Compression ratio
11-09-04, 11:26 PM
#2
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The easy answer is no...
The real answer is yes, but only on Turbo cars...
Compression on a rotary is set by the amount of "dish out" on the surface of the rotor, Turbo cars have a larger divot on each face, thus they have a lower compression ratio..
This is why you will see guys running N/A rotors in turbo motors for race purposes.. you get more HP out of it, but the lifespan of the motor can be measure in track passes.
This is also why guys who turbo their N/A motors for street use usually limit their boost to below 10 PSI so that they don't puke their motor in a week of driving!
The idea of a turbo car is to get a larger VOLUME of air into the compression chamber and thus be able to burn more fuel. Squeezing the charge too much will lead to detonation in a hurry as air heats up as it gets compressed (some high compression piston motors will see temperatures of 700F from the compression alone)
In an N/A, the volume is pretty much static, so by increasing the compression, you can squeeze more power out of the available air/fuel, hence, n/a's have a higher compression ratio.
AS for the power / PSI of compression increase.. no freakin clue dude...
for a 13b motor.... there is 1 size of rotor housing and two choices of rotors.. its not like a piston motor where you can bore the cyliners, add larger pistons, deck the heads, or change the stroke length to change the compression ratio.. here, you have two choices!!!!
The real answer is yes, but only on Turbo cars...
Compression on a rotary is set by the amount of "dish out" on the surface of the rotor, Turbo cars have a larger divot on each face, thus they have a lower compression ratio..
This is why you will see guys running N/A rotors in turbo motors for race purposes.. you get more HP out of it, but the lifespan of the motor can be measure in track passes.
This is also why guys who turbo their N/A motors for street use usually limit their boost to below 10 PSI so that they don't puke their motor in a week of driving!
The idea of a turbo car is to get a larger VOLUME of air into the compression chamber and thus be able to burn more fuel. Squeezing the charge too much will lead to detonation in a hurry as air heats up as it gets compressed (some high compression piston motors will see temperatures of 700F from the compression alone)
In an N/A, the volume is pretty much static, so by increasing the compression, you can squeeze more power out of the available air/fuel, hence, n/a's have a higher compression ratio.
AS for the power / PSI of compression increase.. no freakin clue dude...
for a 13b motor.... there is 1 size of rotor housing and two choices of rotors.. its not like a piston motor where you can bore the cyliners, add larger pistons, deck the heads, or change the stroke length to change the compression ratio.. here, you have two choices!!!!
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Dysfunctionalrx7 (06-15-20)
11-09-04, 11:38 PM
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the max you can get is 10.0 (ussing renesis rotors, which is possible but not realy practical for a few reasons). otherwise the options are as follows (assuming they will be used in a peripherial exhaust 13b
9.7---from 89-91 n/a
9.4---from 86-88 n/a
9.0---89-99 all turbos (13bt, 13b-re, 13b-rew, 20b)
8.7 (or is it 8.6?) 87-88 turbo
i cant remember the comp on pre-'86 13b's but im sure it was less than 9.4.
also all of the '89+ rotors are lighter than the 88 and earlier ones.
any of theses rotors can be interchanged in any prepherial exhaust (non renesis) 13b, you just need to make sure you have a matching e-shaft and counterweights for the rotor sets.
9.7---from 89-91 n/a
9.4---from 86-88 n/a
9.0---89-99 all turbos (13bt, 13b-re, 13b-rew, 20b)
8.7 (or is it 8.6?) 87-88 turbo
i cant remember the comp on pre-'86 13b's but im sure it was less than 9.4.
also all of the '89+ rotors are lighter than the 88 and earlier ones.
any of theses rotors can be interchanged in any prepherial exhaust (non renesis) 13b, you just need to make sure you have a matching e-shaft and counterweights for the rotor sets.
11-09-04, 11:48 PM
#4
I wish I was driving!
Originally Posted by andrew lohaus
8.7 (or is it 8.6?) 87-88 turbo
i cant remember the comp on pre-'86 13b's but im sure it was less than 9.4.
i cant remember the comp on pre-'86 13b's but im sure it was less than 9.4.
Before S4's? Who cares.
11-10-04, 07:07 PM
#5
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Originally Posted by soundwavetsunami
Is there anyway to up the compression ratio on the rotorary engine?
And whats the average hp gain per psi?
And whats the average hp gain per psi?
Upping CR is lowering your safety buffer.
People who really want to do this already know the answer.
So, why do you want to do this?
-Ted
11-10-04, 09:19 PM
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maybe he wants better fuel economy in a NA situation.... apparantly the 9.7s (along with lighter weight) get 1 mpg better than the 9.4s on both city and highway tests 
I wonder if you had like a 12.1 compression ratio if higher octane gas would still be uneeded in the long combustion chamber.....
