intake question

If you have never been so poor as to have had to install a complete early 318 top-end and cam onto/into a hi-compression 340, then you have missed a very interesting tire-frying combination.
IMO, with 3.55 gears,27" tires,and a 2800TC; the intake port size for a streeter,is a non issue in first gear , and won't be until about after 60mph in second.

With a high-compression 360, you could run a big 2bbl, and a cam at least one size smaller; and on street tires, ET zero to 60 very close to your current combo..... just with a lil less tire-spinning drama, in second gear.
When I swapped out the DC 292 for a Hughes 270, I was a happy happy guy. The 270 traded away ~600 rpm at the top ,which with 3.55s this being after 65mph, was not helping me at all; whereas the newfound torque at sub 2000 (manual trans) was extremely beneficial.

Same goes for the XE 274; it's a great cam! but the power peak in 1.45 second gear with 3.55s, comes at ~5100= 75 mph. At 60 the rpm is ~4000, and most of the power of that cam is on the speeding side of 60mph.
Whereas, the next smaller cam will peak at about 300 rpm sooner.
Ok yeah; the absolute power will be less, but the average second gear power, below 60 mph, could be greater.
It's all about gearing for the application. For the 274 to be effective, you would want the power peak to be at about 300rpm SOONER than the ending speed. So if you are looking at a zero to 60 contest, you would want to gear the car to cross the line at ~5400, and that would require 4.56s for 60=5180, or 4.88s for 60=5540. Like a streeter would ever run 4.56s; YR excluded,lol!
But another ugly thing rears it's head with those deep gears; called tirespin. On the street, with street tires, traction in first gear is nowhere to be found; you will need to spend a buncha buncha money to try and make it hook. So first gear (with 4.56s or more) is a throw away gear, used just to get into second.
But if that's true, then, couldn't you just regear to get the equivalent gearing in first? Why yes you could, But now you are underpowered in first..... so you either need more stall, or a new cam with a lower operating speed, or a bigger engine.
With 4.56s and a 1.45 second gear, your gearing at 60 was 6.61.. You can get that in 2.45 first with 2.69s rounds to 2.76s, and 60=5300 badaboom! But just try taking off with 2.76s and an XE274 cam, in an 8/1 360 .... The 2800TC will help, but you really need more like a 3500, cuz at 2800 the lo-compression 360 is, well, sluggish I think would be fair to say.
To use the 2800TC with 2.76s would take a completely different cam, and more cylinder pressure would be a huge improvement.
Both the 2800 and the 3.55s are a testimony to the lo-compression 360's soft bottom-end with the XE 274 cam.
I have done all these tests over the last 20 years so I'm not just talking math, The math supports the real-world experience.
This is one of the reasons I run the 3.55s, the Commando 4-speed and the GVod/splitter... together with the Hughes 230/237/110 cam at 11:1Scr. It's the mother of all my combos.
Of course not everyone cares about the zero to 60mph speed contest.

Now here comes the point;
>Your combo is NOT set up for zero to sixty anyway; (but rather for 75 mph),
>so I would just slam any old low-rpm dualplain intake on it, with a small 4bbl, and go have fun.
> and now you know the why of it.
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To know where your power peak is; you just need about 5 things;
1) a helper, with
2) a digital stop watch, with at least .01 accuracy; as in 3.06 seconds,as opposed to just 3.
3) a smooth working speedometer, or tach; accuracy not critical
4) a rear seat, and
5) a pencil,paper, graph-paper, and a clipboard
I said about 5,lol.
Install your helper in the back seat with the tools, and head to a deserted road. You will be running thru the power peak in 5mph blocks if using the speed-0 , and your helper will be timing the blocks.
You will need to be in a high enough gear to not have tirespin when you floor it.
If the speeds get excessive, defeat the secondaries.
If the time periods get to be too short to accurately measure, you will need a higher gear or less power, install a throttle stop. The object of this exercise has nothing to do with power, only accuracy.
So in your case I have arbitrarily assigned a powerpeak of 5100 to your combo. I could be wrong and you can prove it.
So, 5100 in first gear is 45 mph, and with a 4bbl you will be whacking thru there way too fast. In second 5100 is 76 mph, and yur gonna run outta road in a hurry, that's if you don't get a speeding ticket..... I ain't paying it.
So whadda you do. I suggest you use first gear but defeat the secondaries and install a throttle stop to limit your primary throttle opening to a repeatable setting, that makes the rate-of-acceleration repeatable, and slow enough to be able to accurately time, and and still allows the rpms to climb to 5800. I use a length of coathanger wire looped over the KD pin and and anchored at the other end in a way that it cannot interfere with the normal operation of the throttle arm and return spring. I install a small wireclamp on it in some way to make the stop adjustable.

Ok the first test is to go out and see if the engine will hit 5800 plus or minus about 100; adjust your throttle-stop until it does and is repeatable.
Now the test can begin.
If you have a tach, you can use it instead of the speedo; it's just as accurate and is probably easier for your helper to read.Choose your first window;I suggest increments of 300rpm until you get the hang of it.
I suggest the first window to be 4600 to 4900. You will begin the test about 200 rpm sooner and end about 100rpm later, but your helper is only gonna record the time from 4600 to 4900.
Next convert this number to seconds per 100 rpm, if it took 4 seconds, then 300/3/4=.750 . if it took 3 seconds then 300/3/3= 1.00, and so on. Write the converted rate of acceleration number down together with the window.
The next window will be from 4700 to 5000, and the next from 4800 to 5100, and so on to end at ~5500.
Your job is to friggen drive the car and not hit anything on the deserted road you chose..
Let your helper run the show, telling you when to hit the gas and when to lift off.
Take your time, this is not a speed contest.

Now, get a piece of graph paper plotting rpm on the horizontal, and rate of acceleration on the vertical. Put your data on the graph,at the center point of the test window and connect the dots. You should get a curve, rising to a peak and then falling; with the fastest rate of acceleration coinciding with the power peak. If you don't have a falling side, repeat the last test adding 100 rpm, same as before.
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You can use this curve to determine your shift points, but with an automatic, you will need an rpm range of at least 2600, ending at ~5800 . Your 727/904 has a .59 split (or 59%) between 2.45 first and 1.45 second. That means if you outshift at 5800 the Rs will drop to .59x5800=3400 so your range is 2600rpm.
But if you outshift at 5200, then the rpm drops to .59x5200=3100, a range of 2100.
That rpm range is called your first gear powerband requirement. Second gear is 69%
So, you will need to start your rate of acceleration at say 3100 less 200, and finish at 5100 plus I think ~700.
To make this test easier and faster, you can stagger the windows to every 500 rpm instead of every 100, because supreme accuracy is not required here, because we are just establishing a baseline. So start at 2500 then 3000, then 3500 and so on to 5500, and again plot the rates in the midpoint of the tests
So as before plot your data and connect the dots. You will get a longer higher line.
To determine your shift points; connect two points on the curve, between about 3400 and 5800, that have very similar rates. This line has to be a 59percenter, meaning that if you choose one point at 5800rpm, the other has to be 59% of that 5800 or 3422, rounds to 3400. If you choose 5400, then the other end has to be at .59x5400=3200.. You may have to go back, and get a finer resolution at the end points.
Whatever line you choose, the big money is on the line being parallel to the base or sloping towards the lower rpm start-point, NOT the other way, altho that way is more fun,lol. It's kindof neat when you outshift second and third gear makes the car jump ahead,lol.

Ok so waaaaay off topic I know, but, that's the AJ-way