Cold Air Intake

str8maxn · 01-15-2002, 12:26 PM

I am planning to make my own CAI and have a question regarding what size of Mandrel bent piping to use 2.5" or 3"? Could some tell me what size the HS intake is or PRI?

What is the benefit or 2.5" over 3"? Would there be a noticeable difference between the two sizes?

Thanks

AznVirus · 01-15-2002, 02:49 PM

the Hotshot CAI is a 3" diameter, i would go with a 3" diameter because the TB is close to 3" than 2.5". id assume the 3" pipe gets more air, but could offer more resistance. 2.5" might be more free-flowing.

Cue-Ball · 01-15-2002, 03:44 PM

The different sizes of intakes doesn't really have anything to do with resistance, it has to do with smooth/laminar flow of air. It also has to do with what RPM will be best for the given size of tubing. You get better power when your intake and exhaust are free of restriction. However, if the pipe is too large the air swirls around inside because it doesn't have enough force to keep smoothly flowing. So, smaller diameter tubing is better at low revs because the relatively low volume of air moving through the system can flow smoothly without restriction. Large diameter is better at higher revs because the larger volume of air requires more space in order to flow freely. That's why a 3" diameter exhaust will give you more top end but at the expense of low to midrange and a 2"-2.5" exhaust will give you better power down low but will not be able to breathe well in the high revs. That's also why most stock 4 cylinder cars have very tiny exhaust systems. The manufacturers know that the average driver will get more use out of 5 extra HP at 3KRPM than 15HP at 7500RPM. If you want top end horsepower i'd go with the 3". If you want more low-end, usable power (but less of it) i'd go with the 2.5".

Why don't you get ahold of a dyno chart for the HotShot CAI and see if the gains are what you want. If so, try to copy their design. Or, just save yourself the hassle and cough up the money for the real thing.

-Grant

AznVirus · 01-15-2002, 06:16 PM

Quote:

Originally posted by Cue-Ball
The different sizes of intakes doesn't really have anything to do with resistance, it has to do with smooth/laminar flow of air. It also has to do with what RPM will be best for the given size of tubing. You get better power when your intake and exhaust are free of restriction. However, if the pipe is too large the air swirls around inside because it doesn't have enough force to keep smoothly flowing. So, smaller diameter tubing is better at low revs because the relatively low volume of air moving through the system can flow smoothly without restriction. Large diameter is better at higher revs because the larger volume of air requires more space in order to flow freely. That's why a 3" diameter exhaust will give you more top end but at the expense of low to midrange and a 2"-2.5" exhaust will give you better power down low but will not be able to breathe well in the high revs. That's also why most stock 4 cylinder cars have very tiny exhaust systems. The manufacturers know that the average driver will get more use out of 5 extra HP at 3KRPM than 15HP at 7500RPM. If you want top end horsepower i'd go with the 3". If you want more low-end, usable power (but less of it) i'd go with the 2.5".

Why don't you get ahold of a dyno chart for the HotShot CAI and see if the gains are what you want. If so, try to copy their design. Or, just save yourself the hassle and cough up the money for the real thing.

-Grant

ya what he said

2002G20Racer · 01-15-2002, 09:10 PM

Quote:

Originally posted by AznVirus

ya what he said

Uhhhh huh.

JustinP10 · 01-16-2002, 03:30 AM

Hey guys, before you go too far on this idea... It's already in the works to test a 2.5" vs. 3" CAI... also every combo of the two intakes, 3" top pipe w/ 2.5" lower pipe, etc.... All the setups are going to be dyno tested and we'll find out what combo works the best for top end power, mid range, low end, etc....

Willy Estrada · 01-16-2002, 09:27 AM

Ive seen some Hunduh intakes that are wide at the end (filter side) maybe 5 to 6 inches and narrow near the back. but thier made out of plastic. Maybe this design is hinting to a better performance at low and high end revs. .

Hey Justin, when will that data be out?? Im thinking of making a custom CAI with the $tillen intake on it

Nissan_2.0 · 01-16-2002, 09:05 PM

Quote:

Originally posted by Willy Estrada
Im thinking of making a custom CAI with the $tillen intake on it

Just buy the intake from JWT--Stillen uses the same intake element...i believe the only difference is the machined Stillen logo...and a few bucks.

JustinP10 · 01-16-2002, 10:06 PM

Quote:

Originally posted by Willy Estrada
Hey Justin, when will that data be out?? Im thinking of making a custom CAI with the $tillen intake on it

I'm hoping to get to the dyno later this month, possibly early in February (only a couple weeks away, month at the longest) when we have our next SERCA dyno day here in Az. I have all the components readily available to me, i'd just need to get to the dyno. I'd also like to wait and do it at the dyno day, as it'd help a lot if i could save a couple dollars on the dyno time, as i'm a poor college student.

Cue-Ball · 01-16-2002, 10:45 PM

Quote:

Originally posted by JustinP10
Hey guys, before you go too far on this idea... It's already in the works to test a 2.5" vs. 3" CAI... also every combo of the two intakes, 3" top pipe w/ 2.5" lower pipe, etc.... All the setups are going to be dyno tested and we'll find out what combo works the best for top end power, mid range, low end, etc....

Most car manufacturers make the inlet to the intake larger than it is at the point it enters the throttle body/carburetor. The reason for this is that it speeds up the air going into the engine. A large amount of air enters the intake and as it gets smaller the air has nowhere to go but into the engine. In order to fit the same amount of air in a smaller space, it has to speed up. This venturi effect increases horsepower.

...or something like that.

str8maxn · 01-17-2002, 10:29 AM

I'll really like to see the dyno results between the Home made and other CAI's.. Please keep us posted.

napakapa · 01-17-2002, 08:50 PM

I really would like to see the difference between made by the size of piple, good idea justin

cliffud · 02-14-2002, 05:19 AM

Justin-

Did the data come back yet?

I didn't even know you were collecting info that the dyno day for that kinda stuff.

sweeeeet!

-clifford

P10DET · 02-14-2002, 07:41 AM

Quote:

Originally posted by Cue-Ball
Most car manufacturers make the inlet to the intake larger than it is at the point it enters the throttle body/carburetor. The reason for this is that it speeds up the air going into the engine. A large amount of air enters the intake and as it gets smaller the air has nowhere to go but into the engine. In order to fit the same amount of air in a smaller space, it has to speed up. This venturi effect increases horsepower.

...or something like that.

Actually, the opposite of that. When it goes from larger to smaller, the air slows down.

Cue-Ball · 02-14-2002, 03:07 PM

No, George, i believe you are incorrect.

A certain volume of air is already in the tube. If the tube gets smaller, the air has nowhere to go but through it. In order to fit the same (large) volume of air through a smaller space, the air must speed up. This effect is used often in air intakes.

I'd dig up my book on this subject and quote it, but i'm leaving for California tonight and won't have time. If i remember i'll try to post some references when i get back from CA on the 20th.

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