Sizing carburetor

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It is nice to see Schneider thinking 'out side the box' with the reverse pattern cam!!!
Keep it! I have been using them for 20 yrs. Many were used in the Engine Masters Contest.

Jon Kaase won the EMC [ he is a multiple winner ] with a 400 Ford engine. It made 660 hp at 6000 rpm.....with a 246/238 @ 050 flat tappet cam. So much for the nonsense about needing extra exh duration to make hp.....
When you increase int duration & lift......the engine ingests more air. When the exh opens, there is now more gas pressure in the cyl.....to push out the exh. Sort of self adjusting to an extent.
The other benefit is smoother idle, more vacuum from reduced overlap because it is the exh component of the olap that has the greatest affect on idle.
The 650 AVS2 would be the best choice. If you have some carb experience, a TQ would also be good but will likely require tinkering...
And sure as hell you can go too big with carbs. Remember the tortoise & the hare......
I have seen, felt & read of incredibly good acceleration times from cars with just a small 2 bbl carb...
 

junkyardhero said:
AVS #1602 650 or a Holley 3310, 3310-1 (so you get vac 2ndaries, metering blocks and 780cfm with dogleg boosters).
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And that’s why it’s difficult for me to pick a carb as you’d think you want to pick a carb by the cfm but with Holley it’s 100 more than eldelbrock. I’ve been looking at those two carbs, the Holley 670 street advenger, and also the quick fuel slayer 750
 
Bewy said:
It is nice to see Schneider thinking 'out side the box' with the reverse pattern cam!!!
Keep it! I have been using them for 20 yrs. Many were used in the Engine Masters Contest.

Jon Kaase won the EMC [ he is a multiple winner ] with a 400 Ford engine. It made 660 hp at 6000 rpm.....with a 246/238 @ 050 flat tappet cam. So much for the nonsense about needing extra exh duration to make hp.....
When you increase int duration & lift......the engine ingests more air. When the exh opens, there is now more gas pressure in the cyl.....to push out the exh. Sort of self adjusting to an extent.
The other benefit is smoother idle, more vacuum from reduced overlap because it is the exh component of the olap that has the greatest affect on idle.
The 650 AVS2 would be the best choice. If you have some carb experience, a TQ would also be good but will likely require tinkering...
And sure as hell you can go too big with carbs. Remember the tortoise & the hare......
I have seen, felt & read of incredibly good acceleration times from cars with just a small 2 bbl carb...
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Correct and that is one reason I went with this can is the smooth idle, also the great rpm range it offered.
 
rymor92 said:
And that’s why it’s difficult for me to pick a carb as you’d think you want to pick a carb by the cfm but with Holley it’s 100 more than eldelbrock. I’ve been looking at those two carbs, the Holley 670 street advenger, and also the quick fuel slayer 750
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anything from 625 to 750-ish is going to be more than adequate. TQ's and Q-jets were 800+ and they came factory.

the avenger and slayer are not only different CFM, but the offer different details: the avenger has 4 corner idle, with metering blocks with jets on the primary and 2ndary and easy change 2ndary spring. the slayer has airbleeds and metering plate 2ndary. obviously there's a little more to it than that, but you get the gist of it.

i don't know your level of skill with tuning a carb or if you're even willing to swing wrenches, so my suggestion was based off of which two carbs i know would most likely work straight out of the box pretty well, be kind of close jetting wise, and be fairly easy to dial in with resources available online (here or u-tube vidyas).

there is also the consideration of what the planned use of the car is; a street/strip car, friday nite burger cruiser or touring car could ostensibly all use the same carb, but ideally each would have a carb best suited to their intended purpose.

and just to ruffle all the feathers: realistically, you could grab a used carter/edelbrock afb 625 for next to nothing, throw a rebuild kit at it and it would run just fine.
 
junkyardhero said:
anything from 625 to 750-ish is going to be more than adequate. TQ's and Q-jets were 800+ and they came factory.

the avenger and slayer are not only different CFM, but the offer different details: the avenger has 4 corner idle, with metering blocks with jets on the primary and 2ndary and easy change 2ndary spring. the slayer has airbleeds and metering plate 2ndary. obviously there's a little more to it than that, but you get the gist of it.

i don't know your level of skill with tuning a carb or if you're even willing to swing wrenches, so my suggestion was based off of which two carbs i know would most likely work straight out of the box pretty well, be kind of close jetting wise, and be fairly easy to dial in with resources available online (here or u-tube vidyas).

