170 GPH Holley mech fuel pump and 8AN lines - Chevelle Tech
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post #1 of 28 (permalink) Old Nov 6th, 19, 3:38 AM Thread Starter
 
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170 GPH Holley mech fuel pump and 8AN lines

Curious what your experience has been with the Holley 12-327-20 mechanical fuel pump on small blocks (170 GPH free flow, assuming 8AN fuel line in/out). I'm setting our 560 HP 383 (AFR 210s, .640" lift 253/259 @.050", Vic Jr, Mighty Demon 750) up and had some 3rd and 4th gear lean-out with 3/8" / 6AN lines. Lean out was going from 12.5:1 air/fuel to 13.2:1 in 3rd and 14:1 in 4th before I saw that and let off the gas. I swapped out the .110 needle and seats for .130s with viton, which helped, but figure I should throw on a proper 8AN line from tank to pump and a 40 micron fuel filter to more 8AN to the deadhead Holley regulator and then 6AN lines to carb.

Thoughts welcomed.
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post #2 of 28 (permalink) Old Nov 6th, 19, 7:26 AM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

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Originally Posted by stantaur View Post
Curious what your experience has been with the Holley 12-327-20 mechanical fuel pump on small blocks (170 GPH free flow, assuming 8AN fuel line in/out). I'm setting our 560 HP 383 (AFR 210s, .640" lift 253/259 @.050", Vic Jr, Mighty Demon 750) up and had some 3rd and 4th gear lean-out with 3/8" / 6AN lines. Lean out was going from 12.5:1 air/fuel to 13.2:1 in 3rd and 14:1 in 4th before I saw that and let off the gas. I swapped out the .110 needle and seats for .130s with viton, which helped, but figure I should throw on a proper 8AN line from tank to pump and a 40 micron fuel filter to more 8AN to the deadhead Holley regulator and then 6AN lines to carb.

Thoughts welcomed.
I was going to use the highest output Holley mechanical fuel pump at one time too, ( I believe that's the same one you're talking about) but then I began reading some claims on the net that due to it's heavier springs, it puts a greater wear on the camshaft lobe that operated the pump arm, and allegedly some guys have worn out that fuel pump camshaft lobe with the use of that pump. I had bought that pump at one time, and when I took a look at the pump lever arm, and saw a double spring underneath it where the other Holley pumps have a lighter single spring, then the things I was told about wearing the cam lobe down seemed believable.

Just a guess on my part, (although a somewhat educated guess) but I think you'll eventually end up changing that dead head fuel set-up to a return line one that sends the unused fuel back to the tank/cell. As you probably already know, dead head set-ups are much tougher on fuel pumps, and tend to cause fuel pressure surging or pulses that can really beat-up pumps and reduce their life, but also that isn't great for performance either. I know that set-up is fine for lower horsepower cars, but when you begin making considerbly more power, the dead head set-up is quite a compromise. Just sayin. I hope this helps
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post #3 of 28 (permalink) Old Nov 6th, 19, 8:04 AM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

The pump should have sufficient flow for your combo. What is the fuel pressure at the carb doing when you see the car going lean? If fuel pressure isn't falling off, there is gas in the bowls. The car should not be going lean unless its a carb issue. I assume this engine was dynoed and the carb was tuned? It can happen that a carburetor needs more jet in the car based on high speed airflow characteristics compared to stagnant dyno testing.
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post #4 of 28 (permalink) Old Nov 6th, 19, 8:49 AM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

Sumping the tank and running two 3/8" steel lines to a tee at the pump will make a world of difference on how well that pump keeps that motor fed.. That was one of my tricks I used for keeping those Quadrajets full..

Make sure the pump has a true 3/8" opening, some pumps need to be opened up..
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post #5 of 28 (permalink) Old Nov 7th, 19, 2:38 AM Thread Starter
 
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Re: 170 GPH Holley mech fuel pump and 8AN lines

Thank you. Yes, the pressure drops from 6.5 PSI down to 4-ish in 3rd and 4th gears. Did not know if that's normal given fuel is being used up from the bowls. The .110 needle & seat may be a bit small, as I tried .130 viton which seems to have cured the problem in 45 degree F weather.

Still planning to upgrade the fuel line to 1/2" from tank to pump and 8AN from pump to regulator (and 3/8 from regulator to carb bowl) to help with when weather gets warmer and this janky E10 gas vaporizes at lower temps than when the car was originally dynoed (2004 on 93 octane E0 gas).
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post #6 of 28 (permalink) Old Nov 7th, 19, 11:50 AM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

I'd say that with your hp level an 850 cfm carb is not unreasonable.

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post #7 of 28 (permalink) Old Nov 7th, 19, 2:26 PM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

Since you still have 4 pounds of fuel pressure I would look into the carb. You have jet extensions, right? Maybe bring the rear float level up a bit.

