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as BW rolls out more and more turbo options the choice which was pretty easy earlier, pick A or B.... becomes more complex,
there is the easiest question to solve...
will a 8474 92 pound (95 is choke, you won't want to go there) make 700 rw rotary hp (RWRHP)?
of course.
from there it becomes a bit murky.
given it has the girly man 8374 turbine wheel will the 8474 have some early spool advantage over the 9180?
maybe
working against the small (in relation to the compressor) turbine wheel which favors low to mid range is the compressor TRIM and it is almost off the charts as to magnitude.
high Trim disfavors low/mid range and favors top end.
the 8474 compressor is trimmed for top end and one look at the compressor map backs this up..
while compressor "Trim" is generally not a front page subject on this forum it can be very important and the 8474, at 66, is an outlier. it is the reason for the small (7.1 sq inches V the 9180 at 7.85) compressor wheel biased towards the right side of the compressor map.
the 9180 and 8474 compressors have the same inducer area 5.63 but 8474 exducer is only 8.57 V the 9180 at 10.07.
8474 compressor trim is 66
9180 compressor trim is 56
8374 compressor trim is 55
lower trim favors low and mid range, higher trim disadvantages low mid range and favors top end.
as i mentioned mid range can be impacted by trim. if you dig a bit deeper you can see this in the (important) efficiency islands.
the 70% efficiency island at 20 psi boost for the 8474 starts at 38 pounds and ends at 71 pounds.
the 70% efficiency island for the 9180 starts at 33 pounds and ends at 67 pounds.
not only does the 9180 with the smaller trim start FIVE POUNDS EARLIER but it is wider by 1 pound.
since you are wondering, the 8374 starts at 28 and ends at 60 and is 2 pounds narrower than the 9180.
the interesting question re the 8474 is...
you have a clearly top end bias on the compressor due to a maxxed out trim and you have a small driver which favors low/medium performance. how do these two items net out on our rotary?
smallish turbine wheels on a low drag rotary setup exert a cost in terms of EMAP and higher EGTs...
it is not an insignificant cost. when i swapped my BW SX-E 62, 1.0 A/R 76 hotside for my 9180 my EGTs dropped over 100 F and my EMAP dropped 20%. this was going from a 6.31 sq inch hotside (76) to a 7.18 hotside (80).
all our engines have overlap and if they are ported have more overlap. both the exhaust and intake are in communication and if you are running 20 psi boost you have 25 to 45 pounds of backpressure. if you have more backpressure than boost, which you do, you have non-oxygen bearing very hot flow entering your intake stroke. it is pretty obvious you want to do everything you can to limit this potentially engine threatening flow.
plugging up the path out the engine by running a crappy turbo manifold or small hotside wheel or housing is not how you want to fixture your setup... gasoline autoignites at 458 F and you don't want the exhaust anywhere near it.
in the Turbo Technology Section of my site i have a section on the relationship between turbine size (area) and compressor flow and if you examine the relationships you will clearly see Borg Warner's thinking as to where they switched from the 76 wheel to the 80 wheel in the SX-E line. here's a copy of that part:
"While the newer 8474 makes 92 pounds of air and the 9180 makes 87, i prefer the 9180 for the rotary as it has a 21% larger turbine wheel. Rotaries need approximately 30% more air than a piston engine and that means they need to flow 30% more exhaust. Rotaries need LARGE hotside turbine wheels. A larger hotside wheel will lower EGTs and exhaust back pressure. While the 5.91 average square inch hotside wheel might work O K for the 8374 i do not like it matched up with a 92 pound per minute compressor wheel on the 8474 for the rotary. When i swapped in my 9180 ( 7.14 square inch turbine wheel) after testing a SX-E with a 6.31 inch wheel my EGTs dropped 100 F and my backpressure was 20% less.
The best way to understand this important relationship is to compare the turbine wheel average area (TWAA) to the maximum compressor output in pounds per minute (PPM) of air. We end up with a helpful ratio:
EFR
8374 72 pounds per minute (PPM) / 5.91 turbine wheel average area (TWAA) = 12.18
As we draw conclusions from the above relationships keep in mind that the rotary exhaust differs significantly from the piston engine: requires approximately 30% more airflow versus a piston engine and therefore produces 30% more exhaust flow due to no exhaust valve and a straight shot from the combustion chamber is approximately 300 F higher temperature both of these factors place an important premium on a larger turbine wheel and hotside housing.
Consider the above ratios... blue is rotary friendly, red is not.
