I am in the market for a new intercooler so I've been doing some reading/research (here and elsewhere) and I'd like to hear your input. My question is about what size will help limit or not exacerbate turbo lag. I may be overthinking this but I want to make the best choice.

Car:
NA Miata 95 bottom/99 head and intake manifold
250-260 WHP
Garrett 2560r (outlet is clocked upward )
Artech 2.5-->3" downpipe.
2" hot and cold side (up till TB)
CX Racing Radiator 52mm (still holding up after 4 years). OEM fans. Mostly water inside the rad.
Coolant reroute.
A/C
CXRacing Intercooler (27.5"x7.25"x2.5)

Pending:
CSF Supermiata Radiator
Air dam with splitter along with adequate ducting

Water temp management has been an issue in the past both at AX events and on the track. No issues while street driving.

The car is mostly used for competitive autocross (usually fighting for FTD) along with some HPDE's and street driving/grocery getting.
Turbo lag is your worst enemy during autocrosses especially on smaller lots. So I want to reduce the size of the IC to help reduce lag (open to oether suggestions) but I know that too small will be ineffective at cooling and hot air in the intake is no bueno. Another benefit will be increased airflow to the radiator.
I am not opposed to getting another ebay IC but again I just want some advice as to what size might be most beneficial for me.

Some options I was looking at:
Fab9 Stage1 26"x6.50"x3.25"
CX Racing 25.5x7x2.25
CX Racing 23.5x7x2.5
CX Racing 28x6x2.5

Let me know if you need more info and thanks in advance.

 

Intercooler size and piping length do not contribute much to "lag". The air is moving extremely fast and the compression of the air due to changes in velocity is pretty small. It doesnt take long for the increase in pressure from the compressor to be communicated to the inlet manifold.

Get a core that will support the cooling you need on the track. Use good ducting. Simple as that.

 

The intercooler size will not affect turbo lag in any way that you would be able to measure from your own experiences. It fills way too quickly.

Let's just say for argument's sake your turbo is moving 300 cubic feet per minute free air. That's 5 cubic feet per second. For reference you can get about 7.48 gallons of liquid in a cubic foot. So if you were looking at it it would be putting 37.4 gallons of volume per second. How many gallons do you think your intercooler and piping will hold? How many fractions of a second do you think it would take to fill them?

You can probably figure out exactly what the CFM output of your particular turbo would be and get really precise but the answer is that's not where the lag problem is. You will want to improve the aggressiveness of the turbo's response.

A smaller AR turbine housing, lighter rotating components within the turbo, electronic boost controller, higher mechanical compression ratio, are a few ways to make it transition more quickly.

 

Slight point of correction, turbo volume flow is inlet, not outlet. The outlet volume is equal to the displaced engine volume (in general). This isn't 100% true when an IC is used, but it is good enough for nearly all purposes.

 

Check out the size I use in the MKTurbo setup. It is probably perfectly sized for you. But really I think you need better EBC control or something. I am with the others that IC piping and IC size should not be a noticeable problem.

 

I think the best thing you could do is a less restrictive exhaust... But it likely won't be a huge difference. Oh, and check for boost leaks.