MR.Pizza

I believe this is telling me that our turbos are about at their max as it is.

BostonBoy

nice picture, what is it?

Blackout06LS

It is a turbo flow chart, but why did you post? Geez.

I'll go to google.com to see if I can find out the flow chart formula again. Along with PMing this to Blake. He is good with flow charts.

It's been awhile since I've even looked at the formula. But you take in a lot of factors to figure out the turbo flow, etc. Which actually did this for a SS/TC not long ago. Let me send a few PMs to the guys who were mostly discussing it as they are not online.

Red2.4SS

I believe that it is running clost to peak on the OEM turbo.

This is typical as OEM is looking to get as quick of a spool up as possible so the turbo size is usually as small as they can get away with.

I cant tell you much off of just the map alone, I'm not even sure what the max boost pressure is on the SS/TC?

SSpdDmon

Until they figure out the PCM a little more, I think we're stuck at 22~23psi. After that, the car will go into a limp mode.

BostonBoy

ME??

MR.Pizza

Thanks, yeah this is the SS/TC turbo graph converted using Garretts method. I found it on the Sky/Soltice forum, however they never really discussed it other than to argue about the math.
Well I think the max boost is aprox 20 psi so looking at the graph the K04 is nearly peaked? I see that Borg Warner makes more efficient k04's we could swap in. Sorry if this has already been covered.

XenSS06

iTrader: (4)

Efficiency chart you want to be as close as possible to middle ring or in it i believe otherwise you out of the zone and heat and other factors get greater.

I dont know though im not a turbo Guru.

MARIN007

I've never seen more than 110 kPa (15.9psi) so looks like it's in the efficient ring always. I'd love to feel 19-21psi though.

peachpuff

Who added the hp numbers to that chart? They were not on it originally. If someone can translate the bottom numbers into actual flowrate it would be easier to understand, such as lbs/min or cfm.

IsItFast?

Those numbers dont line up with what we are seeing... someone did their math wrong on the HP numbers, and that calls into question the validity of the entire compressor map. However, the PSI units added to the map appear to line up with what we have discovered so far on the upper limits of the turbo - 21-22psi being about the highest safe boost you can run, and looking at the map above this is just at the top of its efficiency curve, while the stock 15 ish psi is dead center of the map. Id like to see the true, unedited version.

Maybe this is it?


Using (P1 + P2) / P2 = Pressure Ratio
P1 = Desired boost pressure in psi
P2 = ambient atmospheric pressure (14.7psi)

We get almost perfectly what whomever calculated the PSI on the left hand side, so appears to be correct.

Our engines are almost 122 CID, so at 100% VE our engines should flow close to 220 CFM. Assuming 80% VE this means approx 176 CFM at 6,250 RPM, which is approx 12 lbs/min at that rpm

Bottom line, the HP part of that map doesnt line up, but I think thats just because whoever added it didnt do the math correctly.

MR.Pizza

Thanks, it was wonder about the HP numbers. They didn't seem to be correct but wasn't sure how to convert it. Anyway you could reconvert those hp numbers correctly?

REIGN SS

http://www.s4biturbo.com/k04/RS4K04.xls

I found this on a BMW forum, it helps explain how to read a compressor map: http://forums.bimmerforums.com/forum...d.php?t=258035

MR.Pizza

Thanks that explains it...

IsItFast?

Quick calculations (it takes several calculations to calculate a single data point on that map) show our 260hp to be at about the 0.12 mark on the X axis. I believe the X axis is Kg/s, so you can convert to lb/min if you want to by multiplying the numbers by 7. (7 is not the exact number to convert, but it will get you very very close and is easy to remember)

This also assumes many variables that are not listed here such as air temperature, altitude (assuming 14.7 psia for sea level), VE of the engine (does anyone know the VE of the LNF? 80-90%?), etc.

Using assumed variables, and assuming that this chart is the correct one (lots of assumption there), that would seem to indicate that at the very outside edge of the efficiency island is around 22 psig before the compressor will surge - this lines up with both the overboost protection in the computer and what some tuners have run into already. 21 is about the max safe boost level on the stock K04 (which is what Hahn's tuner sets the boost to, so this lines up as well).



Edit - I must be blind. The chart shows the calculation used to achieve nredV using 183.5, which means they are using 83.5% VE for their calculations. Doesn't really change what I wrote though, still close enough.

cessblood

Sorry for bring this thread back to life but I'm going to watch this thread. I'm thinking about getting the new turbo cobalt ss.

peachpuff

Turns out the map in the first post is from a different turbo and not the one used in the lnf, here's the real one courtesy of BaldTurboFreak
He's also stuffed a slightly larger wheel in there, he's currently testing that setup.