And I agree with Dan. With that much cam and head you would be better off with more carb. 850, 1000, even a Dominator would be better.

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post #8 of 28 (permalink) Old Nov 7th, 19, 3:52 PM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

Make sure the tank has a big enough vent.
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post #9 of 28 (permalink) Old Nov 8th, 19, 1:12 AM Thread Starter
 
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Re: 170 GPH Holley mech fuel pump and 8AN lines

Solid advice here, all. Thank you. At 45F air & fuel temps, the problem of 3rd and 4th gear lean-out (to 13-14:1 in WOT) has been solved by the .130" needle & seat.

When temps are warmer (60F-80F), the air/fuel gets leaner in 3rd/4th, which is counter to what I'd expect from air being warmer. Theory is the E10 fuel vaporizes more (thus leaning things out) at these temps than the warmer air would richen things up.

I'm hoping going from 3/8" to 1/2" helps reduce this impact of the vaporization enough to keep the lean-out from recurring.

Your idea of the larger carb is interesting as well. The good folks at AED actually talked me out of changing carbs by recommending the changes to needle & seat and fuel level in bowls. They talked through either 750s or 850s, and they lean toward 750.

Will let you guys know what the car runs like with 1/2" line. Thanks again.
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post #10 of 28 (permalink) Old Nov 8th, 19, 6:35 AM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

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Originally Posted by stantaur View Post
Solid advice here, all. Thank you. At 45F air & fuel temps, the problem of 3rd and 4th gear lean-out (to 13-14:1 in WOT) has been solved by the .130" needle & seat.

When temps are warmer (60F-80F), the air/fuel gets leaner in 3rd/4th, which is counter to what I'd expect from air being warmer. Theory is the E10 fuel vaporizes more (thus leaning things out) at these temps than the warmer air would richen things up.

I'm hoping going from 3/8" to 1/2" helps reduce this impact of the vaporization enough to keep the lean-out from recurring.

Your idea of the larger carb is interesting as well. The good folks at AED actually talked me out of changing carbs by recommending the changes to needle & seat and fuel level in bowls. They talked through either 750s or 850s, and they lean toward 750.

Will let you guys know what the car runs like with 1/2" line. Thanks again.
AED is a great company. But when I bought a carb from them a few years ago, they did NOT routinely include installed jet extensions with their carbs. I had to ask for them. I was kinda surprised at that. But if the lack of jet extensions was your problem, then I would think that the problem would occur in first gear the most, rather than in 3rd gear, since the G-force is greater during the first 60 feet of the 1/4 mile run. Especially during the launch.

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post #11 of 28 (permalink) Old Nov 8th, 19, 12:22 PM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

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AED is a great company. But when I bought a carb from them a few years ago, they did NOT routinely include installed jet extensions with their carbs. I had to ask for them. I was kinda surprised at that. But if the lack of jet extensions was your problem, then I would think that the problem would occur in first gear the most, rather than in 3rd gear, since the G-force is greater during the first 60 feet of the 1/4 mile run. Especially during the launch.
If you watch a video of what happens during a run inside the fuel bowls you see that the fuel moves to the rear and stays there the whole time. What isn't as easy to see is that there is considerable pressure on the fuel pushing against the jets in the primary bowl. The pressure on the primary jets can force enough extra fuel on the primary side to mask the effect of the secondary jets being uncovered partially if an extension isn't being used. That pressure subsides as the car's acceleration declines and it will lean out because the fuel is still pushed away from the rear jets. They may not be uncovered entirely, or even at all, but the level is lower and the fuel has to move farther through the wells to get to the nozzles. Jet extensions push the jets back to where the fuel is higher thus giving an advantage of the gravity of a taller fuel column and the shorter path through the main well.

I'm not saying this is definitely the problem here but it's one variable we can eliminate cheaply.
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post #12 of 28 (permalink) Old Nov 8th, 19, 1:22 PM Thread Starter
 
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Re: 170 GPH Holley mech fuel pump and 8AN lines

Excellent point and one I should have mentioned - I installed the jet extensions and associated change to the float (allowing full range of travel, since regular float will bottom on the extended jets) when I installed the .130 viton needle & seats.

The .130s had to be adjusted all the way down until no threads were showing / graspable by the adjusting nut - just to get the fuel level to nudge the very top of the sight glass on the float bowl. Quick drive around the block confirmed this was useless due to fuel sloshing out the vent on turns or braking. Put the .110s back in and regained float adjustment to mid-line in the glass, but still had the lean-out in 3rd and 4th.