I wonder if you had like a 12.1 compression ratio if higher octane gas would still be uneeded in the long combustion chamber.....
11-10-04, 09:30 PM
#7
I wish I was driving!
Originally Posted by sar
maybe he wants better fuel economy in a NA situation.... apparantly the 9.7s (along with lighter weight) get 1 mpg better than the 9.4s on both city and highway tests
I wonder if you had like a 12.1 compression ratio if higher octane gas would still be uneeded in the long combustion chamber.....
I wonder if you had like a 12.1 compression ratio if higher octane gas would still be uneeded in the long combustion chamber.....
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11-10-04, 09:32 PM
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This is just added info, nothing more:
ROTOR YEAR COMPRESSION WEIGHT (LBS)
12A-----------------76-82-------9.4---------------10.15
12A-----------------83-85-------9.4---------------9.60
13B-----------------74-78-------9.2---------------11.58
13B-----------------84-85-------9.4---------------11.58
13B N/A------------86-88-------9.4---------------10.04
13B Turbo---------86-88-------8.5---------------10.04
13B N/A------------89-92-------9.7---------------9.54
13B Turbo---------89-92-------9.0---------------9.54
13B Twin Turbo---93-95-------9.0---------------9.54
NOTE: Weights of rotors include rotor bearings, but do not include seals or springs
Brian
ROTOR YEAR COMPRESSION WEIGHT (LBS)
12A-----------------76-82-------9.4---------------10.15
12A-----------------83-85-------9.4---------------9.60
13B-----------------74-78-------9.2---------------11.58
13B-----------------84-85-------9.4---------------11.58
13B N/A------------86-88-------9.4---------------10.04
13B Turbo---------86-88-------8.5---------------10.04
13B N/A------------89-92-------9.7---------------9.54
13B Turbo---------89-92-------9.0---------------9.54
13B Twin Turbo---93-95-------9.0---------------9.54
NOTE: Weights of rotors include rotor bearings, but do not include seals or springs
Brian
11-10-04, 09:46 PM
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Guys their is a way to create higher compresion rotors.
You Take light weight S5 and you add material to the divits than you use water displacement to measure. This is a messed up way of doing it but it works.
A side note rotor must be rebalanced after this procedure sense you alter the mass of the rotor. I will not tell you what material is used in this process or the technique used to fuse it to the rotor. Im sorry but I went through alot to figure it out. Anyway power gians are not that signifigant at 10.0 you gian around 10hp after about 4k in the power band untill redline.
You Take light weight S5 and you add material to the divits than you use water displacement to measure. This is a messed up way of doing it but it works.
A side note rotor must be rebalanced after this procedure sense you alter the mass of the rotor. I will not tell you what material is used in this process or the technique used to fuse it to the rotor. Im sorry but I went through alot to figure it out. Anyway power gians are not that signifigant at 10.0 you gian around 10hp after about 4k in the power band untill redline.
11-10-04, 11:14 PM
#11
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RX7goZoomZoomBoom that's quiet interesting. I hope if you've done something like that you'd share it with others in some way, profitably or not. 
Did you attempt to go higher then 10:1?
Did you attempt to go higher then 10:1?
11-10-04, 11:17 PM
#12
I wish I was driving!
Originally Posted by RX7goZoomZoomBoom
Guys their is a way to create higher compresion rotors.
You Take light weight S5 and you add material to the divits than you use water displacement to measure. This is a messed up way of doing it but it works.
A side note rotor must be rebalanced after this procedure sense you alter the mass of the rotor. I will not tell you what material is used in this process or the technique used to fuse it to the rotor. Im sorry but I went through alot to figure it out. Anyway power gians are not that signifigant at 10.0 you gian around 10hp after about 4k in the power band untill redline.
You Take light weight S5 and you add material to the divits than you use water displacement to measure. This is a messed up way of doing it but it works.
A side note rotor must be rebalanced after this procedure sense you alter the mass of the rotor. I will not tell you what material is used in this process or the technique used to fuse it to the rotor. Im sorry but I went through alot to figure it out. Anyway power gians are not that signifigant at 10.0 you gian around 10hp after about 4k in the power band untill redline.
You haven't done this.
11-10-04, 11:18 PM
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Arright, thanks alot guys. I was just wondering about that.
And its just that I had heard somewhere that the average hp-gain per psi was 10 hp. and to me that sounds rediculous.
And its just that I had heard somewhere that the average hp-gain per psi was 10 hp. and to me that sounds rediculous.
11-10-04, 11:26 PM
#14
I wish I was driving!
Originally Posted by soundwavetsunami
Arright, thanks alot guys. I was just wondering about that.
And its just that I had heard somewhere that the average hp-gain per psi was 10 hp. and to me that sounds rediculous.
And its just that I had heard somewhere that the average hp-gain per psi was 10 hp. and to me that sounds rediculous.
