I think you're trying to compare two different things here. The tips I've seen don't let any reversion take place. The openings simply don't allow that to happen. The (fresh air) openings are angled in such as way as to introduce airflow to aid in scavenging the exhaust and nothing else. If I had a pic, that would be worth a thousand words.
maybe something like this then? Now don't get me wrong here.. I'm not arguing for the sake of ego or proving anything.. just trying to understand how any type of tip(regardless of design).. is going to actually help scavenge exhaust, is all. Reduce reversion slightly yes.. but not actually scavenge or pull. Anywho.. it's no big deal, I guess. Was just having a tough time picturing it and wondered if I missed something in my studies. I hate it when that happens.
That's it. The air flow introduced thru the openings I take it is supposed to help scavenge the exhaust coming out. Like you, I'm not sure how well it works, it's just my assumption that this is the purpose of these tips. The venturi effect is well documented though. Without it we'd have never seen carburetors.
wouldn't it be like...sucking on a pop bottle? isn't the exhaust pushed out with the piston? without it open on the other end, how can it...scavenge? I by no means am an expert...:sorry: if anyone thought otherwise...
you just about nailed it bud. the carb venturi analogy that baddad used would only be relevant if the flow were going in the opposite direction to actually go from larger to smaller and create the effect as it speeds up when transitioning into the smaller pipe. And the outer pipe would need to be sealed/merge into the smaller one in the middle to do so just like a carbs bore. So, as I imagined.. that's just a ported exhaust tip and it's physically impossible to increase airspeed(venturi effect).. or unlikely to improve scavanging effect(inertial) with that design. It would only allow a slight anti-reversion effect(reduce wave reflection) back into the main tailpipe, IMO. Although.. I do have to wonder if as the gas is cooled and made denser as it steps through the larger pipe.. maybe there could be some slight increase in negative pressures behind it? But then wouldn't that potential extra negative pressure created by the denser mass be canceled out due to the ported design? That might be a good one for the pro's over at speedtalk. lol I do like the design itself from an aesthetic standpoint.. but unfortunately those designs also allow wave reflection back under the car and aren't the greatest design if sound control is already an issue. PS. you crack me up Frank.. and I really dig your humor.
Maybe instead of discounting this, you should take a closer look at the tips. After looking at them, there is some effect as to helping to pull the exhaust out of the pipe, (thus reducing backpressure) how much it affects the exhaust, only the engineers that designed it could tell you. The outer pipe isn't a single diameter, it flares out towards the rear, not sure what diameter is towards the inlet side. It is smaller in diameter in the middle, thus the "venturi" part of my explanation. Not sure how you'd think the airflow being reversed would help here Groberts ? That makes absolutely no sense to me.
By reducing the air pressure at the exhaust pipe outlet. A Venturi creates a drop in air pressure, that's the force that creates a vacuum. Pretty simple for even me to understand, even though it's been awhile since staying at a Holifday Inn.
Gees you guys are complicating the hell out of this. Its a street car thats hardly driven. Hes not going to notice a slight change in exhaust flow. Just make it fit and drive it Scoop. Square,oval,round ....whatever fits. IF it looks restrictive it likely is.
Well we kinda went off on a tangent, sorry if this is confusing to some. It's not intended for Scoop's car, just something that needed to address a question earlier on in this thread as to how tips (or their angle) could affect the flow.
huh?.. you can't change atmospheric pressure at the tip with that design even if you were to spill it out into a 20 inch pipe with a fancy turbulator at the end. If that was the case then everyone would have tips like this to turbocharge their cars. The pic above shows the inner pipe as constant diameter and flows outwards into a LARGER pipe. Maybe study the venturi design once again and explain how that design is even REMOTELY similar to a venturi? And "venturi" chanracteristics are not what you seem to be talking about here either. What you seem to be talking about here is a "booster" which implies that if you reverse this booster.. .. it will still work like a venturi? And if that's really the case here?.. then it serves no purpose to try and learn anything new from this specific tangent as it just defies the laws of physics. As with most anything physic's related.. you don't get something from nothing regardless of how much you "believe it should work". On the other hand.. I guess it never hurts to dream though.
there are two things the driver behind you should always see when you fly by- your exhaust tips and your taillights