3 angle or 5 angle

[nip]

What would be the best valve job, a 3cut or 5
cheers nip

[Flat on my back]

.

For bang for buck...3.

[nip]

For bang for buck...3.

Cheers Carlos

[JP]

The I5 seats are too narrow for a 5 angle seat as you end up with too small a seating width for a reliable roadgoing head. If you couple the 3 angle seat with swirl polished backcut valves you'll see 7-8% intake flow gains and 12-14% on the exhaust if you ball nose the guide on the exhaust side.

[RustyNut]

Can you guys give a brief explanation of what you're talking about for us thicko's. Cheers.

[JP]

LOL.

Where the valve meets the cylinderhead there is a strengthened seat insert. In order to seal against the valve the valve and seat are both cut at opposing 45degree angles to create an airtight seal.

Air likes to flow straight and not round corners. So as the air passes past the valve and seat it looses some of its maximum airflow potential of the cylinderhead port. However you can add additional angles to the seat either side of the 45 to create a smoother curved seat which allows a greater volume of air to pass as it has less extreme turns to make.

Traditionally 30,45&60degrees is the main 3 angle seat. Add 15 and 75, and you have your five angles. Your I5 head comes as standard with 45&75 cuts.

Depending on the combustion chamber design and the cam lift, you can use different combination of angles to achieve maximum flow for a given cam.

Hth JP

[RustyNut]

Perfect, many thanks for the condensed tutorial. At what point would I have to consider adding an additional cut to the seat? My 45 & 75 cuts are doing just fine atm but upgrades are always being considered!

[nip]

LOL.

Where the valve meets the cylinderhead there is a strengthened seat insert. In order to seal against the valve the valve and seat are both cut at opposing 45degree angles to create an airtight seal.

Air likes to flow straight and not round corners. So as the air passes past the valve and seat it looses some of its maximum airflow potential of the cylinderhead port. However you can add additional angles to the seat either side of the 45 to create a smoother curved seat which allows a greater volume of air to pass as it has less extreme turns to make.

Traditionally 30,45&60degrees is the main 3 angle seat. Add 15 and 75, and you have your five angles. Your I5 head comes as standard with 45&75 cuts.

Depending on the combustion chamber design and the cam lift, you can use different combination of angles to achieve maximum flow for a given cam.

Hth JP

Lol rusty
Cheers jp, we had noticed there is very little space to cut, going to swirl polish them hopefully this week, old guides to be removed tomorrow.

[volcano rs]

Lol rusty
Cheers jp, we had noticed there is very little space to cut, going to swirl polish them hopefully this week, old guides to be removed tomorrow.

you are just a muppet i explained this same thing to you on friday evening but obviously it wasn't ggod enough for you

[Ross]

I need more education on head work and the effects, seeing as I'm looking at a rebuild on my RS2 head. Is it worth doing this and what's a ballpark figure?

Currently with 7A cams / MD147 but planning on returning to RS2 cams (only have inlet at present, that may have to do) and stock turbo or something very similar.

Also - staggered by your gains with the port + polish JP, again what effect does this have on an RS2 set-up? (JP or anyone else with the knowledge!) From my understanding I may see slightly earlier spool and won't have to push the turbo so hard to get peak power, but not neccesarily a higher peak.

[JP]

First of headwork will not create earlier spool or put less strain on a turbo but I'll explain this below. Cams however when making the lobe separation greater can give earlier spool at the sacrifice of top end as more of the turbo's airflow is contained in the cylinder every combustion cycle.

Cylinderheads themselves can be ported to various levels depending on end user requirement and obviously financial means. For example there is no point in doing a balls out exhaust port design to then fit a restrictive exhaust manifold which chokes it upon port exit.

Best thing to do is understand the basic principles/dynamics of an FI engine with respect to boost pressures.

When looking at your boost gauge what you are seeing is the pressure left in the intake manifold that cannot be used by the engine. If you were to remove a vacuum hose of the intake manifold it would obviously create a leak which results in lower boost pressure. Or your boost control unit will make the turbo work harder to compensate for the pressure drop to bring it back to its original value.

