some rear turbo testing
01-30-2013, 01:32 PM
#1
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some rear turbo testing I thought this was interesting for coming from a none f-body forum. explains quite alot of misconceptions and other stuff that could be help full to rearmount junkies. if im allowed and moderaters allow it ill see if i cna post the link if it can be read better, but this works pretty well
Rear mount turbos, Turbine housing A/R's, and everything you thought wouldn't work...
Gross Polluter
2JZ? No ****
Posts: 606
Joined: May 2011
Post: #1
Rear mount turbos, Turbine housing A/R's, and everything you thought wouldn't work...
Did some experimenting at work today to troubleshoot why a customers car wasn't making the power that I felt it should have been making and thought I'd share the results of my experiment. What I'm about to share isn't anything new or groundbreaking, but it is a real-world example of a keyboard racing topic.
I'm going to preface this post with the car I'm dealing with. It's a 2002 Pontiac Firebird LS1 6spd. Customer brought the car to us back in February to have an STS turbo kit installed. It's the basic rear-mounted kit made by the only company that can make it. Simply connect it to the rear exhaust tube and a little plumbing and away you go. To be more specific, the turbo in the kit is a T67 compressor in a 60A/R T04E compressor housing and P trim T04 turbine in a tangential .82 A/R turbine housing. The charge pipe traverses the frame rail in a 2.25" tube to a front mounted intercooler. From the intercooler is a considerable length of 2.5" tubing that couples to the MAF then the throttle body with two 90 degree silicon couplers mounted in close proximity. It's a less than ideal setup, but for the space constraints you deal with in an F body, it works. The owner of the shop, Mike, originally tuned the turbo kit on a completely stock motor. The car left the shop with 465whp and 508ftlbs of torque at 8psi boost.
The owner of the car wanted moar power so he returned with a set of 317 LQ9 truck heads (larger combustion chamber = lower compression, but flows equivalent to Z06 heads) and a Comp "blower cam" kit. His goal he had in mind was close to 600whp. It's a bit unreasonable considering the setup, but who am I to say that? We installed the heads and cam kit and put the car back on the dyno to get the new setup dialed in. Immediately I noticed the engine LOVED the new cam, pulling completely to 6500 rpm without dropping off in power. The stock cam made peak power at 5200 rpm and fell off violently beyond that. The new heads lowered compression a considerable amount, allowing for a higher boost threshold and consequently more timing required to make more power.
I started the tune at wastegate boost level, 4.5 psi. The car made 405whp which seemed reasonable for such a low boost level. I started ramping up the boost to the final pump gas boost level of 8psi before I started to tune on methanol injection. I wasn't too happy with the final pump gas number of 489whp. Hoping for better numbers on methanol with a bit more timing, I backed off the ECU's power enrichment to maintain the target AFR with the methanol injection. At 10psi I hit 508whp. 11psi made 507whp, 12psi 508whp, and 13psi made a final number of 509whp. I was baffled. No matter what I tried, I could not break out of the ~510whp area. Once the engine reached that power around 4500rpm it just hung out there until redline. The only difference turning up the boost made was it hit 509whp quicker. Once it got there, however, it stayed.
I was baffled. Sure, the rear mount turbo is not the greatest, but this engine SHOULD be making more power than this. I've seen this turbo in the 630whp territory on DSM's, albeit at a much greater boost level well into the compressors efficiency range. I started to think about things I could do to figure out what the problem was. With the customers goal of 600whp, his head/cam package only netting only 40whp with 5psi more boost, and some unfortunate circumstances in the shop, he wasn't going to be happy. I had to figure something out, if only to explain to him the exact reason why the car isn't making the power it should.
I began to do some research online to see what other people were making with the same turbo kit. My findings showed that most people pushing the kit were making about 520-530whp, a marginal 5% difference from my dyno. I could chalk it up to mere differences in dyno readings (and many of my customers complain my dyno reads way low.) But, I had to find out what the issue was. Why is a mid 600whp turbo topping out at 500whp on this car?
