Power Valve Selection

[Bewy]

72blu,
News flash for you! Millions of GM cars idled with high compression engines & cams with less than 200* @ 050 duration cams. You obviously have no idea about combustion at idle.
My GTO idled at 26* on the show room floor.. It did that using vac adv connected to manifold vacuum. See the link below from the 1967 manual.
As for 440s & 35* at idle? Been there & done that many times. Latest one idles with 42-44*, cannot remember the exact figure; 20* init + 22* added with man vac adv.

Bud, here is another news flash for you: as far as best idle timing is concerned it makes NO difference whether the carb has a PV...or metering rods.

 

[Bewy]

And the MVA success stories continue....idle vac increased 2"...

 

[Bewy]

And a near smooth idle with MVA....

 

[Bewy]

And....

 

[mopowers]

This is true, but the generic estimate of using the idle vacuum helps with putting you in the ball park for the cam you have. If you have a lower idle vacuum than "standard" you will likely need to bump the PV rating down as well. If you have a fairly stock engine than the out of the box 6.5 PV should be close. And then you drive the car and determine where the PV is coming in and adjust from there.

I have a nice uphill section of freeway I use, plus my AFR gauge, to figure out where the PV is coming in. It's a bit easier though for me because I have mechanical secondaries, so, I know the throttle position when those start to come in.

True, their guideline may get someone in the ballpark. I was just pointing out that "selecting" a power valve using an idle vacuum is not the correct method. Sure, it may get you in the ball park, but the actual "selection" and tuning of the proper PV should be based on what the engine wants during certain driving conditions as @Carnut68 (and you) described. Turns out, mine wanted a 10.5 version and could probably benefit from a higher one than that.

 

[RustyRatRod]

What? No sir. His cam is more mild than the one in my 340, he does not need 25° of idle advance. Not even close. I do just fine with 18°, which is about where I need to be so my transfer slots are covered correctly. I doubt that minimum fuel consumption at idle is anyones goal here. Total timing advance with mechanical and vacuum all in is a totally different story.

I really want to know if you've ever tried to hot start a 440 with 35° of advance at idle. Because even when I was up at 22° on my 340 the basic denso starters aren't happy with a hot start. Which is a real pain in the *** for a street car. You've seen where people say to advance the timing at idle until the starter kicks back on a hot start I assume? Or does you book not mention that? Oh, wait, it literally says "though not commonly realized". Wonder why?


Wrong carb bud. No metering rods in a Holley. No step up springs.

And again, yes, you can add timing advance at idle which helps with a large cam. But that is not a cure all, there are limits and there is a balance. And really the OP's cam isn't radical at all. His in gear vacuum is a little low for what he's got but none of this is extreme or radical.



Take a look at the Holley videos you linked and go from there. Based on your car, carb and cam my extremely basic advice is that an 8.5 PV is probably a little too high, and the 64 jets are a little too small. I would try going down to a 6.5 PV, and up to 68 - 70 jets to start. If you decrease the PV rating you will need to increase the jet size, especially with a higher PV rating because it will be open quite frequently.

So for tuning, if you've got no throttle in at all, you're in the idle circuit. If you're in part throttle, you should be in the primary circuit for steady state. As you first tip in to part throttle from idle, that's the transfer slots. As you first add throttle from steady state, there's a pump shot in addition to the primaries. From part to mid throttle, steady state, with lighter loads you should be all primary. The PV should come in with acceleration or added load (as the vacuum drops), and bridge the gap between the primaries and the secondaries opening up. You've got vacuum secondaries, so they come in with further vacuum drop under load or heavier acceleration.

I would work on the primary jets first, since the primary jets will control most of your off idle mixture. Then you tune the pump shot and PV to deal with different levels of acceleration and load.



This is true, but the generic estimate of using the idle vacuum helps with putting you in the ball park for the cam you have. If you have a lower idle vacuum than "standard" you will likely need to bump the PV rating down as well. If you have a fairly stock engine than the out of the box 6.5 PV should be close. And then you drive the car and determine where the PV is coming in and adjust from there.

