Log in
Register
Reply With QuoteHow do you calculate what cfm the turbo gets at any certain PSI?Originally Posted by Jet Black
OK here goes:
Engine Volumetric Flow Equation
VAF(Volume Air Flow in cu. ft/min) = (Enging RPM x engine cid) / (1728 x 2)
So in a 2.4L
VAF = (6200 x 146.458) / 3456 = 262cfm
Ideal Gas Law/Mass Air Flow
The Ideal Gas Law is a handy equation to have. It relates the air pressure, temperature, volume, and mass (ie, pounds) of air. If you know any three of these, you can calculate the fourth. The equation is written:
P(absolute pressure) V(volume) = n(related to the number of air molecules, which is an indication of the mass (or pounds) of air) R(constant number) T(absolute temp)
Lets assume that we are at sea level.
8psi of boost(psig) = 22.7psia(14.7+8)
The absolute temperature is the temperature in degrees F plus 460. This gives degrees Rankine, or deg R. If it is 80 deg F outside, the absolute temperature is 80 + 460 = 540 deg R.
n(lbs/min)= P(psia) x V(cu.ft./min) x 29 / (10.73 x T(deg R))
Lets say you are running an intercooled setup and temps in the intake manifold are 130F and you are still running 8lbs of boost:
Absolute temperature = 130 deg F + 460 = 590 deg R
Absolute pressure = 8 psig + 14.7 = 22.7 psia
n(lbs/min)= (22.7 psia x 262 cfm x 29) / (10.73 x 590 deg R) = 27.24 lbs of air per minute (ideal)
lbs air per minute actual = 27.24 x 0.85 = 23.16 lbs air/minute
Volumetric Efficiency
If life was perfect, we could fill the cylinders completely with air. If we had 17 psi boost in the intake manifold, we would open the intake valve and get 17 psi in the cylinder before the intake valve closed. Unfortunately, this doesn't usually happen. With some exhaust remaining in the cylinder and the restriction offered by the intake ports and valves the actual amount of air that flows into the cylinder is somewhat less than ideal. The amount that does flow divided by the ideal amount is called the volumetric efficiency.
To take this into account when we calculate flow into the engine, we multiply the ideal amount of air by the efficiency to get the actual amount of air:
actual air flow = ideal air flow x volumetric efficiency
Now the lower your FMIC/cooling system can cool the air by the time it hits the intake manifold, the more lbs air/min you will move. So an intercooled turbo setup vs a non-intercooled setup will vary greatly!
Compressor
The compressor is the part of the turbocharger that compresses air and pumps it into the intake manifold. Air molecules get sucked into the rapidly spinning compressor blades and get flung out to the outside edge. When this happens, the air molecules get stacked up and forced together. This increases their pressure.
It takes power to do this. This power comes from the exhaust side of the turbo, called the Turbine. Not all of the power that comes from the turbine goes into building pressure. Some of the power is used up in heating up the air. This is because we lowly humans cannot build a perfect machine. If we could, all of the power would go into building pressure. Instead, because of the design of the compressor, the air molecules get "beat up", and this results in heat. Just like rubbing your hands together will warm your hands due to the friction between your hands, the friction between the compressor and the air and between the air molecules themselves will heat up the air.
If you divide the amount of power that goes into building pressure by the total power put into the compressor, you get the efficiency of the compressor.
For example, if the compressor is 70% efficient, this means that 70% of the power put into the compressor is used in building air pressure. The other 30% of the power is used heating up the air. That is why we like high efficiency compressors; more of the power is being used on building pressure and less is used heating up the air. You want to be in the 65% and higher efficiency range.
How to read a compression map(that I posted above)
Figure out the pounds of air that you are moving through the engine. We are passing 29.77 lbs/min of air, at inlet conditions of -0.5 psig and 70 deg F. Now correct that flow to the standard temperature and pressure.
Corrected flow = (actual flow x (Tin/545)0.5) / (Pin/13.949)
The standard temperature is 545 deg R, or 545 - 460 = 85 deg F.
o we are correcting the flow from 70 deg F and -0.5 psig to 85 deg F and -0.75 psig.
Tin = 70 + 460 = 530 deg R
Pin = -0.5 + 14.7 = 14.2 psia
Corrected flow = (23.16 x (530/545)^0.5) / (14.2/13.949) = 22.45 lb/min
Now for Mitsu maps, they use CFM, Garret uses lb/min. Every 10 lb/min is equal to 144.72 cfm. So:
CFM = (22.45 lb/min / 10) * 144.72 cfm = 324.9 cfm
So we mark that point on the bottom of the graph, and draw a straight line upward from that point.
The next step is to figure out the compression ratio, using absolute pressures. Using our example, we had 8 psi boost in the intake manifold. Let's suppose the pressure drop from the turbo outlet to the manifold is 3 psi; so the actual compressor outlet pressure is 3+8=11 psig. The air pressure is 0 psig, but since the turbo is sucking air to itself the pressure at the inlet is lower than that. Let's say it is -0.5 psig at the inlet. Then the compression ratio, Pout/Pin is :
Pout/Pin = (11 + 14.7) / (-0.5 + 14.7) = 1.81
So then we find about where 1.81 is on the left side of the graph and draw a line horizontally from that point. Where the two lines meet is where the turbo will operate.