there is also the consideration of what the planned use of the car is; a street/strip car, friday nite burger cruiser or touring car could ostensibly all use the same carb, but ideally each would have a carb best suited to their intended purpose.

and just to ruffle all the feathers: realistically, you could grab a used carter/edelbrock afb 625 for next to nothing, throw a rebuild kit at it and it would run just fine.
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Another one that’s easy to use is the 750 street demon. I’ve just seen mixed reviews so I’ve been unsure with it. I don’t go too in depth with tuning. Less is more in my mind but I’m also not racing it so I’m not tuning to get every hp I can either. Also why I liked the slayer over the hr series as less adjustments.
 
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George Jets said:
Like your old school cam grind numbers.

Here is hands on >

I usually run the Edelbrock 600 1406 on most everything stock build.

Friend had an AVSII 650 cfm for me to test out on the stock fresh build 360 on the engine run stand, with the 340 cam.

Dropped it on, ran perfect right out of the box. Quick starts, great throttle response, nice idle.

Kind of felt like fuel injection. I was running the Mopar HEI distributor that I converted and the basic 60,000 volt E-Coil that I am sure helped with the quick starts and good throttle response, with the hotter spark output.

Oh and 360 has the Weiand 8022 Stealth square bore intake on it also, probably helps too > gasket matched to the stock heads.

Now the 650 AVSII was too much for my friend's 318 so he had me try it.

I felt the AVSII 650 with the Annular Boosters was the perfect match carb for that stock build 360.

It was right for the increased cfm of the 360.

View attachment 1716217145

View attachment 1716217146

View attachment 1716217148

View attachment 1716217150

My experience, I had good results.

Your expectations may be different and may require more fuel.

The jump to 800 AVSII is a pretty big jump.

Have fun experimenting.

☆☆☆☆☆
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The revised boosters on the AVS2 make a big difference in throttle response, for sure. When I put an AVS2 650 onto my 408 as a test, the throttle response was very much like an EFI. Much better than the Holley style I normally run.
 
rymor92 said:
And that’s why it’s difficult for me to pick a carb as you’d think you want to pick a carb by the cfm but with Holley it’s 100 more than eldelbrock. I’ve been looking at those two carbs, the Holley 670 street advenger, and also the quick fuel slayer 750
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There's no magic formula for picking a carb, if you want optimal you may have to try some know some peeps came borrow from? Or go by the experience of the last 75+ years of people hot rodding and racing.
 
Some of you guys need to learn to read that cam card,
on the left is advertised
on the right is at .020 tappet.

020 tappet at 1.5 ratio, is .030 valve.
and .300 x 1.5=.450 valve
and .030 plus .450 = .480
case closed.
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I like that cam.
With plenty of cylinder pressure, the right timing curve, long-tube headers, and a free-flowing exhaust, my guess is that it could make excellent street torque, and I'm sure I could gear it to run 65= 1600, and with a manual trans, make point-to-point fuel-mileage in the high 20s, with a small TQ.
I mean check it out, it has 118 degrees of power extraction! In a long stroke 360, that alone has a lotta potential.
However, in per the camcard, the Ica is 65*, so, to make pressure with that is gonna take a fair bit of Scr.
The numbers look screwy, but once it's mapped out, the only things that take a hit are the effective overlap, and cylinder pressure. You can't do much about the overlap, but you can deal with the Ica.
For on a budget, I'd run it. It's like a factory 360 2bbl cam except with 340 intake duration. I'd even run it with the 188 valves.
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as to carb size, on the street, anything over 500 will work, cuz with 3.23s you're only going thru the PowerPeak the one time, and probably spinning the tires anyway. Getting into Second she'll top out at about 65@4200@10% slip; so you can just run whatever you already have, that is known to work.
Now, if you have to buy a carb, and intake, that's another story..
In that case I'd like to run a metering-rod Spreadbore, like a TQ. But I would not run any spreadbore carb on an adapter to a sq-bore intake.
That cam is gonna peak at around 4900/5000rpm so the AirGap intake is more than you need.
If you already own it, then fine, just stick any old carb on it.
But, if you don't have an intake, just grab anything, even a small-port, small plenum, single-plain, but then I wouldn't bother porting those X-heads ................... which I wouldn't bother with anyway for this particular cam.
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But you know, what do I know......
According to some; you should run a 273.
Anybody that knows anything around here, knows that 273s are the bees knees.
Oh, sorry, I meant 318s are the bees knees.
Oh, sorry, you should run a 7500 rpm 283 Nova with a powerglide,
Oh, sorry, you should stroke it.
Whaaatever.
This place is like the ocean;
everyday the tides go out and the tides come in,
and one day it's calm, and another the waves are raging.
Going fishing is a crapshoot; you can have the best equipment, and you can stay out all day, and you can still go home hungry.
 
