Red-Rx7

Hey gang. I know this has been hashed a few times, but the topic usually goes south quickly.

I started a new project. My 20B conversion. Some items are already on the way.

Within the next two months, I will have to decide on an appropriate turbo for the car. I was thinking about going with a T66.

But here is my question... On a 13b, the T66 isn't all that great until you get into the sweet spot right? Sweet spot being 17ish + boost.

Well on a 20b, how is it different? My goal on the 20b is to keep the boost low, in the range of 9-14psi.

Normally, on a 13b people would suggest a 60-1 for this range, but what about the 3 rotor? Is it going to be breathing to little? to hard?

Opinions please.

Thanks,

Mike

zyounker

Well, first you need to decide how you are building the engine..


Are you gonna have it ported? is it even gonna be rebuilt?

Are you gonna put in FD exhaust sleaves?

I think the T66 is a little small for a 20B, but that depends on how much power you want to make.


The Stock twins modified to run in non-seq will be arounf 10-13Psi for the sweet spot. they are very small too. I have heard some people run them up to 15, but don't know how hot the air comming out was..


-Zach

Red-Rx7

Well! Good questions.

I will have the engine rebuilt, pinned, with all the goodies.

I believe I was leaning toward a street port on the block. Nothing too aggressive.

My goal is 450 - 500rwhp with a lower boost level, playing it safe.

One question, what do you mean FD exhaust sleaves?

Thanks,

mike

Kurgan

You can do that with the stock twins. No need for an expensive single turbo upgrade.

If you do want to go with a nice sized turbo though, The T-76 is VERY similar on a 20B to a 60-1 on a 13B. A T-72 will spool up a bit faster and not give you as much HP up top, but if you are only going for 500 or so, this turbo will do it at that boost, maybe less. I suggest either sticking with the stock twins and seeing what it can do for you, or going with a T-76 (turbonetics), PT-76 (Precision Turbo) or an innovative turbo GT-76 (ball bearing, a bit more costly). Greg at importformace can get you the Precision turbo or the Innovative tubos, he also can get some killer deals on Turbonetics stuff.

As far as a wastegate goes, you need a large one, and a BOV to match. I suggest either getting the tried and true HKS GT 60mm wastegate, or possibly the new titanium springed Tial 60mm (this is the one I'm going with). The Greddy Type R BOV will do you fine as well.

Kurgan

oh yeah, about the exhaust sleeves. The stock 20b rotor housing's exhaust sleeves are angled to direct exhaust pulses into the stock twin turbo system. They are not machinable (to any degree that will help), so you either have to have them removed and replaced with 13bt or 13brew exhaust sleeves... or, go with some 13brew rotor housings.

Red-Rx7

Kurgan-

Thanks for the reply. I do not want to have to boost more than 14 psi, and be able to be in the 450 - 500 RWHP figure. Anything under 14psi of boost is much more "safe" in my opinion.

If the T76 can produce 500rwhp @ 13ish lbs of boost, then that will be turbo. I am also concerned with the power band itself. I don't believe there will be really any "Lag" due to the excessive amount of torque from the engine. The torque should "hide" the actual lag from the turbo. Would I be assuming this correctly?

Thanks for your opinion. I wait to hear from you again.

Thanks,

Mike Haun

Greg

Running that T76 at 13 psi is a waste.

Red-Rx7

But will it produce 450 - 500 rwhp @ that number at a reasonable RPM (aka little lag)?

Evil Aviator

Compressor Maps:
http://www.turboneticsinc.com/comp_maps/fig1.html

How to Read them (use 240 cu in displacement for a 20B):
http://www.gnttype.org/techarea/turbo/turboflow.html
and
http://www.amazon.com/exec/obidos/se...simart_detail/

Have fun!

Red-Rx7

Hmm. Interesting.

