Well i found a big rig turbo from a junk yard, it was 5 bucks and the turbine spins freely, can this be used on a rotary?

You can use it but I would NOT advise it. Deseil turbo are not ment for high rpms. Depending on what turbo it is you can buy a new hotside for it and use it that way otherwise I wouldnt do it.

[quote name='fc3s4utnv' date='May 9 2005, 06:01 PM']You can use it but I would NOT advise it. Deseil turbo are not ment for high rpms. Depending on what turbo it is you can buy a new hotside for it and use it that way otherwise I wouldnt do it.


[/quote]

uh, I would like to hear your explanation of how RPM has anything to do with a turbo spinning when your talking about a diffrent motor.



The only thing the turbo cares about is exhaust flow.

Exactly as psyclo said, depending on how big that turbo is, you might not be able to spool it until HIGH rpms on the rotary.

[quote name='psyclo' date='May 9 2005, 04:13 PM']uh, I would like to hear your explanation of how RPM has anything to do with a turbo spinning when your talking about a diffrent motor.



The only thing the turbo cares about is exhaust flow.


[/quote]

Have you ever worked with desiel trucks, those turbos are meant for high flow low rpm. Some of the Holset turbos you can buy the different hotsides so that they are more compatible.



And rpms and turbos= this turbo is only balanced to _________rpms, so actually it has alot to do with it.

yes and if the turbo is flowing XXX cfm that means it has YYY spindle speed. spindle speed will be the same, at the same pressure, on a rotary as a deisel so long as the flow past the exhaust turbine is the same. A 5+ liter diesel truck will outflow a rotary until the rotary is at a high (usualy very high) rpm.

True is see where you could have misunderstood what I was talking about. I wouldnt want to attempt it either way though.

Is it just me or did this thread get really complicated, really fast? It went from "I got a big truck turbo for cheap, will it work?" to engineering math equations that my english major ass would never understand.

Let's sum this up





Turbo from junkyard off "bigrig"





I work on "bigrigs"







So, exhaust side used to seeing 14.6 L displacement, dropping down to 1.3...





I don't think it'll spool up too fast







Answer = no









If you got it at the junkyard, you don't have the resources to make it work, simple as that



It's another story if you bought it brand new and are prepared to take the neccessary fabricating, and turbine/engine design to make it happen

[quote name='fc3s4utnv' date='May 9 2005, 08:34 PM']Have you ever worked with desiel trucks, those turbos are meant for high flow low rpm. Some of the Holset turbos you can buy the different hotsides so that they are more compatible.



And rpms and turbos= this turbo is only balanced to _________rpms, so actually it has alot to do with it.


[/quote]





Only balanced to like 20,000 rpm





Do YOU ever work with diesel trucks?



The turbo doesn't spin the same rpm as the motor, it spins more



RPM doesn't matter, it's all flow



Trucks have a low powerband so the flow design is totally different. You just think rpm matters.....

Yes i do, I was saying one it does get spinning the turbo will spin faster than what it was designed for. If you got a Holset HC1 or something like that would work better, and also a turbo you get off of a "big rig" will have the wrong pitch, and completely wrong impeller design. I would guess that a rx7 could spool one but it would not be fast, you would have to have an external gate and not use the internal bc it would be way to much for the engine. The wastegate only regulates how much "boost" gets to the motor not how much "flow" the turbo sees.



And yes I do realize that desiel trucks have a differnt powerband, they are more oriented on pulling power than anything.

20,000 rpm's? Try more like 130,000-150,000 rpm. It's not Flow that spins a turbine, it's Heat with flow being way less important. Diesel trucks run about 1200F EGT, which is cold compared to a F/I gas engine. That's why they need Huge efficient turbines. A rotary running 1700F+ can easily overspin a turbine of the same size. Depending on how big the turbine is, you can run into turbine rpm limitations. Bigger turbines will be balanced to a lower rpm, so with a small A/R, high EGT, and a large turbine, you could easily overspin it if you lost control of your EGT's. More exhaust heat will yield a quicker spool, so it doesn't matter if you are running 3 or 30 psi, the turbine is still spinning the same speed. That's how turbos end up with shaft play! - rotational vibrations from spinning the turbine too fast!

OK defrag wanted to get picky. Above flow is exhaust manifold pressure, which is a function of flow, and temperature and the like. So true he has a point that the higher the temp the more pressure you have but I dont think your right in assuming that heat does all the work. I could head up a trubo and exhaust manifold in an oven but is that going to spin the turbine?

i just like how he said its for diesel trucks, its meant for high rpms.



any diesel truck ive ever been in doesnt rev too high.



kevin.

[quote name='fc3s4utnv' date='May 9 2005, 04:01 PM'] Deseil turbos are not ment for high rpms.


[/quote]

Does that help?

Right, except you're taking it a little out of context. https://www.nopistons.com/forums/pub...IR#>/smile.png Heat does not do all of the work, it just does most of it. Without any heat, boost would be non-existant.



