[Kenfrog]

Just for fun, I'll throw this into the mix: I have the original Rochester 7029202 spread bore that came on the car. It's been sitting in a box since I took it off the car back in 1976, so I had it rebuilt at the same time I had the 4160 rebuilt. I'm curious, how does that carb compare to all these Holleys we're discussing. Just from looking at it, I get the feeling that they are a bit of a different animal to deal with.

 

[SY1]

Wow. You know your stuff. You should charge for the "carb school" training I'm getting. With a 100k mile motor, (tho' I have good compression on all) I'll bet my motor is less than 85%, and I'm not going above 5500, (I don't need to blow this thing up at this point) and I'll go with a weaker spring as you suggest…so, if the formula at 6000 and .85 says 516 why not just go with the 570cfm? (The formula at 5500 and .80 ve gets me 445cfm.) I'm not disagreeing with you, just trying to learn. Thanks.
[/QUOTE

I really like the 580 HR that ilikeike suggested. I wished I had known about these when I started this crossram project rabbit hole.

I know you were looking at the refurbed, they are cheaper, but dont include all the features this one has. If it were me I would go with Ilikeike's HR 580. It has everything you could ever want for your application. Think of the grief you wont have to go through upgrading anything.

Upgraded my 600s to center hung & installed QFT tunable VS actuator housings on both carbs. According to QFT these will fine tune the VS system after selecting the optimum spring to get you in ballpark. Mine runs but yet to drive and dial all in. Crossram kind of sucked the joy out of this car, so taking a break. Dont let that happen to your 47 yr old passion. HR 580 it and enjoy the ride!

 

[SY1]

Just for fun, I'll throw this into the mix: I have the original Rochester 7029202 spread bore that came on the car. It's been sitting in a box since I took it off the car back in 1976, so I had it rebuilt at the same time I had the 4160 rebuilt. I'm curious, how does that carb compare to all these Holleys we're discussing. Just from looking at it, I get the feeling that they are a bit of a different animal to deal with.

Well I had one on a 74 Z28 I owned back in 1979. I knew nothing about quadrajets and still dont. But I took the car to a local guy that knew about them and it worked reall well when he was done with it. I know some swear by them, some swear at them. If you find someone that knows how to set them up it would be very cool to have another original piece on that gem!

 

[Kenfrog]

Well I had one on a 74 Z28 I owned back in 1979. I knew nothing about quadrajets and still dont. But I took the car to a local guy that knew about them and it worked reall well when he was done with it. I know some swear by them, some swear at them. If you find someone that knows how to set them up it would be very cool to have another original piece on that gem!

Thanks. If I sell this car, it will go with it, along with the intake, air cleaner, fan etc. These carbs have been suggested as good options. They have some interesting additional features the Holley doesn't. But I kinda understand the Holleys now. Do you have an opinion? Any experience with these? Any hearsay? Any rumors?Quick Fuel FRHR-580-VS HR-Series Carburetor 580CFM VS-Factory Refurbished. Summit Racing SUM-M08600VS Summit Racing™ M2008 Series Carburetors | Summit Racing

 

[Kenfrog]

RPM to open for secondary springs are also dependent on the size of the carburetor relative to the maximum potential airflow of the engine (displacement, headflow, camshaft, etc.). If the carburetor is oversized, then yes something like a purple spring may not achieve full open. It's only going to open as far as it needs to supply the maximum amount of air. That's why a 402 with purple spring opens the secondaries quicker and reaches full open sooner than on a 350 for the same size carb. So for the above formula posted, just use rpm, VE, and displacement to calculate minimum carburetor size, and don't worry about the affect of the secondary spring (that's just a tuning device).

