I have been experimenting with different intake/exhaust setups on my '91 'vert, and I have a very interesting observation regarding cone intakes

The car is a '91, 5-spd, N/A, convertible Rex. It has 84,000 miles, and is very well maintained. I currently have Rotary Performance's cat replacement and presilencer pipe installed, with a dual exit Dynomax cat-back. (As a side note, this exhaust combo sounds amazing. I highly recommend it, as it has a deep sound and flows nicely). I had installed a cone intake, with the stock snorkel and stock airbox cover directing air to it. (I removed the stock airbox's cover, and kept it attatched to the snorkel, then put it in place over the cone intake). But, I noticed that with the cone intake the car did not pull to redline smoothly. Around 7K it started loosing power, and pulled much more slowly up to 8K. So, I removed the cone intake and put the stock airbox back in.

The result: Car now pulls smoothly (and more aggressively) all the way to redline, instead of losing power above 7K. What I can deduce from this is that unless you have a designated cold air box, with the stock snorkel plus another source of cold air feeding it, DO NOT INSTALL A CONE INTAKE. You WILL lose performance.

 

Just a cone filter will suck in to much hot air..

Thats why just have a k&n drop in, with small holes cut on side of the box, on the "cold air" side. Works great and still keeps the stock look.

 

Yeah, that is the point I was trying to get across. I was just wanted to let people know that a first mod should not be a cone intake, unless some ducting is done to get more cold air to the filter. I know when I wanted to first modify a car, before I knew much about cars, the first thing I thought to do was get a cone filter - but from what I have shown that is not so.

 

try taking out your passanger side flash to pass lense..directs cold air right to the cone filter,atleast it works for me

 

I don't think hot air is your problem....

I had the same setup on my 89 GTU, had the same probelm... checked it with a wideband.. above 6500, the car started to richen WAYYYY out... I'm talking down to 10.5 A/F by 7500.... put the stock airbox back on and the richest reading i got was 11.75.

I think it way have something do to with the MAF overloading at high RPMS with a cone filter. I put a S-AFC on the car and adjusted it to take out fuel at High RPMs and then the bitch pulled like a raped ape all through the powerband..

WARNING... don't start taking fuel out unless you have a wideband to check it with.. I kept the A/F around 11.5 to 12 and it was good to go.. get any leaner than that and you're in danger of detonating..

this is where the cold air box comes in.. cool air has a less potential for detonation.. why do you think i just spent an ungodly amount of money on a FMIC for my TII>????

 

I've been saying that for years but it's hard to convince some people.

No it doesn't. There's no path for air to get from the hole in the bumper to the filter. Go and have a proper look. Any perceived performance increase is in your head. All you're doing is making the car look broken.

 

Very true.

 

I second that.

 

ok did you guys even read this? Knowledge>assumptions

 

Yes I read it, but "I think it way have something do to with the MAF overloading at high RPMS with a cone filter" is more of an assumption than anything else posted here. The negative effects of elevated intake temp are well proven, but any AFM problems are not.

 

Are you guys ready for another assumption?

I think that because the engine is pulling in so much hotter air, the ECU is richening up the mixture to prevent predetonation of the much hotter air/fuel mixture.

 

edit: double post

(why aren't we allowed to delete our own messages?)

 

I've seen this problem on Subaru's...the amount of hot air is not the problem. The air isn't much hotter with a cone intake than with the stock intake.

It's a matter of the air flow sensor not knowing what to do with so much MORE air than stock...therefore the ECU will overcompensate with extra fuel, to avoid any damaged which would happen with a lean running engine.

 

it would be simple to check it with a voltmeter, but alas i have no s5

 

That does not make sense to me. The airflow sensor is moved by the pressure of the air being sucked past it. This means, that for a set amount of air, a certain voltage is being sent to the ECU, where a lookup table is consulted to determine fuel to be injected.

The ECU, then, must be tuned to run rich at that airflow/airtemp. It is not that the AFM just doesn't know what to do with the extra air, it is that the car is tuned that way.

