Graphs! And Numbers! Who else loves them?!

I plotted the pressure ratio and volume flow for the stock pulleys (blue line) and 62mm supercharger pulley (redline) on the IHI compressor map.

SLK32AMGcompressormapmarkedup2_zps1ed80ee6.jpg

The first thing I notice is that the AMG engineers did a great job selecting a supercharger to match the engine. The stock pulley curve shoots right across the adiabatic efficiency sweet spot on the compressor map. The efficiency ranges from 66% to 59%. The peak power required to drive the blower is 68 HP (at 6000 RPM), and the discharge temperature is 248* F. Not bad for a positive displacement blower.

I only graphed 4 points. The first is at the RPM my car leaves the line at. (stall 1400-1800 RPM, immediately jumps to 2300 RPM). The top three points roughly identify the low-mid-high range of the powerband when shifting through gears at WOT.

Obviously, I extrapolated some of the points on the right side of the graph.

The red line for the 62mm pulley (185mm pulley would be nearly identical) shows some interesting things too. The increased pressure ratio and volume flow put the curve out of the peak efficiency of the supercharger. The adiabatic efficiency ranges from 65% to 56%. That is still not bad! The peak power required to drive the blower is 89 HP and the max discharge temperature is 320* F (!).

I agree with the conclusion others have come to that this looks to be about the max for this supercharger. Even with the 62mm pulley, it looks GREAT through the midrange, but toward redline the discharge temperature and power to drive the blower are increasing a LOT.


Lysholm compressor maps have been compared to the AMGs so I couldn’t resist. Here are the same points graphed on the Lysholm 1600AX compressor map:


Lysholm1600compressormapmarkedup_zps2ebc9d18.jpg

Very similar results. The most notable exception is that the Lysholm would appear to take a little bit less power to turn. Very similar efficiency though.

So… What would it look like with the larger IHI supercharger from a …55 AMG engine? Would it be more efficient? Could we run more boost? I couldn’t find a compressor map, so we will have to make due with the Lysholm 2300R map.


Lysholm2300compressormapmarkedup_zpsa040ae73.jpg

More interesting results! The Lysholm 2300R clearly has a higher volume flow capacity, but is less efficient at higher pressure ratios. It makes sense that it would be this way since it was designed for higher displacement engines. Comparing the graphs of the Lysholm 1600 and the 2300: the 2300 would operate at slightly lower adiabatic efficiency, higher discharge temperature, and would take more power to drive. So that does not look like an upgrade! The higher displacement supercharger won't do us much good without a higher displacement engine.


The airflow numbers I used for both the stock and 62mm pulley graphs are inclusive of supporting mods. HP estimates are: stock pulley: 394 HP, 62mm pulley: 472 HP. For an otherwise stock car, the graphed points would shift to the left slightly. Mods that would increase power, but actually decrease pressure ratio, such as Needswings intake manifolds, would shift the graphed points down slightly (a good thing!).


Numbers!

compressormapcalcs_zps5d35a6b5.jpg

The pressure ratio data points were calculated from boost readings logged during actual ¼ mile runs.
The volume flow data points were calculated from engine RPM, pulley ratio, supercharger displacement, and volumetric efficiency estimated from the compressor map below. I didn’t realize until afterwards that the Lysholm 2300R and 2300AX are slightly different compressor maps.
HP estimates assume 1.5 CFM/HP.

Lysholm2300volumetricefficiency_zps638b39e6.jpg

 

maybe you should consider this calc for volume requirements.....
- Its just another view....
6 ------------- Cylinders
89.9 mm------ bore
6348 mm2 ----X-Sectional Area
84 mm--------- stroke
0.059 L-------- null space (top of cylinder)
0.533 L-------- Capacity (per cylinder)
3.2 L ----------------------Total Engine Capacity/displacement (doesnt include null)
0.592 L --------Cylinder Capacity incl. Null
9.0 :1 ----------Compression Ratio
3000 cycles ---Cylinder Intake strokes per min. at 6000rpm
20 ms ----------1 x 360deg stroke period
377 cfm -----Cylinder Intake Volume Required
10.66 m3/min --Cylinder Intake Volume Required
222 g/sec ------Air Mass (1.25kg/m3)
17.8 g/sec -----Fuel Mass (at 12.5AFR-mass ratio)
6.9 cfm Fuel ---Volume (at 122g/mole, 22.4L/mole)
370 cfm --------Cylinder Intake Volume Required (air)
734 cfm-------- Air Intake Volume Required (14.5psi)
847 cfm --------Air Intake Volume Required (19psi)
21 m3/min -----Air Intake Volume Required (14.5psi)
24 m3/min -----Air Intake Volume Required (19psi)

It does assume the 14.5psi is present in the cylinder - which is a loose assumption as there will be losses at the valves - maybe 0.5psi

I'm also interested in your calc which indicates the psi increase wrt to rpm....Isnt it linear?
That is with the SC (v turbo) the psi is relatively constant, since its a positive displacement machine and is pumping into a void which is matched to the cylinder take volume (via the crankshaft) - hence the boost (say above 2000rpm) is relatively constant (negating eff.)?

 

I didn't get the increase in boost pressure with RPM from a calculation, that's straight from my data logs at the drag strip.

734 CFM sounds way high at 14.5 psi. That would equate to closer to 500 HP by the 1.5 CFM/HP rule-of-thumb, and our engines don't make nearly that without additional boost. Actual cylinder filling of an engine is nowhere near 100% volumetric efficiency. If it were, the 350ci V8 in my Vette would have made a lot more than 185 HP from the factory!

 

gotta remember the air+fuel in burn (enthalpy released) only accounts for 20% of the rear wheel horsepower....
the other 80% is losses.....some manufacturers/designs are better at extracting efficiencies than others.

