Test




preliminary flowtesting the 20v inlet ports - here with a cotton trace and flowrig depression 10". Very low valve lift here. Nothing remarkable - certainly not showing a marked preference for following the port floor and short radius (SSR - the tighter side of the bend adjacent the valve throat). The plasticine stops a random 'sharp-edge entry' loss at the intake and the shape of the clay is surprisingly unimportant, so long as it presents a reasonable radius as shown.





open up the valve a bit and you can see how in the port outer section the main high velocity airstream (that grabs the trace) follows the centerline but over the SSR region (which is very long), instead of neatly following that curvature, the airstream is bounced upwards by turbulence.



Here you can see the peak standard port flow at 10" depression. The flow with valve-in peaks at 10.5mm valve lift (both valves fitted of course) with a valve-in loss of 3.7cfm - something that I'm always interested in. You lift the valve higher and it won't flow any more. The valve-in loss at peak (ie: the valve lift where the flow stops increasing)is a function of the valve region discharge coefficient - the factor by which the perfect flow is reduced and it's affected by:

1. Valve shape
2. Seat angles
3. Valve throat diameter (this is invariably the ID of the valve seat insert)
4. Extent of any shrouding in the chamber around the valve
5. The shape of the SSR and port sides adjacent to it. (The long-side radius has little influence and the guide is too far away to affect the valve-in-flow).

1,2 and 5 are perfectly capable of generating the flow-robbing turbulence that stops the air getting thru the valve region.

3 and 4 are physical restrictions (as is valve stem diameter but to a much lesser extent - it is frequently cited as being more important than it actually is).



this is the simple lift setup to open the valves incrementally





No valve is fitted on this 'bare port flow' (BPF) test. You always want to know this value if you're flowtesting because later when you test with valve you can assess the valve-in loss. BPF is the most the port will ever flow and the valve will always represent an intrusion into the airstream, except maybe at high lift. Some setups will have no valve-in loss at peak valve lift, some will have a massive loss. A good 4 valve-per-cylinder setup should ideally only develop a minor valve-in loss and you shouldn't have to lift the valve an unusually high amount to find the maximum flow with it fitted. You will often find that on a 4-valve head like this the standard head will develop peak flow at near the same lift the standard inlet cam develops. Giving a valve more lift than needed to achieve max flow ('overlifting')doesn't make much technical sense really - if you want to augment the flow - better to bulk up the cam flanks. If the valve springs will work OK with new accelerative rate that is. You can extend the duration too but that can simply have the effect of taking longer (in the induction cycle)for the valve to get to peak lift - the faster you open it so the better.
You can see the depression manometer at left (vertical) and the inclined flowscale one where the % flow is read off to compare with Superflow charts to give the flowrate. A temperature correction has to be applied because the air heats up during test.

this is what the port downdraft angle looks like on the 20v - the more downdraft and the more acute the angle betw port axis and valve stem the better the flow distribution around the valve head will be, and thus the better the response of the head when the valve is fitted. At all lifts? Not necessarily...



standard (OE) Fiat inlet valve - is the shape right? Could be - they are pretty good at this. Testing will show..




combustion chamber - in standard trim not at all bad as they go. Not much sticking out (intrusions) into the flamefront and valves placed nicely opposite each other -I mention this because on some heads the valve placement is awful - Peugeot and VW 16v units being prime examples. It is important that the ex valve can 'see' the inlet on overlap because that assures good 'crossflow' around TDC on the scavenge phase, ie: when both valves are open around the end of the ex stroke. If one valve is recessed lower than the other it doesn't exactly help. The ridges around the valve seat inserts need to go (I mean, ideally one should get rid of them but if you're paying for this it does take a long time). Usually better to 'dress' the chamber before doing valve seats. And they won't get done till the head's been ported (gasflowed) and that won't get done till the old guides have been taken out. I don't agree with the practice of porting with old guides in far less 'shaving them'. You want race material guides - ductile and better heat transfer. Cast iron guides ARE prone to crack at the stem seal end under the high side-load of competition cams and if you shave the port end for flow it is very difficult to get a true center to grind/cut the new/race seat angles.



