Ok, I've been reading the ongoing debate about turboing the NA 13b in the 2nd gen forum. I thought I'd post my question here so it woudn't get flammed.

I keep reading that the NA can only hold 6 lbs of boost and I remember reading last year sometime was that at 6-8 lbs of boost the NA was at approximately the same compression as a t2 at 10-12lbs. In theory, to run higher boost, wouldn't the next step be to up the fuel with a better fuelpump/ injectors? I've read that the t2 internals can hold over 1.8 bar of boost with proper tuning. That is alot more than to the max of the stock turbo 2 turbo, so with proper fuel an NA should be able to reach the max that a stock t2 turbo can dish out right??

I want to know the main differences between the 13b and the 13bTurbo engines. I know the rotor's themselves have a different compression, the front cover and housings are different along with the porting. Is one signifcantly stronger than the other? Also from what I understood all the seals are basically the same between all the 13b's.

I think I confused myself with all this rambling, but I'm asking because I think running over 10 lbs of boost on an NA is not impossible if you just tune right, and some people in the 2nd gen forum think otherwise.

Zeff

 

Let's see if I can help any without getting flamed. Different people have claimed that the stock 6 port engine can only hold 6 psi of boost safely. This is what Mariah motorsports claims is the maximum safe boost for a Paxton supercharged nonintercooled engine w/factory computer (actually 7psi). Others say you can't safely exceed this without the risk of detonation. Racing Beat and Hayes Rotary say that a compression ratio as low as 7.5:1 should be used on anything over 5 psi of boost. Uh..wrong! The key is in the tuning of the engine. With a stock computer system you are very limited by what you can do. Remember that an n/a computer is not designed to see boost of any kind so anything made to work with it is a bandaid. The T-II computer can adjust itself accordingly (to a point) for added boost unlike the n/a. This is part of the reason people say don't use the 6 port engines. Many assume you still have the factory n/a computer. Rotary Performance has put several engines together using 89-91 n/a 9.7:1 rotors in 3rd gen engines running over 400hp with proper tuning. It can be done. Your margin for safety against detonation is somewhat smaller so you must be careful. Eventually you will arrive at a horsepower level on the higher compression engine where timing needs to be retarded so much from a lower compression engines that you are making less horsepower than the lower compression engine for a same amount of boost. The thermal stresses on the engine are much greater with a higher compression engine so it will take less boost to kill it than if you used lower compression rotors. How much a stock T-II can hold is subjective to how hard you drive it and how well it is tuned. Remember that 1.8 bar on one turbo is not equal to 1.8 bar of pressure on a more efficient turbo. The 87-88 engine castings are smaller around the dowel pins then the 89-91 units. Some people have had problems with this part of the engine splitting over 400 hp. although many have had good results that high. Since I have not broken one like this I can't prove it. The diffeences between the 13B engines is numerous so I will just stick to 2nd gen. 13B's only. From 86-88 the engines of both the n/a and T-II had the same weight rotors: 10 lbs. The front covers are different since the oil return from the turbo is located here. The oil pump on the turbo engine is larger. The n/a engines have a 6-port configuration vs. the turbo's 4 port version. the compression on these year models is 9.4:1 for the n/a and 8.5:1 for the turbo. 89-91 models changed a little. Again the rotors between both style engines of this era were the same weight as each other: 9.54 lbs. which is 1/2 lb. lighter than the 86-88 rotors. The compression ratios on both were increased. The n/a went up to 9.7:1 while the turbos compression went up to 9:1. The front covers were virtually the same style however these are not interchangable betweend the 86-88 and 89-91 styles without also changing the waterpumps. Mazda decided to change the shape of the front covers in 89. The port configurations inside the 89-91 are the same as the earlier ones. Many people don't realize it but the side seals are different between the turbo and nonturbo engines. The turbo's are slightly larger although you would be hardpressed to notice it by looking at them. The remaining seals are the same. Anyways now that I wrote a small (or big) book, I hope I helped answer your questions. You can run over 10 lbs of boost on a higher compression engine. I'm currently working on putting a turbo on my stock GSL-SE 6 port engine but I am only going to run 10 psi max. I just want a little more pep.

Fred
'84 GSL-SE
'88 SE-converted
Single IHI turbo
FMIC
BIG Streetported 89 Turbo Block
Haltech
Custom Aluminum upper manifold
List is too damn long...

 

I read that just once, but I'm sure I'll go back over it. I'm in a similar situation as you, as I'm planning on turbocharging my 89 na engine, I'm going a different route than what Aaron Cake did though. I'm basically stripping down my block and putting all t2 parts on it, from the intake manifold (that'll take some port work) to the front cover. I've got alot of parts together already but I'm still scrounging around for some more parts. I'm gonna get this to work and just run it until I can afford an actual t2 block as I've got a friends t2 computer sitting around.

Thanks for replying, I didn't think anyone would see this thread.

 

with an 89 the t2 ecu goes right in. you may want something to control the timing, its going to need to be different than a low comp motor. um well rotary god covered it pretty well, i want to add the david lane has had a turbo on his gsl-se for like 10 years, he is on motor #3 (#2 was a bum rebuild) he runs about 9 psi. the gsl-se is only 9.4?:1 not 9.7:1 so hes got it a little easier. also you might want to look for a post from rice racing, its something about the strength of the rotary engine.

for the flames: its very easy on an 89+ to put the whole t2 motor in there, and all of the aftermarket is designed around that, it may be a better idea to do that. it seems like it would be less work too, but hey i know where your coming from

mike
running 20b fc

 

hey rotarygod -
can you explain that to me? i'm not tyring to be wise-*** or anything, i just don't think i understand the concept behind that ...

thanks!


well, i have the answer to this one ... mazda coated the apex seals of the T2 with molybdenum ... that's the difference in size.

and just an opinion here, but wouldn't be easier and safer to just use the T2 internals instead of changing so much to run more boost with the higher compression? or maybe have someone machine the rotor recesses to a slightly lower compression than stock ...

just a thought ...

