FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: 427LX on July 08, 2018, 08:46:45 AM
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In today's Super Stock racing how are the vacuum secondaries tuned for quick positive opening?
Are they using the short yellow or white spring or the a slightly stiffer spring without the check ball?
I would think given the high RPM they run at they don't need the check ball.
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I have no knowledge of what SS racers do.
That said, what I do is this:
-Use the ball, but drill a .040 or so hole at an angle as an air bypass.
-I use the light spring, typically the short yellow.
-If more signal is needed, or if a stiffer spring is needed, I install a brass tube through the VS channel into the primary. This signal amplifier greatly increases the force available to open the secondaries. If used on a 600cfm carb the secondaries will dang near be 1:1 with the primaries with a light spring.
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x2
eyebrow tube works really well
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People love photos.....
Drilled hole to bypass the check ball:
(https://scontent-mia3-2.xx.fbcdn.net/v/t1.0-9/29472537_221577068581032_3543649062047711232_n.jpg?_nc_cat=0&oh=53942403deb124ab39f49fec77ec6bd8&oe=5BE81A6D)
Signal amplifier tube:
(https://scontent-mia3-2.xx.fbcdn.net/v/t1.0-9/29497331_221577851914287_3209803942779158528_n.jpg?_nc_cat=0&oh=10a43211d15b83e7ca7ed52a7313ef4e&oe=5BD278DD)
(https://scontent-mia3-2.xx.fbcdn.net/v/t1.0-9/29541648_221577235247682_2119740667528740864_n.jpg?_nc_cat=0&oh=22797287ac9209d3f67ab46e8f888af0&oe=5BA75EBF)
To install, you remove the lead plug, being that it's soft, it's easy to catch with a drill bit.
The passage should be about .120, so I drill an entrance into it at .128, the middle section I drill to .125, and the last little bit I leave.
This is ever so smaller than 1/8 brass tubing so it'll be hard to knock in, but it isn't going anywhere.
The brass tube is 1/8. I cut it about 3/4 inch and file the end for the 45degree end.
Hammer it in with a small punch, making sure it's aligned correctly.
Make sure the VS passage is fully clear to the secondaries, as once they crack open they help pull the VS's open.
When done, I drill and tap the entrances at 8-32 and plug with a set screw.
Best to use a marker on a small drill bit to gauge depth when doing any of this.
FLikr isn't working right, so I pulled these pictures from my fb page, hope they work.
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Thanks for that info! That tube rang a bell as I remember some of the old 780's having that on the primary.
My thoughts are that with a pair of vac. secondary carbs would not the vac. signal be weaker than with same sized carb in a single 4 bbl. setup?
I setup my GoPro cam on top of my clear lexan air filter lid,dual 650 Holleys on my 427 Windsor, and recorded a 2nd gear WOT from a low speed roll. Midway thru the quick run the tires started to break loose so made 3rd gear shift at around 5800 RPM. Video showed the rear carb secondary opening maybe 1/4 or less opening...wasn't much.
Car weight is 2970 with me and 1/2 tank of gas and HP and Torque 500+ along with a 3.50 gear and T-600 trans.
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I am running the short White spring and have the check balls removed with a drilled aluminum restrictor with .058 hole sitting in check ball hole. No bog and it seems to want all you can give it.
Would LOVE to try sideways mounted 650 Double Pumpers but is the cost really worth it.
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We have an original untouched pair of the 1968 426 Race Hemi Holley 770 carbs used on my brother's cross ram Hemi.
Might examine those and see what they used as those seemed to work VERY well!
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why not just run the 660's mechanical secondaries?
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Thanks for that info! That tube rang a bell as I remember some of the old 780's having that on the primary.
My thoughts are that with a pair of vac. secondary carbs would not the vac. signal be weaker than with same sized carb in a single 4 bbl. setup?
I setup my GoPro cam on top of my clear lexan air filter lid,dual 650 Holleys on my 427 Windsor, and recorded a 2nd gear WOT from a low speed roll. Midway thru the quick run the tires started to break loose so made 3rd gear shift at around 5800 RPM. Video showed the rear carb secondary opening maybe 1/4 or less opening...wasn't much.
Car weight is 2970 with me and 1/2 tank of gas and HP and Torque 500+ along with a 3.50 gear and T-600 trans.
If the front secondary is opening, plus 1/4 of the rear one, you probably have about 950cfm there. "Double your horsepower" would be about 1000cfm, so maybe that's all the air it wants!
If you block the front secondary SHUT, does the rear one then open up fully?
What about a balance tube? (Mine ran better WITHOUT one on the GTECH)
Good idea to try the other carbs though, it might just "like" them better.
