Next step for V8 performance mods

[Walking-Tall]

A 600 double pumper, with the same venturi diameters (AIRFLOW) as a 600 vacuum secondary (1-1/4" primary and 1-5/16" secondary), probably did not have the secondary opening link opening the secondaries fully, in order to generate less power. (Because) By the way, a "670" Street Avenger is a 600 vacuum secondary by it's venturi diameters... as well as a whole host of other troubles... all that I have seen (and remedied) have primary and secondary idle air bleeds that are too big, idle feed restriction sizes imbalanced and not specific for anybody's engine/vehicle combination, primary power valve channel restrictions too big, (<--- if at ~0.054", they attempt to compensate for) secondary jets that are too small, they frequently have metering blocks with idle mixture needle tip passage holes that are too big (0.100"+, original sizing meant for the blunt tip "reverse idle" mixture screws... making finding any sort of correct idle mixture next to impossible... standard idle (clockwise lean) mixture metering blocks require 0.063" passages for the sharp tip idle mixture screws), as well as air bleeds in the rear face of the primary metering block way up high in the "dog leg" of the main circuit air channels into the main wells (originally intended for metering blocks with "emulsion" tubes in the main wells... there haven't been "emulsion" tubes in main wells in Holley metering blocks in about 30 years...)... in a nutshell, I'm afraid I deem them another of the "new and improved" well-waxed expensive garbage of the utmost caliber.

You don't know how much camshaft is in it. How much idle vacuum will it presently generate? That'll give an idea on 0.050" intake duration, and subsequent correctly sized idle feed restrictions...

In general, you'd probably be miles ahead figuring out what's wrong with the 4776 and reusing it, or better yet, going with that 4777.

I don't have your cylinder heads, but my 306 is sporting most else yours is, including a bit over 9:1 and 218-degrees at 0.050 intake duration (she's bumpy enough idling at ~750rpm, and generates ~14-15"Hg vacuum), RPM intake with a 750 vacuum secondary, 14-degrees BTDC initial for starters (18 is possible (38 total mechanical) with a re-curved DuraSpark II distributor that's limited to provide only 10-degrees (distributor - 20 crankshaft degrees, "all in" at about 6000rpm... which is what a healthy small block Ford has always liked (it's the SBC's with their inefficient chambers that always needed the much-touted-by-magazines XX-degrees "all in by 2500rpm" nonsense... and with (the faster burning than the good (better than SBC) chambers SBF's have always had) combustion chambers like yours, you'd be best to re-curve the distributor to limit total mechanical advance to 32 or 34 degrees for best power))... it's not officially road-ready yet, but mine jalopy with 87-octane in the gas tank and one rip up the road and back and she's a real happy camper initially... super tuning to follow once road ready...


Additionally, after perusing all of the thread posts:
The blue (air:fuel ratio) line on the dyno sheet graph image of yours shows what I'm talking about above... the measuring of AFR starts off rich at 2500rpm @ 11:1 (matching the torque dip off the start), then dips richer yet at 3000rpm to 10:1, and then works it's way upward/lean (assuming secondaries open for sure by about 4000-4500rpm) and past 5000rpm it's gone onto the lean side of things @ 13:1 (producing the nervous looking, zig-zag saw blade-ing of the torque/hp lines). This is precisely how most "new and improved" carburetors that I have seen (and fixed) work... rich and mediocre at best everywhere down low and for acceleration and for cruise (lack of) fuel mileage, and then off into the most dangerous of danger zones for a carburetor to go lean, up top and at maximum operating rpm...

A correctly (and safely) calibrated and tuned carburetor will very quickly head straight to (richen, dip down to, from efficiency everywhere else like idle, low speed, light part throttle acceleration, cruise, etc.) a WOT AFR of about 12.5:1, and remain right at that AFR like a horizontal line all the way cleanly to the engine's red line rpm... most violent, smoothest torque and horsepower, bottom to top... with no danger then of blowing the engine to hell while fully loaded and at high rpm.

[6for2]

Holley metering blocks i... I'm afraid I deem them another of the "new and improved" well-waxed expensive garbage of the utmost caliber.

