Jump to content
SAU Community

Recommended Posts

here is how to begin analyzing a turbo compressor map, this will help you learn what makes turbo cars move, and why it is that some cars can run on stock turbos during elevated boost, and others are barely running in stock form on the turbo they have.

1) pressure ratio. This number represents the boost you intend to run, it makes up the Y axis of the graph. The numeric pressure ratio value is calculated by taking your target psi (15 psi for example) then adding 1 Atmosphere(14.7psi) and dividing the total by 1 bar(14.7 psi). The equation looks like this for our example:

15 + 14.7 = 29.7

29.7 / 14.7 = 2.02

2.02 is the refrence number that you would look at on the Y axis.

2) The X axis of the graph represents airflow in pounds per minute. As a general rule, each pound of air generated represents 10hp. This is flywheel hp and not wheel hp, so don't confuse the two. When looking at this be sure to account for driveline losses when you estimate your power output.

3) The third area represents the efficiency island. This is the target area you want to keep your boost at. This is where the turbo is at it's peak efficiency and thus runs the best.

4) These are the outer rings of efficicncy or wheel efficiency. As you can see from the numbers, each ring drops in efficiency and thus drops in power output. The percentage of efficiency lost and power loss vary from turbo to turbo, but as a rule of thumb you want to remain as close to your efficiency island(center island) as possible.

5) This dashed line is the surge limit. Any points to the left of this line indicate that the compressor wheel in quesation is too big for the expected boost and power output you are planning for. There would not be enough exhaust gas volume to spin the wheel fast enough to make useable boost.

6) This area to the right of the graph plots overspin choke. This means that the compressor wheel is too small and will have to spin too quickly to make the target boost/power. At these extreme speeds, efficiency goes out the door because the wheel chops the air so badly, this will likely cause a dramatic loss of power.

7) This is the compressor wheel speed in rpm. This measures the shaft speed of the compressor wheel. The faster it is spinning the hotter the outlet charge will be, and thus the lower your power output becomes. This is where a good intercooler comes into play.

Turbo Matching:

From your newly (or reviewed) skill on reading a turbo compressor map, you'll now need to be able to decode it into how it fits your engine, this will require numerous equations, all of which can be done simply without the use of advanced mathematics and will bring a great deal of illumination to the problem of perfect boost vs. monumental lag. This part of the process requires a sacrifice, but it's not so bad if you have a stock engine, or at least stock compression. A person with the 2.3T or 2.4T (and now 2.5T) engine is going to be @ a relatively high compression ratio, the hpt engines run a 8.5:1 CR and the lpt run 9.0:1 CR which means at elevated boost, especially over 20 psi, you're going to need either to reduce your compression ratio, or install a water injection kit, and even then it is not advised to go much over 20 psi at all on stock compression in the hpt engine, the lpt engine with it's 9.0:1 compression and less beefy cylander walls shouldn't exceed 15 psi without water injection and should be advised to be cautious above this level.

The main point of using a compressor flow map is to determine if the compressor part of a turbocharger is sized properly for your engine. In order to do this, you need to know how much air the engine flows. The volume air flow (VAF), measured here in cubic feet per minute (cfm), is a linear function of engine displacement (here in CI), compression cycles per minute (RPM/2), and volumetric efficiency (VE). After doing some searching online, it seems that our engines operate at approximately 19.4 lb/min, knowing that every 10 lb/min is equal to 144.7178 cfm, our CFM equals roughly 266.28 ft^3/m. THIS IS AT 10 psi, if you increase your boost levels, you can expect to see:

Stock:

18.4 lb/m @ 10 psi: 266.28 cfm

Modified Boost:

23.0 lb/m @ 16 psi: 332.85 cfm

24.2 lb/m @ 18 psi: 350.22 cfm

27.1 lb/m @ 20 psi: 392.20 cfm

If seen on the 15G map provided above, you'll notice that we're on that very narrow island of efficiency at 10 psi, and that once you're at 15 psi (around 319 cfm) you're really starting to heat things up over stock. However, you'll also notice how TALL the efficiency range goes, and how (compared to others shown below) much more efficient the midrange of this turbocharger is, especially compared to the obviously lightweight and heavyweight turbos we'll see soon.