I thought about installing another MAP sensor on the dyno analog in and plot the pressure differential across the charge piping from the turbo to throttle body. But, at the time I didn't have a second MAP sensor. The next thing to try was changing the A/R of the turbine housing. I had a 1.32 A/R housing at home that had been sitting around from a turbo I bought way back in the day. Figured I'd give it a try. I came into work this morning, installed the housing, and threw it back on the dyno to observe the results.
As expected, boost response was way way laggy. Like, unbearably laggy. But, it made boost so I could still conduct the experiment. Like before, I started at wastegate boost of 4.5psi. I was surprised at the results I saw. From just a changing the housing from the .82 A/R to the 1.32 A/R I picked up almost 50whp. But, the drop in area under the curve I thought I'd see with all of the induced lag didn't seem to exist on the dyno plot. In fact, the transient power between both housings seemed to be nearly identical. Take a look for yourself:
Image has been scaled down 4% (985x627). Click this bar to view original image (1021x649). Click image to open in new window.
Mind you, full boost with the .82 housing was around 3.5k and with the 1.32 housing full boost is at 4.5k. Furthermore, 448whp at 4.5psi on a low compression LS1 is no joke. I was anxious to turn up the boost to see where I could go.
I worked my way through the boost range. Initially, I was seeing gains of 60whp per psi of boost right off the bat. But, as I approached 10 psi that number tapered off to about 10whp per psi of boost. I called it a day at 11psi. But, before I explain why, take a look at the dyno chart:
Image has been scaled down 4% (985x606). Click this bar to view original image (1017x625). Click image to open in new window.
The red plot is the .82 A/R housing at 13psi of boost. You can clearly see what I meant by the engine hitting 509whp and just hanging out there until redline. It's nearly a flat line. The blue plot is the 1.32 A/R housing at 11psi of boost. Yeah, at 11psi the 1.32 A/R housing not only made almost 50whp over the .82 housing, but it did it with 2 psi less boost too! Adding insult to injury, while the 1.32 makes full boost 1000 rpm later, it still makes the same power in the transient range as the smaller housing.
This is where things get interesting. While I'm happy with the result, I'm not happy with the fact that this motor should be good for 14psi of boost, and beyond 9psi I'm loosing my hp/psi boost ratio very quickly. Now comes the pressure differential readings. I don't have that data available to post, but interestingly enough here were my findings in today's dyno session:
-At 4.5psi boost there was a 1.8 psi drop across the system and no fall in boost
-At 9psi boost there was an initial 2psi drop across the system increasing to 3psi at redline and a consequent drop to 7psi boost at redline.
-At 10psi boost there was an initial 2psi drop across the system increasing to 5psi at redline and a consequent drop to 8psi at redline.
-At 11psi boost there was an initial 2psi drop across the system increasing to 6.5psi at redline and a consequent drop to 9psi boost at redline.
What was happening is I was approaching the limits of the 20 feet of induction plumbing, 15 feet of that being the 2.25" piping that connects the turbo to the intercooler. There was an advantage to this situation, however. At 11psi of boost my pressure differential between the turbo and throttle body was 6psi. This resulted in a pressure ratio of 2.15 at the compressor. What was happening here is the pressure ratio due to the restriction in the piping was actually placing me in an area of the compressor map that allowed around 65lb/min of airflow. The smaller turbine housing never dropped boost toward redline, so it was reasonable to assume the pressure drop was closer to 2psi over the entire powerband. That would have put the compressor ratio around 1.8 where the flow was only in the 45lb/min territory, or about 500whp. Regardless, I'm making close to 640bhp through 15 feet of 2.25" piping. Put that in your pipe and smoke it, before you think you NEED 3" IC piping for your 300whp redblock.
I called it a day at 11psi because I started to observe the pressure drop was increasing about 2psi for every pound of boost. Had I gone for the target boost of 14psi, the pressure drop would have been symmetrical with the actual boost pressure. Fundamentally, it didn't make sense to do that. Not only that, but this was just an experiment to explain to the customer with data why he's not making the power he wants to make.
Cliffs: 2.25" IC piping is good for 640bhp. A bigger A/R housing induces lag on a rear mount turbo kit, but never loses power over the smaller housing and only makes more power were it counts. 555whp on a stock low compression LS1 bottom end at a mere 11psi dropping to 9psi at redline is no joke.
