4-1 Collector & "Silencer" Sizing

[Kronos]

I know F1 cars don't a have a silencer, but how do the teams determine the area for the section following the collector?

I have a flat-four with a 1-4-3-2 sequential firing order that i'm building a new exhaust for. I've the headers made, and I'm wondering if the cross-sectional area of the "silencer" section/that bit after the collector should equal:

1) The area of a single header pipe, because only one cylinder is delivering gas at any one time.

2) The sum of the areas of the four headers, because:

At maximum RPM (~5800), there may not be enough time for any one cylinder to fully exhaust its contents before the discharge from all of the other cylinders reaches the silencer. Therefore a situation exists where at high RPM, the volume (or mass) flow rate through the silencer equals that flowing through the sum of the four headers.

Obviously number this depends on the gas velocity (and therefore temperature) and header length, but I can only guess at the velocity, which is making things more difficult.

My aim is to keep the cross sectional area of the entire system the same, so no additional backpressure is generated, and so that gas velocity to the very end remains equal to that in each of the headers. The 4-1 collector obviously messes this up, because of the step increase in area, but my question about the silencer area still confuses me.

I haven't found this clearly explained elsewhere in the forum, so perhaps someone could advise?

- Kronos

[strad]

In part it matters whether you are looking for top end or mid range power.

[Jersey Tom]

Why have a cross section change?

Wave reflection.

(-not a powertrain guy)

[Kronos]

In part it matters whether you are looking for top end or mid range power.

Could you explain what's best to do in this situation if I were looking for either one of these please?

Why have a cross section change?

Wave reflection.

(-not a powertrain guy)

I'm trying to not have cross sectional area change, but I'm actually unsure of what I should keep the area the same as. One header, two, three..?

The total system length is optimised for what I believe to be the best pressure wave timing. As far as I understand, the diameter of the silencer may well affect the pressure wave reflection also.

- Kronos

[hardingfv32]

[As far as I understand, the diameter of the silencer may well affect the pressure wave reflection also.

Wouldn't the function of the silencer by definition kill or dampen the pressure wave?

I have always found the pressure wave generated by the primaries to to be many times more important than all of the other wave activities.

Brian

[strad]

There are silencers/mufflers that flow more than a straight pipe.
Something like this...

The vacuum effect of the Aero Exhaust Muffler actually improves performance over just a straight pipe. It's simple aerodynamics

Get ya a good four into one for best top end or a tri y for better midrange..since you don't have money or time to experiment I'd suggest just getting a good set from Hooker or one of the top exhaust specialist.


[youtube]http://www.youtube.com/watch?v=iDTTOa77efs[/youtube]

[PhillipM]

Anyone that believes that c**p needs their head checking.

[strad]

Works on our dyno
What class is this thing anyway.
FF? Is it open wheel?

[PhillipM]

Works on our dyno
What class is this thing anyway.
FF? Is it open wheel?

Haven't seen many strapped onto racecars myself. Are you sure it worked on the dyno or did you just test it versus a straight pipe and forget you'd changed the resonance frequency....

[RaceFaceXC]

wouldn't tuning the collector for the same rpm as the primary length/diameter be the best way to max potential of the design? in other words a collector designed for mid rpm performance after primaries designed for high rpm performance would be destructive to performance, no?

If this is indeed the case, what are the primary size/lengths and what rpm did you target for peak efficiency when designing them?

[hardingfv32]

wouldn't tuning the collector for the same rpm as the primary length/diameter be the best way to max potential of the design?

He is using a silencer on the end of the collector, what does that do for the pulse tuning of the primaries and collector?

I think there is a question about whether the volume of the silencer can be tuned to compliment that pulse tuning of the primaries and secondaries/collector.

Brian

[Kronos]

Works on our dyno
What class is this thing anyway.
FF? Is it open wheel?

It's for a Formula VEE single seater. Open wheel, yep.

If this is indeed the case, what are the primary size/lengths and what rpm did you target for peak efficiency when designing them?

Sorry, but how do you tune the collector? The primaries are all 1.1 metres long to the collector.

At the 4-1 collector, the area increases instantaneously to ~4 times that of a primary. This step area change is unavoidable with this design. The silencer is a straight-through design, so what I'm still unsure of is if it's best to maintain the area of the collector through the remaining (silencing) pipe, or reduce it again.

He is using a silencer on the end of the collector, what does that do for the pulse tuning of the primaries and collector?

So yeah it seems understandable that the holes in the silencer's surface do affect the pressure-pulse return up the primaries. If it didn't, it wouldn't be "silencing". So, is this an undesirable affect, and how large is it?

- Kronos

[RaceFaceXC]

Sorry, but how do you tune the collector? The primaries are all 1.1 metres long to the collector.

At the 4-1 collector, the area increases instantaneously to ~4 times that of a primary. This step area change is unavoidable with this design. The silencer is a straight-through design, so what I'm still unsure of is if it's best to maintain the area of the collector through the remaining (silencing) pipe, or reduce it again.

What is the primary diameter? Is the collector a quality merge design? I don't think a 1:4 ratio is ideal for your application as it will allow gas velocity and temp to drop more than ideal. To design a "perfect" header for your engine you need to know target rpm for peak effiency (tq), exhaust valve size, cylinder displacement. I am probably forgetting something, its been 5 years since I designed and built my subarus headers.

He is using a silencer on the end of the collector, what does that do for the pulse tuning of the primaries and collector?

So yeah it seems understandable that the holes in the silencer's surface do affect the pressure-pulse return up the primaries. If it didn't, it wouldn't be "silencing". So, is this an undesirable affect, and how large is it?

I my research I found that the collector outlet size/design is most important for determining gas velocity and that the pressure wave bounces from the end of the primary, so collector and after should have minimal effect on pressure wave tuning.

Pipe sizing after the collector should remain a constant diameter to maintain velocity, unless there is a need to speed up or slow the exhaust gases. If the silencer outlet diameter is sufficient for your flow needs, keeping the piping after the same size would probably be best for getting the exhaust out quickly.

Check out burns stainless website. They have some brief tech articles about header and exhaust design and reference some good sources you could investigate for more detailed and in depth info on header and exhaust theory.

http://www.burnsstainless.com/techarticles.aspx

[strad]

Totally agree....You might want to talk to these people..give em a call
http://roxannesheaders.com/

[hardingfv32]

Or me! harding'fv32'

Fab my own stainless systems which I test on my own dyno. Years of experience with 1200, but have some current data on 1600.

PM me

Brian