Is the air filter really a restriction on a stock truck?

[boonsur]

A simplified definition of boost would be "packed" air, ready to rush into the cylinder. If there is boost, then there is plenty of air, ready to go. If there wasn't enough incoming air, then the boost would be lessened (in vs. out defines pressure). A free-flowing filter would allow more "in", and thus more pressure. But, the wastegate will limit how much pressure is developed.



In an otherwise STOCK TRUCK (no wastegate mod's. ), does a free-flowing filter really yield any benefit? Is there a lot of room, before the wastegate is utilized? (I don't have gauges, yet). Or is all the "extra" air, just spit-out.



The turbo may spool slightly faster (doesn't have to work as hard to draw air), but will it really be that noticable to performance?

 

[rbattelle]

Remember that pressure and mass flow rate are not a linear relationship. You can certainly increase or decrease the mass flow rate without any effect on pressure ratio across the compressor (until you hit your surge line or stall line). What you do effect is efficiency and/or compressor speed.



Any way you slice it, lower intake restriction means better compressor performance. In the jet engine business it's called inlet pressure recovery: the closer it is to 1 the better. In other words, the closer your compressor inlet pressure is to ambient, the better. Always. Better how? More compressor efficiency means faster spool up and better fuel economy in the long run (but granted, fuel efficiency improvement on these trucks would probably be negligible). Lower restriction may also menifest itself in slightly lower EGT (again, possibly negligible). But the faster spool up would be noticeable.



Someone smarter may correct me or have more to add...

 

[Buffalo]

Air Filters

From the "For what it's worth Dept. " I have a '91, W-250 and an '03, 3500. The 91 is slightly modified. Had a K&N in the stock airbox and with a 30 lb. boost guage, could bury the needle, on full throttle. The K&N let in too much dirt so, I went back to a stock filter, for now. My maximum boost, with the stock filter, is 25 lbs. Just installed the A. F. E. System with the Proguard 7 with the Pre-filter in the 03. No guages yet so, I can't give you figures but, you can feel the difference. Nothing dramatic. But it does have a little more performance. Hope this helps. Joe Fihn. PS- There was a thread, here just recently, pertaining to the cubic feet per minute of flow of a couple of filters. I believe the stock filter, the BHAF, and one of the A. F. E. 's. I found it very interesting. Would be worth looking it up.

 

[boonsur]

Buffalo,



I was watching that thread, which actually caused me to post this question. Does the CFM rating of the filter really matter if the engine, at maximum (wastegated) boost, only uses a certain amount?



The other part of your post confirmed what I thought. Maybe we can acheive more boost before the wastegate takes over. Which would yield a significant performance gain.



I am still wondering (maybe someone can answer), exactly how much boost the wastegate will allow (stock), and what a typical (stock) truck usually runs at. (Do they often/usually hit the w/g)?