Pulled .110s out along with the float assembly. Iteratively bent the tang on the floats upward about 1/8" and re-assembled float into bowl, checking how much range of adjustment I'd have. Eventually settled on an adjustment range that didn't over-fill or under-fill the bowl based on where an imaginary line at 3/4 of way up the float was, in relation to the sight glass. Worked perfectly with the .130 vitons installed, with full range of adjustability, no bogs or slosh issues, and no lean-out in 3rd and 4th (so far - temps here are in mid-50s this time of year; will wait to see what we get next summer once this and the 1/2" fuel line setup is there).

For now (in 40-60F weather) this simple, old-school carb & mech pump seems to be "working as designed" and "good enough" for my needs with air/fuel ratio being 14.7:1 idle and cruise and mid-low 12s when WOT in all gears. Close enough for Sat early morning drives through the twisties in a car that I don't park/leave anywhere but in our garage.

Much cheaper than the "plan B" I was considering with Aeromotive's Gen 1 Stealth Tank (their Stealth 2's foam scares me longevity-wise) which would then go to "plan C" if needed with a Stealth Sniper setup (which requires solving/preventing a ton of RFI issues that need debugging from what I've seen on forums, vs. this simple solution). Sure the EFI would be easier to tune (I've been tuning laptop load/RPM cells since 2005 on AEM, MoTec, Hondata) vs. what I grew up tuning (HSABs, IABs, IFRs, main jets, dist springs/weights) since '85), better cold-start, transition, etc. but it seems like a $2K-$3K beta test when all parts are considered and there are this many issues people are still seeing in the field.

Thanks again for the collective wisdom. You guys are the best.
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post #13 of 28 (permalink) Old Nov 8th, 19, 1:40 PM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

Man, you're on top of it. You're adding to a great knowledge base and I thank you.

You'll get it sorted, I have no doubt.

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post #14 of 28 (permalink) Old Nov 8th, 19, 2:06 PM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

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If you watch a video of what happens during a run inside the fuel bowls you see that the fuel moves to the rear and stays there the whole time. What isn't as easy to see is that there is considerable pressure on the fuel pushing against the jets in the primary bowl. The pressure on the primary jets can force enough extra fuel on the primary side to mask the effect of the secondary jets being uncovered partially if an extension isn't being used. That pressure subsides as the car's acceleration declines and it will lean out because the fuel is still pushed away from the rear jets. They may not be uncovered entirely, or even at all, but the level is lower and the fuel has to move farther through the wells to get to the nozzles. Jet extensions push the jets back to where the fuel is higher thus giving an advantage of the gravity of a taller fuel column and the shorter path through the main well.

I'm not saying this is definitely the problem here but it's one variable we can eliminate cheaply.
Tom, I haven't seen any video like that, so I cannot honestly comment on such a video. However, I don't see why it would matter if a main jet is submersed by one inch of fuel, or by one hundred inches of fuel. As long as the jets are submersed, that's all that should matter, since the fuel is not yet mixed with air while it's inside the fuel bowls, and you cannot compress liquid.

The main force of the fuel being moved through the main jets is simply the vacuum coming from the downward movement of the engine pistons during their intake strokes. Not by any internal pressures going on inside the fuel bowls. So I'm not too quick to share your viewpoints on that. The one part of your post above that I am quick to agree with, is your final thought about jet extensions being cheap insurance, and I'll add to that by saying that not only are they cheap, they're easy enough to install, (particularly the screw-in ones. I must admit that it seemed kinda strange that after I did request that AED install jet extensions in the Dominator carb I bought from them, it came with pressed-in extensions rather than screw-in ones. But that's another sub-topic anyway. I digress).

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post #15 of 28 (permalink) Old Nov 8th, 19, 4:09 PM
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Re: 170 GPH Holley mech fuel pump and 8AN lines

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However, I don't see why it would matter if a main jet is submersed by one inch of fuel, or by one hundred inches of fuel. As long as the jets are submersed, that's all that should matter, since the fuel is not yet mixed with air while it's inside the fuel bowls, and you cannot compress liquid.
Billy, if what you're saying were true then float level would have no effect on on AFR but we all know that it does. The level of fuel in the float bowl is the level of fuel in the main well behind the jets. The higher that level the easier it is to move the fuel to the nozzles. So yes, there are pressures within the float bowl. Fuel has mass and as such has gravity.

Fuel isn't simply sucked out of the nozzles by vacuum. It is pushed out by way of emulsion holes in the main wells that are fed high-velocity air introduced by the main air bleeds. There's a lot of pressure, both positive and negative, in a carburetor.

If you doubt what I'm saying enlarge the emulsion holes in your metering block and observe what happens to your AFR when you're on the main.

Hint...it goes rich. Adding emulsion air increases the positive pressure used to move the fuel from the main well to the nozzle. The higher the fuel level, the closer it is to the nozzle and the easier it is to move with positive air pressure supplied by the main air bleed.

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