3rd Gear
Quote:
ORIGINAL: CumminsPilot
Apparently you've never checked drive pressure on a turboed vehicle. A properly tuned setup will require slightly more backpressure (exhaust boost pressure as you're stating it) than the boost it is producing (1:1 is ideal, but very hard to achieve). In my pickup, at 52 psi boost, I run slightly over 60 psi drive pressure into the turbo. That is without a wastegate. When I actuate the wastegate, drive pressure drops to around 40 psi and boost to 45 psi...but my egt's skyrocket because I'm not getting the massflow neccessary to cool all the fuel. In this case, the turbo is still on it's map at 52 psi, and therefore the wastegate is worthless (ie, I don't have enough fuel to push the turbo past it's limit). Granted, everything above is in regards to a 500rwhp diesel engine, but when it comes to forced induction, the concepts are the same.
Turbo on a diesel & a gas engine are totally different. Diesel push a TON more air then a gas engine. The compression ratios are not even in the same ball park. Wategate controls for a diesel are totally different. Diesels also run a lot cooler compared to a gas engine. When your pushing 52psi into the engine, your going to get about the same out of it. Boost in, is boost out. So as you increase intake boost, you will get more pressure & temp out of the exhaust. There directly proportional.ORIGINAL: CumminsPilot
Apparently you've never checked drive pressure on a turboed vehicle. A properly tuned setup will require slightly more backpressure (exhaust boost pressure as you're stating it) than the boost it is producing (1:1 is ideal, but very hard to achieve). In my pickup, at 52 psi boost, I run slightly over 60 psi drive pressure into the turbo. That is without a wastegate. When I actuate the wastegate, drive pressure drops to around 40 psi and boost to 45 psi...but my egt's skyrocket because I'm not getting the massflow neccessary to cool all the fuel. In this case, the turbo is still on it's map at 52 psi, and therefore the wastegate is worthless (ie, I don't have enough fuel to push the turbo past it's limit). Granted, everything above is in regards to a 500rwhp diesel engine, but when it comes to forced induction, the concepts are the same.
My point was, in a gas engine, where the muffler is, there is NO pressure there. Especially compared to off the manifold. We were not talking about a boosted car, were talking about the stock pressure of a 2.8 NA engine.
2nd Gear
badass, something different, I love it
and building boost at 1500 rpm is a lot better than i expected
and building boost at 1500 rpm is a lot better than i expected
Junior Member
Quote:
ORIGINAL: 2k S4
Turbo on a diesel & a gas engine are totally different. Diesel push a TON more air then a gas engine. The compression ratios are not even in the same ball park. Wategate controls for a diesel are totally different. Diesels also run a lot cooler compared to a gas engine. When your pushing 52psi into the engine, your going to get about the same out of it. Boost in, is boost out. So as you increase intake boost, you will get more pressure & temp out of the exhaust. There directly proportional.
They're not as different as you want to make it. Compression ratio has nothing to do with our current conversation. We are talking about forced induction and how you make boost. The amount of boost is irrelavent...I used my Cummins as an example because I KNOW what it does at what boost pressure. Close to 1:1. In your original post you stated that "The exhaust really doesn't make boost or psi. If you measured the "boost" of the exhaust it would be very low, my guess around a couple psi & high RPM." which is not correct for THIS discussion. The reason I say it's not is that you are saying that there is no drive pressure available for the turbo...well, once you put the turbo on, there is...see, circular reference. I would agree that w/o a turbo, there is very little drive pressure (and the less the better for NA, right?)ORIGINAL: 2k S4
Turbo on a diesel & a gas engine are totally different. Diesel push a TON more air then a gas engine. The compression ratios are not even in the same ball park. Wategate controls for a diesel are totally different. Diesels also run a lot cooler compared to a gas engine. When your pushing 52psi into the engine, your going to get about the same out of it. Boost in, is boost out. So as you increase intake boost, you will get more pressure & temp out of the exhaust. There directly proportional.
Quote:
My point was, in a gas engine, where the muffler is, there is NO pressure there. Especially compared to off the manifold. We were not talking about a boosted car, were talking about the stock pressure of a 2.8 NA engine.
Agreed 100%. But we were talking about a boosted car. My point was, in a gas engine, where the muffler is, there is NO pressure there. Especially compared to off the manifold. We were not talking about a boosted car, were talking about the stock pressure of a 2.8 NA engine.