That's all. Carry on.....
(This post was last modified: 08-17-2011 04:11 AM by Gross Polluter.)
Rear mount turbos, Turbine housing A/R's, and everything you thought wouldn't work...
Gross Polluter
2JZ? No ****
Posts: 606
Joined: May 2011
Post: #1
Rear mount turbos, Turbine housing A/R's, and everything you thought wouldn't work...
Did some experimenting at work today to troubleshoot why a customers car wasn't making the power that I felt it should have been making and thought I'd share the results of my experiment. What I'm about to share isn't anything new or groundbreaking, but it is a real-world example of a keyboard racing topic.
I'm going to preface this post with the car I'm dealing with. It's a 2002 Pontiac Firebird LS1 6spd. Customer brought the car to us back in February to have an STS turbo kit installed. It's the basic rear-mounted kit made by the only company that can make it. Simply connect it to the rear exhaust tube and a little plumbing and away you go. To be more specific, the turbo in the kit is a T67 compressor in a 60A/R T04E compressor housing and P trim T04 turbine in a tangential .82 A/R turbine housing. The charge pipe traverses the frame rail in a 2.25" tube to a front mounted intercooler. From the intercooler is a considerable length of 2.5" tubing that couples to the MAF then the throttle body with two 90 degree silicon couplers mounted in close proximity. It's a less than ideal setup, but for the space constraints you deal with in an F body, it works. The owner of the shop, Mike, originally tuned the turbo kit on a completely stock motor. The car left the shop with 465whp and 508ftlbs of torque at 8psi boost.
The owner of the car wanted moar power so he returned with a set of 317 LQ9 truck heads (larger combustion chamber = lower compression, but flows equivalent to Z06 heads) and a Comp "blower cam" kit. His goal he had in mind was close to 600whp. It's a bit unreasonable considering the setup, but who am I to say that? We installed the heads and cam kit and put the car back on the dyno to get the new setup dialed in. Immediately I noticed the engine LOVED the new cam, pulling completely to 6500 rpm without dropping off in power. The stock cam made peak power at 5200 rpm and fell off violently beyond that. The new heads lowered compression a considerable amount, allowing for a higher boost threshold and consequently more timing required to make more power.
I started the tune at wastegate boost level, 4.5 psi. The car made 405whp which seemed reasonable for such a low boost level. I started ramping up the boost to the final pump gas boost level of 8psi before I started to tune on methanol injection. I wasn't too happy with the final pump gas number of 489whp. Hoping for better numbers on methanol with a bit more timing, I backed off the ECU's power enrichment to maintain the target AFR with the methanol injection. At 10psi I hit 508whp. 11psi made 507whp, 12psi 508whp, and 13psi made a final number of 509whp. I was baffled. No matter what I tried, I could not break out of the ~510whp area. Once the engine reached that power around 4500rpm it just hung out there until redline. The only difference turning up the boost made was it hit 509whp quicker. Once it got there, however, it stayed.
I was baffled. Sure, the rear mount turbo is not the greatest, but this engine SHOULD be making more power than this. I've seen this turbo in the 630whp territory on DSM's, albeit at a much greater boost level well into the compressors efficiency range. I started to think about things I could do to figure out what the problem was. With the customers goal of 600whp, his head/cam package only netting only 40whp with 5psi more boost, and some unfortunate circumstances in the shop, he wasn't going to be happy. I had to figure something out, if only to explain to him the exact reason why the car isn't making the power it should.
I began to do some research online to see what other people were making with the same turbo kit. My findings showed that most people pushing the kit were making about 520-530whp, a marginal 5% difference from my dyno. I could chalk it up to mere differences in dyno readings (and many of my customers complain my dyno reads way low.) But, I had to find out what the issue was. Why is a mid 600whp turbo topping out at 500whp on this car?
I thought about installing another MAP sensor on the dyno analog in and plot the pressure differential across the charge piping from the turbo to throttle body. But, at the time I didn't have a second MAP sensor. The next thing to try was changing the A/R of the turbine housing. I had a 1.32 A/R housing at home that had been sitting around from a turbo I bought way back in the day. Figured I'd give it a try. I came into work this morning, installed the housing, and threw it back on the dyno to observe the results.
