amused

regardless of the debate over how good 'Maximum Boost' is for the advanced in here, it's been an interesting read sofar for me and i consider myself a beginner with my FC TII being my first turbocharged car ever owned

reted, I had a thread in the 2nd gen forum that was moved before anyone saw it to the lounge, but what i was hoping to find out was if there was an easy way to convert some of bell's formulas he's using to calculate engine cfm for a piston to a 13bt? i'm typically very bad at mathamatics so my head already spins when reading half of this book, but i'd like to get it right because i'm hoping to do a t04 upgrade this winter on my TII and i want to figure out what power curves i'd see from the different sizes out there.

amused

<punt>

RETed

To make it easy, we usually use 30 lbs/min as a general rule of thumb for a 13B.&nbsp Pressure ratio just minus 1.00 and multiply by ~14 to get psi equivalent.&nbsp It's easy to stare at the compressor maps using this shortcut...


-Ted

Evil Aviator

The common cfm formulas are intended for 4-stroke piston engines which only fire half of their displacement for each revolution of the output shaft. A rotary engine, much like a 2-stroke piston engine, fires all of its rated displacement for each revolution of the output shaft. Therefore, just remove this function from the formula, which will either be a 2 in the denominator, or a 0.5 in the numerator.

The Supercharged book is better than the Maximum Boost book, and shows compressor charts in the more modern lbs/min format as opposed to the older cfm format. Corky Bell has a lot of experience with rotary engines, but for some reason he has left them out of his books. Shame on him!

Other Corky Bell corrections or explanations that I can think of off the top of my head:

1 bar = 14.5 PSI, not 14.7 PSI. This is not to be confused with his Pressure Ratio formula of PR = (14.7+boost)/14.7, which is correct.

Rotary engines tend to prefer very thick, solid header flanges as opposed to those individual runner flanges shown in the book.

His comments on water injection are from a road racing and street car standpoint.

If you can get his intercooler sizing formula to work in real life, please let me know. Otherwise, I'm sticking to the Spearco charts.

RETed

Check out...

http://www.thecarricos.com/ACRE/

The "New-tech..." and "Recent-tech..." .PDF files should be SAE papers someone converted.

If not, the titles are:
S. Tashima et al, "Sequential Twin Turbocharged Rotary Engine
of the Latest RX-7", SAE paper 941030

Takumi Muroki
Recent Technology Development of High-Powered Rotary Engine at Mazda
SAE paper 841017
(This one is one of the .pdf files mentioned above.)



-Ted

rx7tt95

Ted, you mention 30lbs/min for a rotary...standard port? What would I be looking at ballpark for Cosmo ports, very large secondaries and moderate primaries? Trying to decide which GT40 compressor and turbine would be best for a very nice street setup. Seems like the GT40 82mm, 50 trim, .58 a/r would be better around 1.1kg (16psi "ish") than the 88mm 54 trim, .72a/r. The 88mm looks as if you could "grow" into it for racing purposes and it seems to flow very well at lower boost levels in it's highest efficiency range. Which turbine would match up well, the 84 trim 1.19a/r divided? The 73 trim looks too small at 30lbs/min? Am I reading this right?
http://www.turbobygarrett.com/turbob...%2017%2013.pdf

rx7tt95

Must add, what I have now, GReddy T78, uses what I believe to be a GT40 compressor wheel with the stock T78 exhaust housing/turbine. I'm sure the Garrett GT turbine/housing is a bit more modern and efficient. I'm not sure, given my current setup, that the GT40 compressor wheel and the Mitsu turbine are a perfect match.

RETed

30 lbs/min as a rule, but if we're talking ported motor, I look at the 30lbs/min to 40 lbs/min "range".


