Cylinder head swirl and flow data.

MarkoP

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I think you're using Bernoulli's equation for that. Bernoulli only applies for incompressible flows; beyond Ma≈0.3 the flow can no longer be considered incompressible, so you must use the long equation I gave a few posts up for isentropic flows. When you go past Ma>1 and have a normal shockwave, both equations don't work (because the flow is not isentropic across the shockwave, but I digress... :p )
My calculation was theoretical with incompressible flow.. but 102m/s starts to be so close to speed limits of intake port that I do not care =)
Well.. not speed limit, but it ain't going to make much power above that.
Past 1Mach flow goes supersonic and I am not interested about downstream pressure =)

Yes you can. It is explained by other factors. You can have less smoke with more airflow but less swirl because you're simply running an effectively higher lambda. There's nothing really wrong with doing that, but there may be circumstances that you want to target lambda/smoke because it's a sign of how efficient the combustion is with the available air (air utilisation rate).

Most people here won't care about that, but say you're racing in an air-restricted rule regime, so you want to get the most performance (most fuel burn) out of a given amount of air you can get into the engine. Or, you want to reduce trapped air mass in the interest of targeting PCP if you're already at the bleeding edge.....
Sorry, I meant with same fueling.. or actually depending which direction MAF/MAP numbers go, usually MAP is not so sensitive.

I do! :) And if you find a way to have a great flowing head whilst keeping a healthy amount of the useful form of swirl, then you've hit upon a holy grail of Diesel performance tuning and I want to be in on it. :D

The numbers do show that what you describe is perfectly true, but the normalised numbers (because it's a ratio of the swirl-velocity divided by the axial velocity component of the total mass flow) also will not drastically change, which is my original point.
Your right.. when calculating percentual increase, flow did increase only ~1% more than swirl, obviously swirl does not happen without speed or mass.
But still both increased ~4%.. BOTH =)
 

TDIMeister

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Your right.. when calculating percentual increase, flow did increase only ~1% more than swirl, obviously swirl does not happen without speed or mass.
But still both increased ~4%.. BOTH =)
Right, meaning the ratio of both numbers is ~1, so the swirl number as previous defined and plotted on the graph a few posts back, did not change. :)
 
Last edited:

chapelhill

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No, really, do you think that by incresing flow @ 2000-2500rpm by reducing swirl could yield to reduced smoke?
My believing is that added air helps from the point when engine starts to starve on air.
Increased low lift flow typically reduces power under to at least torque peak of N/A engine.. on forced engines torque peak is more or less "artificial" depending how turbo is sized.
From my understanding the swirl is most important at high rpm as at 4000rpm there is 1/2 the combustion time of 2000rpm so i would expect flow increase would have more impact than swirl/tumble reduction at 2000rpm, but that is not to say you did have a swirl/tumble reduction.

I think the rpm factor adds one too many additional dimensions.

Yes you can. It is explained by other factors. You can have less smoke with more airflow but less swirl because you're simply running an effectively higher lambda. There's nothing really wrong with doing that, but there may be circumstances that you want to target lambda/smoke because it's a sign of how efficient the combustion is with the available air (air utilisation rate).
Most people here won't care about that, but say you're racing in an air-restricted rule regime, so you want to get the most performance (most fuel burn) out of a given amount of air you can get into the engine. Or, you want to reduce trapped air mass in the interest of targeting PCP if you're already at the bleeding edge.....
Are not most of us working with a restricted boost (Our turbo limit), so where is the best compromise? The VW engineers were probably trying to optimise the Tumble/swirl for the stock boost limits.

When doing my head i plan to try to concentrate on improving the swirl as a priority over flow. If i was to measure I would be looking for the %increase in flow to be double the reduction in swirl, which would have to be averaged over the injection cycle by then giving a higher weighting to the higher lift values.

On the picture kindly posted by TDmeister on his post here:
http://forums.tdiclub.com/showpost.php?p=3276972&postcount=27
What do people think about the flow pattern depicted? I don't think it is rmissleading, the flow shown down the port around the valve I feel contributes to the Tumble, and the circumferential component comes more from the port bias which is not shown. The swirl dam does look like it will help to bias even more of the flow closer to the cylinder wall increasing the swirl momentum.