So, using some of the basic numbers (and not knowing what our VE is), here is my sample data:

1) Outside temp is 80F (TIN)
2) Intake Temp is 90F
3) Running 14PSI of boost @ sea level
4) There is a -.5 psig at the inlet (PIN)
5) VE is 85%
6) 466 is the cu ft / min

(7000 RPM X 230 cu = 1610000 / 3456) = 466 cu ft / min

With that in mind, our ABS Tempature is:

90 deg F + 460 = 550 Deg R

Our ABS Pressure is:

14 psi + 14.7 = 28.7 psia

To calculate the flow per minute with tempatures:

N = 28.7 (psia) X 466 (cuft min) X 29
----------------------------------------------
10.73 X 550 deg R

= 65.72 lbs/min

Now, to correct that number for turbonetcis graphs:

TIN = 80 + 460 = 540 deg R
PIN = -.5 + 14.7 = 14.2 psia

65.72 (lbs/min) X (540 deg R/545)^.5
-----------------------------------------------
(14.2 psia / 13.949)

= ~64 corrected.

Now, time to figure out the compression ratio:

Pout = 3 + 14 psi = 17

(17 + 14.7) / (-.5 + 14.7) = 2.16 %

===--=--=====

Ok, so looking at the T76, I draw my nifty lines.

2.16 & 64

That puts me in the 76% range and above the 85,200 rpm spinning blade.

==--=-=

So, I assume that is good right? But what does this mean? How do I relate the 76% back into a somewhat HP figure?

My numbers correct?

Thanks!

Mike

Red-Rx7

Also... If I were to run 8 psi, that would put me (guestimate here) in the 78% range...

So greg, how is it a waste to run this turbo at that psi for these figures?

Mike

Evil Aviator

Oh boy, that's a lot to look over at this time of night.

The 20B is closer to 240 cu in, not 230. Did you correct your figure for volumetric efficiency? I can't seem to find where you multiplied by the .85 that you stated at as a given. Anyway, you will have more than .85 Ev with porting. No, I don't have exact Ev numbers, sorry.

You can estimate horsepower at different points on the compressor map with this equation. (My apologies to the engineers on this forum for using such a hack method, but dammit Jim, I'm a pilot not an engineer, hehehe).

BHP = (Airflow lbs/min) / ((BSFC / 60) * AFR)

BSFC will be about .60 to .65
Best power AFR is about 12:1 with unleaded pump gas

So with the 64 lbs/min number you got, that would calculate to about 492bhp at .65 BSFC and 12:1 AFR.


See the attachment...
By your numbers, here is what you should end up with:

Under WOT, the boost will build up somewhere around the blue lines depending on your AR, the inertia and friction of the turbo, engine load, etc. The calculations for how fast a turbo will spool up are very complicated, so it is usually best just to see what others are using, and see what results thay have had. Back to the compressor map, you will not make boost to the left of the surge limit line. If you read down to the airflow lb/min numbers, you can reverse engineer your equations to figure out what rpm they represent. As you can see, with your numbers, max boost will happen no earlier than the rpm corresponding to about 40 lbs/min (the intersection of the surge limit line and the green max boost line).

Once the turbo reaches the green max boost line, it will follow it to the right. The red line is your redline (how about that, lol). Assuming that volumetric efficiency is constant (which it isn't), this is your max flow rate. Also, technically the red line is not vertical as depicted on the map, but I'm not going to get into that.

The yellow area is the turbo operating range for your engine. While the turbo will follow the blue and green lines at WOT, the rest of the yellow area is used when not at WOT, like when accelerating at half throttle, or when partially letting off the gas before reaching redline, or when at cruise and then pressing the gas to increase boost, etc.

Here is more good turbo stuff, but it's for piston engines, of course:
http://www.turbofast.com.au/javacalc.html

OK, I'm tired, so now it's time for others to tell me if my numbers are correct.

Kurgan

Running the T-76 at such low boost is a waste, thats why I suggested something smaller, like the T-72. But personally, I don't see what the point of going to a single turbo (besides simplicity) if your goal is 450-500 rwhp. You can do this with the stock twins, they may require a compressor upgrade, but 14 psi on the stock twins will net you what you want.

The T-66 is too small of a turbo for a 20B. You will choke your engine with that small of a compressor.

Anyone know off the top of their head what compressor or turbo combination flows in the 90-100 lbs/min spectrum?

