id me

[Brian (up north) Morris]

can anyone tell me what this manifold would have originally come off...just curious :-)

[Brian (up north) Morris]

@ james id say thats definetly it. what did that come off..?? interesting debate gents :-)

[James Doulton]

When I say 'adjacent' cylinders I mean adjacent in the firing order, not adjacent in the engine layout., so cylinders 2 and 3 are not adjacent in the way that I meant.

[James Doulton]

At 6000 rpm (i.e. 100 revs per second) then there are 200 exhaust pulses per second (50 per cylinder). 200 pulses per second is 1 pulse every 5 ms. with a speed of sound of around 300 m/s then each pulse is about 1.5 m apart. So the difference in length between adjacent cylinders would need to be 1.5m for them to coincide.

Some exhaust systems (e.g. 4 into 1) are designed with each exhaust runner being separate for around this sort of distance so that there are pulse reflections to aid scavenging at the end of the exhaust stroke. The length in this case is based on the time that the exhaust valve is open for, so that the positive pulse created when the valve opens is reflected back as a negative pulse (created by the sudden cross-section change where the pipes join) that returns just before the valve closes. So the pipe length is tuned to the particular engine speed that you want to boost the power at.

I don't know how much of an effect the pulse tuning creates but it is not much use for a road car where you care about a wide power band. Mostly we just want low restriction.

[Adrian Southgate]

@BV - I was talking about the exhaust pulses, I would have thought that when the engine reached a certain RPM the pulses would have arrived at the pipe conjunction at the same time. Gas can only travel so fast 

[James Doulton]

Here is another view of it.

[James Doulton]

I think that this is what your manifold looked like originally. It is not as heavily cut down as I thought.

[James Doulton]

I would guess that it was an after market manifold that has been cut'n'shut. I'd guess that it was sliced just after the two y-joins, Then the final join would have been about 2 foot further away, The short sections where it is 2 pipes would have been salvaged from that 2 foot section.

Not a bad idea, just not very good implementation. Exhaust pipe is quite difficult to weld - I think my first attempt with an arc welder looked much like that.

[Jim (across the pond) Adamek]

If you use the cast iron manifold lower rev power will be about the same but at high revs the power will be lower.

[Jim (across the pond) Adamek]

If you use the cast iron manifold lower rev power will be about the same but at high revs the power will be lower.

[Brian (up north) Morris]

:-)))))