Porting a type 4 head, Not much of a short side Options

[Shivers]

Because the port is almost straight, with little long side short side concerns, with what there is , do you find it necessary to slow the flow down on the “short side” to get good flow out of the valve. I was reading about something mepstein posted a picture of. Small divots, like a golf ball. So I’m going to do that on the long side, just wondering if there is any reason not to also do it on the short side. Thanks guy’s (IMG:style_emoticons/default/smile.gif)

[Brett W]

The Intake port isn't the problem. You can easily over port the intake side and screw up the balance across the intake and exhaust ports. Bigger ain't better. Its all in the shape.

[Shivers]

The Intake port isn't the problem. You can easily over port the intake side and screw up the balance across the intake and exhaust ports. Bigger ain't better. Its all in the shape.

I have not even begun yet. Did some reading by an engineer regarding fluid dynamics and the use of divots. The guy was saying the divots are only necessary at the source. So thank you (IMG:style_emoticons/default/smile.gif) , I will clean up the intake and exhaust, divots go under the carb on the manifold. Last set I ported for myself were 1.7 heads, lots of meat for porting. Not much on the bone with these 2.0l heads. If my budget was bigger adding some weld in some spots would be nice. I did catch a look at something special that Bob Burton had and posted pic's. Can't remember who's work it was but this guy ported the intake port and the manifold in the only place that was possible. I have that picture somewhere.

[technicalninja]

Exh port is where the restriction lives IMO.

Doesn't look like there is a good fix for it...

Serious turn in a very short port.

A proper "fix" will end up looking like a 6-cylinder 911 port.

This would require new head castings.

"When you give a mouse a cookie"...

The little dimples actually HURT flow a little tiny bit. (unless they are on the backside of a curve).

https://www.youtube.com/watch?v=fcjaxC-e8oY&t=158s

What they do is to decrease/eliminate port wall wetting. This can be very important if fuel is in the intake charge.

So, carbs could work better with dimples. Port FI will not.

[brant]

You really need a flow bench to measure whether you’re helping or hurting the flow. It’s not just bigger. And years of verified flow bench experience would also help

Besides cleaning up castings. You should consider a qualified builder with a lot of experience and a flow bench


I think my race heads were thousands of dollars with the Colorado builder that does this and specializes on type 4 and 911 heads


My old race motor was a 2.0/4 and also were run on his flow bench for porting

[Shivers]

Exh port is where the restriction lives IMO.

Doesn't look like there is a good fix for it...

Serious turn in a very short port.

A proper "fix" will end up looking like a 6-cylinder 911 port.

This would require new head castings.

"When you give a mouse a cookie"...

The little dimples actually HURT flow a little tiny bit. (unless they are on the backside of a curve).

https://www.youtube.com/watch?v=fcjaxC-e8oY&t=158s

What they do is to decrease/eliminate port wall wetting. This can be very important if fuel is in the intake charge.

So, carbs could work better with dimples. Port FI will not.

@brant

Thanks guy's. This is the kind of bed side reading I've been doing. I tried to find another particularly dry but insightful study by a fluid dynamic's engineer. Couldn't find it. But he was the one that said it only needed dimples near the source. I'm looking for the best velocity without boost. I put a link to another study, where I got the quote. A flow bench would be best.

"The red line represents linear dependencies between heat transfer and pressure drop properties of
surface roughness achieved with different techniques. Figure 2 shows that VHTE (vortex heat transfer
enhancement) provide the best heat transfer with the least pressure drop then every other technique.
Simulating the flow over golf ball shows that dimples create vortexes on the surface, these vortexes are
increasing the momentum near the wall and serve to reattach the flow after the dimple[6]. Simulations
prove that flow over a dimpled flat surface achieve higher velocity due to the fact they are creating a
favorable pressure gradient [7]. This publication is focusing on using dimple technology in inlet
manifold for achieving higher volumetric efficiency"

https://iopscience.iop.org/article/10.1088/...68/1/012050/pdf

[914sgofast2]

just polish the exhust port and leave the intake port alone if you are running fuel injection.

[Shivers]

just polish the exhust port and leave the intake port alone if you are running fuel injection.

Thanks, carbs. That is the plan for the exhaust. I saw some cutaways of the 1.7l and the 2.0l, there is little to no room on the intake and none at all at the exhaust. The factory ported the heck out of the 2.0 head.

[HAM Inc]

Hey all. It's been a while since I jumped into a discussion. I'm glad to see that folks are still passionate about their 914's.

I'm not going to get out in the weeds on esoteric theory but want to address a common misconception about T4 heads. A couple of decades ago I think we had it pretty well tamped down, but like bell-bottom jeans it seems to come in vogue every twenty or so years.

