How much boost on pump gas do you run?
On my EVO9 ..... I have built a race and pump gas map. I've logged both. My airflow and load numbers are nearly identical between the two. Adding boost only adds a tad of airflow prior to 5500 rpm. The gains I see at the track are primarily from timing and leaner AFR.
I'm sure if I had a bigger turbo I would see more gains from adding more boost. Trying to push the stock unit to 28psi simply creates more heat not more airflow.
For dicking around town I prefer to keep the boost spike to 23psi with a solid 20psi at 7k. I run 6* peak and 14* at 7k. This doesn't kill my turbo, doesn't heat soak the FMIC, doesn't blow IC hoses, doesn't kill my clutch, and doesn't leave me wanting more.
I'm sure if I had a bigger turbo I would see more gains from adding more boost. Trying to push the stock unit to 28psi simply creates more heat not more airflow.
For dicking around town I prefer to keep the boost spike to 23psi with a solid 20psi at 7k. I run 6* peak and 14* at 7k. This doesn't kill my turbo, doesn't heat soak the FMIC, doesn't blow IC hoses, doesn't kill my clutch, and doesn't leave me wanting more.
The same 25.5ish tapering to 23ish with 2-3* at max torque 0 counts of knock on 93 with WI @~12 AFR on an VIII w/ 272s and stock manifolds & 9.8 turbo.
Last edited by honki24; Nov 14, 2007 at 09:04 AM.
A lot of you guys talk about efficiency of the stock turbo, and say that it's not efficient at higher boost levels. Well i'm gonna beg to differ.
For one thing i think it's pretty obvious that a stocker will not hold more than ~22 at redline, because the small turbine becomes a big restriction, the backpressure is too high. You cant really "push" it to run higher, well maybe with a bigger wastegate, that can dump more exhaust gases...
So when people say "i run 30" or "i run 21" they talk about boost at peak VE. The spike.
And let me tell ya the stocker is pretty efficient there, and you can up the boost and get gains. Now granted i never ran more than 22 on pump, when i upped the boost from 22 to 28 running a stock 9.8 16G on E85, i picked up around 50tq.
Dave is right about the camshafts playing a role in this, that's why i asked him what cams they have on that 30psi 9 turbo car...He never replied though
But i was thinking if the cam is too big and you get a big overlap, the back pressure created by a smaller turbo will push exhaust gas back into intake therefore producing knock and making one reduce boost or timing. And that makes me second guess my move from HKS 272 to HKS 280. I think i've been seeing more knock since then. I'm hoping it's because bigger cams increased cylinder pressure, but maybe they are too big...
In any case my point is stock/green turbo is very efficient at lower rpm range and that's why you can make more torque than 35r on those, so running 30psi, if you can accomplish it, is not a bad idea.
For one thing i think it's pretty obvious that a stocker will not hold more than ~22 at redline, because the small turbine becomes a big restriction, the backpressure is too high. You cant really "push" it to run higher, well maybe with a bigger wastegate, that can dump more exhaust gases...
So when people say "i run 30" or "i run 21" they talk about boost at peak VE. The spike.
And let me tell ya the stocker is pretty efficient there, and you can up the boost and get gains. Now granted i never ran more than 22 on pump, when i upped the boost from 22 to 28 running a stock 9.8 16G on E85, i picked up around 50tq.
Dave is right about the camshafts playing a role in this, that's why i asked him what cams they have on that 30psi 9 turbo car...He never replied though
But i was thinking if the cam is too big and you get a big overlap, the back pressure created by a smaller turbo will push exhaust gas back into intake therefore producing knock and making one reduce boost or timing. And that makes me second guess my move from HKS 272 to HKS 280. I think i've been seeing more knock since then. I'm hoping it's because bigger cams increased cylinder pressure, but maybe they are too big...
In any case my point is stock/green turbo is very efficient at lower rpm range and that's why you can make more torque than 35r on those, so running 30psi, if you can accomplish it, is not a bad idea.
Last edited by mplspilot; Nov 14, 2007 at 09:16 AM.
I wouldn't go down the road of turning up the boost and turning down the timing without monitoring EGTs along the way. Also, "zero knock" in an isolated WOT 3rd gear pull or two, especially on a non-load-bearing dyno, doesn't mean that the tune is "safe" for all conditions, especially long pulls in 4th and 5th gear on a warm summer day.
In any case, pushing a tune to the edge of the knock limit is silly IMO. If you really want more power, then do it right and make the appropriate modifications for the power level you want. If what you want is bragging rights for the internet, then go to it by doing a special tune for one day on the dyno or at the strip, but don't try to run the same boost/tune on a daily basis under all conditions.
In any case, pushing a tune to the edge of the knock limit is silly IMO. If you really want more power, then do it right and make the appropriate modifications for the power level you want. If what you want is bragging rights for the internet, then go to it by doing a special tune for one day on the dyno or at the strip, but don't try to run the same boost/tune on a daily basis under all conditions.