SO using my 1337 skills in MS Paint:
Here the efficiency range for those turbos on the 2.4L:
14b = 72% @ 400cfm
Small 16g = 76% @ 495cfm
Big 16g = Borderline 71% @ 475cfm
Evo3 16g = 74% @ 540cfm
18g = Upper end of 77% @ 540cfm
Now these calculations are all at 8psiag at a 6200RPM redline. They all are pretty efficient for our cars. Technically you want the turbo that is most efficient for our engines. at all RPMs. At redline, the 18g proves most efficient. But that also comes with a higher spool rate which I am not going to calculate simply because I do not know how.
7g for life!
How do you calculate what cfm the turbo gets at any certain PSI?
7g for life!
bookmarked
I draw the horizontal line all the way to the last ring on the graph.How do you calculate what cfm the turbo gets at any certain PSI?
i.e. (stealth316.com)
I draw the horizontal line all the way to the last ring on the graph.How do you calculate what cfm the turbo gets at any certain PSI?
Ok, so how do you get 1.6bar = 8-9psi? Isnt that the P(out)/P(in) which = ~1.81 with our motors at 8psi?
7g for life!
.6<span style='font-size:16pt;line-height:100%'>psig</span> x 14.7psi= 8.82 <span style='font-size:16pt;line-height:100%'>psig</span>I draw the horizontal line all the way to the last ring on the graph.How do you calculate what cfm the turbo gets at any certain PSI?
Ok, so how do you get 1.6bar = 8-9psi? Isnt that the P(out)/P(in) which = ~1.81 with our motors at 8psi?
p(out)/p(in) =PSI<span style='font-size:16pt;line-height:100%'>a</span> Ratio
:shock: i cant wait until i can really understand this language
im with you...i can halfway understand it.. but im not sure exactly what it all means.. maybe we should start a thread for stupid people like us.. who dont speak turbo language...
www.anti-rice.com
lasthopeskrispy: so i was fucking this guy in the ass over the weekend and you know what he decides to do....he reaches around and cups my balls. I was like hey what a fag!
Let's suppose the pressure drop from the turbo outlet to the manifold is 3 psi(since there always is a pressure drop, we do not live in a perfect world); so the actual compressor outlet pressure is 3+8=11 psig. The air pressure is 0 psig, but since the turbo is sucking air to itself the pressure at the inlet is lower than that..6<span style='font-size:16pt;line-height:100%'>psig</span> x 14.7psi= 8.82 <span style='font-size:16pt;line-height:100%'>psig</span>I draw the horizontal line all the way to the last ring on the graph.How do you calculate what cfm the turbo gets at any certain PSI?
Ok, so how do you get 1.6bar = 8-9psi? Isnt that the P(out)/P(in) which = ~1.81 with our motors at 8psi?
p(out)/p(in) =PSI<span style='font-size:16pt;line-height:100%'>a</span> Ratio
Let's say it is -0.5 psig at the inlet(slight vacuum). Then the compression ratio, Pout/Pin is :
P(out)/P(in) = (outlet pressure + 14.7)psia / (inlet pressure + 14.7)psia
Pout/Pin = (11 + 14.7) / (-0.5 + 14.7) = 1.81
Is that wrong? I dont understand your equation for P(out) / P(in)
Top forumla is for converting psig to psia. .6 psig = .6 psi on a boost gauge. Im new to this stuff too, just trying to understand your concept :oops:.6<span style='font-size:16pt;line-height:100%'>psig</span> x 14.7psi= 8.82 <span style='font-size:16pt;line-height:100%'>psig</span>
p(out)/p(in) =PSI<span style='font-size:16pt;line-height:100%'>a</span> Ratio
7g for life!
wow much thanks to seth. I am now going with a small 16g because i think it's he best all around. iIt is not to big for my app at least i dont think i can run more boost with it when i upgrade to lower compression pistons and it is the second to best efficient beside the 18g which would probably be to big for what im trying to run right now.
I agree, the small 16g is an all around great turbo for the price. Maybe sizing it with the 7cm^2 bullseye housing to start, or after you run out of breath on the stock housing. Good thing about the bullseye housing is that it can be use with any tdo5/6 housing including the 18g or 20g just incase you want to upgrade.
http://www.slowboyracing.com/more.php?id=53&
MHI Small 16g
http://www.bullseye-power.com/product_info...&products_id=35
Bullseye housing.
Ask DOHCstunr about the housing, he is currently running one on his 14b
7g for life!
Ok it looks like our math is basicly the same for the most part. The only reason we got diffrent numbers if because your taking into account pressure drop, where as I'm not.
I have some more reading to do concering pressure drop, afaik its not something that can be too easily computed as it depends on a wide variety of factors...afaik. And just to add, my main source of referance, stealth316.com, doesn't even begin to talk about pressure drop when reading a compressor map.
