OST-020: Variables

[oldeskewltoy]

My client for OST-020 sends me an email asking me for a head. He explains to me he has a specific aftermarket piston that has a STATED compression ratio of 8.6 to 1, and he his target compression ratio of 9.0 to 1. He further informs me that the block and pistons have already been machined to go together.

Now why did I title this Variables?? Well, lets look @ the variables for this build and see............


Variables:

With 39cc chamber as manufacturers specs calculate too
#1 - bore 3.189", stroke 3.031", gasket thickness .028", deck .005", piston volume -4.1cc, chamber 39cc = 9.36 static CR

Odd... isn't it...(#1) the manufacturer of this piston shows an advertised compression ratio of 8.6 to 1, but math doesn't lie... and using THEIR stated specifications... doing the math - the compression ratio isn't 8.6, but rather 9.36!


#2 - 3.224", stroke 3.031", gasket thickness .028", deck .005", piston volume -4.1cc, chamber 39cc = 9.53 static CR

THIS is my clients piston. The oversize (going from 3.189 to 3.224) is the reason for the added .17 in the final compression number.


Now... if you looked carefully you will see that they use a 39cc chamber, while the stock chamber volume on a 4AG is 36cc...

With 36cc chamber(stock volume before deshrouding)
#3 - 3.224", stroke 3.031", gasket thickness .028", deck .005", piston volume -4.1cc, chamber 36cc = 10.1 static CR

OUCH... a bit higher then my client would like....



So... now that we are working with KNOWN variables.... with 37cc deshrouded chambers, a 1.6mm gasket* and client measured deck

#4 - 3.224", stroke 3.031", gasket thickness.06299", deck 0.0", piston volume -4.1cc, chamber 37cc = 9.18 static CR

* - HKS metal 1.6mm gasket

You will note the gasket thickness has "grown" from .028" to .063"... and you might be thinking that this is a bit large for squish... and to some extent it isn't ideal, BUT it isn't bad either.... for example... a stock head gasket is .047", the stock deck on a 4AG .015"... simple math and you get .062". So for all intentions... we are using the stock squish.

So 9.18 is perfectly doable, and should yield a nice static compression ratio for a boosted 4AG.



Ok, now that the math is out of the way... we can begin the head. The client asked for a smallport head, this one was one of my inventory.



The first thing to note on this head is the massive amount of deposits in the coolant passages (below the chambers in above photo) Note the coolant passage that lead between the exhausts valves is so clogged you can't hardly see them



Now here is the same head after very thorough cleaning (including a .005" re-surface to accommodate the use of the HKS metal headgasket)... all of the coolant passages that lead up between the exhaust valves are now fully cleared and the passages themselves have had all the scale removed. This should keep this head well cooled.


All of the exhaust guides were bad and were replaced, the intake guides were all still within specification. Anytime you replace a guide you need to machine the seats to properly align the valve contact area so the valve seals, this is not a 3 angle valve job.

Interesting note... I have found more fwd heads with guide wear then rwd heads... at least so far.

This head will receive the following... matching bowls and seats, deshrouding and balancing chamber volume to 37cc, exhaust re-taper and polish, intake port blending, and roof reshaping, overall deburring and polishing cam journals, and hand lapped valves.






and this builds first multi-panel photo showing the differences in the exhaust ports from old used, to cleaned and prepped for porting.

More to come.......

[oldeskewltoy]

My, my, my, my, my............ I had a busy week, the O/S valve head (OST-017) is on its way back to its owner....

so now I can fully focus on OST-020. To rehash....

The head is in process...
FROM....

TO....


and now I begin the work on the bowls and seats



The sharp of eye will see the 4 intake bowls on the right have begun, while the 4 on the left are still untouched... as are all of the exhausts bowls


A closer view of what I'm doing inside the bowls show more than just seat to bowl blending, the outer port walls are the topic in this 2 panel... note the intrusion on both outer port walls into the port.

photo is showing 2 different chambers/sets of bowls.


