snike3

I recently got my new engine into my 75, and now I'm trying to figure out the best way to setup my air filter. The original air box and filter will not fit on my new carb, so that's out. The new carb is a Quick Fuel HR-680-VS (Holley square bore style) if you're wondering. I have a stock 75 hood which has the cowl induction and I really don't want to change to a high rise hood (hard enough to see as it is and I just don't like the look...).

Anyway, I have a Proform black Chevrolet logo cleaner. With it's 1.5" drop base and a 3" filter, it ends up being about 3" from flange to hood. This leaves the cleaner top pretty much touching the hood when latched. I measured from the top of the carb (not the flange, but the highest point) to the top of the filter, and the carb top is about 1/4" down. I'd really like to get this so it's not touching the hood, but I'm also interested in possibly doing an air box to get more cool air.

Here's my ideas, I need feedback on what's the best plan. Been going round and round about what to do and I just can't make up my mind.

1. Get a slightly lower air filter and use a different air cleaner top to
get more space.
Filter
Top
or just
Complete Unit

2. Get a new cowl induction air box and use the hood's induction system. Looking at the duct, it doesn't seem like enough air would get in to me, but several forum posts seem to indicate otherwise.
Cowl Air Box

3. Have my hood modified to look like Ecklers twin turbo hood (I would hire a fiberglass guy to do that) and use a universal air box.
Cold Air Box
Hood Modifications

4. Use the cowl induction from number 2 and then get the front ducts from a later model C3. Modify the air box to have two intake ports for the added ducts. (For me this seems like the most difficult).
76-81 Air Cleaner Ducts

5. Use the cowl induction from number 2 and then do custom duct work and hood modification like in number 3. This may be a bit excessive...

I'm open to other suggestions, I saw one person that modified their radiator support to get more clearance for a duct. I'd rather not do that unless it's a very small modification.

I'd like to keep the cost down, but I'd rather do it right the first time.

KenSny

Easy solution: use a 2" filter.
Since you are not taking advantage of the cowl induction it doesn't really matter. With an open element filter of any size you are getting feeding hot engine air to the carb.

rkingce

yep..... Use two inch filter and filter top... KN

snike3

No thoughts on using the built-in cowl induction? I've done a lot of reading on the forums about using it and it seems like most people think it's beneficial...

KenSny

Yes, I prefer the cowl induction setup. But the carb must be sealed to the hood, not open to the hot engine air. If you use the stock cowl induction air cleaner with dual snorkels getting air near the fan, it is a very effective system. Getting air to the snorkels from the front-top of the radiator as GM did in later years is even better.

But the original OP did not seem to target his questions in that direction.... and he's using a Holley so he would need to modify the stock air cleaner.

MelWff

be carefull with the 2" filter idea. The Holley requires a minimum clearance of about 1" above the bowl vents and you might not have it with the lower filter.

snike3

In the original post I listed the ideas that I came up with, and most of the options (2, 4, and 5) use the cowl induction but with an aftermarket air box. The links I provided take you to the parts I was looking at. I then said other suggestions are welcome... Seems pretty clear to me that the original post was asking for the best option and not the easiest (see the last line of the post).

The original air box and cleaner do not show up in my original list of ideas simply because it won't fit. After I saw a forum member's post of their '75 that used the cowl induction and the front snorkels off a '78 I checked it out. That's why option number 4 takes the front snorkels into account.

snike3

You are correct! I measured from the flange on my carb to its highest point. It needs a minimum clearance of 2" (that's at the tip of the bowl vents), so a 2" filter will not work for me. In order to use a 2" filter I would need to use a raised or flat base. Because of this, it's just as good to run a 3" with a drop base.

Mike Ward

If you're referring to the stock '73-'75 cowl induction system- I did some experiments several years ago that pretty much proved that it doesn't work worth a d*mn. Why GM didn't incorporate a feature to close off the two snorkels when the hood flapper opens is a mystery as it kills any possible temperature drop or pressure rise at the inlet.

MelWff

You are really not interested in just putting an L-88 style hood? Think it would be cheaper than having someone customize your existing hood.

scottyp99

I think this is how it works: If you understand how a carb works, you'll know that the whole thing operates because of the pressure of the atmosphere on the fuel in the fuel bowls. The fuel is exposed to atmosphereic pressure through the bowl vents. If the top of the air cleaner is too close to the vent, the velocity of the air being drawn through the filter into the carb can produce a venturi effect, which lessens the pressure on the fuel in the fuel bowl, creating a lean condition in the engine. If you have a 1 1/2" dropped base air cleaner, the top of the air cleaner will be awful close to the top of the bowl vents with a 2" element. Put a wad of crumpled up aluminum foil on top of the highest vent, and install the air cleaner lid to see how much clearance you have now. Subtract an inch to see what you would be dealing with if you went to a 2" element. I've heard people say you can get away with 3/4", but I'd play it safe and try not to go less than 1".

Here is a link to a thread that you might find interesting:

http://forums.corvetteforum.com/c3-t...ir-intake.html


Keep the shiny side up!
Scott

redman76

I've looking to do the exact same thing as you. I bought the '75 air cleaner setup but since I have RPM intake, it sits too high.so I'm using as template to make my own. I was going to use my drop-base and fabricate my own air box that would seal to hood. I was going to use an open air cleaner lid like you showed or one like this. However, I have the same concerns as you whether I can get enough air through the cowl.

To address the air volume issue, I thought about using a couple of the driver's side style air ducts and use fiberglass to form an intake on each side above the radiator. Hope all that make sense . . .

snike3

The only reason I don't want to go to that is that I really just don't care for the look of the L-88 style hood on this body. However, it does seem like a big improvement on the cold air system... Now would be a good time to get it with Eckler's having a sale (http://www.ecklerscorvette.com/corve...1973-1976.html). One question looking at it, you have to get that fresh air chamber too or can you pull the original off?

snike3

Made sense to me... I thought about using one of those Airaid cleaners too. If you end up making them, I'd love to see the fiberglass intakes for above the radiator. Custom fiberglass looks pretty difficult to me, but then again I've never tried it.

pauldana

my fix...

snike3

pauldana, I think I've seen your pics on another thread before... What's the front duct? Did you fab all of that yourself? It looks like you took out some of the radiator support and took off the cowl induction stuff from the hood...

MelWff

The hood you chose in the link doesnt have the fresh air chamber it is optional.

pauldana

The front part of the unit is from a 96 C4, the back part i made a from a mold, which I fabbed it myself. all radiator brackets are there and stock. i had no cowl induction on a 79

Carlos840

Are you still planning on building a few and selling them?
I would buy one of those...

pauldana

i am shipping one out to a Forum member next week.... going to wait to see what he thinks and get some input....

kind of worried about complaints .... dont need the headaches..