I like the EFR 8374 and the EFR 9180... I like the SXE 62, 63 with either wheels and the 64 with the larger wheel. BW recognized this important relationship and does not offer the 66 with the smaller wheel. The 66 looks really good for the rotary and has a small 52 trim bringing mid range to the high power party. BW uses the same larger wheel for the 69 and 72 and you can see it is small for the compressor output."
i will be interested to see how the 8474 works out and my real interest will be EGTs and EMAP, not power.
as to power and the FD... i have always been only interested in dual purpose builds up to a max of 600 rwhp. the most recent (Sep 2019) Road and Track interviewed Tadge Juechter who is the Chief Design Engineer for the mid engine Corvette.
the first question was.... WHY?
" Biggest reason was the limit of performance. We knew we were in trouble when we were bringing out a 638 hp (that would be 542 rwhp) C6 ZR1 and we had a hell of a time beating the 505 (429 rwhp) ZO6's 0-60. it was only because of the Michelin tires we were able to do this.... we couldn't hook it up."
given Chevrolet had to rear bias the weight to get more performance around 450/550... i personally wonder why we need turbos that make more than 600 which is 80 pounds...
but that is just me.
Last edited by Howard Coleman; 09-03-19 at 07:15 PM.
Nobody is arguing that a rotary loves a solid turbine wheel. Back pressure hurts both power and engines.
Based on what I am seeing so far I am not convinced the 8474 offers much over the 8374 in terms of power just yet and it definitely doesn't make what the 9180 makes.
That is incorrect. 9280 will have lower EGTS, and EMAP vs the 9180.
Real world is already showing this on the 9280 dynos.
Please explain how adding more compressor without changing anything on the hot side will yield lower egt and less backpressure. I've spent alot of time on the engineering side of various fluid and pressure systems and I'm extremely curious as to why you say that is the case as it goes against any design principle I have ever heard of, and common sense.
If you cannot explain it or post any real data driven results, then its either just a sales ploy to hype something new and sell more stuff or you have no idea what you're talking about.
If you cannot explain it or post any real data driven results, then its either just a sales ploy to hype something new and sell more stuff or you have no idea what you're talking about.
Skeese
Perhaps it's how the turbine is trimmed and/or the turbine design itself was tweaked slightly? 🤷🏻*♂️
Perhaps it's how the turbine is trimmed and/or the turbine design itself was tweaked slightly? 🤷🏻*♂️
Turbines are all the same.
I used to think the same way for the longest time, then realized I was missing part of the equation for emap. Plenty of dyno sheets proving what I have said are online( just look around piston forums).
Please explain how adding more compressor without changing anything on the hot side will yield lower egt and less backpressure. I've spent alot of time on the engineering side of various fluid and pressure systems and I'm extremely curious as to why you say that is the case as it goes against any design principle I have ever heard of, and common sense.
If you cannot explain it or post any real data driven results, then its either just a sales ploy to hype something new and sell more stuff or you have no idea what you're talking about.
Skeese
Since you are apparently the only one who knows what they are talking about? Show us YOUR data that backs your claims?
Don't be like your friend who is calling everyone out to be Garbage while he is blowing up engines in the back ground....
Where is this data that shows a larger compressor wheel causing higher EGT's and higher back pressure ?
Perhaps it's how the turbine is trimmed and/or the turbine design itself was tweaked slightly? 🤷🏻*♂️
Your nose is very brown on this thread.
Originally Posted by rx72c
Don't be like your friend who is calling everyone out to be Garbage while he is blowing up engines in the back ground....
I didn't built a **** motor with 75kPa of vacuum at idle and sharp bridgeports... It wasn't a tuning issue. Corner Seals caught on a Garbage Life motor build.
Let's move past this. I have a 9280 that's never been installed. I will mail it back to turblown or another reputable shop, and if they have their own car or a customer willing to participate, they can run it back to back with another EFR and post results.
It has to be a legit shop and needs to be public, as I want my turbo back after haha
Since you are apparently the only one who knows what they are talking about? Show us YOUR data that backs your claims?
Don't be like your friend who is calling everyone out to be Garbage while he is blowing up engines in the back ground....
Where is this data that shows a larger compressor wheel causing higher EGT's and higher back pressure ?