I will try and read some of the good links that have been posted this weekend and have a play with the scrap head again!
 

TDIMeister

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The streamlines are only for illustration purposes. I'll try to find a better image to visualise the flow.
 

MarkoP

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From my understanding the swirl is most important at high rpm as at 4000rpm there is 1/2 the combustion time of 2000rpm so i would expect flow increase would have more impact than swirl/tumble reduction at 2000rpm, but that is not to say you did have a swirl/tumble reduction.

I think the rpm factor adds one too many additional dimensions.

Are not most of us working with a restricted boost (Our turbo limit), so where is the best compromise? The VW engineers were probably trying to optimise the Tumble/swirl for the stock boost limits.

When doing my head i plan to try to concentrate on improving the swirl as a priority over flow. If i was to measure I would be looking for the %increase in flow to be double the reduction in swirl, which would have to be averaged over the injection cycle by then giving a higher weighting to the higher lift values.
Many "16v" heads utilize butterfly flap in filling channel that is opened at higher RPMS.
I am certain that only purpose of those is not that eventually they will drop and engine will lunch them :D

At lower engine speeds swirl is naturally less because of flow speed and it increases with larger Delta-P.
Roughly said at 4000rpm swirl has double the speed as what it does have at 2000rpm.

If cylinder head has flow potential to even reverse flow at end of induction cycle at low RPM I can not see how added CFM would help.

I bet stock swirl is made for stock RPM, stock flow (air mass) and stock injector penetration.
How do you believe more boost is affecting swirl generation?

Increasing swirl by flow expense is not mandatory.
But obviously that could be done, then you need to adjust more boost to compensate loss in mass flow if there was not excessive air amount to start with.
Like if you need to have 2.2bar of boost to be smoke free, then you keep swirl approximately same, but increase flow by 10%, you should get away with 1.9bar or even less depending of compressors island flow.
Personally I port as well most.. well every head whether its Gasser or Diesel or anything so that most flow increase is from mid to high lifts.
That could be easily changed vice versa, but I would rather try to kill low lift flow to get even more to higher lifts.
 

MarkoP

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Right, meaning the ratio of both numbers is ~1, so the swirl number as previous defined and plotted on the graph a few posts back, did not change. :)
Ratio remained same, but both increased.
Alex got more flow and more swirl at that lift point =)

In theory swirl increases with flow, but swirl port can also do unexpected things to flow..
Swirl can not be considered as separate subject to flow or actually flow speed and air dynamics through that area.
At least I had problems making port flow and sound good without removing the swirl.. but I might not be as smart as some =)
 

Alex22

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Sorry Alex22 - Didn't mean to hijack your thread here. A before/after test with/without the swirl meter and comparing CFM's is a good idea to see how much of an effect the swirl meter has on the flow rate.

Keep up the good work!

This seemed like a good way to end the night of porting. Here is the comparison of the latest test with and without the meter in place. The biggest difference in flow only works out to a 1.4% difference, When I am happy with a final port design I will remove the meter again to test just the volume flow.




I was able to get the flow up to 139CFM on a stock valve at one point by adding clay to build up the port in certain areas, but the port lost a significant amount of swirl (~2500RPM). With just the right amount of clay I was able to make acceptable improvement in flow without much of an effect on the swirl. If things keep going the way they are going now the intake port is going to be a real work of art...

Here's where I left off tonight. There are still areas in the port that I haven't even modified yet.


The shape of the valve head has a huge effect on the swirl but not as much of an effect on the flow. I have seen over a 1000RPM change from modifying an extra intake valve and testing with no changes made to the port. Some shapes help the low swirl numbers while others help the higher numbers, which now means that I have to flow the same intake port with multiple valves before I can go back to the porting bench.

I haven't even started on valve seat profiles and seating angles. The shop has a Sunnen VGS-20 and a rack of at least 40 different seat profiles and I have the option of having a custom profile made if I don't like the existing cutters.

~Alex
 

MarkoP

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I bet swirl is really sensitive to port angle / approach to swirl.
Did you notice any flow instability issues when raising floor?

