Performer EPS vs Performer Air-Gap?

[WillSquared]

I'm starting to look into changing my intake and carb out. Pretty much decided on the Thunder series 650cfm carb but I'm torn on the intake. What are the benefits of each of these and which would you choose?


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[HotRodPC]

I've got the EPS on my SBC350 truck since it came with it when i bought it. Very throttle responsive and good low to mid range pull just like it should. Maybe just a fancy Performer, but Eddy claims the EPS will give 5-10 more hp over the Performer. I don't buy to much hype into the Air Gap. Of all the tests I've seen on the Air Gap by Magazines and such, the gain just isn't there. Not much more to speak of over a standard Performer in most cases. Now this is all on the big blocks that I've seen articles about, both Chevy and especially Olds. The Air Gap gave no more hp or torque on the Dyno test on the Olds test, they recommend just going with the Performer and even then, it didn't add much over stock since the Olds OEM intake works pretty well as is in the late 60's and early 70's as long as it didn't have an EGR valve. In the BBC, the gain was so minimal it just wasn't worth the money.

 

[Green79Scottsdale]

All the tests I have read about the Air-Gap are... conditional, I would call it. The theory is sound on the Air-Gap, separating the runners from the intake bottom to cool the intake charge. That WILL happen, but you will only see the difference installed in a vehicle, IMO. That is why most of the dyno tests don't show "improved" power, the whole theory of the air gap engineering is removed.

So say you do install the Air-Gap, now you have the pro/con of the cooler charge. Great for summer and warm weather driving! But if you drive your truck in cold weather regularly, you will want to make sure your heat stove set-up is operational along with the thermostatic valve that is in your air-cleaner. (Personally I would recommend them regardless) This will allow the engine to get up to optimal operating temp quicker and improve your truck drive-ability.

The EPS looks to be a solid design, can't go wrong with it. Not that it's too much of worry, but the EPS will fit under the hood easier as it is shorter. And (at least at Summit) it looks to be $100 cheaper to boot. If you are keeping your motor basically stock, I would say go with the EPS and use the $100 on the nickel and dime stuff you will run into.

edit: A guy at work is running an Air-Gap on his 389 sbc Chevelle. He has absolutely no complaints, so I would say the Air-Gap is also a good intake that you can't go wrong with. I was NOT knocking it in my explanation, just presenting some of the common "issues" people bring about to try and knock it down unnecessarily.

 

[WillSquared]

I was leaning toward the EPS due to not having the stock intake and I'd read similar things in that the AirGap in cold weather takes a long time to get the engine up to correct op temps etc.

I've got long tubes to go on soon and a new exhaust. Eventually I will do new heads and a cam but that'll be the extent of it. The engine has less than 5k on it (Goodwrench 260hp) so I'm leaving the bottom end alone. But I do want to get rid of EGR and my stock carb is not working properly so I figured I'd upgrade there also.


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[MadOgre]

I was leaning toward the EPS due to not having the stock intake and I'd read similar things in that the AirGap in cold weather takes a long time to get the engine up to correct op temps etc.

I've got long tubes to go on soon and a new exhaust. Eventually I will do new heads and a cam but that'll be the extent of it. The engine has less than 5k on it (Goodwrench 260hp) so I'm leaving the bottom end alone. But I do want to get rid of EGR and my stock carb is not working properly so I figured I'd upgrade there also.


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If you look at the air gap and the EPS side by side, there really isn't much of any difference in there design, only the air gap difference. Like its been said in cold weather the air gap can be miserable to make run. They really are meant for warm weather applications only. The EPS with felpro 1256 with the cross over ristrictor plates installed is the best way to go.

I am redoing my qaudrajet with new throttle shaft bushings and using epoxied threaded pipe plugs to seal the fuel well plugs, on a performer 2101, and im installing Eddy's 1806 carb and EPS 2701 on grandpa's truck next week.

 

[WillSquared]

I am redoing my qaudrajet with new throttle shaft bushings and using epoxied threaded pipe plugs to seal the fuel well plugs, on a performer 2101, and im installing Eddy's 1806 carb and EPS 2701 on grandpa's truck next week.

Be sure and post up info/review on that 1806/2701 combo. That's exactly what I was looking at.


