Just out of curious I checked this out and these are the numbers I got, I'm just wondering if they're right or wrong because I've been wondering this for quite some time now. (by the way the numbers are from total jdm)
BB ('90-94 Bluebird) - 8.5:1S13('Black-Top 94-98 Silvia) - 8.5:1S13('Red-Top 91-93 Silvia,91-93 180SX) - 8.5:1S14('94-98 180SX) - 8.5:1S15('99+ Silvia) - 10.0:1
(I've also been wondering what the compression ratio has to do with having a turbo in your car, i hear alot that the ratio has to be low for it to be "turbo friendly" why's that?)
:help
SR20DET Compression Ratios
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compression
- Posts: 392
- Joined: Mon Aug 11, 2003 10:08 am
Its all about cylinder pressure, A high compression motor (i.e. 11:1) compresses the air much much more than a 8.5:1 motor. This is proven when you do a compression test on an SR (about 160psi) and B18C5 honduh motor (270psi or so). Normally aspirated motors get their power through this high compression, generally speaking the higher the compression ratio the more power it will make (with the right fuel). But with too much compression, the mixture will spontaniously ignite before it is supposed to, also known as knock, preignition, or detonation. This can be hazardous to an engine. High octane fuels have a greater resistance to preignition.Now with a turbo motor, you want a low compression ratio because you are going to be increasing the cylinder pressure with the turbo when you are at full boost. If you slapped a turbo on a 11.5:1 engine, it would knock llike crazy on 91 octane at elevated boost levels. Thats why we can boost these old nissan motors to 20psi without much worry, nice low compression.But the downside is that when the motor is not in the boost, it is not making much power, its basically a 8.5:1 compression normally aspirated engine until you get to the boost.
p.s. i use "engine" and "motor" interchangably. if someone tells you that "motors are elecric" you say "then why do they call it motor oil!"
p.s. i use "engine" and "motor" interchangably. if someone tells you that "motors are elecric" you say "then why do they call it motor oil!"
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dj_lennon_franz
- Posts: 496
- Joined: Wed Nov 20, 2002 2:24 pm
- Car: 1992 240sx
Well this brings up a few more questions.
What exactly is PSI and how does it work, I have a faint idea but not too sure about it and just want to get some more info on it.
Another question that just poped into my head was that i noticed how much higher the compression ratio was in the S15 than the S14 are these numbers right and if so should i look into buying an S14 because of those numbers or would it not hurt anything that bad?
Ohh and how would you make Octane ratings higher?
What exactly is PSI and how does it work, I have a faint idea but not too sure about it and just want to get some more info on it.
Another question that just poped into my head was that i noticed how much higher the compression ratio was in the S15 than the S14 are these numbers right and if so should i look into buying an S14 because of those numbers or would it not hurt anything that bad?
Ohh and how would you make Octane ratings higher?
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dj_lennon_franz
- Posts: 496
- Joined: Wed Nov 20, 2002 2:24 pm
- Car: 1992 240sx
PSI is the rating for how much air is being pushed into yer engine by the turbo...it means Pounds Per Square Inch (the metric rating is called BAR...im not sure what i means though) your stock boost is set at 7PSI..the stock turbo on the SR can handle up to 15psi safely
octane ratings can be made higher with the use of octane booster or finding a gas station that sells 100 octane...we have alot og 76 stations here in vegas that sell 100 octane for $4.26 a gallon (use to be 3.96 but we can thank our government for the price hike) the SR20 will actually run better with higher octane as the lowest octane it was made to run on was 93....youll notice the engine will smooth out and have a bit more power with 100 octane...ive noticed that with 100 i get about 80km more (i have the metric cluster in my car) than i do on 91 (91 i get about 400km to a tank on 100 i get about 450-480 depending on how i drive the car) octane boosters wont take your ratings that high either...i think the highest u can get is like 95
you can always mix your octanes
half 91 + 100 = 95 octanequarter 91 + 3/4s 100 = 98 octanequarter 100 + 3/4s 91 = 93 octane
thats a pretty accurate chart...i ALWAYS run a full tank of 100 when i take my car to the track for drifting (just to make SURE i dont get ANY engine knock) when you start boosting higher with the motor its not recommended to run ANYTHING BUT 100 as you will begin knocking/pinging (this is pre detonation in your cylinders...this can cause you engine to go BOOM...it sounds like marbles knocking around in your motor) for daily driving on stock boost 91 is fine...but once u start upping ur boost its a wise idea to start upping your octane ratings as well...i generally only run 100 octane in mine...especially during the summer