A 570cfm-600cfrm would work fine based on your 350/5500rpm. Going back to what I said in a previous post, I'd find a 4150 something with downleg boosters for better signal. The downleg boosters do slightly impact flow compared to straight, so the carbs tend to be rated lower for the same throttle bore size. Both the QFT HR Series and Brawler have downleg boosters from what I see. Interestingly the Brawler states straight leg in the specs, but the pics show downlegs (there's also an online MT article that talks about them having DL boosters). Both also use an adjustment screw for the secondary, so you don't even have to remove the secondary spring. It has a purple spring factory installed, and then the screw just adds/subtracts preload.

Thanks. That's very helpful. So, based on your explanation above (about the secondaries opening only when the engine demands it) if I was to take my carb and add a softer secondary spring so that it opens at a slightly lower RPM (since my black spring is pretty stiff for my 350) my car might actually run worse if/when the secondary opens all the way?

 

[Everett#2390]

It could, but it's a simple effort changing spring,
You might try it

 

[FbodyMike]

Thanks. That's very helpful. So, based on your explanation above (about the secondaries opening only when the engine demands it) if I was to take my carb and add a softer secondary spring so that it opens at a slightly lower RPM (since my black spring is pretty stiff for my 350) my car might actually run worse if/when the secondary opens all the way?

Correct. What usually happens is, to much air too soon will actually reduce torque. Keep going lighter in increments. At some point, you'll get this feeling like the secondaries aren't responding but then they kick in like gangbusters at higher rpm (kind of similar to a large camshaft). What you're really feeling is the power is not as linear because the secondaries have opened too quickly creating a soft area transitioning from 2bbl to 4bbl operation. When you reach that point, go back one step heavier.

 

[travisch]

Is it idling fat? First thing I'd do I pull it off, flip it over and check how much of the idle transfer slots are exposed. If too much (~ 0.02" is the spec) that will render the idle mixture screws useless as too much fuel will be bleeding from the slots and not the idle circuits. What you describe is the textbook result of too much slot exposed. As mentioned, assume engine is warmed up and choke off.

Cant stress this enough. You can play with a carb for hours and get it just OK if the transfer slots are over exposed but if they are correct it should start and idle like its fuel injected.

 

[Kenfrog]

Cant stress this enough. You can play with a carb for hours and get it just OK if the transfer slots are over exposed but if they are correct it should start and idle like its fuel injected.

Thanks. I got them correct, now. The real issue was the 4160 6619 has that goofy reverse idle circuit. The idle mixtures screw make it leaner as the screws come out. Richer in, leaner out, the opposite of what everyone expected.

I would think that 670 would be a good carb for your 350. Throttle bores are the same as the 600 warrior and it worked great for me. Plus it has quick change VS spring cover, 4 corner idle mixture screws, electric choke which I really miss (simple hook up to your fuse block). Dont know what trans you currently have but if it is an auto 700R you could need another $70 worth of hardware to hook up the linkage according to Holley, which they have. No its not too big, ventury bores being 600 venturis, the purple VS spring installed will not fully open secondaries until 6950 rpm, which I dont think you are going to see. The yellow or yellow short spring will both fully open around 5700 if you so choose to try later. Plus Holley says you get the kit of VS optional springs with this carb if I read that correctly.

CFM estimated
Engine CID x max rpm/3456 x Ve = cfm potential

Ve is volumetric efficency. Holley considers most hi perf engine = 85%, full modified racing engines 95%, smog motor low perf 75%.

So 350 cid x 6000 rpm/ 3456 x .85 Ve = 516 cfm. I assumed 6K redline, 350 hyd flat tappet cam street motor. Remember the purple spring is never going to fully open second secondaries for another 950 rpm beyond that and doesnt start opening until 1915 ish. Assuming the secondary actuation is linear, and I dont know it is or not, at a 6K redline at WOT (wide open throttle) your secondaries will only 80% open. Which would mean in theory to me 20% of cfm capabilty is left on the table, so 670 x .80% = 536 cfm @6K & WOT w/ purple spring.

Maybe some others can chime in here to confirm or correct.