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[MadOgre]

It looks like a good set up, but I wasn't happy with any of the aftermarket brackets for running a 700r4 behind it. I figure a properly done Quadjet will still give me the performance with better fuel mileage. So grandpa gets the 1806/2701 as he has the th400.

 

[rich weyand]

Lots of misconceptions about the air-gap manifolds. Let me try to straighten it out.

First, you must use the air-gap manifold with the thermostatic air cleaner. That much is true. Without hot-air induction in the winter, the carb will never heat up and the engine will run like it is stone cold pretty much all the time.

The idea of the air-gap is to keep the carb and runners from being heated by the oil. This is done by separating the valley cover from the actual intake manifold. The old Studebaker 289 separated them by having a separate valley cover with what was called a spider manifold that stood up off the valley cover, like a spider standing on its legs. Take a look at one at your local car show or cruise-in night and you will see what I mean. The air-gap manifold is the same thing, but cast in one piece.

The concept is simple. There is an optimum temperature for the induction system to run at. The best way to maintain this is to insulate the induction system from engine heat, and then temperature control the incoming air. The air gap manifold is the insulation. The thermostatic air cleaner will pull hot air from around the manifold/header when the incoming air is too cool, and will pull through the snorkel when the incoming air is too hot. Used with a cold-air induction tube from the front of the radiator bulkhead to the snorkel, temperature control gets pretty good, particularly because the GM thermostatic air cleaner is not either/or, it will actually mix the two to maintain temperature. With the cold-air induction tube removed, I can see the air door, and it will sit in intermediate positions -- not all the way open or all the way closed -- to maintain temperature.

The concept is like insulating a house, and then installing a furnace and A/C to keep the temps where you want them.

The air-gap manifold will show little or no performance gain over similar dual-plane manifolds operated at optimum conditions. When conditions are not optimum, when it is 95 degrees out, or when it is 20 degrees out, the air-gap manifold will maintain the performance achieved under optimal conditions, where a standard manifold with an open-element air cleaner will suffer significant performance, driveability and fuel economy degradation.

Saying the air-gap manifold achieves no performance gain in testing compared to other manifolds is like saying you tested an uninsulated house with no furnace and no A/C against an insulated house with a furnace and A/C, at 70 degrees ambient temperature, and both were equally comfortable, so insulation, furnace and A/C offer no comfort increase. Sure, at 70 degrees that's true. It is not true at 20 degrees or 95 degrees, not because the comfort of the insulated/furnace/A/C house increased, but because the comfort of the unequipped house decreased.

All carburetors are temperature sensitive. Edelbrock Performer carburetors (the old Carter AFP) are more sensitive to heating than some others. A partial solution is an insulating spacer between the carb and the manifold, but that only helps on the "too hot" side.

I have run both, and have the air-gap manifold with the thermostatic air cleaner and cold air induction now, and love it. During the winter, when the engine starts, it does what all engines do when started in the winter. It starts OK, and then as the vaporization of gasoline starts cooling the carburetor, it starts running rougher. For about two minutes. As the headers heat up, and the warm air is drawn in, the idle smooths out. You can easily hear this occur. Literally from that point, maybe three minutes total from start, the truck drives like it is 70 degrees out, even when it is five below. And in the summer it can be 100 degrees out, and the combination of the insulating air-gap, cold-air induction and evaporative cooling of the carb keeps carb temperatures in the optimum range. And my fuel mileage is pretty much the same year-round.

 

[MadOgre]

Lots of misconceptions about the air-gap manifolds. Let me try to straighten it out.

First, you must use the air-gap manifold with the thermostatic air cleaner. That much is true. Without hot-air induction in the winter, the carb will never heat up and the engine will run like it is stone cold pretty much all the time.

The idea of the air-gap is to keep the carb and runners from being heated by the oil. This is done by separating the valley cover from the actual intake manifold. The old Studebaker 289 separated them by having a separate valley cover with what was called a spider manifold that stood up off the valley cover, like a spider standing on its legs. Take a look at one at your local car show or cruise-in night and you will see what I mean. The air-gap manifold is the same thing, but cast in one piece.