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AJ/FormS said:
Some of you guys need to learn to read that cam card,
on the left is advertised
on the right is at .020 tappet.

020 tappet at 1.5 ratio, is .030 valve.
and .300 x 1.5=.450
and .030 plus .450 = .480
case closed.
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Maybe you need to take your own advice. We are talking about using less exhaust timing and lift.

I can see nothing good about that. As displacement goes up and the valve size (exhaust valve) stays the same or gets smaller you need to start adding time/area to cam timing.

As I've said, single pattern cams have a place but not on these big engines being built today. I had to change my thinking on that.

And a reverse pattern cam? I'll pass.
 
@AJ/FormS is right, I commented that the lifts didn’t match the listed rocker ratio and it never occurred to me that the timing and lifts at the right were at .020 tappet rise.
 
Newbomb Turk said:
And a reverse pattern cam? I'll pass.
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Doug Dutra found out that they were worth nothing on a slant 6. He experimented with several different reverse grinds and even got Erson to make a few, but they showed no power increases over a standard grind.
 
The thing with carburetors is, an 800 Holley is not the same as an 800 Eddelbrock AVS an 800 Thermoquad, yet, no matter how much you try and preach it, people will not listen. AT ALL. So, all I can say is, all my stuff through the years has run well and hauled ***. There's just no way in HECK I'd ever run an Edelbrock 1406 on anything that was what I wanted to be a "performance" engine. They are NOT performance carburetors. All they are is a factory replacement base model four barrel. They have a very lean system. The 1405 is the performance version. Now if all you're interested in is mileage and a factory type running engine, grab the 1406. They can get good mileage. But if you have a better than stock four barrel intake, cam and headers, you will always be chasing a lean condition IF you try to tune it for performance. But again, you simply cannot communicate that to some people.
 
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an AVSII opens the secondaries based on engine demand. It's one of the reasons they are so forgiving right out of the box. Will 800
cfm be too much? Here's 2 500 Eddie AFBs on my pretty mild 340. I think your 360 can take it - with an AFB or AVS better too much than too little.

STR 12 #3.JPG
 
There is nothing wrong with the cam card. For some reason Schneider has elected to use 0.020" as the lifter checking height [ not the more common 050 ]. Perfectly ok with a hyd lobe as the clearance ramps are short...& at 020 well past them for an accurate reading with a degree wheel.
This is from the cam card:
- 220/210 @ 050
- 250/236 @ 020.

Some will never get it about exh duration......
Comp Cam 12-402-4. 212/218 @ 050. Blower cam
Comp Cam 12-400-4 218/212 @ 050. Turbo cam
Crower Cam 00979. 226/208 @ 050. Turbo cam 6500 rpm +.
Since turbo & blown engines have MORE exh gas to expel, Crower reckons 208 @ 050 is enough duration to 6000 rpm with a 6500 redline. Hmm.
 
str12-340 said:
an AVSII opens the secondaries based on engine demand. It's one of the reasons they are so forgiving right out of the box. Will 800
cfm be too much? Here's 2 500 Eddie AFBs on my pretty mild 340. I think your 360 can take it - with an AFB or AVS better too much than too little.

View attachment 1716217727
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that is a thrill seeking setup for sure great job
yes its better to be to big then to small
 
I think some will just never get it when it comes to carb cfm.......
There was a YT video of a bloke putting a lawn mower carb on a 289 Ford.....& getting quite good acceleration.

The engine takes the cfm it wants from the carb. Put a 750 carb on a 340; it might use the 750 cfm IF it is a high output engine that revs to close to 7000 rpm...with a 100% VE. Less VE, less air ingested.
A good way to see this in action is to see an engine on the dyno with an air valve sec carb like an AVS or TQ. And an overhead camera. A big engine will pull the AV open at lower rpms than a smaller cube engine.

