How size matters. Compressor map illiterate? By Zero R
 

Sean, (A-spec) will answer your questions in this thread about:

https://www.rx7club.com/spec-tuning-154/how-size-matters-478915/

This thread contains some great info for those of us who are compressor map illiterate.

Later, Jeff

my question for sean is how does rotor compression calculate into the equation....obviously a set of 9.4 rotors will produce more power at 15psi than 8.5 ...also....what is the conversion for CFM to lb/min?....thanks for the useful info

1lb/min ~ 14.27046CFM

What efficiency % is consired "efficient"? Anywhere between the surge and choke lines? I attached what I thought was my compressor map, but unfortunately it's not quite. I have the super H wheel and this is the regular H map. based on my calculations I'm into surge at 4250rpm and 1 bar of pressure. Does this not matter because I won't build that much pressure that quickly?

I'm no expert, but I have read through your write ups, and it seems that this compressor wheel is pretty well matched to an FD looking for quick spool and moderate numbers (400whp).

But, will the increased exducer of the Super H change this map significantly? Also what turbine wheel/housing is recommended (KD street ported)? The turbo was a q-trim but I've heard from many that the q is too much for this compressor. I planned to match the Q with a divided .84 or 1.00 to keep good response. I was told by Bryan at BNR that a .84 would choke the engine even with the q-trim. Any help would be MUCH appreciated.

I know its off topic but could you elaborate on the intercooler stuff, the information so far is awesome keep it coming!

Anything above 70% is good.
Anything above 60% is okay.
Don't go below 60%.


No.
I think Turbonetics quotes like 10% to 15% better efficiency with the Super wheels.
It's just a 3.00" exducer versus the normal 2.75" exducer.


Now that has nothing to do with compressor maps, does it? :D


-Ted

Hey guys, sorry I didn't even see anyone posting in here I will try and asnwer all these over the holiday.

-S-

Do you have a POV system available? Would this require a closed loop system with two pressure sensors, one before and one after the throttle body for adequate response? This would greatly help in pressure spiking too.
Next year funds willing I would like to do something like this.

Thanks

Hey Sean. Thanks a lot for the great and detailed write-up. I found it very easy to understand and follow. I was wondering if you had links to any other compressor maps and also, the main reason I'm writing this post, if you could please explain about trim (in general) as well as sizing of the houses and what the wheel diamter is also called or if it is just called the wheel diameter. Thanks so much!

Craig

This has some rotary maps as well.

http://www.forcedinductions.com/help.htm

any turbine maps for o, p, and q trims?

Greate link , really usefull , but it not apears the GT40R ):

OK, then what is a 13BT lb/min rate?? :squint:

Jeffshoots formula I calculated equals about 578.79 CFM or 40.50 @7000 rpm.
The site by JZ 97 SS 1500 says that the max lb/min rate of a 13B is 20lb/min @7000rpm

I am trying to figure out which trim to use in conjunction with my TO4B.

H-trim is at 72% effeciency with 40.50 lb/min @ 2.0PR BUT with the 20lb/min it is at surge limit.

S-trim is below 50% effeciency with 40.50lb/min @ 2.0PR OR 72% effeciency with 20lb/min

V-trim is @ surge limit with 40.50 lb/min @ 2.0PR OR 72% effeciency with 20lb/min

I got all these figures off of the comp maps at Turbonetics site w/ their TO4B.

I used a V-trim and was really happy with the results.

I found this great site with tons of maps.

http://www.squirrelpf.com/turbocalc/...any=5&family=1

Cool thread very informative. Thanks for posting it.

What sbout for a 12a do you just substitute 2.2 instead of 2.6????

Thanks for the thread. Very helpful.

Sorry for the thread revival, but I'd sure like to understand a few things better.

First, regarding the calculations on www.forcedinductions.com, I'm fairly certain that they are using 1.3L for the displacement, hence their almost perfectly uniform reduction in calculated mass flow by a factor of 1/2.

My question is primarily concerned with the value used for the density of air. The density of air varies significantly with pressure and temperature. The value used in Zero's calcs is that of air at ~14.7 psia and ~100F.

Since we're actually doing calculations for psig, for a PR of 2, shouldn't your value be almost double that value? This will obviously correspond to double the power for a given VE, RPM, and PR.

Would accounting for the variation of air density with pressure and temperature while using a value of 1.3L for the displacement be more accurate for generating a plot of lb/min vs RPM for various PRs?

I apologize if my question isn't clearly phrased.

It is valuable to me to know what the efficiency of the turbo(s) will be at various RPMs and PRs because on road courses, you aren't concerned with just redline. Optimizing the efficiency will be highly dependent on the answer to the above question.

Thank you kindly.

I have a turbo that I bought and have not put into my car yet that says its good for 700-1000 HP but its a pretty decent size turbo... Would the bigger the turbo mean the more turbo lag?

Quick question. Has anyone actually logged how many lbs/min of air one of our motors gets at said Pressure ratio? Its just odd we say 90%V.E. Is it possible our V.E. is just a lot lower and what not? Everyone says that we out flow turbos which would be true according to compressor maps. I'm just wondering if anyone has logged said air flow from turbos? Because even though we outflow certain turbos people still end up crank the boost and making more power with certain fuels and aux injections. Just curious

We don't have valves. Its very easy to get what looks like an exaggerated VE with a free flowing intake and exhaust. Of course porting helps.

thats pretty awesome. I never read anything like this before.even on other forums lol

this is very helpful! will definitely be referencing back to this!

Anyone know why I can't see the thread? It appears to be locked.