If this is correct 536 cfm is what you can expect to deliver and 516 cfm is what Holley formula feels is required for 350 w/6K redline & .85 Ve. So seems like a good fit.

OK. Here's where I am: The car is/was running great (the front accelerator pump linkage needed a slight adjustment, and I could tell it ran better) but I decided to look inside the carb to see what was in there, just for fun. (I can always get a new carb later.) People on here suggested maybe putting a new PV in—just in case the backfiring damaged it (I probably should have left a sleeping dog lie, but I may never have another opportunity to put my old and newfound knowledge to use.) The car pulls a steady 16.98" vacuum at idle (so I'll say 17) and I bought an 8.5 PV just to see it there was a difference.

Expecting to see a 6.5, it has 7.5 power valve, so one step up may not be too noticeable either way.

The blue front bowl gasket has a little tear in it, but that may have happened when I removed the front bowl (it kind of popped off) but I have a new spare.

Here's the problem: I put the new PV in and I'm trying to put it all back together. When the front bowl popped off, the front to rear fuel transfer tube obviously popped out too along with the o-ring. Now I'm trying to get the tube back into the rear bowl, but I'm not sure how the get it all to go inside that opening in the rear bowl. It doesn't want to go in with the o-ring on the tube. Is there a trick? Should I just work the o-ring in by itself first?

Also the tube is kind of loose in the front bowl with the whole thing off. Can I assume that's normal? I also ordered a quick-change secondary spring set. I haven't done that yet, but in my test-drive I tried the paper-clip trick and at WOT up a steep incline thinking that would be more load on the engine, after about a 4200 rpm run, the paper clip only moved about 1/16" I didn't expect it to go much further since a black spring is pretty stiff—unless the rebuilder changed that too based on his experience.

 

[ilikeike]

Thanks. I got them correct, now. The real issue was the 4160 6619 has that goofy reverse idle circuit. The idle mixtures screw make it leaner as the screws come out. Richer in, leaner out, the opposite of what everyone expected.




Here's the problem: I put the new PV in and I'm trying to put it all back together. When the front bowl popped off, the front to rear fuel transfer tube obviously popped out too along with the o-ring. Now I'm trying to get the tube back into the rear bowl, but I'm not sure how the get it all to go inside that opening in the rear bowl. It doesn't want to go in with the o-ring on the tube. Is there a trick? Should I just work the o-ring in by itself first?

I use to put a bit of lube on the O-ring and just wiggle or twist back and forth as I put it together.

One of the reasons I don't like the 4160 single feed carbs, as I mentioned earlier in this thread. post #77

 

[Kenfrog]

I use to put a bit of lube on the O-ring and just wiggle or twist back and forth as I put it together.

One of the reasons I don't like the 4160 single feed carbs, as I mentioned earlier in this thread. post #77

Thanks. That worked fine. I remembered your post, that's why I was wondering if there was a secret to it. It's all back together runs fine and no leaks. So far so good. It's raining now so I'll need to wait to see if the 8.5 makes any noticeable difference. Did you notice my question about the jets? What's a #642. I thought they had 2-digit sizing?

 

[ilikeike]

Thanks. That worked fine. I remembered your post, that's why I was wondering if there was a secret to it. It's all back together runs fine and no leaks. So far so good. It's raining now so I'll need to wait to see if the 8.5 makes any noticeable difference. Did you notice my question about the jets? What's a #642. I thought they had 2-digit sizing?

Sometimes those jet stamping aren’t that great.
it more likely a 64.
I use a magnifying glass a lot more now days to read jets when the stamping crosses the tool notch

 

[Kenfrog]

Sometimes those jet stamping aren’t that great.
it more likely a 64.
I use a magnifying glass a lot more now days to read jets when the stamping crosses the tool notch

I used one and it definitely says 642. Could still actually BE a 64 jet, I guess... that's smallest they make. Do those jets affect the idle circuit at all?