The misconception is that the exhaust port on these heads is the weak point restricting performance. In terms of flow nothing could be further from the truth.
We have spent hundreds of hours flowing every T4 head VW produced and they all, from 1.7 to 2.0 914, have a 70-72% exhaust port. Meaning the exhaust port flows 70-72% of the intake port. This is an excellent target for a N.A. engine.

I found many years ago that when working with 1.7 and 1.8 heads that if I spent ten minutes improving the exhaust port I would have to spend 20 minutes on the intake ports to maintain that same flow %. The exhaust ports on the 2.0 914 are pretty well maxed out by the factory. We make our big gains on them with seat work and changing the throat/valve O.D. ratio.

The shortcoming of the exhaust ports isn't flow related but rather the fact that it makes a very hard turn directly under the combustion chamber in a location that's about as far from the spark plug as you get. This area is more likely to see detonation. Because of the sharp turn the cross-section thickness between the exhaust port and the chamber is relatively thin and is therefore weak and subject to distortion when heat spikes, especially when detonation is present. The heat and pressure will push the chamber downward into the exhaust port. Of course you can't see this with the naked eye, but the area of distortion carries the exhaust seat with it, leading to serious leakage and eventually a burned valve if it gets bad enough and if it gets really bad the head will pull away from the cylinder creating a head leak.

My advice for the O.P. is to leave the ports alone. I have a hunch that there are plenty of other areas of his 914 that need attention.

[Shivers]

Hey all. It's been a while since I jumped into a discussion. I'm glad to see that folks are still passionate about their 914's.

I'm not going to get out in the weeds on esoteric theory but want to address a common misconception about T4 heads. A couple of decades ago I think we had it pretty well tamped down, but like bell-bottom jeans it seems to come in vogue every twenty or so years.

The misconception is that the exhaust port on these heads is the weak point restricting performance. In terms of flow nothing could be further from the truth.
We have spent hundreds of hours flowing every T4 head VW produced and they all, from 1.7 to 2.0 914, have a 70-72% exhaust port. Meaning the exhaust port flows 70-72% of the intake port. This is an excellent target for a N.A. engine.

I found many years ago that when working with 1.7 and 1.8 heads that if I spent ten minutes improving the exhaust port I would have to spend 20 minutes on the intake ports to maintain that same flow %. The exhaust ports on the 2.0 914 are pretty well maxed out by the factory. We make our big gains on them with seat work and changing the throat/valve O.D. ratio.

The shortcoming of the exhaust ports isn't flow related but rather the fact that it makes a very hard turn directly under the combustion chamber in a location that's about as far from the spark plug as you get. This area is more likely to see detonation. Because of the sharp turn the cross-section thickness between the exhaust port and the chamber is relatively thin and is therefore weak and subject to distortion when heat spikes, especially when detonation is present. The heat and pressure will push the chamber downward into the exhaust port. Of course you can't see this with the naked eye, but the area of distortion carries the exhaust seat with it, leading to serious leakage and eventually a burned valve if it gets bad enough and if it gets really bad the head will pull away from the cylinder creating a head leak.

My advice for the O.P. is to leave the ports alone. I have a hunch that there are plenty of other areas of his 914 that need attention.

Thank you for your time. And yes plenty to do. Summer around here is hellish, so I was going to do a temp work area in the living room. I won't be welding for a few months so polish the exhaust ports and divots in the manifolds. (IMG:style_emoticons/default/biggrin.gif)

[Charles Freeborn]

The heads on my previous race car built by Allen Johnsen (AJRS).
In short, he'd build up the heads where the manifolds mounted with weld which allowed him to port much more aggressively. The valves were enormous (48/38 as I recall, and the intake manifolds were also built up with weld and ported.
The car was built for PCA GT5s spec so 2.0L max, but unlimited head work. Cam was a Webcam 86b if memory serves.

[Shivers]

The heads on my previous race car built by Allen Johnsen (AJRS).
In short, he'd build up the heads where the manifolds mounted with weld which allowed him to port much more aggressively. The valves were enormous (48/38 as I recall, and the intake manifolds were also built up with weld and ported.
The car was built for PCA GT5s spec so 2.0L max, but unlimited head work. Cam was a Webcam 86b if memory serves.

That is pretty cool, thanks for sharing. Bet that was a pain. Big valves, wow mine are 42.5 X 36.5. Feeling a little inadequate (IMG:style_emoticons/default/unsure.gif) . (IMG:style_emoticons/default/biggrin.gif)

[brant]

I used to run the same AJRS heads in the 1990's on a type 4

38x48, thin stemmed valves, Dual valve springs, and titanium retainers with holes drilled in them

[Shivers]

I used to run the same AJRS heads in the 1990's on a type 4

38x48, thin stemmed valves, Dual valve springs, and titanium retainers with holes drilled in them

That is pretty serious.