I don't need turbo-to-turbo data to back up an understanding of the system design. For example if you consider the 9180 vs the 9280 where the hot side turbines are the same size and are talking about a turbo-to-turbo comparison on the same manifold, same motor, same exhaust its a fair known fact that the larger compressor will FLOW more air at the same pressure. So with both turbos at the same 15 PSI, the 9280 is pushing MORE air into the engine requiring MORE fuel to balance to the same target AFR. More air + more fuel in the same compression stroke is going to equal HIGHER cylinder/rotor-chamber pressure, which is where the additional power comes from between the two turbos at the same boost level. With cylinder/chamber pressures this high (100+ PSID before boost pressure), temperature is DIRECTLY related to pressure. The higher the pressure is...the higher the temperature driven up (please refer to Boyle's law: the pressure-volume law states that the volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the temperature and mass are constant, PV=nRT) SO....we have gasses coming out that ARE hotter.
Now next is mass flow. With the larger compression flowing MORE air requiring MORE fuel... you have MORE combustion MASS and more exhaust flow with everything else the same. If that flow is going into the same manifold and turbo housing into the same turbo wheel you are going to have MORE mass inside the SAME hot side volume with the same restriction that you had with the turbo that had a smaller compressor, which is....pressure! Think...if you have a pipe and you push XXXX amount of air/exhaust into it to get it to say 18 PSID, what happens when you force MORE into the same pipe? Pressure goes up. If you don't add flow, pressure will go up.
Making things worse, the exhaust temps are higher from the higher cylinder pressure which only compounds the fact that you're putting more mass into the same volume by adding more HOT mass. All of which brings me to the point that adding compressor without adding turbine and holding everything else the same WILL BY FACT bring up EGT and backpressure. You can't force more into something with the same size outlet and expect temps or pressures to go down...that just isn't how it works.
I'm not saying the 9280 is a bad turbo. I'm stating it will generate higher EGTs and more backpressure than the 9180, because it will.
Yeah naa at the flow limit of the 91 where it is only doing 55% compressor eff and the other is 70% how the **** do you have a lower EMP if you need 30% more shaft power delivered from the turbine? The only way you can increase shaft power at the same rpm is more exhaust manifold pressure to impart that to the turbine.
Yeah naa at the flow limit of the 91 where it is only doing 55% compressor eff and the other is 70% how the **** do you have a lower EMP if you need 30% more shaft power delivered from the turbine? The only way you can increase shaft power at the same rpm is more exhaust manifold pressure to impart that to the turbine.
I think its very important to note that the isentropic efficiency of a compressor does not equate to work but rather enthalpy change in the system. They're certainly tied, but completely different.
Compressor work per unit mass flow is directly driven by the inverse of efficiency. What you are suggesting is that anyone who wasn't concerned with outlet temp would not have worked on impeller design to improve efficiency for power consumption like in mine ventilation fans where outlet temp is irrelevant, that is obviously not the case.
Compressor work per unit mass flow is directly driven by the inverse of efficiency. What you are suggesting is that anyone who wasn't concerned with outlet temp would not have worked on impeller design to improve efficiency for power consumption like in mine ventilation fans where outlet temp is irrelevant, that is obviously not the case.
I'm suggesting that enthalpy of the system and work produced are not 1:1 which is what I understand your post to say.
That is incorrect. 9280 will have lower EGTS, and EMAP vs the 9180.
Real world is already showing this on the 9280 dynos.
Originally Posted by Skeese
Please explain how adding more compressor without changing anything on the hot side will yield lower egt and less backpressure. I've spent alot of time on the engineering side of various fluid and pressure systems and I'm extremely curious as to why you say that is the case as it goes against any design principle I have ever heard of, and common sense.
If you cannot explain it or post any real data driven results, then its either just a sales ploy to hype something new and sell more stuff or you have no idea what you're talking about.
Skeese
Explanation is simple psysics :-)
If everything else is equal AND you change the 68mm inducer compressor wheel in favor of a 73mm inducer -> THEN the shaft speed requirement for the turbo to spin is going to be MUCH LOWER for the same airflow! -> i.e. more exhaust will go through WG(s) much sooner and the same turbine wheel/hot side will rotate with less rpm for the same compressor flow = I.e. much LESS exhaust back pressure and temperature
The now required much lower turbo shaft speed (again everything else equal) will result in earlier surge and spool-up on the same overall turbo. The added air moved from the larger compr. inducer wins by far against the minor added weight in the alu compr. wheel
Having bigger compressor inducers than turbine exducers are excellent for smaller Twin Scroll displacement applications. Strategy here is, that you DO NOT want to harvest air flow from low efficiency areas far out right in the compressor map. Instead you relax and step up in compr. inducer and hereby lower the speed shaft rpm required for the same lbs. Result is both added spool-up, lowered inlet temperature, lowered boost, lower back-pressure, and you STAY near high efficient compressor areas/islands - All with same air flow as before.
