Cold air intake

Let’s arrange the half-strokes as columns, with the Y axis being the cylinders

one full turn of crankshaft = any two columns

  1. intake - compr - power - exhaust
  2. exhaust - intake - compr - power
  3. power - exhaust - intake - compr
  4. compr - power - exhaust - intake

No matter how you arrange the cylinder firing sequence, no matter what order you put the cylinders in, in each half stroke one and only one will be on the intake stroke.

Remember that there are four cylinders and four cycles. The thing that makes it confusing perhaps is that each “cycle” is only a half turn of the crankshaft.

I agree that boxed CAI systems are generally a waste of money. And can create problems. And I tipp my hat to you for bringing the thread back to the original question.

OK…this I can not only agree with, but endorse. Which is half (twice?) your earlier post:

“Nope. In a 4-banger with a 180 degree crank, there’s one cylinder on the intake stroke at every revolution.”

Faith has been restored. :slight_smile: Had you said cycle, or stroke, I wouldn’t have thought twice about it. Revolution, well, that’s different.

Sometimes I trip over the language piece. I know what I mean, but don’t always convey it clearly.

Have a great evening.

“Keith, you’ve made an excellent point that the effect can be different than expected. These things don’t always work as advertised. But sometimes, when they don’t, one can learn from the adventure.”

Now for the rest of the story. This is a NISMO cold air intake. He has since installed the NISMO cams, headers and exhaust. It’s a lot faster now. The point I want to make is that these systems are engineered to work together. Adding a part not engineered for the system, or putting on only part of the system is usually counterproductive.

Same for suspension systems. Changing only the struts or springs to some high performance upgrade usually turns out to be a downgrade. You have to put in the whole system.

While I understand your point Keith, I’m not sure I’d totally agree. The caveat is in knowing what you’re doing.

For example, installing a CAI or a header may not do anything at all. Installing both may not even do anything at all, even if they’re both the same maker. And doing so may cause operating problems. In my car, the primary cat converter is in the exhaust manifold. This approach is being used to heat the catalyst up faster and better for lower emissions. Replacing this with a header might reduce restriction, but it also requires fooling the ECU into thinking the converter is stilll there. And, without knowing if the rest of the exhaust system is the true obstruction, it may not help.

Yet, adding the system I did, my home brew, really did help, and without creating problems. In engines that have significant restriction in the intake system, a CAI system might help.

There’s no question a cam helps, but only if the springs are able to keep the valves from floating and only if the injectors aren’t already near saturation.

For the suspension, changing only the shock rates or only the spring rates does make a difference. The upgraded antisway bar I installed (39% stiffer in the “road” setting according to the literature) really did reduce body roll and understeer, and really did make the car more stable on the highway. And it did that all by itself…I’ve changed nothing else on the suspension.

The only blanket statements I’d feel comfortable making with these aftermarket bolt ons is (1) know exectly what the bolt on will change, and (2) if you’re adding power, expect your mileage to go down. The energy is in the gasoline, and to get more you need to use more. Don’t believe the “increases power AND improves mileage” statements. It ain’t likely.

I am a strong believer that you can increase both power and gas mileage if you are willing to increase emissions. That’s how cars were built for years. Recent advances in combustion chamber design and feedback fuel/timing systems have made it less true, but haven’t eliminated it.

Until the mid 70s, when catalytic converters got installed, the air/fuel ratio was often 10% richer than today’s mandated 14:7:1 “chemically correct” mixture. Peak gas mileage occurred at about 10% richer. Peak power occurred about 16% richer. The rationale is since it’s impossible to provide combustion swirl that gives you 100% complete air/fuel mixing, if you added extra fuel, you increase the chances of having fuel particles adjacent to every available bit of oxygen during the burn.

In 1975, when catalytic converters showed up, carburetor jet sizes shrunk across the board - because the 14.7:1 mandate kicked in.

I’m sure in today’s engines with better combustion swirl design, that the 10% number is far smaller. But I can’t believe it’s been driven down to zero.

Both power and mileage can be increased but not on an existing engine with bolt on accessories. Only with new technology.

I would argue that the mix was richer because it needed to be. Only those hydrocarbon molecules in the gasoline droplet that are in direct contact with oxygen get torn apart and bond to the oxygen atoms. Fuel droplets essentially burn through in layers of molecules, like an onion peeling. The time frame available to do this and make usable power is very limited.

Carburetors operate using the differential in pressure between the fuel in the float bowl and the wall of the venturi. That pressure differential is small, so the droplets are large, like squeezing a windex bottle slowly. Thus, in order to get sufficient surface area to create some power, more fuel was necessary.

Fuel injectors use a much higher pressure differential. 40 psi or more squirting through the orafice. Thus, it has a much larger surface to volume ratio, much more surface area, than the fuel through the orafice of a carburetor and it combusts faster, providing more usable power per fuel volume.

Moving the injectors to the intake ports and timing them in synch with the intake valves is even better. The fuel doesn’t have to swirl around in intake manifold plumbing and coalesce. Shooting the fuel directly into the chamber is even better.

Emissions are reduced by obtaining more complete combustion of the fuel, using more of its stored energy, preferably at the top half of the power stroke. Power is also increased by using more of the fuel’s stored energy. With the advent of the emissions technology, we’ve both improved power and reduced emissions. It doesn’t need to be a tradeoff. With advancements in valve timing, direct injection, combustion chamber design, ignition design, forced induction, and other technologies, we probably will be able to squeeze a more power out of the gas while still continuing to reduce emissions.

