View Poll Results: Where is best mounting location for a turbo
On the exhaust manifold
24
44.44%
In the engine bay - in front of engine
16
29.63%
Rear mounted
12
22.22%
other
2
3.70%
Voters: 54. You may not vote on this poll
Turbo placement - where is best ?
02-08-2008 | 12:39 PM
#76
Registered User
Joined: May 2004
Posts: 31
Likes: 0
From: MD
You can't have a peaky powerband and still have a large area under the curve. You have one or the other. Apparently it's peaky. This is precisely the response that made me state that if you ask owners of these vehicles about their powerband that they'll tell you it isn't that bad. If you describe it as peaky, it apparently is that bad. You just don't realize it.
No! Duh! See detailed response below.
No actually you have no clue how it could work. There is a very good reason why the exact same turbo spools slower at the rear. There is less energy back there. As I've stated before you need to change the exhaust side of the turbo to account for this. You have lost alot of energy through the walls of the exhaust in the form of heat. It isn't the heat itself that spins the turbo though. The effect heat has on the system is that hotter air takes up more space than cooler air. There is the same amount present but since the molecules are more excited, their greater movement takes up more physical space. When you lose some of this heat, the air condenses into a smaller space. There is still the same amount of air present. It's just more compact. Since it's more compact, it takes a smaller exhaust housing to render the same spool effect. This doesn't mean that a smaller a/r is more restrictive though. It isn't because the cooler air requires less flow area.
What happens to turbo spool rate and potentially boost when a cat is removed? What happens to spool rate when a free flowing muffler is installed in place of a restrictive one? Lag goes down and boost goes up. So does power. If you remote mount a turbo with nothing behind it, there is nothing to slow it down such as a cat. If it's sized to spool up nicely you'd be shocked at how little lag there actually is.
Beind farther from the engine with cooler gasses going through it also means it isn't as hard on the oil flowing through it. That's a good thing. You are less likely to coke the oil in the turbo. If the turbo doesn't get as hot, that also means that it's less likely to hold and transfer heat to the intake side. I know people claim this doesn't really happen but it's worse than many think it is. Less heat on the intake side is more efficiency.
A big downside is oil scavenging. I agree that this is an issue. Fortunately since the turbo doesn't get as hot and is easier on the oil than a conventionally mounted turbo, there is a viable alternative. Install a small oil cooler and pump in a closed loop system that is dedicated to the turbo only. This isn't hard to do and would work quite nicely. No need to worry about taping into the stock oil system or running lines a long distance. If one can fab up a remote mount, making this setup would be simple.
I also agree that getting the intake piping back to the front would also be an issue. It takes space. As pointed out, there are downsides to remote mounting just as there is with any other system. EVERY system is a compromise.
You CAN NOT use the exact same turbo (on the exhaust side) for remote mounting as you do for conventional mounting. This is completely ignoring the system requirements. Typically you need to go down at least 2 a/r housing sizes when mounted at the rear. You will not have any greater restriction due to a difference in air density based on heat and will get benefits from the location that will nearly cancel out any lag that you'd get from remote mounting. Sure there is always a point of diminishing returns. Can't get around this. If you mounted the turbo down the street you'd definitely see lag. The back of the car just isn't as far as people make it out to be. Not at the intake and exhaust airspeeds that we are talking about. No I wouldn't use this setup at 24 psi on a race car. For a street car at low to moderate boost levels however this could easily be done with little to no discernable turbo lag. The reason why I wouldn't use it at high pressure levels on a race car isn't to say it sucks. It's just that each system has it's own strengths and weaknesses based on what is required of them. I'd never run a peaky 24 psi boosted engine on the street. EVER! That's a poor combination for the job. Then again that's just my opinion.
No! Duh! See detailed response below.