The concept is simple. There is an optimum temperature for the induction system to run at. The best way to maintain this is to insulate the induction system from engine heat, and then temperature control the incoming air. The air gap manifold is the insulation. The thermostatic air cleaner will pull hot air from around the manifold/header when the incoming air is too cool, and will pull through the snorkel when the incoming air is too hot. Used with a cold-air induction tube from the front of the radiator bulkhead to the snorkel, temperature control gets pretty good, particularly because the GM thermostatic air cleaner is not either/or, it will actually mix the two to maintain temperature. With the cold-air induction tube removed, I can see the air door, and it will sit in intermediate positions -- not all the way open or all the way closed -- to maintain temperature.

The concept is like insulating a house, and then installing a furnace and A/C to keep the temps where you want them.

The air-gap manifold will show little or no performance gain over similar dual-plane manifolds operated at optimum conditions. When conditions are not optimum, when it is 95 degrees out, or when it is 20 degrees out, the air-gap manifold will maintain the performance achieved under optimal conditions, where a standard manifold with an open-element air cleaner will suffer significant performance, driveability and fuel economy degradation.

Saying the air-gap manifold achieves no performance gain in testing compared to other manifolds is like saying you tested an uninsulated house with no furnace and no A/C against an insulated house with a furnace and A/C, at 70 degrees ambient temperature, and both were equally comfortable, so insulation, furnace and A/C offer no comfort increase. Sure, at 70 degrees that's true. It is not true at 20 degrees or 95 degrees, not because the comfort of the insulated/furnace/A/C house increased, but because the comfort of the unequipped house decreased.

All carburetors are temperature sensitive. Edelbrock Performer carburetors (the old Carter AFP) are more sensitive to heating than some others. A partial solution is an insulating spacer between the carb and the manifold, but that only helps on the "too hot" side.

I have run both, and have the air-gap manifold with the thermostatic air cleaner and cold air induction now, and love it. During the winter, when the engine starts, it does what all engines do when started in the winter. It starts OK, and then as the vaporization of gasoline starts cooling the carburetor, it starts running rougher. For about two minutes. As the headers heat up, and the warm air is drawn in, the idle smooths out. You can easily hear this occur. Literally from that point, maybe three minutes total from start, the truck drives like it is 70 degrees out, even when it is five below. And in the summer it can be 100 degrees out, and the combination of the insulating air-gap, cold-air induction and evaporative cooling of the carb keeps carb temperatures in the optimum range. And my fuel mileage is pretty much the same year-round.

Interestingly enough that sounds pretty logical. Do you have any pics of your thermostatic air cleaner setup with headers?

Sounds quite interesting.

 

[rich weyand]

Oh, and if you put a chrome dome on it, the thermostatic air cleaner doesn't look so bad. It's like $10 for a chrome lid. I got the thermostatic air cleaner at a junkyard and cleaned it up and just put a new thermostat in it. That's a 4" aluminum dryer tube to the bulkhead intake fitting. Those fittings were stock on some engine options. I picked it up at a junkyard.

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[rich weyand]

Here's a write-up I did on another forum. Not hard to do at all, once you think it through and find the right parts to modify.

http://www.fullsizechevy.com/forum/...s/498719-induction-system-350cid-headers.html

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[rich weyand]

I guess I should put that write-up here in case the other forum dies. Since this was published, I have fuel numbers. Running a base 350 crate engine with a Comp Cams 12-300-4 cam, I get 12 mpg on the highway, and about 10 mpg in town. That's in HI (unlocked NP208) and hubs FREE.

=============================================
(Originally posted on another forum 5-11-2012)

OK, so I put a new GM Performance 350 in my '78 when the original started blowing green water out the tailpipes. I kept the Edelbrock 1406 carb, but put an Edelbrock 2601 air-gap intake manifold under it. The air-gap manifold lifts the carb and fuel runners up off the lifter box cover to keep the engine oil from overheating the carb. The problem is it also keeps the engine from heating the carb.

Somewhere along the line the original induction system, with the thermostatic air cleaner and heat riser and all that, was removed and they put one of those "two chrome pie plates" deals on it. This solves the problem of what do you use for a heat stove and heat riser when you put headers on the engine. But, it gives you no carb heat.

"Carb heat" is what the flyboys call it. They put a wrap around a header, called a carb heat muff, and run a duct to the air intake. This has a pull cable to the interior so the pilot can select between ambient air and heated air from the carb heat muff. They also put a carb temperature gauge on the airplane.