 

What kind of difference are we talking about with one of the K&N setups that trainwreck was talking about? Worth the $50?

 

Your assumption is probably correct. The uses the air temp sensor in the UIM (NA) or TB (Turbo) to make corrections to fuel and ignition outputs. It's safe to assume there is a protection strategy in the correction maps that lessen the chance of detonation.

That's not correct. The Subaru's AFM is perfectly able to measure the amount of air entering the engine, but as is so common with modern engines, the factory mixtures get richer and richer as boost gets higher. This is simply the manufacturer building a safety net into the ECU in case of overboosting.

The Subaru uses a hot-wire AFM, not a flapper. Subaru's (and other more modern cars) should not be used as examples when discussing our clunky old EFI systems.

 

Didn't know that!

 

hot wire MAF's are the ****. most definately the way to go, but i think most companies didn't use it cause GM had a patent on it or something like a contract with Bosch. ahh, who knows. they work and i wish 7's had them

 

still, there's no conclusion.
NZ, you pointed out that "I think it way have something do to with the MAF overloading at high RPMS with a cone filter" is just an assumption, but never argued A/F test.
it is known and not argued that hot air has a negative effect, but it hasn't been "proven" that the air is significantly hotter enough to cause a negative effect (as more air is ideally being added).
seems that both sides have good basis for arguement, but then add probablies and assumptions.

years of decay, is "WARNING... don't start taking fuel out unless you have a wideband to check it with.. I kept the A/F around 11.5 to 12 and it was good to go.. get any leaner than that and you're in danger of detonating.." aimed at turbos? i see you have both cars and those look like typical turbo numbers, though it looks as though you were still referring to your gtu.

 

No, the effects of air temp on engine output were theoretically proven and practically demonstrated many decades ago. It is ridiculous to state this is only an assumption.

As a simple theoretical example, air at 40degC (underbonnet temps easily exceed this) is 7% less dense than the same volume of air at 20degC. What do you think is going to happen to an engine's output if you remove 7% of the oxygen available to it?

 

i dont know why you always go esspowsing tehcnical jargon like you are some sort of phd.speeking gospel. there are many different ways and circumstances in which cone intakes get employed. and it is obsurd to say that everyone of them is worse than the stock air box.

until you give me dyno numbers as to how much worse it is in our SPECIFIC APLICATION. im going to stay on the fence and except that a pod filter (without a cold air box) sacrifices some intake temp for the sake of better flow. now when you factor in how the ecu reacts to that combo all bets go out the window on this kind of situation.

without extensive measurements it is imposible to tell to what extent this happens so realy there is no need trying throw around your numbers like they mean anything that couldnt be countered by an other aspect of a pod filter install.

 

i WOULD SAY THAT THE CONE FILTER MUST BE RESTRICTIVE BECAUSE IF YOU REDUCE THE AMOUNT OF FUEL THAN THAT MEANS THERE IS LESS AIR.

fROM MY experience, I installed a drop in K&N filter into my RX-7 and it pulled more smoothly all the way up to redline, on a side note the old filter was old an dirty. Did the same think to my moms accord and no notable differencess where noted, same **** different tile, so i replased it with a brand new OEM one and noticed no difference eather. Althow the K&N did get dirtier and more restrictive, fuel economy whent down.


GIl

 

if you remove both of the ftp lenses just to keep things balanced and cut some of the wal behind the headlight and form a duct you can infact get direct cold air to the cone intake!

I am also goign to get a headlight cover with a duct from it to the cone intake also... this in the end will produce more than enough cold air! And still have the extra flow allowed by the cone filter...
I also have a turbo engine with a large FMIC and a stand alone so I will be able to safely tune!

 

right, which i said we all agree on. theoretically "proven" and put to practice. wow, let's leave that as established, shall we?
now, back to actual temp of air.. you could compare 40C to whatever number, but i was more aiming towards the actual temp of the air from both simple cone versus stock and then amount of air from both. i don't doubt your theory by any means, just saying actual supportive numbers are always fun to see.