Bench inlet clearance

[jsa]

The top of my bench will have a 5" hole and fixings. It is going to be a reverseable flow bench.

I am wondering how far the side walls of the bench need to be from the entry hole to avoid affecting results ?

Pitot flow measurement will be away from the entry and baffled, I mainly thinking about getting unaffected flow into and out of the cylinder adaptor.

[Thomas Vaught]

My plenum is basically two 24"x24"x21" cubes with a orifice plate
inbetween so the actual height is 42 inches. After I did this I then realized that the cylinder was going to be several inches above that height but it actually worked out very well with the aluminum heads that most want flowed. Cast iron heads are harder to lift to that height but I have a 12" step that makes the job a lot easier on the back.

That volume will cause no affected airflow issues. The baffle inside the box is a 12"x12" plexiglass plate centered in the box.

Tom V.

[Tony]

jsa, I don't see that it really matters much. You will not be testing just the bare inlet hole.

The bench top needs to be large enough, and with enough clearance to mount whatever sized cylinder heads you are interested in testing. Testing the end cylinder always means there will be a lot of cylinder head hanging out beyond the test hole, especially on six cylinder heads.

It may be better to have the test hole at one end of the bench top, rather than dead centre if it is a small bench.

[jsa]

I am looking at a 4'x2' bench top.

1'x2' at each end has motors and valving.

Leaving a central 2'x2' for entry, plenum and metering, the 5" entry is in the middle of this.

I am thinking I might have to drop down to 18"x18" for the entry hole area so that I can have longer pitot pipes behind. Any thoughts on whether this would be enough space from the 5" entry ?

Tom,

My workbench is 1025mm high and the flow bench will be similar because I find it a comfortable work height. I thought about setting flow bench height so that the dial gauges and port were up towoard eye level, but your right those big iron heads are an effort. Better off sitting on a bar stool.

I'd think more volume the better.

Tony, True there is a cylinder adaptor and head over the hole. My concern is that having a side wall to close to that entry might make air favour one side of the bore adaptor and subsequently the head.

A mate has a Jag so I'm sure he'll be round, might be a design advantage to be unable to fit that.

I am thinking 2' from entry to end should get enough bench under a straight 6 or V12 head. I'm thinking an offset entry might not work if a particular side of the head had to face out into open space for putting on extractors as an example.

[Tony]

The biggest six I have ever worked on is a 4.2 litre Ford. I just went out to the shed and measured one. Centre of the last bore to end of cylinder head is 24 inches, but it probably doesn't matter if a bit hangs over the edge of the bench.

Some DOHC heads can also be pretty wide, so best keep the test hole as far away as possible from any rear panel.

[jsa]