Looking for some confirmation on turbo sizing...

[Dr Tweak]

Okay, so I've got this guy who wants to get about 250 hp out of his 4EFTE. The engine is a stock turbocharged 1.3 liter making something like 145 hp. I figure that another 100hp is about a 66% increase in power, needing another 9 psi of boost over stock which I believe is 7 psi or so.

So, I assuming that we need around 15 psi total. Now, a 1.3 engine running at 7500 rpm (stock redline) and assuming an 85% volumetric efficiency (probably a little better than that), I figure that the engine consumes 145 CFM:

79 x 7500 x 0.5 x .85 / 1728 = 145 cfm

Now, if we're running 15 psi, the pressure ratio is a touch higher than 2.0. So, 2.0 x 145 = 290 which is the cfm under boost.

We have to convert the cfm to lbs of air per minute for most compressor maps, so going with a temp of 85*, 290 x .073 (weight of air at that temp and sea level) is about 21 lbs of air per minute.

So, looking at a T3 Turbo with a 50 trim, 21 lbs of air per minute and 2.0 pressure ratio is sitting right around 73%. On the other side of the map, assuming boost is made at 50% of max RPM (which is about 3750), then 10 lbs per minute is at 70%. Now drawing the line down to 20% of max airflow, around 4.5 lbs/min, it goes right along the 70% line and stays well inside the surge limit.



So it should look like this:


So, is this a good turbo and are my calculations correct? Or am I wrong somewhere? Is there a better turbo that you would suggest?

*Edit*
This GT22 looks pretty good as well, in 60 trim:

[bgrieger]

My take: You won't move that much air or generate that power on 15psi of boost

1) stock 7psi is going to be 135hp per the literature I've seen on the 4e-fte.
2) Ok, now to the calcs. You've got the math down, but it's all based on the starting assumptions. Here's the ones I used to check what you got:

NA horsepower: 97 crank
Engine: 1.3L, 80ci
RPM range - 3000-6500
psi boost:7
volumetric efficiency: 90%, all RPM (unrealistic, but not knowing the engine, the peak will be higher, and the low end will not get past the low 80's but gives a ball park)
IC Pressure drop: 2psi
inlet pressure drop: .5psi
inlet temperature 85F
barometric pressure 14.7 - sea level
IC efficiency 70%
NA ideal airflow: 135 cfm

With this, I get 135hp stock in the calculators as the baseline...matches the literature, so it is probably reasonably correct give or take a couple of percent. Increasing pressure to 15psi, I see 175hp at 245cfm. The T3-45 trim is the more ideal at this point as the spool up is quicker than the T3-50 for the same output power.

To reach 250hp crank, given these assumptions, my calculations (confirmed by a turbocharger calculator) say you need really near 30psi, at 315cfm to pull it off. However, I can't find a single map that extends that far up with any efficiency.

Now, if he's planning to build the internals and do up the piston compression, the pressure points to given power drop, but the risk of detonation increases to the point he'll want race fuel for the streets...

[Dr Tweak]

Thanks for the help. You are correct about it being 135hp stock, my bad. I don't really know how much boost this baby will take without being built more, but maybe I'll see where we end up if we up it to 18psi. There will be other mods as well to help get up near 250hp, not including the needed ones to boost that high. The guy is willing to give up low engine speed response in turn for higher power up top.