Jimmy2222

iTrader: (3)

So, I just finished up doing some calculations after looking through some stuff in the single turbo section and how to read compressor maps and stuff. I'm aiming for 300-350'ish range so I started working "backwords" kind of.
I took a desired rwhp of 350 and took rwhp = cfm/1.92 (1.92 cf/min for one rotary horsepower). So that came out to 672 cf/min of air plugged that in to cf/min = (lbs/min)(14.471) and it came to 46.438 lbs/min of air. Now, on FC3Spro, ted highlights the 30-40 lbs/min sections, but in Howard's thread (https://www.rx7club.com/3rd-generation-specific-1993-2002-16/feeding-turbo-rotary-horsepower-airflow-fuels-881992/) he's talking about how rotaries make 561 rwhp @ 73 lbs/min with a TO4Z/equiv turbo.

My question is, if I were to aim for that ~46 lbs/min to get 350 rwhp, would I be able to make that number? How big would my ports have to be to flow that much air?

Now to turbo sizing. If I were to try to run 12-15 psi of boost, it looks like a GT35R isn't really as good a match as say a T66. The 35R reads in the 72% efficiency plateau at a pressure ratio of 2 (~15psi), just outside of 79% efficiency. While the T66 shows approx 76% efficiency at 46lbs/min, 2 PR (pressure ratio). Now, from what I've gathered, a T66 is a fairly big sized turbo and ted says that some people say it's too big. He also says this turbo can make 500 hp. Now, my goal is much more conservative than 500, my question is. How similar are these turbos? I know many people use a 35R because it spools really nicely and has really good qualities to suit our applications. But would a T66 be more optimal to my setup or will a 35R suffice? I'm primarily looking into spool and throttle response (yes I know big ports will kill a bit down low). I'm pretty much spitting out numbers trying to figure this out as I go along (although I must say, I think I have a pretty good grasp on all this for just last night and today of skimming/reading).

Also, my net cc/min at a 70% max duty cycle with a desired afr of 12.2 came out to be 2270.87 cc's. Is 70% duty cycle too high (would I even need to run it that high?)? Is it necessarily bad to have a high duty cycle? I know 85% is usually the limit but is it bad to be running 70%? Is 12.2 a reasonable afr also?

Thanks for the help guys. I know I have a lot of questions and I've tried to understand this as best I can but it's my first car and I just want to figure this out before I really tackle it and start buying crap.

Any help appreciated.

For reference, I used the following two links:
http://fc3spro.com/TECH/TURBO/compmap.html
https://www.rx7club.com/showthread.php?t=881992

87turboIIpat

12.2 afrs are way to lean. i would go with the 35r

Jimmy2222

iTrader: (3)

What is the most desired number for performance? afrs around 11 then? I know it's a good idea to tune on the rich side too just to be safe, just looking for optimal numbers to richen up from, a starting point if you will.

RTRx7

iTrader: (2)

35r hands down.

In the end it depends on where and how you want your powerband. A t66 would be cheaper but will not have the mid range that a properly sized gt35r will.

K-Tune

iTrader: (26)

11.4 is a good target WOT afr.

Evil Aviator

The main difference is from something called Brake Specific Fuel Consumption (BSFC). Ted is assuming a well-tuned engine around 15psi boost, while Howard is assuming a poorly-tuned engine at very high boost.
http://en.wikipedia.org/wiki/Brake_s...el_consumption
http://www.land-and-sea.com/dyno-tec...using_bsfc.htm
http://ntrs.nasa.gov/archive/nasa/ca...1991010801.pdf

Also, for performance planning you should use flywheel horsepower and lbs/min rather than rear wheel horsepower and cfm. Howard's calculations make the rotary engine look a little more drastic because he is also figuring in a fudge factor for estimated drivetrain losses.

Airflow can be increased by either pressure or volume. More boost will increase the pressure, and more porting will increase the volume. How you want to mix and match that is up to you. For your stated goals I would probably choose street porting, but that's just me.

If you were choosing a turbo for an industrial generator that operates at a static engine rpm, then that would be a good way to look at it. However, for a street car engine, you should also look at other factors such as the spool time and where the surge line falls on your target PR line.

To give you a road race example, a friend of mine had a SPO race car with a 13B engine and T61 turbo producing 442hp @ 15psi, and the car turned slower times when he "upgraded" to a T64.

Most fuel injectors tend work best in the 60-70% range for sequential fuel injection, or 65-80% for batch fire.

Just so you know, you will make some mistakes no matter how well you plan. It is a great idea to try and minimize those mistakes, but I just didn't want you to get frustrated when things don't work out 100% as planned. Were engineering a perfect science, there would be no such things as test pilots and crash test dummies.

O2 sensors are designed for economy tuning, not performance tuning. Only novices tune to a target AFR number, and that is only to minimize potential destruction due to incompetence rather than increasing engine output. AFR, EGT, and gas analyzers are good tuning tools, but if you want performance then you need to look at dyno numbers, accelerometer numbers, track times, and the butt dyno (throttle response, boost threshold, etc.).

RTRx7

iTrader: (2)

Well said there.

t24todd

iTrader: (7)

pretty much sums it up... plan it spend it do it fix it repeat

j9fd3s

iTrader: (3)

true, but when sizing the fuel system, you wanna pick something with enough capacity to run anything the engine might want. so when sizing a turbo fuel system you'd probably want something that could give you extra fuel without blowing up the injectors. or handle an accidental overboost.

so a 10:1 AFR number is pretty valid that way.

Jimmy2222

iTrader: (3)

Thanks Evil and everyone else. Like you said, I know it won't work out 100%, most things rarely ever do when you have them written down on paper (how I ended up with my T2 actually haha).

Yeah, the GT35R was my first choice even before I started getting into the technical nit picky stuff. Saw rez's T2 with a 35R and he claims full boost (1.3 bar) at 2700 rpms. That's what initially attracted me to it. (See below)

http://www.youtube.com/watch?v=Ty85qzSQKcE

Again, thanks for the help everyone.

Edit: While I'm at it, how would running a 50/50 water/meth injection change afrs? I plan to run AI when I get my whole turbo setup figured out and done (Just rebuilding it for now and porting it). And if I were to run a setup like this (GT35R and AI @ 12-15psi), would I be able to run it on an Rtek or should I go for something a bit better, not necessarily stand alone (if I find one for the right price I will most likely buy it though) maybe a Haltech Platinum Sprint RE?

MadScience_7

+50

Jimmy2222

iTrader: (3)

Also, with S5's mazda trix says that the weight for S5 turbo and NA rotors are the same weights. If I'm using 9.7 rotors, will I need to get counter-weights from an NA too or only if I have different lettered rotors?

Evil Aviator

It depends on how you look at it. Methanol is a fuel, so adding methanol will increase the fuel portion of the ratio. However, it gets a little complicated because methanol burns at a different AFR and has a different density than gasoline. Water is inert, but will allow for a leaner detonation threshold. If you don't know how to tune, then you will need to take your car to a professional tuner. I have many years of related college courses and tuning experience, but I still don't attempt to tune my engines without help.

I recommend asking that question in the Rtek subforum to see what they think. Personally, I prefer a full standalone EMS, but I tend to waste more money on cars than other people on this forum.

You can swap the S5 NA and TII rotors without rebalancing anything as long as you stay near the stock engine redline.

arghx

iTrader: (3)

how fast your turbo reaches full boost depends a lot on the hotside and manifold. If you get a 35R with a T3 .63 A/R divided turbine housing it's going to spool quick, although most people don't go with anything less than the 1.06 T3. Your power goals are too high for an Rtek realistically.