Rear Mount Turbo Progress??????
12-16-2005, 04:47 PM
#46
Originally Posted by heinrich
Better? In what way?
In that it allows the stock induction to remain in-place, or
In that it requires no real mods or
In that it costs little or
in that it develops less heat and encapsulates less heat due to its size and location or
In that it can deliver the same amount of horsepower as a twinscrew?
There are so many pros and cons. Each works and each makes sense. I doubt there's such a thing as "better". Better in what sense, is the question. Regarding sc vs turbo. you guys crack me up. So now the 928 list here has singlehandedly undone the many decades of technological engineering truths? namely that a supercharger is generally able to boost at far lower revs than a turbo, because the turbo can only work once the engine has revved (at least a little)? Or, the fact that a turbo needs to be sized for the entire rev range and most turbos I've driven have NO TORQUE at all below a goodly amount of revs, mostly 4k ..... or how about the fact that turbos usually require lower compression.
How is it that we're making these changes to what has been known for decades regarding the technology?
Turbo is obviously just as cool as supercharger. Better?
suuuuuuuuuuuure.
In that it allows the stock induction to remain in-place, or
In that it requires no real mods or
In that it costs little or
in that it develops less heat and encapsulates less heat due to its size and location or
In that it can deliver the same amount of horsepower as a twinscrew?
There are so many pros and cons. Each works and each makes sense. I doubt there's such a thing as "better". Better in what sense, is the question. Regarding sc vs turbo. you guys crack me up. So now the 928 list here has singlehandedly undone the many decades of technological engineering truths? namely that a supercharger is generally able to boost at far lower revs than a turbo, because the turbo can only work once the engine has revved (at least a little)? Or, the fact that a turbo needs to be sized for the entire rev range and most turbos I've driven have NO TORQUE at all below a goodly amount of revs, mostly 4k ..... or how about the fact that turbos usually require lower compression.
How is it that we're making these changes to what has been known for decades regarding the technology?
Turbo is obviously just as cool as supercharger. Better?
suuuuuuuuuuuure.Depends on the turbo you use. You can make a turbo spool up almost instantly, but it will run out of air at a relatively low RPM range. This is the rationale behind a sequential turbo.
2)" Or, the fact that a turbo needs to be sized for the entire rev range"
A S/C has to be properly sized to the engine also. You would never want to put an 8/71 SC on a 2.0 liter 4 cylinder.
3)"and most turbos I've driven have NO TORQUE at all below a goodly amount of revs, mostly 4k ....."
That is a flat out mischaracterization of turbo performance characteristics. In almost every turbo car on the road full boost is achieved by 4k rpm, and at least 1 psi is present in almost all cases by 3000rpm(usually lower, for instance my T-type at 2800rpm would stage at 10psi of boost!).
Further, having the power higher in the RPM range can be an ADVANTADGE if you have- or expect to have- launch traction issues.
4) " or how about the fact that turbos usually require lower compression."
They require no lower compression PSI of boost for PSI of boost than an S/C with an equivelant system efficiency.
5)"turbo is obviously just as cool as supercharger. Better?
"Laugh all you want, turbos are clearly superior because they require far less power to spin than a belt driven supercharger, espeically as boost levels are increased. End of story.
But to give you a for instance, on a top fuel hemi the SC consumes approx 600hp to power itself!!!
The same engine with a properly sized turbo delivering the same CFM of flow would require less than 100.
Which is EXACTLY why turbos were banned from top fuel competition. They gave a completely unfair advantadge over the long established 8/71 SC's.
But you are right, it is long established that one is superior, which is why Porsche ONLY uses Turbos on their cars.
12-16-2005, 04:55 PM
#47
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ooh ouch I hit a nerve 
Well, let's see. Do you have a turbocharger on your 928? Why not ... could it be cost? HUGE JOB perhaps?
Could you afford a supercharger? Yes? Why is that ... could it be cost and ease of installation?
And while it *could* be an advantage to have boost later, how about my buddy Shane who INSISTS on POWER NOW DAMMIT
..... how cool would he find the turbo ... how "better" .... I think not.
Again. turbo is NOT better than supercharger. Not for everyone, and not even for MOST. Why is that Sniper? Cause no-one has the time or money to turbocharge, but superchargers are cheap and easy now. That, a turbo can never be. You have to replace your intake and exhaust; you should mill your pistons; you have to pipe oil, and you have to intercool. So, where in all of that is the "better" of the turbo?
Well, let's see. Do you have a turbocharger on your 928? Why not ... could it be cost? HUGE JOB perhaps?
Could you afford a supercharger? Yes? Why is that ... could it be cost and ease of installation?