You don't know how much camshaft is in it. How much idle vacuum will it presently generate? That'll give an idea on 0.050" intake duration, and subsequent correctly sized idle feed restrictions...

.

I am running a Quick Fuel secondary metering block. We did dyno and tune a primary metering block as well, but it was very time-consuming, and the resulting primary block was pretty much undriveable on the street. Maybe I'll mess around with it some more.

The engine vacuum was pretty low, IIRC, and I run a 4.5 power valve. I'll check the vacuum when I get home.

Thanks,
David

[erratic50]

IMO you would be well served to have Walking-Tall sell you a carb that's setup to make this beast of your perform properly. Can about guarantee that it will only take a few (say 1) run on the dyno will prove its money well spent.

Timing figures mentioned are a lot lower than I've often seen, but timing should only increase to the point necessary to extract the power potential and no more. any more and you're going backwards.

The rule of thumb I was always told is you kill the last 3 degrees of power picked up for every 1/2 degree too far you go.

So for example if an engine likes 13 degrees of base and you give it 14.5 you could have just as well given it 5.5 base as you'll get the same power output.

Its not always a dead-on thing, but it hasn't disappointed that often either.

BTW -- how much oil pressure are you running and how heavy of valve springs are you running?? That can make a huge difference too.

[Walking-Tall]

The following really should be carved into stone for ANY Holley 4-barrel (or clone like QFT, or AED, or other) carburetor, double pumper or vacuum secondary, (and for jetting and such suggestions later) that's got 1-1/4" primary and 1-5/16" secondary venturi diameters, and 1-9/16" throttle bores/plates... AKA 600 cfm Holley 4-barrel...

First, always relocate (especially primary) idle feed restrictions to the original down low location, so that they do their job of metering idle and low speed fuel only, instead of a variable cluster-F*** ((ratcheting air:fuel ratio, especially with sportier than stock/mild camshafts) of fuel and air (possible/inevitable from the close proximity to the idle air bleed) when located in the "new and improved" up high location)... and whatever wizard with too many drill bits has been done in the "emulsion package" department, in the case of some of the new/newer Holley's or the clones, UNDO IT, to be just like the old school Holley metering blocks with 2 BOOSTER AIR CORRECTION bleeds per barrel, at 0.028" each...


(note that the uppermost "emulsion" bleed to use is the one that's about even with the bottom of the accelerator pump passage... depending on the "new and improved" metering block, this might be the top one, or it might be the 2nd from top one...)

The above is what's been tried and true for about a hundred years closely to it's original design, in combination with correctly sized main circuit air bleeds, which are to counter the behavior of a booster in a venturi's tendency to exponentially flow more fuel (than a consistently increasing rock-steady ratio of say 12.5:1) with greater airflow past/through it... it works... it always worked... it will always work... do it... you'll be glad you did... instead of potentially not even being able to buy jets big enough to richen up the mysterious top-end lean out of the "new and improved" without making the carburetor stupid rich and not-really-drive-able everywhere else, like you indicated...

To be continued with bleeds and jetting considerations...

[Walking-Tall]

Pretty much any carburetor with 1-9/16" primary throttle bores/plates (like any version 600 Holley 4-barrel) should have 0.026" primary idle feed restrictions for an engine/vehicle combination that is stock or mild, in a submerged location in the carburetor, and for safe starters, 0.070" primary idle air bleeds. If there's some more camshaft in 'er, the primary idle feed restrictions should get bigger... say up to 220-degrees intake duration @ 0.050", 0.026" should suffice... another 10-20 degrees and they should be 0.028"... on upward into wild territory, where 0.030" primary idle feed restrictions might be better to start with... although, 0.070" primary idle air bleeds is always a good safe place to start... experimenting later with bigger (if the combination will stand it prior to any light part throttle surging or "trailer hitching" felt while driving) primary idle air bleeds, say +0.002" at a time, is where surprisingly sharp throttle response and maximum fuel efficiency comes from.

