Thats a ton of pressure...

 

1 atmosphere = 14.69 PSI at sea level
1 atmosphere = 1.01325 bar
1 bar = 14.5 PSI

Make your game !
Cheers

 

Thank you sir...

 

I wouldn't go much beyond 70% efficiency without some form of cooling... so 26psi w/o injection on race gas.. else u can push a 30psi outta it with a 51/49 water meth

 

Those are both high imho no offense

 

This is some good info. I like the comparision saying that the 27 psi and 32 psi have about the same power. That says something about efficiency. I wouldnt run above 28 then, just like WRX said.

 

i'm a little confused by your statement...

turbos are barely 70% efficient at adiabatic compression even at their max efficiency, so saying your wouldn't go "Beyond" i'm not sure if you mean you wouldn't go higher then 70%, or if you wouldn't go lower...

just to clarify, those "islands" in the compressor map are efficiency islands. efficiency refers to how well they adiabatically compress the air. what does that mean? with 100% adiabatic compression, no heat enter or leaves the system, so the temperature increase is as follows:

Tout = Tin*(Pressure ratio)^.286

the pressure ratio is exactly that, the ratio of the outlet pressure over the inlet pressure, both in atmospheric... (or another words, (your boost in psi+14.7)/14.7)

now because we already know the turbo is not perfect at compressing the air, it gives us an efficiency, which we can use to see exactly how much it has increased...

so inefficient outlet temp = inlet temp +(100%efficient adiabatic compression temp delta)/Compressor efficiency. so hopefully that makes some sense.

in laymens terms: you want the most efficient compressor possible, and you want your operating range (air mass flow rate, and pressure ratio) to be in the most efficient islands on the map.

hopefully that helps

 

So, what do you think the maximum efficiency for power and safety is on my IX turbo on 93 and 100% methanol injection?

 

its really not as simple as saying, what PSI should i run, because that is going to make a difference on how much air you are flowing at that psi, and also the engine volumetric efficiency is going to play a HUGE role in how much boost you actually can run.

to start using a compressor map you want to know the flow rate scale. some are in lb/min others are in cfm. lb/min IMO is the better way to do it, but cfm we can work with. first make an estimate on what RPM you want to see peak boost... lets say 4000rpm. next, we know the displacement in liters, we need to convert that to cubic ft. 2L = .0706 ft^3... and sense the rate is 2L every 2 revolutions, and we have 4000 rpm, that is 4000 liters/min or 144ft^3/min at standard atmospheric pressure and temp.

now you need to take a guess at what volumetric efficiency you have... i would say 90% just for this calc. that means only 90% of that 144 is what we are actually sucking into the engine. so 144*.9 = 129.6cfm.

last, what is the pressure ratio you want to operate at? lets say you want to run at 32 psi. that is a pressure ratio of 32+14.7)/14.7 = 3.17
multiply that by our flow rate = 129.6cfm*3.17 = 410cfm

that is where you are on the compressor map. 3.17Pr on the y-axis, and 410cfm on the x-axis. if you plot that, you see it is right about on the 65% efficient line. that is how efficient you are at adiabatically compressing the air. so lets make the next calc to see how hot the air is coming out of the turbo:

65% = compressor efficiency = CE
3.17 = pressure ratio = PR
say starting temp = Tin = 67deg F = 20deg C = 293deg K

ok: Tout = Tin*(PR)^.286 = 293*(3.17)^.286 = 407deg K for 100% efficient.

real Tout = 293+(407-293)/.65 = 468deg K = 382 degrees F is the actual temperature you should see coming out of the compressor at 4000rpm with 90%VE at 32psi and 67degF ambient temp.

thats pretty hot! the temperatures you would see at 28psi are:

VE = 90%
RPM = 4000
PR = 2.9
AFR = 375cfm
CE = 65% ( not any more efficient at 28psi then it is at 32psi at 4000rpm and 90VE)

because we aren't compressing it as much our temps wont be as high though even though the CE is the same.

Tfinal = 355 degF, or about 30 degrees F cooler. for having 4psi less boost.

that is a 8% increase in temperature for a 9% increase in flow. to me it would seem worthwhile at 4000 rpm to run more boost assuming the intercooler can still efficiently take temp out of the intercooler. but in your case you still have the meth which works better then an intercooler at cooling the air.


at 7000 rpm, lets say you have a spectacular engine that is well built with cams made for high flow rates. and at 7000 rpm you have a 85% VE, also 2L.

RPM=7000
VE = .85
Pr = 3.17
AFR = 662 cfm at 32 psi. if you try plotting this on the chart, you will see you are WAAAAAY of the map. this means you have choked the turbo and it will not flow that much air, this boost will drop off or air flow rate will (both actually). this is the taper we see. lets see what we could get at 7000 rpm:

at 2.6 PR we have 543cfm, which is in the extreme top right of the efficiency map, or about 60-62% efficient. that is at 23.5psi. this would be about the absolute most boost pressure you could see at 7000 rpm assuming you had a 85% VE. the temp increase would be very large: 343 degrees F for only 23psi. thats about the same outlet temp as at 28psi at 4000 rpm simply due to the compressor efficiency.

one last thing, the more efficient your engine is (i.e. ported head, higher lift cams, less exhaust back pressure, less intake restrictions), the more ineffiecient the turbo will be at higher rpms. this is because the flow rate will be greater, pushing everything off the right of the compressor map, choking the turbo.

(if i have made any mistakes for anyone reading this, please chime in and correct me, i'll fix it.)

 

oh and my disclaimer is: these calcuations were done using a compressor map posted here. this map may very likely not be the same as the turbo you have on your car, in which case all the numbers could be different. do not run 32psi just cause my math said you could. an engineer would test the actual outlet temps to see what efficiency you are actually looking at before attempting 32 psi. oh, and the amount of cooling you have and octane fuel is also just as important as compressor maps. so take that into consideration as well.

 

Thanks a ton man.

 

i wanna know mine spikes at 22 then drops to 17...plus when i floor it i dont go anywhere...but if i let off the gas about a half an inch of the floor it gets all the power back

 

Thats normal. You are fine sully. It will always drop at redline under WOT.

 

that's great...Kevin came in and "dorked" it up like we are at FSAE design finals...
I still need to get the temperature and pressure sensors tapped to test...but first I guess the motor has to go back together
it'll be a 2.3 now instead of a 2.0 so top end VE's will undoubtably be lower than the 2.0 set up we had being the head should be unchanged.

 

lol