750 Brawler vs 650 AVS 2 at the track, right OOTB !
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33IMP
Well-Known Member
A REAL 68 hemi dart or barracuda (your example) is a high dollar car. I agree with you, I like cheap fast cars. I had somewhere around $9000 in this 9 second car.....
This is why I get my ducks in a row and get what I want out there in the first few post. Meaning, I do the update and results at the same time. Next update will be a new thread. I'll return to answer a question if I'm paged. Field is open, have at it ... 
mopowers
Well-Known Member
It's too bad a thread like this has to turn into an argumentative **** storm. 318WR was doing a fun comparison while having a great day at the track with his Mopar and wife. Take it for what it is.
I'd like 318WR to do a test with 1500 cfm.
MopaR&D
Nerd Member
The correct boosters atomize the fuel more with less of a vacuum signal so it vaporizes at the right time instead of staying in liquid form during the power stroke.
Correct except in an engine built for any level of performance it's actually the scavenging effect of the exhaust pulse creating the vacuum before the intake valve opens far more than the piston moving down the cylinder during the intake stroke. The key point is that air is a compressible fluid and has inertia so the vacuum created at the intake valve can easily be lost trying to travel to the carburetor or throttle body especially during WOT if the intake port and runner design is bad.
No but he/she can apply the lessons in any engine even if it's not a Pro Stocker. This isn't something you need a wet flow bench to discover anyway, OEMs figured it out before that was popular all you need is a way to draw air through a port while injecting some kind of liquid with a dye. If the port isn't keeping the fuel atomized the liquid will show up as a dribble or stain running down the chamber walls.
You "crutch" a port that causes fuel separation by increasing restriction which absorbs flow energy (thus power) or like you said, add heat which also reduces power by decreasing the charge density. Get the port right and you make max power because those "crutches" aren't needed anymore.
Your example of the big Ford running better with the smaller carb is precisely an example of that, the port design was bad enough to where there was a net gain in power by increasing manifold vacuum at WOT because the intake charge quality was trash. If the intake ports and runners were corrected it would have made more power with a bigger carb.
Sorry to the OP for getting sucked into the shitstorm but I think this is useful info for everyone. It applies to his situation as well because if the engine has decent intake flow characteristics it will indeed benefit from having a properly-dialed 750 cfm DP carb over the 650 cfm AVS with the annular boosters. Booster types can be easily swapped in Holley-style carbs anyway. If the carb is "too big" for the application and more booster signal and fuel atomization is needed at lower RPM then converting to annular boosters fixes that issue better than going to a smaller carb because it's not creating an airflow restriction, at least not nearly as much.
Your doing back flips thinking this proves you right cause the 650 shows less than a 1% gain in mph, so far and unless 318willrun cares to do a full shootout all we know ootb on this combo on this day there pretty much on par with each other and if we were to make wild assumptions with the little we know, it goes against the case you make so far cause either A the 750 is vaporizing the fuel just as well as the 650 or B it's not but it makes little difference in performance anyways.
What it kind of proves though is why 650 and 750 are popular choices for a small block.
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No they don't. Both triple stage boosters and annular boosters increase signal because the are more restrictive. What is "correct" is to reference the booster signal required to the vacuum generated by the engine. Again stick a Dominator (1050) on a 318 and tell me all about atomization when you don't create enough vacuum to actually lift the fuel up through the main well and out to into the booster channel.
Triple stage Boosters actually double the depression by multiplying the depression created by the initial booster.
Here's none other than John Kaase clearly showing the pulsations that take place in a manifold. What do you think is pushing his finger back towards the carbs? Look at all that "atomized" liquid fuel on the walls and runners making its way to the intake valve..........
Amazing Video: Jon Kaase Tests Airflow Dynamics With His Finger
What do you think those pulsations will do to carb signal? What do think all that black **** on the underside of the air cleaner is and how does it get there?
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Only a 1% gain difference in performance from a lot less cfm.........Weren't they expecting a 2 tenths difference on the assumption the extra airflow would equate to more power? There's a clear difference in airflow yet not performance. Didn't the 650 have issues as well........Looks like it needs more time tuning than the 750?
That was also 30 years ago...
I would like to see 318 do the filming and the wife making a pass.
Close... I've got 1200 cfm's on the 318....
We've done that ... in the Van of War. If I remember right, I was a hundredth quicker and she was .01 mph faster....
Rat Bastid
Dunamis Metron
Save yourself the headache and call William Baldwin at Baldwin carbs and let him build you a custom carb. The cost is more but in the end you end saving time and money. A lot of time and money.