Greg

Mike, the T76 is high boost efficient turbo. 25psi + I wouldnt be suprised if you made close to the same number with a T64 @ 13psi as the T76 at 13 psi. Also, on a 3 rotor if you are looking for 500 rwhp and the stock non sequential tubos cane make that power. Me personally if I wanted quick spooling and Big power on a 20b Id go with a T66 1.32 dual ball bearing turbo.

Red-Rx7

Greg-

See, this is where I get confused.

What is the point of doing all that math and determining the % and rpm from those maps?

Its confusing to me. Doing all the math and then plotting it on the compressor maps, gets me what? It says its in a good range, but there are better turbos and ranges correct?

Also, the 1.32 AR, how does this effect the compressor maps? None?

Mike

zyounker

Actually you probably would not want a 1.32 AR, that is a divided turbine housing i believe..


The A/R just moves where the powerband is. so the larger it is the more power you have up top.



-Zach

Evil Aviator

The % (efficiency islands) tell you how much heat will enter into your intake airstream. Much like a cold air intake, the cooler the better.

The rpm's will show you where the respective turbos will make boost. Try plotting the same stats on the T66 map, and you will see that it will make max boost at a lower rpm, although it starts losing efficiency as it approaches the redline.

It will change the blue line on the example that I attached. A smaller AR will move the blue line closer to the surge limit which means less lag, but the turbo may run out of steam at the engine's redline. A larger AR will move the blue line further away from the surge line which means more lag, but will help allow for a strong-spinning turbo at the engine's redline.

Corky Bell's "Maximum Boost" book has the best explanation of the AR that I have seen. You should get the book before you spend $3K+ on a turbo system.

Red-Rx7

Ok, more calculations and correction. Thanks a bunch thusfar for everyones help and assistance (Evil, zyounker, kurgan & greg!)

New questions at the bottom:

"Hey gang!

I am asking for help on turbo compressor maps, airflow, and how this relates
back to me in a decision for a turbo for my winter project.

If you are still interested, please continue reading below (for it gets
pretty lengthy)!. I DO wish anyone knowlegeable on this subject please take
10 minutes out and help! Thanks!

-=-=-=-=-=-

Background:

Doing the 20b Conversion process to my 1995 R2 rx7 this winter. Having
trouble determining which turbo to use to reach my goals.

Objective:

- Learn more about Turbo compressor maps, and how it will assist me.
- Choosing a turbo that best suits my needs
- Making 450 - 500 RWHP between 8 - 14 psi of boost
- Gaining opinions, and making friends. yay! :P

OK!! Off to the races!

When looking at the turbo compressor maps, you need two pieces of
information:
-Pressure Ratio
-LBS/MIN Airflow.

Now to obtain those:

1) First determine the volume of air per minute without additonal factors:
CU ft/min = RPM X CID / (1728 X 2).
(answer)
486 = (7000 X 240)/3456

So, its 486 for the cu ft/min

2) Determine the Absolute temp.
ABS Temp is Manifold tempature in F + 460 = XXX deg R
(answer)
90 + 460 = 550 deg R

3) Determine the Absolute Pressure
abs pressure = (boost running) + 14.7 = XXX psia
(answer)
14 (my psi) + 14.7 = 28.7 psia

4) Do the math for the lbs/min with the cooling added:
(lbs/min) = (value (psia) * value (cu ft/min) * 29 ) / (10.73 * value (deg
R))
(answer)
~68.54 = (28.7 * 486 * 29) / (10.73 * 550)
So, the uncorrected lbs/min is currently at 68.54 with the turbo boosting at
14psi and rpms at 7000, with an intake MANIFOLD tempature of 90o F.

5) Convert the uncorrected to uncorrected with VE involved:
actual air per min = uncorrected * VE
(answer)
Now, I am guessing my VE% here. ***anyone has an better guess, please let me
know***
65.11 = 68.54 * .95
SO! My uncorrected VE Airflow / Minute is 65.11

6) Calculate the "Corrected" Airflow for the compressor maps turbos:
Corrected Flow = (value (uncorrected ve airflow) *
(tin/545)^.5)/(PIN/13.949)
TIN (deg R) = (Inlet Tempature) + 460
PIN (psia) = (pressure drop intake spining) + 14.7
(Answer)
85o F + 460 = 545 deg R
-.5 + 14.7 = 14.2 psia
--
(65.11 (uncorrected ve) * (545/545)^.5)/(14.2/13.949) = 63.96 OR bascially
64.

