Got any room to deck the block? Are they stock boss pistons? Are they oversize?

 

we have angle miled a number of different open chambered cleveland heads.

they get thin ....

the pushrod angle out of lifter can get slightly better... but it will get worse going into the rocker.


I AINT going to tell you all the little secrets...

...but you first better look at the valve relief AT DECK , in bore, that is needed to clear the valve......
many better setups have the piston cumming out of deck, A BUNCH ......
this combined with "sometimes" a angle mill will be great.


but all in all, it is still better and far easier to use the small chamber 2V head...or the normal 1970 small chamber 4 V cleveland head.



you are going to have to cut up into 4 pieces and flat mill / or angle mill a sacraficial head to find out yourself...!!!

 

Thanks for the info Kato. You said a lot!!!

I noticed that on an angle mill deal, the exhaust valve would be moved closer much to the piston than the intake valve is going to move for sure.

If I cut from ".080 to zero" for example, the ex valve is definitely going to move more than the intake valve... (.210 dome piston), and I will need to do some careful measuring. I can see a lot of clay use or sectioned chamber heads....with with an intake in one half and an exhaust in the other so I can see what is going on inside....
The plug boss also gets into the OC problem as it divides the chamber volume and the chamber area is still deeper around the intake than the exhaust...I haven't thought that through yet as far as what it might to do combustion......

So I'll stick to what I know and just straight mill .040-.050 to get the chamber size I want... I will probably end up doing a set of cc aussies for the 302 this week or the next, and this set of OC heads will probably end up on a flat top cleveland that will be around 9.5:1 on compression with the straight cut....

 

you might try section cutting a head into four chamber pieces...and then ROLL the head (pivot cut in center of chamber) to make intake port side and exhaust port side "gain and loose" the same amount.

angle milling MEANS that all the material is removed off one side of the chamber or head face...


eventually either the valve seat or the sparkoplug will get into the gasket surface.

 

a common 3.000 inch stroke...it is VERY DIFFICULT to get high (11:1) compression... if it is all done with a DOME on piston, the cam that it takes to make power will then need deep reliefs in piston to clear... so, what you thought you gained in dome ,..........probably HALF of the gain of dome volume will then be "removed" when you cut relative-needed pockets to clear the larger low lift duration cam.

dont forget that basically when you "angle mill" the head, since both valves are canted,...one valve will then need a relatively DEEPER pocket in piston....

thus,
"rolling" the head will help to "center" the amount that both valves are open at cam overlap....
this will make the depth of pockets in piston a little bit closer to each other....


is it all worth it...???
it is a lot of work and calculations...

we have done it
to try and use the larger chamber / cheaper castings... but, is it worth it... !!!!????
it is still best and easier to just use the small chamber heads....

 

i have some 12.5 to 1 forged 351C pistons dome basicly creats the closed chamber. TRW made them but there no longer avalable.

 

wrist pin height is different when you wanna use a common rod length in a 3.00 stroke / 8.200 tall deck block....than what you have in the cleveland piston.

some cleveland pin heights can be used if a stroker crank and "other" rod lengths are fitted.

 

note.

when certain pin height pistons are fitted, the issue is that the top ring will fall out/ run over the needed bore relief CUTOUT to clear the valve....because the effective "tallness" makes piston higher up into chamber.
canted valve pistons have the top ring usually lower on piston from deck than a comparative W type straight valve head type piston.

 

TRW did offer a set of 12.5 pistons for the Boss 302 that appear on Ebay from time to time that would get the OC heads to about 10.5 on the 8.2 block but they are are .400 dome and not popular....The best way for me to get 10:5 or higher is obviously with the CC heads and .210 dome pistons and a bit of milling...

I played with an OC head all day and gotta admit that I am going to straight mill this set for the other projects.....too hard on my brain....I barely think I understand the method of going at the head twice.....so it's off to get some head flow numbers from the local shop... although the angle milling might improve the angle that the intake port gets by making it more verticle...

I am hopeful that the short side radius is not destroyed but actually improved... the 2v head ports are cleaned up and bowl ported with streamlined guides..some pushrod pinch opened up--that pinch varied by the port I found...some ports better than others...#1 or #8 better than the others...

Short side radius...It appears that if NOT fixed, the stock short side radius looks like it destroys bowl flow as it cascades off the factory ledge unless you fix it....so I have eased the sharp transition by comparing it to GT40's P's, rpms, and cutting back a ways to get the roll to a point that the flow feels like it will stick.....the 65 289 head had kind of an interesting factory treatment....it had a chamfer on top of a chamfer at the int short side radius...I did not copy that but mention it.

The factory divot or depression at the intake port entry, I assume, is a low flow area, so filling it with a bit of epoxy to help the short side might not be really as helpful as it is on 4V heads, but I am thinking about filling one divot before I take it to the head shop for a reading before I start another set..the roof area seems to be pretty much limited to clean up and mild radius corners...

Since the heads reputedly stall at .550 lift, around 240cfm int flow, I figure that a solid roller cam will keep the lift where it should be with a heavy valve train around that lift figure, at 5800- 6000, which I figure is the limit for this combo...but only time will tell that....rebuilt ribbed cap 289 rods with milodon bolts and an early crank...in a mex block that miked out at 4.00-4.001 (no taper) and the NOS pistons at 3.996-97, (will be finish honed on a sunnen) before assembly and zero decked..hope to have it together by august...am going to use the edelbrock eboss manifold..

 

I have a set of Boss TRW pistons not shure of the compression they are std bore. Not shure what rods you are using I only have 3 stok boss rods left. The rods are full floating. Just mentioned the 12.5 351 C pistons in that domed ones were once avalable.