winter grade fuel they would use. Worked fine when it was 20 below zero but they wouldn't switch back to summer grade until April and it never failed we would have that weird weather in February or March where temps would be 60 or 70 degrees for a couple days, and that winter grade fuel hated that. But like they say in Ohio, don't like the weather, wait a day and it'll change, lol.

Don't have that fuel grade problem in Arizona, it's hot all the time and the 91 octane is the same crap fuel year round LOL

[Brentco]

Originally Posted by 78w72

as brentco mentioned, robbmc doesnt recommend a true return line with their pump, he explained to me that it will reduce the psi too much on a mech pump, im sure it might work for some applications but shouldnt be needed for most situations.

That’s interesting. I had a pretty detailed discussion with Robb about the use of a bypass regulator with his pumps about a year ago, and he told me he doesn’t recommend them with his mechanical pumps because with a bypass the needle on a fuel pressure gauge bounces a lot, especially at low rpm. He said he wasn’t sure if this caused any problems and had only tried it in a couple set ups. I’m not sure why it would reduce the psi too much on a mechanical, given that bypass regulators are normally open, so they shouldn’t reduce the psi below what the pump puts out unless they’re adjusted to a lower psi. And the 1100hp RobbMC pump puts out 12 psi pressure (max), which is more than enough to keep a constant pressure over 6 psi at the regulator.

A lot of the manufacturers say not to run a bypass regulator on a mechanical pump. Despite a lot of searching of online sources, I couldn’t find any rationale or explanations as to why this might be an issue though. Does anyone know why? I don’t see any reason why there would be a particular problem with a mechanical pump, or why a deadhead regulator would be any better.

In any event, I run a bypass regulator with the RobbMC pump on a 468, with a Speed Demon carb, 1/2” line throughout, including a full 1/2” return line, and it works great. I haven’t seen a lot of psi bouncing on my fuel pressure gauge, but my gauge isn’t the greatest.

A vapor return will cure the vapor lock issues. A full return will also cure vapor lock and the cooling effect from having fuel constantly circulating is a big plus, in my book.

PS — there is some great discussion and a lot of great info in this thread.

[Formulajones]

I'm pretty sure all of Robb's mechanical pumps now come with the return line as standard issue, it's no longer an upcharge. If you don't use it you simply plug it.

The only upcharge on his pumps now is if you want an extra outlet port.

[Formulajones]

Originally Posted by Brentco

A lot of the manufacturers say not to run a bypass regulator on a mechanical pump. Despite a lot of searching of online sources, I couldn’t find any rationale or explanations as to why this might be an issue though. Does anyone know why? I don’t see any reason why there would be a particular problem with a mechanical pump, or why a deadhead regulator would be any better.

I find that funny, the bypass/return part, because the factory did that on many applications. A 69 Nova or Camaro with the 350/300hp or the 396/350hp comes to mind. They used a stock mechanical dead head style pump but used a special external fuel filter with a return built in and an extra line running off that going back to the tank.

Plus the fact that Robb now sells all his mechanical pumps with the return option built in.

[Brentco]

Originally Posted by Formulajones

I find that funny, the bypass/return part, because the factory did that on many applications. A 69 Nova or Camaro with the 350/300hp or the 396/350hp comes to mind. They used a stock mechanical dead head style pump but used a special external fuel filter with a return built in and an extra line running off that going back to the tank.

Plus the fact that Robb now sells all his mechanical pumps with the return option built in.

Yeah IIRC, the RobbMC pumps come with an extra gauge port and he sells a fitting with a restriction that you can use to add a vapor return.

For the factory applications, are you talking about full return lines or vapor returns?

I’m curious about the aftermarket units because Holley’s bypass regulators clearly state (in big bold text) that they’re not for use with mechanical pumps. The only ones I’ve found that affirmatively say they can be used with mechanical are one from QF and some from Aeromotive (with Aeromotive price tags). Just wondering what the reasoning behind this is, and why I’ve been able to use the Holley regulator with a mech pump with no issues.