No actually you have no clue how it could work. There is a very good reason why the exact same turbo spools slower at the rear. There is less energy back there. As I've stated before you need to change the exhaust side of the turbo to account for this. You have lost alot of energy through the walls of the exhaust in the form of heat. It isn't the heat itself that spins the turbo though. The effect heat has on the system is that hotter air takes up more space than cooler air. There is the same amount present but since the molecules are more excited, their greater movement takes up more physical space. When you lose some of this heat, the air condenses into a smaller space. There is still the same amount of air present. It's just more compact. Since it's more compact, it takes a smaller exhaust housing to render the same spool effect. This doesn't mean that a smaller a/r is more restrictive though. It isn't because the cooler air requires less flow area.
What happens to turbo spool rate and potentially boost when a cat is removed? What happens to spool rate when a free flowing muffler is installed in place of a restrictive one? Lag goes down and boost goes up. So does power. If you remote mount a turbo with nothing behind it, there is nothing to slow it down such as a cat. If it's sized to spool up nicely you'd be shocked at how little lag there actually is.
Beind farther from the engine with cooler gasses going through it also means it isn't as hard on the oil flowing through it. That's a good thing. You are less likely to coke the oil in the turbo. If the turbo doesn't get as hot, that also means that it's less likely to hold and transfer heat to the intake side. I know people claim this doesn't really happen but it's worse than many think it is. Less heat on the intake side is more efficiency.
A big downside is oil scavenging. I agree that this is an issue. Fortunately since the turbo doesn't get as hot and is easier on the oil than a conventionally mounted turbo, there is a viable alternative. Install a small oil cooler and pump in a closed loop system that is dedicated to the turbo only. This isn't hard to do and would work quite nicely. No need to worry about taping into the stock oil system or running lines a long distance. If one can fab up a remote mount, making this setup would be simple.
I also agree that getting the intake piping back to the front would also be an issue. It takes space. As pointed out, there are downsides to remote mounting just as there is with any other system. EVERY system is a compromise.
You CAN NOT use the exact same turbo (on the exhaust side) for remote mounting as you do for conventional mounting. This is completely ignoring the system requirements. Typically you need to go down at least 2 a/r housing sizes when mounted at the rear. You will not have any greater restriction due to a difference in air density based on heat and will get benefits from the location that will nearly cancel out any lag that you'd get from remote mounting. Sure there is always a point of diminishing returns. Can't get around this. If you mounted the turbo down the street you'd definitely see lag. The back of the car just isn't as far as people make it out to be. Not at the intake and exhaust airspeeds that we are talking about. No I wouldn't use this setup at 24 psi on a race car. For a street car at low to moderate boost levels however this could easily be done with little to no discernable turbo lag. The reason why I wouldn't use it at high pressure levels on a race car isn't to say it sucks. It's just that each system has it's own strengths and weaknesses based on what is required of them. I'd never run a peaky 24 psi boosted engine on the street. EVER! That's a poor combination for the job. Then again that's just my opinion.
Reallistically, you will change exhaust A/R to compensate for the amount of air flow.
But let's just say the A/R was the same. Rear mounted will suffer in spool.
I went from fast spooling stock turbo, then 3076r. If I wanted a nice fast spooling street turbo, I could've stayed with the stock turbo and run 350whp all day long.
You'd never run a peaky 24psi boosted engine on the street? Then don't.
Some people don't mind the lag, and some people like you make big deal about lags on the street car.
I like the way my car runs right now, and I'm happy I've upgraded from 3076r.
In fact, in the future I plan to use meth and run 30+psi daily on the STREET.
Oh, that sounds too rediculous to you too huh?
02-08-2008 | 12:43 PM
#77
RotoRocks Powered
Joined: May 2006
Posts: 1,236
Likes: 6
From: Delray Beach, FL
Spool rate and peak boost pressure has nothing to do with each other.
You set your peak boost pressure with your boost controller.
If you boost controller is set at let's say 12psi. What the hell would faster spool give you extra pound or two pounds of boost?
That's exactly what you said.