Interesting what you say about the compression logs v rpm....might have ot have a "technology huddle" with the other engineers here. We had one on this topic before - obviously requires a revist.

 

Here's a curio for you.....

Using your results from below....
.....same supercharger rpm speed yields 5psi higher pressure.....

Are there any other compressor maps around?
these two are very different animals and it would be good to get the "Real McCoy"

I've done a lot of searching without success.

 

I don't understand what you are saying. What is different?

 

Well I managed to get things to work out....

The supercharger is simply a high pressure air pump.

Key here is that the supercharger pumps and the cylinders taketh away.
If the SC pumps more than the Cylinders, there is obviously a pressure (density) increase until the cylinders are taking away the equivalent mass.

I constructed the table below from BoostMonkeys data by;

- knowing the volume intake requirements of the engine displacement at a certain rpm....
- assuming 100% of the pressure is going into the cylinder (loose assumption due to some valve losses)
- from the Manifold pressure readings he's tabulated....(yellow cells include intake loss adjustments for throttle+air intake)
- you can work out the mass of air entering the cylinder (grey shaded cells)

- now the SC's gotta be pumping that same mass
- using an intake pressure (atmospheric minues intake losses) you can work out an intake density (
- from that you can work out what volume is required to match the mass of air required by the "engine section" above.
- because you know the super charger rpm- you can then work out the volume per SC pulley revolution

After that you can plot supercharger rpm versus Supercharger volume and you see that for both pulleys the results are very similar. This is what we call in my business as "normalising" and attempts to simplify the system.

This is what was confusing me from Boost's first post...why was the SC pumping higher pressure even though the SC was running at the same speed for the 62 or the 74mm pulley. (my vertical red lne in the previous post)
From the what I've learnt now, the increase is not necessarily due to the pulley so much, but I prefer to look at it as the engine is not taking the volume away as quick for the same SC rpm....maybe a case of tomato/tomayto...

Anyway - coincidentally the SC volume per rev came out at a good number...1.6L/rev sounds good based on what others have presented.

The reason why I started looking at this is because I wanted to know - if you were to change out the 3.2L motor for a 3.7L block....would the supercharger be able to cut it?.....(more on that later).

Finally - although I'm reticent to use it (as I'm not convinced it's the right chart), I scratched out an update the compressor map. This needs a little more work - especially getting more confidence in the right chart....I'm not convinced this baby is the one.....

PS Boostmonkey - do you have some IAT's to go with the psi numbers you showed originally?
I've just assumed 50C (122F) intake temp.

 

You know just an old fart with a lead foot. I can tell you my seat of the pants **** factor goes way up from stock pulley to 62mm. Like a fast but controllable car to oh **** try to steer straight ripping the tires off wow factor. That is good enough for me.

 

Agree with doc ......went from the stock to the 65mm to the 62mm pulley and the diff from stock to the 65 was huge. Then the 65 to the 62 was noticeable more in the upper and mid ranges but still an improvement. The 62mm took .4 off my et at the track and added 6.9mph through the 1/4 over the 65mm. My IAT went up with the 62mm but there is always a give and take.

 

Yes - I'm glad to see you guys have a healthy perspective.
At the end of the day enjoying the rush is mostly what it's about.
Kudos to u.

But I (and hopefully someone else) also like hitting the numbers.

 

I know this is old, but this seems very far fetched. Do you have any other data to go with this? I promise im not trying to start a fight, just trying to make sense of everything.

 

I have time slips......... with no other mods except to adjust the tire pressure for the conditions for that day at the track. I do not know how much of a difference being at 5800' makes at Bandimere but the best time with the 65mm was 13.1ET 107.75mph and the best with the 62mm was 12.7ET 114.85mph no other changes to my setup. I have not switched back and forth on the same day because I lent the 65mm to another CCC member so would be hard to do that experiment. I was just going off of the time slips. But the runs are pretty consistent with each pulley with over 10 runs on each and those 2 numbers represent the best for each.

 

I do have some mods to my car ........so far from a stock setup.

 

Don't miss understand my statement. If it weren't for those crunching the numbers, these go fast parts would never exist. Just not all of us are trained in this area. Some of us just recognize from testing and results at the tracks, what good parts are, and using the information given, how to install and achieve the same results or better. Each car or motor is just a little different, and some will perform just a little better. At the strip, races are won in the one thousandth of a second. I appreciate the numbers.

 

I agree. I'm not even going near the track on streets with the 62 installed. Downright dangerous.......and expensive. DR's should be the answer.

 

Well, it may come to that, as I am not done. I have one more mod up my sleeve, well, Rudy's and I sleeves...lol. It should add to the wow factor big time. But without the numbers to prove we didn't waste our money...who would know...except my fatass....

 

attached volume calc for SC

 

Your chart yields an 86.9% VE at point pressure ratio 1.0 / volume flow 13.9 m^3/min and 80.0% VE at PR 2.2 / VF 12.8 m^3/min for a 1.6 liter supercharger. That is consistent with the volumetric effeciency approximations I was using.

Are you trying to say you think the supercharger is smaller than 1.6 liter? All the information that we have indicates that it is a 1.6.

Dividing the volume flow per revolution of one PR point vs another at the same RPM describes the effect that pressure ratio has on the volumetric efficiency, but is not a way to calculate the VE. VE describes the dynamic filling of the supercharger vs ideal.

 

I use the forum for these type of discussions cautiously these days - will PM instead.
I can't work out how to post jpg via PM's though - hence the post.

 

alternate example using the LYS2300 attached
So this and other reasons - I'm calling our SC a 1400cc/rev