View down standard inlet port and at a glance I can tell - high loss due to small size and surface roughness, intrusive nose on the splitter (the bit that separates the barrels). One's obviously thinking about new dimensions now and that is where flowtest comes in..



Survey of the port - the floor should ideally be flat from entry section where the manifold bolts on right to the short side radius. Is it? No. Will it be made so? Yes, hopefully. There certainly isn't going to be a metal thickness problem, every alloy head ever made is at least 4mm thick everywhere. Don't like the gap under the ruler at the SSR end, looks way too long that SSR, separation of the airstream a is very real possibility and that can disrupt the whole port flow ie: block it.



Photo above shows why I am concerned - the long distance from the start of the short radius (elliptical)to the last bit the charge 'sees' before it enters the cylinder ie: the 45 deg contact face. There isn't much I am going to be able to do about this other than try and optimise the curvature of the radius, truth is the port floor is just too high above the seat insert. This is a critical design feature and many cylinder head designers get it, well 'wrong'; that said if the engine meets its power and emission targets they wouldn't be in the least bit concerned...



here just making a note of the placement of the splitter relative to the head face. Interestingly some splitters cause a 'horseshoe' vortex which spirals thru each barrel. That is very pronounced on the Integrale type head (16v) which has a very long splitter vane. A vortex is unavoidable - all aerofoil type sections have them and yes they do cause a flow loss. Is there a gain from the turbulence induced into the airstream - ie: does it help the burn and offset the flow loss? Well, the splitter is only there to support the port - given that the head has two seat inserts, and the trend with some designs in recent years has to go for shorter and shorter ones a well-radiuse radius and this reduces the horseshoe effect considerably (removes it entirely some heads). So I figure the answer is no.

One can see at a glance that the 'ratio' of surface roughness to port cross-sectional area is not in the head's favour on this one. Roughness (up to point) causes friction and flow loss; once again there is a trend towards bigger and bigger ports - so big in fact that you can smooth them as much as you like and it will not alter the flow at all.



It's important to survey the various regions of the port. Here looking at the cuvatures present in the port roof downstream of the injector recess. The latter incidentally I have never found to have any influence on flow at all, you can smooth it or fill it in, the air doesn't even 'see it'. On tests with the inlet manifold on I have often filled in and then opened up the injector port and found it doesn't make the slightest difference to the flow.


having a look at the shape of the port sides. Invariably, unless it's a very long head, you are going to get a convergence in the inner port region and actually provided the curvature is aerodynamically good, it doesn't matter. Air flows over curved surfaces quite smoothly if the surface is smooth and of sufficiently large radius. If the radius is small and bumby or very rough you will definitely get loss. By rough - from a practical point of view - I mean coarser than 80 grade carborundun paper. I have not found much benefit going finer though as rule I finish to 120 grade because an 80 grade finish looks pretty grim (cosmetics do count, do they not?).



It's vital to record the inlet entry section dimensions , here ..



and here. Note where I am measuring to - this is the effective height of the port at entry. These dimensions are useful if for no other reason than you can compare with other heads for which you have quantifiable flow and dyno data. I've often seen heads where the entry section has been massively and unnecessarily enlarged..

and here is the 'width'. The main entry section is what I would call 'semi rectangular and at dimensions of c 40 x 26mm it will have an entry area of considerably less than 1040 sq mm, and (below) the runner on the outboard section (the plenum) at c 35mm dia is the same as the entry section on the inboard manifold below which is just over 962sq mm so that is probably not going to to generate a massive bolt-on loss in itself. *



the inboard section of the inlet manifold flows 108.7cfm @ 10" in standard form - more or less the same as the port (106.7cfm). So after entering thru a big hole the air is squeezed, reshaped, sent round a bend and subjected to a fairly rough as-cast surface. That's all well and good - as a rule provided the inlet manifold flows same or more as port and the axes of both align in the same plane (ie: the manifold isn't bolted on at some weird angle) then the bolt-on loss should be modest (even none sometimes), but when the thing is bolted to the modified port (all being well..) this item is going to need significant enlargement. *



* edited by me after my flawed arithmetic as pointed out quite plainly in the discussion thread. Apologies for the misleading statements about modifying the inlet manifolds, I am working from memory and I was not engaged to do anything to them.

