Thread: Restricting Airflow a Positive Thing?

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Originally posted by 1stGenCamaro
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 e 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.

and he still wont be able to drive it to the store for a 6 pack.

As a minor detour on the basic thread....

To quote Richard:

If you use a manifold that has too much volume, then the motor cannot pull a negative pressure in the short amount of time that the intake valve is open at low rpm's. A high volume intake will work at higher rpm's, a low volume intake will work at low rpm's

Could a manifold like the tunnel ram be equipped with a "bladder", a flexible internal mebrane which would contrict with vacuum?

It would have to follow the internal profile of the aluminum casting like a skin. The gap between the aluminum walls and the bladder would be vented to normal atmospheric pressure. At idle and low load conditions the bladder would reduce the internal volume (both plenum and runners) increasing air velocity, as the throttle opens and vacuum drops the bladder would relax to the internal walls allowing full flow. Best of both worlds it seems.

The basic thought is a passive design, but the venting action could be managed by a CPU as well.

Then again, I was drinking last nights......

Regards, Mark

You guys are all great, and I apologise lt1s10 for jumping on you earlier in the thread. I have learned a lot. (don't worry I'll still get my hands on some good induction books, any suggestions?) This thread is going to be saved on my PC so I can reference to it. so wow theres way more to carbs than I thought.... to make things simpler I'll keep an eye out for the 390cfm'ers unless someone makes a smaller 4bbl.



Thanks again everyone....


Mike...

Originally posted by Gyva
You guys are all great, and I apologise lt1s10 for jumping on you earlier in the thread. I have learned a lot. (don't worry I'll still get my hands on some good induction books, any suggestions?) This thread is going to be saved on my PC so I can reference to it. so wow theres way more to carbs than I thought.... to make things simpler I'll keep an eye out for the 390cfm'ers unless someone makes a smaller 4bbl.



Thanks again everyone....


Mike...

no problem gyva, maybe will meet under dif. circumstance next time. there's not a lot of tunnels rams on the st. and there is a lot of reasons why not. i had a friend that run one for awhile until it got cold and the gas would ice up in the tunnel ram going down the road, so he had to take it off for that reason. to me its not a good profiling motor. i agree they look awesome though. later.

damn streets u act like predators are a grand or something .............scooter

It's usually to much somethin, like to much cam, to big of headers to much carb, to much gear, to tall of tire, etc. Get out a couple of manuals or Chevy build'em books and research what is usually required to run 900cfm on a small block.
You will find that there is no such thing as 'stock'.
Go with 1 5/8" primary headers, use what Comp cams tells you to use, Ray Gun Blaster ignition stuff, Free flowing heads (don't use CAL smog models), you can see a trend starting to form here.
All the goodies gotta be balanced and/or compatible with each other and with their intended use.
Good luck

well the 69 z/28's had the cross ram with twin 780's equaling 1560 total cfm on a stock motor but then again it also had higher compression a good cam. <take hint here> get it bored.30 or .60 with some domes a good cam you'll be fine and as for that stuff about not being able to drive a tunnel ram on the street it depends on your motor i know a guy who has made his work great and he drives it every day int he summer but its not stock either hehehe. i mean i could run a tunnel ram on my motor because itd use the fuel but a stock motor wont.....just my 2 cent worth of rambling.. ...scooter

I run a crossram system on my vette with four side draft weber carbs , BUT it is an IR system . Some will look at a system like that and think that it is over carbed. The truth be known it is actually a bit on the smallish side . The ir system allows the tuner to [ too much time on his hands] actually tune each individual cylinders fuel aircharge. The result is an engine that is very responsive at any point in the rpm range .

The weber carb CFM range is easily changed and therefore can be made to provide the necessary fuel air charge velocity to give the engine a good ventuuri vacuum signal . Simply put , the gas and air will mix really good together when they should .

So as soo many others have pointed out to you ,,,engine system component selection is critical . There is a tendency when starting out in this hobby to go BIG [ don't ask me how I know ] and it is usually the wrong path to take . Good luck in your journey !

Geo