4-1 Collector & "Silencer" Sizing

[strad]

there ya go

[olefud]

With FV, as I recall, you’re dealing with stock cams, i.e. little overlap. The intake valve has to be open substantially when the pressure wave returns in order to induce more intake charge (actually, in my view, a denser charge). If you exhaust flows freely, it’s probable the best your going to do. Length won't be very important.

[hardingfv32]

With FV, as I recall, you’re dealing with stock cams, i.e. little overlap. The intake valve has to be open substantially when the pressure wave returns in order to induce more intake charge (actually, in my view, a denser charge). If you exhaust flows freely, it’s probable the best your going to do. Length won't be very important.

Actually the tuned exhaust functions the same as any race engine. The primary lengths have a sensitivity of say 1" at a given RPM measured a low dollar dyno. You probably are right about limited results from the exhaust system do to all the engine restrictions.

Brian

[strad]

Actually in that case scavenging is even more important I think.
You want a simple test for playing with your exhaust?
If ya have to give it more jet it's better,,it you have to take some jet out,,it's not.
Seriously and I repeat I would rely on the expertise of people like Hooker or Roxannes Headers or even Brian than just playin around on your own..Unless of course you have easy and free access to a dyno

[Lancelot28]

Get ya a good four into one for best top end or a tri y for better midrange.

[strad]

In answer to your earlier question...
I would paint my collector and run the car....where the paint stops burning off is about the length you want the collector,,,but that trick is best for WOT operation like drag racing,,but it should be close..cut the collector and if necessary attach the silencer at that point. I still say an Aero,,but as you no doubt know many use SuperTraps or the like. I would want the silencer to be another expansion point. imo

[Edis]

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

3 None of the above

Normally an area ratio of 6 is a good starting point for a merge collector, this will in turn set the diameter for the secondary pipe after the collector.

This area ratio is the area of all primary pipes except one plus the area of the secondary pipe divided by the area of one primary pipe.

Adjusting this area ratio will affect the reflection pulse created in the collector.

[hardingfv32]

Normally an area ratio of 6 is a good starting point for a merge collector, this will in turn set the diameter for the secondary pipe after the collector.

This area ratio is the area of all primary pipes except one plus the area of the secondary pipe divided by the area of one primary pipe.

I have never heard of this calculation in all my many years of exhaust research. What is its source?

My F1 Renault V10 collector has a area ratio of 5.2 . The primary dia is 61 mm/2.4" and the collector 66 mm/2.6". The distance from primaries to the collector is an amazing 112 mm/ 4.4". A very compact merged collector made with U-bend tubing sections.

Brian