Lower Compression Rotors for the REnesis
12-22-2010, 03:23 PM
#76
^ well ask 10 people on the internet about side seal failures in a turbo renesis and you'll get 10 different answers as to the causes, how frequently it occurs, what the breaking point is, etc. So few people have tried a 9:1 rotor in a Renesis that you can't really say it's going to instantly lose a side seal as soon as you hit even 15 or 16 pounds on just plain old 93 octane.
But isn't this the real conversation we need to be having? 300 to the wheels has been done on factory 10:1 rotors and I'm not going to say you should drop the compression for this. That's just a waste of time and money.
300 to the wheels doesn't cut it though. An Rx-8 is not a Lotus Elise. It's pretty much the same time and money investment to run 10 pounds as it is to run 15 or 16, if you were going to rebuild the motor, buy the turbo and the plumbing, install new injectors, tune the car, etc. The only difference is that additional expense of getting low compression rotors. But if those lower compression rotors allow more boost and a bigger turbo (in a practical sense) then you are getting a lot of return on your money.
300 to the wheels doesn't cut it though. An Rx-8 is not a Lotus Elise. It's pretty much the same time and money investment to run 10 pounds as it is to run 15 or 16, if you were going to rebuild the motor, buy the turbo and the plumbing, install new injectors, tune the car, etc. The only difference is that additional expense of getting low compression rotors. But if those lower compression rotors allow more boost and a bigger turbo (in a practical sense) then you are getting a lot of return on your money.
Last edited by arghx7; 12-22-2010 at 03:26 PM.
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Brettus (05-09-2021)
12-22-2010, 04:47 PM
#77
lets back up a little here. Now i could point out that an RX8 with 300hp to the wheels will beat a stock C5 vette on a road coarse etc etc because the car is better than just the engine, but thats another topic.
Lets say if you where building an engine from the beginning and the power level you wanted was 300hp to the wheels, which would be the safest street/ track toy build? A motor that has 9:1cr or one that has 10:1cr running 93 octane with 10% ethanol in the hot south?
Mechanically which would be the stoutest? Tunes being equally adequete.
Lets say if you where building an engine from the beginning and the power level you wanted was 300hp to the wheels, which would be the safest street/ track toy build? A motor that has 9:1cr or one that has 10:1cr running 93 octane with 10% ethanol in the hot south?
Mechanically which would be the stoutest? Tunes being equally adequete.
12-22-2010, 04:57 PM
#78
^ well ask 10 people on the internet about side seal failures in a turbo renesis and you'll get 10 different answers as to the causes, how frequently it occurs, what the breaking point is, etc. So few people have tried a 9:1 rotor in a Renesis that you can't really say it's going to instantly lose a side seal as soon as you hit even 15 or 16 pounds on just plain old 93 octane.
But isn't this the real conversation we need to be having? 300 to the wheels has been done on factory 10:1 rotors and I'm not going to say you should drop the compression for this. That's just a waste of time and money.
300 to the wheels doesn't cut it though. An Rx-8 is not a Lotus Elise. It's pretty much the same time and money investment to run 10 pounds as it is to run 15 or 16, if you were going to rebuild the motor, buy the turbo and the plumbing, install new injectors, tune the car, etc. The only difference is that additional expense of getting low compression rotors. But if those lower compression rotors allow more boost and a bigger turbo (in a practical sense) then you are getting a lot of return on your money.
But isn't this the real conversation we need to be having? 300 to the wheels has been done on factory 10:1 rotors and I'm not going to say you should drop the compression for this. That's just a waste of time and money.
300 to the wheels doesn't cut it though. An Rx-8 is not a Lotus Elise. It's pretty much the same time and money investment to run 10 pounds as it is to run 15 or 16, if you were going to rebuild the motor, buy the turbo and the plumbing, install new injectors, tune the car, etc. The only difference is that additional expense of getting low compression rotors. But if those lower compression rotors allow more boost and a bigger turbo (in a practical sense) then you are getting a lot of return on your money.
As far as the power department goes if you have any use for low compression rotors then you're probably the owner of a track toy.
In that case then chassis\suspension tuning and a serious diet are way more important than just raw power
Have you ever driven an rx8 with 340rwhp with the right suspension work done? It could be a good experience for you in the case you didn't. I totally love the power curves that the renny produces!
lets back up a little here. Now i could point out that an RX8 with 300hp to the wheels will beat a stock C5 vette on a road coarse etc etc because the car is better than just the engine, but thats another topic.