[Formulajones]

Originally Posted by Brentco

Yeah IIRC, the RobbMC pumps come with an extra gauge port and he sells a fitting with a restriction that you can use to add a vapor return.

For the factory applications, are you talking about full return lines or vapor returns?

I’m curious about the aftermarket units because Holley’s bypass regulators clearly state (in big bold text) that they’re not for use with mechanical pumps. The only ones I’ve found that affirmatively say they can be used with mechanical are one from QF and some from Aeromotive (with Aeromotive price tags). Just wondering what the reasoning behind this is, and why I’ve been able to use the Holley regulator with a mech pump with no issues.

The factory used what they called vapor return but you'll still find they move a small amount of fuel. They aren't a full on return like you would have with a return style regulator.

What I'm not clear about is the RobbMC pump and whether the return on his pump is meant as a vapor or a full fuel return. Either way it'll still be returning some fuel. Might be something to ask next time I get in touch with him. That's what I thought was funny when he said he doesn't recommend a return on a mechanical pump, but all his pumps come with them now.

I'll be experimenting with one of his pumps in the near future, using the return and hooking that to the factory 1/4" return line.

[Brentco]

Originally Posted by Formulajones

The factory used what they called vapor return but you'll still find they move a small amount of fuel. They aren't a full on return like you would have with a return style regulator.

What I'm not clear about is the RobbMC pump and whether the return on his pump is meant as a vapor or a full fuel return. Either way it'll still be returning some fuel. Might be something to ask next time I get in touch with him. That's what I thought was funny when he said he doesn't recommend a return on a mechanical pump, but all his pumps come with them now.

I'll be experimenting with one of his pumps in the near future, using the return and hooking that to the factory 1/4" return line.

Yeah the whole “vapor return” nomenclature is messy. That’s my understanding — that the vapor return doesn’t actually separate out vapor from liquid fuel, so it actually sends a mix of vapor and a bit of fuel back to the tank. But the restriction on the vapor return is tiny, so the amount of liquid fuel that circulates through the vapor return must be very small. I believe that was the factory set up. I know it had a small return line, something like 1/4”, and believe it also had a small restriction at the pump?

I probably could have been a bit clearer in what I was talking about re: what RobbMC says about a return. The instructions don’t say no return whatsoever, they just say you can’t use a return-style regulator (which have full returns) and can only use a deadhead regulator. The return for the RobbMC set up is a “vapor” return. They say to either hook up the 1/4” return line to the metered port on the pump or you can plug the extra port on the pump and make your own fitting by drilling a .040 hole in a blank, which you then plumb into the line to the carb. So either way there’s a restriction letting just small amounts of fuel through the return line.

I see now what you’re saying about the pumps coming standard with a return. The FAQs say that the all pumps come with a metered port for a return line. It’s just in the instructions, at least for the Pontiac pump, that say you have to buy the separate fitting for the return line. I didn’t look at the extra port on mine, but I assume the instructions are old and they’re actually shipping with metered ports now. Either way there’s supposed to be a restriction, so it’s meant to be a “vapor return.”

In general, I assume the return needs to be either metered through a small restriction or through a bypass regulator — at least those are the only ways I’ve heard of it being done. In other words, you can’t just plumb the 1/4” return directly into your fuel lines. It would make sense that either a restriction or a bypass valve would be needed to maintain the pressure in the system.

And jumping back a couple posts — I hear what you’re saying about winter grade fuel! California does the exact same thing. The fuel grades change according to the calendar, but you’ll get hot streaks all the time during the “winter” period, and your whole tune and fuel system goes wonky (maybe one of the reasons why I like controlling fuel temp by circulating through a full return).

[Brentco]

Why are my posts getting so long? Yuck.

[78w72]

Originally Posted by Formulajones

The factory used what they called vapor return but you'll still find they move a small amount of fuel. They aren't a full on return like you would have with a return style regulator.