So!!! My Corrected Airflow in LBS/MIN is ~64.

7) Calculate the Pressure Ratio:

Pout/Pin = (value (Inlet pressure drop and manifold total) + 14.7) / ( value
(inlet pressure drop itslef) + 14.7)

Inlet pressure drop & manifold total = dropped psi + actual running boost.
Inlet pressure drop = -.5
(Answer)
16 psi = 2 (dropped pressure) + 14 (boost being ran)
-.5 = Inlet drop
(Real answer)
~2.16 = (16 + 14.7) / (-.5 + 14.7)

-=-=-=
Ok, all this math, here is what we got.

My pressure ratio is : 2.16
My corrected airflow in lbs/min is: 64

Now, looking at the turbos at the turbonetcis website
(http://www.turboneticsinc.com/comp_maps/t76.html), and the T76 in
particular, it puts me in the 76% range and turbo rpm above 85,000.

=-=-
Putting it all together:

Now, assuming this is good? Its effiecent, but is it? People note "That
turbo is being misused. Its a High PSI turbo". This maybe true, but what
is this telling me?

From my understanding, being in this efficency range causes my exhaust
tempatures to be MUCH lower than being in a less efficent range, hence less
work for my intercooler and more power to be made.

1) Is this a fair comment to be made by me?
2) Can this turbo make my power requests? I guess the AR determines that,
and lets discuss that.
3) What about lag? I see the surge limit on the left and know I am limited
to max airflow by that line, so can we reverse engineer this madness to
determine lag?

THANKS!!!! PLEASE RESPOND! I am affraid I am scaring people away because of
the excess writing.

Thanks a bunch again!

Mike Haun

Greg

The divided turbine housing will not affect the spooling and performance as much as you guys are thinking. ALOT of people run the divided turbine housing on their setups. The difference is barely noticable. I also dont think you guys know how much air the 20b moves, anything smaller that a 1.32 will choke the 20b at higher rpms.

ForceFed

I have a question. Are you guys saying that the 20B displaces 240CIs? How do you arrive at that? If a 13B displaces 79 cubic inches, then 79/2= 39.5.
39.5 x 3 = 118.5 cubic inches. Where is the 240 coming from?


Darril

Red-Rx7

Darril, I honestly do not know. But I believe the number is used from conversion when calculating cfm, cuft/min, etc.

Red-Rx7

And a new addition to the question:

Ashraf-

Thanks for you reply!

<Snip>

"> No, you are above 65,000 rpms, not 85,000rpms.
> Not your fault -- bad diagram/drawing @ poor resolution.
> Look at the T-66 plot
>
> As you go up on the axis, RPMS increase, and for that point to be 85,000,
> the next two lines would be 95,000 and 105,000 most likely.
> If you plot a straight line from your pressure ratio an intersect it with
> the airflow, you are in between the most efficient, and 2nd most
> efficient efficiency bands."

Ahh yes, it was my mistake. The numbers are difficult to see, but I didn't
look at the next hash marks. And you mean T76 right? :P

Ok. Your comments were well taken. I guess what I am looking at now, is
even though the turbo is in its efficient band, it STILL might not be the
best choice... Correct?

The choice comes to what ones specific goals are. If I were to pick a turbo
that had a smaller compressor, it moves it to the right of the graph.
Therefore, the turbo is working much harder, and causing much more heat out
of the exhaust ports.

BUT..... if the intercooler does its job and keeps it where my goal intake
temperature is, I could actually pick up a turbo that spools "quicker", yet
makes the same HP at the desired levels of boost.

Now, this brings into the new topic, of :

"If the turbo is XXX efficent, and makes XXX less heat, how much more HP
will this gain" and the comparison, "Is this HP gain worth the XXX more
RPMS it takes to achieve the same boost from another turbo?"

