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S4 throttle body butterfly thoughts

Old 01-08-2018, 07:59 PM
  #16  
Marti
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Originally Posted by ptuomov View Post
Hereís what I believe. The 928 cylinder filling and temperatures are different depending on whether one runs stock exhaust manifolds or long-tube headers. Most of the filling imbalances, residual gas fractions, AFR variations, and timing requirement differences are caused by exhaust blowdown interference inside the stock exhaust manifolds. The original poster in this thread will run headers so most of the imbalances at peak power will be automatically resolved by the headers. At mid range rpms, Iíd expect the long intake runner cylinders (2, 3, 6, and 7) to fill a little better but at peak power the intake runner length shouldnít be cause a huge imbalance. Opinions vary on this, of course.
You guys are very technical and it's fascinating to see the level of analysis applied to any given challenge.

My approach is far more rudimentary, I understand that the longer headers will produce better cylinder filling by simply creating a bigger vacuum effect which is probably helped with a longer tract which affects the front most cylinders most - which happens to be the cylinders with the biggest inlet manifold challenges. This will be helped by the change in cams also.

The inlet manifold 'runners' to me look terrible for the front most cylinders and inside the plenum chambers the bell mouth design / set up is a mess (sorry Porsche but you could have done better). I will make limited changes to the inlet manifold to clean up castings, match components and help the mess inside the plenum chambers - I can't employ too much science as I don't have the time to measure the individual changes or replicate the engine flow properties but I can have a best guess based on everything I see here which is the next best thing!
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Old 01-08-2018, 08:00 PM
  #17  
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Originally Posted by PorKen View Post
Basic by-cylinder retard tuning patch (for ST.BINs):
https://rennlist.com/forums/928-foru...ard-patch.html
Many thanks, I had not seen this thread before and it will be used when I start to shark tune in a few weeks
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Old 01-09-2018, 03:12 AM
  #18  
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Originally Posted by Marti View Post
Hi

I was looking for feedback on increasing the size of the throttle body butterfly on the S4/GT/GTS inlet manifold for a S4 engine running the Colinís cams and MSMD headers with a X pipe and remaining exhaust system being standard. The car is also running shark tuner and uprated injectors.

As bolt on replacement performance manifolds are not quite there yet I am working on modifying the S4 manifold to clean up the airflow as best I can which I hope will help. I am trying to investigate options on fitting a larger butterfly. I believe the existing butterfly is 75mm and some people have increased this size, i would like to know what size is possible and where parts are sourced

I am working on the theory that with the increased airflow now being sought by the engine that this may be worth doing especially since I have the parts off the car at present.

Many thanks
I've made 2 of these for testing on a 6.5 liter.

No gains over stock, for me.
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Old 01-09-2018, 03:16 AM
  #19  
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Originally Posted by SeanR View Post
Oh heck with all that. I just want one so I can say "Hey, I've got a large throttle body"
Just put in some plenum spacers....even better, since people can see them.
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Old 01-09-2018, 07:14 AM
  #20  
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Originally Posted by GregBBRD View Post
I've made 2 of these for testing on a 6.5 liter.

No gains over stock, for me.
That is disappointing not to see any increase although there are clearly gains to be made with a completely new manifold.

Hmm, that would suggest the changes you made didnít improve the area which is causing a drop in HP.

Some on here have shown increases in HP with changes to the standard manifold, what modifications did you make and what are your thoughts on why that didnít show any gains?
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Old 01-09-2018, 09:17 AM
  #21  
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Boring out the housing and installing an oversize 80mm throttle blade increase the air flow by only 4,2% which hardly will make a noticeable gain in power. Adding a proper porting job to the housing, the air flow increase is measured to 16,5% which is the best that can be achieved and should bring with it a good power gain.
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Old 01-09-2018, 09:54 AM
  #22  
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Originally Posted by GregBBRD View Post
Just put in some plenum spacers....even better, since people can see them.
Did that years ago and love the look. Bling Bling.
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Old 01-09-2018, 10:06 AM
  #23  
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Originally Posted by Strosek Ultra View Post
Boring out the housing and installing an oversize 80mm throttle blade increase the air flow by only 4,2% which hardly will make a noticeable gain in power. Adding a proper porting job to the housing, the air flow increase is measured to 16,5% which is the best that can be achieved and should bring with it a good power gain.
Ňke
16% more throttle body CFM will only give you a few ponies for a stock engine, but as hp and air flow demand go up, the power gains become larger.