And while it *could* be an advantage to have boost later, how about my buddy Shane who INSISTS on POWER NOW DAMMIT
..... how cool would he find the turbo ... how "better" .... I think not.Again. turbo is NOT better than supercharger. Not for everyone, and not even for MOST. Why is that Sniper? Cause no-one has the time or money to turbocharge, but superchargers are cheap and easy now. That, a turbo can never be. You have to replace your intake and exhaust; you should mill your pistons; you have to pipe oil, and you have to intercool. So, where in all of that is the "better" of the turbo?
12-16-2005, 05:32 PM
#48
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sniper wrote:
I disagree. I would really like to see an 8/71 on 4 banger. 
It would be something to see a combo where the blower is actually bigger than the short block.
You would never want to put an 8/71 SC on a 2.0 liter 4 cylinder.
It would be something to see a combo where the blower is actually bigger than the short block.
12-16-2005, 06:17 PM
#49
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Originally Posted by m21sniper
1) "namely that a supercharger is generally able to boost at far lower revs than a turbo"
Depends on the turbo you use. You can make a turbo spool up almost instantly, but it will run out of air at a relatively low RPM range. This is the rationale behind a sequential turbo.
2)" Or, the fact that a turbo needs to be sized for the entire rev range"
A S/C has to be properly sized to the engine also. You would never want to put an 8/71 SC on a 2.0 liter 4 cylinder.
3)"and most turbos I've driven have NO TORQUE at all below a goodly amount of revs, mostly 4k ....."
That is a flat out mischaracterization of turbo performance characteristics. In almost every turbo car on the road full boost is achieved by 4k rpm, and at least 1 psi is present in almost all cases by 3000rpm(usually lower, for instance my T-type at 2800rpm would stage at 10psi of boost!).
Further, having the power higher in the RPM range can be an ADVANTADGE if you have- or expect to have- launch traction issues.
4) " or how about the fact that turbos usually require lower compression."
They require no lower compression PSI of boost for PSI of boost than an S/C with an equivelant system efficiency.
5)"turbo is obviously just as cool as supercharger. Better?"
Laugh all you want, turbos are clearly superior because they require far less power to spin than a belt driven supercharger, espeically as boost levels are increased. End of story.
But to give you a for instance, on a top fuel hemi the SC consumes approx 600hp to power itself!!!
The same engine with a properly sized turbo delivering the same CFM of flow would require less than 100.
Which is EXACTLY why turbos were banned from top fuel competition. They gave a completely unfair advantadge over the long established 8/71 SC's.
But you are right, it is long established that one is superior, which is why Porsche ONLY uses Turbos on their cars.
Depends on the turbo you use. You can make a turbo spool up almost instantly, but it will run out of air at a relatively low RPM range. This is the rationale behind a sequential turbo.
2)" Or, the fact that a turbo needs to be sized for the entire rev range"
A S/C has to be properly sized to the engine also. You would never want to put an 8/71 SC on a 2.0 liter 4 cylinder.
3)"and most turbos I've driven have NO TORQUE at all below a goodly amount of revs, mostly 4k ....."
That is a flat out mischaracterization of turbo performance characteristics. In almost every turbo car on the road full boost is achieved by 4k rpm, and at least 1 psi is present in almost all cases by 3000rpm(usually lower, for instance my T-type at 2800rpm would stage at 10psi of boost!).
Further, having the power higher in the RPM range can be an ADVANTADGE if you have- or expect to have- launch traction issues.
4) " or how about the fact that turbos usually require lower compression."
They require no lower compression PSI of boost for PSI of boost than an S/C with an equivelant system efficiency.
5)"turbo is obviously just as cool as supercharger. Better?
"Laugh all you want, turbos are clearly superior because they require far less power to spin than a belt driven supercharger, espeically as boost levels are increased. End of story.
But to give you a for instance, on a top fuel hemi the SC consumes approx 600hp to power itself!!!
The same engine with a properly sized turbo delivering the same CFM of flow would require less than 100.
Which is EXACTLY why turbos were banned from top fuel competition. They gave a completely unfair advantadge over the long established 8/71 SC's.
But you are right, it is long established that one is superior, which is why Porsche ONLY uses Turbos on their cars.
And better is a term used depending on what you want. But, results are results.
Anyways no need begin this arguement. I know both sides of it. I have owned all three types of FI and they all have their nitch.
I know what I plan on putting on my shark
12-17-2005, 04:41 PM
#52
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Originally Posted by Barry Johnson
Imo... If I'm reading correctly, you SC'd your 85 for under a grand?! Do tell...
https://rennlist.com/forums/928-forum/203527-paxton-sc-instead-of-ac.html
https://rennlist.com/forums/928-forum/230334-first-time-at-the-drags-with-the-sc.html
The setup has chnaged a little since thelast picture was posted. At themoment I have one HKS Race bypass valve insted of the 2 small ones I had on before. In a few weeks I'll start fabricating the intercooler setp too. Also a test pipe will replace the cats. I'm shooting for mid 12's.
