Originally Posted by team-integra.net

A. Short Ram vs CAI


When hooked up to a single stage runner intake manifold, the old AEM CAI (single chamber design) provides some gains in the upper rpms and an increase in power from 4000-5000 rpm ( known as the " AEM hump" where it was first seen. I guess since the Injen CAI has a very similar design to the AEM, we can now also call it the " Injen hump").

However, does a CAI make more power than a short ram with the same diameter and filter material? For folks with single stage runner intake manifolds and mega cams that can rev up to 9000 rpm or more, the AEM/Injen- style CAI actually stops making more power after 8000-8300 rpm . The gain in power for AEM that is quoted in the ads occur at the famous "AEM hump" and not in the upper rpms after 7000 rpm.

Believe it or not, a short ram with the same diameter does pretty well in the upper rpm range from 7000-9000 rpm ! Is it just about getting "colder air" that makes the CAI appear to be better? What role does the intake tube's length play in making big all motor power? Is having a constant diameter different from having a tapered tube?

You may not have noticed this isolated gain from 4000-5000 rpm before on the AEM CAI's and single stage manifolds but look at any Integra LS, Type R, or Civic B16a dyno with an AEM CAI and there it is sticking out like a sore thumb by itself....this is what most people "feel" as a noticeable gain on the butt dyno after installing one of these. The more relevant gains at the upper rpms where the truly faster cars (with proven timeslips) make power are not "felt" by the butt dyno.

Sakai's Intake in his 2000 Championship N/A Daily Driven ITR :

In the 2000 NIRA Comp4 all motor championship final, Stephen Sakai ran his 1997 ITR to a high 12 sec et beating Jeff Taylor's B18C5-powered GSR using a homemade 3 in. diameter short ram intake with a K&N RU3130 filter in green . Jeff's car had an AEM CAI (see dyno below).

http://sgt.b16a.com/tuning.html

Here's a dyno of Jeff's and Stephen's cars back then before the finals:

Quote: Originally posted by Jeff Taylor 1999 and 2001 NIRA Comp 4 Champion

basically you can see from these (dyno) plots why Steve just killed me on top end and my car was being held back by the jdm 4-1 that I modified. It's actually very interesting. It also shows that blast of power the aem gives you (only) from 4-5k rpms...lol. yup...thats about all it does. This is where they can make crazy hp statements....they aren't really fibbing...look at the HP increase at a given rpm...Steve was telling me it was the short ram intake....but that damn aem had me fooled until I did this comparison and saw for myself. He gets the credit for it.

I'm not saying that ram air isn't better...I'm saying that short ram in my opinion seems (remember I said "seems") to be fine. Look at the (aem) plot...its nothing more then a power spike. I'm sure it's useful but once you get past it, its very difficult to tell if its beneficial to any degree

Here's Val's comparison of a 3 in. diameter short ram in red and a 3 in. diameter AEM CAI in blue on his B20 nonVTEC with Crower 62404 cams, a JDM 4-1 and 2.36 in. exhaust. The short ram version was not tuned to it's potential either. Remember this is a comparison of the 2 intakes on the same engine. The only thing that has changed is the intake.

When the diameters of the intakes are identical, there is virtually no difference between the 2 intakes after 5700 rpm to the redline. The CAI is superior only at the AEM hump.

Now some of you CAI people may argue that a chassis dyno does not take advantage of the colder air, since the car is stationary and in a moving vehicle, cold air feeds the CAI. That test, comparing a CAI with a fan blowing air to the fenderwell to a short ram (with the same diameter and filter material), on the same car may show a difference, since the temperature differential may be greater than on a typical chassis dyno pull...or will it?

The temperature differential between the outside ambient temp. and engine bay temp. under the hood at the short ram intake opening has been measured while an Integra is travelling at speed. There is virtually no difference. We can expect the temp/ effect between short ram vs. CAI to be not as big as people think.