I have a nice uphill section of freeway I use, plus my AFR gauge, to figure out where the PV is coming in. It's a bit easier though for me because I have mechanical secondaries, so, I know the throttle position when those start to come in.



Good grief man.

It doesn't matter whether the kits are "ethanol friendly" or not. My point was that the stoichiometric ratio for alcohol and gasoline are totally different. So the jet sizes, PV's etc are all very different from gasoline to ethanol. Stoichiometric for gasoline is 14.7:1, pure ethanol is 9:1. E85 is ~9.9:1.

There's a reason that most Holley's come with a 6.5 PV, because most gasoline engines will work well with that PV. If you have a more aggressive cam, then you need to LOWER the PV rating so it's not open more often than it should be.

If you have to get your PV out of an alcohol kit because you're running a 12.5 PV, it indicates you're not using the PV and jets as intended. With an average cam and compression ratio with gasoline you should be looking at a PV below 8.5-9, which is literally what Holley says, you can follow the links the OP posted above if you want. And I dunno, they build the carbs, so they might have a decent idea on that. And really, unless you're doing something really radical a couple steps in one direction or the other from the off the shelf settings should cover it. So if you need to double the off the shelf settings, well, either something isn't right or your combination is really radical. Which doesn't apply to the OP really, his combo isn't that crazy.

The power valves open based on vacuum readings. Period. All we're doing is telling him there's more than one way to tune for a power valve. He's smart enough to make his own decision on how to do it and he can even try both ways if he wants. It's up to him. Certainly not worth you getting all upset over. lol

 

[Bewy]

And all I am trying to point out is that there is a sequence involved in carb tuning [ no matter what the brand is ] once the engine is modified.
A sequence.

Just like when you fit a new tyre. You put air in it before you balance it.....

Likewise with the carb: the starting point is getting the correct amount of timing at idle. That is because timing affects T slot position, which has to be correct for the carb to properly function; this, in turn, affects idle vacuum, which becomes important for PV selection.

 

[Mattax]

Now I do know that there are a couple ways to select the power valve based off of either the idle vacuum in gear, or the cruise vacuum halfed - 2. So I know the idle vacuum in gear is roughly 8-9 inHg. cruise at 50-70 mph has the vacuum at 18-19 inHg. So I think I am close with the pv, but it may be coming in a little soon. based off of the 18-19 cruise vacuum I should be having a power valve of 6.5-7.5. Is my line of thinking correct?

Using cruise vacuum as a parameter at least shows some understanding that enrichment relates to moderate versus heavy load for that engine and fuel distribution.

From Holley.com

View attachment 1716288923

Well that's a set of "rules" which are not based in fact.
A. The main jetting typically has little to no effect on the "idle circuit". Watch Mark show that here on you tube.
There are exceptions - which is why a blanket absolute statement either way can be proven wrong.
B. Follow the fuel path from the idle discharge port (or the transfer slot) back to the bowl. Then tell me if the person who posted that "rule" has any claim to knowledge, nevermind expertise.

1/2 the idle vacuum in gear works. The PV should not be the first thing that comes in to add fuel, you have the accelerator pump and squirters that can be adjusted with the pump cam. The PV should come in after that.

The 750 double pumper on the 340 in my Duster came with a 6.5 PV, that’s a pretty standard off the shelf PV. If you have to double that, that should tell you something. My 340 runs 9-10 for idle vacuum, the 6.5 was too early. I run a 5.5 now, with 68 jets and 31 pump nozzles.

The fact that the OP his running really small primary jets and a PV that opens early should be an indication that things aren’t right.

It may work, but its not founded in engineering. I'm not sure of the origin of this one - but it goes back quite a ways. It probably relates to the belief that low number power valve must be for radical cams. Tuner gave his perspective on that a few years - see my post below.

You have to test to find out what pv works best. Find a spot where you have a flat spot on the road that slowly starts uphill. Gently roll into the throttle and if the engine hesitates go up a number on the pv so it adds fuel sooner. Whenever the hesitation goes away you found the right pv. Give the engine what it wants not what you think it wants.