Between S5's and S6's, Mazda raised the boost 2.5 psi and saw a gain of roughly 50 hp.
Pretty much the only really useful reference point: stock cars to stock cars.
Whenever you compare modded cars, too many factors come in to play for this to work...
11-11-04, 12:20 PM
#15
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Originally Posted by scathcart
Between S4's and S5's, the boost was raised 2 psi and saw a gain of roughly 40 hp.
Between S5's and S6's, Mazda raised the boost 2.5 psi and saw a gain of roughly 50 hp.
Pretty much the only really useful reference point: stock cars to stock cars.
Whenever you compare modded cars, too many factors come in to play for this to work...
Between S5's and S6's, Mazda raised the boost 2.5 psi and saw a gain of roughly 50 hp.
Pretty much the only really useful reference point: stock cars to stock cars.
Whenever you compare modded cars, too many factors come in to play for this to work...
I think see your point, but we all know that from the S4 to S5 turbo they also upped the CR, etc. and that the HP increase was ~20hp. These factors would only further strengthen your the case I think you were trying to make.
11-11-04, 11:06 PM
#16
I wish I was driving!
Originally Posted by Snrub
I think see your point, but we all know that from the S4 to S5 turbo they also upped the CR, etc. and that the HP increase was ~20hp. These factors would only further strengthen your the case I think you were trying to make.My mind is going as I get old.
03-10-05, 07:57 PM
#17
Originally Posted by scathcart
Between S4's and S5's, the boost was raised 2 psi and saw a gain of roughly 40 hp.
Between S5's and S6's, Mazda raised the boost 2.5 psi and saw a gain of roughly 50 hp.
Pretty much the only really useful reference point: stock cars to stock cars.
Whenever you compare modded cars, too many factors come in to play for this to work...
Between S5's and S6's, Mazda raised the boost 2.5 psi and saw a gain of roughly 50 hp.
Pretty much the only really useful reference point: stock cars to stock cars.
Whenever you compare modded cars, too many factors come in to play for this to work...
the 40hp gain between s4's and s5's can be credited to the compression ratio i guess, but there are a few other things too... (like the change in design of the turbo and manifold)
and compression ratio has nothing to do with the power gain from s5>s6... (they're both 9.0:1) again, the turbos flow way more air and the ports (all being stock) are bigger.
03-11-05, 07:13 AM
#18
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Originally Posted by soundwavetsunami
Arright, thanks alot guys. I was just wondering about that.
And its just that I had heard somewhere that the average hp-gain per psi was 10 hp. and to me that sounds rediculous.
And its just that I had heard somewhere that the average hp-gain per psi was 10 hp. and to me that sounds rediculous.
Just turn up the godamn boost for christsake?
-Ted
03-11-05, 10:25 AM
#19
Old Rotary Dog
how do you tell which rotor is which
okay, I have a question: how do you identify which rotor is which?
if you are holding a rotor in your hand, and have nothing else to compare it to, how do you tell if it is an S4, S5, NA, TII, etc...?
-bill
if you are holding a rotor in your hand, and have nothing else to compare it to, how do you tell if it is an S4, S5, NA, TII, etc...?
-bill
08-16-05, 11:27 PM
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Originally Posted by wrankin
okay, I have a question: how do you identify which rotor is which?
if you are holding a rotor in your hand, and have nothing else to compare it to, how do you tell if it is an S4, S5, NA, TII, etc...?
-bill
if you are holding a rotor in your hand, and have nothing else to compare it to, how do you tell if it is an S4, S5, NA, TII, etc...?
-bill
Keen to get an answer on this too.
08-17-05, 01:36 AM
#21
I wish I was driving!
Originally Posted by KillerRx4
Keen to get an answer on this too.
S5 are machined.
To tell the difference between turbo and non-turbo, you need to measure the dish depth.
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Re-Build (10-17-19)
08-17-05, 03:10 AM
#22
^ I thought there were miniature Japanese characters or a number stamped (or something) on the face by the apex... I don't know for sure, just remember a dude at Atkins trying to clean off a random rotor's face to show me (after I asked the same question).
08-17-05, 03:28 AM
#23
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Originally Posted by eriksseven
^ I thought there were miniature Japanese characters or a number stamped (or something) on the face by the apex... I don't know for sure, just remember a dude at Atkins trying to clean off a random rotor's face to show me (after I asked the same question).
The characters are there to denote which side is which; it's the equivalent of use labelling A, B, C, etc.
-Ted
08-17-05, 05:44 AM
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Originally Posted by scathcart
S4 rotor dishes are cast.
S5 are machined.
To tell the difference between turbo and non-turbo, you need to measure the dish depth.
S5 are machined.
To tell the difference between turbo and non-turbo, you need to measure the dish depth.
Got figures for those measurements scathcart?
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