Is it so that back cuts increase low lift swirl?

Your flow numbers look really close to what I have measured from stock and ported.
With stock valves I have seen typically around 15+cfm increase at high lifts after seats are machined, without filling the ports.
Depending of swirl configuration there might or might not be much increase at mid lifts, but it can anyhow yield to more than 300hp on dyno which is a hard stretch with a stock head.
 

Alex22

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I bet swirl is really sensitive to port angle / approach to swirl.
Did you notice any flow instability issues when raising floor?
Is it so that back cuts increase low lift swirl?
Your flow numbers look really close to what I have measured from stock and ported.
With stock valves I have seen typically around 15+cfm increase at high lifts after seats are machined, without filling the ports.
Depending of swirl configuration there might or might not be much increase at mid lifts, but it can anyhow yield to more than 300hp on dyno which is a hard stretch with a stock head.
From the testing that I have done with the swirl meter in place the shape of the head of the valve is not as cut and dry as you may think. This port and valve configuration has to be looked at as one system, not broken down into components. I now find myself having to test multiple valves without touching the port before I can decide if what I did to reshape the port was beneficial or not.
You should really attach your swirl meter and do some testing, it only takes a few bolts and a wire then BAM, swirl readings.:cool:
-Alex
 

MarkoP

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I have most of stuff ready for swirl meter.
DC meter is already mounted to flowbench, but it would require something where to mount small DC motor and blades to DC motor.. so not much to do really.

I tend to define how I'd wish to see whole system, RPM, HP, usage, etc. Then I break it in to a components and try to make different parts to work together.. like shortside to match required lift, minimum CSA to support required RPM, combustion chamber to support lift range, guide clearance for high EGT, camshaft duration for specified RPM, etc.
..Which at the end makes one running system =)

Some shortside shapes or some seat shapes do not like at all back cuts.
Usually I shape short side and use seat profiles that allow use of back cut as that brings maximum flow to a lower lifts and I can use a tad smaller cams on street.
Down side is increased low lift flow, but I have handled that with other methods. =)
 

Fix_Until_Broke

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This seemed like a good way to end the night of porting. Here is the comparison of the latest test with and without the meter in place. The biggest difference in flow only works out to a 1.4% difference, When I am happy with a final port design I will remove the meter again to test just the volume flow.
Cool - good to see that the swirl meter does not effect the flow readings.

You've got some nice resources at your disposal - I'm envious :)

I'm definately curious as to what you find with the valve shape and it's effects on flow and swirl. You're definately right that the system must be considered, not just individual components.

Something I've always wondered is how much will the port flow and swirl with the valve removed completely? I think it would help determine how much of a restriction the valve/seat itself is compared to the port. Similar to changing valves and seeing different results as you've seen. If the port only flows (making up a number here) 150 cfm without a valve and ~125 cfm with a valve, then the port is likely a more significant limitaton than the valve. If the port flows 500 cfm, then there's probably a lot of potential gains to be had with the valve/seat interface and less with the port itself.
 

Alex22

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No free lunch.
If you spend most of your Friday and Saturday shoveling snow off of the roof then not only do you get time and a half but you also get "free" pizza.;)

A few days of clearing snow and roof repairs ended with me being either too wet or too tired to want to stay late and play with the TDI head on the bench, but I'm back at it now. Here are the results from the best test that I did today, there is no clay or weld in this port.

I was finally able to get rid of that instability that caused the drop in both the flow and the swirl, I was so excited that I stayed even later to do some more work. The next few tests after this one took small losses at just about all valve lifts, the only way to know just how much the port likes something you need to go until there is a loss while taking good notes. I'm just about ready to move onto a fresh port and apply all that I have learned from this one. It turns out it is possible to improve flow and swirl at most lift points if you are willing to put hours upon hours of testing with an open mind ignoring the conventional porting ideas. A modified or custom intake manifold may could be used to help induce the swirl

Ratio remained same, but both increased.
Alex got more flow and more swirl at that lift point =)

In theory swirl increases with flow, but swirl port can also do unexpected things to flow..
Swirl can not be considered as separate subject to flow or actually flow speed and air dynamics through that area.
Now MarkoP, don't get too excited about being right about you're earlier comment, The port has been reshaped in almost every area and the valve has had work done to it. I still say that TDIMiester's comment about there being no free lunches in the porting world are true for a lightly ported port, one WILL be traded for the other.
The swirl Should increase with the flow, but if the port volume increases more than the flow then its velocity will be slower giving the air less kinetic energy resulting in less swirl. There are two separate flow paths in the intake port to keep in mind while porting. They both have to be enhanced without disturbing the other.