If you can imagine your cylinderhead to now be the leak as you make your cylinderhead more and more effective/efficient through port work you are in effect making the leak bigger and bigger meaning that your turbo has to work harder and harder to achieve the flow required to reach the original peak target. The end result being that peak boost is achieved later on the rpm range than on a lesser flowing stock head.

This is where it gets confusing because your engine being volumetrically more efficient than before will now produce more power at any given rpm and boost pressure level than before. So when comparing power curves without the visual representation of boost it will appear to be on boost sooner based on the power curves alone.

When driving on the street the ported head will give the illusion of a bigger capacity engine through the improvement in power delivery being smoother more consistent and pulling stronger for longer. The significance in the difference between before and after will not only be down to what level of headwork one opts for but also the adjoining modifications.

For example on a small turbo which can not flow the top end that is required by the headwork will have an end result of improved low and midrange but no real gain at top. So although there is much more area under the curve and car feels smoother and stronger to drive the peak power figures are not necessarily much different. Use a slightly bigger turbo and the power delivery will be that of the smaller turbo with the ability to carry on pulling at the top end and making larger peak figures with no loss of driveability low down compared to before.

As a real life example using my mates 1.8t.
Originally stock largeport head, stock cams, gt3071 0.82 hotside running 1.8 dropping to 1.7 bar made 456hp with full boost at 4200rpm and power tailing of after a peak at 6400rpm.
His new setup with a rather extreme ported head which involved welding and reconfiguring the original port design, with solid lifter long duration solid lifter cams, a gt4094 with 1.06 hotside at 1.5 bar on a street map makes 600hp with full boost at 4800rpm and power tailing of after a peak at 8300rpm.
Looking at those figures and specs you think well he has sacrificed low down/midrange for the top end pub figures. In reality when you overlay the power plots the 4094 setup produces 2-3hp more at every 500rpm marker up untill 4500rpm where it carries on climbing rapidly to a 8300 peak. Whereas the 3071 setup starts to slow down its ascent to it's peak of 6400. So an improvement in driveability including top end gains. which took the car from a previous pb of 11.3 on the quarter to an instant 10.6. Unfortunately once using the 750+ race map he ended up with nothing but constant transmission/driveshaft/cv issues meaning that the extra 150 ontop of the 600 never got him any faster last season. £6+K invested in the drivetrain later and he's hoping to be better this year.

The stroker RS4 that runs the same head configuration as the 1.8t utilises two porsche K24 hybrids which produce a power curve low and midrange identical to it's smaller k16 counterparts. Once again climbing to a higher redline after full boost is achieved.

My particular cylinderhead is a prototype based on the original 1.8t design which involved a lot of ally welding remachining the guide holes and basically making freshly shaped ports compared to stock. Once the gains where confirmed on a flow bench I went on to repeat it on the designated head for someone else. Couple of months later I sat there looking at the prototype head and decided to weld and repair the cracked combustion chamber, fit a new exhaust seat, machine the water manifold holes and weld on a cam sensor boss so I could chuck it on my car. That same head was subsequently removed for further development including the fitting of oversized valves and will make a re-appearance on my new stroker project sometime this year. (will update the project thread at one point).

hth JP

[Billman]

great explanation!

We are getting very often in the discussion about when boost comes in and when is full boost achieved or at what RPM 1 bar etc when comparing cams and setups and it's clears that there are so manyy variables....
makes me wonder what HP does my low boost (95 RON) map makes on the stroker with the reclocked cams and the rest!

[bazburn]

First of headwork will not create earlier spool or put less strain on a turbo but I'll explain this below. Cams however when making the lobe separation greater can give earlier spool at the sacrifice of top end as more of the turbo's airflow is contained in the cylinder every combustion cycle.

Cylinderheads themselves can be ported to various levels depending on end user requirement and obviously financial means. For example there is no point in doing a balls out exhaust port design to then fit a restrictive exhaust manifold which chokes it upon port exit.