Above, dressing a stone for the Peg 10 grinder at 30 deg. I have found a benificial gain in lower lift flow from a 30 deg top grind coupled with a 30 deg back-grind on the inlet valves on several engines incl X19 type SOHC and 8V TC Fiats. You have to be careful with this because it drops the valve deeper into the head. Go too wild with the grind (ie: taking out too far beyond the seat insert) and you end up making the head unshimmable. This is a trial op along with the others in this section to see how, by 'optimising' the valve region, the flow is affected.
It's worth doing this first - before modifying the port - because there is only a finite amount you can do here - the controlling section is the valve throat at around 26.7mm and there is only so much alteration you can make. With that optimised you can then turn your attention to port enlargement and there you have a lot more latitude - simple enlargement.

Below you can see the wide 30 top grind ready for superposition of the 45 deg contact face.





Measuring the width of the top grind so I can repeat on the others.





Above - generating the valve contact face. I have never found that going super-thin on the inlet contact region works. However going a bit wider thans shown usually makes little difference.



As this is a development trial I am working with the old guides still in place. If they are badly worn it's quite risky, because when the race guides are fitted the valve center will shift a bit and the seat will have to be reground - so clearly if you grind the contact face way-thin you might find you've no metal left.

Below - how to get a reasonably good idea of the valve tip height - the other end of the calliper is on the valve spring platform. Also recording the 'tip to cap' distance with collets fitted. This is to allow me to work out the available space for the spring pack.





Below - having settled on a valve tip height that's 'workable' I am opening out the upper section of the valve throat (the area below the contact face) at 75 deg. I have generally found 75 deg to be optimal on downdrafted heads. This is all rather hit and miss and that vague statement is based on doing hundreds of times on good and scrap heads.. Sometimes the finished throat needs to be blended (at 120 grade or finer) but it varies from head to head. I would never use 75 deg on anything other than a downdrafted head BTW - if you use it on a semi-sidedraft like the SOHC X19 unit or 8V TC it will have a disastrous effect - they need a sharp 70 deg angle for sure.






Above - finished valve angles - sufficiently modified for my test purposes - albeit sitting in a standard chamber. The 75 deg leads the airstream nicely to the 45 deg section and at the same time narrows down the contact face to the width I want. Note that the 75 deg grind does not extend all the way thru the insert - the lower section is parallel and as a rule you should keep it that way. On standard valves I have never enlarged the parallel section - it will almost always be right and if you do that - you will usually wreck all the other angles. I have experimented at great length on so-called 'multi-angle' seats - complete waste of time with little valves like this. Might work on giant V8s I suppose..



Above - the standard form of the short radius - pretty bumpy all in all. I don't want to alter the shape really at this time,just smooth it and see how good it is. The carbide burr I'm going to use is shown below.




Above - SSR & a bit of metal removal - won't do any harm, might do some good even. Below, installing valves for trial test





Above - unit on test at this stage and some significant gains already. The increase in bare port flow will not be coming from the valve seat mods - on the inlet side the air will not be affected at all - only when the valve is fitted. It's true to say that valve and seat mods only affect the valve-in response. The gains are coming from the minor reshaping on the SSR. Would just a few minutes work make your engine more powerful? On its own absolutely no idea - but if you did a nice set job too then yes. 'Blueprinting' to coin a long-dead expression has always, in my experience, made a very significant difference to performance and no 'head prep/gasflowing/porting' job should be done in isolation without it.