Something I've always wondered is how much will the port flow and swirl with the valve removed completely? I think it would help determine how much of a restriction the valve/seat itself is compared to the port. Similar to changing valves and seeing different results as you've seen. If the port only flows (making up a number here) 150 cfm without a valve and ~125 cfm with a valve, then the port is likely a more significant limitaton than the valve. If the port flows 500 cfm, then there's probably a lot of potential gains to be had with the valve/seat interface and less with the port itself.
What you are referring to is commonly called the "port potential." Here are the results from a test I did yesterday. You can see that the valve is in the way of the volume flow but it helps to create the swirl at higher lift points. This port potential can only be compared to this test since the potential changes every time the port is modified. There weren't any major changes to the port between this test and test 21 VJ-2B (above these results in this post) I am getting close to the port's potential. I haven't ever heard of a port that flows better with a valve in the way so its a good way to see just how good the valve and seat profile are.



Good job sir! I wish I had more time to play around on a flow bench :(. On the SF600 I played around with a while back, I was able to pick up a 22-24% gain on both ports after porting. They sure are a fun toy!

While I did not measure swirl, even when you remove as much of the swirl dam as you can, it's still very much a swirl port. I may not be an expert on the topic at hand from an engineering side, but from my experience a "race" ported head on a street tdi has no ill side effects from removing as much as possible of the swirl dams.

To test this on somewhat of a "control" vehicle (compared to the frakensteins I usually build), I offered to race port a head with a Colt S2 cam for my friends 99.5 with a vnt15, 10mm and pp764s. Just got it running last week and so far its runs very strong, gets great mpg, and no weird smoke or throttle response issues at low rpm.
Matt, did you get a chance to use you're 81mm bore adapter for flow testing?


I realized that since I knew the velocity parallel with the cylinder wall and the circumferential velocity then I could calculate the helical velocity and helix angle. On one of the days I went home at a normal hour wet and cold I made a spread sheet to calculate the velocities and angles. Not sure if the information is useful or not so here it is. 0* is even with the deck and 90* is pointing at the piston.
 

Alex22

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The results I've been getting from the latest tests are continuing the trend of loosing low lift (below .150") and increasing the swirl at higher valve lifts. Does anybody have any data to say which valve lifts would benefit from the increased swirl more, or loose less from the lack of swirl at certain lifts?

I made these 37mm intake's up today for flowbench testing, should have results in the next few days.



~Alex
 

chapelhill

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I don't have any data, but as far as I understand we are trying to achieve the maximum net rotational velocities and tumble in the piston bowl afetr it has all been compressed so that the injected diesel can react with the oxygen. So we need velocities for the air to be able to move through a minumum of an injector spray seperation angle (5/360 roughly 70 degrees) during the injection/combustion event. At 4000 rpm we would be looking at approximately 25 meters per second or more.

As most the inlet charge ends up compressed into the piston bowl I think what is important is to maximise the net angular momentum (which will still be retained in the piston bowl) and as piston speed/displacement loosly follows valve lift the higher lift will be responsible for most of the net volume/mass transfer and hence I would put my vote of swirl being more important with higher lift than lower lift.

It would be interesting to see a graph of mass air charge in cylinder versus crank angle and cam lift for something similar to our diesels.
 

