Thread: Restricting Airflow a Positive Thing?

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Ok here goes my question,

most people want more airflow to their engines, what if you had too much cfm's for your carburated engine. Could you restrict air flow by simply putting on one of those thin tiny air cleaners then re adjust air fuel mixture?




situation: dual quad induction on SBC 350/w two 450 cfm carbs.

What are the pros and cons of using these tiny airchoking filters in this situation? could it benifit this one? thanks



Mike...

Is that not a valid question? untill I get books can I not ask? I though this place was for questions?


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Mike....

If your getting to lean of a mixture because of to much air then, you could run a restrictor plate like the 1's that are used in Nascar, you could also rejet your carb and get the same effect, which, I would do. If your carb is too big ( CFM wise ) then, you could tweak the carb jets a little to get by, otherwise, a smaller carb is needed. The situation with your dual quad 450 CFM carbs, get 2 390 holley's and sell the 450's, if that's what's your asking. I'v never heard of too much airflow unless, what you mean, is too big a carb.

Matt167 is correct,,,,,you need to either rejet your carbs,,,or change your carbs to the correct CFM rating for your motor.

Originally posted by Matt167
If your getting to lean of a mixture because of to much air then, you could run a restrictor plate like the 1's that are used in Nascar, you could also rejet your carb and get the same effect, which, I would do. If your carb is too big ( CFM wise ) then, you could tweak the carb jets a little to get by, otherwise, a smaller carb is needed. The situation with your dual quad 450 CFM carbs, get 2 390 holley's and sell the 450's, if that's what's your asking. I'v never heard of too much airflow unless, what you mean, is too big a carb.

hi gyra im just guessing but with 40 inch tall tires and 950 cfm carbs u have a couple things out of wack with each other. it is common for folks to have tooo much carb, that is too much fuel. i will venture to say that 1 of those 450 carbs would be nearly enough for your ride,considering that the rear gear ratio is probably sky hi. u could try a set of shorter tires if u doubt what im saying here. hope i didnt make u mad caose i could be wrong but i have seen this same type of engine-eering before. anyhow let us know if this helps any. Ives

Very interesting post ,,,,,,,,,, gotta see where this goes from here . Can't help my self I'm carb crazy !!!!!!!!!!!!!


Geo

Originally posted by Gyva
Is that not a valid question? untill I get books can I not ask? I though this place was for questions?


Quoted from above:

"Photo galleries, forums, links, classifieds, and a whole lot more! Take a moment to register and join in on the conversations, share your insights, ****or just ask a whole bunch of questions.**** Enjoy!"


Mike....

the problem gyva is, youve asked this ? before and was told it wont work. anyway you cut it you cant run a 900 cfm carbs on a stock motor. you cant rejet it down enough because the fuel and air mix has to be with in a certen ratio or it not gonna run like it should. what denny was saying i think is you need to read up on carb. a little because if you understood carb. a little better you would know you cant do this and it would take a long time to explane it to you here on the forum.. you really wont somebody to tell you ok , go ahead and do it, but its not gonna work.

lol this isn't going in my Jimmy lol with the 40 inch tall tires. That motor is just fine the way it is, built it 2 years ago and running strong through the pits with 4.56 gears.



And I said I'm starting with a stock motor I will alter what ever I need to make it work, and I still get people telling me it wont work ok I get it a stocker won't cut it... so I'll add all the other componets to make it work. So lt1s10 I guess the problem is your not reading the thread. I know the stock 350 wont work.

Originally posted by Gyva
Ok here goes my question,

most people want more airflow to their engines, what if you had too much cfm's for your carburated engine. Could you restrict air flow by simply putting on one of those thin tiny air cleaners then re adjust air fuel mixture?




situation: dual quad induction on SBC 350/w two 450 cfm carbs.

What are the pros and cons of using these tiny airchoking filters in this situation? could it benifit this one? thanks



Mike...

When you say "tiny airchoking fliters" are you refering to the diameter or just the height of the filter? If it's the diameter, I'm gonna thump you with a large crescent wrench..... Diameter has NOTHING to do with the airflow, however the height (or thinckness) does. Too thin of a filter can limit airflow but will only cause the carb to run even RICHER. If it's that restrictive, then you may have problems getting it to lean out again. Definately NOT a solution for your problem.

Like the others are saying, maybe you should get a few of those Performance Books they sell at local speed shops and read a few on engine building and induction systems to better understand what you're about to get into.

You can get the "audio" version now......

Originally posted by Gyva
lol this isn't going in my Jimmy lol with the 40 inch tall tires. That motor is just fine the way it is, built it 2 years ago and running strong through the pits with 4.56 gears.



And I said I'm starting with a stock motor I will alter what ever I need to make it work, and I still get people telling me it wont work ok I get it a stocker won't cut it... so I'll add all the other componets to make it work. So lt1s10 I guess the problem is your not reading the thread. I know the stock 350 wont work.

then what are we talking about if you gonna add to the motor why are we still trying to lean out the carbs? i think you need to read your thread . i cant read your mind.

Ok,,,the very least you can do if you are bound and determined to use those carbs, on that manifold, on that motor,,,is Cam it...and...
Go to a Multiple spark discharge set up. "MSD" ignition.
Get some Header,s,,,,and go have some fun.
But like i said,,,,,Cam....Cam.....Cam....performance cam.

Nice job tech. But i think I'll try and dumb it down a little. Just in case. Your motor can only handle so much air/fuel at one time. As such, you can only put so many cfm on a standard motor and expect optimal results. With your motor, you are trying to force more air down inside the cylinders than the vacum off from the motor can compensate for. If you run a simple yet effective cold air intake, match it up with a good 600-ish cfm carb, you should find yourself in good shape.

Gyva there are lots of helpful folks giving you some very good advice . Listen closely to what they are offering ,,,,,, there not much fun driving a rod that drops dead when you step on the go pedal .

Geo

Another thing for ya Gyva. If you restrict the airflow by using smaller filters then you are only sidestepping the actual problem. The carbs do not work as well with VOLUME, as they do with VELOCITY. If you use small filters to cut down on the air going in you can really restrict the velocity (especially with a big volume tunnel ram that won't see much velocity in the first place) which will make the motor run crappy even if it did have a lot of better components and ran higher rpm. The carbs would be hell to tune in that situation as well. If you had a cam that ran from 3500-7000 rpm with those big carbs and tunnel ram, and other components that can stand those consistent rpms obviously then I imagine they could work...but in that case you wouldn't be using the smaller filters anyhow. Think of an engine as an air pump with a certain volume of air capacity. Due to intake and exhaust design, pumping losses and friction and whatnot this air pump usually never ever sees 100 percent volumetric efficiency unless it has a blower or turbo. SO, even if you ran 8000 rpm with a 360 *way overbored 350* and 90 percent efficiency, which is really really good for a naturally aspirated motor, you would only be able to pump 750 cfm through that motor anyway. You would have to run 9600 rpm with a 360 at 90 percent efficiency to get 900 cfm flowing. My suggestion, stroke the damn thing and make a 383, keep the intake, get some 1 5/8 or 1 3/4 headers, big cam, some lightweight but strong (bigger skirt too) pistons (if thats possible) or normal weight and buy some forged rods. Depending on the rpm and power a cast crank may be fine, but if you got money then go out and get a forged (why not, right??). Stud the mains and heads, get some aftermarket heads like Dart, AFR, Victor Jr, or your personal preference. Make sure you have some good ignition for those high rpm blasts. I am pretty sure you know most of this but I figured I would let my opinion out.