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Old 07-20-2012, 12:17 AM   #1
nxtruck
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Default Holley 4150 HP metering

What is it with the HP Holleys' rich part throttle calibration? I have 2 HPs, a 950 and a 1000. Both of them run pig rich at part throttle on my 434 sbc. I've played with jetting, power valves, idle air bleeds,and idle mixture screw settings in an attempt to clean up the a/f ratio. On my wideband, the a/f runs in the 11.4 -11.9 range @ 2600 or so with the 950 and only slightly better in the 11..9 - 12.4 range @ the same rpm cruising with the 1000. The plugs agree with what the wideband is saying, as they're dark after a fairly long drive.
Now, as far as idle and wot a/f ratios go, they both idle clean in the 14.0 range and both run in the 12.5 - 13.0 range at wot. I've heard of some guys going back to the older-style 1850 metering blocks in an attempt to clean up the part throttle on these carbs. Is this worth looking into versus trying some expensive billet blocks, only to find out that they do run much cleaner than the Holley blocks? What mods besides different block gaskets are needed to try this?
Thanks in advance!!
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Old 07-20-2012, 04:35 PM   #2
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Default Re: Holley 4150 HP metering

Anyone? Hasn't anyone tried this metering block swap?
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Old 07-20-2012, 05:40 PM   #3
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Default Re: Holley 4150 HP metering

You probably have three emulsion hole blocks. Thread the middle ones 6-32 and buy brass set screws to plug them off. Run .026 in the main air bleeds. Use at least a 6.5 PV on the primary, block the secondary, and jet your primary side down as needed to get your cruise AFR where you want. To get WOT fuel back up you open the PVCR size. A couple other things that can help idle and lower RPM cruise is to move the idle restriction back to where the original Holley carbs had them, shown on the billet block below.


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Old 07-20-2012, 07:00 PM   #4
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Default Re: Holley 4150 HP metering

Mark have you ever considered writing a book on carbs and tunning? If you haven't you should.
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Old 07-20-2012, 10:04 PM   #5
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Default Re: Holley 4150 HP metering

Lol at Sbnova2! You're not lyin'!
Mark, thank you for giving me some direction with this. Yes, they both have 3-emulsion hole blocks. I run a 6.5 p.v. in the front of both and the rears are plugged. I run 74 pri. and 84 sec. in the 950 and 80 pri. and 90 sec. in the 1000, as these jet settings seem to be the best compromise between correct wot a/f ratios and the best cruise a/f ratios I can get w/o getting too lean up high. I have considered enlarging the pvcr in both and jetting down, as you suggested, but am not sure how much larger to go with the pvcr.
Also, could you explain what's involved in relocating the idle restrictions in these HP blocks? Sorry for the ignorant questions, but I hate to make changes, only to find out that I ruined a block.
Thank you again for your help Mark!!
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Old 07-20-2012, 10:08 PM   #6
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Default Re: Holley 4150 HP metering

Mark, one more question: Are you suggesting, along with plugging the center emulsion holes, that I leave the remaining emulsion holes alone?
Thanks!
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Old 07-20-2012, 10:35 PM   #7
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Default Re: Holley 4150 HP metering

Relocating the idle circuit requires threading the passage with a 6-32 bottoming tap, only deep enough for the set screw to be flush with the bottom of that slot between the holes. You can get 6-32 x 1/8 brass set screws from McMaster-Carr for about $5 for 50, and with a 1-60 drill set from Harbor Freight drill four of them with a .040 bit. You can also use the angled channel next to it that leads to the main well, and if by chance you messed up threading both the metering block is still fine. Once you successfully tap the threads you drill the brass restrictions out at the top. Take your time, use lots of lube when tapping, and tap in small amounts checking the depth with a set screw. Once one is done you can use a nut on the tap to set the depth to stop at on the other three.

And yes, plug the center and leave the others. If you don't like the results you can pull out the set screw.
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Old 07-20-2012, 11:47 PM   #8
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Default Re: Holley 4150 HP metering

Thank you sir for the help!! I will give this a try!
Thanks again!!
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Old 07-21-2012, 11:38 AM   #9
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Default Re: Holley 4150 HP metering

The .040” idle jet is too large for the 4150 with 1 11/16” or 1 ¾” throttles. .040” is the size IJ you would use with a 4500 with 2” throttle bores. The idle jet in the 4150 should be about .031” to .033, occasionally .035” in some engines with extremely long duration cams. With 1 ¾” bores .033” should be good to start, using a .070” idle air bleed. Adjust the air bleed to suit.



