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Old 09-15-2019, 05:38 AM
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Default Carb Changes Going To Edelbrock Heads

So, my basically stockish 455HO motor has been through some changes.

What's the same:
455HO block +.030 with the old style forged pistons and stock rods (about zero deck)
RAM Air manifolds
2.5inch Flowmaster system with H pipe
stock HO intake manifold
QuadraJet 4MV 7041262

What's different:
Edelbrock round port heads EDL-61529-2
replaces stock 197 HO heads
Crower 60919 cam
replaces a Melling 068 cam clone

Now, the first challenge I had was just getting this to run without pinging. You can see my other threads for more on that. As far as the carb goes I didn't seem to have to do much apart from set the idle speed and mixture. The car does actually run pretty well but I noticed some changes that make me think it probably needs to be recalibrated.

The original calibration I was running with was:
73 jets
45 rods
the stock BU secondary rods
(this is all on the old iron heads and the old 068 clone cam)

I bought a full rebuild/recalibrate kit from Cliff for my old combination and he sent drill bits:
.0625 idle restrictions (which I drilled out)
.1015 idle bypass (which I drilled out and then partially blocked again with a roll pin -- it was too much for the old combo
42 rods (but I ended up at 43 for crisper performance)
DA secondary rods (too fat for the old combo so I went back to BU)
In all fairness to Cliff I should add that some of the lobes were going on the old cam also. Something I wasn't then aware of.

So, with the new heads and cam I did decide to revisit the secondary rods because that's stupidly easy. I tried the DA rods that Cliff sent that were too fat before. The car definitely liked the more fuel at WOT. It was obvious.

So, at this point my setup was as above except with the DA secondary rods.

Next, Jay emails me and says DA sounds too small. You should be at CC or something. I looked them up and CC are seriously fat. I saw there was a CE rod that fell between the CC and DA. I tried those. Again, the car loved the CE secondary rods.

So, now I'm thinking. Although the car drives very nicely with the current primary setup there is no way that the engine wants all that extra fuel at WOT on the secondary side unless the primary side is currently also too lean. But as you QJet guys know, jet and rod swapping isn't as easy on the primary side. This is especially so for me because my little tower for the accelerator pump rocker roll pin is epoxied in place and really easy to break free when you drive the pin to open the carb. It makes me want to open and close it as little as possible.

So, given the above, where would you go? I was thinking just to start with like a 74 jet and same rods. This would just give a little more fuel across the board. Anyone with experience have a good idea what sort of jet and/or rod changes were needed going from low comp iron heads to high comp alum?

Sam

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Last edited by glhs#116; 09-15-2019 at 05:44 AM.
  #2  
Old 09-15-2019, 08:41 AM
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Couple of comments.

NEVER use CC metering rods in a Q-jet. The upper section is too fat, poor taper, and poor included angle leading to the tiny .030" tips. Right on the dyno I've went from DA's to CC's and the A/F went leaner, not richer. We had to manually bend the hanger arms up a LOT with a pair of pliers before we saw them go richer on the pull and even then you could tell there was a very slight lean spike at the onset of the pull due to the big fat upper section. So proceed with caution there and make sure you don't put some pistons in the oil pan messing around with secondary metering rods with smaller tips in your quest to fatten things up to cure a detonation at full throttle issue.

We use a lot of DA rods because they are readily available and smooth transition to the longer tips. AX and CE are also good choices, currently available, and well designed in the same areas. All of them are so close in tip size that it's unlikely you'd really see any difference in power on the dyno or ET/MPH at the track. If doing a seat-of-the-pants assessment the differences would be difficult if not near impossible to tell. Now granted they are shaped/sized a little different above the tips so it may take a very minor hanger change to really bring each one into it's own but for all practical purposes the end results would be too close to effectively evaluate differences with a full throttle street test (butt meter).

You mentioned the factory BU rods. Going from memory they are actually very slightly smaller (richer) at the tips than DA's. Once again they may require hanger changes to effectively position them in the secondary disks to really see full potential or true differences between a better made medium to rich tapered rod with longer tips that were close in diameter. Not trying to be overly critical of your testing, just keep in mind that hanger changes are going to be REQUIRED here unless all of your metering rods are custom machined on a lathe from the same cores with the same tip length and included angle leading to the tips. I discovered this requirement decades ago and ALL of our customers who race (win and hold records in various racing classes) own a fully machined set of secondary metering rods, some as so precise with their tuning they will have me do them in .002-.003" increments from about .030" to mid .060's, FWIW.

