Ok not everyone is wrong but I just read yet another post about airflow with what I believe is misinformation. Most of what I am going to say Jester has said before and I apologize for repeating it but too many people must have missed it.

First thing people do wrong is use that cfm formula and come up with 550cfm as enough to feed a 502blown big block at 9000RPMS's. Ok its not that bad but you get the idea.
That formula only give you the AVERAGE airflow to fed the engine.
Your engine does not suck air at a constant rate. It pulses maybe requiring 800cfm for a microsecond and then 400cfm for another micro second. This averages out to 600cfm but a 600cfm carb will choke the engine most likely. People that get by on smaller carbs/tbi's usually have a LARGE volume intake below it. Now instead of requiring 800 cfm of air from the carb/tbi, it can get 600 from the carb/tbi and 200cfm from the extra intake volume. So this is kind of a band-aid not a fix.

Second thing is your engine doesn't flow air perfectly to every cylinder, even in the intake. I'm not 100% sure about this but I believe the older mustang? had a firing order of something that would be eqivilent to our cylinder #1 and then #8 firing right after it. It sucked its air to the #1 cylinder and then the air flow had to almost be reversed to go to the number #8 cylinder. It was not efficient for it to do this. In fact i believe a kit was made to change the firing order so cylinders closer together fired together. So there or other things that impede airflow you may not even know about.

Lastly TBI vs Carb CFM. This is where so many people post bad info and say a 670tbi can support these huge engines.
A 670cfm carb will flow much more then a 670 tbi.
A 4bbl carb flows 670cfm at half(1.5in) the vacum of the 670tbi.(3in) Picture this. You have a glass of water and you have to drink it through a straw. First you are given a big straw and lighty suck as you would any softdrink. You can drink it in a couple minutes with ease. Now pretend you are given the same drink and told to drink it through one of those red straw things people stir coffee with. You must drink it in two munutes also. Well you can suck till your red in the face and your mouth hurt and probably drink it, in the same time. However the second straw is way less inefficient. The second straw is TBI. You can make the 670tbi flow 1000cfm if you put a big enough pressure drop under it. Now put that same pressure drop under the 670 carb and it will flow 1500cfm. Again think how fast you could empty the soft drink with the big straw sucking as hard as you could.
Having one myself I am convinced a 3600# camaro with a built 350 (vortec heads, lt4 hot cam, etc) and a 670tbi is hitting a wall around the 13.5 mark N/A.
The way to get around this would be to make more torque off the line but your max HP is going to be limited. I want someone to prove me wrong and go in to the 12's, but I don't see it happening.

Ever notice how TBIs react with a 1.5 second reduction in e/t while tpi's usually only gain 1 second with the same shot. It's almost like someone found a way to get more air past that tbi and intake

OK, I'm done. Let the flames begin. It's midnight so I don't know how coherent I am.

 

The 'older' mustang you refer to (Fords in general, I cant remember the year but its pre-81 or pre-85, thinking 85) have the same firing order as a Chevy if you ignore the numbers and concentrate on the cylinders.

Did you mean to post that on this board? Maybe I missed something...

 

I posted here because I saw a post last night on this board where people where talking about some of the things I addresses in my post. I wanted them to see it. You can move it to TBI if you want.

 

I think nobody is quite sure WHAT pressure drop FI stuff is rated at. 2bbl carbs are rated at 3" but that doesn't necessarily mean a 2bbl TBI is rated the same way, unless I missed a memo somewhere.

IF IF IF..... 2bbl TBI units ARE rated at 3" pressure drop then a 670 CFM TBI would roughly equate to the flow potential of a 450 CFM 4bbl carb.

i.e. I tend to agree with you.

 

Search the archives. There have been numerous times I have suggested using an Offy or Edelbrock twin intake with two TBI220s. I haven't heard much about anyone trying this, and I may be the guinea pig on my S-truck. I agree that the intake restriction is probably due to the TB flow, and have offered a suggestion to fix that. The '83-'84 CFI system was close to this, but that system tried it with long tube runners. We have since learned (via the LT1) that our firing orders can survive and flourish with almost no runners, and do so very well. Hence, a twin intake with very short, de-tuned runners (like a Victor) and enough TBI units to flow may be an answer.

As for the firing order comparisons, I think Max is right. The older design Ford Clevelands and 460s had a less than optimal firing order, but if you ignore the differences in numbering, their order follows exactly the same pattern as the SBC, but in reverse:



Isn't it odd that the "new" LS1 is the same order as the older Cadillac engines? Study all the schemes, and you'll see a lot of similarities.

 

So everyone should run the biggest carb they can find. You didn't mention anything about going too big in the way of airflow. With a carb this is a problem if not enough velocity is going past the venturi's. All you seem to be looking at is air flow required at wide open throttle at the redline--sure a bigger carb/more airflow is a good thing. Alot of us don't get to launch off the line at the redline. Using the intake as a 'buffer' between the engine and carb isn't a band-aid if it works just as well. You really can't use a carb as an example when you compare it to FI. The carb needs a resonable amount of air velocity to work effectively. If you want to talk about TBI, stick to just TBI--you would be hard pressed to find a TBI that has too much airflow for most any engine.

 

Vader-my next thing will be to replace the 670 with a 900cfm tbi. Both reside on top of an edelbrock intake. I will try and run only 2 85pph injectors at first as two avoid any computer problems. We'll see what this does.

82camaro- I think you missed the point. Basically the 670tbi is not
as good as people think IMHO. Carb was just a comparison. Since FI doesn't require vacum (it does, but it's programed in to the chip) like a carb to determine fuel. You can get by one a bigger TBI as long as the chip is right.
With carb, talk to ODB(although he got banned). I am not trying to tell people they need a bigger carb. I am just saying don't compare tbi cfm to carb cfm as equal.
You can run a huge carb on a 305 but you won't have vacum and you will need to rejet to compensate. ODB made a post about this. You can search the archieves for this. BTW ODB's 383 camaro is killer so he either knows something or got lucky.

 

I got your point, just wanted to add that throwing in the carb comparison makes your argument less strong--since it is a completely different animal. With FI, if you can get it enough fuel, more cfm is usually better.