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Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

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Old 01-28-2005, 02:08 AM   #21
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Quote:
Originally Posted by willwren
It helps a tad with carbureted cars. But how many of those are still on the road?
Not enough? Well atleast stuff from 64-72....

I saw something once where it was a muffler deal that claimed to speed up the air from it'* shape. Maybe like a venturi, but it was complete BS.
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Old 01-28-2005, 05:55 AM   #22
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I'm with project on the backpressure deal, its probably one of the more rampid myths running around. With that, he'* dead on. If you could change the laws and make high velocity with NO backpressure whatsoever you'd have one hell of a setup. You don't want/need backpressure, its an unwanted byproduct. As he said, why would you want the engine to try harder to push the exhaust out? Because they do tend to go hand-in-hand I can see how people get the wrong idea. But its like saying "My supercharger isn't running hot enough" when referring to the need for a smaller pulley. Point: Backpressure is not the goal.
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Old 01-28-2005, 02:49 PM   #23
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there are three (more too) different effects that an efficient exhaust has, but a big one being low to no backpressure to restrict exhaust flow (more air+fuel = more power) and allow unrestricted escape of each cylinders exhaust gases.
But the most important things you can tune in any exhaust system is each cylinders scavenging effect (where by a hot gass flowing at a high velocity through a small tuned ex pipe will actually help draw in the intake air/fuel (cams valve lobe overlap) because as the high momentum of the gasses will draw a vacum in the cylinder) a big part of this is keeping the exhaust gas heat in the exhaust gases-hence wrapping your exhaust to prevent this)
The other part of the scavenging problem is fighting reversion (much less common on possitive displacement blowers (intake manifold pressurized)) where the exhaust gases (whether by too large a primary exhaust tube size for cylinder displacment, or wrong rpm/powerband tuning) will have too low of a velocity to scavenge the cylinder properly and will actually stop flow and start to get sucked back into the combustion chamber hindering the combustion process (try driving at WOT with your EGR open and see how much it hurts perf)
Reversion tends to happen at lower engine RPM'* (some manufacturers actually tuned this effect for various EGR'less systems) but can be helped by using a "stepped" primary tube design (small prim tube goes to a larger primary tube with a "step" that helps keep the exhaust from commin' back) and tunning it to the RPM/powerband of the engine (the distance from the cylinder port the "step" is).
scavenging is a little more complicated depending how you join the primary tubs to the header collector (per the firing order etc) and their length you can gain efficiency with the scavenging effect or loose it completely.
and since a good scavenging design at it'* tuned power range can give much better VE in the engine (it'* like a free 1-2psi of boost!) for good demonstration some of the better bracket racers/sportsman racers have gotten an extra 20-30Hp (in the tuned powerband) outta a high performance V8 JUST switching to a good set of scavenging headers (doug thorley etc)
allota physics/ research is used to go really fast when ya got a full time racing buisness (like Jegs/Summit/Heddman etc)
hope this gives ya some more fer this myth
also,
BonneMeMN Posted: Fri Jan 28, 2005 12:08 am Post subject:
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"I saw something once where it was a muffler deal that claimed to speed up the air from it'* shape. Maybe like a venturi, but it was complete BS. "

however there are several venturi type exhaust collectors (where the primaries go into a common collector pipe) where (depending on tuning) there is a tunable/replacable venturi inserted into a normal collector to help the scavenging effect (or the venturi is part of the collectors body design) this has shown on some V8'* to be an easy 5-10Hp is certain area'* of the powerband
as for a venturi muffler...eh it'* probably a restriction and doesnt do much as the exhaust gases have cooled and slowed down by the time it gets there.
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Old 02-01-2005, 01:06 PM   #24
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ok ive been doing some thinking about the twisty air things..
i dont think they would help people with carbs that much either, because in a carb u dont want the air to swirl untill after the carb, because the venturi is going to need the air to be straight anyway, which will straighten out the air before it is even mixed with the fuel, so from the looks of it a twisty air thing is only a restriction to airflow
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Old 02-01-2005, 01:54 PM   #25
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The tornado helps carbureted cars in a different way. The ineffiecient intake manifold designs didn't flow very well. The twisting air was able to turn corners more efficiently to flow through the intake. It wasn't meant to help flow in the carb itself.
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Old 02-02-2005, 01:11 AM   #26
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but wouldnt the carb straighten the air out before it got to the manifold
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Old 02-02-2005, 02:41 AM   #27
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Nope. Doesn't work that way. Think of it literally as a tornado, twisting and turning. They actually work in the right application.
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Old 02-02-2005, 10:24 PM   #28
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It'* not a product but a common practice. Removing your MAFF screen is NOT a good thing, and in MANY cases hurts performance. It is one of those things that is deffinately there for a REASON.

Oh, and glad some know this.. BACKPRESSURE IS NEVER GOOD! You will never get rid of all of it but the more the better.

Dumping your exhaust either by removing the catback or running a cutout will really only help on higher power cars. Cutouts work good, you will see more gain on higher power cars. The closer you can get to the block the better, as you will still have velocity.
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Old 02-08-2005, 01:12 AM   #29
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ok found another one the "Smog Buster Fuel Disk" by gofueldoctor.com
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Old 02-08-2005, 01:16 AM   #30
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Quote:
Originally Posted by caminated2k
It'* not a product but a common practice. Removing your MAFF screen is NOT a good thing, and in MANY cases hurts performance. It is one of those things that is deffinately there for a REASON.
Depends on the application. I've proven it myself with a scantool and FSM. But it requires a VERY good intake setup to delete it. Also, remember that there are different diameters of throttle bodies, and the air flows through the LIM of the Series 1 a bit different than that of the Series 2. Some may benefit, others may not.
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