Once that turbo goes on, you have the drive pressure. Formalities of the conversation, eh? 
3rd Gear
Quote:
ORIGINAL: CumminsPilot
They're not as different as you want to make it. Compression ratio has nothing to do with our current conversation. We are talking about forced induction and how you make boost. The amount of boost is irrelavent...I used my Cummins as an example because I KNOW what it does at what boost pressure. Close to 1:1. In your original post you stated that "The exhaust really doesn't make boost or psi. If you measured the "boost" of the exhaust it would be very low, my guess around a couple psi & high RPM." which is not correct for THIS discussion. The reason I say it's not is that you are saying that there is no drive pressure available for the turbo...well, once you put the turbo on, there is...see, circular reference. I would agree that w/o a turbo, there is very little drive pressure (and the less the better for NA, right?)
Your missing my point. In NA trim, your cummings moves a lot more air then the 2.8 Audi engine. Most high output engines, like the Vett, put out much more exhaust pressure, & in general move a lot more air. You will NEVER get a 1:1 on a gas engine. Compression ratio has a lot to do with it. The higher the compression ratio, the faster & hotter the exhaust gas will be.ORIGINAL: CumminsPilot
They're not as different as you want to make it. Compression ratio has nothing to do with our current conversation. We are talking about forced induction and how you make boost. The amount of boost is irrelavent...I used my Cummins as an example because I KNOW what it does at what boost pressure. Close to 1:1. In your original post you stated that "The exhaust really doesn't make boost or psi. If you measured the "boost" of the exhaust it would be very low, my guess around a couple psi & high RPM." which is not correct for THIS discussion. The reason I say it's not is that you are saying that there is no drive pressure available for the turbo...well, once you put the turbo on, there is...see, circular reference. I would agree that w/o a turbo, there is very little drive pressure (and the less the better for NA, right?)
My main point is, that the 2.8 does not push a lot of exhaust gas stock, throwing a turbo on it in the *** end, will make a very slow spooling turbo, & be very inefficient. All the piping will have a very high pressure drop, so 2 psi @ the turbo, will be much less at the throttle body.
1st Gear
Ok, this might seem a little stupid, but when you think about it, the 30v is in the same ballpark as a 5.7L Vette as far as size to hp ration goes.
2.8L = 190
5.7L = 350 was it?
So the only thing that the LS1 has is displacement. In fact, American engines are considerably less effective than import counterparts in making big power in small packages. Look at the 4.2L from Audi. Makes 340hp base, and makes 420hp in the RSpackage right? that's 80.5hp/Litre just in the s4 form. Vette (not C6, they have a larger displacement engine) is only making 61.40hp per litre. I think that what I was trying to get to, is that the 30v is a decent motor, and that if a motor twice it's size, with twice it's power can make 2 turbos spool, then the 2.8 with half the size, and half the power of the 5.7 can make half the turbos spool. That's my theory anyways.
2.8L = 190
5.7L = 350 was it?
So the only thing that the LS1 has is displacement. In fact, American engines are considerably less effective than import counterparts in making big power in small packages. Look at the 4.2L from Audi. Makes 340hp base, and makes 420hp in the RSpackage right? that's 80.5hp/Litre just in the s4 form. Vette (not C6, they have a larger displacement engine) is only making 61.40hp per litre. I think that what I was trying to get to, is that the 30v is a decent motor, and that if a motor twice it's size, with twice it's power can make 2 turbos spool, then the 2.8 with half the size, and half the power of the 5.7 can make half the turbos spool. That's my theory anyways.
3rd Gear
Quote:
ORIGINAL: brmiddle
http://www.hennesseyperformance.com/...ctionReq=Where
I guess these people don't know what they're doing either. This Jeep is rear mount I believe.
ORIGINAL: brmiddle
http://www.hennesseyperformance.com/...ctionReq=Where
I guess these people don't know what they're doing either. This Jeep is rear mount I believe.
It's a semi rear mount, after the trans, it's there, cuz, there is NO ROOM any where else for it. Yes, it is less efficient back there. This is a fully built big V8 engine. Much different from the 2.8l. Rear mount does have some applications, but it's never going to have the same efficiency as a manifold mounted one. Every inch you move back is going to yield less performance & cause more lag.
I'm sure if you ask them, it was a compromise putting the turbo there. I'm sure they built the engine, & played with the electronics to get most from it.
