Technical > Matt Shaff's Engine Shop

Zoomies vs collector headers

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masracingtd1167:
When we first tested with collector headers was a long time ago and yes it was same day same conditions . That being said we were running injected on gasoline in c/d so a tenth was a huge gain ! So I stuck with that theory for years ! Like I said we put the zoomey on recently and noticed no change but it was different days . This season I will try a a to b to a test just to see what happens !

denverflatheader:
My first response would be the glass of water is in what could be termed a low pressure condition.  Within an engine’s exhaust system, there would be again what I’ll term low pressure condition as long as the engine is not expelling exhaust.  Once the exhaust pulses start, the low pressure condition would diminish, and as the engine rpm increases from idle to redline, the low pressure condition may not be measureable.  My guess is the Bernoulli effect shown by Roger’s example may also diminish with higher rpms.  That being the case, design the exhaust exit for optimal forward thrust and traction.

Agree there’s hp increases with properly tuned exhaust, however, even more hp gain with camshaft options.  Back to Roger’s question; if you want every single hp, you must design your exhaust system properly.  If you have headers and collectors with incorrect tube diameter and length for your engine and camshaft application, you might be equal or even outperform that "mistake" with a suitable set of zoomies.

Here’s a well written article on effects of camshaft design on scavenging from Specialty Products Design, Inc., Company started by Jim Hill.  Note possibility on achieving greater than 100 percent volumetric efficiency:

“The exhaust systems role in increasing engine performance centers around improving volumetric efficiency. Volumetric efficiency (VE) refers to the ability of an engine to intake and expel gases (i.e.: air/fuel and exhaust gas), in relation to the actual pumping volume of the engine. Free flowing intake and exhaust systems help an engine to achieve this. Achieving greater than 100% VE is done in part by optimizing exhaust gas scavenging to draw out exhaust and bring in air fuel mixture during valve overlap. As the piston reaches the top of the exhaust stroke, it dwells as the crankshaft sweeps across the top of its stroke. This is where valve overlap occurs. Before the piston reaches Top Dead Center, the intake valve begins to open. The trick is to design the exhaust system so that the exhaust pulse (pressure wave) leaves behind a pressure drop or vacuum to take advantage of the valve overlap. If successful the combustion chamber will exchange residual exhaust gases for a fresh air/fuel mixture before the piston has any real effect on the intake charge.

To design a successful exhaust system or tuned header, the tube size and length are selected based on a list of engine specifications and application characteristics. The tube size controls the speed of the exhaust pulse, too big and the velocity (energy) is lost. The tube length is all about timing the pulse to synchronize with the cam in a specific RPM range. 

At the collector, the timing of the pulses is crucial to scavenging. Imagine a four lane freeway on ramp merging into one lane. If you get the timing and speed right, the pulses draft each other like stock cars at Daytona, increasing their speed.  This is where the Merge Collector comes in. It makes that transition from primary tube to collector as smooth as possible. This reduction in turbulence helps maintain velocity through the collector, thus increasing the scavenging power of the header system.”

wideopen231:
Ok while we are on exhaust flow and zoomie. Old thing from harleys especailly with drag pipes.They made a cone shaped piece that goes in between pipe and head.Idea it icreases velocity.Band aide for improper pipe being used.Dragpipes suck IMO.They add some needed restriction also.

question has anyone tried this on N/A engine,especailly with zoomies? Have thought about making a set to test at some time.

Probably well know but here is another thing on flow.The adapters made for sbc running bigger pipes that relocate bolt holes can also increase exhaust.Ind cylinder heads was selling plate for Hemi heads at one time 500 per set.Mine cost 100 per 3 sets and two days on mill.You have to match ports in basically make it a longer port.Now this was all done on blower motors and be beifit for N/A motors.

dusterdave173:
I know that when I ran a door car we ran about an 18 inch torque tube on the end of the collector--we started with about 2 ft --put a yellow tire marker crayon line down the tube--made several good runs and the wax crayon would be burnt to a certain distance we cut he pipe off right there--Car ran faster and the 60 ft was better--the sound of the car changed so much I could not believe it--folks beside the starting line always covered their ears after we 'tuned" that header--it was awful to be inside or beside of it during burnout!! Would knock your ear drums out

dreracecar:
Jim Fueling (rip) came up with those anti-reversion cones/headers back in the late70's, if they worked, they would still be used today you think?
 Again, long runs at a constant rpm could show some improvment (B'ville) but for the short duration of a drag race and that the classes that allow collectors are index/bracket---whats the point??

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