Alex22

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Do you work on edge of valve port?
This is the place where his most important gain for low lift.
Dieseleux
Are you referring to the narrowing angles under the seat (angles steeper than 45*) leading into the port? If that is the area that you are referring to then yes, I've spent the last few nights working on that area.... Results ranging from big gains to big losses depending on the changes I made.
~Alex
 

Alex22

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I have never seen or even heard of a port who's port potential (flowing the runner with the guide plugged off and no intake valve) will flow less than the head when the valve is installed. After cutting the seat to take a 37mm I lost flow in some areas and didn't improve the upper lift numbers by much. After trying a few different valve seat cutters and combinations of bowl/seat throat cutters I was barley able to get an improvement of 3 CFM at usable lift increments. For the final test of the night I checked the port potential and was very surprised to see that the flow with no valve in was 3.2 CFM lower than the best flow with the valve. The only explanation that I can think of at the moment for that is due to the swirl shape of the port the intake valve is needed to stabilize the flow of air into the bore.

Results:

This is the best that I was able to get while using an OEM 36mm valve, I think I can get more out of the port after I start over on a fresh port.


I installed a 37mm intake and the only change made to the port were the valve seat profiles and depths. The port needs to be enlarged quite a bit in order to take full advantage of a larger valve. Unless I am able to increase the flow without porting through to the water jacket in the critical areas larger intake valves may be unnecessary from a cost to gain standpoint. I don't have enough information at the moment to make the final call on valve size. The port has only been opened up a total of 5.8cc's which is not much in the porting world. The valve does not have a reduced stem but when I continue testing with this larger valve I do plan on reducing the stem diameter, from what I can see so far it should help once the port is opened up.



Here are the results for the OEM valve vs the 37mm valve, this will give a better idea of why I said that larger intake valves might not be necessary. Again, there was no work done in the port after the larger seat was installed, only seat cutters and the valve depth in the head were changed between tests. Once the port is enlarged in the right areas flow should increase.


At least I can say that after 40+ hours of work into this port I've picked out the seat cutter I want to use on the intakes and how I want to reshape the OEM intake valve. I keep forgetting to bring in my stock AHL intake and my brother's modified D24 intake manifold to see what effect they have on flow and swirl.

~Alex
 

Alex22

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More testing results...

This port went awfully turbulent after ~.300 lift, but it had some good flow numbers. I could watch the manometer go up as the swirl meter went down and then it would swing the other way. The computer takes 10 readings and then averages them to get the flow reading. I average the swirl meter readings as well.



I spent a few more hours working on this port today and overall the bigger valves are just making a complex port even more difficult to work on. Only spending 30 seconds with the die grinder is able to add 20 CFM on the top end flow when done in the correct spot. Duplicating this will be a challenge and I may just let the CNC machine take care of the porting.


~Alex
 

ryanp

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some really nice work here! drop me a line if you want any PD heads for porting practice.

Ryan
 

Alex22

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With another dozen or so tests I have only been able to break 150 CFM using a 37mm intake valve without the flow going horribly turbulent at just about all lift points. I did not get a new volume number for the intake port but I can say that it is significantly larger than before without a large gain in flow. I will have to get a new volume measurement in order to compare the percent increase in flow to the percent increase in port volume.

I do have a stock ALH and a cut down long runner D24 intake that I'm going to be testing on this head before I move to a new port.

One thing that is worth mentioning is that I acid ported an intake manifold for my friend's turbo 5 cylinder gasoline Volvo engine and he said that the boost levels were more consistent when he got into high RPMs. Many who port heads for forced induction engines believe a large port volume is better for building a reservoir behind the valve for better high RPM performance. Since "high RPMs" for a TDI is well within the normal driving range for a gasoline engine a smaller, higher velocity and higher swirl port may perform better than a larger port with slightly higer flow numbers but lower flow and swirl numbers.

~Alex
 

Alex22

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This little guy showed up the other day.


It's an ultrasonic transducer with the correct frequency for testing aluminum. Hooray for non destructive testing.:cool:

~Alex
 

TDIMeister

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Very nice work, 30% improvement on the 8V VE head is a big accomplishment! I'd love to see one of your worked heads paired with one of Shorty's 11m lift race cams and flogged on the dyno.
 

TDIMeister

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By the way, compare your stock head cfm numbers with that of Whitbread's. Your numbers seem to be 10-13% higher between .200-.400" than his for stock heads. :confused: I have yet another measurement set that I'll send to you via e-mail.
 