Below - flow status by test 5



Bare port flow lines (no valve fitted) are horizontal. Ideally one wants intersection of valve-in and BPF at some reasonable valve lift but frankly only the very best heads do this. The ex BPF is so near inlet it's not going to be a problem in itself here we have 95% - and that test (don't have a photo) is with standard ex valve seats - modifying the ex seats certainly DOES have an impact on BPF because the air is flowing thru the seat region outwards. If you have over 73% ex-inlet BPF ratio you're home dry. But if the ratio is that high it is more a sign that the inlet side is underperforming relative to the ex ports - no way do you need 95%, 80% would be perfectly sufficient. Inlet ports just don't flow near enough really, given that the valve-valve ratio is 75% - one should expect the port BPF ratio to be similar. The curious hump in the flow curve now apparent is to do with the SSR profile - turbulence is disrupting the flow at mid lift.

more to follow...

All:
Please note this thread is not yet complete.
Please keep all Comments on the thread below:

20v Head Prep - Discussion Thread

Can't continue this thread till someone with rights uploads my latest batch photos to the server as previously.

Do members wish me to continue?

G

Yes please. (Mods / Admin delete this post as appropriate).

Who's been uploading them for you Guy? I don't mind doing it if you send me a link to the pictures.

However, please continue

The "Tunning" forum is far more interesting to read with this cyl head topics.
DOn't ask again that please.....

with the seat region as modified as I care to make it at this time now we move to the outer port region to look for a response from mods there.

Before making the assumption that the outer face region needs enlargement I'll see what happens if the splitter bores are increased in area. They are roughly circular and I want to kinda keep them that way - weird shapes don't flow well. Mod means removal and I want to remove metal more or less all the way round, but incrementally - ie: not a massive amount - that way I can establish a trend. Incidentally one hard and fast rule of doing enlargement there is that if the BPF does NOT go up it is a sure sign the SSR is WRONG. So never keep enlarging if the flow doesn't go up - you could be wasting your time. Remember too that except for a bit of smoothing the SSR is of standard form - and there is no guarantee it's 'perfect' (or at least as perfect as the human hand and eye can make it..)

Here using a coarse 50 grade ATAband to smooth the as-cast surface and eliminate bumps (not worried about decent curvatures) and also reshape the splitter nose. See how I am avoiding change to the shape of the port entry. I just want to know about effects in a particular region - if you change too many things during dev porting you can easily a) waste time and b) draw the wrong conclusions





Interim dimensional check..



and here the large band being rammed right thru and another size check with callipers -





view thru



and a look at an intrusive bump at the port outer lower section - I want a straight run here





by the time I have reworked that bit the ruler should make full contact with the port floor right from entry to the short radius (as itstands). Below you can see the effect of the abrasive band which I have run right over the valve guide region up to the 'well' below the valve.



now turning attention to the sector just below the seat insert -





and then joining that up with the rest of the port in a smooth arc with a larger burr whose contour nicely generates the shape - easy to make it bumpy here and whilst it doesn't matter overmuch on the port roof between guide and seat it looks dire if not done with care..







burr followed by smoothing at 50 or 80 grade with a bit of WD40 or light oil spray which increases the removal rate with burrs and abrasives..





the SSR gets some smoothing and blending into the adjacent port regions but nothing radical at this juncture..







at the area marked by the black pen (above) we want as shallow a curvature from the splitter to the seat as possible - the tighter (smaller) the curvature the lower the flow will be due to separation..





last shot above shows a 'split-fork' deburrer made from a 6mm bolt slit at one end to accept a bit of Norton Abrasives tape, non-invasive, self-centering and great for final finishing..

status at this point and flow tests up to test 10 including valve-in with back grind on the inlets. I wasn't sure of the exact back-angle on them so superimposed a 30deg angle on them just behind the contact face







BPF is up (bigger splitter bores) and you can see in the flowtest with valve-in (T10) we've picked up measurable flow gains over 5mm lift (ie: a nice valve-in response to the higher port flow - doesn't always happen..) and fractionally reduced the valve-in loss at peak lift relative to BPF. The latter almost certainly due to the work around the valve seat region - you remember I mentioned 'discharge coefficient'earlier. The blue line of T10 also shows up a fractional improvement in the lower lift flow - almost certainly due to the sharp-edged 30 deg back grind on the valve. I did say the OE valve shape might not be optimal - it's not. It is important BTW that the valve and seat contact faces are of equal width. If you can't get them the same always avoid making the valve contact face wider than that of the valve seat insert, narrower is OK but equal is optimal.