Well, lets run a few number shall we? :P

How hot the air is coming out the compressor:

Formula:

Tout = TIN + ((TIN * (-1 + (Pout/Pin)^.263)/(efiiciency))
(answer)
Assuming :
1) an inlet tempature of 85 deg F
2) Suction pressure of -.5 psig
3) Discharged pressure of 14 psi
4) Using a T76 turbo running in the 76% efficency

TIN = 85 deg F + 460 = **545 deg R**
Pin = -.5 psig + 14.7 = **14.2 psia**
Pout = 14 psig + 14.7 = **28.7 psia**
Pout/Pin = 28.7 / 14.2 = **2.02 compression ratio**
-----
Tout = 545 + (545 * (-1+(2.02)^.263)) / .76 = ( *** 690.65 deg R *** -
460 ) = ****230.65****

So, theoretically, the outlet tempature of the compressor housing is 230.65
deg F. Assuming my goal of 90 deg F manifold pressure, that would mean that
my intercooler would be at a 61% cooling factor? (Math = 90 deg F / 230.65
= 39 - 100 = 61%)

*****Are these numbers correct? If they are, then lets get some
intercooling efficency #'s. What is the standard off the market intercooler
efficency #? Someone please answer this question. Please note if that is
customer intercooler or off the shelf. ****

Now, on the flip side, say I used a T66 turbo. Same data, just differernt
efficency zone.

The zone on the T66 would be in the 65% range. Same math equals this
number:
****255.30 deg F****
Which correlates to an intercooler cooling capacity of 65% cooling capacity
to achieve these numbers.
---
Again, putting it together:

Once we know what the intercooler cooling capacity should be, we can use
that number to determine the Actual intake tempature to figure a new AIRFLOW
in LB/MIN which again, changes everything. Then that requires to find the
new ISLAND (if change) and re run the numbers. BUT, by doing so, it further
narrows down the piece of the puzzle.

Anyone else find this confusing?

So again, can anyone give me an example of spool up time difference on the
two turbos in question (T66 and T76) on a 20b? I think if we can get a few
more questions answered we can make a logical decision on LAG vs Efficency
and extra HP.

Wonderful.

Thanks again everyone!!!

Mike Haun
(btw, the compressor maps are at
http://www.turboneticsinc.com/comp_maps/t76.html)

Mr rx-7 tt

iTrader: (5)

Originally posted by Red-Rx7
Hey gang. I know this has been hashed a few times, but the topic usually goes south quickly.

I started a new project. My 20B conversion. Some items are already on the way.

Within the next two months, I will have to decide on an appropriate turbo for the car. I was thinking about going with a T66.

But here is my question... On a 13b, the T66 isn't all that great until you get into the sweet spot right? Sweet spot being 17ish + boost.

Well on a 20b, how is it different? My goal on the 20b is to keep the boost low, in the range of 9-14psi.

Normally, on a 13b people would suggest a 60-1 for this range, but what about the 3 rotor? Is it going to be breathing to little? to hard?

Opinions please.

Thanks,

Mike

Mike,
I got your pm I will get back with you. It looks as if more people are going 20B.
You and Gordon should swap e-mails together as he is doing the same thing over the winter. I believe granny's speed shop makes or is making a cradle for the triple rotor. The Pettit cradle is around 4000.00, kind of out of sight for an engine cradle. Also, check with Alamo Rotary as they have done several of these conversions and may have some tips/parts etc. that could be useful and save you time and money. Anyhow I think that's fantastic... Chris

BTW Here is the link for Alamo:
http://www.alamorotary.com/

zyounker

Well, i didn't say to go smaller, i just said to go un-divided.. because it is going to effect flow (although maybe not that much) it will.


I think you could pick good A/R that will spool better then a divided one. You could probably go to a larger A/R with an Undivided because you are removing a restriction before the turbo.

(I am just guessing on this one, although in theory it is correct )



-Zach

j9fd3s

iTrader: (3)

how about exhaust manifold design? the 13b is simple to picture, the 20b is more complex....

mike