12-18-2005, 11:00 AM
#53
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Heinrich ...I do hope you are not too far on the SC bandwagon yet. I'll prove by mid year that $ for $ the turbo will deliver more HP than any supercharger system available for the 928 today. Twin screw, centrifugal, et at. I'm not talking peak numbers, but an area under the curve comparison. That is all that really matters. Maybe you and Shane can come to NC next year. I'll bring the Depends. 
Remember, there are 951s out there with 2 valve heads putting down well over 400 HP with one turbo. 2.5 liters, one turbo, 2-valve heads. Think about that for just a minute and then transfer that up to the 928. The potential is incredible. 650 HP would not even be pushing the limits too hard.
My Audi will make full tilt 25 psig boost in 1st gear by about 4,500 RPM. That's a big RS2 turbine and just 2.2 liters driving it. Shift to 2nd, she is on full tilt 300-400 RPM after the clutch engages. As the gear ratios go up the boost response becomes even better. 5th gear, roll on from 2,500 I have 25 psig by 3,000-3,200 RPM. The turbos I have picked for the S4 will be exceptionally responsive and they will not be a choker up top. Modern Garrett hardware...I've changed my turbo selection this weekend. The new GT line is simply awesome. I'd challenge you that some lag on a big V8 is a good thing for traction. I don't need full boost at 2,500 RPM to make 9 mile burnouts. I'd rather have it roll in hard once the car is rolling. This adds to the "amusement ride" feeling with the turbos.
The turbo work on 928s has just started....more updates as they become available. In the next two weeks I'll be hitting the streets with the 4.5 K-26/Tial/HK upgrade.
Remember, there are 951s out there with 2 valve heads putting down well over 400 HP with one turbo. 2.5 liters, one turbo, 2-valve heads. Think about that for just a minute and then transfer that up to the 928. The potential is incredible. 650 HP would not even be pushing the limits too hard.My Audi will make full tilt 25 psig boost in 1st gear by about 4,500 RPM. That's a big RS2 turbine and just 2.2 liters driving it. Shift to 2nd, she is on full tilt 300-400 RPM after the clutch engages. As the gear ratios go up the boost response becomes even better. 5th gear, roll on from 2,500 I have 25 psig by 3,000-3,200 RPM. The turbos I have picked for the S4 will be exceptionally responsive and they will not be a choker up top. Modern Garrett hardware...I've changed my turbo selection this weekend. The new GT line is simply awesome. I'd challenge you that some lag on a big V8 is a good thing for traction. I don't need full boost at 2,500 RPM to make 9 mile burnouts. I'd rather have it roll in hard once the car is rolling. This adds to the "amusement ride" feeling with the turbos.
The turbo work on 928s has just started....more updates as they become available. In the next two weeks I'll be hitting the streets with the 4.5 K-26/Tial/HK upgrade.
12-18-2005, 11:57 AM
#54
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Originally Posted by Herr-Kuhn
Heinrich ...I do hope you are not too far on the SC bandwagon yet. I'll prove by mid year that $ for $ the turbo will deliver more HP than any supercharger system available for the 928 today.
I love the idea of a turbo setup; I want to see you and Mark succeed with your projects. One point Heinrich was trying to point out is many people love the Centrifugal SC setup due to simplicity. How about those in a restrictive testing area that forces you to remove the forced induction every two years. The Centrifugal SC setup wins this hands down. Ultimate performance is not the #1 priority on most 928 owners list. 400rwhp is plenty for the majority around here, can be had in a short afternoon.
Originally Posted by Herr-Kuhn
The turbo work on 928s has just started.
Last edited by hacker-pschorr; 12-19-2005 at 12:56 AM.
12-18-2005, 01:12 PM
#55
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Herr-Kuhn wrote:
I think this is one of the more insightful comments made about 928 motor mod tuning. It seems that we are really preoccupied with dyno sheets when it comes to mods, and not the feel of how the power is delivered.
In my younger days, everyone was preoccupied with putting in monster cams, big carbs, and 4.11 gearsets. What you were left with was car that had no power out of the hole, and short burst of top end. They didn't feel fast, although they pulled a decent quarter mile. I kept the taller gear set (3.3), actually built the motor for a bigger cam than stock (increased C/R, bigger valves), but then installed a milder cam than my buddies. I kept the vaccuum secondary 4 barrel and went to a little lighter diaphragm spring, but didn't go totally light so as to open the secondaries right away. The resulting power delivery was great torque out of the hole, and a monster transition through the midrange. You could feel the car pulling you into the top end, as opposed to just rowing a gear box. My car felt faster than my friends rides, although it wasn't as quick in the quarter. These guys were always wanting to drive my ride. Dyno sheets and timeslips are great, but tuning to make the car fun to drive should be part of the equation. I think its great that Mr. Kuhn sees this as a critical part of his component choices.