One area where there may be some additional gains is that the ported and bored S4 throttle body may allow one to run the intake manifold in the flappy closed mode at high loads and high rpms. I speculate that Porsche designed the intake manifold to be run with flappy closed at the high rpm region to utilize the second Helmholtz resonator peak. In practice, it appears that one of the sides in the throttle body doesnít flow well enough to run properly with flappy closed at high rpms. Consequently, the stock engine runs as well or better with the flappy open at high rpms, simply because one of the up chimneys needs to support the other plenum thru the resonance pipe. This despite the flappy closed mode bring slightly better from resonance tuning point of view based on a simple model. This is all speculation at this point.

The frustrating part about the S4 throttle body is that so many time consuming operations are needed in the current process to get to that 16% CFM gain. Especially the welding and remachining. Time to do some head scratching to see if the process can be simplified.

The main intake manifold casting will likely look the same from notification perspective. Iím staring at it, and itís going to be hard to modify that effectively with in a cost effective (efficient) way.

A final note: my goals with this manifold are a little different from many othersí goals. Iím trying to improve the flow like everyone else, but Iím also looking for ways to shift the (first) flappy closed torque peak rpm as needed, currently the greatest need being shifting it down. I want that high VE and torque at the point where turbos are about to spool.
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Old 01-09-2018, 02:04 PM
  #24  
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Originally Posted by Marti View Post
As bolt on replacement performance manifolds are not quite there yet I am working on modifying the S4 manifold to clean up the airflow as best I can which I hope will help.
Alright, since you're set on modifying the existing manifold, I have an idea for you, and it's slightly counter intuitive.

The biggest problem with the stock intake is its inability to equally fill the cylinders. Because of this, the tune must be compromised to accomdate the manifold's best-flowing cylinders, 2 and 6. As we know, for the most part, 2 and 6 will be 'perfect' as far as air/fuel goes while the remaining cylinders will be too rich to varying degrees with 5 and 8 the richest. Also, timing will be set to accommodate 2 and 6.

Since it is impossible to make 5 and 8 flow as well as 2 and 6, how can we help equalize flow to all cylinders?

What we can do then, is to decrease the flow thru 2 and 6, thus bringing them closer to 5 and 8.

But how can we do that without worrying about the new restrictor breaking-off and being ingested into the engine?

How about simply cutting the trumpet-ends off of runners 2 and 6?

The flow difference between a straight-ended pipe versus a pipe with a trumpet is quite dramatic depending upon which paper you read.

So lets go conservative and say there will be a 5 to 7 percent difference, thus, 2 and 6 will now flow 5 to 7 percent less air because their trumpets are now missing.

This will bring 2 and 6's flow much closer to 5 and 8. What one can do next is retune, and the new tune can be more aggressive and safer, now that overall cylinder filling is more equalized amongst them.

Of course I haven't performed the surgery nor dyno'd the result since I thought that up while programming today. However, theoretically, it does make sense.

The best part about the idea, it's a relatively easy fix/compromise to help get around the short-comings of the stock 32v intake.
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Old 01-09-2018, 03:19 PM
  #25  
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Originally Posted by SwayBar View Post
Alright, since you're set on modifying the existing manifold, I have an idea for you, and it's slightly counter intuitive.

The biggest problem with the stock intake is its inability to equally fill the cylinders. Because of this, the tune must be compromised to accomdate the manifold's best-flowing cylinders, 2 and 6. As we know, for the most part, 2 and 6 will be 'perfect' as far as air/fuel goes while the remaining cylinders will be too rich to varying degrees with 5 and 8 the richest. Also, timing will be set to accommodate 2 and 6.

Since it is impossible to make 5 and 8 flow as well as 2 and 6, how can we help equalize flow to all cylinders?

What we can do then, is to decrease the flow thru 2 and 6, thus bringing them closer to 5 and 8.

But how can we do that without worrying about the new restrictor breaking-off and being ingested into the engine?

How about simply cutting the trumpet-ends off of runners 2 and 6?

