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I have an old EWdl drop base air cleaner.
My dyno guy says it is costing me 20 hp.
Is there something newer and better?
I saw something conical that looked interesting?
From: At my Bar drinking and wrenching in Lafayette Colorado
I have made multiple posts about this. Here are the facts:
A few years ago, I did a bit of dyno testing on air cleaners. What we found to have the greatest effect on engine power and performance is the distance from the top of the carb's airhorn to the bottom of the air cleaner lid. Once this distance gets tight, as it does when people use the drop-base air cleaners with a low-profile air filter to gain hood clearance, power is dramatically affected. I found that the minimum distance from the carb's air cleaner gasket on the airhorn to the bottom of the air cleaner lid, to avoid serious upper-rpm performance problems, is 3 inches. Most air cleaners have a 1" "dome", which means that the minimum distance from the air cleaner gasket on the carb to the top surface of the air filter is 2 inches. Anything less than that and you will have issues. So, for instance, you cannot run a 2" tall air cleaner on a drop base - it puts you way below the 2" minimum height required above the carb. Check your heights and clearances - this can affect you more than the style of air cleaner you're using... Run the tallest filter you can, and get the air cleaner lid as far above the airhorn as you can without hitting the hood.
If you violate the minimum height (3") noted above, you will have serious power problems. If hood clearance is tight, you will gain power going to a lower profile intake manifold. Your other option is using a taller hood.
Lars
Is it the drop base that's the problem or the height of the filter element? When I got mine it had probably a 1 1/2" 14" dia filter element with probably a 3/4" drop base - it's the one seen in my avatar. I went to a 1 3/4" drop base so I could use a taller filter - I have a 2 1/2" filter on now, at some point I'm going fabricate a fiberglass air cleaner cover that fits the contour of my high-rise hood that will let me use a 3" filter element. I can't use a bigger drop because of the throttle/TV cable bracket.
I don't have any comparative numbers to know what if any change between air cleaner setups, just going on the notion that a taller filter is better due to more surface area as per what I was advised in here.
Last edited by brassplyer; Feb 2, 2025 at 02:56 PM.
How much do you want to spend to get the extra 20 hp?
To start, the problem begins with whatever aftermarket intake manifold you have on the engine.
You’ll need to swap to a flat oem style intake if you want to run a spacer under the carb and no drop base air filter.
This could cause a big drop in performance.
If you want to run the current intake, a carb spacer and no drop base air filter, you’ll probably need an aftermarket tall L88 high rise hood.
Figure $1200.00 for the hood and shipping then depending on how critical you are on fit, finish and paint another $3000.00 to have it professionally done.
Trust me I know this for a fact!
I’m running a Edelbrock Air Gap intake, 1.5” drop base, 3” air filter element and a flat air cleaner lid, which just fits under a tall L88 style aftermarket hood
Just to get the hood to close, I had to remove the carb spacer and swap out the doomed air filter lid for one that is perfectly flat.
Thanks OCB!
Then I would have an extra hood that I didn't need.
My thoughts exactly.
We do have some fg people who could put an L88 scoop on my properly fitting hood.
Not that desperate for 20 hp.
I am considering CNC porting and headers if/when I refresh the eng?
I would like to get into the 12s and 160mph in a mile someday. Eek
From: At my Bar drinking and wrenching in Lafayette Colorado
I have made multiple posts about this. Here are the facts:
A few years ago, I did a bit of dyno testing on air cleaners. What we found to have the greatest effect on engine power and performance is the distance from the top of the carb's airhorn to the bottom of the air cleaner lid. Once this distance gets tight, as it does when people use the drop-base air cleaners with a low-profile air filter to gain hood clearance, power is dramatically affected. I found that the minimum distance from the carb's air cleaner gasket on the airhorn to the bottom of the air cleaner lid, to avoid serious upper-rpm performance problems, is 3 inches. Most air cleaners have a 1" "dome", which means that the minimum distance from the air cleaner gasket on the carb to the top surface of the air filter is 2 inches. Anything less than that and you will have issues. So, for instance, you cannot run a 2" tall air cleaner on a drop base - it puts you way below the 2" minimum height required above the carb. Check your heights and clearances - this can affect you more than the style of air cleaner you're using... Run the tallest filter you can, and get the air cleaner lid as far above the airhorn as you can without hitting the hood.
If you violate the minimum height (3") noted above, you will have serious power problems. If hood clearance is tight, you will gain power going to a lower profile intake manifold. Your other option is using a taller hood.
Lars
If you plan to refresh the engine in the future, build it for the space you currently have under the hood.
You could easily design and build an engine to put you in the bracket you want to run in using Lar’s formula while keeping it under the oem hood.
