I dug up some old info showing the stock TII turbo efficiency as well as the stock intercooler efficiency and pressure drop. This little bit of info goes out to all those people who criticize other forms of forced induction such as roots blowers on the grounds that they aren't "efficient".

The stock TII turbo at it's MAX efficiency point is only 49% efficient!!! Ouch!

The stock TII intercooler is only 68% max efficient. Let's not even get into where it's located. Again, ouch!

Stock TII intercooler pressure drop at only 5.5 psi of flow from a stock turbo is 1 psi! Again, ouch, ouch!

If you raise boost up to 10 psi on a stock TII turbo, you are in the low 40's in terms of efficiency which is downright scary. Not to mention the fact that you've got an almost 2 psi pressure drop through the intercooler at that point. When BDC ran real high boost through his stock i/c with a large turbo, he was probably seeing 5-6 psi of pressure drop!!! Yikes!

The point of this isn't to say that there are other types of FI out there that are better. It's not even to criticize turbos. I just remember seeing people criticize roots blowers long ago on the grounds that turbos are always more efficient. Not true yet some wouldn't concede to that saying that they are. Anyone driving a stock TII can prove this. Not ALWAYS. All things being equal with properly designed systems is typically what this statement is based on though but that's apparently not how things are always designed. Keep in mind I'm not advocating the use of roots superchargers over turbos. Not at all. Just using it as an example although they do have their place in the world.

What can we take from the above numbers? You can use a nice aftermarket turbo and NO intercooler at stock boost levels and be fine is one thing I see. Of course no one installing a new turbo wants to do that. What fun would that be? Because of efficiency issues, don't ever assume a certain level of timing is safe or a certain a/f is safe. It all depends on the setup and each is different. Also, if you have a stock TII and want performance, it's pretty obvious what areas you need to address to get it.

I just thought some people would find that info a bit interesting. At the very least it'll make people rethink wanting to bolt stock TII turbos onto high compression n/a engines!

 

Ever looked at the BNR hybrid turbos?

 

Wow. Just for comparison, assuming you are in the middle of these types of numbers, how bout posting some efficiency numbers for other common turbos, roots blowers, Lysholm etc.


Very interesting!

 

On a more serious functional note though

RotaryGod - based on the effeicency of lack thereof from the stock TMIC. Are you suggesting that there are notable performance gains to be had by using a GOOD FMIC and the stock turbo? We have all seen the posts about what a waste a good FMIC is on a stock turbo and now I'm curious. Especially becuase people have always touted the stock TMIC as a great core

Also, what would you consider to be a good effiecency for an aftermarket intercooler?

 

It's hard to formulate an intelligent response to your post without reading your sources in context.

 

Are we talking thermal efficiency here or through flow efficiency?

Just trying to get a context on the discussion

 

Thermal efficiency! It's horrid!

 

The stock i/c isn't terribly efficient at rejecting heat at 68% but it could be worse. It's got a pretty high pressure drop. 1 psi is acceptable under normal conditions for an intercooler and that's what the stock one is with the stock turbo at stock boost levels. It's adequate for stock and that's about it. Of course upgrading to a more efficient one with less flow restriction is going to be better. However since it does do something, it can still be used for a while. I'd argue that you could get away with it up past about 250 hp or so but above that you should really consider changing it. That's just a number I'm throwing out though.

I for one think that the turbo should be addressed first though as 49% peak efficiency is horrible no matter how you look at it. Keep in mind the turbo isn't always in it's peak efficiency area and is almost always below it. If you could replace the stock turbo with one that was say 70% efficient, that's a very big deal. A BNR hybrid would do a good job on the compressor side but the exhaust side is still pretty restrictive. Fixing anything is better than doing nothing and the BNR's can do pretty well for those wanting more but not 400+. Keep in mind that the more restrictive the exhaust side, the more likely an engine is to detonate so ultimately above a certain point this should really get some attention too.

 

ah, then yes I am surprised it is even 68% efficient. I would have expected much closer to 50%

 

While I do like turbos and have used them and would again, I'm going to flat out disagree with you on the grounds that you probably have no actual basis other than personal opinion with which to back up your statement hence the use of the fictitious term "free power". That and the fact that the single nicest forced induction system for the RX-8 is a twin screw supercharger from Hymee. Turbos aren't free power. That's impossible. They never have been and they never will be. They unlike superchargers however do use SOME wasted horsepower (in the form of heat and exhaust flow) but some of the power required to spin them is in fact parasitic. It is because of "some" that they don't rob as "much" as superchargers do. This however does not mean that superchargers don't have their place. They do.

 

Archive. Good info.

 

Good read, good thread. A+++

 

How would one go about improving the efficiency of the exhaust side of a hybrid turbo (like the BNR) without switching completely to a custom exhaust manifold and turbo setup?

Just trying to see if there's a way to address the concerns while still maintaining the simplicity of a bolt-on upgrade.

Would you also have any efficiency numbers (both thermal and heat rejection) of upgraded top mounts such as the HKS, ARC or RE-A?

 

Actually I think Bryan at BNR does deal with the hot side as well. At least on some of the upgrades. I don't know exactly what he does though. He'd obviously know better than I would.

 

I don't have numbers on anything else. I got these off of old papers I found while cleaning the house. I've got stacks of rotary related papers going back to the early 80's and this was a part of them. Apparently someone did some testing and research when the TII first came out. I wish I could take credit for it but I can't. It's still good info to know though and since I've never seen it anywhere else online I thought I'd share it here.

 

That's fine, thanks for the great info!

 

I know he clips the turbine wheel to reduce back pressure, I think that's it though.

 

I think the BNR 4 uses a P-trim turbine wheel.

 

I think a good sized street port and a good supercharger would make one very fun rotary. The fact that there is less "lag" w/ a supercharger and the rotaries tendency to not have as good lower rpm power would lead me to think it could make a great combination. Turbo's are great for huge hp but a supercharger has its place imo. I think I'll stay N/A though thank you. My friend just got an S4 GXL w/ LWFW, full port (intake ported as well as engine), S5 rotors, and full Racing Beat road race exhaust! Feels almost just as fast as my S5 TII was.

 

If you've ever seen camden RX in person you would know better than to talk bad about a super charged 13b. I for one will keep an NA or super charged RX as I like the feel alot more than that of a turbo car.

 

the turbo II is an over 20 year old design,probably designed sometime in 1985 , of course its outdated and not that efficicent by todays standards..

id sure hope modern turbos intercoolers and blowers have much better efficiency...

 

Two words

Sequential twins

Of course while they are ubber fast in response they do generate a fair amount of heat, or so I've been told. I think the key to extracting reliable power from them is not only a very effiecient intercooler core, both heat rejection and pressure loss, but in making the the overall "system" as effiecent as possible. I will say they don't create nearly the backpressure that everyone claims they do

 

What is the source of your information?

 

Considering that even roots blowers from 50 years ago were hitting the efficiency of the stock TII turbo, I really doubt that it was anything special in 1985 either. Turbos were more efficient than 49% far earlier than that. Only Mazda knows why they designed that turbo the way they did.

 

So with what we have stated here, one could select a modern ball bearing turbo with higher efficiency at a desired PSI, and with the same to slightly higher flow rating (is this stated in pounds of airflow?) and have an earlier spooling, higher horsepower, cooler running, less detonation prone, higher miles per gallon car than the FC as it came from the factory?

Not talking about creating horsepower monsters, but more area under the curve?


What am I missing?