Calculating airflow for Turbo matching

[Darkness and Light]

I'm trying to calculate airflow for the KA24DE to compare different compressor maps. My data set is:

132 cubic inches6800 rpm redline85% volumetric efficiency

Using the formula: (cid*rpm *0.5 *Ev) / 1728 = Airflow rateI calculated 220.76 cfm

Using the formula: cfm / 14.27 = lb/minI calculated 15.47 lb/min

Using a compressor map I found for a TB22 turbo off a 300ZX TT, I found the efficiency at several different boost levels to be:

7 psi (1.48 bar) 22.9 lb/min About 60%9 psi (1.61 bar) 24.9 lb/min Off the map, 55%?14 psi (2.0 bar) 30.94 lb/min Way off, 50%?

Obviously the TB22 is way too small its barely usable even at 7 psi. On the other hand I was looking at a baseline dyno of a KA24DE and peak power is made at about 5500 rpm. The power drops off badly afterwards and there is over 1300 more RPM till redline.

Since power is largely dependent on how much air and fuel an engine consumes I would assume this to mean that based on that dyno maximum airflow occurs at 5500 rpm. Would it be appropriate to base my airflow calculation on an RPM of 5500 rather then 6800?

Using an RPM of 5500 changes the airflow rate to:178.56 cfm = 12.51 lb/min

At the specified boost levels, efficiency becomes:

7 psi (1.48 bar) 18.51 lb/min Near 65%, 68%9 psi (1.61 bar) 20.14 lb/min Near 65%, 68%14 psi (2.0 bar) 25.02 lb/min 68%

Conservatively assuming a 60% efficiency from a SR sidemount intercooler, the turbo has a total efficiency of 87.2% Assuming 138 rear wheel hp the turbo should be able to push 258.34 hp, well beyond my 180 hp initial goal and my final 200-220 hp target.

Although not great, its still a reasonable efficiency. Obviously a better solution would be to buy a bigger turbo with better efficiency, but would using this particular turbo be reasonable for my needs?

[eazye2000]

Would it be appropriate to base my airflow calculation on an RPM of 5500 rather then 6800?

Nah, I wouldn't think so. Although it would give you a little bit of a 'buffer' if you will. You can throw some cams in there and pick up the rest of the power that's left in there. Just a thought.

[WDRacing]

The T2 flanged turbo's are by and large considered to small to be efficient for the KA. In order to be considered efficient I mean two things. One, the turbo can't become a heat pump if the boost is set to more then 5. The turbo has to able to maintain boost pressure for the entire rpm band.

The smallest turbo I would ever install is a T3 super 60. Going forced induction simply is not worth the effort IMO if you aren't going to use the parts best designed for the job.

If you have decided that a T2 flanged turbo is the one you're determined to use because of the cheap ebay manifolds, then a T25 that's bigger then the 300ZX unit is a must.

There is also more to calculate then the compressor as well. The AR of the exhaust housing and the actual size, meaning T3 or T2 is actually more important IMO.

WD

[C-Kwik]

I had a tough time interpreting what you were actusally trying to determine. But after reading your post a few times, it seems you are trying to estimate the maximum airflow of the engine. Frankly, this approach makes little sense in trying to choose a compressor or determine how well a specific compressor matches a motor.

The best approach is to calclulate estimated airflows at many different RPM points for the motor. Perhaps every 500 RPM. Then apply this to different turbos to determine where on the compressor map each point lands at the intended boost levels. This will give you the best look at which RPMS the best efficiencies of the compressors will be observed, allowing you to make the best decision for your needs. Choosing a compressor based on peak airflow alone doesn't give you a very broad view of how the turbo will be working with the motor.

[Darkness and Light]

I decided I wanted to go with a T2 bottom mount setup because I wanted to minimize the amount of fabrication necessary and use as many SR stock parts as possible. Right now I have a SR sidemount intercooler, turbo outlet and downpipe. A T3 turbo would be more efficient, but more expensive and I would have to commission fabrication work.

I asked about that particular turbo because I already have it. I'm still looking around for another turbo, but I'm trying to figure out what to do with it.

Basically the point of this post is I'm asking if its safe to use that turbo at all. Initial calculation said an emphatic NO, its completely incapable of flowing that much air. However, it occurred to me that the KA24DE does not have 85% volumetric efficiency at 6800. Peak horsepower and thus maximum airflow occurs much lower and based on that, it has enough airflow for my needs and at a somewhat reasonable efficiency across the board as well.

Its not the ideal solution but it seems like it would meet my needs adequetely. My inner perfectionist rebels at a substandard solution, but my cheap, DIY, scratchbuilding side is giving it a kick and telling it to shut up. I've used plastic engine plugs to make bushings for the bit holding up my hatch and made a privacy cover for the hatch compartment. I've even used a wooden golf tee to replace the plastic piece on the brake pedal to turn off the brake lights (I eventually replaced it)

[eazye2000]

This thread is full of big words that us publicly educated folk' just can not understand....

However.....

...I've even used a wooden golf tee to replace the plastic piece on the brake pedal to turn off the brake lights

^THAT, I understand to the "T"

You must be part RedNeck like myself..... I'm so happy <-tears of joy

[Jookmasta]

lol at eazy's remarks. to the OP, although u may have components which are better suited to the t25 route, this doesn't mean that you could sell that stuff and go a different direction. honestly it all depends on what the goal is for the car. if you want to double your hp and torque, then a t25 route will work. if you want to triple your hp and torque, then a t25 route won't work. it is obviously going to be easier to do one setup instead of having to do two.

you've found out that the turbo will become a heat pump after a certain amount of boost so that's a given. only other thing i can tell you is to make sure you don't boost too much with that stock SR sidemount. ur gonna have to keep the boost under 10 psi methinks unless u wanna play with fire.

[jbracy7]

i say just use a sr turbo it'sbig enough not to go hair drier on u but small enough not to lag to hard. oh and 1-2 gears will be use-less un less u like burn outs

[Darkness and Light]

I went to public school too, but my mom's a teacher. I live in Hilo, Hawaii and pretty much eveyone on this island is a 'Hawaiian Redneck'.

[eazye2000]

.....pretty much eveyone on this island is a 'Hawaiian Redneck'.

That's what I'm talking about! I would love to get stationed over there. I would get in trouble though, I think...

[240rbpwrd]

Can you please send me the compressor maps you got for the TB22 i have the auto M24 A/R.48 turbo off a tiwn turbo 300zx and i think with it you could max out 370cc injectors around 200whp or more and it would have a redline of 5500. That is where i see power falling off. In trade i will offer my equations, I followed a book that goes through everything 1 by 1. Remember that all info must be exact or the end result is just a guestimate.

Thanx [email protected]

[240rbpwrd]

sry that was supposed to be [email protected]