I wanted to be sure the hump in the flow curve with valve in was 'real' so I blocked off each barrel and retested (below) and sure enough there it was again. Ignore the test with a light rad on the valve - I shall come back in detail to valve shape later with some very interesting results which prove the efficacy of my sharp-edged sharp back grind. The test barrel-barrel proves there ar tow distinct flow regimes at work - the shift in gradient shows the port is under-performing at higher lifts. First time I saw this I figured the flow was being disrupted at higher valve lifts by turbulence over the long SSR. Ultimately as you will see that by reducing the length of the SSR (from the straight port floor to the seat insert) and increasing the radius of curvature near the seat I was able to reduce that disruptive tendency - but not entirely eliminate it. The truth is on these heads, the port floor is just way too high above the seat for that kind of downdraft angle and the air just cannot stay adhered to the surface on such a long curve.



You have to do pretty accurate porting to generate curves like this by the way. Amazed myself with this one. If you sum the barrel BPF it should equal the whole in case you're wondering, yes. With the port status at that time. If it doesn't your splitter bores are not the same size or the nose of your reshaped splitter isn't central in the port.

the BPF per barrel in that comparative was:

front barrel - 56.4 cfm @ 10"
rear barrel - 52.3 cfm

total 108.7 cfm so down some on 118.7 at Test 10, dunno why, not really bothered to be honest.

Bit of investigation into valve shape, here OE valves reground to 45 deg with contact face width more-or-less as standard (3.2mm) allowing for the removal to clean them up, then lapped (the old guides are still in):



you can just make out the OE 30 deg angle behind the contact face, OK but it does not have a sharp edge at the stem side - something I have often found beneficial.







the contact face width on the seat insert is 1.5mm wide at this time but on the valve the 45 deg face is way too wide for good flow as I mentioned earlier it ideally wants to be the same

superimposing a 30 deg back grind..



here the valve with full radius connecting the 30deg back grind to the rad at the bottom of the stem..



and below a valve with plain back-grind (sharp edged 30 deg), contact face 1.5mm wide..

(photo to follow)

The radiused valve is similar to those I've used very successfully in Vauxhall XE 16v heads which are superbly downdrafted so I tried this shape at Test 24 in conjuction with light radius superimposed on the 75 deg throat grind and with it sharp-edged as well, made no difference either way from which I concluded straightaway there was no point radiusing the inlet valve seat angles. That may seem a 'long-shot' but so much of this kind of work relies on having huge experience to judge what is worth pursuing and what is not. It can take you months (trying every single option) to be able to say with reasonable certainty what works - and what doesn't. Pretty sure also that this head is going to prefer a sharp back grind to a radiused one..



below you can see the smoothing (radius work) on the seat insert up to the 45 deg contact face. You might find it odd that such a tiny region could be in any way influential or important - but it can be.



and below (status test 29) the 75 deg lightly done again to generate the sharp juncture from 45 into the (parallel) throat..



what seems to happen as far as I can judge is:

1. If the angles are sharp (from parallel to 75 to 45) the air separates briefly as it flows over the change of angle
2. If the angles are radiused the air separates to a greater extent, given that the radius of curvature is very small ie: not aerodynamically good.

Big assertion I know and what you do varies markedly between designs (according to port downdraft and valve angles)and results have shown time and again something along those lines could well be happening. Moreover I have tried 'multi-angle' seats (very, very popular with some esp big US units) and got absolutely terrible flowtest results.

Here are some graphs indicating results from varied valve shapes. I can't go exactly in sequence so don't be to alarmed to find the tests suddenly jump to T29! I did not plot graphically every single test..