I'd rather have it roll in hard once the car is rolling. This adds to the "amusement ride" feeling with the turbos.
In my younger days, everyone was preoccupied with putting in monster cams, big carbs, and 4.11 gearsets. What you were left with was car that had no power out of the hole, and short burst of top end. They didn't feel fast, although they pulled a decent quarter mile. I kept the taller gear set (3.3), actually built the motor for a bigger cam than stock (increased C/R, bigger valves), but then installed a milder cam than my buddies. I kept the vaccuum secondary 4 barrel and went to a little lighter diaphragm spring, but didn't go totally light so as to open the secondaries right away. The resulting power delivery was great torque out of the hole, and a monster transition through the midrange. You could feel the car pulling you into the top end, as opposed to just rowing a gear box. My car felt faster than my friends rides, although it wasn't as quick in the quarter. These guys were always wanting to drive my ride. Dyno sheets and timeslips are great, but tuning to make the car fun to drive should be part of the equation. I think its great that Mr. Kuhn sees this as a critical part of his component choices.
12-19-2005, 02:31 PM
#56
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Hey Barry, sorry for the late reply. I was thinking that the thin wall aluminum would shed heat better than the exhaust pipe on the cold side. I really don't want to add an intercooler, if I don't have to. I want around 8 psi of boost, but I'm hoping that the ambient air extracting heat from the cold side piping will be enough charge cooling to handle it. I'm just a backyard engineer, so I don't know if my thinking is correct. I'm not sure of the specs on the T3/T4. What size, AR and all that should I be looking for for proper spool up and boost levels??????
Lance, I removed my back seats and rear air about 2 years ago. Definitely adds some room while losing weight.
Thanks DR for the line on the 951 valve. So what is the final verdict, do I need one or two of them to handle the volume of air????
And to those of you arguing over what type of forced induction is the best, START YOUR OWN THREAD!!!!!!!!!!!!!! Don't hijack this one. This thread is about REAR MOUNTED TURBO's on a 928, and any info that has been learned in the forced induction world that will cross over and be applicable to the RMT.
Tom M., I'm doing the stand alone oil system, so the engine supplied info doesn't help much, but thank you. What about the turbo size/type?? Did you ever find out the specs??? TIA.
Lance, I removed my back seats and rear air about 2 years ago. Definitely adds some room while losing weight.
Thanks DR for the line on the 951 valve. So what is the final verdict, do I need one or two of them to handle the volume of air????
And to those of you arguing over what type of forced induction is the best, START YOUR OWN THREAD!!!!!!!!!!!!!! Don't hijack this one. This thread is about REAR MOUNTED TURBO's on a 928, and any info that has been learned in the forced induction world that will cross over and be applicable to the RMT.
Tom M., I'm doing the stand alone oil system, so the engine supplied info doesn't help much, but thank you. What about the turbo size/type?? Did you ever find out the specs??? TIA.
12-20-2005, 01:46 PM
#57
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Hi Chris,
>Thanks DR for the line on the 951 valve.
No problem.
> So what is the final verdict, do I need one or two of them to handle the volume of air????
I know they are used on the 911 Turbos, and the billet versions you see advertized are supposedly for higher boost levels and are the same physical size. I have no experiance with Turbos and can't say for sure, but you might could send Mark Robinson a PM and ask his opinion.
Merry Christmas to you and the family AND the cats and dogs, including the new German Shepard! Can't wait for Thor to meet her!
>Thanks DR for the line on the 951 valve.
No problem.
> So what is the final verdict, do I need one or two of them to handle the volume of air????
I know they are used on the 911 Turbos, and the billet versions you see advertized are supposedly for higher boost levels and are the same physical size. I have no experiance with Turbos and can't say for sure, but you might could send Mark Robinson a PM and ask his opinion.
Merry Christmas to you and the family AND the cats and dogs, including the new German Shepard! Can't wait for Thor to meet her!
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12-20-2005, 02:19 PM
#58
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Originally Posted by Chris Lockhart
Thanks DR for the line on the 951 valve. So what is the final verdict, do I need one or two of them to handle the volume of air????
12-20-2005, 02:24 PM
#59
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>The 951 BOV is different from the 993 version. Interchangeable, but the 993 has a metal >diaphragm and cost a few $ more. Well worth the upgrade.
Yep, one is $20ish and the other is $30ish.
Scott, are you at home or work, I need to call you.
Yep, one is $20ish and the other is $30ish.
Scott, are you at home or work, I need to call you.
12-20-2005, 02:27 PM
#60
Originally Posted by atb
sniper wrote:
I disagree. I would really like to see an 8/71 on 4 banger.
It would be something to see a combo where the blower is actually bigger than the short block.
I disagree. I would really like to see an 8/71 on 4 banger.
It would be something to see a combo where the blower is actually bigger than the short block.