As expected, boost response was way way laggy. Like, unbearably laggy. But, it made boost so I could still conduct the experiment. Like before, I started at wastegate boost of 4.5psi. I was surprised at the results I saw. From just a changing the housing from the .82 A/R to the 1.32 A/R I picked up almost 50whp. But, the drop in area under the curve I thought I'd see with all of the induced lag didn't seem to exist on the dyno plot. In fact, the transient power between both housings seemed to be nearly identical. Take a look for yourself:
Image has been scaled down 4% (985x627). Click this bar to view original image (1021x649). Click image to open in new window.
Mind you, full boost with the .82 housing was around 3.5k and with the 1.32 housing full boost is at 4.5k. Furthermore, 448whp at 4.5psi on a low compression LS1 is no joke. I was anxious to turn up the boost to see where I could go.
I worked my way through the boost range. Initially, I was seeing gains of 60whp per psi of boost right off the bat. But, as I approached 10 psi that number tapered off to about 10whp per psi of boost. I called it a day at 11psi. But, before I explain why, take a look at the dyno chart:
Image has been scaled down 4% (985x606). Click this bar to view original image (1017x625). Click image to open in new window.
The red plot is the .82 A/R housing at 13psi of boost. You can clearly see what I meant by the engine hitting 509whp and just hanging out there until redline. It's nearly a flat line. The blue plot is the 1.32 A/R housing at 11psi of boost. Yeah, at 11psi the 1.32 A/R housing not only made almost 50whp over the .82 housing, but it did it with 2 psi less boost too! Adding insult to injury, while the 1.32 makes full boost 1000 rpm later, it still makes the same power in the transient range as the smaller housing.
This is where things get interesting. While I'm happy with the result, I'm not happy with the fact that this motor should be good for 14psi of boost, and beyond 9psi I'm loosing my hp/psi boost ratio very quickly. Now comes the pressure differential readings. I don't have that data available to post, but interestingly enough here were my findings in today's dyno session:
-At 4.5psi boost there was a 1.8 psi drop across the system and no fall in boost
-At 9psi boost there was an initial 2psi drop across the system increasing to 3psi at redline and a consequent drop to 7psi boost at redline.
-At 10psi boost there was an initial 2psi drop across the system increasing to 5psi at redline and a consequent drop to 8psi at redline.
-At 11psi boost there was an initial 2psi drop across the system increasing to 6.5psi at redline and a consequent drop to 9psi boost at redline.
What was happening is I was approaching the limits of the 20 feet of induction plumbing, 15 feet of that being the 2.25" piping that connects the turbo to the intercooler. There was an advantage to this situation, however. At 11psi of boost my pressure differential between the turbo and throttle body was 6psi. This resulted in a pressure ratio of 2.15 at the compressor. What was happening here is the pressure ratio due to the restriction in the piping was actually placing me in an area of the compressor map that allowed around 65lb/min of airflow. The smaller turbine housing never dropped boost toward redline, so it was reasonable to assume the pressure drop was closer to 2psi over the entire powerband. That would have put the compressor ratio around 1.8 where the flow was only in the 45lb/min territory, or about 500whp. Regardless, I'm making close to 640bhp through 15 feet of 2.25" piping. Put that in your pipe and smoke it, before you think you NEED 3" IC piping for your 300whp redblock.
I called it a day at 11psi because I started to observe the pressure drop was increasing about 2psi for every pound of boost. Had I gone for the target boost of 14psi, the pressure drop would have been symmetrical with the actual boost pressure. Fundamentally, it didn't make sense to do that. Not only that, but this was just an experiment to explain to the customer with data why he's not making the power he wants to make.
Cliffs: 2.25" IC piping is good for 640bhp. A bigger A/R housing induces lag on a rear mount turbo kit, but never loses power over the smaller housing and only makes more power were it counts. 555whp on a stock low compression LS1 bottom end at a mere 11psi dropping to 9psi at redline is no joke.
That's all. Carry on.....
(This post was last modified: 08-17-2011 04:11 AM by Gross Polluter.)
