k24em2

As many of you know, the angle at which a merge collector "merges" is one of the variables you can change when building a header. I see alot of collectors that are very steep angles, and some, such as burns which typically use between a 10-20 degree merge depending on few different things. Why would a shallow merge angle be preferable over a steeper merge angle? I'm not asking for people to give away propietary info (casey *cough* ) but it would be nice to see what reasoning people have behind their designs.

DaveF

i am by no means an engineer or anything close to it.

but my understanding of a nice "long" collector is that the exh. gas will flow more smoothly into the turbine, and will have less turbulance than a collector with more of an angle on it.

RMF

The different angles are for different RPM ranges.A real short steep angle is for a higher RPM range.A long one would be for lower RPMs


Modified by RMF at 9:00 AM 12/21/2005

Ekasey

We used 15 deg. on most applications because with the particular way we size our collectors, it works very well, and yes we have verified this through rigorous testing on the engine dyno.

We use a 25 deg. quite a bit too on turbo stuff for packaging reasons


lets get your brain really ticking
I have seen multitudes of different collector configurations in F1 even flat collectors and collectord with merge angles as large as 45 Deg.

RMF

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Casey@Burns &raquo;</TD></TR><TR><TD CLASS="quote">We used 15 deg. on most applications because with the particular way we size our collectors, it works very well, and yes we have verified this through rigorous testing on the engine dyno.

We use a 25 deg. quite a bit too on turbo stuff for packaging reasons


lets get your brain really ticking
I have seen multitudes of different collector configurations in F1 even flat collectors and collectord with merge angles as large as 45 Deg.</TD></TR></TABLE>
Me too .I mostly use 15deg. I have tried the real steep F1 type but lost alot of power down low and mid.Remember when we talked about that about a year ago? Case

beepy

Speaking from a pure fluid dynamics standpoint, I cannot think of any reason why you wouldn't want as acute of an angle as possible. (Sorry for the double negative)

Thinking in generalities; if the collector had an angle of 0° it would be a straight pipe and would be the best thing possible, while a 90° collector (like a log manifold) is known to create much more restriction than a collector.

Therefore, the shallower the angle, the less head loss the manifold will experience at the header. The only reason people don't use 5° collectors is because of space issues.

tony1

That makes sense, but i think there's more to it than that. I mean, if F1 used 45 deg. at one point then there has to be. Maybe casey or RMF can explain more.

Ekasey

10 deg is a different angle then the 15 and if i remember my data correctly the 15 showed more promisig results
'
I belive the formula 1 stuff used 45 deg. stuff due to packaging constraints

beepy

It may simply be that the 10° collector had more volume than the 15° collector. Taking into account the volume of the total manifold, there is bound to be a ideal case where the most power is made.

RMF

Its not the flow .Its the scavenging.The faster the air goes through,The steeper the angle also the area inside too.

99_GS-T

Collector volume could be easily controlled and manipulated with merge angle. I could be wrong, but an exhaust header with a larger collector volume will have a more pronounced resonance tuning peak. This could effectively increase the exhaust scavenge thru a limited RPM range.

It seems like a collector with larger angles between the runners would have a higher amount of pressure drop however. If the header isn't tuned to a certain RPM range designed to accentuate certain aspects of the motor, I would think the steep collector could easily hurt power thru much of the RPM range with small gains on the top end from the increase in collector volume.

It's kind of like an intake manifold. Tune the plenum volume to match the head, cam and runners and you can pick up large gains in a limited RPM range with minimal losses thru the rest of the RPM range. Screw up and put the wrong plenum volume on the manifold for the rest of the motor and you lose power everywhere but above the HP peak.

Seems like the best idea for the average fabricator that doesn't know the math and everything else behind resonance tuning and all that jazz would be to make the merge as shallow as the space they have available will permit them to make. It might reduce the resonance tuning effects of the manifold, but if they didn't calculate everything out to begin with, this could keep them from building a manifold that has a higher amount of pressure drop.