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The eyebrow tube was found on several Holley carbs back in the day before cost savings took over (they were often just straight ended - probably not as effective as Drew's angle cut one). Despite the name, its not really vacuum in the traditional sense that opens them - its airflow through the (mainly...) primary side going past an orifice. Increasing the signal strength will open them more positively and you can then control the rate with spring and/or orifice.
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Yup, airflow.... I test all of my VS carbs to assure opening. Plus after you've done a few you can get a good feel for the right spring opening rate, or at least can make a pretty decent educated guess before tossing it on an engine.
https://www.facebook.com/AirFuelSParkTech/videos/221842335221172/
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On the Stock/Super Stock carbs, a smaller orifice with no ball seems to be more positive, and on bad air days, more consistent. The lightest springs in the kit (you'll have to have two), and also a short diaphragm. The long diaphragms will really squeeze the spring near the top, and won't open all the way with two carbs. It is a reduced signal.
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I'm surely not SS material, but here's my set up.
Lightest springs, balance tube. They do not really do much til high gear(5th). If I lock the secondaries, the 1/8 miles does not change much at all.
I did find out one day, if you leave the balance tube unhooked from one carb it really doesn't run well in high gear. It pulls, falls off, pulls, falls off, etc. Lost that round and wondered WTH? I get back and open hood and realize I left that tube unhooked after doing some tinkering.
Have heard how I need to have DP carbs, as VS carbs are in consistent. Ya, okay. Last Saturday's race, first round and forth round I was dead on with a 4 and dean on with a 3. Not too shabby for a heavy, small tire, stick shift car with TWO vac. carbs on it.
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I'm running the weakest spring and using an aluminum plug which is a slip fit in the ball hole. This has an .055 hole if I remember and I can drill it larger if needed. The passage is about .080 under the check ball.
A shame Holley didn't try the spring loaded air door since it's much simpler in function and adjustment plus you know the throttle plates will be full open.
Another thing I have found is you need to have that primary/secondary link right close to the end of the slot on the secondary shaft when running the weak spring. Sometimes the airflow under the throttle plates will try to crack it open during cruise and can mess with the idle speed.
Now I did try a little test with my own version of a Holley AVS a couple years ago on a single 4bbl. setup!
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Thats a neat little concoction there! How did it work?
Not sure anymore - but it used to be that the purple spring was the only non-linear spring in Holley's vacuum secondary assortment. It was stiff at opening but once moving it opened fairly fast. A personal favorite back when I ran a lot of those deals. The initial resistance prevented the floaty idle that you can get with the white spring if the slip linkage is not snug.
The check ball is/was in there so that when the barrels are snapped shut the secondary diaphragm will empty quickly. Having the slip link adjusted well reduces the need for the check ball. Together they are sorta like having a belt and suspenders...
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What's wrong with the age old screw and nut in the linkage? Unless it's an auto trans I don't see any benefit to vacuum control.
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Forcing the secondaries open, with no pump shot just makes a big lean spot til the air moves enough to pull fuel through the boosters. Even with light springs, it takes a specific time to open and gives the air time to pull fuel.
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LOL, when people did those kits to "defeat" the vacuum secondary, the bog would be justified with "I can feel them kick in now!" Well, um - that's cool.
Some good points here - one of these days I need to get a pair of 1850s set up for t-ram use. I usually start - for a single- with the purple spring. The few times I've used a 600 for bracket racing, the purple spring was more consistent. The air vane setup in the Performer carbs works. They are not adjustable like the newer AVS models and on the setup I ran you could feel the motor start to run out of air, then pick up as they started to open. On that particular 302 combo, it was around 5700 RPM. I'd like to try the AVS units but I have so many carbs ( mostly Holley) stacked up here if a couple more show up my wife may have me committed. :)
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Forcing the secondaries open, with no pump shot just makes a big lean spot til the air moves enough to pull fuel through the boosters. Even with light springs, it takes a specific time to open and gives the air time to pull fuel.
I thought you "three pedal guys" were "on the mat". LOL You are certainly one of the best at it. I am well versed in the dual quad stuff ( 50 years worth) , and yes "on the street" making the secondaries "mechanical" made a huge bog. At the track with my 4 speed Shelby, the fuel was already flowing from the secondaries at my starting line rpm and I didn't notice it. Now I run center squirters ( dual plane Ford intake) with my automatic Shelby.
Randy
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I've never left at WOT. Never had a 2 step. Back when I first start racing, the nostalgia classes would not allow such a thing. I learned to do it the hard way........and 23 yrs later I'm still doing it. Old habits....you know?
I hold the throttle at 5K, 5500, 6K, whatever the track will hold. Then when I dump it, I mash the throttle.
I have a pair of 660's on the blower car, but still not happy with them. Not sure if they are just too beat up? Run okay, but still not right. I tried them on the wagon and got a huge stumble(like on blower motor). Never really figured it out. I have a second pair a friend gave me to rebuild and try. Never have. I have a pair of 735's I converted to single feed and going to try, some day.