 

[FbodyMike]

I used one and it definitely says 642. Could still actually BE a 64 jet, I guess... that's smallest they make. Do those jets affect the idle circuit at all?

It could be a 642 stamping. Holley's jets sold as aftermarket were typically 2 number stampings. However, for OE applications they would have even finer increments designated by 3 numbers to differentiate. Since your carb was intended to be an emission replacement, this could likely be the case. So your jets would be slightly richer than 64s, but still leaner than a 65s.

 

[SY1]

It could be a 642 stamping. Holley's jets sold as aftermarket were typically 2 number stampings. However, for OE applications they would have even finer increments designated by 3 numbers to differentiate. Since your carb was intended to be an emission replacement, this could likely be the case. So your jets would be slightly richer than 64s, but still leaner than a 65s.

Mike thanks for the post. My Holley book showed 642 jets for Ken's emission carb. I had never seen a 3 digit Holley jet number but your post explains it and makes sense. One thing I have learned through this topic is that emission carb is a little different animal from a standard 4160.

 

[Kenfrog]

I used one and it definitely says 642. Could still actually BE a 64 jet, I guess... that's smallest they make. Do those jets affect the idle circuit at all?

Thanks. You guys seem able to find anything!

I looked and looked for 642 info and found absolutely nothing. So a 642 is almost as small as they get. I installed a 8.5 PV just to see if it made any noticeable difference. It didn't. If it makes no difference I may go back to a 7.5 just to save some gas.

I did fool with the idle mixture some more and this time (in drive ~600 rpm) I got a perfectly smooth idle at 17" hg turned out a full 1 1/8 turns...so just a tad leaner than I had it 3/4 turns. (1 1/4 turns out and the vacuum dropped about 1/2")

Before I change the secondary spring (I'm just fooling around): I did another test running it up to 5000 rpm (orange line) and this time it moved the paper clip about 1/8." (Assuming a black spring) I understand a softer spring might ALLOW the vacuum secondaries to open at a lower RPM, but WOULD they? Since, I think you told me, they only open as much as the engine demands, wouldn't they only still open the same amount at the same rpm?

 

[FbodyMike]

Lighter spring will still effect the rate of opening for the secondaries. Opening too soon results in insufficient air velocity across the boosters resulting in a lack of fuel. This results in a lean hesitation until air velocity catches up enough to create a signal. If you experiment with lighter and lighter springs, you'll feel it.

 

[Kenfrog]

Lighter spring will still effect the rate of opening for the secondaries. Opening too soon results in insufficient air velocity across the boosters resulting in a lack of fuel. This results in a lean hesitation until air velocity catches up enough to create a signal. If you experiment with lighter and lighter springs, you'll feel it.

Thanks. I don't want to go too light (or too fast) I just want to see what it feels like if they'd open more than they are.

 

[FbodyMike]

Going too light is how you find the sweet spot of what the engine wants (then you go one step back). Experiment and have fun! You can either just replace the springs (be careful not to tear the diaphragm when screwing it back together). Or you could get a quick-change kit like this: https://www.amazon.com/Holley-20-59-Change-Secondary-Housing/dp/B00029JE4W
Or install one of these, and just adjust it with a screwdriver: Quick Fuel 63-12QFT Adjustable Vacuum Secondary Die Cast Polished

 

[Kenfrog]

Going too light is how you find the sweet spot of what the engine wants (then you go one step back). Experiment and have fun! You can either just replace the springs (be careful not to tear the diaphragm when screwing it back together). Or you could get a quick-change kit like this: https://www.amazon.com/Holley-20-59-Change-Secondary-Housing/dp/B00029JE4W
Or install one of these, and just adjust it with a screwdriver: Quick Fuel 63-12QFT Adjustable Vacuum Secondary Die Cast Polished

Thanks. I have the kit, but I'd never seen the QFT thingie. I assume it'd work on a Holley?