BTW Speaking of switching housings. Is it possible to run a stage 3 T3 Turbine housing w/ a stage 1 turbine wheel? The reason I ask is because the wheel + housing (.48 AR) are tiny for the T3 I bought. Some of the club3g members are predicting cooked pistons due to the back pressure. So is it possible to simply upgrade the turbine housing to relieve some of the back pressure?
The main reason I'm hesitant to change the wheel as well is due to $$$. The T3 that I bought has zero shaft play, and I don't feel like buying a new wheel + housing + rebuild/balancing. Instead it would be MUCH cheaper to just upgrade the housing.
yeah i've been following both your guys approaches, and they both pretty much come to the same results minus discrepencies, but its too small to really get crazy over. good work, this should go to the galant vfaq....if we had one 8)
Ahh I see now.
I would assume so. The bullseye housings are just beefy stock replacements. Email bullseye to be sure, but I wouldnt think there would be a problem. THe bullseye housing would definitely open things up for smaller turbos and the 38mm flapper is a plus.BTW Speaking of switching housings. Is it possible to run a stage 3 T3 Turbine housing w/ a stage 1 turbine wheel? The reason I ask is because the wheel + housing (.48 AR) are tiny for the T3 I bought. Some of the club3g members are predicting cooked pistons due to the back pressure. So is it possible to simply upgrade the turbine housing to relieve some of the back pressure?
The main reason I'm hesitant to change the wheel as well is due to $$$. The T3 that I bought has zero shaft play, and I don't feel like buying a new wheel + housing + rebuild/balancing. Instead it would be MUCH cheaper to just upgrade the housing.
You do not need a large turbo to go fast, a guy just ran a high 10s pass in his 1g awd on a 14b. I doubt it was a stock 14b, but that is still very impressive. Its all about your supporting mods and tuning.
7g for life!
ok sorry if this is a dumb question but this manifold is supposidly off a 4g63t and i am not sure if i can run it here the link
http://cgi.ebay.com/ebaymotors/DSM-4G63-EV...1QQcmdZViewItem
Stay FAR away from xs-power and ssautochrome. Both companys are the same, and they make VERY low grade products. The day their attitudes (towards customers) and products become better is the day I bid on their shit.
exhaust manifold for a 4g63t is what you need, so yes it will fit. stay away from the 1g ones, try to get a 2g
<div class='quotetop'>QUOTE</div><div class='quotemain'>BTW Speaking of switching housings. Â*Is it possible to run a stage 3 T3 Turbine housing w/ a stage 1 turbine wheel? Â*The reason I ask is because the wheel + housing (.48 AR) are tiny for the T3 I bought. Â*Some of the club3g members are predicting cooked pistons due to the back pressure. Â*So is it possible to simply upgrade the turbine housing to relieve some of the back pressure? Â*
The main reason I'm hesitant to change the wheel as well is due to $$$. Â*The T3 that I bought has zero shaft play, and I don't feel like buying a new wheel + housing + rebuild/balancing. Â*Instead it would be MUCH cheaper to just upgrade the housing.</div>
I would assume so. The bullseye housings are just beefy stock replacements. Email bullseye to be sure, but I wouldnt think there would be a problem. THe bullseye housing would definitely open things up for smaller turbos and the 38mm flapper is a plus.
You do not need a large turbo to go fast, a guy just ran a high 10s pass in his 1g awd on a 14b. I doubt it was a stock 14b, but that is still very impressive. Its all about your supporting mods and tuning.</div>
Ya the bullseye products are definetly good stuff. Though I wonder if the 38mm flapper is too big for the stock wastegate flapper (even it is, it should be replacable im guessing).
Ya I really don't want to get a bigger turbo. I just dont want to melt a piston. lol the turbo i have right now is much to small for the V6. I just want to keep the wheel, and increase the housing (thereby allowing for much less back pressure).
Small turbos FOR LIFE!!!
i'm running a bullseye on my 14b. w/ a 38mm flapper.
works great, huge inlet(7cm), and huge outlet(2.5"). i'm still waiting on my sbr manifold with a slightly over 7cm collector. when thats on i should big top end gains. but with just the bullseye housing and a stock unported manifold spoolup is greatly improved and wastegate response is much more effective at controlling boost thus far. i have yet to open up to full 3" from the downpipe back, but i'm confident i will see no creep. running 18psi for now though i could up it, i'm more comfortable here until i get new tires.
but with the bullseye housing i can say that my car pulls harder now than it ever has.
also on a more relevant note:
they do make turbines for the t3. they make them flanged for dsm or t3. with vband exhaust or dsm o2, or t3 o2.
cast steel too, so no more cracking
______________________________
1994 Galant GS-Turbo
<div class='quotetop'>QUOTE(seth98esT)</div><div class='quotemain'>You put down any numbers yet Kevin?</div>
Not yet...I haven't installed my new clutch yet on -G-rim. I am kinda hooked on getting my other project running. :twisted:
1991 Galant VR4 1948/2000_________1996 Galant "S" 5 speed 2.4L turbo
Posting Rules
Bookmarks