Best thing to do is understand the basic principles/dynamics of an FI engine with respect to boost pressures.

When looking at your boost gauge what you are seeing is the pressure left in the intake manifold that cannot be used by the engine. If you were to remove a vacuum hose of the intake manifold it would obviously create a leak which results in lower boost pressure. Or your boost control unit will make the turbo work harder to compensate for the pressure drop to bring it back to its original value.

If you can imagine your cylinderhead to now be the leak as you make your cylinderhead more and more effective/efficient through port work you are in effect making the leak bigger and bigger meaning that your turbo has to work harder and harder to achieve the flow required to reach the original peak target. The end result being that peak boost is achieved later on the rpm range than on a lesser flowing stock head.

This is where it gets confusing because your engine being volumetrically more efficient than before will now produce more power at any given rpm and boost pressure level than before. So when comparing power curves without the visual representation of boost it will appear to be on boost sooner based on the power curves alone.

When driving on the street the ported head will give the illusion of a bigger capacity engine through the improvement in power delivery being smoother more consistent and pulling stronger for longer. The significance in the difference between before and after will not only be down to what level of headwork one opts for but also the adjoining modifications.

For example on a small turbo which can not flow the top end that is required by the headwork will have an end result of improved low and midrange but no real gain at top. So although there is much more area under the curve and car feels smoother and stronger to drive the peak power figures are not necessarily much different. Use a slightly bigger turbo and the power delivery will be that of the smaller turbo with the ability to carry on pulling at the top end and making larger peak figures with no loss of driveability low down compared to before.

As a real life example using my mates 1.8t.
Originally stock largeport head, stock cams, gt3071 0.82 hotside running 1.8 dropping to 1.7 bar made 456hp with full boost at 4200rpm and power tailing of after a peak at 6400rpm.
His new setup with a rather extreme ported head which involved welding and reconfiguring the original port design, with solid lifter long duration solid lifter cams, a gt4094 with 1.06 hotside at 1.5 bar on a street map makes 600hp with full boost at 4800rpm and power tailing of after a peak at 8300rpm.
Looking at those figures and specs you think well he has sacrificed low down/midrange for the top end pub figures. In reality when you overlay the power plots the 4094 setup produces 2-3hp more at every 500rpm marker up untill 4500rpm where it carries on climbing rapidly to a 8300 peak. Whereas the 3071 setup starts to slow down its ascent to it's peak of 6400. So an improvement in driveability including top end gains. which took the car from a previous pb of 11.3 on the quarter to an instant 10.6. Unfortunately once using the 750+ race map he ended up with nothing but constant transmission/driveshaft/cv issues meaning that the extra 150 ontop of the 600 never got him any faster last season. £6+K invested in the drivetrain later and he's hoping to be better this year.

The stroker RS4 that runs the same head configuration as the 1.8t utilises two porsche K24 hybrids which produce a power curve low and midrange identical to it's smaller k16 counterparts. Once again climbing to a higher redline after full boost is achieved.

My particular cylinderhead is a prototype based on the original 1.8t design which involved a lot of ally welding remachining the guide holes and basically making freshly shaped ports compared to stock. Once the gains where confirmed on a flow bench I went on to repeat it on the designated head for someone else. Couple of months later I sat there looking at the prototype head and decided to weld and repair the cracked combustion chamber, fit a new exhaust seat, machine the water manifold holes and weld on a cam sensor boss so I could chuck it on my car. That same head was subsequently removed for further development including the fitting of oversized valves and will make a re-appearance on my new stroker project sometime this year. (will update the project thread at one point).

hth JP

Here endeth the first lesson,we will all be tested on this later in life/project rebuild...

Great explanation BTW Jp, bet your little fingers are goosed now after all that typerwritin'...

[DS2]

good simple explanation man

[Sonic]

good simple explanation man

Who are the recommended people to contact about having your head ported? I've seen Aelred's name batted about.