Think about it this way. The air coming into your engine is going to be the same amount that comes out the exhaust, right? The only difference being the heat from the energy of each combustion. Let's say, for the sake of explanation, that your exhaust was to be the same ambient temp as the intake air. Even though the flow through the exhaust manifold ( pressure is irrelevant to spool charachteristics, rather manifold restriction) is spinning the turbine, it will only spin the compressor just as fast which is the same as the amount of air coming into the engine. It's this logic that confirms why you can not build boost while revving in neutral. Your engine is pumping out xxx cfm @ xxx rpm, no matter what load, but the only difference is the exhaust temperature. This is also why displacement is somewhat irrelevant to turbo spool charachteristics.

What does hot air do? It expands. A sealed ziploc baggie full of hot air with the outside air at ambient temp will inflate the bag to the point where it will burst. Now, while keeping this principle in mind, picture the hot air coming through your turbine housing. It is still flowing the same xxxcfm @ xxx rpm, but now we have Hot air coming through. Following the ziploc baggie principle, the hot air flowing past the turbine at xxx cfm has more stored energy (heat), so the hot air means the turbine will spin faster than it would at a lower temperature at xxxcfm. This is why you actually build boost at 5k rpm in 4th gear vs. 5k rpm in neutral. Your engine has a larger load, and is creating more exhaust heat, which spins the turbine faster than it would just by blowing air past it.

At ambient air temp, the air moving past the turbine will only spin the turbine at a certain rpm (value based on turbine efficiency and airflow in cfm). This means that the turbine is only spinning as fast as the air is flowing by it, which is the same amount of air that is coming into the engine and past the compressor wheel. To build positive pressure (boost), you are going to need the compressor wheel to spin faster than it would spin with the amount of ambient air flowing past it. To achieve a faster rotational speed, the compressor relies on the turbine to spin faster than the formula for turbine rpm at a certain efficiency and airflow in CFM. So to build boost, the turbine needs to spin faster than the flow of air that is going through the manifold. This is how heat plays the most important role in building boost, because the stored up energy from the exhaust gasses is released on the turbine, spinning it faste and faster than it would ever spin with just ambient air temp alone.



Again, using this logic, it makes sense that the "hotter than the rest" exhaust gases of a 1.3L rotary engine can spool larger turbos than larger displacement piston engine counterparts. My 2.0L 4g63 talon, which has quite a lower average EGT, could spool a large turbine at let's say, 4000 rpm. How is it that a 1.3L rotary can spool the same turbine at a substantially lower rpm? Heat is the answer. Following this, it will become more obvious that Displacement ( a.k.a Airflow) does not play nearly as an important role as heat does in spooling up a turbo. In conjunction, a 6Litre engine with a 1000F EGT temp will have similar turbo spool charachteristics to a 1.3L rotary engine blowing out 1600-1700F exhaust temps. Does it make sense now? https://www.nopistons.com/forums/pub...IR#>/smile.png

I think your both right, The heat creates x amount of expanded air that needs to flow through an x amount of space. Without either of those in the right proportions, you will not have the ratio of air volume between exhaust and intake to make boost.



Which means the "big rig" turbo is prolly too big.

yep. Airflow spins the turbine, and the heat spins it faster to create boost. https://www.nopistons.com/forums/pub...1047683894.gif

^^ thats what I was getting at. https://www.nopistons.com/forums/pub...IR#>/smile.png

wholy ****, that was technical. lets just say send the turbo out to a turbo shop tell them to make the nessesary changes so that it will work ok, i belive the turbo im runnin came from a small mack truck and works great now that it has been worked over from majestic

Mitsubishi Fuso trucks are a good source of turbos.



What kind of turbo?

^ the early model fusos had 12cm 18G's, and the later models had the same hotside with a 20G compressor. Great if you can find a junkyard with one of those in there and the 'yard dog' doesn't realize what kind of turbo it is. https://www.nopistons.com/forums/pub...IR#>/bigok.gif

[quote name='Il RX8 lI' date='May 9 2005, 05:56 PM']Is it just me or did this thread get really complicated, really fast? It went from "I got a big truck turbo for cheap, will it work?" to engineering math equations that my english major ass would never understand.


[/quote]





Its actually very easy to understand all you need is a basic understanding of math and science

i was going to say what defrag did, but in dummer terms just cuz i couldnt get that technical, i have limited knowledge of turbos but if you understand the basic principle that the cold air that goes in per xxxrpm has the same mass as the air that comes out at xxxrpm but the volume changes drasticaly because heat makes things expand. air going in at 70 degrees F has a much smaller volume than the same air coming out at 1600 degrees F. so if the mack truck or whatever has a displacement of lets say 7 liters and an exhaust temp of 1000 degrees and has a redline of 5 grand. and the mazda has 1.3 liters of displacement, an exhaust temp of 1700 degrees and a redline of 8 grand its possible that the mazda wuld move an equivalent amount of air at a higher rpm and a higher exhaust temp. In theory its possible but highly improbable. sorry for the horrible spelling and the ziploc baggie was a good example.