The issue is that gasoline, when it vaporizes, takes on the heat of vaporization from its surroundings, in this case the carburetor. In the right weather conditions, say 50 degrees and high humidity, the carb can condense ice and freeze up. I didn't have those problems, or haven't yet, but I had poor performance on the cruise circuit and bad gas mileage -- only 7.5 mpg on a 350! -- until the carb heated up, which could take a long time, or not at all depending on ambient temperature.

OK, so I fixed it, and boy does it make a difference. No mpg numbers yet, but driveability is vastly improved.

I started out by getting an air cleaner body, lid, heat riser tube, and front bulkhead fitting from the local junkyard, which has several late 70s c/ks in stock. I cleaned them all up with EvapoRust and Aircraft Paint Stripper, starightened them out a bit and repaired some thigns with JBWeld, then repainted with Rustoleum Rusty Metal Primer and Gloss Black straight out of the can. Nothing fancy, it's a truck and a DD. I also got a new PCV breather line, cap, and filter, and a new air cleaner thermostatic vacuum switch. The existing air door and motor worked fine. I also needed a 3/4" air cleaner spacer to fit the stock air cleaner body over the Edelbrock, due to a conflict at the Edelbrock's fuel entry.

Installation of all the above was straightforward. For the cold air induction line from the air cleaner to the front bulkhead, I used an aluminum dryer vent tube. For the heat riser, I used a Gibson 500415 Polished Stainless Steel Exhaust Tip. This is a "turndown" style. I had a local machine shop mill off the turndown part to be flush with the bottom of the straight part and mill three 1/2" wide, 1/2" deep slots across the bottom side of it. This I band-clamped to one of the header pipes. The Hooker headers have one pipe that heads back before it turns down and it was perfect for that.

The heat riser was an issue. I tried a "flexible stainless steel exhaust pipe repair kit" in a 1-1/2" diameter, but it would not bend tight enough to get out from under the air cleaner snorkel without hitting the valve cover. What I ended up doing is cutting the original heat riser pipe up into its component elbows, and using them with sections of the flexible between them to build up what I needed. I slotted the upper flange so I could clamp it to the stub on the bottom of the air cleaner and take any strain off the header, and assembled the whole thing with JBWeld, primed, and painted.

So this is what I got:

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As I say, driveability is much improved. It takes about 30 seconds at idle for the header to heat enough to start warming the inlet air drawn through the heat riser, which is much faster than using a stock manifold because the header tubes are so thin and they heat up rapidly. It takes about five minutes at idle for the air door to open. It does not just flip open, but is proportional. Very nice. And when you get on it hard, the vacuum motor loses vacuum and the air door opens the four-inch pipe from the bulkhead whether the air cleaner is warm or not.

Before I had the worst of both worlds: hot underhood air when the engine and weather are hot, and cold underhood air when the engine or weather are cold. Now the inlet air temp is regulated, which means all the carb tuning I did with a warm engine will actually be spot on whenever I drive, hot, cold or in between.

We'll see what the mileage numebrs come out to, but I can tell you right now that I am using much less pedal to get around. I drove over to Nashville, IN and back tonight and was maintaining 60 mph on the carb's cruise circuit with maybe 1/4" of pedal. Maybe not that much.

So, a couple things for you all. One, do not use the air-gap manifold unless you have a thermostatic air cleaner setup. The carb will run so cold under most conditions that you will get terrible carburetion, poor performance, and bad gas mileage.

Second, if you want to put headers on your engine, and want to keep the thermostatic air cleaner setup, it is not hard to mod the existing heat riser pipe and connect it up with a turn-down style exhaust tip with a little machine shop work.

 

[WillSquared]

Great info fellas. I think I'm gonna go with the EPS. The logic on the more consistent performance makes sense on air gap, but I figure the eps will work fine for me and it's cheaper, so win/win.


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[rich weyand]

Great info fellas. I think I'm gonna go with the EPS. The logic on the more consistent performance makes sense on air gap, but I figure the eps will work fine for me and it's cheaper, so win/win.

Biggest issue is that you get hot down there, so you might think about a heat-insulating carb spacer. You don't get as cold there, so the insulator won't hurt you as much in the winter as it will help in the summer. And a thermostatic air cleaner will help over an open-element setup, particularly if you have cold-air induction from in front of the radiator.

 

[GTME94]

Did you have to do anything to that dryer duct to make it fit other than making it oval? I'd thought about using one but it seemed too big.