Spectre Intake?

[Eggman]

IMO, reducing the pipe diameter and/or lengthening the intake pipe would be what I would do to make a custom intake.

Why lengthen the intake pipe?

[Daox]

It increases low rpm power.

[NotoriousJT]

Where could I get a cold air intake filter that supports a 2" ID?

I got the maf sensor housing and going to be getting some pipe here soon so I can make a custom coi.

[namco]

Why lengthen the intake pipe?

the longer the intake path the more low end power you will achieve. think about race cars setup with itb's, they stay in high rpm all the time as much as possible, so that's where you want all your power to be. on a street car, they put longer intake systems to give better bottom end for the get-up-n-go.

older import trucks with 4 cylinders have really long intakes, instead of a short pipe to throttle body to intake manifold (which is also straight) into the 4 cylinders, you have a long intake pipe going from one side of the engine bay to the other, then the throttle body, then an S shaped intake manifold to extend this distance even more, this gave a 4 cylinder engine the kind of torque a truck needs to do what it does, granted, you also have to TUNE for it to use it well. Any change needs a tune for proper gains..... Just slapping on a longer intake on any car wont do anything until you tune it.

[Eggman]

the longer the intake path the more low end power you will achieve. think about race cars setup with itb's, they stay in high rpm all the time as much as possible, so that's where you want all your power to be. on a street car, they put longer intake systems to give better bottom end for the get-up-n-go.

older import trucks with 4 cylinders have really long intakes, instead of a short pipe to throttle body to intake manifold (which is also straight) into the 4 cylinders, you have a long intake pipe going from one side of the engine bay to the other, then the throttle body, then an S shaped intake manifold to extend this distance even more, this gave a 4 cylinder engine the kind of torque a truck needs to do what it does, granted, you also have to TUNE for it to use it well. Any change needs a tune for proper gains..... Just slapping on a longer intake on any car wont do anything until you tune it.

I think you are contradicting yourself here.

Your example of ITBs does not correlate to a longer length intake. With ITBs, the intake diameter *likely* increases for each cylinder. With this example of longer intake pipes, the diameter remains unchanged. If the diameter of the intake extension is larger, then as Daox suggests it will cause other problems. In your conclusion, you admit that the mod needs proper tuning.

I owned a '70s era Datsun pickup, and I don't recall any long intake in that engine bay. I do remember there was no throttle body... I suppose your idea of 'older' import trucks might be different than others.

If the concept is akin to a tuned exhaust on a motorcycle, then why do motorcycles not use long intake pipes?

The pipe diameter needs to be the same as the stock diameter or it will throw off the MAF readings.

In the effort to use an intake extension of a larger diameter, the MAF housing becomes a choke point.

So, if I follow everybody correctly, either the longer intake acts as a tuned intake, much like a tuned exhaust, but only if it is the same diameter along it's length.

So, unless there is data proving increases in engine output (for the 3A92), or I am missing something else, it is only an exercise in vanity. That is why I was asking these seemingly simple, basic questions. I am curious as to why someone would pursue this, and wanted to hear some insight from those who have and what benefits are gained. I'm sure someone has some data to share.

Otherwise, why wouldn't manufacturers take advantage of this?

[cyclopathic]

@ Eggman: read on Helmholtz effect (cavity resonance) By tuning cavity to specific frequency you can optimize it to specific RPM (5% improvement at resonance, 2% at following harmonic as I recall) to increase pressure and reduce pumping losses. It would be surprising if OEM intake isn't already tuned.

[Daox]

Here is a good article on testing different intake lengths. Actually its on an engine that is larger, but the power output is pretty comparable to ours.

Pipe Dreams - Autospeed.com

[namco]

I think you are contradicting yourself here.

I didn't contradict myself at all. Longer intakes will give low and mid end power, shorter intakes give better mid to high end power. ITB's are an extreme and thus make great top end power. All have to be tuned to get an effect because the stock ECU cannot handle such a radical change. Even in the old days, the individual throttle bodies of today back then would have been individual carburetors, which is basically the same thing just for older technology.

Although I said older, I wasn't really thinking 70's, more like early 90's. I think its the toyota b2000 (it came into my shop for a quick battery job, dude was too old to be ****ing with his **** lol) and the intake ran from the passenger side to the driver side, then had an S shaped intake manifold. Many other import trucks from that time frame have relatively long intakes compared to some of today's vehicles.

Here is a good article on testing different intake lengths. Actually its on an engine that is larger, but the power output is pretty comparable to ours.