(Wrote the following yesterday afternoon before Mark posted and then got distracted by the phone and going to the races)

Have you tried a smaller idle jet?

If your HP blocks have the idle jet high in the block at the top of the idle well, that is part of the problem.

Nearly a hundred years ago it was determined fuel flow through a small orifice discharging into air is erratic and flow through a submerged orifice is more consistent. The erratic flow requires the idle jet be larger than necessary than if a submerged jet is used, because the minimum flow condition must be rich enough to avoid lean misfire. Consequently, the maximum flow condition (of the erratic surging flow) is too rich.

The idle jet should be below float level. That is one thing changing to earlier metering blocks accomplishes, it moves the idle jet to below float level.

The other issue is the HP blocks and many other “new and improved” blocks have too much “emulsion package” with too many or too large emulsion bleeds. Many (most, actually) new carbs have too large a main air bleed supplying too much air and overdriving the main well bleeds.

At part-throttle and the low airflow conditions present near the beginning of and in the lower range of main discharge flow, the addition of emulsion air causes richer fuel delivery with the same size jet and venturi vacuum signal because the addition of air to the fuel in the main well pushes the fuel up the well toward the discharge nozzle in the booster (the same as carbonation foam pushes beer up and out a longneck beer bottle). In carbs with the main system flow path dimensions similar to the common Holley 4150, adding emulsion air causes low flow to be richer before it causes high flow to be leaner.
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Old 07-21-2012, 03:54 PM   #10
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Default Re: Holley 4150 HP metering

He's right about the idle jet, I'm still in Dominator mode. For the bigger 4150 carbs a .035 is usually OK. This require a 61-80 drill index.
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Old 07-23-2012, 11:37 AM   #11
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Default Re: Holley 4150 HP metering

OK,
Thank you both very much!! I'm getting ready to order a set of precision bits and pin vises so that I can fix this.
Let me ask this: would there be any advantages to keeping the HP blocks, rather than using an older set of blocks? The reason I'm asking is because I can find the older blocks dirt cheap and if there's no real reason the stay with the HP blocks, I may just swap to the older blocks and be done with it.
Thank you both very much!!

Last edited by nxtruck; 07-23-2012 at 11:41 AM.
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Old 07-23-2012, 02:53 PM   #12
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Default Re: Holley 4150 HP metering

Very interesting thread. I do not mean to hi-jack, but I have a very similar problem. I have a 950HP on a 383 running about 500hp. It is a street strip car and has the exact same issue at part throttle on the street. With just a crack of throttle as is the case during cruise on the highway, it runs low 12s AFR. As you crack the throttle more, it climbs into the high 13s without hitting low vacuum to cause PV to open. WOT is a nice 12.5. Primary with PV is high 12s low 13s. I have tried numerous metering blocks including a billet style with removable emulsion ports (Quick Fuel). The carb is a Pro Systems. Patrick's metering block was super rich at part throttle, which is why I went to a tunable billet plate.

Jet 73/86
LSAB 76/76
HSAB 34/34
Emulsion Port (Top down) .028,.028,.028,0,.033
PVCR .063
IFR .036

It is still rich but not as bad. Suggestions?
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Old 07-23-2012, 02:57 PM   #13
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Default Re: Holley 4150 HP metering

HSAB 26/26
Emulsion Port (Top down) .028, plug, plug, plug
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Old 07-23-2012, 05:55 PM   #14
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Default Re: Holley 4150 HP metering

Quote:
Originally Posted by yeti View Post
HSAB 26/26
Emulsion Port (Top down) .028, plug, plug, plug
Wow, so basically you want to almost kill all the emulsion? Why do they make these billet plates with so many ports? I will give it a try.

I read one of the other posts about a similar topic where they talked about emulsion ports above the fuel level, at the fuel level, and below the fuel level. My question on that is the well fuel level proportional to the fuel bowl level? How do you know where the well level is in a metering block?

Thanks for the HiJack and info.
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Old 07-23-2012, 05:58 PM   #15
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Default Re: Holley 4150 HP metering

Does that include the kill bleed? You want to leave that open and at least one e-bleed, or the top and third e-bleed plugging the rest.
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