But I also recognize that at some point it becomes impossible or cost prohibitive to try to squeeze any more out of the fuel. At least with current technology.

In describing the combustion process I think we’re saying much the same things. We diverge on the subject of whether more power can be gained without increasing emissions. My theory is that gaining more power and reducing emissions are both results of the process of burning the fuel more completely. They’re entirely compatible. If I’m understanding correctly, you’re saying that in order to gain more power at this point we need to add more fuel and accept more emissions.

Currently we lose a lot of the fuel’s energy out the tailpipe. I’m convinced that someone will find a better way.

TSM is correct. Bolting an intake onto an engine is not going to increase both mileage and horsepower. Bolting a new engine into the car along with that CAI might - if, for instance, you replace the engine in a Model-T with a D-series Honda engine, you’d go up by roughly 10-20mpg and 50-80hp.

But bolting a CAI onto your Honda-powered Model-T (Model-H?) would not give you gains in both categories, if indeed it gave you gains in anything.


If I’m understanding correctly, you’re saying that in order to gain more power
at this point we need to add more fuel and accept more emissions.

Not exactly. It’s not the only way to gain more power, but it is “a way” to gain more power and improve gas mileage.

After reading your post, I think we’re in 99% agreement. If we didn’t have places where our view on a topic differed, I wouldn’t be able to learn anything from you.

I agree, it is a way to gain more power. On any existing engine it’s really the only way to gain more power. I do believe, however, that new technology will allow us to gain a bit more power without additional emissions. But I also think that the amount we’ll be able to do that is very limited. With direct injection I think we’ll have just about maximized fuel metering, and valve timing and ignition timing are already being controlled. I suspect that power gains without added wmissions will now come from areas like reducing friction and reducing other losses…weight reduction on reciprocating and revolving components, for example. A “blind” mandate to increase mileage to 54+ mpg is, I believe, unrealistic.

To do that manufacturers will have no choice but to do things like use exotic lightweight materials, and that’ll be expensive. Pretty soon we’ll see in regular sedans not only carbon fiber “tub” construction, but hyper lightweight engine pulleys, connecting rods, etc. Unless, of course, everything turns to plug-in hybrids and the feds accept the rated gas mileages of those as part of the average. Either way, the vehicle cost will rise substantially.

I saw a “letters to the editor” letter recently that was responding to an article praising the federal tax credits to buy hybrids. The writer expressed my feelings perfectly. It said “Wait a minute. You’re telling me that $3,400 of MY tax dollars should be used to help someone else buy a new car they can’t afford that will in coming years require an $8000 battery pack replacement?”

I know I got a bit off-topic, but I think there’s relevance. And I do agree that we’re 99% in agreement. Perhaps even 100%. I too enoy the exchange, and I too learn a great deal from these discussion. It also keeps my mind active.

I’ll chime in with my expericences with aftermarket cold air intakes. I had on my 1995 Bronco from the time it had 60k miles on it, until I sold it when it had 252k miles on it. Never had a MAF sensor failure. You just have to put the proper amount of oil on the filter when you’re cleaning it, many people go overboard with the oil and that’s when problems happen. I also have an aftermarket CAI on my Mustang. When I was having it dyno tuned, for sh*ts and giggles we did a pull with the stock air filter assembly and and then another with the aftermarket on. The runs were done back to back on the same day, within 15 minutes of each other, the aftermarket unit was good for 3 extra RWHP (peak). I’ve had the aftermarket CAI on my car for about 40k miles now, and have had no problems.

I know I’m the minority here, but although the gains aren’t much, I’ve never had an issue with these things. In the case of the Bronco, I probably saved a little cash in the long run as I used the same filter for 190k miles, only spending maybe $4 to clean it every 40k miles or so.

Actually, I don’t think you’re “in the minority”, I think you’re just confirming what we’ve all said; the gains if any are typically minimal and there is a risk of contaminating the MAF sensor, albiet if one over-oils it.

I think a lot of it goes back to something I mentioned and you’ve confirmed, that is that it’s important to understand how they work and what you hope to accomplish. That keeps you out of trouble and also keeps your expectations realistic. Unfortunately there are lots of people out there, especially less experienced young people, who see and ad, buy into the sales pitch, and both things on, without ever knowing what they’re doing. That’s a good way to get into trouble.

You’re probably happy with the CAI systems because you understand how they work and how to properly service them and your expectations are realistic.

To do that manufacturers will have no choice but to do things like use exotic lightweight materials, and that’ll be expensive.

Or, they’re just going to have to stop selling sedans that go as fast as Lamborghinis did 20 years ago. I’ve done this rant before on here, but my TL is considered slow because it only does 0-60 in around 7 seconds. That’s ridiculous. If we were serious about fuel economy, 7 seconds should be an amazingly fast sedan. We do not need that kind of acceleration in a normal street car.

While engine efficiency has improved, manufacturers have seen this as the go ahead to make more powerful engines rather than keeping engine power the same and benefiting from the increased efficiency.

54mpg is I think very reachable (hell, I had a CRX HF that got 50mpg in 1988 and it didn’t use anything even approaching exotic). We just have to have the will to reach it.

I think compromises in performance will definitely be part of the answer, but it’ll stiill take exotic technology and materials.