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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.

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.

My point is why guess which to go when you can measure what you got and make a more informed decision. 1.7 is fairly restrictive so can be 1.2 depending on application. Pumping loss can kills hp, mpg etc.. also.

Is there any proof that a 500 automatically gives better fuel mileage ?

Measure manifold vacuum on a full throttle run and see how restrictive the 600 is 1st. Go from there.

An engine at idle only makes enough hp to run, so it's not moving much air, it's gonna have really poor velocities/etc.. even in stock form nevermind built, probably making less than 1% of it's peak hp potential.

What you say comes across that smaller carb, head etc.. always equals better. I'm Not saying opposite is always true either. Generally the engines putting out higher lbs-ft per cid run big cams, carbs, heads etc.. very built race car engines. Not stock very restrictive engines even at very low...

No the over emphasis on that one aspect, a lot of time it's easier to make more HP/E.T. by displacing a lot more fuel and air over time at a lesser efficiency than try to squeeze every last hp out of lesser amount of fuel and air. Especially since there narrow window of efficiently available to...

For that particular car, if that was the norm most drag cars would be running smaller carb sizes.

You really like this article, you found one instance that backs your theory up, how many go the other way, unfortunately the only real way to know test a few different carbs, I'm sure once the OP gets his carb setup he'll be satisfied.

Even before I'd think of changing to a different cfm I'd put a vacuum gauge on it and see what it pulls, why guess when you can measure, I'd just rebuild what you got.

A couple of 700-750hp engine masters competition engines. They seem to respond to tall carb position for whatever reason.

Wouldn't a tunnel ram be the ultimate extension of this idea.

If you look at the best Engine Master Competition engines which are looking for best average power the major run very tall plenums and large carbs sounds like it's got merit to me.

I bet a lot of this carb nonsense has come from bolting on like a 750 or 750 dp with zero or near zero tune carb and ignition and wonder why it don't work.

I'd say right size is where there's no more appreciable gain in power by going larger minus where you can tune it with acceptable idle driveability etc.. For the application eg.. race only, street strip, street etc.. Probably only one way to find out experiment.

So wouldn't the question be what's the ideal vacuum compromise for different applications eg.. Race only, street strip, street machine, daily driver etc.. Seems like almost no one run's 1.5" hg.

Continued.. Go larger is gonna stop given hp gains at some point say on the 400 hp engine eg. Above 850 stop showing real gains so 950 made 400 hp and 850 did the same a 750 was down 5 hp, 650 down 15 hp, 550 down 25 hp etc... Choose your compromise :) Plus people just know what works there's...

Say your building a 400 hp engine and say 400 hp is a about 550 cfm, i'm not talking carb size but the actual amount of air pumped through the engine each minute "550 cubic feet". Now no matter what carb you put on a 350 450 550 750 1050 etc.. About 550 cfm with be displaced each minute making...

I doubt the M1 will give you any usable gain over the Air Gap especially in the streets and after if it seems you need less bottom and more top you could always try the M1 , if I was to only try one it would be the air gap even for the track.

If I was to guess the air gap will be better in the streets and even maybe at the track, single plane might help it hook up easier in the street with the loss of down low torque. I'd try the M1 1st then air gap since you'll probably like the air gap better in the street.

You have both why wouldn't you try both and see which one you like.

I used a lot of magazine builds that had dyno especially ones with head flow info or heads you could find the info for and put the specs into the program to see how it compared to real world to get a feel for it. Even though lots believe magazines lie but funny when the same builder on this site...

This is the one I got, good for heads and cam, intakes and other parts are general. DeskTop Dyno5 Main Page Don't get caught up in the hp torque number but the trends and curves.

Also buy one of those desktop dyno programs and play with different head cam and cid combos and see the trends with those.

Best thing is to look at tons of builds with dyno result no matter the engine brand and look for the trends. When thinking about my 273 I looked at a lot of Ls4.8l and 2v ford 4.6l and even 302/305 since there's little info on 273's. You'll see similar head flow cams cr cid will have similar...

You Never know what your given up, Nascar F1 etc.. engines are so expensive cause all of the dyno time trying different things, Say your building a hot street strip car even after all your efforts you might have to try 2-3 different cams carbs rear gears stall converter tires etc.. until you...

I went down the same rabbit hole when I was designing a project that never happened 400-425 hp 273 for Time Attack 65 Cuda, Nothing wrong trying to figure all this **** out but for the most part these are all ballpark formulas and make builds way more complicated and expensive if you let it...

My Guess is when it comes to race engines, they are more single purpose something like nascar everything is taken to it max ability. For a hot street street strip or mild performer there's a lot of ways to accomplish your goals, look at modern hemi or LS engine they use heads that flow enough to...

I plan on a return line.