^^^This^^^

To me, a power valve shouldn't be selected based on a vacuum reading. It should be selected based on when the engine wants the extra fuel like Carnut said in post #18. There's no magic number since it's dependent on so many external factors - vehicle weight, gearing, etc.

^^^This^^^
In addition to the engine's natural needs, the enrichment point can be thrown off by timing that doesn't match the engine's needs and the fueling.

There's a reason that most Holley's come with a 6.5 PV, because most gasoline engines will work well with that PV.

Yes. Holley thinks that 6.5 will be ballpark for most of the customers of those carbs. This is where Barry Grant's carbs had a big advantage. They sold a wider variety of calibrations with simple guidelines that got them closer to the engine's needs. Note that many of Holley's classic carbs had 8.5 and 10.5 PVs. Skim through Holley's carb list and check out the 4777 - 4780 double pumpers, the 1850s and of course the 3310 and related vac secondary carbs of yore.

If you have a more aggressive cam, then you need to LOWER the PV rating so it's not open more often than it should be.

This is the low number power valve myth I mentioned earlier.
Actually its generally the other way around. These engines are more radical tend also to have poor part throttle fuel distribution. They need enrchment well before 80 or 90% max load.

 

[Mattax]

Cut and paste from myself in Power Valve Selection thread.

Fuel mixture should be lean at part throttle. It should get leaner with more throttle. Somehow all the magazine experts somehow missed this and misled most of us for years.

The power valve, or step up, is needed when the engine gets close to putting out maximum power for the rpm.

In this engine, they found it needed relatively early enrichment. That would be something like a 10.5 Power valve on an engine that cruised at 17 or 18"Hg. An engine that didn't need to go rich until 80 % load might be more like a 8.5 PV, and so forth. Wideband

A somewhat practical method on a modified engine is to note the vacuum when increasing throttle doesn't bring a gain in acceleration. Then try a PV that opens at or before that vacuum.

Mike Urich, at the time a VP at Holley, discusses something like that method in Holley Carburetors and Manifolds. Back then, it had to be done on a track with a stop watch while "crowding" a vacuum. I've tried it using the vacuum gage and datalogger with accelrometers and its hard to do. A flat spot will show up though. (as @Carnut68 and @mopowers wrote earlier)

A more technically precise method requires equipment not usually available to the hobbiest.
But if you happened to be so lucky as to know a place with NOx gas measurement and a load dyno then it can be done by observing the combustion.
"The purpose of the power valve selection is to enrichen the mixture prior to the combustion temperatures going too high. To set a powervalve correctly requires a NOx sensor. Different engine combinations need fuel enrichment at different power levels."
Bruce "Shrinker" Robertson. post #4 "Another Power Valve Question" archived Innovate Motorsports forum

In addition to the engine's natural needs, the enrichment point can be thrown off by timing that doesn't match the engine's needs and the fueling.

When the enrichment begins, vacuum advance goes away. Vacuum advance is for leaner, less dense, fuel mixtures that take longer to burn - just like Chrysler explained in its Master Tech Conference years ago.

the low number power valve myth I mentioned earlier.

Posted by Tuner, 12-15-2006, 01:00 AM

The history of the power valve hysteria has a few different influences behind it, corporate, media spin and international events that affected Big Oil.

The corporate influence came with Colt Industries when they bought control of the Holley Corporation in the late 60’s. When the genuine "old-school" boys were out of the way, the new wave of MBA’s started telling the ME’s how the business would be run instead of the other way around. Read that as profit became more important than quality. I was employed in speed equipment sales at the time and the declining quality was evident from that point on. One cost cutting measure was a reduction of maintenance of the injection molds and machines that made the parts. Die makers are highly skilled craftsmen, almost able to name their own price if they’re really good, especially in the days before CNC. We started noticing main bodies with more core shift, etc.

Every time a part is made in an injection mold, the molten zinc or aluminum dissolves some steel from the die cavity and carries it off in the part. As more aluminum is alloyed into the zinc, this process is accelerated. Zinc alloy higher in aluminum content is less expensive initially, but it increases maintenance cost. After a few 1000’s of parts are made the die cavities and the parts they make are no longer the original size but they look the same because the cavity erosion is uniform. I trust you see where this is headed.

