Ironman404

So I've read through the forumail, and it seems that the general consensus is that cold air intakes are no good on these cars.

Is there anything I could/should do to improve the air intake system? Switch filters, build a custom air box, etc. My buddy is a very talented welder, builds custom headers, choppers from scrap, buggies, etc. And offered to build me one.

Also, my air pump is missing, but I was told that since I don't have a cat all I have to do is seal up the tube coming from the air box that would attach to the air pump and I'm good to go.

clokker

iTrader: (2)

A real "cold air intake" is always a fine thing, the problem is that most intakes aren't real.

Before you can improve the system, you must first identify its weaknesses and that's hard to do without some equipment and data collection.
It would help to know what engine config you're working with but if it's a NA, I can speak from experience that the only real improvement you can make to the the stock system is aesthetic.
In other words, you can significantly alter the appearance of your bay but you'll never feel much difference in performance.

Should you decide to continue, the next big hurdle is to figure out exactly where the "cold air" is going to come from. The stock system takes a very convoluted route and if you're going to "improve" on it, yours should be simpler and more direct...otherwise, what's the point? You will find that this is trickier than it appears.

If you have a S5, the airpump powers your aux ports, so you'll need to figure that out.

Ironman404

I have an 88 N/A convertible

WondrousBread

There's been some conjecture on whether or not altering the intake will provide any real gains. Honestly, you would have to do quite a bit of planning and fabrication just to match the stock intake, let alone surpass it. As it is, the snorkel rams (or at least theoretically rams) cold air from the front, ducts it through the filter and maf and then into your throttle body. There are some problems to look out for. First, the maf must stay in the same orientation. Two, if you change to a cone filter, you will be inhaling hot engine bay air rather than cold air from outside. This means you have to construct a custom cold air box, and find a way to duct it from behind the headlight or in front of the rad. If you duct it from in front of the rad, then you will have essentially put in an enormous amount of time and effort simply to replicate the stock intake. The intake on N/A Rx7s is fairly well thought out, and each piece complements other pieces. There was a lot of though put into the design at the factory, and it is pretty well optimized (ugly as it may be).

There may be some slight gains to be found, but it is a lot of effort to find them. Also, if you are on stock ports, there is only so much extra air you can squeeze in there before the bottle neck is your engine block. I don't know exactly what the power limit is on stock ports, so someone else may have to weigh in on that.

You are probably better off spending time and money on exhaust modifications.

Ironman404

Thanks you...awesome insight.

So for my model, 1988 N/A 13B convertible, are there any negative impacts caused by not having the air pump?

rx7racerca

iTrader: (1)

This. There are easy gains to be made on exhaust, before the intake becomes a worthwhile consideration. Replace the pre-cats and main cat with a single, high flow cat, you'll literally pick up 10x the (maybe) 2 hp gain a proper cold might give (or an RB mid-pipe/pre-silencer - I've had both, and it took the car from running out of breath at 7800rpm to pulling strong up to 8700, with a very noticeable improvement in power above 5000). After exhaust, the vane-type MAF on S4s is probably worst restriction on the intake side. Drop in a K&N filter in the stock airbox and call the intake done (you won't notice the difference of the K&N either, but it's probably as much improvement to the intake as a much more elaborate, well done cold air setup will yield).

Ironman404

Awesome. My buddy is actually fabricating a heads to exhaust tips system for me. I don't currently have a cat on it at all...would I be better off installing a high flow one or simply leaving it off altogether?

WondrousBread

If you need to pass emissions, a cat is a necessity (unless you feel like swapping it in every time you get tested). If not, you can leave it out. Keep in mind though that in most areas it is illegal to remove emissions devices, and if a police officer pulls you over you can get a hefty fine. Also, it will smell badly and be loud unless you put in a silencer.

I'd just get a high-flow and be done with it, but I daily drive my Seven so it's basically necessary for me. You will have to make that call for yourself.

Also, you will need to put in an air pump if you have a cat. Otherwise, the air pump serves no alternate purpose on your engine so don't worry about leaving it out if you don't install a cat.

Evil Aviator

Yes, because most people on this forum have not the slightest clue about building one, but they don't let that stop them from trying. Also, the car basically already has a cold air intake in stock form, so there isn't a lot to gain like there would with a stupidly-designed Honda that has the air intake right in the middle of the hot engine. See this link for an actual cold air intake, and you will understand why most people don't have this on their street car.
E/P Convertible

Take the internet description of 'restriction' with a grain of salt, as it is flow-dependent. What restricts an 800hp engine may work great on a 600hp engine. This applies to any flow through a tube, such as a carb, throttle body, intake tract, and exhaust system.

Great, give him this link:
Rotary Tech Tips: Exhaust System Configurations

Be sure to use good mufflers from Racing Beat, Apexi, GReddy, HKS, or other high-quality aftermarket vendor that specifically makes mufflers for rotary engines. Popular V8 stuff like FlowMaster will burn up in the hot rotary engine exhaust, which is why their warranty does not cover rotary engines.

j9fd3s

iTrader: (3)

this is an excellent point. the stock FC airbox is a little restrictive on a 200hp turbo engine, but it flows enough for a 146hp engine.