I couldn't care less if it makes me look bad.
You set your peak boost pressure with your boost controller.
If you boost controller is set at let's say 12psi. What the hell would faster spool give you extra pound or two pounds of boost?
That's exactly what you said.
I couldn't care less if it makes me look bad.
Yeah i set the max boost to 12 PSI, but I also stated that by 4K RPM my system develops 10PSI of boost, and not 12. You are either imagining things, or simply not paying attention. Take some of that Ginko Biloba (or whatever it is called) stuff. It helps with improved brain activity and concentration.
02-08-2008 | 12:46 PM
#78
Registered User
Joined: May 2004
Posts: 31
Likes: 0
From: MD
Where in my question did I even mention the peak boost pressure?
Yeah i set the max boost to 12 PSI, but I also stated that by 4K RPM my system develops 10PSI of boost, and not 12. You are either imagining things, or simply not paying attention. Take some of that Ginko Biloba (or whatever it is called) stuff. It helps with improved brain activity and concentration.
Yeah i set the max boost to 12 PSI, but I also stated that by 4K RPM my system develops 10PSI of boost, and not 12. You are either imagining things, or simply not paying attention. Take some of that Ginko Biloba (or whatever it is called) stuff. It helps with improved brain activity and concentration.
I'm done with this.
Have fun with your fast spooling , less than 300whp , kick *** rx8!!
how about some 10ml of euthasol by the shot?
That would help you out alot.
02-08-2008 | 01:15 PM
#79
RotoRocks Powered
Joined: May 2006
Posts: 1,236
Likes: 6
From: Delray Beach, FL
and yet you keep on going...
like I said ^^
Well, you are wrong again. Based on the intake temperature, the AF ratio I run, and the boost pressure, by my estimation, it should be making around 330-340 at the power pique. I have a good intercooler too, you know.
Did I just enter into a sensitive area with my food supplement suggestion? I promise not to make fun of you anymore. It's not nice of me. I am sorry. 
like I said ^^
Well, you are wrong again. Based on the intake temperature, the AF ratio I run, and the boost pressure, by my estimation, it should be making around 330-340 at the power pique. I have a good intercooler too, you know.
02-08-2008 | 01:23 PM
#80
That's not quite true.
Besides the obvious differences in manipulation of the waste gate (which always affects both in direct proportion, which is why it is useful to have a "start" setting on your boost controller), when you select a compressor, you do so knowing what your peak flow is going to be. If you have optimized the flow map, you will have effectively set your boost threshold as well.
So, for people that build using a bigger turbo with the idea that they will turn up the boost later, even though they are using a Pr that might be equivalent to the target of those with a smaller turbo, they have delayed onset by increasing the trim of the compressor.
EvilBada - I understand where you are coming from on this. However, I think your understanding of much of this is skewed by your experience, which appears to be with older stuff that is not properly sized - especially by modern standards.
Today, the actual is much closer to the theoretical than it was 3 years ago. There are a few of us who are way past 300 HP with boost thresholds in the 2k range and full boost before 4k.
Besides the obvious differences in manipulation of the waste gate (which always affects both in direct proportion, which is why it is useful to have a "start" setting on your boost controller), when you select a compressor, you do so knowing what your peak flow is going to be. If you have optimized the flow map, you will have effectively set your boost threshold as well.
So, for people that build using a bigger turbo with the idea that they will turn up the boost later, even though they are using a Pr that might be equivalent to the target of those with a smaller turbo, they have delayed onset by increasing the trim of the compressor.
EvilBada - I understand where you are coming from on this. However, I think your understanding of much of this is skewed by your experience, which appears to be with older stuff that is not properly sized - especially by modern standards.
Today, the actual is much closer to the theoretical than it was 3 years ago. There are a few of us who are way past 300 HP with boost thresholds in the 2k range and full boost before 4k.
Last edited by MazdaManiac; 02-08-2008 at 01:27 PM.
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