There is also Mark Whitener at Lightning carbs. He is building the best annular boosters for 4150’s (and Dominators) you can get. His carbs also work very very well.
And Dominic at Thumper Carbs. He is also a custom carb builder that builds them one at a time. He does great work. A buddy just bought a very nice 1150 Dominator from him. That engine should be going across the dyno here soon.
Any one of those three guys will hook you up. IMO its better to spend more money up front and get a quality product than it is to save some money up from and pay through the nose at the back end.
Rat Bastid
Dunamis Metron
Once again, you are talking bullshit. There are annular boosters out there that do NOT restrict flow and make more power. Just because you don’t know it doesn’t mean it’s not there.
And EXACTLY how many CFM does an annular booster drop flow? Maybe 5 CFM? so thats 20 CFM per carb. Maybe. Yet there is 100 CFM difference between a 650 and a 750 so you still have (potentially) 80 CFM more.
Your “use a small carb” (or port, or header or whatever your slant is at the moment) to “vaporize” the fuel better is a CRUTCH. And it’s the WRONG answer for performance.
MopaR&D
Nerd Member
Annular and triple-stack boosters increase signal because they are more sensitive to the pressure differential and air velocity through the venturi.
The "vacuum" used to draw fuel through the boosters is created by the venturis themselves. The simple fact that there is air flowing through them does it; it has no relation whatsoever with the amount of vacuum in the intake manifold below the throttle butterflies. If it was dependent on manifold vacuum then there would be no purpose in having a venturi in a carburetor in the first place; even if you put a lawnmower carburetor on a big block so it has 10 in-Hg vacuum at WOT it won't function without a venturi.
@318willrun stuck dual 600 cfm carbs on a mild 318. There's probably hardly any manifold vacuum to speak of at WOT yet it has excellent response and power if you go watch his videos. I'm over arguing about this, believe what you want.
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Here you go Hysteric proof a Dominator can be too big
Why can it be too big?
Deep Roots explains it well:
Annular booster carburetor flow test
By being more of a restriction the Same volume of air has to move faster around and through it. The engine pulls more fuel.
Main air bleed, jetting, and pvcr’s need to be changed to accommodate that.
Evaluate the well designed Autolite carburetors that came with annular boosters. Pump shot is small, idle circuit pretty much just addresses idle, transition is almost non-existent as the booster starts early and does almost all of the metering. The rest is addressed with bleed air.
most people over carb their cars engine can only use so much , after that it is all show
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What creates the airflow through them?
Why did it take a carb about 4 times the calculated optimal size too not function properly?
And carb twice the size of calculated optimal size made best power through out the rpm range on a turd of an engine? How does this go along with your arguments? Don't worry I don't expect you to come up with a valid explanation just more strawman argument.
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So the engine didn't make the most power everywhere with the Dominator? Why not........But you gave it more air didn't you?
Um......its 292 cubes is it not? You think a 650 is too big for a nearly 300 cube engine?
Didn't Mopar put Thermoquad's on 318's?
Ford put thermoquads on 302's locally........How much do the smaller thermoquads flow? 750 to 800 cfm?
Like I said earlier in post 88
A milder engine can tolerate a bigger carb.........Why is that?
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Like I said strawman, who's arguing that there's not a limit to workable carb size and that there's an optimal carb size or more correctly carb.
For an small ish engine that hp peaks at 3800 rpm the carb formula would say 300 cfm at best.
I'm not saying it's too big, on the dyno it's obviously not. Your pushing that a 750 is too much for a mild 360 and a 650 is way better, so in your mind how is a 650 not to big for a big 6 that makes 40% the power. A 450 ish hp @ 5500 rpm 451 calculates to about 650 cfm carb.
So make up your mind what side of the fence your on lol
How can a 750 be too big for a mild 360 but 750-800 fine for a stock 302-318?
or how a 650 is good for a 150 hp 292 and a 350 hp 360 at the same time?
rpm x cid /3450 = max cfm, A cheater way 345 ish displacement is to drop a zero off rpm, 360 is close enough 360 x 5500/3456 = 573 cfm or 5500 drop a zero = 550 cfm and that's 100% VE which were not at.
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Am I? Here's my original post:
Reductionism at its finest.
How about you use yours? Maybe just maybe that 360 doesn't use more air than that 650 already provides.
Can you grasp the difference between a spread bore design and a square bore design? Both can be rated at 800 cfm but have totally different metering characteristics.
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