The rest, in conjunction with proper, well-functioning metering blocks like above... a very good "recipe" for starters:
- 0.028" primary main air bleeds, #65 primary jets, and 0.046" primary power valve channel restrictions
- at least a 6.5"Hg power valve as a default, or an 8.5 or 10.5 as per vehicle combination/needs (a 4.5 power valve doesn't even have a place on a bogged down under-powered laboring lawn mower engine... more on this later if anybody's inclined to be curious about the subject)
- 0.028" kill bleeds ("siphon break" in the image that I created posted above) if there are down-leg boosters, into the angle channels to the boosters in the metering block - no kill bleeds for straight-leg boosters
- 0.025" secondary main air bleeds, and #73 secondary jets (this is if with secondary metering block with jets, obviously... otherwise, look up/use a #39 secondary metering plate or create it's equivalent)
- same size as primary for secondary idle feed restrictions if down-low, or if up high in a metering plate or metering block, 0.030" secondary idle feed restrictions are standard fare, and 0.028" secondary idle air bleeds work well for nice quick secondary opening rates
- a purple or quicker secondary spring if we're dealing with a vacuum secondary carburetor
- a #25 (increase if more shot earlier is needed) primary accelerator pump shooter is usually enough pump shot for acceleration, and a white/green/blue (mild--->wild, or lighter to heavier vehicle) accelerator pump cam
- a double pumper 600 should be fine with a #31 secondary shooter with a same/similar to primary pump cam

That's about it for a great functioning 600cfm Holley on a healthy small block Ford (or other).

As for the timing advance stuff... anybody who would like to argue with the old Ford Muscle Parts Program suggested advance amounts and rate for a healthy SBF 289/302, or Carrol Shelby for that matter (albeit yes regarding the early and very efficient 54cc SBF chambers... but the amounts and rate isn't far off to what any of them like very much), is asking for catastrophe or at least pitted pistons from too much too soon ignition advance.

[6for2]

IMO you would be well served to have Walking-Tall sell you a carb that's setup to make this beast of your perform properly. Can about guarantee that it will only take a few (say 1) run on the dyno will prove its money well spent.

Timing figures mentioned are a lot lower than I've often seen, but timing should only increase to the point necessary to extract the power potential and no more. any more and you're going backwards.

The rule of thumb I was always told is you kill the last 3 degrees of power picked up for every 1/2 degree too far you go.

So for example if an engine likes 13 degrees of base and you give it 14.5 you could have just as well given it 5.5 base as you'll get the same power output.

Its not always a dead-on thing, but it hasn't disappointed that often either.

BTW -- how much oil pressure are you running and how heavy of valve springs are you running?? That can make a huge difference too.

I advanced the timing from 12 degrees initial to 14, which resulted in a total going up from 34 to 36 degrees. There is a track day coming up soon, so I will try to get down and make a few runs, if it isn't raining.

Oil pressure is 50-60 psi when the engine is cold, and then drops to maybe 20 at idle and 30-40 at cruise

I will have to check the head build sheet for the springs.

[6for2]

That's about it for a great functioning 600cfm Holley on a healthy small block Ford (or other).

Thanks for all of that. I checked the idle vacuum, and it reads 9". That's why I selected the 4.5 power valve, using Holley's instructions. So i should move up to a 6.5? Would the primary jetting need to change?

I started tearing down the junk 4777 again. It must have lived a hard life. Even after soaking the whole thing and blowing it out when I rebuilt it the first time, there is some unpleasant residue on the jets and power valve. Maybe the second time's the charm.

I have the big box of Holley jets. Is there a similar selection of bleeds for the QFT metering blocks?

[Walking-Tall]

9"Hg of idle vacuum is a pretty stout camshaft indeed. Yeah... forget about Holley's instructions if that's what they're still telling people (divide idle vacuum in half)... all I have recently seen is that they sabotage their own products (carburetors, most all other clone brands snarfed up now too, that is) and parts, besides of course the high buck fuel injection stuff they peddle that's at the top of their products list on the web site.... designers doing things over there today should be forced to daily drive with their own sh*t, and maybe then things would be better. Yes, install at least a 6.5 power valve... power valve activation has to do with when some extra fuel is necessary for a level of increased part throttle load on the engine, as well as obviously when at full throttle... power valve vacuum opening rating has absolutely nothing at all to do with idle vacuum levels, and whether or not a power valve and power valve channel restrictions are open into the main wells also has absolutely nothing to do with what fuel gets metered to the idle/low speed transition circuit - idle feed restrictions are jets, the dictators of how much fuel gets into the idle and low speed and transition circuits... and no, a power valve vacuum rating change won't directly affect jetting necessity... if with a 6.5 you get any protest or roughness or surging with light part throttle acceleration that's still above 6.5, put an 8.5 into it to bring the augmented fuel into the main circuit a little earlier.

