Ford Drag Race engine development

[Guy Croft]

The port is not fully circular, slightly elliptical. This is unfortunately necessary sometimes according to the style of the original design.

G

[Maki]

The port is not fully circular, slightly elliptical. This is unfortunately necessary sometimes according to the style of the original design.

G

This I do understand I don't actually understand what you measure there? for example you mentioned "I went 41 wide and 30.8mm high with 24mm thru" this is pretty much cleare to me. (look at the picture) only those 24 thru are not clear to me.... like 27.5mm vertical and 26.3mm horizontal thru on the intake side... is it ment to be the inside diameter? I can't even imagine how to meassure it inside?

[Guy Croft]

My dimensions are thru the splitter bores which are the 'controlling section'

GC

[Maki]

My dimensions are thru the splitter bores which are the 'controlling section'

GC

Splitter is the part in the middle?

[Guy Croft]

Yes,the splitter is the vane (aerofoil section in the middle) and the splitter bores are the sections with the yellow lines which is where my dimensions come from. From memory I did not enlarge the port outer area.

I did not keep very good records on the Zetec because I did not enjoy working on it at all and would not do another. I have never been a 'fan' of Ford engines or heads and I've worked (reluctantly) on more than most (Pinto, XFlow, Duratec V6 and 4cyl).

You can see the valve combo on this shot, the head in full-spec circuit race trim made about 245bhp on 45 DCOE which is about the limit, would do about 260 on the right injection setup I am sure but that would be the limit as an atmo engine with those valves. I have never used bigger so cannot say how easy it is to do, but typically a 34/30mm combo might (I stress might) be good for 275bhp IN THE RIGHT HANDS. The latter emphasis in CAPITALS because it requires the most expert head and engine prep with superb FI calibration. When all the 'talk is over' few people - in my experience - are actually capable of that in reality and they would ONLY be professional race engine experts.

G

[Maki]

Will try to do my best with all you gave me, but I will never know If I did any good as there are no flow benches around here. Main problem I see is how to do them four ports evenly.

[Maki]

Hi,
like planed I changed the anlge of the inlet manifold, now started the porting. Took the head to the machine shop to open the seats to the true diameter of valves. The only question was where on the valve to do the contact surface as the valve itselve has 3 mm wide path. The machine shop sugested to do in the midle alghough I wanted on the outside diameter (to have the abiliti to open up the throat as much as possible) but they esplaned to me that this way the valve will get burned?

[Guy Croft]

Look at this dwg for a seat insert fitted and machined for a 34mm inlet valve, it tells you all you need to know.

If you don't cut or grind the contact face out to full valve diameter there is no point fitting bigger valves. The contact face on the seat - 1.5mm - 2mm wide is perfect. The throat on yours will almost certainly need to be enlarged too if bigger than std valves are used, again - if you don't bore thru there it's pointless fitting bigger valves because that is the controlling section.

G

[Maki]

I understand why I have to open them up, the question is ilustrated. Which way is the right way?

[WhizzMan]

Outer. Otherwise you could just as well fit 2mm smaller valves and still have the same flow.

[Guy Croft]

Whizzman is right.

The valve has a wider seat than the insert in your 'outer' dwg, so I would advise a back grind (may be 30 deg, depends on the valve shape) to 'pull' the valve contact face back to the same width as the seat insert one.

Your machine shop are being lazy/ignorant about this. Often I see valves overlapping the contact face on the insert (on so-called 'big valve conversions' simply because the firm or person doing the job can't be bothered to fit bigger inserts. I have seen this from 'big names' in the UK many times.

Find a shop who knows what they are doing. In every case I have seen, 'wild assertions' that 'they know better' are a danger sign that nothing they do will ever be 'right'. The machine-shop and reconditioning 'trade' is notorious for this all over the world. At GCRE we I go to inordinate lengths (frequently at cost to me) to get things as technically perfect as a thing can be and this I trust is reflected in the things I post on this forum.

GC

[Maki]

At the moment it's only opened (75 deg cut), without last (45 and 15) anlge cuts, so I could ask them to open it even more? But they most probably will charge me again :(
And there is one more comment I would like to share with you. On turbo charged engines some tuners suggest to have wider contact face than on NA engines, say instead of 1,5 mm like you suggested to have at least 2 mm. They say it helps to take away the heat from the valve.

[Guy Croft]

yes opinions do vary. You have to decide who to trust.

In my own exp the optimum contact face widths are around:

inlet 0.035" per 1" of valve diameter
exhaust 0.042" per 1" of valve diameter

You don't need to convert everything to Imperial measurements, just multiply your metric valve size like this:

34mm inlet valve x 0.035 = 1.2mm
42mm inlet valve = 1.5mm (appr)

29mm ex valve x 0.042 = 1.2mm
36mm ex valve = 1.5mm

You will NOT find a better 'rule of thumb' and I wrote that one myself for my 1st book and still use it. Nothing that i have seen on flowtest indicates otherwise and if you have seen my DVD you will know I have test more heads with more varied port/seat/valve combos than most will ever do in a lifetime.

You can go wider on contact face (up to about 40-60% wider) but you should not thinner, unless it is a very old tired head and you are willing to 'take a chance' on it to avoid putting new inserts in. I have to do this from time to time with Gp4 stuff. I don't like it but there we are.

Going wider (within limits) will make no difference to anything, flow or heat transfer. The issue of heat transfer affects the ex valves only and the contact face width (and its effect on that) depends on more than mere width. Other factors are the guide and seat insert material and type of valve (eg sodium cooled). Be aware that the wider the contact face the lower the contact pressure (for given spring type) and reduced contact pressure can definitely lead to layers of carbon/debris deposition building up on the interface which in itself reduces heat transfer and leads to burning of the valve and/or seat, loss of compression etc.

Conversely I know of no head where thin and esp 'knife edge' seats work well (in flow terms). Precisely how well the valve-seat combo performs does depend to an extent on the contact face width. Certainly the valve contact face can be left wider than that of the insert but the other way round will certainly impact on flow and a throat grind to reduce its width should always be considered. That upper section of the throat should always have a taper cut or grind - to allow for regrind when reconditioning**, in other words don't parallel bore the throat (the region thru the seat insert) right up to the contact face, leave some in hand.

** looks like your shop has gone thru with an 'on the limit' parallel cut by the way...



GC

[Maki]

Understood, thank you, will stay with 1,5 mm.

P.S. you mentioned "I went 41 wide and 30.8mm high" on exhaust part, but you didn't say anything about intake, what should I aim at?

[Guy Croft]

As posted earlier in this topic:

"On inlet I went for 27.5mm vertical and 26.3mm horizontal thru. On the exhaust on 138cfm head I went 41 wide and 30.8mm high with 24mm thru and got final 103cfm ex flow, giving final E/I shown which is fine. You can get a lot more ex flow by going bigger. The previously worked ex ports on one head had been (unnecessarily) enlarged and I when I finished it, it was 26.9mm thru and 44mm x 31.8mm outer section with E/I flow ratio of over 85% which is certainly not needed on an atmo engine. I didn't make it bigger, it was massive already. There is definitely no point deliberately going any bigger thru the ex port than the ex valve throat diameter (about 3mm less than valve) on any head, the throat is the controlling section."

I would just add to that the 27.5mm and 26.3mm is thru the splitter bore on the inlets, I don't recall that on the outer port section I enlarged it any although I did a lot of smoothing, knife-edged the splitter vane and made the port floor outboard of the short radius as flat as I could.

Do we have a picture of the car this is going in?

Hope this helps,

G