Megasquirt Advice and discussion.

[RotaryProphet]

15psi is always 15psi, but 15psi at 80 degrees is not the same as 15psi at 160 degrees; this being what compressor efficiency is measuring (heat added to the intake charge). A larger compressor will generally have better efficiency numbers higher up in the airflow range, and a wider efficiency island.

You aren't changing the "flow", persay. Given a certain engine condition with a better compressor, you're flowing the exact same volume of air (assuming you have the exact same pressure), but the better compressor will be pushing a cooler, and thus denser air charge. (Which would be mass, as opposed to volume).

This is why a MAP based system also requires an intake air temp sensor to correctly calculate the air density. A MAF system measures mass directly, and is probably more accurate under a wider range fo circumstances, but the restriction to inlet flow leads me to use a MAP/IAT system 90% of the time. I would choose a MAF for things like hill-climb motors where rapid changes in altitude would necessitate the wider operating range, and self barometric correction would be more desirable.

[RETed]

Originally Posted by RotaryProphet

15psi is always 15psi, but 15psi at 80 degrees is not the same as 15psi at 160 degrees; this being what compressor efficiency is measuring (heat added to the intake charge). A larger compressor will generally have better efficiency numbers higher up in the airflow range, and a wider efficiency island.

You aren't changing the "flow", persay. Given a certain engine condition with a better compressor, you're flowing the exact same volume of air (assuming you have the exact same pressure), but the better compressor will be pushing a cooler, and thus denser air charge. (Which would be mass, as opposed to volume).

This is why a MAP based system also requires an intake air temp sensor to correctly calculate the air density. A MAF system measures mass directly, and is probably more accurate under a wider range fo circumstances, but the restriction to inlet flow leads me to use a MAP/IAT system 90% of the time. I would choose a MAF for things like hill-climb motors where rapid changes in altitude would necessitate the wider operating range, and self barometric correction would be more desirable.

Sorry, but you are dead wrong.

TTT is right.
Pressure (i.e. "psi") is only one variable when talking about turbo potential.
AIR FLOW the other big variable.
To ignore air flow is downright stupid.
15psi with a T3 is not the same as 15psi with an HKS T51R SPL...

Air temperature is tied into the whole thing (see PV=nRT), but it's a relatively minor variable.
To emphasize air temps over air flow is downright...ignorant.


-Ted

[RotaryProphet]

Originally Posted by RETed

Sorry, but you are dead wrong.

TTT is right.
Pressure (i.e. "psi") is only one variable when talking about turbo potential.
AIR FLOW the other big variable.
To ignore air flow is downright stupid.
15psi with a T3 is not the same as 15psi with an HKS T51R SPL...

Air temperature is tied into the whole thing (see PV=nRT), but it's a relatively minor variable.
To emphasize air temps over air flow is downright...ignorant.


-Ted

You're in such a hurry to contradict me, you didn't pay any attention to what I actually wrote. You need to re-read what I wrote, and what I responded to, and rethink your statement. We're not talking about total turbo potential, we're talking about two turbos on the same engine, both capable of making a given pressure at a given flow rate (CFM).

Flow and pressure are directly related; unless you have enough flow to over-supply the engine, you can't make boost. Thus, increasing flow in a system increases the pressure. With a larger turbine, you can't "flow" any more air into the engine at any given boost level than with any other turbo capable of flowing the same amount (assuming, of course, identical hot-sides, and thus equal exhaust backpressure at that boost level). So where does the power come from when you swap to a larger cold side? Increased efficiency, and thus a cooler air charge.

Being capable of flowing more air doesn't mean you actually do, it just means that it takes less work for the compressor to flow the air you do need, and less work means less heat.

[RETed]

Originally Posted by RotaryProphet

You're in such a hurry to contradict me, you didn't pay any attention to what I actually wrote. You need to re-read what I wrote, and what I responded to, and rethink your statement. We're not talking about total turbo potential, we're talking about two turbos on the same engine, both capable of making a given pressure at a given flow rate (CFM).

That is not possible unless we're talking about IDENTICAL turbos here.
(And even with two same turbo models, there is still miniscule differences in efficiency cause of production machining tolerances.)
AFAIK, there is no such thing as two different turbo models flowing exactly the same specs - do you have proof of such beasts?

Flow and pressure are directly related;

That only holds true if we narrow our conversation to a single turbo.
You cannot say that when talking about different turbos - which we are.

So where does the power come from when you swap to a larger cold side? Increased efficiency, and thus a cooler air charge.

I think you're overemphasizing air temps.
By nature, PV=nRT comes into play, and you're just stating the obvious.


-Ted