The metal part of the power valves wandered off the blueprint but the diaphragm didn’t. The crimp process that assembles the casting, the diaphragm and the retainer washer wasn’t maintained well either, so some were loose and some were too tight, cutting the diaphragm. You can see how a backfire can cause a leak with a valve compromised like that. They pretty well have a handle on it now. A normal healthy valve can stand backfires, for that matter, nitrous backfires.

The low number valve for radical cams thing was influenced by this situation too. Smog regulations began dictating how engines were tuned in 1966 nationally (a few years before that in California) and by 1968 they were getting pretty lean and retarded. Before that almost all high output factory engines used #85 or higher power valves. The `65 425HP 396 Chevy used a #105 primary and #85 secondary. The purpose of that is to get it rich before it has much load on it so it won’t knock. Because the HP carbs had high number valves, that was what people wanted and what we sold. The low number valves were for dump trucks and economy cars. However, when the debacle with the poorly manufactured valves began, the valves we (and speed shops and warehouses across the country) had in stock that didn’t leak were the old pre-Colt Industries low numbered ones that didn’t sell before because they weren’t romantic enough. People didn’t want a Rambler power valve in their "Fueler 327" with the 950 3bbl. How this got tangled in the valve timing is it was in the same era when cams started getting much more radical. In 1965, most people thought a big cam was 250º at .050". By `70 or `71 durations had grown to pretty much what’s available today. When a low numbered power valve fixed a radical cam engine that wouldn’t idle folks fixated on the number, they might not catch that the valve they replaced was leaking. Brand new carbs came with valves in them that leaked. Once somebody jumped to that conclusion and the enthusiast media picked it up it spread by plagiarism and became lore.

OK, so there’s the corporate influence and media spin, now on to international events and Big Oil. Starting in `71, the highly leaded fuel was phased out down to "low-lead" (.1gm per gal.) by `72. That EPA mandate and the 1973 oil crisis, during which OPEC cut off the supply of middle-eastern oil to the US, brought about a change in the chemistry of the gasoline. American industry had agreed on standards describing materials compatibility for fuel and fuel systems that could not be met with the crude available and the amount of gasoline necessary to be made from it. This affected more than just power valves. The soft parts in fuel systems, hose, pump diaphragms, gaskets, o-rings, tips of inlet needles, floats, you name it, if it was soft the gasoline dissolved it or soaked into it and made it swell up. Inlet needle tips would swell and push the float to the bottom of the bowl. The floats soaked up with gas and sunk. (That was a big part of the bad rap the media played on the QJet.) The rubber would just sort of rinse off the diaphragms. If you handled a wet accelerator pump diaphragm it would smear off on your fingers. Needless to say, power valves made with the early materials leaked. The metering block gaskets expanded into the air and idle channels on the face of the block and plugged them. All the carb components had to be changed. Like a flammable game of musical chairs, the new parts had to push the old parts through the system. It took a couple of years for stuff for the less common carbs. Still, once in a while someone shows up with an old carb kit and it’s like déjà vu all over again.

originally snipped from: deadlink:innovatemotorsports.com/forums/showpost.php?p=29053&postcount=9
Archived here: Trouble with vacuum signal to power valve in Holley

 

[carfreak6970]

thank you everyone for your replies. Well I decided to try to dive into this issue but hit a snag... so while I was looking at changing the power valve I noticed that the carb has 72 jets and not 64 like the documentation says it should have. I don't have any record of me changing them when I installed carb... so I am not to sure what happened. Whether they started sending this carb with 72's, or somehow it was a mistake. However everything I saw online says the jets for 750 holleys should be anywhere from 70-78 for a 440. Unfortunately the only jets I have on hand are 60-69 sizes, which not only appear to be too small but everyone says that if you change jets jump 2 sizes... So Ill order a bigger kit that includes jets in the 60-99 range. So Ill drop the power valve to a 6.5 for now until I get more jets. No point in diving too deep into the PV area before I get the jets right.