Pipe Dreams - Autospeed.com

While I really enjoy that link as showing how different sizes matter, they didn't tune the motor, all they did was slap parts on to see, in stock form, which would perform better. I guarantee their results of intake length matches what the stock air box would have achieved, thus why the aftermarket of that length was best for this test.

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On a separate note, every little thing you do to a motor is going to change it. For example, in a force induced engine, lets say the subaru wrx sti, increasing the intake pipe diamater from 2 something to 3 inch, changing the exhaust from the turbo back to 3 inch, and tuning the engine, can result in up to a 80 hp gain, usually more around 30-50 hp because of conservative tunes that are "safe".

Even back in the day, my 93 del sol, without a tune, I had the stock intake, a short aftermarket, and then a custom made intake. The best results came from my custom intake, which was longer in length then both the stock and aftermarket, and same diameter as stock. The short intake was 3". The shorter aftermarket intake caused me to lose low end power (you could tell) but gained top end acceleration. When I switched to the S bend pipe that was same diameter as stock but longer, my bottom end came back but I lost in the top end. It was all noticeable in change. If I had actually tuned for it I could have gotten more. Most cars have a little lean in ecu tuning that allows for minor changes. This is especially true for older honda's (pre 2000's, dunno about newer but i would assume so).

Think about the intake length on the mirage, its pretty long, you have the induction tube running up the left back towards the firewall, over into the filter box, the filter box itself can store air (helps with the whole rpm band), and then a decent length pipe to throttle body, include the intake manifold runners and you have your total length. compare to other cars and its pretty long.

If I also go back to honda's for another example, the whale penis intake. (password jdm "powerchamber" intakes) they did a ton of research to build an intake that performs in the whole rpm range instead of short (high end) or long (low end). You can do the same thing with our motors, sticking to the throttle body diameter for the beginning and end of the intake and having a "power chamber" in between, like a 3" or 4" diameter mid section. This would dramatically change how the engine operates. Granted I wont be doing that because I plan to turbo, so the only real upgrade I am looking to do soon is exhaust from the catalytic converter back.

EDIT: also, look at exhaust manifolds. 4-1 makes great top end power while a 4-2-1 makes a better overall power band as a whole. there have even been attempts at a 4-3/1-1 that offered a vast change in engine power band characteristics....

[Eggman]

namco: I can tell you are quite serious about your cars and their performance. I guess I'm more dubious about the return on investment on some of these mods.

Here's a modification that makes sense to me, one that I can get behind:

Warm Air Intake installed today, saw 69 mpg on a short test drive.

I have no instrumentation to tell me that information. My guess would be 120F. You can fine tune it by proximity to the manifold.
Of course if you pull a lot of air the temps will drop.

Green temp light went off this AM in .2 mile, compared to .8 in mid summer and 1.2 in winter. Block heater on for 2 hours.

The changes in driveability are easily measured and quantifiable. In my understanding, an engine experiences the majority of it's wear at cold start when the oil has not yet come up to temperature. The Mirage will tell it's driver if the engine is cold, using the dashboard temp indicator - presumably to tell the driver to take it easy. This mod should help with engine longevity.

As you said earlier, the Mirage already has a long intake.

Think about the intake length on the mirage, its pretty long, you have the induction tube running up the left back towards the firewall, over into the filter box, the filter box itself can store air (helps with the whole rpm band), and then a decent length pipe to throttle body, include the intake manifold runners and you have your total length. compare to other cars and its pretty long.

If someone can measure before and after performance with a long(er) intake, then we'll all have something to go on. Until then, it's all speculation.

In my view, these are cheap economy cars. While it is fun to get more out of them, they just aren't built for speed.

If I wanted a performance car I wouldn't spend my money on one of these. To me, their performance is in their economy.

[Daox]

IMO it would be best to combine the two designs for best FE. Increasing torque at lower rpms should also increase fuel economy. Thus, a longer intake pipe combined with a warm air intake could provide even better benefits to fuel economy AND improve lower rpm power which is where most of us drive.

Of course there are guys who want to squeeze a bit more power out of their engines, and they can do that too. The autospeed article shows how you can have whatever you want, it'll just take some testing on your own to figure out exactly how your modifications have altered the engine's behavior.

Or, you could go all out and make up a fancy intake that is vacuum actuated to pull air from two different sources, hot and cold. At low manifold vacuum near WOT (wide open throttle), it would switch to cold air. But, for higher vacuum (lower engine loads), it switches to the hot air. OEMs have done this on production vehicles.

It really just depends what you want out of your car and how much you want to and/or enjoy messing around with things. The sky really is the limit.