What I'm not clear about is the RobbMC pump and whether the return on his pump is meant as a vapor or a full fuel return. Either way it'll still be returning some fuel. Might be something to ask next time I get in touch with him. That's what I thought was funny when he said he doesn't recommend a return on a mechanical pump, but all his pumps come with them now.

I'll be experimenting with one of his pumps in the near future, using the return and hooking that to the factory 1/4" return line.

the robbmc pontiac pumps have an option to buy a "vapor return" fitting PN1010 that has a small .040 metered hole to send vapor & a very minimal amount of fuel to the tank to help with vapor lock, it is not a full return or intended to act like one. the pumps dont come with that, its a seperate part to buy, the pumps come with a port for a fuel gauge or to add the vapor return fitting or plug it if not using either one. i use the 1100 on one of my cars deadhead & havent had the need to use the vapor fitting, robb says it will reduce the pressure about 1psi.

a full return regulator would obviously reduce the psi quite a bit more than the vapor port on robbmc or factory pumps or filters, some may be able to get away with that if their carb/engine doesnt care about the reduced psi but it might be a problem for higher hp or drag racing if you are at the edge of psi/flow needs for the engine. probably why holley & some other return regulators say to not use on mechanical pumps.

the robbmc mech pumps are designed to be ran deadhead so a full return regulator doesnt have much benefit unless you actually need a full return regulator for some reason & the pump can support the loss of some psi.

[Formulajones]

Yeah, the fact that Robb says hooking up his "vapor" return line as everyone calls it, drops the fuel pressure by 1 psi, tells me that it is in fact moving some fuel back to the tank. Which is fine, the car has that factory feature already and I want to keep that function.

It'll be fine for what I'm doing with it.

[Singleton]

For the past 5-6 years I have been using a Robbmc 550 pump in conjunction with a bypass regulator. Have the return port plugged on the pump, and a bypass regulator down stream of the carb. Fuel pressure is 5-6 lbs, so I’m sending about 1-2 psi worth back to the tank. No issues running out of fuel at full throttle, 495 cid, pro-systems 950hp carb, and 340 cfm Eheads from sdperformance.

[78w72]

Originally Posted by Singleton

For the past 5-6 years I have been using a Robbmc 550 pump in conjunction with a bypass regulator. Have the return port plugged on the pump, and a bypass regulator down stream of the carb. Fuel pressure is 5-6 lbs, so I’m sending about 1-2 psi worth back to the tank. No issues running out of fuel at full throttle, 495 cid, pro-systems 950hp carb, and 340 cfm Eheads from sdperformance.

thats awesome the 550 works for you on that engine. the regulator is "downstream" of the carb? so its after the carb? or between the pump & carb? edit: just saw the pic, never heard of putting the reg after the carb, most places recommend putting it before & close to the carb. wonder if maybe the carb sees full psi how you have it, then the reg bleeds off after it?

have you drag raced the car? a 495 with 340 heads should be making well above 550hp, curious why you went with the 550 pump? robb would usually recommend the 1100 for that engine. im sure the holley style carbs 2 big bowls helps a lot with fuel supply... i have a hard time keeping the single small q-jet bowl full on hard launches at low 11sec runs... but its perfectly fine at WOT on the street, even the edelbrock pump i had before the robbmc was ok on the street, dragstrip was a completely different deal.

[Singleton]

I have a 550 pump only because it’s a holdover from a previous engine. I can send this one back to Robbmc and have it converted to the 1100, but haven’t seen the need to yet. No, never drag raced, so don’t know if fuel issues would arise there, very possible though.
Yes, the bypass regulator is after the carb. It acts as an adjustable restriction to the fuel system. The more it is opened the less fuel pressure in the entire system. Fully open there would be no pressure in the line anywhere; free flow. Close it completely and get full pressure. It’s basically barely open now, allowing a small amount of fuel return to the tank. Keeping the fuel moving and cool at idle and low engine speed is what I’m trying to accomplish.
As far as horsepower, never dynoed, but would expect north of 600 easily, but no more than 650

[Brentco]

Originally Posted by 78w72

a full return regulator would obviously reduce the psi quite a bit more than the vapor port on robbmc or factory pumps or filters, some may be able to get away with that if their carb/engine doesnt care about the reduced psi but it might be a problem for higher hp or drag racing if you are at the edge of psi/flow needs for the engine. probably why holley & some other return regulators say to not use on mechanical pumps.

