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torxxx

Air intake questions - carb'd EA82

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So I've been testing my SPFI air intake I put on my carb'd EA82. With the air intake and air box from a SPFI Ea82 with the pcv lines hooked up to the air intake, I notice a lot of resistance around 3500 RPMS. It lags really bad and then after about 4100 RPMS it pulls like a champ.

 

Either the PCV lines going directly into the air intake is oiling the carb passage and intake and causing the engine to run like crap. Or could it be that the SPFI air intake is too long and the filter is too much for a carb to pull air through. I have a brand new WIX air filter in the airbox.

 

When I run with the air intake completely unhooked, I get good power all the way to red line.. One constant pull, not start, lag then go like it is with the air intake hooked up correctly.

 

So what are my options here? I had a cone filter on it 2 years ago, hooked to the SPFI air intake and it seemed to work alright, other than the fact that the filter was simply too small. Maybe I need to get one of those wanna be ricer air intake fans? lol

 

Either way, muddin season is coming up and I need to have filtered air going into my engine. Gimme some ideas please

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Drill some holes in the airbox?

 

Try it with just the box and no filter to test the filter flow idea....

 

dunno - the SPFI should need more air than a carbed block, so it shouldn't make too much difference.... although the ECU on the SPFI has the ability to know the airflow from the meter, and adjust fuel accordingly....

 

Lots to consider, and tests to be run I think.

 

GD

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Yeah I got a bunch of holes in the bottom of the airbox.

 

It sucks cuz I wanna run it without the filter because it runs so much better.

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i'm about ready to do that. I unplugged the PVC lines from the air intake and plugged the holes, and I took the clamp off the MAF side of the intake. it seems to be doing better, but not like it does with the open carb.

 

This creates a bigger problem for the snorkel conversion I was gonna do. If the carb can't suck enough air through a 2 foot rubber hose, how in the hell am I gonna get it to suck through 6 feet of PCV pipe?

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I've been running an air filter box from a SPFI with my Weber. I use a length of dryer duct to connect it to a plenum I built for the carb out of sheet aluminum. I'm not running any vacuum lines to the air box, just the carb (for the distributor) and the manifold (brake, vacuum contols). It seems to breathe pretty well all the way to redline.

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if you're going to be sucking through 6 feet of pipe, it needs to have around/about twice the cross-section of the old hose - it'll be able to suck reasonably easy then. Pipe length shouldn't be too much of a factor, just as long as it isn't too restrictive (bends, nooks, crannies - in other words, the inside of the pipe needs to be totally smooth, because ridges etc. cause interference, and Venturi's principle says that when you suck air around an impurity such as this, there's a small region of air around this impurity that doesn't move, basically constricting the airflow through the rest of the pipe. The faster you suck in air, the larger this region of air becomes. This is why the mouth of the stock air intake will be flared, not just a straight pipe - and is also why, if the stock intake has a grille on it, the mouth will be quite a lot larger than the pipe itself).

 

The reason why the rubber pipe is the cross-section/length it is, is because in the engine's mid-range there's usually a little dip in power output - you'll find the resonant frequency of this pipe is about the same frequency as the engine sucks air at that mid-range RPM, so the air inside the pipe resonates at that RPM, providing an almost resistance-free travel of air through the pipe, though it dumbs down the top-end a bit due to the pipe needing to be reasonably thin. If you were to make this pipe big enough to not constrict the top-end, it'd only be about a foot long, and would void the whole purpose of the pipe anyway.

 

So in the end, using a bigger pipe or removing the rubber one totally will rob you of a little mid-range but will provide you with some more top-end to compensate.

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fbh thanks man that makes sense. I can see how the ridges in the SPFI intake would make problems with air swirling into the carb.

 

I guess I'm looking for a bolt on filter straight to the carb like the weber guys run. Is the neck of the hicrappy carb the same size as a weber?

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Should probably be - though if you take off the neck altogether and just bung a high-efficiency filter on there, you'll sacrifice a little mid-range power for some not-bad gains in the high end...

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