The absolute best method for selecting a power valve that I have heard of and seen is to run the car without one, with a power valve plug installed, with easy driving with no foot-to-the-floor stuff obviously, and see when on a vacuum gauge during part throttle acceleration that it wants/needs the extra fuel from the power valve augmentation circuit. Say you're motoring along easily but above about 2500rpm, so that we know that we're operating on the main circuits, the boosters, and let's say that the vacuum gauge is reading 18"Hg... you then accelerate mildly, vacuum dips down to let's say 8"Hg, and there's some obvious protest or surging because it's not getting what it wants... you've just found the lean limit of the main jets, and that tells you that they are too lean then for that amount of load... an 8.5"Hg power valve would work well in a situation like that... bringing on the extra enrichment earlier and in anticipation of that extra loading, instead of later in response.

I say that if you want a good one, get an old one. Call 'em junk if you like, but they, even if something's broken or needing repair or something replaced... it's nowhere near the BS hair-pulling lunacy of something newer that is comparably horrendously calibrated, immediately IMHO needing to be thoroughly checked through for manufacturing defects/omissions and machining debris and then re-calibrated as job 1 right out of the box to even just function normally, never mind making good power.

The last QFT metering blocks that I dealt with... if everything is screw-in stuff, pretty sure the idle feeds and power valve channel restrictions are 8-32 thread and the "emulsion" bleeds are 6-32 thread... so regular brass socket set screws, either as blanks to block or as precision drilled feed/bleed restrictions, can be (off the hook less expensive than mainstream sold stuff) substituted.

[6for2]

...

I say that if you want a good one, get an old one. Call 'em junk if you like, but they, even if something's broken or needing repair or something replaced... it's nowhere near the BS hair-pulling lunacy of something newer that is comparably horrendously calibrated, immediately IMHO needing to be thoroughly checked through for manufacturing defects/omissions and machining debris and then re-calibrated as job 1 right out of the box to even just function normally, never mind making good power.

The last QFT metering blocks that I dealt with... if everything is screw-in stuff, pretty sure the idle feeds and power valve channel restrictions are 8-32 thread and the "emulsion" bleeds are 6-32 thread... so regular brass socket set screws, either as blanks to block or as precision drilled feed/bleed restrictions, can be (off the hook less expensive than mainstream sold stuff) substituted.

You've given me a lot to think about. Thanks for that. I only called my 4777 "junk" because it came in a box of junk, all in pieces, filthy, and missing some parts. I'm going to try to get it into running shape. Is there a carb that you recommend for a 306 configured like mine? You said that you run a 750. Would something that large be preferable?

[6for2]

Turns out that track night was a bust, due to an out-of-adjustment clutch cable, so that I couldn't shift quickly. With the advanced timing, I lost 3 mph, though that might have been partially due to long-ish shift times.

Walking-Tall, do the unused emulsion holes in the Quick Fuel metering blocks need to have "blanks" screwed into them, or should they be left open? Is there a specific air bleed set that I should get? The QFT 36-75 hass .025-.035 sizes

[Walking-Tall]

Yes, "blanks" means to block the unnecessary ones shut... if the "emulsion" bleed passages have 6-32 thread, regular brass 6-32 socket set screws with no drilled restriction in them can be used. For bleeds there and all else I make my own restrictions/bleeds with brass socket set screws the thread size needed and with precision drill bits for the restriction/bleed size needed. You'll have to ask somebody at Holley what thread size that QFT kit's bleeds are, because it's not listed... in my experience, when they talk about their air bleeds, they're talking about the shouldered 10-32 threaded air bleeds that screw in up top of a carburetor, the idle and main air bleeds...

