PTS Flowbench Forum

Has anyone here played with different bore adaptor depths and noticed a significant change in flow? for example a 6 inch high adaptor vs a 4inch, same internal diameter

If you use a bore adapter that's longer than the engine stroke and it shows a difference, Would you consider it a realistic test Owen?

If it flows better how would you use that Data? Stroke the engine ?

Jim

I have often thought about that to I remember asking John Holm about
it he said he him self use a flow stand that was a total of 6 inches tall

You could think about the distance from the top of your flow bench to the baffle or internal orifice plate
with out a bore flow stand

Why would you match the bore adaptor up to your engine stroke? Your engine doesn't sit at BDC with a few vacuum cleaners attached to it.

I think the answer is long enough to have a fairly developed flow in the bore and short enough that the bore isn't creating unrealistic wall friction pressure drops etc, although I imagine the bore would have to be pretty damn long to see that.

Which leads me to my next musing....has anyone set up their flow bench to draw across the chamber? ie putting a piston in the bore and flowing the head in the overlap region through the intake and exhaust port?

OwenMM wrote:Which leads me to my next musing....has anyone set up their flow bench to draw across the chamber? ie putting a piston in the bore and flowing the head in the overlap region through the intake and exhaust port?

I doubt that would give a realistic measurement because when a cam is in overlap the flow of the intake would be restricted by the flow of the exhaust. I think the only realistic way of doing this would be to have a piston actually moving in a bore at the same speed it would in an engine and even then you are missing out on the exhaust flow (of a running engine) pulling intake flow through at subsonic speed.

Possibly, my general rule of thumb is the flowbench is close to useless for anything involving exhaust gas anyway.

OwenMM wrote:Possibly, my general rule of thumb is the flowbench is close to useless for anything involving exhaust gas anyway.

Really? Close to Useless? Like to elaborate as to why you think that?

Jim

OwenMM wrote:Possibly, my general rule of thumb is the flowbench is close to useless for anything involving exhaust gas anyway.

I disagree with you on this.

A flow bench is a tool to measure airflow using static pressures, an engine doesn't operate at static pressures but rather at a wide variety of pressures throughout the operating cycle. What a flow bench does is lets you know if any modifications to the port etc have increased flow at the static pressure, if it has then flow will also increase at the engines variety of operating pressures.

If you think a flow bench is close to useless for exhaust then I have to wonder why you would want to use a flow bench at all.

Temperature, viscosity etc. The intake side is somewhat (barely but we make do...) close to the conditions an engine sees, the exhaust side not even close, not to mention the fluctuations within a single cycle. Maybe useless was a bit of a strong term but I wouldn't develop an exhaust port based on flowbench behaviour. Thats just me though.

OwenMM wrote:Temperature, viscosity etc. The intake side is somewhat (barely but we make do...) close to the conditions an engine sees, the exhaust side not even close, not to mention the fluctuations within a single cycle. Maybe useless was a bit of a strong term but I wouldn't develop an exhaust port based on flowbench behaviour. Thats just me though.

It is alleged by some very well known tuners that the flowbench is a viable tool that will model well the steady state pumping cycle of either the intake or exhaust. In Hale's 7 process model, exhaust pumping is low on the list of priorities that need to be just so (Intake pumping is #1), but the augment is the chain is always limited by it's weakest link. I don't spend a lot of time focused on exhaust side flow, but I would not suggest to ignore it either.