Alex22

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That's a fun little tool! Don't be surprised when you find very thin walls on the intake ports, there isn't much meat in some areas. http://forums.tdiclub.com/showthread.php?t=266569
I used those pictures for references when I started porting, thanks for posting them. After a few weeks of testing the same port it can get hard to keep track of just how much has been removed which makes the ultrasonic tester great.

By the way, compare your stock head cfm numbers with that of Whitbread's. Your numbers seem to be 10-13% higher between .200-.400" than his for stock heads. :confused: I have yet another measurement set that I'll send to you via e-mail.

There are a few big differences in the methods and setups for the flow testing done by Matt that you referenced. Matt used a 4 inch bore (not sure what he used to block the water jackets though) and no clay radius leading into the intake port. I used a 80mm bore and a large clay radius for my testing, the different testing parameters void the comparisons.
I started over on a new port today and used the opportunity to run a test that was similar to Matt's. I left off the swirl data because we are only comparing flow at the moment.



One explanation for the differences in flow at mid lift can be that Matt was reading the manometer himself and recording the data and the bench that I am using has a FlowCom and Port Flow Analyzer hooked up. The flowcom works with the computer software to take 10 readings in a row and then average them with the push of a button. The airflow at mid lifts is turbulent in the stock port and I can watch the manometer rise and fall as the sound and swirl change. Matt' do you remember if you recorded the high or low readings or did you take an average?

~Alex
 

Alex22

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I flowed my stock port again today using lift increments of 2mm to compare to MarkoP's stock flow numbers with and 82mm bore but did not say if he used a clay radius. IIRC Marko is also using a SF600 flow bench.


I spend the rest of the night trying out different intake seat cutters and reshaping the top of the valve and was able to pick up up to 10CFM without the swirl taking a big loss, It's just too late to post up entire flow sheets. I should have time over the weekend.

I have also decided against using the clay radius for the remainder of the flow testing in favor of a leftover chunk of a D24 intake manifold. Moving air has momentum and the standard way of flow testing a cylinder head using a large radius works great for a conventional engine when the intake port opening faces the plenum (V8 and V6 engines.) In our case the plenum is directly above the head and the moving air's momentum doesn't want to make the corner. The closer I can make the testing conditions to what the head will see on an running engine the more validity the results will have, with the ultimate validity numbers being on the dyno with EGT, boost and MAF readings.

~Alex
 

Alex22

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I eventually poked a hole into water on the previous test port with the larger valve installed so I started over on a new port and here's where I am at the moment, still a work in progress though. For these tests I also have an injector and a glow plug installed instead of blocking the holes off with clay or tape from the outside of the head to make the tests as accurate as possible. The flow is off from some of my previous tests, but the flow is much more stable than before.







These showed the other day, Thanks to RyanP and Chapelhill. The DHL driver gave me a strange look when I told him that there was a head and a half in the package he was carrying.


I haven't had a chance to get either of these on the flowbench yet but I will update when I have some info. The exhaust port does feel better than the ones in the VE style head and flow improvements have been documented by a few on the forum.

It looks like I will be able to use my brother's MK4 Jetta to get some dyno numbers once I finish up a head.

~Alex
 

TDIMeister

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No TDI cams have more than 0.435" of lift, so it would seem more productive for overall performance to optimise the flow, velocity and swirl below this figure than to get a maximum headline cfm number and percent gains with lift be damned. JMO.
 

Alex22

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TDI
2014 Jetta
No TDI cams have more than 0.435" of lift, so it would seem more productive for overall performance to optimise the flow, velocity and swirl below this figure than to get a maximum headline cfm number and percent gains with lift be damned. JMO.

I agree with you're first statement but the flow at valve lift higher than where the cam will ever lift to is necessary check the port's stability. In a running engine the pressure differences can be much greater than 28" of water which means more flow and higher velocities in the port. Opening the valve past the maximum cam lift will continue to increase the flow and therefore velocity until the valve cannot be opened any more. The reason that I cannot test at pressures over 28" of water is that the swirl will spin the swirl meter over its maximum rating.

~Alex
 
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