Lets say if you where building an engine from the beginning and the power level you wanted was 300hp to the wheels, which would be the safest street/ track toy build? A motor that has 9:1cr or one that has 10:1cr running 93 octane with 10% ethanol in the hot south?
Mechanically which would be the stoutest? Tunes being equally adequete.
Lets say if you where building an engine from the beginning and the power level you wanted was 300hp to the wheels, which would be the safest street/ track toy build? A motor that has 9:1cr or one that has 10:1cr running 93 octane with 10% ethanol in the hot south?
Mechanically which would be the stoutest? Tunes being equally adequete.
12-22-2010, 06:41 PM
#79
lets back up a little here. Now i could point out that an RX8 with 300hp to the wheels will beat a stock C5 vette on a road coarse etc etc because the car is better than just the engine, but thats another topic.
[quote[Lets say if you where building an engine from the beginning and the power level you wanted was 300hp to the wheels, which would be the safest street/ track toy build? A motor that has 9:1cr or one that has 10:1cr running 93 octane with 10% ethanol in the hot south?
Mechanically which would be the stoutest? Tunes being equally adequete.
[quote[Lets say if you where building an engine from the beginning and the power level you wanted was 300hp to the wheels, which would be the safest street/ track toy build? A motor that has 9:1cr or one that has 10:1cr running 93 octane with 10% ethanol in the hot south?
Mechanically which would be the stoutest? Tunes being equally adequete.
As far as the power department goes if you have any use for low compression rotors then you're probably the owner of a track toy.
On my personal Rx-7 I have 8.5:1 compression. I put 93 octane in it and drive it. I don't put methanol in it, I don't premix, I don't run race fuel. It runs at 17psi. I don't have a MAF sensor so I don't know what kind of grams/sec this is. It's a Garrett T67/T04R turbo so it's got to be at least 450 considering it does around 60 lb/min at that pressure ratio. last dynojet numbers from about 2.5 years ago (old 60-1 turbo) were 386rwhp
12-22-2010, 06:54 PM
#80
Registered
A set of RX7 9 to 1 rotors, in place of the stock 10 to 1 rotors, dropped my 13 PSI engine to 11 PSI with no other changes. (more chamber volume for the same amount of air to be forced into)
I suspect a turbo could build back to the original boost level, if it could flow enough, but my SC moves X amount of air per engine revolution.
So, I spin the blower faster to go back to 13 PSI; with my current pulley set, I would be running almost 16 PSI if I had 10 to 1 rotors.
I suspect a turbo could build back to the original boost level, if it could flow enough, but my SC moves X amount of air per engine revolution.
So, I spin the blower faster to go back to 13 PSI; with my current pulley set, I would be running almost 16 PSI if I had 10 to 1 rotors.
12-22-2010, 07:33 PM
#81
Administrator
Thread Starter
Not only do low compression rotors fail to address the ultimate limitation of the Renesis engine, they will push you to that limit sooner. Reliable FI Renesis power up to that limitation will be had either at the expense of lower boost (street)or higher quality fuel (track unless you have E85 access).
12-22-2010, 07:45 PM
#83
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Thread Starter
once we are at that point ( and I think we all are or close to it) then we can go forward to WHEN it makes sense.
you comment goes in the nutshell for denny
12-22-2010, 08:51 PM
#84
zoom---- thanks.
This thread has some good info in it and I think I am getting it.
Now Rote8's post is interesting, here is a guy actually doing it. Time for questions to him?
From what I have heard --some may be surprised at what his set up is doing?
OD
This thread has some good info in it and I think I am getting it.
Now Rote8's post is interesting, here is a guy actually doing it. Time for questions to him?
From what I have heard --some may be surprised at what his set up is doing?
OD
12-22-2010, 09:40 PM
#85
rev it up
A set of RX7 9 to 1 rotors, in place of the stock 10 to 1 rotors, dropped my 13 PSI engine to 11 PSI with no other changes. (more chamber volume for the same amount of air to be forced into)
I suspect a turbo could build back to the original boost level, if it could flow enough, but my SC moves X amount of air per engine revolution.
So, I spin the blower faster to go back to 13 PSI; with my current pulley set, I would be running almost 16 PSI if I had 10 to 1 rotors.