The flow difference between a straight-ended pipe versus a pipe with a trumpet is quite dramatic depending upon which paper you read.

So lets go conservative and say there will be a 5 to 7 percent difference, thus, 2 and 6 will now flow 5 to 7 percent less air because their trumpets are now missing.

This will bring 2 and 6's flow much closer to 5 and 8. What one can do next is retune, and the new tune can be more aggressive and safer, now that overall cylinder filling is more equalized amongst them.

Of course I haven't performed the surgery nor dyno'd the result since I thought that up while programming today. However, theoretically, it does make sense.

The best part about the idea, it's a relatively easy fix/compromise to help get around the short-comings of the stock 32v intake.
What evidence do you have that, say, cylinder 6 fills better than say cylinder 3 at 6000rpm? My data says that, with stock exhaust manifolds, cylinder 6 actually fills relatively poorly at and above 6000rpm compared to other long-runner cylinders. Cylinder 6 does knock relatively easily at high rpms with exhaust manifolds, but that's not because of the better filling. Both poor filling of cylinder 6 and its high likelihood of knock are both caused by the cylinder 5 blowing into the exhaust manifold right after cylinder 6 and causing a pressure spike at high rpms in the exhaust port of cylinder 6 during cylinder 6's overlap. That prevents the cylinder six from filling well with fresh charge and contaminates the charge with hot exhaust gas. In my opinion, how each cylinder runs at each rpm changes pretty dramatically if you switch from stock exhaust manifolds to headers.

Since the original poster is planning to run headers, I would recommend the following. Up the compression as much as the cams and available fuel allow. 11:1 at least? Get the experimental JDS Sharktuner code version that allows for cylinder-specific ignition trim if there's any indication that the long-intake-runner cylinders knock easier at mid range rpms, and selectively back off timing from those cylinders. When porting the intake, don't intentionally make any runner to flow worse than it could, just get the most flow out of each cylinder without increasing the cross-sectional area any more than necessary. What this means in practice is improving the bell mouths and somehow smoothing over the head-to-intake transition without expanding the cross-sectional area. Finally, don't worry too much about fueling, as all indications are that the power that 928 S4 makes isn't very sensitive to small variation in fueling in the neighborhood of low-thirteens AFR. That's what I'd do, anyway. Goes without saying, this is just my opinion.
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Old 01-09-2018, 03:42 PM
  #26  
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Originally Posted by ptuomov View Post
What evidence do you have that, say, cylinder 6 fills better than say cylinder 3 at 6000rpm? My data says that, with stock exhaust manifolds, cylinder 6 actually fills relatively poorly at and above 6000rpm compared to other long-runner cylinders. Cylinder 6 does knock relatively easily at high rpms with exhaust manifolds, but that's not because of the better filling. Both poor filling of cylinder 6 and its high likelihood of knock are both caused by the cylinder 5 blowing into the exhaust manifold right after cylinder 6 and causing a pressure spike at high rpms in the exhaust port of cylinder 6 during cylinder 6's overlap. That prevents the cylinder six from filling well with fresh charge and contaminates the charge with hot exhaust gas. In my opinion, how each cylinder runs at each rpm changes pretty dramatically if you switch from stock exhaust manifolds to headers.

Since the original poster is planning to run headers, I would recommend the following. Up the compression as much as the cams and available fuel allow. 11:1 at least? Get the experimental JDS Sharktuner code version that allows for cylinder-specific ignition trim if there's any indication that the long-intake-runner cylinders knock easier at mid range rpms, and selectively back off timing from those cylinders. When porting the intake, don't intentionally make any runner to flow worse than it could, just get the most flow out of each cylinder without increasing the cross-sectional area any more than necessary. What this means in practice is improving the bell mouths and somehow smoothing over the head-to-intake transition without expanding the cross-sectional area. Finally, don't worry too much about fueling, as all indications are that the power that 928 S4 makes isn't very sensitive to small variation in fueling in the neighborhood of low-thirteens AFR. That's what I'd do, anyway. Goes without saying, this is just my opinion.
That sounds a reasonable approach to me except I donít plan to raise the compression as that will require piston change. What you mention does remind me to pay close attention to the match between the head and headers to ensure this is optimised to reduce any pulse from flowing backwards into the cylinder. Do you have any templates showing the match between the two?
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Old 01-09-2018, 03:46 PM
  #27  
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Originally Posted by Marti View Post
That sounds a reasonable approach to me except I donít plan to raise the compression as that will require piston change. What you mention does remind me to pay close attention to the match between the head and headers to ensure this is optimised to reduce any pulse from flowing backwards into the cylinder. Do you have any templates showing the match between the two?
You can and should resurface the heads and continue to use the thinner head gasket. That'll up the compression a bit.