If you look carefully @ the right hand bowl in the top of the above 2 panel, you can plainly see the bowl wall is FLAT. The lower view shows the bowl walls carrying the same arc as the inside of the valve seat. The guides have also been tapered back to allow for additional airflow

more to come...

[Bean]

freshly cleaned parts are best

nice work as usual

[oldeskewltoy]

Bean Bandit Wrote:freshly cleaned parts are best

nice work as usual

Thank you... got your email...


The intake side is nearly complete... I've got 3 of the 4 ports shaped, just one more to go...



The port walls were given a mild cancave, to better match the shape of the valve while the roof got re-tapered, and the "pocket" removed.




The "pocket" is the dark shadowy area in the right view where the port wall, the roof, and the guide boss all converge


So I've got 6 of 8 intake bowls and seats blended, and 3 of 4 intake ports are now shaped. Along with a good start on the exhaust bowls and seats.



Exhaust port work still to come.




Can anyone tell me why I only cut this head .005" while I cut OST-019 .015"??


More to come

[Bean]

stock valve size untouched squish areas... so no major cc increase by your work and therfore less cutting needed.

[oldeskewltoy]

Bean Bandit Wrote:stock valve size untouched squish areas... so no major cc increase by your work and therfore less cutting needed.

variables...............

from another forum Wrote:Im going to have to say, it has something to do with doing 37cc chambers vs 36cc?

and you'd be absolutely right! If you remember back to OST-019 I mentioned I was going for a 36cc chamber after deshrouding... since stock is 36cc, and deshrouding adds volume, the only way to remove volume is by cutting the head back. In this head, I'm hoping to "open" the chambers out too 37cc... so with a minimal cut, the standard chamber changes a tiny amount, and so it is easier to get to 37cc without doing major chamber work like I did in OST-017 and OST-007.


Now on to the head work... yesterday I spent a large part of the day working the exhaust ports - I got three finished. The most obvious flaw found in those three ports.... besides the typical, was this casting mis-match.




Note the shadow line in the left hand panel. That was an area, that when cast, stuck out into the air stream, the panel on right is showing just raw shaping.

Yesterday was also a first for me... I met my client, and he got a chance to see/feel the work that I've done. Since I frequently assemble the head for the client, they don't usually get a chance to feel the short radius or to see/feel the changes in the exhaust ports. In fact my whole purpose to only doing 3 intake ports and 3 exhaust ports was so that my client could see, both with his eyes, and finger tips the changes as they occurred.




I took a liberty in making the 3 panel above.... besides the crappy mixing (roughness of overall photo) what liberty did I take???


more to come....

[oldeskewltoy]

talking about 3 panels........



needless to say... exhaust side is finished......




........ more to come.....

[oldeskewltoy]

The final views of the intake ports, and the short radius.......

#1


#2


#3


#4



Valves to lap in (then back cut), chambers to deshroud, and a few goodies the client will be bringing over for final assembly


More to come......

[oldeskewltoy]

oldeskewltoy Wrote:Valves to lap in....

More to come......

speaking about lapping in valves...



How many of the exhaust seats above have been lapped in?????

Bean - give others a chance... :wink:



While you figure that out... the client dropped off those goodies I was talking about....




Supertech valve seals and keepers... and HKS valve springs.




Here is the whole thing - head, valves, springs, seals, retainers and keepers... later this week I'll get the valves back cut and then I'll de-shroud and set chamber volume to 37cc.


more to come......

[oldeskewltoy]

oldeskewltoy Wrote:Valves to lap in (then back cut), chambers to deshroud, and a few goodies the client will be bringing over for final assembly


More to come......

Well... the lapping went fine... but the same can not be said about the back cut. To make a long story short, the client now has/had a reason to purchase the Supertech valves he wanted........



The Supertech valves were then lapped into their respective seats. The above view was immediately after I checked chamber volume... all @ 37cc....



....just like the one below



You can see that the brows that normally are part of the chamber have now been blended away.

Here is a 3 panel, in this view you can see the heads transition.



Note the deshouding of the chamber from the middle view to the bottom view. Besides the chamber work, the bottom view shows the minimized valve guides, and my typical bowl work.


More to come.......