octane ratings can be made higher with the use of octane booster or finding a gas station that sells 100 octane...we have alot og 76 stations here in vegas that sell 100 octane for $4.26 a gallon (use to be 3.96 but we can thank our government for the price hike) the SR20 will actually run better with higher octane as the lowest octane it was made to run on was 93....youll notice the engine will smooth out and have a bit more power with 100 octane...ive noticed that with 100 i get about 80km more (i have the metric cluster in my car) than i do on 91 (91 i get about 400km to a tank on 100 i get about 450-480 depending on how i drive the car) octane boosters wont take your ratings that high either...i think the highest u can get is like 95
you can always mix your octanes
half 91 + 100 = 95 octanequarter 91 + 3/4s 100 = 98 octanequarter 100 + 3/4s 91 = 93 octane
thats a pretty accurate chart...i ALWAYS run a full tank of 100 when i take my car to the track for drifting (just to make SURE i dont get ANY engine knock) when you start boosting higher with the motor its not recommended to run ANYTHING BUT 100 as you will begin knocking/pinging (this is pre detonation in your cylinders...this can cause you engine to go BOOM...it sounds like marbles knocking around in your motor) for daily driving on stock boost 91 is fine...but once u start upping ur boost its a wise idea to start upping your octane ratings as well...i generally only run 100 octane in mine...especially during the summer
Nice explanation dj_lennon. Especially the fuel chart. =) One thing though, I am not sure exactly what you are referring to as "high boost" but on the stock turbo, you can run 93 at 14-15 PSI. I've even ran 91 w/o any problems, but I really do reccomend 93. The stock timing maps are pretty conservative so that helps a little bit.
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compression
- Posts: 392
- Joined: Mon Aug 11, 2003 10:08 am
I guess I can add some stuff. PSI= pounds per square inch, its a unit of measure for pressure.Do some research in fluid dynamics to see how pressure works and what flow is and how they are related. Its a little beyond the scope of this forum.The octane of a gas is a measure of its resistance to knock. The higher octane the better resistance. Higher octane does not have more "punch" when it is ignited. With all other things constant, you should not be making more power when running a higher octane.If you are noticing changes when running a higher octane on a stock SR, then it is most likely due to adjustments in timing and fuel by the ecu. The ecu cuts back fuel because it is not noticing any signs of knock.THere are some things that you can adjust to help eliminate knock:-retard the ignition timing-richen up the air/fuel mixture-lower the boost level-increase the octane of the fuel
I guess the S15 engine has a higher compression ratio because they want it to feel strong even when it is not in the boost. They probably have a conservative timing map in it and add a little extra fuel to richen it up to keep her from knocking. If you can afford an S15 engine, go for it, make sure it is tuned right if you plan on turning up the boost. Otherwise dont sweat it too much, with proper tuning and enough money, anything is possible!
Do you guys really push the stock turbo 15psi? That is way high for that little thing and out of its efficiency range! Are you getting the airflow you need at that pressure? Be careful, the turbo may die prematurely at that rate.What would you push a S15 T28 to?
I guess the S15 engine has a higher compression ratio because they want it to feel strong even when it is not in the boost. They probably have a conservative timing map in it and add a little extra fuel to richen it up to keep her from knocking. If you can afford an S15 engine, go for it, make sure it is tuned right if you plan on turning up the boost. Otherwise dont sweat it too much, with proper tuning and enough money, anything is possible!
Do you guys really push the stock turbo 15psi? That is way high for that little thing and out of its efficiency range! Are you getting the airflow you need at that pressure? Be careful, the turbo may die prematurely at that rate.What would you push a S15 T28 to?
compression wrote:I guess the S15 engine has a higher compression ratio because they want it to feel strong even when it is not in the boost. They probably have a conservative timing map in it and add a little extra fuel to richen it up to keep her from knocking. If you can afford an S15 engine, go for it, make sure it is tuned right if you plan on turning up the boost. Otherwise dont sweat it too much, with proper tuning and enough money, anything is possible!
Do you guys really push the stock turbo 15psi? That is way high for that little thing and out of its efficiency range! Are you getting the airflow you need at that pressure? Be careful, the turbo may die prematurely at that rate.What would you push a S15 T28 to?
The S15 doesn't have a higher c/r.
I run low boost 99% of the time which is set to roughly 10psi. High boost is set at 14psi. I agree that 15psi is too much for that turbo.
As for the S15 turbo, I believe people run 19-21 psi on it.
