Hi,
Most likely an easy question for most, but I have to ask.
My 77 has an L-48 with the Rochester 4bb carb. When I got it it had an aftermarket air filter and assembly on it. (like 9" diameter). I have gone to see if I can get a new housing for it and am coming up short. However, I have been able to find larger units.
Does size matter?
As long as it fits to the carb does is make any difference?
Thanks for any advise.

Kenny

 

According to flow research by K&N, the 14 X 3 configuration provides the most optimal flow. Contrary to what one might think, other configurations, such as the smaller diameter cleaner you mention, interfere with the optimal flow. This is no secret to GM as the Corvette used this setup for years. Now the L88 hoods and the 73-up rear hood induction systems also use this same dimension, but use the high pressure area at the hood/windshield intersection to ram air into the carb. These have been proven to be more effective than forward facing scoops. The other factor is keeping the incoming air cool. The cooler that the incoming air can be kept, the better because cooler air is more dense and has a higher concentration of O2 per sq inch. This is where the ducting systems come into play on the mid and later 70's cars. These cleaners use the 14x3 configuration, but duct the air from the outside, whereas the open cleaners allow the air to be heated because it flows up over the hot motor before entering the engine. NCRS did a large article on the L88 type inductions systems. I was convinced that this would be the optimal way in terms of volume and temperature to get air into a carbureted car.

 

Cold air is good air. The stock set up looks like this...........

 

I wouldn't loose any sleep over element size as long as it's of high quality and clean.
I run two little 6x2 inch washable cotton gauze type filters on a 6-71 blower that moves a lot of air with no problem....

 

Yes esp. w/ typical paper filters. You might get by w/ 14 x 2 on yours. It's possible to get 14 x 2.5 which would be better if it fits w/ your Q-J. You are fine w/ less than 3" which fits w/ a Holley & drop base filter.

 

It matters the size but ALSO the filter design for best flow...

I wonder why only very few (or am i alone here?) use a stack cone design filter, like the one below?



This kind of cone designs have been always used on carbed (and multi throttle bodies efi) race cars and bikes...

 

That's more a screen than a filter....

 

Panic, according to Vizard, those old school velocity stacks don't increase airflow. Better to use a breather and/or device such as a K&N Stub Stack designed to reduce or eliminate turbulence and straighten air flow as it approaches the carb. Can be worth significant HP. The limited area of your "filter" could be a restriction, unless it has a very high flow efficiency. Also, you're missing out on the very real benefits of an isolated cold air induction, which can deliver a higher pressure supply of much cooler air than found under the hood. In addition to the denser charge, you could probably run more ignition advance...

Get a copy of David Vizard's "How to Build Horesepower, Vol. 2 - Carburetors & Intake Manifolds". Great technical read that's full of useful tips and info.

 

Well, this velocity stack might not be as specialistic as a forced induction cold air set up but for sure works better then this one...



I have tried both, and the second one also with different sizes and with and without the upper filtered screen.
the stack gives you a faster respond to throttle and, following my engine builder opinion, gives also a few extra ponies IF you keep it's top fed with cold air during the driving, which is what i actually did, modifying my hood to keep a stream of air just on its screen.

Another advantage: you can reach much easier all the carb screws AND can see it at its best, no big filter in the way (check both pics).

Ohh, and dont forget the fantastic sucking noice at wot...a bit like the carbed 2 strokes racing bikes of once upon a time

 

Thanks a bunch.
Great advice.

Kenny Z.