 

S’funny the things people say.
The number to think about with turbos is effective compression ratio (ECR), which is the engine’s static compression ratio multiplied by absolute pressure ratio (manifold pressure divided by atmospheric pressure). Confused yet?!
Say you run the stock S4 6.6psi boost, that means the absolute pressure (atm. + gauge) in the manifold is 14.7 + 6.6 = 21.3psi. Divide by atmospheric to get the absolute pressure ratio: 21.3 / 14.7 = 1.45. This is basically how much pressure the turbo’s adding to the engine (45%). So for a stock S4 with a CR of 8.5:1, the ECR is 8.5 x 1.45 = 12.3:1
Once you understand all that, you should be able to see that if the engine’s CR is increased, only a small reduction in boost is required to return the engine to exactly the same ECR as before. It also means you can figure out what boost can be run on an NA engine.
Consider your example above, running 12psi boost on an 8.5:1 Turbo engine. This is exactly the same (in terms of ECR) as boosting a 9.4:1 NA engine to 9.5psi.
The NA engines are strong enough to hold lots of boost. I’ve seen 20psi boost in old 4-port 13B’s in Aussie drag cars! It’s the fuelling and ignition that determine whether it goes hard or dies fast.
Hope that all made sense.

 

This is just a project that I'm gonna be working on for the next couple months, I plan to run my current na engine to the ground with this turbo setup and then drop in a t2 core. I've been talking to 'busy13b' about how a t2 with the high comp rotors do, but he's using the NA intake manifold setup which I will not be doing. I'm going this route so I won't need a custom dp or ic initially. There's a guy 'angel guard' I think that has done the t2 intake manifold conversion but I can't ever get in touch with him.

Another question, as mentioned previously and from other posts, the 89+ harness fits the t2 ecu but is it only for the 89-91 t2's or will an older 87 ecu work?

NZ that made sense, but sometimes I wish I went into engineering instead of music technology.

Thanks everybody

Zeff

 

I'm not rotarygod, but you're missing the entire concept of air flow volume (expressed CFM)...



-Ted

 

Jeez rotarygod you've answered questions I didn't know I even had!

Airflow is what makes power, PSI is just a loose way of judging how much airflow we're moving, because we have to compress the air to stuff it into the engine. A more efficient turbo can compress the air and heat it less - more air mass for the same PSI. Remember airflow, not PSI, makes power. (Kinda like how cars are more powerful on cold days... the air is denser so you get more air mass into the engine)

One thing we have to remember though is with the higher C/R, the volume is gonna be compressed more, so it's going to heat up more and be more likely to detonate. The point of lower C/R is so you can get more mass of air into the engine without making the peak pressures too high. When you turbo a high C/R engine you need to run lower boost and use more timing retard to keep the peak pressures below the "oh crap I blew another engine" level. Which means less power, but it'll still work. Go too low on the C/R and you lose off-boost response... There are two lines of thought - run low boost and higher C/R for better off-boost response and take a power hit, or run low C/R, higher boost, make more power for the same/lower thermal stress and suffer with soggier off-boost driving.

 

basically what he is sayin is a small turbo at 10 psi might make 200 hp. a bigger turbo with the same amt of pressure will flow more via more hp.

 

Sorry it took me a while to get back. I've been porting my GSL-SE Let me see if I can explain the psi difference thing on different sized turbos. Peejay pretty much got it right with his last reply. A smaller less efficient turbo will heat up the air more for any given pressure than a larger one. I'm not going into compressor surge or efficiencies of any particular turbo here. This is just a basic expanation. More heat equals less dense air which in turn means less power. However the exhaust a/r ratio plays an important part here too. A larger exhaust wheel or a/r will make more power than that of one with a smaller one. Again just a basic explanation without going to the extremes. I know the arguments. This is true of course unless the compressor is too small to begin with. As a general rule (but not set in stone!) in takes 2 psi of boost pressure to overcome every 1 psi of exhaust backpressure. If you have an a/r that is 1 psi more efficient than a smaller one it will be like adding 2 psi to the other engine. The turbo will boost faster and higher. Ever noticed how much faster your car was without the cats? These are true to a point but there are exceptions that are beyond the reach of this question. I hope I ansered the question without adding too much confusion.

Fred

 

I just noticed an earlier question. Yes the GSL-SE compression ratio is 9.4:1. The rotors on the pre 86 13B weighed 10.5 pounds. A half pound more than the 86-88 styles. 3 mm seals.

Just for some weird info: I pulled my GSL-SE engine apart today and noticaed an error that Mazda made during the engine assembly. I posted this on a different thread. The rear exhaust port was physically smaller than the front exhaust port. This engine has never been rebuilt before. After a little research it is believed that a rotor housing from a different assembly line made its way to this one. Different countries had different sized porting than we did. Europe during the early '80s had rotaries with larger ports than we had. they didn't have the emissions rules of gas guzzler tax we have. Not sure which spec the housing is or which one is the correct one. They are both MUCH bigger now On a side note me aux 5th and 6th ports are going to be bridgeports. I've toyed with the idea for some time and now I'm doing it. A streetported motor below 4k and a bridgeported one above 4k rpm! I will be done by the end of the week. I'll post results when it is done. Can't wait to bolt the turbo to it.

Fred