I suspect a turbo could build back to the original boost level, if it could flow enough, but my SC moves X amount of air per engine revolution.
So, I spin the blower faster to go back to 13 PSI; with my current pulley set, I would be running almost 16 PSI if I had 10 to 1 rotors.
skc
12-22-2010, 09:41 PM
#86
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someone asked- i guess it was inspired since the post is gone
julio don http://www.alkycontrol.com/ at least thats who I believe Ray meant.
julio don http://www.alkycontrol.com/ at least thats who I believe Ray meant.
12-22-2010, 09:43 PM
#87
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^ well ask 10 people on the internet about side seal failures in a turbo renesis and you'll get 10 different answers as to the causes, how frequently it occurs, what the breaking point is, etc. So few people have tried a 9:1 rotor in a Renesis that you can't really say it's going to instantly lose a side seal as soon as you hit even 15 or 16 pounds on just plain old 93 octane.
BTW - three hundred and forty two seventeen and a half point two five PSI... whew, there, now I'm talking about boost PSI and playing with the big boys
Glad I'm not stuck in trying to see the whole picture, to include mass, heat, and gas laws
12-22-2010, 10:27 PM
#90
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OD, I was pushing 290 to the wheels at 8 psi with the stock greddy kit and mm tune no water or meth. This included 4 months at fort benning.
The key was increasing flow, and reducing temps. I coated the entire exhaust with high temp ceramic and polished the intake pipes (the inside).
Plus I talked to Charles and he said some engines just flow better.
Your goal should be easy on a stock engine if you do a few un sexy supporting mods
The key was increasing flow, and reducing temps. I coated the entire exhaust with high temp ceramic and polished the intake pipes (the inside).
Plus I talked to Charles and he said some engines just flow better.
Your goal should be easy on a stock engine if you do a few un sexy supporting mods
12-22-2010, 10:42 PM
#91
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someone asked- i guess it was inspired since the post is gone
julio don http://www.alkycontrol.com/ at least thats who I believe Ray meant.
julio don http://www.alkycontrol.com/ at least thats who I believe Ray meant.
It was me thanks for the info.
I will state one last thing. You will not notice much if any difference in the 9:1 and 10:1 like everyone thinks. I don't have a lab or all the dyno's saved, but I have built enough motors off similar setups w/ 8.5,9,9.4, and 9.7 CR rotors to tell you that it is not that much difference out of boost. You can theorize all you want but I have tried it in the past and it creates more room for error as stated above. Take that for what its worth.
Rotary AIT's are as vital as keeping the motor cool. The AIT's need to be cooler than our piston counter parts. I'll leave it at that.
12-23-2010, 03:31 AM
#92
This thing is going like 4 different directions..LOL
Are we talking turbo's or SC's, 300 or 400WHP, etc etc....
Again, if the turbo is MORE efficient at higher PR's than the engine is, lower static compression = more power. And vice versa (I don't think anyone here would argue that a 10:1 CR running 2 PSI of boost would outperform a 9:1, same compressor, same boost, and be perfectly safe).
Superchargers (non-centrifigal) has other issues since it will not gain efficiency and it is tied to engine RPM. Aggresive timing can only do so much.
So at some flow rate, the desired PR required will lead to lower static compression to survive... and I think everyone can agree to that (unless you can get a VVT working I guess). The question is what is that flow rate, it's not 30 lb/min for sure... or even 40/lb's. I think as we creep to 50 lbs/min we are going to find it.
BTW - a 9:1 engine, gains about 1% thermal efficiency per ATA over a 10:1 everything else being equal. *It actually loses 1%, but for sake of argument, gaining = additional heat just from compression.*
So an 80 ci engine looking to move 50 lb/min of air would be operating at a MINIMUM 200% load at 9000RPMS ideally (I am way oversimplifying). So if the compressor is 70% efficient and the engines have a 2% thermal difference at 2 ATA, no matter what you do, you have to overcome a MINIMUM 91 degree temperature increase in the chamber. Versus, the 6 degree difference at 113% load.
To visualize, a 9:1 Compression engine at a 200% load would be the equivalent to running a 10:1 compression engine at the same load in the artic....think what your margin for error is at 0F. Conversly, driving an RX8 at 14+PSI would be the equivalent of trying to drive an FD when the temps are 160 degrees or more outside!!!!