For the primary side, and this is something folks have trouble getting their head wrapped around, metering changes with the jets will allow more fuel to the engine across the entire load/speed curve. Even though it is available, fattening up part throttle fuel may not really show up much richer unless the original calibration is off some. This happens because having a little more fuel available at light part throttle may result in a little less throttle opening to make the engine happy. If less throttle is now required to get things done, the change in throttle angle, pressure differential above and below the venture/booster areas will alter fuel delivery (A/F), or simply the carb will delivery a leaner mixture to the engine simply based on those items based on the metering area change.

The problem folks have with this part of the equation is that they think in linear terms, or "static" instead of "dynamic". Now lets throw in timing, mostly from the VA and it trumps everything as leading the timing further allows for a leaner mixture to be burned w/o negatives (within limits). So simply adding 2 degrees timing at light part throttle, for example, could make the engine happy without going into the carb and changing metering area when the power piston is down (light load/light part throttle).

Sorry for being a little scientific with these things, but I'll add here that testing in these areas, especially once you get really close to making the engine happy, often involves weeks if not months of evaluation and many tanks of fuel while operating the vehicle in different weather and street driving conditions. Folks need to read that sentence at least one more time, and keep in mind that you just can't drop in a part or make a very minor change, go out, blast down the road, cruise around the block once or twice and make an accurate evaluation to whether or not there was an improvement or loss, unless of course something in the "mix" of things wasn't even close to on par right to start with.

I remember when I used to be in the Military and drive 600 miles one way door to door to see my family (they were in Ohio and I was in Virginia). I had several vehicles for the commute (at least once a month) and spend countless hours testing jet and metering rod changes in conjunction with ignition timing (springs and VA).

I discovered after scores of trips back and forth the limits based on the laws of physics with this sort of thing. I could literally write 200 pages here outlining the results, but in short form I never once saw a total improvement across the board going in the lean direction targeting light load/part throttle. Superficially I could get improvements, but over the course of the long 600 mile drive then driving all around either in Ohio or in Virginia outside the base trying to run lean too often required heavier throttle openings to accomplish certain amounts of "work" and overall fuel economy would be WORSE than giving the engine a little more metering area and making it happy in more driving scenarios with LESS throttle opening, ie, climbing steeper grades, accelerating in traffic to get up to speed, etc. So I was able to make improvements to fuel economy going lean (and adding a little VA timing) but it required that I drove around like a 90 year old woman and pretended there was an egg between my foot and the accelerator pedal that I didn't want to break!

Anyhow, sorry for being so long winded, but I'll mention the two primary vehicles that were Q-jet equipped that I used as testing platforms and the results I got from them.

1979 K-5 Blazer, 406, 9.8 to 1 compression, 198/204/112 cam with 1.6 ratio rockers on it, TH350, stock converter, 3.07 rear gears with 32" tall tires. Best ever 16.5 mpg (trying to push the envelope a bit too far for VA timing and lean part throttle tuning). Typically 13.5 to 15.5 for all driving with the best tune I could muster in it.

1979 Chevy Impala, stone stock everyplace, (only added dual exhaust/free flowing mufflers with "H" pipe), 350/300hp, TH350, probably 2.73 to 3.08 gears (never checked them). 20 to 22mph highway under any/all conditions. Never had a tank drop below 18 no matter how hard I "pushed" it. Average mileage combined city/highway typically in the 15-18 range.

I'll add that neither one of them started out nearly that good and it took considerable testing to find the best settings and practical limits with timing/fuel curves based on them being "happy" in all driving situations in any weather. When you look at the results compare them to modern vehicles of similar size/weight and you'll notice that they are pretty close if not better than many factory vehicles with FI and ECM's to keep things in check. I'll also add that those engines made considerably MORE power than newer stuff (that 406 SBC was a BEAST in the K5 Blazer), at least until recent years when the engineers decided to quit using pathetically "low" compression, crappy combustion chamber shapes, and pathetically tiny camshafts resulting in poor power production and lacking in efficiency just to make the EPA (not the consumer) happy.....FWIW..........Cliff