Any normal long-tube 4-1 headers will achieve the pulse separation you need.
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Old 01-09-2018, 04:06 PM
  #28  
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Originally Posted by ptuomov View Post
Cylinder 6 does knock relatively easily at high rpms with exhaust manifolds, but that's not because of the better filling. Both poor filling of cylinder 6 and its high likelihood of knock are both caused by the cylinder 5 blowing into the exhaust manifold right after cylinder 6 and causing a pressure spike at high rpms in the exhaust port of cylinder 6 during cylinder 6's overlap. That prevents the cylinder six from filling well with fresh charge and contaminates the charge with hot exhaust gas. In my opinion, how each cylinder runs at each rpm changes pretty dramatically if you switch from stock exhaust manifolds to headers.

....indications are that the power that 928 S4 makes isn't very sensitive to small variation in fueling in the neighborhood of low-thirteens AFR.
Some interesting comments there. I found that 6 and 2 control the amount of advance that can be applied at higher rpms. I also assumed that those cylinders were flowing more air thus running leaner so your comment is interesting. What I did find through experimentation with the patch that Ken wrote for me was that 6 and 2 need to be pulled by about 3 degrees to get similar knock characteristics in the higher rpm range but then the patch was an across the board type of thing, not cell specific. This led me to wonder whether one can increase the timing across the board and rely on the knock sensors to pull timing on the "noisy cylinders" as needed. This also told me that the motor needs 98 RON and that 95 RON is a bit limiting. That I had to pull a bit of timing compared to stock was a bit disappointing thus but then I later learned that having a faster exhaust compared to stock also suggests less advance needed.

I also found that AFR did not impact advance in the value range 12 to 13.5. I was also advise dthat the 928 inlet manifold is quite efficient and that best power is typically made in the low 13's.

Hopefully Marti will advise what he finds when Sharktuning.
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Old 01-10-2018, 06:43 AM
  #29  
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Originally Posted by ptuomov View Post
You can and should resurface the heads and continue to use the thinner head gasket. That'll up the compression a bit.

Any normal long-tube 4-1 headers will achieve the pulse separation you need.
On the exhaust side I was more thinking about the join between the head and headers. From experience it helps if the header size is larger than the port size in the head as this presents a barrier to exhaust gas flowing backwards and hence helps generate vacuum to put the inlet mixture through.

I will try and take a template of the mounting surfaces for the head and headers in orders to show a comparison.

I also get your point on the pulse separation which I am taking for granted with the longer runners on the headers. I believe the difference in port size to be a key point.

I would like to pump up the compression which I wish could be done by skimming the head, any idea how much material can be removed and what difference it would make?

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Old 01-10-2018, 08:54 AM
  #30  
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Originally Posted by Marti View Post


On the exhaust side I was more thinking about the join between the head and headers. From experience it helps if the header size is larger than the port size in the head as this presents a barrier to exhaust gas flowing backwards and hence helps generate vacuum to put the inlet mixture through.

I will try and take a template of the mounting surfaces for the head and headers in orders to show a comparison.

I also get your point on the pulse separation which I am taking for granted with the longer runners on the headers. I believe the difference in port size to be a key point.

I would like to pump up the compression which I wish could be done by skimming the head, any idea how much material can be removed and what difference it would make?
In my opinion, for what you’re building and the long exhaust duration that you’ll have, it’s more important to have small enough primaries off the head than creating a step. What exhaust can duration will you run again? If it’s what I think it is, you don’t want to go larger than the port for the first part of the primaries. Just an opinion.

Greg and Ňke can more intelligently comment on how much can be shaved off the heads. I’m on the turbo track so I don’t know much about that. The amount coming off my heads is the absolute bare minimum to clean them up.


Last edited by ptuomov; 01-10-2018 at 12:29 PM.
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