[Charles Freeborn]

I used to run the same AJRS heads in the 1990's on a type 4

38x48, thin stemmed valves, Dual valve springs, and titanium retainers with holes drilled in them

Allen is quite the wizard. The most impressive (to me) aspect is the weld build up to allow porting. He cut o-ring grooves in the mating surface of the intake manifolds...
I'm not sure of the valve stems I had, definitely not lightened retainers, but dual spring. Very well thought out and executed.

Very nice guy too. I spoke on the phone a couple of times. Got some parts, etc. Old school honest.

[Shivers]

I used to run the same AJRS heads in the 1990's on a type 4

38x48, thin stemmed valves, Dual valve springs, and titanium retainers with holes drilled in them

Allen is quite the wizard. The most impressive (to me) aspect is the weld build up to allow porting. He cut o-ring grooves in the mating surface of the intake manifolds...
I'm not sure of the valve stems I had, definitely not lightened retainers, but dual spring. Very well thought out and executed.

Very nice guy too. I spoke on the phone a couple of times. Got some parts, etc. Old school honest.

Thanks Charles. (IMG:style_emoticons/default/smile.gif) The RPM's must have been impressive. How did he get it to breath out as well as he got it to breath in? That exhaust port, especially the 2.0 heads have little that can be removed. Did he weld those up too or is it big valve, massaging the port right after the valve and polish...Kind of hope for the best? Some of the work these Guy's do is real magic

[Charles Freeborn]

I used to run the same AJRS heads in the 1990's on a type 4

38x48, thin stemmed valves, Dual valve springs, and titanium retainers with holes drilled in them

Allen is quite the wizard. The most impressive (to me) aspect is the weld build up to allow porting. He cut o-ring grooves in the mating surface of the intake manifolds...
I'm not sure of the valve stems I had, definitely not lightened retainers, but dual spring. Very well thought out and executed.

Very nice guy too. I spoke on the phone a couple of times. Got some parts, etc. Old school honest.

Thanks Charles. (IMG:style_emoticons/default/smile.gif) The RPM's must have been impressive. How did he get it to breath out as well as he got it to breath in? That exhaust port, especially the 2.0 heads have little that can be removed. Did he weld those up too or is it big valve, massaging the port right after the valve and polish...Kind of hope for the best? Some of the work these Guy's do is real magic

People with more experience than me can better explain, but as I understand the GT5s class was not weight limited so it was largely about light weight. I think that car weighed around 1800 lbs. The engines were limited to stock displacement so it was that. Stock 2.0 crank, rods p/c's. All lightened and balanced. Lightened flywheel. It only had a 4 point cage so I couldn't run under the GCR classes.
Hi revs were not on the menu. I had the limiter set to 6k. The T4 was essentially a VW Bus engine engineered for low rpm / high torque. It pulled like a mule between 3500-5000.Above that it just made noise. Getting high rpm out of pushrod engines can get expensive in a hurry, not to mention explosive. Itwas a fun car, but hard to find a race class for. I did add more to the cage to get it past tech, but at 2.0 it fell into a no-win class (VP2 or EP) which isn't a fair fight against modern cars. My current engine is a 2.6 which may be comptetetive in VP2 on certain (technical) tracks, but even there it'll be a struggle to keep up. If I stay in this game for any length of time I'll look for a 1.8 to build out and run in VP1. That could be really fun up against the other small 4 cyl cars like Sprites, etc. That displacement, properly done, could achieve some higher RPM numbers. We'll see...

[brant]

The GT classes in PCA were designed to run 110hp per a liter

Making the 6 cylinders more competitive at any displacement than a -4

But our redline was 7k and the type 4 can be made to do that easily

There is a really competitive guy out here with a 2.0
Great driver too
And redlines at 7500 rpm

[Shivers]

Thanks everybody, I am motivated. (IMG:style_emoticons/default/smile.gif)

[Charles Freeborn]

The GT classes in PCA were designed to run 110hp per a liter

Making the 6 cylinders more competitive at any displacement than a -4

But our redline was 7k and the type 4 can be made to do that easily

There is a really competitive guy out here with a 2.0
Great driver too
And redlines at 7500 rpm

I don't doubt one can spin a T4 with the right balancing and a lightweight valvetrain. I'd be inclined to go with bigger bore and shorter stroke for a high hp / rpm engine.