# How size matters. Compressor map illiterate? By Zero R

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**How size matters. Compressor map illiterate? By Zero R**

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

https://www.rx7club.com/showthread.php?t=478915

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

Later, Jeff

https://www.rx7club.com/showthread.php?t=478915

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

Later, Jeff

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**4**DETH TRP

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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'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.

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**6**Lives on the Forum

Originally Posted by

**4CN Air**What efficiency % is consired "efficient"? Anywhere between the surge and choke lines?

Anything above 60% is okay.

Don't go below 60%.

But, will the increased exducer of the Super H change this map significantly?

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.

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.

-Ted

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**8**Lift Off in T-Minus...

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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

Next year funds willing I would like to do something like this.

Thanks

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**9**DRFTRX7

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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

Craig

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Originally Posted by

**JZ 97 SS 1500**
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**13**5 and counting.

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

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.

__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 @7000rpmI 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.

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**14**W. TX chirpin Monkey

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Originally Posted by

**FC3S Murray**__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.

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**19**On flats

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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 psi

Since we're actually doing calculations for psi

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.

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 psi

**a**and ~100F.Since we're actually doing calculations for psi

**g**, 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.

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**20**Silver Bullet

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?

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**21**I'm sorry wha?

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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