A lot of you guys talk about efficiency of the stock turbo, and say that it's not efficient at higher boost levels. Well i'm gonna beg to differ.
For one thing i think it's pretty obvious that a stocker will not hold more than ~22 at redline, because the small turbine becomes a big restriction, the backpressure is too high. You cant really "push" it to run higher, well maybe with the bigger wastegate..
So when people say "i run 30" or "i run 21" they talk about boost at peak VE. The spike.
And let me tell ya the stocker is pretty efficient there, and you can up the boost and get gains. Now granted i never ran more than 22 on pump, when i upped the boost from 22 to 28 running a stock 9.8 16G on E85, i picked up around 50tq.
Dave is right about the camshafts playing a role in this, that's why i asked him what cams they have on that 30psi 9 turbo car...He never replied though
But i was thinking if the cam is too big and you get a big overlap, the back pressure created by a smaller turbo will push exhaust gas back into intake therefore producing knock and making one reduce boost or timing. And that makes me second guess my move from HKS 272 to HKS 280. I think i've been seeing more knock since then. I'm hoping it's because bigger cams increased cylinder pressure, but maybe they are too big...
In any case my point is stock/green turbo is very efficient at lower rpm range and that's why you can make more torque than 35r on those, so running 30psi, if you can accomplish it, is not a bad idea.
For one thing i think it's pretty obvious that a stocker will not hold more than ~22 at redline, because the small turbine becomes a big restriction, the backpressure is too high. You cant really "push" it to run higher, well maybe with the bigger wastegate..
So when people say "i run 30" or "i run 21" they talk about boost at peak VE. The spike.
And let me tell ya the stocker is pretty efficient there, and you can up the boost and get gains. Now granted i never ran more than 22 on pump, when i upped the boost from 22 to 28 running a stock 9.8 16G on E85, i picked up around 50tq.
Dave is right about the camshafts playing a role in this, that's why i asked him what cams they have on that 30psi 9 turbo car...He never replied though
But i was thinking if the cam is too big and you get a big overlap, the back pressure created by a smaller turbo will push exhaust gas back into intake therefore producing knock and making one reduce boost or timing. And that makes me second guess my move from HKS 272 to HKS 280. I think i've been seeing more knock since then. I'm hoping it's because bigger cams increased cylinder pressure, but maybe they are too big...
In any case my point is stock/green turbo is very efficient at lower rpm range and that's why you can make more torque than 35r on those, so running 30psi, if you can accomplish it, is not a bad idea.
To say that the stock turbo is efficient at 30 psi is just a wrong statement, unless your definition of efficiency is different than mine. I agree that it can run at that psi for a short period of time, but it doesn't mean it is healthy for the turbo. You are right about the backpressure being an issue, but the compressor wheel is a limiting factor in how much mass airflow the stock turbo can flow. It doesn't matter how big of a hotside you use. A 42-43 lb/min compressor wheel won't flow much more than that. That's one of the main reasons why the stock turbo tapers boost so much when trying to run max boost. You're basically following the choke flow of the compressor.
Point some plots on the stock compressor map and it will make a lot of sense. If need be, I can do it and post up a graph.
Edit: I think people are getting confused what is possible and what is smart, safe, and reliable. Hell, why do you cruise at 65mph in 5th gear on the highway? Why not just ride second gear at 7500 RPM? Again, what can be done and what is smart and reliable are two different things.
Eric
Last edited by l2r99gst; Nov 14, 2007 at 09:23 AM.
A lot of you guys talk about efficiency of the stock turbo, and say that it's not efficient at higher boost levels. Well i'm gonna beg to differ.
For one thing i think it's pretty obvious that a stocker will not hold more than ~22 at redline, because the small turbine becomes a big restriction, the backpressure is too high. You cant really "push" it to run higher, well maybe with a bigger wastegate, that can dump more exhaust gases...
So when people say "i run 30" or "i run 21" they talk about boost at peak VE. The spike.
And let me tell ya the stocker is pretty efficient there, and you can up the boost and get gains. Now granted i never ran more than 22 on pump, when i upped the boost from 22 to 28 running a stock 9.8 16G on E85, i picked up around 50tq.
Dave is right about the camshafts playing a role in this, that's why i asked him what cams they have on that 30psi 9 turbo car...He never replied though
But i was thinking if the cam is too big and you get a big overlap, the back pressure created by a smaller turbo will push exhaust gas back into intake therefore producing knock and making one reduce boost or timing. And that makes me second guess my move from HKS 272 to HKS 280. I think i've been seeing more knock since then. I'm hoping it's because bigger cams increased cylinder pressure, but maybe they are too big...
In any case my point is stock/green turbo is very efficient at lower rpm range and that's why you can make more torque than 35r on those, so running 30psi, if you can accomplish it, is not a bad idea.
For one thing i think it's pretty obvious that a stocker will not hold more than ~22 at redline, because the small turbine becomes a big restriction, the backpressure is too high. You cant really "push" it to run higher, well maybe with a bigger wastegate, that can dump more exhaust gases...