Now there has been a lot of talk of timing. I am not to sure if I included that but as of now the initial timing is at 14 deg btdc (vac advance connected to ported not manifold vacuum) with a total mechanical advance of 11 (22 at crank) coming in at 2700 rpm (5400 engine rpm) for a total mechanical of 36 with the vacuum canister adding up to 3 degs (6 at crank) at 9-12 inHg with a total of 8 deg (16 deg at crank) at 18 inHg [Now I believe that's how it works - Crank turns twice for one rotation of the dizzy/cam shaft. So 600 rpm at the dizzy would be 1200 at the crank. I also believe that works the same for the degs of timing - 2 degs at the dizzy would be 4 degrees witnessed at the crank]. I just verified the timing curve on my sun distributor machine.

the transfer slot was set to .040 but I had to close the throttle blades a half of turn of the idle speed screw to get it down to 650-700 rpms



all that said, I'll attach a picture of the number 4 spark plug (I am running NGK XR5's, magnecor wires, a Mopar electronic dizzy with the ballast bypassed using a GM 4-pin module powered by a GM E Coil) . to me and from the references I see online it seems a little white and probably could go a little bigger on the jets. am I on the right direction?

 

[Mattax]

The carb is a 750 Holley with vacuum secondaries, 64 jets, and currently an 8.5 pv.

This carb came with the 64 jets, which I thought was fine since the original 4160 holleys came with the 64 jets

Holley has made a dozen 'Model' 4150/60 carbs many of them marketed as '750s'
a. To know more about the carb on hand - look for the 'list number' and then look it up on Holley's Carb List.
If the carb has a choke tower its stamped there. It may or may not also be on a metering block.

My biggest issue with the car was I had it out a couple weeks ago and floored it from a stop. I was not met with spinning tires but something that may have been a stumble or a bog. It finally got over it and off we went. Well I tried it again last night and the car spun the tires no issue. My initial thought was coming off idle I had the squirts and the power valve dumping too much fuel in. But it appears that may not be the case. Other than that I think in other driving conditions the car performs pretty well.

Accelerating from a dead stop involves almost all, if not all of the circuits and adjustments in the carb.

The main jets are mostly to control high speed cruise fuel mixture. To be more accurate, the main circuits contribute fuel when the air velocity past the boosters is sufficient to create pressure differential that pulls fuel. IF the system is calibrated properly, this will typically occur on flat ground steady conditions (no trailer, etc) above 45 mph, and be dominating the fuel contribution by 60 to 65 mph. With a new fangled carb with additional emulsion holes and weird air bleed combinations etc, then those have to be fixed first.

When looking at a spark plug, one has to know something about the conditions it was subject to.
If that plug was a full wide open throttle run in top gear, the porcelain looks lean - but's just the tip - and there's a ring of carbon on the first thread.
If that's a fresh plug with mostly cruising and a couple of accelerations to 60 mph, maybe its a bit lean under some conditions. Closest to the gap is where the flame is converting from an electricity supported kernal to a self sustaining flame front.

Anyway. That's a long way of getting around to this.
If you've driven it on the highway without problems, its not too lean in the primary main jets.
Go drive it on the interstate like a normal driver. No wide open throttle. Add moderate throttle as needed for hills, normal passing, etc.
If it is jetted too lean the engine will rev and die or nearly die. Slow down, take it home and go up a size or two primary main jets.

If you want a decent info from Holley find yourself a used copy of Holley Carburetors and Manifolds by Bill Fisher and Mike Urich, any edition.
You're buying for a good intro into how carbs work and the diagrams, not the marketing content.
Alternatively for less, the smaller Holley Carburetor Handbook, Models 4150 & 4160, Selection, Tuning & Repair By Mike Urich

The sequence of tuning does matter. Sometimes we have to go out of order, but it then means some more iterations of testing.
Remember to start by checking the fuel level in the bowls.
Then Tune for Performance

 

[Mattax]

70 charger, 440, 727, 3.55 rear. The cam is the Comp Cams XE274H-10

How much compression?