It's dependent on how your turbo exhaust manifold is built.&nbsp For a totally divided turbo exhaust manifold (the GT40's all some with divided turbine housings), the 0.94 A/R turbine would make for super quick spool-up.&nbsp With a collected manifold, it should still be quick spooling, but tame on boost onset.&nbsp The 1.19 A/R turbine would make for a nice powerband all the way to redline (i.e. 7kRPM) with a collected turbo exhaust manifold - too bad you can't gank the 1.34 A/R turbine from the 54 trim and stuff that on a divided turbo exhaust manifold!

I would recommend going with the 54 trim comp and the 84 trim turbine with the 1.34 A/R turbine housing and stuff everything on a divided turbo exhaust manifold.&nbsp Boost should easily come up in the 3,500RPM range and pull all the way to redline.&nbsp Even at low boost levels like 7psi (~1.5 pressure ratios), the efficiency plateau is still in the mid 70% - the top plateau is 78% max, so it's not a big drop.&nbsp The turbo should work very well with a nice, ported 13BT, Cosmo 13B-RE or FD 13B-REW...


-Ted

rx7tt95

Excellent! Thanks for the info! I currently have a non-divided GReddy T78/88 manifold (first design, the present day designs are fully divided) and thus I'm not completely happy w/boost response on my current setup. The primary runners are also larger than on the newest design

You lost me on the last sentence, first paragraph "The 1.19 A/R turbine would make for a nice powerband all the way to redline (i.e. 7kRPM) with a collected turbo exhaust manifold - too bad you can't gank the 1.34 A/R turbine from the 54 trim and stuff that on a divided turbo exhaust manifold!"

Why can't you run the 1.34 turbine housing on a divided manifold with a 54 trim? Isn't that what you're saying to do in the first sentence, last paragraph? Am I just confused? :-)

RETed

Yeah, you got it - I wrote that late at night, and I think I confused myself.

Good luck!



-Ted

the_glass_man

iTrader: (2)

Do you think the 1.19 A/R turbine would be a good compromise between spool and power?

Carl Byck

My thoughts on GT40R sizing;
The more research I do the more I think I'd like to put a T66 in my car.(The car is a fully built 13brew rotary road race car with a goal of 550rwhp) At the same time I'd like to take advantage of the relatively low cost, and great performance of the Garrett GTBB series Turbos. With this in mind I've been comparing the specs on various GT turbos to the Turbonetics Q trim T66. I am basing this on a 1.00 ar T66 since I know of a couple of guys who are using it on a T66 with good results. A GT40 comes the closest, although the compressor turbine pairing in the Garrett catalog seems to use a larger turbine than the T66 with a comparable compressor.
Turbonetics T66 specs(assuming I am reading their catalog correctly)
compressor;
90mm wheel,2.58minor,3.584 major=52 trim
turbine;
78mm, 2.693 minor, 3.111 major=75 trim, 1.00ar

Garrett GT40 Ball bearing standard specs;

(1.) 82mm 50 trim compressor, 77mm 73 trim .94 ar turbine
or
(2.) 88mm 54 trim compressor 77mm 84 trim 1.34ar turbine
QUESTIONS;
How will the first Garrett option(your initial suggestion) spool compared to the T66, and how will the ultimate HP compare? or should I(can I) try to get the larger Garrett compressor with the smaller Garrett turbine (almost the same as a T66 Qtrim) ie
T66-- 90mm 52 trim compressor, 78mm 75 trim 1.00ar turbine
GT40-88mm 54 trim compressor, 77mm 73 trim .94ar turbine
Do you know if the dispacement recomendations in the Garrett catalog are based more heavily on compressor or turbine sizing?
Garrett lists the suggested displacement for a GT35 @ 2.5L-3.2L, and a GT40 @ 3.5L-5.0L, and since a GT35/40 uses a GT40 compressor(?), I am guessing the displacement recommendation relates more to turbine size(yes?)
I'm convinced the 35/40 is a bit small for 550rwhp. Carl

little rotor

Hey Ted. You don't know how pleased I was to find all that information. Thanks.