3" or 2.5" intake pipe for a 2L 97 tiburon. i have both already made(cai). i just want to know which will give me better performance. i've heard a few times the a 3" intake would be too big but i want to know for sure. thanks in advance.

also.. what if i used both? like start with 2.5" at the TB then half way down go to 3" to the filter. kinda like how iceman goes from small to big.

 

A good question, but there is no conclusive answer. Here is a good link to an article that covers better than I can post the answer to your question. This link was original posted over on HP.com by skeird.

Intakes

 

3" is too wide for a CAI on our cars (IMO). Ideally, if the engine developed a perfect vacuum and was pulling air through a pipe, the flow would be a function of the pipe "resistance". A narrower, or rougher, or "bendier" pipe would offer more resistance than a larger, smoother, straighter pipe. However, for a given flow (volume of air per second), the average velocity of the air is determined by the diameter. A wider pipe has a lower velocity and the narrow pipe has a faster velocity.

Think of a garden hose. You have the flow coming out in a steady stream. now pinch it towards the end or block the end with your thumb. You've reduced the flow a bit, but you've increased the velocity substatially. That's the trade-off with intake design.

You want to have more velocity of the airflow into the cylinders, but you also don't want to restrict it in any way. So you look for an optimum pipe diameter. One that maximizes flow and keeps the flow velocity high. I believe this is around 2.25 to 2.5 inches in diameter. 3" would slow the flow down a lot, but be much less restrictive. 2" is more restrictive, but a much faster flow.

Of course, this is for a simple pipe. Once you add bends, and factor in the throttle plate opening and closing (and the fact that the engine develops less vacuum the higher the RPM), and you get into many design issues. Random's design was pretty good as was the "martini-shaker" one that I think Red designed (it looked like a martini shaker in shape, narrow at one end, widened at the other, then narrowed quickly; there's a pic around here somewhere).

Simple answer, I'd go with the 2.5" pipe.

good luck,
ac

edit-- I based the above analysis on our CFM requirements. The above article is about Hondas with a higher redline (although I don't know the displacement). If your engine was craving a lot more flow, a wider pipe may work better. But for us, I think 3" is too big (I tried 3",2.5", and 2.25" when making my CAI).

[ February 21, 2003, 08:49 AM: Message edited by: Curtas ]

 

thanks for your help. smile.gif

 

the diameter size chosen also depends on where you want the power increase. as curtas said, the smaller pipe would yield a higher intake charge velocity, but would offer more restriction. the smaller pipe would be better for lower-end power, whereas the 3" pipe would be better for high-end power. with a large pipe, you may actually lose a little bit of your low end, but will be gain more top end. the reason a smaller pipe would help with your bottom end is the rate at which the cylinder gets filled with air, which depends a lot on the velocity of the air, but then you need to take into consideration the rest of your intake system, and the cfm requirements of the engine. furthermore, when it comes to intakes, you're not going to gain a massive amount of hp anyway, so the difference in piping size is pretty miniscule, unless you're contrasting 1" vs. 4" pipe. i have a 3" on my tib, and i love it. i haven't tested other diameter pipes. to understand this better, think of bornoulli's (i think that's how you spell it) law. basically, the smaller space air has to travel through, the lower the air pressure and the higher the air velocity will be. forumla one cars benefit from the few millimeter ride height they run because this creates a low-pressure area under the car, which aids in downforce.

[ February 21, 2003, 01:17 PM: Message edited by: turbulence ]

 

well what so you guys think about the half 2.5 half 3" idea like iceman?

 

The only problem I see is that airflow hates change. Anytime you have a sudden change in diameter, you get turbulence. Turbulence is already in there, but the sudden change will make it worse, which makes the pipe seem smaller to the airflow. So, the more turbulence, the more resistance (like I said, just like using a smaller pipe).

So, the transition from 2.5 to 3" would have to be gradual, or at least smooth. You would definitely want the 3" pipe off the TB and the 2.5" by the filter. Reason being: you would have sort of a "resevoir" of air in there for shifts. When the throttle plate opens quickly, there's more air right there, rather than a slight delay while the air gets sucked up a narrower pipe. I've read this theory several places, and I'm not convinced it makes a huge difference; but I haven't tried and tested it myself, so it may work.

Ideally, you would want some sort of variable geometry intake that would optimize itself for the engine load, rpm, and throttle position. Figure out how to do that cheaply and lightly and you will be a millionaire. smile.gif

If you can find it, why not split the difference and get 2.75" piping?

just a thought.

ac

 

Uh..have you see the New AEM V2 Heimholtz resonator intakes? There is a proven sonic/aerodymanic theory in using a smaller diameter pipe then increasing diameter in a "dramatic" fashion. By changing the diameters/placement of the size change, and the "scale" of of the size change, you can "tune" the intake to perform better over a certian RPM range, or over the entire RPM range.


After doing about 75-100 tests on various different intake styles, tubign sizes lengths, etc etc etc. I can make a few reccomendations.
#1. Go with 2.5" piping. The 2.5" intake will have more air speed, the air speed is what helps fill the cylinders.
#2. make your bends as smooth and gradual as possible. One of the reasons the 'random special" CAI works is that you CAN'T make sharp bends with that tubing.
#3. make as few bends as possible, and make them as complex as possible. What this means is that rather than 2 45 degree bends(one left 45 degrees and one down 45 degrees), have 1 complex dual bend (it goes left AND down 45 degrees in one bend). Again, this is one of the reasons why the flexable piping in the random specal worked.
#4. Make the intake as SHORT as possible, but long enough to get to cold air.

 

ok so what i am understanding from everyone is that i should just go with the 2.5"? there is only one semi hard bend... maybe like 65degrees but the rest is almost straight.

Curtas - i couldnt find 2.75" anywhere

thanks for all the help guys. good to know people still like to help

 

2.75" tubing is a BITCH to find. It's out there though.