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Last edited by Cliff R; 09-15-2019 at 08:48 AM.
  #3  
Old 09-15-2019, 10:28 AM
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PS: slight change to the above response, the Imapla was a 1970, not a 1979.....The 1969 and 1970 350/300hp engines were a culmination of the best of the best far as Chevy 350's from that era were concerned. They had EXCELLENT 041 or 186 castings with very well shaped combustion (small) chambers. Excellent port flow numbers/adequate intake port cross section with no restriction in the exhaust (common in later "smog" castings), very tight squish (they used .020" steel shim head gaskets on them), and very well chosen camshaft for smooth idle, and strong/smooth/broad power curve with superb efficiency in the "normal" driving range.

Folks my age who grew up with those cars and used them for daily transportation can related to the later 60's 327/350's as being about 200 times better in every area as the later "smog" 180-200hp 350's from about 1974 and up with the door-stop 882 castings on them and bogged all down with various emission devices........

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  #4  
Old 09-15-2019, 12:06 PM
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Sam,
Have you got a spare pump rod? Need to modify one so you don't have to mess with the roll-pin. Drill a hole for washer and cotter pin retention or cut a groove for some kind of spring clip or e-clip.

Might try dropping some small washers down the power piston hole. Something that could easily be removed with a pocket magnet. That would limit bottom travel for light throttle and not change full-up when you was pushing it harder. That's all if you've verified piston operation for the vacuum you've got when the ping is happening.

Ping is ping.....Just don't see having to drive the car a long time or long distance to see if it gets better when you richen it up a bit.

Clay

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Old 09-15-2019, 09:18 PM
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FWIW. We run 75 jets on the 455s we have had on the primaries right around 500 hp. We are at around 1000 ft altitude. Surely at sea level you could go richer than what we do. If I recall correctly the CC secondaries are the factory rods on the 70 ram air and 455 engines. Sounds like there is a lot of room for improvement on those. I appreciate Cliffs in depth discussion on that.

  #6  
Old 09-21-2019, 01:49 PM
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So, I didn’t want to comment until I had a little more data. I was working from the standpoint that the part throttle on the primaries felt and sounded a little lean. Combining that with the car seeming to like more secondary fuel I thought I would go from 73 to 74 on the jets and keep the 43 rods.

First impression was that idle fuel went up to the point where proper idle mixture came with idle screws about bottomed. I left them 1/4 out. Part throttle was improved but there was a weird flat spot now at the top of the primaries before going to secondaries.

So, on reflection, I thought I would return to the 73 jet size but go down to 42 rods. Now, all I have in that size are 42B rods. You can see that they actually stay lean longer than the normal ones. Anyway, I put those in, the 73 jets with the 42B rods.

Idle was a good sign. I got proper idle mixture at 1 1/2 turns out. Less drop going in gear also. The flat spot at the top of the primaries is gone and the car drives really well. However, along with all these good things I have one new bad thing. If I move the accelerator down too fast now I get a lean pop backfire. I don’t know if this is down to the B rods. Never had it before. I did verify proper accelerator pump function.

In line with another conversation I also revved it up with the breather pipe open. No smoke at all. In fact, the inside of my air cleaner is so dry now that it started rusting where the paint is flaking. I don’t think I have a ton of blowby.

Anyway, thoughts on the carb tune? Weird it drives so well but will lean pop like that.

Sam

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  #7  
Old 09-22-2019, 02:11 AM
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I posted that last night in a hurry from my phone. Drove to work this morning and it further confirmed my impression that this is the best setup so far (the 73/42B with CE). The idle is more solid and smoother. Cruise, also, now doesn't sound as lean. All the transitions are good. No pops in normal driving. But I know that if I do a really quick hard stab (and to the top of the primaries, because if I floor it the secondaries will compensate) I will get a pop. Nothing in any sort of normal driving though including quick stabs to only partial primaries or even not-quite-so-quick stabs to full primaries.

Anyway, here's a side-by-side of the normal 43 and the 42B to show the profile difference. I MAY have a set of normal 41 rods but I think that might start going too rich. This feels very close to dialed in. But the fact that I can promote a pop tells me something isn't quite where it needs to be.