[Walking-Tall]

You've given me a lot to think about. Thanks for that. I only called my 4777 "junk" because it came in a box of junk, all in pieces, filthy, and missing some parts. I'm going to try to get it into running shape. Is there a carb that you recommend for a 306 configured like mine? You said that you run a 750. Would something that large be preferable?

I would have rather liked to run my 1968 950 3-barrel on mine (because based on experience, I do not subscribe at all to the "too much carb" mantra... there's no harm in giving an engine all of the airflow that it can take in, unrestricted... does a bigger carburetor use more fuel at WOT if that much more air is taken in through a bigger carburetor? Sure it does, and it'll also be making that much more torque and horsepower... and the whole belief that something is doomed to be rich and lazy down low with smelly exhaust and a pig on gas in general is a bunch of nonsense, and does not have to be, with a little tuning of what you've got), but space constraints to the stock flat hood wouldn't easily allow it. A four hole carb spacer with the back web modified for clearance for the large single secondary blade is what's needed to run one... or the rear area of the divider filed/machined down in the intake manifold of a dual plane like the RPM is required... I can't run a spacer and I didn't want to go gouging into the intake... and so I happened to have the parts and pieces to put a 750 vacuum secondary together. I say work with the 650 double pumper that you have and the engine will like it.

[6for2]

I say work with the 650 double pumper that you have and the engine will like it.

Thanks. I got the 650dp working properly, and have scheduled a dyno session for later this week. Feels pretty good, so I'm optimistic about improvements.

[6for2]

Gained 5 horses on the dyno with the 650 dp, but still need to tune the accel pumps. Running the stock metering blocks, with 69/73 jets. Went to the strip last night and ran pretty much exactly the same times as I usually do with the 670 Street Avenger. That probably means that once I get it dialed in a bit more, I will see some improvements.

[Walking-Tall]

Nice work! Those are certainly smoother looking power and torque curves, absent of the zig zag jagged lines (probably slight misfires, rich or lean, because of the jacked up air:fuel ratio "curve") in the first picture you showed us, also with increases at some other rpms (increasing averages, 'area under the curve') as well as your new peak numbers. That's a pretty nice flat air:fuel ratio across the board (like a carburetor is supposed to function), and miles and away better than the previous air:fuel "curve"... it starts heading a bit leaner above about 4500rpm than I like to see... she could use a touch more fuel (jets) for the top end for continued and safe function. Out of curiosity, is that a base LIST-4777 or a dash number after also, like LIST-4777-2, -3, etc? Over time the base installed jetting changed a bit with the newer dash numbers, I'm assuming with main air bleed changes. What shooters and pump cams are on it?

[6for2]

Thanks. The carb is a 4777-7. The shooters are 31/25. The pump cams are both pink. There was a huge, rich ditch when hitting the throttle on dyno runs, so we dialed both cams back to the second hole, and reduced the secondary shooter from 28 to 25. Now the throttle response is very lazy. I was thinking of trying a different cam, but honestly pump tuning isn't something I'm terribly good at.

[Walking-Tall]

Okay, a LIST-4777-7 originally should have come with #67 primary and #73 secondary main jets, #28 primary and secondary shooters, and yes usually with pink pump cams. You've already got a couple numbers more with #69 primary jets, so I would imagine you're good up front, and that #74 secondary jets should bring balance and richen the top end air:fuel ratio a bit... but I do suspect, if power valve channel restrictions and main air bleeds are in the ballpark of usual, that the extra fueling may be needed more so for the secondaries.