The risk of putting big carbs on an engine that will not use the cfm is that it hurts low rpm throttle response. If one size fits all, then that would be what we have....but we don't. You also need to factor in the atomisation/distribution quality of the carb.
David Vizard made 460 hp on a SBC with 48 IDA Webers, one carb bore [ 48 mm ] per cyl, 320 cfm. An 850 Holley on the same engine was down on power everywhere, made 435 hp.
 
It is fair to say that oversizing a carb that uses an air valve AND small-er primaries is somewhat forgiving. The small pris will give good response, even if the throttle is mashed because secondary air flow through the throttle bores does not start until the engine is ready for it. If you use say a 850 Holley double trouble, with it's large pri bores, then the engine, unless it is a monster engine, is not going to need 850 cfm at 3000 rpm.
 
Bewy said:
I think some will just never get it when it comes to carb cfm.......
There was a YT video of a bloke putting a lawn mower carb on a 289 Ford.....& getting quite good acceleration.

The engine takes the cfm it wants from the carb. Put a 750 carb on a 340; it might use the 750 cfm IF it is a high output engine that revs to close to 7000 rpm...with a 100% VE. Less VE, less air ingested.
A good way to see this in action is to see an engine on the dyno with an air valve sec carb like an AVS or TQ. And an overhead camera. A big engine will pull the AV open at lower rpms than a smaller cube engine.

The risk of putting big carbs on an engine that will not use the cfm is that it hurts low rpm throttle response. If one size fits all, then that would be what we have....but we don't. You also need to factor in the atomisation/distribution quality of the carb.
David Vizard made 460 hp on a SBC with 48 IDA Webers, one carb bore [ 48 mm ] per cyl, 320 cfm. An 850 Holley on the same engine was down on power everywhere, made 435 hp.
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That's the main reason Chrysler used TWO Thermoquad sizes. 800 for smaller engines that had small primaries and 850 for larger engines that had larger primaries.
 
Bewy said:
It is fair to say that oversizing a carb that uses an air valve AND small-er primaries is somewhat forgiving. The small pris will give good response, even if the throttle is mashed because secondary air flow through the throttle bores does not start until the engine is ready for it. If you use say a 850 Holley double trouble, with it's large pri bores, then the engine, unless it is a monster engine, is not going to need 850 cfm at 3000 rpm.
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Carbs are an restriction, albeit a necessary one, since that's how they operate, ideally you want the least restriction that will function the way you need it to.
 
agree

what you need it to do is key
Drag racing is a small and specific area where Bigger carb to the detriment of normal driving is better but its the only time you would do that. you choose and tune the narrow higher rpm range you use for 9, 10, 12 seconds. and at or near WOT.

For that you don't need a carb an angle cut pipe ending in the middle of the throttle bore with a restrictor and a simple throttle plate works for that kind of operations. they used to call it fuel injection....! :)

a bit too big, in any other circumstances and you will loose every time you are operating at part throttle.

the more oversized the carb is, the narrower and higher the rpm range it works properly at is.
until you add a band aid like an air door or vacuum actuator :)

A motor with a smaller or even a supposedly too small carb, will involve buying more jets and will involve more fiddling to get it to work properly. but when it works it will work brilliantly for 80% of throttle openings (the 80% you use on the street) and you will only see an impact of the greater restriction imposed on the motor due to the smaller carb as you approach WOT at the Highest RPM you run at. that rpm range will be restricted by the smaller carb.
airflow at all other RPMs will be faster, for the given RPM, so atomisation will be better, leading to better consumption and more torque and cooler running

WOT at lower rpm will produce plenty or torque, and the motor will be a pleasure to drive. because the restriction isn't truly a restriction when the engine doesn't need maximum air flow when its not at its maximum rpm.

an over carbed motor is in my opinion a dog on the street

Dave
 
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Thank you for the replies that’s have stayed on topic instead of complaining about the cam I have.

I’m between the 750 street demon with poly bowl and the 750 quick fuel slayer. I feel from my research and what you guys have said a 750 should be a good carb for my engine. Does anyone have experience with these two carbs and your thoughts on them?
 
Apologies No, but like anything else buy the one from the supplier who will give you the most support and carries the full range of parts. if you buy one that is just too damn unique you will never get a straight answer out of anyone when you need help. Make sure they know what you intend to do with the motor, if they are going to put in a baseline calibration for you.

most carb problems are solved with a better ignition , correct curve and the right plugs :)

Nice fancy carb producing superlative mixture increases pressure in the cylinder and that will highlight failings in the ignition system. i've been there and done that ...:) wasted loads of time


Dave
 
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