Link to comment
https://www.sau.com.au/forums/topic/20018-how-to-read-compressor-maps/
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Any difference in induction noise?
    • If I got a dollar for every flipped commuter missile I've driven past I'd have two dollars   Some people get into wild adventures on the road and I doubt it's gender or ethnicity specific. I'm just glad I don't usually drive during peak times.
    • Just got the car back and gave it a good run back home Power wise, whilst it only made a extra 5 killerwasps up top at 7200 rpm, it made more power everywhere from 2500 rpm and kept pulling much harder all the way, to the point of me relearning when to shift so I don't hit the 7200 limiter, with the old intake it seemed to take alot more time to rev out, and, throttle response is also much improved  As I didn't want to remove the bumper every time I serviced the air filter (basically every aftermarket and fabricated CAI has the filter behind the bumper) it currently has a hektic exposed pod in the engine bay sucking in hot air, this will be rectified shortly after some some of my CAD (cardboard assisted design) for a alloy heat shield feed by the OEM intake tube behind the bumper, this will cop some wrinkle black paint, as well as the intake pipe for that totally OEM look... The only fly in the ointment was that the OEM "strut" brace doesn't fit over the rear runner of the new intake with the 2.5 engine is in the engine bay, as the 2.5 raises the engine up by 20mm, it's not a war stopper, and I didn't notice any difference without it in some twisties, but....... MX5 Mania is bringing in some GWR "fancy pants" braces that apparently do fit, if it bolts up I'll grab it, it is also stiffer than the OEM one, which is a bonus All in all I'm happy with the outcome      Fancy pants "strut" brace that gives the required clearance      This is where the clearance issue was, the GWR extends out past this
    • Well, I'm back from the dyno today. Some things do partially make sense. The pod filter/airbox delete picked up between 6-10rwkw on 98 - because heat soak does kind of affect things and there was playing with tune/timing/AFR. Oddly enough, the car was running much leaner than before. So lean it was audibly pinging on the dyno which I got video of:   70de0dd5-2099-4a71-8b10-6fc833fb9d59.mp4   We're talking going from ~12.7 in the past to the first run being at like ~14.0. It is now tuned to ~12.5 on the Dyno, which correlates to about ~12.1 on my wideband in the car. These matched last time, which is very odd. The dyno plots only show the dyno's reported AFR - should be last time, yet now it no longer agrees and was way leaner. Nobody has an explanation for how a pod can make the car run notably leaner, yet not really give any more power when you add fuel in. A few different types of intake design were tested:   94c22c34-7991-4902-af85-314b5f5bf352.mp4   There was no difference other than IAT with the pod sticking out of the bay. The pod sticking out of the bay (but connected) is actually still warmer than what I usually see on the road. Removing the pod entirely lost about ~2kw. But to be fair, all of the runs could be argued to vary by that amount when temperatures climb etc etc. It's safe to say that the filter isn't causing any restrictions of any note that can be reasonably altered in any way. This is in line with what I'd expect given the Engine Masters testing. 323KW on 98 and ~335KW on E85 is actually a pretty solid result, up about ~45kw from 99% of LS1 cammed combos, with generally much larger cams/exhaust etc as well. It is after all up 42KW (98) and 54KW (E85) from before. +10KW from a pod and removing the box is cheap as chips compared to what the head work cost per kw No, I did not get to drop the exhaust and test. When it comes to exhaust... it all just seems to change frequencies and cost or gain 2hp here or there. I don't realistically think I'll drop this to test it - because there's not much else I can really do about it/route it any other way/make it bigger/just bought mufflers. Engine masters beat the hell out of headers with a hammer to deliberately kink them and didn't lose power at all, I sincerely doubt that going larger primaries would help. If it were even possible for clearance/conversion reasons... which it's not... I may throw the E85 in there at some point and do a drag run to see what MPH it traps for science. It isn't lost on me that ~320kw Skylines do trap about the same MPH that ~370kw F-Body/Corvettes do in the USA for the same  or similar weight. (122-125mph). Of course, if I go there and trap 104mph or something then I'll just 'accidentally' have an accident on the way home from the drag strip and buy a M4.
×
×
  • Create New...