Now I believe that's how it works - Crank turns twice for one rotation of the dizzy/cam shaft. So 600 rpm at the dizzy would be 1200 at the crank. I also believe that works the same for the degs of timing - 2 degs at the dizzy would be 4 degrees witnessed at the crank]

Yes. Distributor timing x 2 = Crank timing. Same with distributor rpm. Distributor is same as cam, but half crank.

the initial timing is at 14 deg btdc (vac advance connected to ported not manifold vacuum) with a total mechanical advance of 11 (22 at crank) coming in at 2700 rpm (5400 engine rpm) for a total mechanical of 36 with the vacuum canister adding up to 3 degs (6 at crank) at 9-12 inHg with a total of 8 deg (16 deg at crank) at 18 inHg

Good start.

The question is what is happening in between.
See here for a factory A134 non-smog high performance 440.
On your combo, assuming nothing out of ordinary on the compression or heads, I'd suggest 16 to 18* initial. Something around 22 to 24 degrees by 1400 rpm, and then very slowly advance to 38 at 5400.

You can see in the link that a 440 with factory intake etc will use a little more vacuum advance than you have dialed in.

 

[Mattax]

Short version.

Clean up the idle and off-idle.

• Try another 2* or 3* initial advance
• This should allow slightly less primary transfer slot exposure. Then trim the idle mix with the idle mix screws. In neutral, run in 'til slight drop in rpm or vac, then open up 1/8 to 1/4 turn. (It needs to be richer in gear than when turning with no load).

 

[72bluNblu]

72blu,
News flash for you! Millions of GM cars idled with high compression engines & cams with less than 200* @ 050 duration cams. You obviously have no idea about combustion at idle.
My GTO idled at 26* on the show room floor.. It did that using vac adv connected to manifold vacuum. See the link below from the 1967 manual.
As for 440s & 35* at idle? Been there & done that many times. Latest one idles with 42-44*, cannot remember the exact figure; 20* init + 22* added with man vac adv.

Bud, here is another news flash for you: as far as best idle timing is concerned it makes NO difference whether the carb has a PV...or metering rods.

View attachment 1716289997

And the MVA success stories continue....idle vac increased 2"...

View attachment 1716289998

And a near smooth idle with MVA....

View attachment 1716289999

All this tells me is you don't know how to set ignition timing at idle on a Mopar. The proper procedure to set ignition timing at idle is to set the factory spec with the vacuum advance DISCONNECTED. Then you hook up the vacuum advance.

From pages 8-46 and 8-47 of the '72 Dodge Service Manual

We're not talking about a GM car, so, really whatever the process is for a GM is completely irrelevant to this discussion. My comments were based on setting ignition timing at idle using the proper procedure from the FSM, not for what the total timing including vacuum advance is. By definition, as you can see above, the ignition timing at idle is set without vacuum advance.

It may work, but its not founded in engineering. I'm not sure of the origin of this one - but it goes back quite a ways. It probably relates to the belief that low number power valve must be for radical cams. Tuner gave his perspective on that a few years - see my post below.

Look, I said it was a guideline, and it is. To say it isn't "founded in engineering" is just being overly dramatic, it's an accepted guideline that still appears in Holley literature regardless of its origin. Is it perfect? Of course not, I didn't say it was. And again, the OP does not have a radical cam.

I also said that I ultimately selected my PV using information from my AFR gauge while slowly adding load going up a large hill at speed on the freeway, exactly as carnut68 described except with the added bonus of have an AFR gauge. I just used the guideline as a starting place, and that is all I recommended. Not everyone has an AFR, datalogging, etc., and the basic guideline got me closer than what the off the shelf setting on mycarb was.

The engine is question is not some crazy outlier with radical settings, applying some basic guidelines and then driving the car to make finer adjustments should improve performance and get the OP closer in the ballpark than he is currently.

Clearly you're all experts, I'm just going to go back to driving my car that happens to be tuned fairly well, apparently by total accident. Have a nice day.

 

[Mattax]

All this tells me is you don't know how to set ignition timing at idle on a Mopar. The proper procedure to set ignition timing at idle is to set the factory spec with the vacuum advance DISCONNECTED. Then you hook up the vacuum advance.

