A quick look at cylinder heads.

[4v6]

Didnt know where to put this so it looked about right being in technical/mechanical...

Im currently fettling a 1B 200 turbo cylinder head that ive been meaning to dive into for a while now, so this week i got going on it.

I wanted to show you a few of the things that can gain you power if theyre done carefully, specifically valve seats.
As you may know i bought a natty bit of kit for doing valve seats and i could barely contain myself throughout the week and get into doing them after the porting was finished.
However lets have a nosey at valves first, intakes, as it happens.

This first picture shows two intake valves.
The left one is from a big valve kv i had a play with and the one on the right is a stock kv intake valve.



An interesting couple of things to note here are the shapes of the heads for one and the seat itself on both valves for another.

The "big valve" jobby is worth precisely dick in terms of extra flow in the case it was used because if you notice the position of the seat, the bright ring around the periphery, its located some half distance from the edge of the valve.
That tells us that valuable flow area (curtain area= lift X diameter) is being wasted here, but thats not the whole story as this valve had a stock valve seat diameter on the insert....doh!
Basically the valve was fitted to a standard seat insert which was crudely parallel bored.
On test it was useless.

On the right valve we have a similar situation going on, some of the perhipery of the seat diameter is being wasted ( its actually close on 1mm).
So we can get a good improvement simply by utilising the full available area that the valve head should present , in the case of this 1b and Kv heads, its 38mm.

How we do this isnt exactly hard if you have the kit ( as im glad to say i do!) but it does take a bit of care and some nerve, well i find it a little daunting at first.

This next photo shows two 1B intake valves.
Take a good look at them.
The left one is as it comes out the box, theres a nasty "ditch cut" on the stem side of the head to try and get some flow, pity the monster wide seat ruins it.
The one on the right is exactly the same valve type but the seat is moved to the extreme edge of the valve, using every bit of available flow area to get a gain.
Also youll notice a backcut that meets partway with the standard cut on the back, cant do anything about that as the backcut starts from the inside of the seat ( its 2mm wide as per stock) and then runs back towards the stem.
Incidentally, the new seat position and width precisely mirrors the ones recut in the head.



Thats achieved by setting up the cutter using a fixture to position the outer edge of the formtools i use thats already been set to the maximum diameter ( radius is actually measured against) of the valve itself.
This a formtool.
It allows the cutting of multiple angles in one go.
Unfortunately i dont have the one id need to do it in one go at the moment (will shortly special order it tho) but it has the necessary 45 degree angle and 2mm width of seat i need.



This photo shows the 75 degree lower angle cutter fitted in the tool holder, it creates a transition from the throat to the bowl and short side radius on the insert fitted to the head.



This photo shows the previous multi angle cutter and a 90 degree cutter for boring out inserts or putting in a parallel cut.
Its extremely useful to open out the insert below the lower angle (75 degree) and help gain a little extra flow.



Which is what im doing here.
At this point the valve seat has been widened to the true valve seat diameter and has a width of some 2mm with the beginnings of a 60 degree lower angle showing which im not worried about at all as it will vanish when the 75 degree cutter goes in.



You can just see the cutter and the new diameter of the throat emerging.



This shot shows the completed seat, widened, lower angle recut and seat insert all bored out.
You can see the remnants of the parallel cut on the arch of the short side radius which needs to be carefully blended in.



Ill do a test shortly and see whether or not applying a 30 degree topcut to the seat will help but theres not much room to do it really, even tho the bentley manual states it has one, it aint really there on the real thing tho!

Hope this proved interesting, its just something i felt was worth sharing.

[type81]

So thats how Honda get more power from there Engines!

This is really informative Nice one

[spaarky]

crackin info - let us know how you get on with the tests !

[Coxy]

as this ladies and gentlemen, is why I get Tony to build all my engines!

[BIGGYIN]

Great,bit of kit.

[Phil Payne]

All well and good, but it's in direct contravention of Audi's quite strong recommendations:

http://www.t85q.com/WR_MB_Manual/2/15-17.jpg

http://www.t85q.com/WR_MB_Manual/2/15-18.jpg

http://www.t85q.com/WR_MB_Manual/2/15-19.jpg

(That's all about an MB engine, but the 1B's valvegear is identical.)

[Isimmo]

I'm sure they do, but you good folk will know for sure, but I thought they 'scavenged' on the first part of the inlet valves lift. this would negate any flow advantage on initial opening anyway.

[4v6]

From what i could see out of the bentley manual, the exhaust valves were specifically named as those being the ones to not be recut on the machine rather than the intake valves.
Im wondering if that was specified because the exhaust valves may be stellite coated on the seats themselves to promote a long lasting seat in the service it has to give with a turbo being in the equation?
In the light of the info supplied by Phil i cant see anything that really contravenes the data supplied.

ie: minimum reface dimension which ive checked diligently during ops otherwise the hydros can lockup, maximum seat depth cut at 9.0 and 9.2mm respectively with all mine at ~8mm, observing seat width dimensions etc.

Basically all ive done is to move out the seat diameter and applied a backcut at 30 degrees to the intake valve to gain some low lift flow.

I cant really see any cause for concern there and modifying the exhaust valves was never on the cards anyway.
I can see Phils point, but if you rigidly stick to the book it means the only ops you can do are to lap the valves in by hand and have the head skimmed to defined limits which isnt really practical.
I dont see any likely impact on seat life, thermal or mechanical operation etc being affected by what is a minor operation to gain a little flow.

[4v6]

Originally Posted by Isimmo

I'm sure they do, but you good folk will know for sure, but I thought they 'scavenged' on the first part of the inlet valves lift. this would negate any flow advantage on initial opening anyway.

Scavenging is a function of exhaust valve flow, ie clearing the cylinder of residuals, some crossflowing during overlap from intake to exhaust is bound to occur if the conditions are right.
If we gain an advantage in low lift flow upon opening the valve on the induction stroke and that it continues all the way until the valve closes, then thats something that we'd like to promote.
Full cylinders, rammed to the maximum is the aim.

[Emjay]

fascinating stuff as always but I have no idea what your talking about. However I do enjoy looking at photo's of shiny metal and man tools