A return-style regulator, as I understand it, only bleeds off pressure (by opening the bypass valve and diverting fuel to the return) when the fuel pressure coming from the pump exceeds the pressure setting on the regulator (set with the adjustable screw). So a bypass regulator would not reduce the psi from the pump across the board like a metered return would. It just limits the max psi going to the carb. For example, if the pump only put out 6 psi, and the regulator was set at 6 psi, the bypass valve would stay closed and fuel would flow to the carb at 6 psi.

[mchell]

One thing I know for certain regarding fuel delivery is you CAN NOT compare setups…. Waaaaaaaay too many variables at play.

For instance:

Years ago, after hearing great reviews on the Robbmc stuff I went ahead and tried it, Robbmc 1100, 1/2 line from carb to tank, 1/2 pickup, vapor return, bypass return, pressure regulators etc etc etc

Car ran ok around town although I did experience vapor lock issues sitting at long lights in summer heat(with vapor return active). However, I was not able to get it down a race track. Played with it for some time before giving up.

Point is, there is no magic bullet here, you simply need to use what works for your combo, which inevitability may require trial and error.

[78w72]

Originally Posted by Brentco

A return-style regulator, as I understand it, only bleeds off pressure (by opening the bypass valve and diverting fuel to the return) when the fuel pressure coming from the pump exceeds the pressure setting on the regulator (set with the adjustable screw). So a bypass regulator would not reduce the psi from the pump across the board like a metered return would. It just limits the max psi going to the carb. For example, if the pump only put out 6 psi, and the regulator was set at 6 psi, the bypass valve would stay closed and fuel would flow to the carb at 6 psi.

thats a good point to bring up, im no expert so cant say that's cut & dry how a return regulator works. the way i would guess it works is that the regulator output psi is adjusted via the set screw as you mentioned, the fuel pump puts out X psi, the regulator set screw will let the valve open & allow only the set amount of psi to the carb. a return regulator still returns all the unused fuel back to the tank, the set screw just adjust the psi thats let out to the carb.

but, the amount of fuel flow the pump puts out constantly is far more than the engine can use 99% of the time, a bypass regulator will allow that excess fuel to free flow & return to the tank. my thinking was that a mechanical pump will lose some amount of psi trying to keep up with that constant flow of a return reg, on the 1100 thats probably not an issue, but on the 550 or other lower flow/psi pumps like the edelbrock or carter, it might be since it only puts out 6psi based on the specs.

i could be wrong on a return regulator causing a psi drop for a lower psi mech pump... any carb or fuel experts able to confirm that or why some places say not to use a full return regulator with a mech pump?

[78w72]

Originally Posted by mchell

One thing I know for certain regarding fuel delivery is you CAN NOT compare setups…. Waaaaaaaay too many variables at play.

For instance:

Years ago, after hearing great reviews on the Robbmc stuff I went ahead and tried it, Robbmc 1100, 1/2 line from carb to tank, 1/2 pickup, vapor return, bypass return, pressure regulators etc etc etc

Car ran ok around town although I did experience vapor lock issues sitting at long lights in summer heat(with vapor return active). However, I was not able to get it down a race track. Played with it for some time before giving up.

Point is, there is no magic bullet here, you simply need to use what works for your combo, which inevitability may require trial and error.

yeah im kinda chasing my tail on the robbmc 1100 & all 1/2" lines & pickup, does great on the street & into the mid to upper 11's, but when i get a good launch & hard run to lower 11's i get cutting out usually around top of 2nd gear. im debating on going electric, preferably in tank if i want to go any faster.

what pump set up did you end going to?