I can't tell you if he knows this, but I can tell you he's been told a bunch of times.
It's also the same for many other makes and models - its a method widely used.
Even the '65 Pontiac FSM provides initial with vac adv disconnected (where it differs from Mopar and also many others is connecting vac adv to manifold vac. instead of port above the throttle plate)

I really want to know if you've ever tried to hot start a 440 with 35° of advance at idle.

Hell he said he made his own custom adapter to make a GM distributor mount on a 440.

Look, I said it was a guideline, and it is. To say it isn't "founded in engineering" is just being overly dramatic, it's an accepted guideline that still appears in Holley literature regardless of its origin. Is it perfect? Of course not, I didn't say it was. And again, the OP does not have a radical cam.

You're welcome to your opinion, and I'm welcome to mine. The engine needs to go rich when the load increase gets the combustion so hot that NOx production shoots up. If we want to find a relationship between more aggressive cams and vacuum at idle, we can find plenty of data that shows more aggressive cams tend to lower idle at vacuum. This would result in selecting a lower power valve opening when in fact most hot rod/race engines will need enrichment at less throttle and higher vacuum.

There's a reason that most Holley's come with a 6.5 PV, because most gasoline engines will work well with that PV. If you have a more aggressive cam, then you need to LOWER the PV rating so it's not open more often than it should be.

Sorry you got offended by my characterization of Holley's guidance, but the engineering (such as in Larew's book) shows the opposite.
In the Holleys that Chrysler used in the late 60s HP v-8s, an 8.5 PV was specified.
The original 3310 (yes for a Chebby) came with a 10.5 PV on the primary side.
IMO Holley in recent years is like MP was in later decades - the people there only repeated what they had been told or heard - the techs and engineers who knew their stuff were long gone.

I agree the XE274 is not extremely radical, but it is more radical than factory. Therefore it could use a bit more initial timing than factory.
Here's a set of guidelines Factory V-8 Engine and Cam Specs by Year 1965-1975

I agree an AFR gage is not needed. I also agree a vac gage is not needed, but can be helpful in testing what is happening before the PV opening point. I think we agree the goal is tune for performance. Performance being whatever calibrations produce the strongest power for the condition being tested.

 

[Bewy]

72 Blu,


Here is ANOTHER news flash for you! By not using MVA during the magic years, Chrys got it wrong. The others got it right.....
Makes no difference what name is on the valve cover, these engines all work on the same principles. What does vary between brands is the actual timing #s, by a small amount.
Chrys, like the other companies, DID use MVA during the 70s decade to cool their engines. The engine was switched from PVA to MVA via an over-heat temp switch. This increased idle rpm, which increased w/pump AND fan speed to cool the engine. Why did the idle speed increase? Because MVA produced more hp & idle rpm increased as a result.

Another happy ending....

 

[carfreak6970]

Holley has made a dozen 'Model' 4150/60 carbs many of them marketed as '750s'
a. To know more about the carb on hand - look for the 'list number' and then look it up on Holley's Carb List.
If the carb has a choke tower its stamped there. It may or may not also be on a metering block.



Accelerating from a dead stop involves almost all, if not all of the circuits and adjustments in the carb.

The main jets are mostly to control high speed cruise fuel mixture. To be more accurate, the main circuits contribute fuel when the air velocity past the boosters is sufficient to create pressure differential that pulls fuel. IF the system is calibrated properly, this will typically occur on flat ground steady conditions (no trailer, etc) above 45 mph, and be dominating the fuel contribution by 60 to 65 mph. With a new fangled carb with additional emulsion holes and weird air bleed combinations etc, then those have to be fixed first.

When looking at a spark plug, one has to know something about the conditions it was subject to.
If that plug was a full wide open throttle run in top gear, the porcelain looks lean - but's just the tip - and there's a ring of carbon on the first thread.
If that's a fresh plug with mostly cruising and a couple of accelerations to 60 mph, maybe its a bit lean under some conditions. Closest to the gap is where the flame is converting from an electricity supported kernal to a self sustaining flame front.

Anyway. That's a long way of getting around to this.
If you've driven it on the highway without problems, its not too lean in the primary main jets.
Go drive it on the interstate like a normal driver. No wide open throttle. Add moderate throttle as needed for hills, normal passing, etc.
If it is jetted too lean the engine will rev and die or nearly die. Slow down, take it home and go up a size or two primary main jets.