Obviously, these are really rough figures, I am just trying to illustrate the point. So my personal opinion, anything above 40-42 lb/min of air on an 80ci engine, you wanna start thinking seriously about your Compression Ratio.
Are we talking turbo's or SC's, 300 or 400WHP, etc etc....
Again, if the turbo is MORE efficient at higher PR's than the engine is, lower static compression = more power. And vice versa (I don't think anyone here would argue that a 10:1 CR running 2 PSI of boost would outperform a 9:1, same compressor, same boost, and be perfectly safe).
Superchargers (non-centrifigal) has other issues since it will not gain efficiency and it is tied to engine RPM. Aggresive timing can only do so much.
So at some flow rate, the desired PR required will lead to lower static compression to survive... and I think everyone can agree to that (unless you can get a VVT working I guess). The question is what is that flow rate, it's not 30 lb/min for sure... or even 40/lb's. I think as we creep to 50 lbs/min we are going to find it.
BTW - a 9:1 engine, gains about 1% thermal efficiency per ATA over a 10:1 everything else being equal. *It actually loses 1%, but for sake of argument, gaining = additional heat just from compression.*
So an 80 ci engine looking to move 50 lb/min of air would be operating at a MINIMUM 200% load at 9000RPMS ideally (I am way oversimplifying). So if the compressor is 70% efficient and the engines have a 2% thermal difference at 2 ATA, no matter what you do, you have to overcome a MINIMUM 91 degree temperature increase in the chamber. Versus, the 6 degree difference at 113% load.
To visualize, a 9:1 Compression engine at a 200% load would be the equivalent to running a 10:1 compression engine at the same load in the artic....think what your margin for error is at 0F. Conversly, driving an RX8 at 14+PSI would be the equivalent of trying to drive an FD when the temps are 160 degrees or more outside!!!!
Obviously, these are really rough figures, I am just trying to illustrate the point. So my personal opinion, anything above 40-42 lb/min of air on an 80ci engine, you wanna start thinking seriously about your Compression Ratio.
Last edited by Kane; 12-23-2010 at 03:35 AM.
12-23-2010, 09:07 AM
#94
My compressor still has some room left if I wanted to go that way. Rote8 has provided info in that regard. In concept what Kane is saying is what I have been basically thinking, but wasnt sure about .
my numbers are 365g/sec at 180 load at 7.5K thats at 9psi with ambient in 80's 35% humidity in ga-- I do not have a ported engine--although I have done some lim work. Oem header with resonated midpipe. I have hit 10.5 psi while on the road course.
Rote 8 says his drivability is minimally affected. he did have to increase his boost to get back his power as expected. He was able to increase his rpm to 9.5K safely due to better balanced rotors.
Funny thing is that his intake temps went DOWN during DD.
my numbers are 365g/sec at 180 load at 7.5K thats at 9psi with ambient in 80's 35% humidity in ga-- I do not have a ported engine--although I have done some lim work. Oem header with resonated midpipe. I have hit 10.5 psi while on the road course.
Rote 8 says his drivability is minimally affected. he did have to increase his boost to get back his power as expected. He was able to increase his rpm to 9.5K safely due to better balanced rotors.
Funny thing is that his intake temps went DOWN during DD.
12-23-2010, 09:19 AM
#95
12-23-2010, 09:30 AM
#96
[QUOTE=Kane;3827556]This thing is going like 4 different directions..LOL
Are we talking turbo's or SC's, 300 or 400WHP, etc etc....
if your turbo isn't getting more efficient at higher pressure ratios (there are limits to this) you've got a weaksauce turbo.
yes. car will still be slow. needs turbo + more boost.
this is merely an academic exercise. car is still slow without bigger turbo + more boost.
another point that is merely academic. the engine needs more boost, a bigger turbo, and lower static compression. this works on every other turbo engine, piston or rotary, so why are there so many doubters here? a tiny group of people, including shops with race cars trying to sell engine services, report side seal failures and everybody runs scared...
use a more thermally efficient turbo and throw more boost at it. more efficient compressor wheel = lower intake temps and less chance of detonation. more efficient hotside = less backpressure and exhaust temperature, meaning less chance of detonation
maybe, maybe not. it's still armchair engineering math. bigger turbo + more boost is the solution.