From: At my Bar drinking and wrenching in Lafayette Colorado
The Air Gap manifold is too tall for a standard small block hood in order to have adequate space above the carb's airhorn for proper airflow into the carb. Check it and measure it: I'll bet it does not meet the minimum height requirements outlined in my post above. Any advantages you think you are getting from the Airgap manifold are lost due to the airflow into the carb being killed from inadequate space between the carb airhorn and the top of the air cleaner.
Lars is absolutely correct. When my engine was built, there was a Dyno tested 15 horsepower difference between a 3 inch tall air cleaner and a 4 inch. I am using the L88 drop base on my engine. What I did to accommodate the 4 inch tall air cleaner was to modify an L88 hood. We raised the front of the scooped part of the hood, but left the windshield side, where clearance wasn't needed, alone. Then, instead of bonding the air chamber to the hood, I riveted the air cleaner base to the chamber and use it like a cold air box. It is totally sealed from the engine compartment and the chamber perfectly follows the contour of the hood. So I have my 4 inch air cleaner and a really effective, easily removable cold air box. The Dyno likes it! In the first picture it was still the 3 inch tall air cleaner, but the 4 inch fits perfectly.
Last edited by 69ttop502; Feb 3, 2025 at 07:46 AM.
A friend has a '74 Corvette with stock hood, with a small block 383.
Last year we had an engine dyno session with his engine. First pulls were in the 485 HP range. After several tuning changes, HP was consistent about 495+ HP.
All pulls were without the air cleaner installed.
His carb is a regular 750DP Holley, without any fancy name at the end.
Withe the air cleaner installed (last pull) resulted a 502 HP
The air cleaner was a stock GM drop base and lid, standard filter.
Why no power loss ?
The only reason I can think of, is that his Holley's main body was replaced with a main body without a choke horn. Better air flow.
If it comes down to a new hood vs a main body change, something to think about. (Assuming you have a Holley carb)
....The only reason I can think of, is that his Holley's main body was replaced with a main body without a choke horn. Better air flow.
I was going to suggest this as well as a cleaner path into the intake. The downside is it will take some idling to warm up enough in the morning to drive the car.
As to Bikespace's suggestion, lots of clearance with the airflow redirected forward, provided you are fuel injected. When I did an LS conversion with a carb (nobody hardly does that) the motor sat a bit higher and I needed a new hood. I now have a drop base and 4" air filter.
Finally going back to the small block discussion, for daily driving with a 383, a 650 CFM carb worked fine, all the up to 5,000 RPM. At the point you could tell the motor was starved for air. If you're not going to operate there, even for a 383, I felt better off in daily driving and fuel economy. Just my experience.
Smoothing air flow from air cleaner into carburetor :)
Originally Posted by Barry's70LT1
For what its worth....
A friend has a '74 Corvette with stock hood, with a small block 383.
Last year we had an engine dyno session with his engine. First pulls were in the 485 HP range. After several tuning changes, HP was consistent about 495+ HP.
All pulls were without the air cleaner installed.
His carb is a regular 750DP Holley, without any fancy name at the end.
Withe the air cleaner installed (last pull) resulted a 502 HP
The air cleaner was a stock GM drop base and lid, standard filter.
Why no power loss ?
The only reason I can think of, is that his Holley's main body was replaced with a main body without a choke horn. Better air flow.
If it comes down to a new hood vs a main body change, something to think about. (Assuming you have a Holley carb)
Hey Barry were you ever with the NS Corvette Club / Quad C ?
Jerry
I believe no power loss is from power gain due to the filter case straightening / directing air flow into the carb.
On my '59 to faciltate nice laminar ? air flow into the carb I run a 3/4" spacer attached to the GM hi-po air cleaner base and using "bondo" have made a nice radius on the air cleaner base going into the carb .
Here are some examples using pictures of my set up.
First, my mistake was to build my engine thinking that what I built would fit under my aftermarket L88 tall hood which is 1.5” taller than an oem L88 hood.
With the Air Gap, Quick Fuel 850cfm with no choke and manual secondaries, 1” carb spacer, 1.5” drop base filter, 3” element and domed lid, the hood would not close.
I have added a vent to the top of the hood that slightly reduces the clearance.
I first removed the 1” carb spacer and there was still contact between the air cleaner lid and the hood.
Secondly I swapped the domed air cleaner lid for a flat style lid, which now gives me approximately 3/4” clearance between the lid and hood with the hood in the closed position.
When I permanently install the hood, I will take an exact measurement of my clearance and if I can squeeze a taller filter in, I will, if not there are other lids designed with a slight dome that will possibly increase the space between the carb base and the air filter lid.
Then again I may do nothing because my engine is putting out more torque than I can ever use, and that little bit of loss won’t make any real difference.
I have solid motor mounts so my motor won’t have much if any movement under the hood, but you’ll need to leave some gap so the air cleaner doesn’t contact the hood.
Moral of this story, don’t build your engine thinking I can just replace or modify the hood and all will be good.
Last edited by OldCarBum; Feb 3, 2025 at 05:01 PM.
Drop Base Air Cleaners.