What this all means compared with Test 10 seen earlier:

Test 18: splitter increased in entry and thru from 23.7mm to 24mm. Seat at Test 4 status, with 34.4mm dia 30 deg top grind, 45 deg x 1.5mm contact face, sharp 75 deg grind in throat into lower parallel section. OE valves with 20 eg back grind and radius, SSR reduced in height to lengthen curvature.

(that last bit about the SSR - not entirely a wild guess at this time, remember that whilst it is great fun chasing optimal setups one at a time I don't want to be there for weeks - nobody is going to pay for that!)

Test 21: at test state 20 which is as above but the short radius lowered fractionally 2mm below the seat insert and radiused right up to the contact face as shown in picture above (valve trials no 11)

Test 24: status as Test 22 where the SSR has been lowered further (effectively what I have done is reduce the height of the minor axis of its elliptical curve) and the regions either side of the central section of the SSR (in line with the valve stem) have been 'flattened out' further(that critical area was marked up in a previous picture '09.178_inlet porting (21)').

By Test 29 in the same graph above, I have cleaned up the whole port section at 120 grade (wet) using bands and the split fork tool, reduced the width of the contact face in the seat insert to 1mm by grinding again at 75 deg, and lef the valve at 1.5mm contact face. In my experience if the 30 deg back-grind is too wide (which it would be if I went down to 1mm on the valve, flow can suffer quite adversely. Here is an example of optimisation therefore, where the valve contact face is deliberately left very fractionally wider than that in the head for a reason I have not mentioned before. I'd be concerned if it was much more than that, which it certainly would be without quite an aggressive back-grind.

Apart from losing out a bit at the lower lift end spec at 29 wins easily over 6.5mm lift. The OE valve wins over the radiused one over 8.5mm. No point dwelling too much on these comparatives however when you hit on a setup (by design or accident) like T29. BPF at that stage is 122.1 @ 10" which is some 14.4% over standard and principally a function of splitter bore.

Next ops: Valve guide removal, combustion chamber prep, final inlet port prep and essential deburr ops.

G

whichever way you try getting the old guides out is a struggle. As I already mentioned I would not prep one of these without replacing the guides and I would always use Colsibro or Trojan copper alloy for the new ones - which I always design myself - for good reason. Valve guide design (for a used head) is actually far more difficult than it might seem.



Above - because they are so long I know they are going to be a 'pig' to get out so I try drilling them out as much as I dare to relieve some of the stress in the guide-head fit. And I try pressing them out in this direction:



all that happens is the valve guide nose fractures. So instead I deliberately fracture the weak seal end of the guides and press them out in the direction they were fitted. In all these ops I have heated the head to 60deg C and spray-oiled the guides (for all the use it was) and yes the head has already been decarbonised..





Success in the end and here are the fracture and pressing tools used:



Final inlet port prep with guides removed. Yes you can port the head with guides in and I have seen it done that way but it is not wise to run a comp spec head of any kind with cast iron guides. Below, ramming the Ataband up and down the port to achieve a smooth surface at 80 grade and then 120 grade free of undulations and bumps that might cause a local upset to the flow..



Here gasket offered up and the effective entry region assessed against gasket shape, you can see my scribed line. You have to make a reasoned assumption about how big the entry section has to be, in this case I reasoned it would be big enough. Invariably - unless it is a very rough casting - it will be big enough in standard trim - and as we know here, the splitter bores are the controlling section not the outer face.





Below - showing the convergence inside the port that most inlets have on multivalve units



and how much does opening it out achieve? Not a lot as you can see below..



Final bare port flow on port 5 ..



and view down finished inlet port finished with split-fork tool at 120 grade with a bit of WD40 spray oil. Outer face has been stoned for true and linished ..





Next step-by-step dressing the combustion chamber. Best done before seats really or you might take too much off around the top of the seat inserts - and you can't put it back on. What do you need to do to the chamber? The smoother the better the burn will be and what you see here can pretty-well be considered ultimate spec. Nice if you have the time and no good 'head man' would ignore this nor consider it 'unnecessary'.

to follow - deburring, ex ports, maybe new guides in that post as well if time permits