I think we can all agree that your basic 300whp turbo Renesis will be ok with 10:1 compression rotors but yes once you get to a certain amount of airflow and horsepower goal lower compression rotors make more sense.
My argument is that the platform is stuck in the low 300s whp range and the only way out of it is the tried-and-true approach of lower static compression and a bigger/more efficient turbo running higher boost, to reliably achieve whatever airflow is necessary.
Are we talking turbo's or SC's, 300 or 400WHP, etc etc....
Again, if the turbo is MORE efficient at higher PR's than the engine is, lower static compression = more power.
Superchargers (non-centrifigal) has other issues since it will not gain efficiency and it is tied to engine RPM. Aggresive timing can only do so much.
So at some flow rate, the desired PR required will lead to lower static compression to survive... and I think everyone can agree to that (unless you can get a VVT working I guess). The question is what is that flow rate, it's not 30 lb/min for sure... or even 40/lb's. I think as we creep to 50 lbs/min we are going to find it.
BTW - a 9:1 engine, gains about 1% thermal efficiency per ATA over a 10:1 everything else being equal. *It actually loses 1%, but for sake of argument, gaining = additional heat just from compression.*
So an 80 ci engine looking to move 50 lb/min of air would be operating at a MINIMUM 200% load at 9000RPMS ideally (I am way oversimplifying). So if the compressor is 70% efficient and the engines have a 2% thermal difference at 2 ATA, no matter what you do, you have to overcome a MINIMUM 91 degree temperature increase in the chamber. Versus, the 6 degree difference at 113% load.
To visualize, a 9:1 Compression engine at a 200% load would be the equivalent to running a 10:1 compression engine at the same load in the artic....think what your margin for error is at 0F. Conversly, driving an RX8 at 14+PSI would be the equivalent of trying to drive an FD when the temps are 160 degrees or more outside!!!!
Obviously, these are really rough figures, I am just trying to illustrate the point. So my personal opinion, anything above 40-42 lb/min of air on an 80ci engine, you wanna start thinking seriously about your Compression Ratio.
My argument is that the platform is stuck in the low 300s whp range and the only way out of it is the tried-and-true approach of lower static compression and a bigger/more efficient turbo running higher boost, to reliably achieve whatever airflow is necessary.
12-23-2010, 09:33 AM
#97
The mathematics of it all can give us some sort of guideline as to what we can expect but it isn't all that rare for humanity's mathematics to also be wrong and for nature to deliver us some surprises.
12-23-2010, 10:01 AM
#99
Registered
My compressor still has some room left if I wanted to go that way. Rote8 has provided info in that regard. In concept what Kane is saying is what I have been basically thinking, but wasnt sure about .
my numbers are 365g/sec at 180 load at 7.5K thats at 9psi with ambient in 80's 35% humidity in ga-- I do not have a ported engine--although I have done some lim work. Oem header with resonated midpipe. I have hit 10.5 psi while on the road course.
Rote 8 says his drivability is minimally affected. he did have to increase his boost to get back his power as expected. He was able to increase his rpm to 9.5K safely due to better balanced rotors.
Funny thing is that his intake temps went DOWN during DD.
my numbers are 365g/sec at 180 load at 7.5K thats at 9psi with ambient in 80's 35% humidity in ga-- I do not have a ported engine--although I have done some lim work. Oem header with resonated midpipe. I have hit 10.5 psi while on the road course.
Rote 8 says his drivability is minimally affected. he did have to increase his boost to get back his power as expected. He was able to increase his rpm to 9.5K safely due to better balanced rotors.
Funny thing is that his intake temps went DOWN during DD.
I would not even say that, my neighbor Lisa said after she drove it; "it drives fine, except for the whiplash..."
I suspect my "Intake after blower" temps going down, is caused by the sheer amount of air flow per PSI of boost, or due to the lower temp (170-185) the engine runs at.
I rarely run any methanol now, that's saved for Summertime...
My thought is, a larger chamber can hold more air/fuel, if that air and fuel is under boost, and with 6 PSI boost available as low as 1500 RPM, I have no problem cramming more air in the extra chamber volume,
Last edited by Rote8; 12-23-2010 at 10:18 AM.
12-23-2010, 10:34 AM
#100
Administrator
Thread Starter
from the first post
There are a myriad of considerations and experience will beat unproven theorems time after time. A bit of forethought and knowledge never hurt your chances, however.