Among the most popular modifications to do to a vehicle is purchasing an aftermarket intake. When one decides to do this they are confronted with a miriad of choices. Short ram, cold air, metal, composite design and so on, I wont even go into the choices on filters.
For most the purpose is to increase the power of an engine. But there is a lot more to intake design than one that will pick up air from a cooler place. True, you want your intake temps to be as close to ambient as possible. However, there are many other considerations such as the overall design of the intake tubing, diameter and so forth. Choose one that is too large in diameter and your MAF will not read correctly and cause fueling issues. Choose one of the wrong material and you will eventually defeat the purpose of the intake to start with.
Personal Experience
When I owned my Focus I struggled early on in getting an effective intake. The design and placement of the intake manifold made it nearly impossible to defeat the effects of heat soak. My first inake, a short ram design, was a metal tube and you could litterally feel the power difference when the tube became heat soaked.
My second intake was a FIPK kit that was plastic. For the most part it takes care of the heat soak issue, but even over a long drive it would still eventually saturate. Furthermore it had an inherent design flaw, a very sharp 90* bend. Couple that with the 90* bend the air flow has to go through with the intake manifold and you soon loose a great deal of the potential of an effective intake system.
While you can pick up a few ponies with an intake on the Focus, the design of the intake manifold works against you in maximizing the potential. I never used a CAI on my Focus due to the hobby I have and the potential ramifications from using such a design but I also was aware that due to the design of the CAI's for the Focus that the benefit from using one was not going to be of such significance versus the cost to warrant using one even if I did not have the hobby I do. You'll see why shortly.
The design and supporting testing
The testing I have read is not for a Focus, but you can bet your bottom dollar the principals are the same. First, you do want cooler air but there is a point of diminishing returns on that quest as you will see. There are also benefits from a properly sized tube and air velocity.
The testing was done on Grand Prix's in order to see what type of set up works best. There are a miriad of aftermarket intakes for the Grand Prix but one of the most popular is what is known as the Fender Well Intake heretofore known as a FWI.
It consists of 3" PVC or ABS tubing and a filter. The drivers side fender, inside the engine bay, has an opening large enough to get a tube through and the fenderwell area is large enough to support a decently sized filter. As well, using something simple like roof flashing you can isolate the filter from the engine bay, effectively reducing intake temps.
I have done the testing and I know for fact that it does reduce temps. In one case I was running some 25* above ambient where as the FWI was less than 10* above ambient. So it does reduce the intake temp but as you will see it negates its benefit before the air even reaches the throttle body.
The test was done (And I didnt do the testing by the way, it was done by an aftermarket company for the Grand Prix that runs a 9s 1/4 mile Grand Prix) using various tubing and configurations common to the Grand Prix. I will comment on a few and if there are any other questions just post them up and I'll do my best to answer them.
First, the results:
CFM | Intake Cofiguration
238 5 inch straight PVC tube, 4" diameter, no filter
227 9 inch straight PVC tube, 4" diameter, clean K&N filter
220 26 inch straight PVC tube, 4" diameter, no filter
183 90* bend added
181 7 inch straight PVC tube, 3.5" diameter, clean K&N filter
159 26 inch PVC w/90* bend, 9 inch K&N filter
119 Stock GTP Throttle Body w/MAF Screen out
107 Stock GTP Throttle Body w/MAF Screen in
Okay, what does this all mean? First, let me explain that the MAF screen in the GTP is a honeycomb type screen that is in the air flow to the blower between the MAF and the throttle body, the purpose of which is to straighten out the air flow for the MAF so it can read better. The problem is, as you can see, it is very restrictive.
First, understand that a 5" length of tube is going to put it right in an extremely hot part of the engine bay because the exhaust manifold cross over pipe runs directly under the throttle body, yet notice that even with all that heat and no filter, the slightly longer tube with a filter was not much worse off.
Notice the effect (the 181 CFM) of tube diameter. 1/2 inch smaller and you loose nearly 25% of the air flow even though you have the engine temps in that area that you do. Notice also the effects (and herein lies the detrimental factor of most aftermarket intake designs) of the 90* bend. The first test @ 183 CFM is again nearly 25% less air flow. The next comparison @ 159 CMF with a much longer tube suffers some 35% less air flow compared to a short no filter set up.
Because the shorter tubes are essentially flowing faster they are not exposed to potential heat soak very long at all. Using a plastic intake such as PVC or ABS is going to further reduce this, some have even went as far as to wrap the tube in reflectix.
So while my Focus intakes where short and in the heat region of the motor, what ultimately was more damaging to their performance, the 90* bends made to turn the air into the throttle body and then the additional 180* bend the air makes inside the intake manifold. Unfortunately the Focus design does not lend itself well to eliminating at least the intake bend.
So what am I using on my Grand Prix. PVC! The length of it was about 9" overall using a Amsoil TS foam filter. When I switched over to the EaA cone filter I had to cut one end off some so that the neck of the new filter would fit over the intake tube. Now my overall length is about 6" at best. My only downfall, a very slight bend of about 22* to clear a couple engine bay components. However, I am now working on an intake that will put the filter within just a few inches of the throttle body and we shall see how that goes.
Conclusion
The testing would seem to support that eliminating all the bends in an intake run that you can is as beneficial as the quest for cooler air. Dont get me wrong, you still want cool air, however, if you have to make bends to get to that source it may be worth consideration whether or not the cooler air will be worth it. Essentially, the straigher the tube the better. Better yet, the straigher the air flow into the engine, the better.
Enjoy.
____________________ My car is a synner! It uses Amsoil Synthetic Lubricants.
2001 Pontiac Grand Prix GTP
It whines a lot, but I like it