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I know about old habits ! 44 years of racing the same car!!! No one can argue with your win record that's for sure. I was still a teenager when I was racing the 4 speed stuff. I was sure "stupid" back then. On the floor slide my foot off the pedal , try to rip the shifter out to the floor, break axles because of wheel hop, driveshafts etc. If I had been a little less aggressive I would probably still be a three pedal guy. The automatic did teach me about how important torque is with respect to ET and 60's. I used to be so screwed up on starting line antics I raced for MPH with the 4 speed cars. Of course the tires were hard rubber compared to today's tires. I appreciate what you do , it's not as easy as the "grandstanders" think.
Randy
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I've never left at WOT. Never had a 2 step. Back when I first start racing, the nostalgia classes would not allow such a thing. I learned to do it the hard way........and 23 yrs later I'm still doing it. Old habits....you know?
I hold the throttle at 5K, 5500, 6K, whatever the track will hold. Then when I dump it, I mash the throttle.
I have a pair of 660's on the blower car, but still not happy with them. Not sure if they are just too beat up? Run okay, but still not right. I tried them on the wagon and got a huge stumble(like on blower motor). Never really figured it out. I have a second pair a friend gave me to rebuild and try. Never have. I have a pair of 735's I converted to single feed and going to try, some day.
What size squirter are you using? my bog using 660's went away with .043 size orifice and 50cc accelerator pumps
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Most of them came with a .025
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Mike:
Can you briefly describe your motor setup?
Most threads you read never suggest such a large squirter let alone a 50cc pump, especially on twins. I just finished a moderate 445 stroker build with a high plenum volume intake and want to minimize the # of iterations it takes me to get them dialed in so soaking up all I can on carb configurations.
Overall, it seems to be very thirsty; using a set of stock BJ/BK carbs (032 squirter) and wondering just how much more fuel a stroker is looking for than a 427/428 back in the day.
I tend to see an ever so brief rich pulse on my A/F followed by lean right now. My setup currently has some segments of RPM range that are excellent and others that I can tell are off, same goes for response from various throttle input rates at various rpms.
Thanks.
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Most of them came with a .025
I used my pin drill set and put the biggest hole I had. Can't recall what it is off hand. It didn't really make any improvement. I know that big windmill needs LOTS of fuel.
with .043 size orifice and 50cc accelerator pumps
I thought they had 50cc pumps on them?
try to rip the shifter out to the floor,
I used to be known for my "aggressive" driving style. Back when I still ran a toploader, I did rip the shifter plate off the transmission. I then replaced the 5/16" bolts with 3/8" and never had that problem again. I'd heard them say I was really jump'n around in the car shifting. I told them I had ONE JOB, and I did it with all my effort! I never missed a gear. With a stock toploader, with brass blockers, you couldn't drive it easy and powershift it at 6K rpm.
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Mike:
Can you briefly describe your motor setup?
Thanks.
Mine were changed with a pin drill also .043 was one of the sizes my cousin had in his tool chest. (We were just taking a stab at it)
The bog off the line went away once we got enough fuel in it. At the time I was running a tunnel port at 427ci with 2 660's.
The car originally had no trans brake and only a 3500 converter. I could bring the rpm up some but when I went full throttle I would get a lean hesitation (bog) from all the air introduced.
It also helped some to delay the accelerator pump shot to coincide with the throttle position so I didn't use up some of the travel and pump shot bringing it up to stall rpm.
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Mike:
Can you briefly describe your motor setup?
Overall, it seems to be very thirsty; using a set of stock BJ/BK carbs (032 squirter) and wondering just how much more fuel a stroker is looking for than a 427/428 back in the day.
Thanks.
Also 660's are not progressive linkage, It's all or nothing. You should be able to use less accelerator pump on progressive linkage and vacuum secondary carbs.
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Stock is 1 to 1 but if you're a 660-870 fan you'll often find the secondary cam reshaped to delay the opening rate. You can do as much damage as good there real quick but it's something I still mess with to even out the bogg or surge you can get from them.
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Thats a neat little concoction there! How did it work?
Worked fairly well on my then 351W. I had it designed so I could remove the secondary pump arm on my 750 DP and then swap on the air valve unit which was held in place by the air cleaner stud. I had to go up in size on the secondary High Speed Air Bleeds to lean the mixture a bit as the door opened. Door tension was adjustable.
Somewhere I have Time slips from a back to back run at the track.
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Neat evenly sure, but comments above look good.
What i can say is i used to have a 3310 times by a local reputable shop, and the secondaries started opening at like 25% throttle. It ran great, but got poor mileage, LoL.