So when people say "i run 30" or "i run 21" they talk about boost at peak VE. The spike.
And let me tell ya the stocker is pretty efficient there, and you can up the boost and get gains. Now granted i never ran more than 22 on pump, when i upped the boost from 22 to 28 running a stock 9.8 16G on E85, i picked up around 50tq.
Dave is right about the camshafts playing a role in this, that's why i asked him what cams they have on that 30psi 9 turbo car...He never replied though
But i was thinking if the cam is too big and you get a big overlap, the back pressure created by a smaller turbo will push exhaust gas back into intake therefore producing knock and making one reduce boost or timing. And that makes me second guess my move from HKS 272 to HKS 280. I think i've been seeing more knock since then. I'm hoping it's because bigger cams increased cylinder pressure, but maybe they are too big...
In any case my point is stock/green turbo is very efficient at lower rpm range and that's why you can make more torque than 35r on those, so running 30psi, if you can accomplish it, is not a bad idea.
Turbos don't max out at a certain PSI ... they max out at a certain flow rate/turbine RPM. PSI is the result of turbine RPM vs engine RPM. So, if the engine spins slower, a given turbine RPM will create more boost since it has more time to pressurize the intake system.
On my EVO9 ..... I have built a race and pump gas map. I've logged both. My airflow and load numbers are nearly identical between the two. Adding boost only adds a tad of airflow prior to 5500 rpm. The gains I see at the track are primarily from timing and leaner AFR.
I'm sure if I had a bigger turbo I would see more gains from adding more boost. Trying to push the stock unit to 28psi simply creates more heat not more airflow.
For dicking around town I prefer to keep the boost spike to 23psi with a solid 20psi at 7k. I run 6* peak and 14* at 7k. This doesn't kill my turbo, doesn't heat soak the FMIC, doesn't blow IC hoses, doesn't kill my clutch, and doesn't leave me wanting more.
I'm sure if I had a bigger turbo I would see more gains from adding more boost. Trying to push the stock unit to 28psi simply creates more heat not more airflow.
For dicking around town I prefer to keep the boost spike to 23psi with a solid 20psi at 7k. I run 6* peak and 14* at 7k. This doesn't kill my turbo, doesn't heat soak the FMIC, doesn't blow IC hoses, doesn't kill my clutch, and doesn't leave me wanting more.
Although I have to say that more boost really doesn't seem to get me more HP up top, only TQ down low. I think I might try a bit of tuning with a 25-26 psi spike but have it come down to 22-23 psi by 5k. This won't really do much for track times but it will make street driving a blast.
Eric, if a stocker can put up 43Lb/min, you would have to agree that making it do that is not *pushing it out of efficiency range*, right? (Until of course the turbine is spinning so fast that it becomes a big restriction, which happens at higher rpm's.)
So let me ask you this - how mush pressure is it creating when it is plowing 43# of air through our engines (regular ones with no headwork, with some cams)? I don't think the maps can tell that.. Do you know? How much air is going through it at 21psi? 25? 30?
So let me ask you this - how mush pressure is it creating when it is plowing 43# of air through our engines (regular ones with no headwork, with some cams)? I don't think the maps can tell that.. Do you know? How much air is going through it at 21psi? 25? 30?
I also want to add that having a 26psi spike and having a 30psi spike will not make much difference on max hp whichh is produced higher in the RPM range where, again most would agree, you cant get any more than 22psi or so from the stocker. That means that by raising boost from 26 to 30 you will gain TQ in the first half of the TQ curve but you won't get any more HP up top, which in a way means that if you do hot lapping it shouldn't matter that you turned it up to 30. You're just not going to see it until you go back to street... IMHO.
Eric, if a stocker can put up 43Lb/min, you would have to agree that making it do that is not *pushing it out of efficiency range*, right? (Until of course the turbine is spinning so fast that it becomes a big restriction, which happens at higher rpm's.)
So let me ask you this - how mush pressure is it creating when it is plowing 43# of air through our engines (regular ones with no headwork, with some cams)? I don't think the maps can tell that.. Do you know? How much air is going through it at 21psi? 25? 30?
So let me ask you this - how mush pressure is it creating when it is plowing 43# of air through our engines (regular ones with no headwork, with some cams)? I don't think the maps can tell that.. Do you know? How much air is going through it at 21psi? 25? 30?
I would say the better way to tune would not be to see how much boost you can run but to see how many lbs you can get out of the turbo.
I also want to add that having a 26psi spike and having a 30psi spike will not make much difference on max hp whichh is produced higher in the RPM range where, again most would agree, you cant get any more than 22psi or so from the stocker. That means that by raising boost from 26 to 30 you will gain TQ in the first half of the TQ curve but you won't get any more HP up top, which in a way means that if you do hot lapping it shouldn't matter that you turned it up to 30. You're just not going to see it until you go back to street... IMHO.