Way too many turbos have a hot side configured to very high shaft speed rpm required to harvest the last sum of air of a given compressor inducer. This is either a diesel strategy or more lately a marketing strategy IMO. There is a continuing "pissing inducer contest" between suppliers competing in marketing and dyno pulls who can supply the most flowing turbo with the smallest compressor inducer. Every year a 15% snake oil fluid tested ultra high flow inducers are introduced .....only problem is some suppliers now lately can not squeeze more air out and now just change the lbs vs. hp ratio .... -> BING continued 15% more hp on same inducer. Fact is, it only take a couple of hours to 3D scan and copy any billet wheel and most of all billet wheels flow all +/- close to each other among the suppliers with only the blade count in difference. Route to market is often driven by most BLING and short marketing statements with a lot of fancy abbreviations.
Using same turbos but configured with slightly bigger compressor inducers result in lowered exhaust back pressure, lower temperature and earlier spool-up among others. It is a very effective configuration for specially smaller displacement twin scroll applications!
If you do not care for spool-up, then just go for biggest hot-side possible to have the eMap vs. iMAP ratio below 1:1 at all time all the way to red line
If everything else is equal AND you change the 68mm inducer compressor wheel in favor of a 73mm inducer -> THEN the shaft speed requirement for the turbo to spin is going to be MUCH LOWER for the same airflow! -> i.e. more exhaust will go through WG(s) much sooner and the same turbine wheel/hot side will rotate with less rpm for the same compressor flow = I.e. much LESS exhaust back pressure and temperature
The now required much lower turbo shaft speed (again everything else equal) will result in earlier surge and spool-up on the same overall turbo. The added air moved from the larger compr. inducer wins by far against the minor added weight in the alu compr. wheel
Having bigger compressor inducers than turbine exducers are excellent for smaller Twin Scroll displacement applications. Strategy here is, that you DO NOT want to harvest air flow from low efficiency areas far out right in the compressor map. Instead you relax and step up in compr. inducer and hereby lower the speed shaft rpm required for the same lbs. Result is both added spool-up, lowered inlet temperature, lowered boost, lower back-pressure, and you STAY near high efficient compressor areas/islands - All with same air flow as before.
Way too many turbos have a hot side configured to very high shaft speed rpm required to harvest the last sum of air of a given compressor inducer. This is either a diesel strategy or more lately a marketing strategy IMO. There is a continuing "pissing inducer contest" between suppliers competing in marketing and dyno pulls who can supply the most flowing turbo with the smallest compressor inducer. Every year a 15% snake oil fluid tested ultra high flow inducers are introduced .....only problem is some suppliers now lately can not squeeze more air out and now just change the lbs vs. hp ratio .... -> BING continued 15% more hp on same inducer. Fact is, it only take a couple of hours to 3D scan and copy any billet wheel and most of all billet wheels flow all +/- close to each other among the suppliers with only the blade count in difference. Route to market is often driven by most BLING and short marketing statements with a lot of fancy abbreviations.
Using same turbos but configured with slightly bigger compressor inducers result in lowered exhaust back pressure, lower temperature and earlier spool-up among others. It is a very effective configuration for specially smaller displacement twin scroll applications!
If you do not care for spool-up, then just go for biggest hot-side possible to have the eMap vs. iMAP ratio below 1:1 at all time all the way to red line
This is probably why EVERONE who drags rotary engines, for decades have always said that rotary engines love MORE COMPRESSOR , and you can figure they are using the example vs piston engines, I heard this way before I had a smart phone and joined an RX7 forum.
Pretty dead in here. I was really curious to see a direct comparison between 8374 and 8474 and 9174 and 9274 with actual data to back up claims. I decided to go with tried and true 9180 since there's conflicting information with new turbos and the rotary at higher boost levels (25+psi).
Both arguments make sense, more compressor on the same size turbine would add more back pressure/egt aka more stress. But also if you're not trying to max out the compressor and wanted to make 600whp, then in theory the 9280 should be better because less boost would be required to that power compared to a 9180...so less or the same stress, but technically more efficient with room to grow on the 9280? I really wish there was a direct back to back comparison on the exact same car/motor with the exact same boost and logs to show the back pressure and egts on both to prove or disprove theories.
09-03-19, 09:39 AM