If you want a decent info from Holley find yourself a used copy of Holley Carburetors and Manifolds by Bill Fisher and Mike Urich, any edition.
You're buying for a good intro into how carbs work and the diagrams, not the marketing content.
Alternatively for less, the smaller Holley Carburetor Handbook, Models 4150 & 4160, Selection, Tuning & Repair By Mike Urich

The sequence of tuning does matter. Sometimes we have to go out of order, but it then means some more iterations of testing.
Remember to start by checking the fuel level in the bowls.
Then Tune for Performance

So thats interesting you bring up that Carb List... So I was not able to find the part number (0-80459SA) on there. Unless using the "Find" feature online isnt actually bringing up that number.

This car has only been street driven with a couple hard pulls for kicks. But mostly just daily driving activities. On the high way it is not bad. handles passing and getting up to speed just fine. But to be honest, I have always been heavy on the throttle because like a child, I still like to hear the engine roar lol. Ill try the "moderate" throttle the next time I have it out to see if I can gather any more information.

thank you for the tune for performance. Seems pretty basic and Ill give that a try.

How much compression?


Yes. Distributor timing x 2 = Crank timing. Same with distributor rpm. Distributor is same as cam, but half crank.


Good start.
View attachment 1716290710

The question is what is happening in between.
See here for a factory A134 non-smog high performance 440.
On your combo, assuming nothing out of ordinary on the compression or heads, I'd suggest 16 to 18* initial. Something around 22 to 24 degrees by 1400 rpm, and then very slowly advance to 38 at 5400.

You can see in the link that a 440 with factory intake etc will use a little more vacuum advance than you have dialed in.

So I am not to sure on the compression... I know it is running the 906 heads, but the heads were shaved, block was decked and I am not to sure what pistons were used/head gasket thickness (I may have found that out at some point)(this whole car was built by my late father and before I knew anything more than turning a wrench). My dad "claimed" the compression was 12:1 after he talked to the machine shop, but from what I was reading online you do not do that to a 440 with iron heads for the street. And his main objective was for a street car with no track use, so that 12:1 has to be bogus. So any guess is a good guess.

Short version.

Clean up the idle and off-idle.

• Try another 2* or 3* initial advance
• This should allow slightly less primary transfer slot exposure. Then trim the idle mix with the idle mix screws. In neutral, run in 'til slight drop in rpm or vac, then open up 1/8 to 1/4 turn. (It needs to be richer in gear than when turning with no load).

When I get some time Ill give that a go. Summit said it wouldnt ship the jets today regardless of when I ordered them over the weekend. So once I have parts and time in hand Ill give this another go ahead.

 

[RustyRatRod]

So thats interesting you bring up that Carb List... So I was not able to find the part number (0-80459SA) on there. Unless using the "Find" feature online isnt actually bringing up that number.

This car has only been street driven with a couple hard pulls for kicks. But mostly just daily driving activities. On the high way it is not bad. handles passing and getting up to speed just fine. But to be honest, I have always been heavy on the throttle because like a child, I still like to hear the engine roar lol. Ill try the "moderate" throttle the next time I have it out to see if I can gather any more information.

thank you for the tune for performance. Seems pretty basic and Ill give that a try.



So I am not to sure on the compression... I know it is running the 906 heads, but the heads were shaved, block was decked and I am not to sure what pistons were used/head gasket thickness (I may have found that out at some point)(this whole car was built by my late father and before I knew anything more than turning a wrench). My dad "claimed" the compression was 12:1 after he talked to the machine shop, but from what I was reading online you do not do that to a 440 with iron heads for the street. And his main objective was for a street car with no track use, so that 12:1 has to be bogus. So any guess is a good guess.



When I get some time Ill give that a go. Summit said it wouldnt ship the jets today regardless of when I ordered them over the weekend. So once I have parts and time in hand Ill give this another go ahead.

You can get a cheap borescope that will plug into your smartphone. Cheap. Like under 20 bucks and you can SEE what type of pistons you have and even see how high they come up in the bore at TDC.