42B next to 43


Sam
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  #8  
Old 09-22-2019, 02:46 AM
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Just a short clip from the drive in. Full throttle in third from low speed (my TH350 kickdown cable is disconnected so I get to command the kickdowns). It's pretty smooth and responsive..

https://youtu.be/stjO3a6wBiY

Sam

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Old 09-22-2019, 06:26 AM
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Is your vacuum pull off fior allowing the secondary's to open somewhat slow as they should Sam?

Besides seing them out and out bad I have seen them leaky which at a certain drop off in vacuum level just allows the secondary air flap to just roll all the way open which will make for a lean backfire / pop.

Your E heads have 25 % more port volume then your iron HO heads had so you will likley need to set up your primary Accelerator pump for a longer duration pump shot to help when that air flap starts to tip open, having a high enough fuel bowl level and static Accelerator pump height is key to this taking place.

Secondary rod wise I would much sooner having jetting on the rich side and loose 3 hp off the peak power of the motor then to loose the motor as a whole!

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  #10  
Old 09-22-2019, 06:33 AM
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Quote:
Originally Posted by steve25 View Post
Is your vacuum pull off fior allowing the secondary's to open somewhat slow as they should Sam?
It's a good thought. The vacuum pull-off was IIRC replaced with a Cliff-provided one as part of the overall tune-up. But it might be the case that I need to tighten up the spring on the flaps a little. Just interesting I never got a pop with 73/43 or 74/43 combo in the primary side. But since it's only on a really quick snap that I get it and since this is the most responsive recipe I've had on the primary side it might just be a case of that little extra that provokes the behaviour.. I last tuned in the behaviour of my secondary flaps when it was the old old combo with the iron 197 heads and the 068 clone cam with some failing lobes. Maybe the "correct" setup for that is a little "loose" for the better current setup.

Sam

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Old 09-23-2019, 04:12 AM
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I think the vac pulloff is OK..

https://youtu.be/nqhyzhUyyH4

Sam

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Old 09-23-2019, 07:09 AM
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PoE working..

https://youtu.be/Vc3OtPReP4M

Sam

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Old 09-23-2019, 07:12 AM
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Pump shot working..

Drv
https://youtu.be/_qPb4INFcnM

Pass
https://youtu.be/TMIbqQnTxyU

Sam

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Old 09-23-2019, 07:14 AM
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Haven't yet triggered an actual pop in real driving in two days. I'll keep an eye on things. It does drive very well and idle sounds more solid and smooth. I bet if I tried the 41 rods I have they would be too rich.

Sam

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Old 09-23-2019, 08:53 AM
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Quote:
Originally Posted by glhs#116 View Post
So, I didn’t want to comment until I had a little more data. I was working from the standpoint that the part throttle on the primaries felt and sounded a little lean. Combining that with the car seeming to like more secondary fuel I thought I would go from 73 to 74 on the jets and keep the 43 rods.

First impression was that idle fuel went up to the point where proper idle mixture came with idle screws about bottomed. I left them 1/4 out. Part throttle was improved but there was a weird flat spot now at the top of the primaries before going to secondaries.

So, on reflection, I thought I would return to the 73 jet size but go down to 42 rods. Now, all I have in that size are 42B rods. You can see that they actually stay lean longer than the normal ones. Anyway, I put those in, the 73 jets with the 42B rods.

Idle was a good sign. I got proper idle mixture at 1 1/2 turns out. Less drop going in gear also. The flat spot at the top of the primaries is gone and the car drives really well. However, along with all these good things I have one new bad thing. If I move the accelerator down too fast now I get a lean pop backfire. I don’t know if this is down to the B rods. Never had it before. I did verify proper accelerator pump function.

In line with another conversation I also revved it up with the breather pipe open. No smoke at all. In fact, the inside of my air cleaner is so dry now that it started rusting where the paint is flaking. I don’t think I have a ton of blowby.

Anyway, thoughts on the carb tune? Weird it drives so well but will lean pop like that.

Sam
If it were me I would take a step back, get some gauge pins (if you don't already have some) pull the carb apart and remeasure Everything. This is pretty much a proven combo so setting up the idle circuit, figuring out the correct jet/rod combo should be pretty straight forward. It sounds like your idle circuit is set up more for the 068 cam you were previously running. Once you get the carb dialed in you may find the timing/pinging more tolerable.

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