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compression
- Posts: 392
- Joined: Mon Aug 11, 2003 10:08 am
Actually it's funny you brought him up because there's a personal trainer I work with that knows him, so when I'm ready to get everything done I'll more then likely get alot of help from him and everyone at SS if everything works out the way i want it too lol, I don't personally know him but hopefully soon enough I'll get a chance to meet him.Dori Dori wrote:You might want to call scott at secret services...he's tunes a lot of s15 powered sr's. Also, check out the maps...from what I've been told, it's the same as an off the shelf GT28.
And by the way I appreciate all the help from everyone
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charlotte240
- Posts: 177
- Joined: Fri Aug 30, 2002 5:36 pm
compression wrote:I guess I can add some stuff.
I guess the S15 engine has a higher compression ratio because they want it to feel strong even when it is not in the boost. They probably have a conservative timing map in it and add a little extra fuel to richen it up to keep her from knocking.
I'm just curious here. So higher octane gas is less volitile? Couldn't I just use diesle or kerosine since they're less likely to burn?
This is a theoretical question. Not anything intended to start an argument.
Also, I'm a fueler at the charlotte douglass international airport (Some of you may remember my story about drifting the fuel truck with 3000 gallons of jet fuel in the cargo tank)...... ANYWAYS, we also fuel planes with AVGAS which is (from what I'm told by the fuel quality control guy) nothing other than 120 octane gas with blue dye in it. The only thing is, I've seen this stuff spilled before and it evaporates QUICK, leading me to believe that this stuff is rather volitle and therefore, prone to quick ignition.
Does any of this make sense?
"Low lead" AVGAS has way higher lead content than any automotive gasoline ever sold. It WILL foul your O2 sensor, heated or not given enough time. 1/2 a tank at a time will take a while, but it will happen.
Use Toulene instead. Available at paint stores, it's an aromatic hydrocarbon that has an octane of 114 and an excellent spread(the difference between R and M in the R+M/2 method). Aromatic hydrocarbons are the primary difference between lower octane gas and higher octane gas.
A few gallons per tankful will give you a very high octane rating, and you should be good to go. Beyond that, I'd just start buying C16 in 55gal drums if you really need octane that high.
Use Toulene instead. Available at paint stores, it's an aromatic hydrocarbon that has an octane of 114 and an excellent spread(the difference between R and M in the R+M/2 method). Aromatic hydrocarbons are the primary difference between lower octane gas and higher octane gas.
A few gallons per tankful will give you a very high octane rating, and you should be good to go. Beyond that, I'd just start buying C16 in 55gal drums if you really need octane that high.
Why is your O2 sensor unplugged? That can't be good for the car when it tries to run in closed loop...
But yea, if you don't have those items, then I'd say you could get away with about a half and half mix of leaded AVGAS and 93 octane. I don't see any halfway streetable SR needing more octane that that.(~107 octane)
But yea, if you don't have those items, then I'd say you could get away with about a half and half mix of leaded AVGAS and 93 octane. I don't see any halfway streetable SR needing more octane that that.(~107 octane)
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charlotte240
- Posts: 177
- Joined: Fri Aug 30, 2002 5:36 pm
I was just talking about the volitility of the fuel. Is higher octane fuel just less volitile? If so, then why not mix in some diesel? (I wouldn't really do it, this is just a conversation question)
And if someone were to say that diesel doesn't contain enough potential energy, then I would say use JetA (jet fuel, and yes, it's unleaded). JetA is like a very very pure form of kerosine and burns very hot (very good for a turbo) because the engine it powers needs that temprature/pressure delta to get the turbine in the jet engine spooling (just like in a turbocharger).
Anyways, I know that JetA is less volitle than gasoline because it runs fine in a diesel engine except the diesel engine doesn't put out black smoke. Well, that and I don't catch on fire when smoking when it's all over me like with gasoline (and yes, I have had that happen to me before. I'm not dumb, just careless).
And if someone were to say that diesel doesn't contain enough potential energy, then I would say use JetA (jet fuel, and yes, it's unleaded). JetA is like a very very pure form of kerosine and burns very hot (very good for a turbo) because the engine it powers needs that temprature/pressure delta to get the turbine in the jet engine spooling (just like in a turbocharger).
Anyways, I know that JetA is less volitle than gasoline because it runs fine in a diesel engine except the diesel engine doesn't put out black smoke. Well, that and I don't catch on fire when smoking when it's all over me like with gasoline (and yes, I have had that happen to me before. I'm not dumb, just careless).