With accelerator pumps, the shooter solely controls when the majority of the accelerator pump fuel gets sent in (bigger=sooner, smaller=later) during the throttle opening cycle, and the pump cam dictates also when but more so how much in total acceleration fuel gets sent in. A whole bunch of accelerator pump shot later in the throttle cycle (pink cam) can be a way too late to the party waste of fuel - wherein also there isn't enough initial pump shot... The last 650 double pumper that I prepared for a fellow with Edelbrock cylinder heads on a real similar engine/vehicle combination to yours - here's it's calibration file image (that I create for my own documentation and provide to the person I'm helping for their records):
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Pump cam profiles information for comparison:
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Lazy throttle response... how much throttle, from at idle, from off-idle? First, make sure that the primary accelerator pump arm isn't resting on the windup throttle return spring on the throttle shaft at idle instead of on the pump cam itself (common with pink primary pump cam... arm bending is necessary if so, so that it will rest on the cam and not spring, if pink cam remains...), and then that they are adjusted just so that there's no slack at idle (tighten spring bolt/nut until there is slack, and then loosen just until there's no slack at idle)... and the early quicker pump cams (white, orange, blue, green) work better, especially when there's a bumpy camshaft in use where lower end throttle response can benefit... that, and as much initial timing as it will stand prior to pinging, and limiting total mechanical/centrifugal to your original 34-degrees sounds like what the engine may have liked better before with the different trap speeds...

Continued good luck with it

[erratic50]

That dog just doesn't want to hunt, does he?! Looking better than it did as WT points out but this is a really challenging problem.


Any idea what your bearing tolerances are at on the rods and mains? They don't happen to be tight do they? Did you plastigauge everything before assembly? Tight engines are always lazy and don't produce even close to what they are supposed to is why I'm asking

Did you check to see how many ft-lbs it took to spin the shortblock over before you started dressing the engine with cam, heads, etc. Did you check it afterwards also?

You don't want them to knock but you also want stuff to spin over like it should.

I'm also curious what the pressures show in each hole when you spin it over with a pressure tester. Don't forget-- those tests are supposed to happen at wide open throttle, BTW.

The engines we ran on on the dirt track and drag racing were always within 0.001 of "loose" spec. Even the stuff on the street was but we'd always go 0.002 tighter on the front main to prevent knocking from accessory drive, AC, etc.

We would always move oil pressure up a notch with a stronger spring if loosening tolerances. But watch this -- don't want to blow the galley plugs out.

On one occasion on a driver I built I went with a high volume oil pump with some fabricated nonsense that gave me 1/2 quart more oil capacity in the pan. Reflecting ..... I didn't check the sump clearance and the sump was now a little too high off the bottom of the pan. I also didn't account for more oil going up means better flow back down is now required. Well -- call it a failed build. Could idle around town all day long, but the moment you took it on the highway for more than 30 seconds oil pressure went to hell and it started knocking...... expensive lesson. Never run a high volume pump without a high capacity pan and work on the engine to help oil get back down to the pan FAST and verifying sump depth vs pickup, etc.

A while back in the thread Jack mentioned valve float then the discussion went in other directions, etc. Can't eliminate that without knowing a lot about the valve train and cam. Worth some diving into

Forgot to ask -- what transmission and rearend are you running. Trying to account for drive-line loss a bit......

[Walking-Tall]

For the record, looking again at the chart image, I'm not sure how the person arrived at plotting the thin blue line, "Blue 2" (blue pump cam in position #2), in the 2nd image that I posted above in post #42, but based on experience using them, and the volume and lift data in the 3rd image posted, it's not physically possible to provide more lift than the big brown "50cc" accelerator pump pump cam. The blue pump cam in position #2 is nearly identical in lift amounts to the quick green pump cam in position #1, so is as quick but is all done with only 0.1425" of lift at 30-degrees of throttle rotation... which is why I installed it on the secondaries of the 650 double pumper carburetor calibration image also shown in post #42 above.

In a nutshell, probably regardless of the beginning rpm, you stomping the throttle and things going too rich (and the car displayed bad behavior (lazy/stumble/hiccup/bog) too?), indicates overall too much fuel being shot in... which is where installing lesser lift cam/s, providing less overall fuel volume shot in, is normally a good direction to head.

[85MUSTANGTGT]

I, too, noticed recently that the Kolk graph doesn't correspond with the lift numbers in the Emanuel book.

For reference, this is per the book:

[Walking-Tall]

I, too, noticed recently that the Kolk graph doesn't correspond with the lift numbers in the Emanuel book.

For reference, this is per the book:

........
.