In Formula car single plenum intake manifold testing, we see that the same rule is consistently seen, when it comes to relating intake length and the location of maximal volumetic efficiency (cylinder filling) along the rpm range (ie. shorter length shifts the maximal filling efficiency higher up the rpm range). Here is the graph showing volumetic efficiency vs. rpm for different length intake tubes in a single plenum, single stage runner IM ( from http://www.eng.ed.ac.uk/~jchic..._html):

Longer pipes shift the max. filling efficiency to a lower rpm and shorter pipes or no pipe shifts the maximum filling efficiency to the upper rpm's.


Some short ram people would say that bigger VTEC race cams would really show how good a short ram can be above 6500 rpm.

For now, Steven Sakai's performance at the 2000 final and Val's dyno (the only one comparing the same diameter) basically says there is no difference, as long as you get the diameter right (i.e. more than 3 in. ID in a single chamber design).

It makes scientific sense from a fluid dynamics point of view :

A bigger diameter tube allows more air to go in but at a slower speed (more cross sectional area). The air flow speed needed to make peak volumetric efficiency occurs at a higher rpm compared to a smaller diameter tube.

A longer tube creates faster air flow compared to a short tube (i.e. more pressure differential from the opening to the TB end) and peak volumetric efficiency will occur at an earlier (i.e. lower) rpm. This is why a longer CAI has an advantage in the midrange over a short ram, regardless of intake temperature differences.

Some people prefer short rams and need their powerband to be higher with bigger cams. They get around the temperature controversy by building their own short ram heat shield.


For those on a budget and who intend to upgrade to big cams, big compression, and a big header, a 3 in. ID short ram with a homemade heatshield may be all you need. For people who want some midrange along with some upper rpm gains, the CAI ensures that butt dyno gets what it expects.

B. Is the AEM CAI Still the King?

The AEM CAI (single chamber design) won the 1996 Sport Compact Car Magazine Intake Comparison in a Civic b16a powered EG hatchback with headers and exhaust by gaining more power and higher top speed . Ambient, intake filter opening, and underhood temperatures were measured in the intake test. The AEM ran much cooler than it's competition at the time which were all short underhood intakes (2nd place went to RS Akimoto Ram 1 ).

Since 1996, AEM has been the undisputed gold standard at the top. The latest innovation to this aging design is the bypass valve for people who get hydrolock anxiety when it rains. There has been one recall already related to a fastening problem with the bypass valve and the valve got sucked into the TB causing engine damage. A new clip has cured this problem. It is noteworthy that the bypass valve lowers power by 2-3whp across the entire rpm range but you can sleep at night.

When you're at the top, the competition shoots for you. People always try to build a better mouse trap. Injen was formed by an ex-AEM employee and it's 2 piece CAI is essentially an AEM design with the ability to convert to a short ram. They now have a 1 piece CAI that looks identical to the AEM. Comptech has their own CAI but it is composed of a short ram with cold air being drawn into a pressurized box much like the stock intake and the Mugen intake. The other more well known CAI's on the US market are: the Iceman 2 piece CAI made by Knight Engineering (Knight7254@aol.com) (not to be confused with the Comptech Icebox) and the Canadian PRM CAI. Neither of these were in the 1996 SCC magazine test and came out just after that test was done: they have been around awhile before the newer Injen and Comptech CAI's.

Based on this dyno comparison done at Comptech's dyno facility (test was independent from Comptech) on an ITR with just header and exhaust, the Injen & Icebox make more power from the ITRs at 5600 rpm up to 7500 rpm. All 3 have essentially the same peak whp. Notice the hump in the AEM (red) and Injen (blue) at 4000-4500 rpm.

There is no independent head to head, independent, published dyno comparison on the same car between the Iceman, PRM, ARC, or Mugen CAI versus the AEM single chamber design CAI, to my knowledge.

Originally Posted by tpr magazine intake test

AEM CAI vs. AEM SRI (test engine is a b16)
aem cai


vs.

aem sri