Quote:
Originally Posted by jran76
No doubt the Stillen makes good power on the dyno compared to the stock boxes, but is hard to simulate what the factory intakes are designed for on a dyno. They are specifically made to operate more effectively while the car is in motion, and designed to force more air in as speed increases (something a dyno cannot replicate). Even with large fans this is difficult to simulate on a dyno.
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There's something to be said for that for sure (the general point that the dyno models street/highway airflow poorly). Keep in mind the limits of that effect though. No amount of increased airflow pre-filter (even a 100mph fan right in front of the bumper) is going to cause any sort of forced induction effect.
Bad airflow could result in a lack of available air/pressure at the filters (i.e. maybe your intake placement is so bad that the engine can't draw in the air volume it wants to, because of a low pressure area near the filters at speed). Most intake designs aren't so tragically poorly tested as to suffer from this problem though.
Mostly intake changes are only going to affect a car significantly in one of four basic ways (most of which can be seen on the dyno, to some greater or lesser degree, or can be seen by monitoring intake air temps while driving):
1) Changing the CFMs allowed to flow through the filters. Assuming the intakes/filters are restricting intake flow to a lower CFM than what the engine would otherwise pull, getting rid of some of that restriction will help at high air flow volumes (high rpm).
2) Changing the temperature of the intake air (IAT) (colder is better, and the more you're picking up external air instead of engine bay air, the colder it gets).
3) Changing the available air volume in the intake tubes (between the filter and the intake plenum proper). I don't claim to fully understand the effect of this. it would seem this would improve response to the throttle plates opening up, since you have more available post-filter air to immediately suck in via engine vacuum. On the other hand, if it effectively acts as an extension of plenum volume (does it?) it would actually reduce your throttle response by a bit.
4) Airflow smoothness. Ideally you want laminar flow, no crazy turbulence to hold up the engine's draw of air. Changing the intake configuration could have large positive or negative effects here.
We know, for example, that it's obvious an intake like the Stillen Gen3 wins over the stock setup on items 1 and 2 (CFM and temps). Even if you put K&N drop-ins on your stock airboxes the G3 still wins on CFM, just look at the filter area and it's obvious.
There are ways to get the stock airboxes to beat the G3 on IAT (e.g. intake ducts cut into the top of the bumper that route directly to the stock holes through the radiator core support), but they look a lot more rain-problem-prone than the default G3 setup. For that sort of thing, I'd rather run an L-shaped duct up to the G3s (e.g. Modshack's custom ductwork) which would tend not to push water up into the intake and again lower IAT further.
As far as airflow smoothness goes, the G3 seems to be designed well. Post-MAF tubes that replace the factory crinkly-tubes probably help with that as well.
I think the only real question where people might have doubts after trawling through all the available evidence and design factors is: what exactly are the effects of the greatly-increased intake tube air volume the G3's have between the filters and the throttle bodies? Whatever your take on that issues is though, I don't believe it would be affected by rolling airflow to the bumper. FWIW my G3 setup has great throttle response in neutral. I don't remember detecting any increased throttle lag from that install.