Street porting a 1.9 big valve head

[jeff denton]

I'm not sure how much angle cut he does, I need to study up on that and ask more questions. I don't think the angle is measured in degrees, but by how much more is cut off one side than the other, thus my wonder about what that measurement comes out to (from the deck to the valve cover rail, checked on each side). His tip is ".080 angle mill" maybe that means zero on the flat side and eighty on the plug side.
Yes, the cut is heavier on the spark plug side, see how nicely that can alter compression ratio? That trick has been around a long time, works so good that it is worth fixing the problems (on a V8) it causes to the intake manifold angle. Timing changes are the issue on the Opel but it is so easy to fix, it freaks a lot of people out but they just aren't seeing how simple it is.
Of course you won't forget to dummy it all together and time it and check valve to piston clearance, you will probably need some reliefs in the pistons, there goes a tiny bit more CR.

[GTJIM]

Originally Posted by Tru-Craft Still alot of work to go, but it's roughed in. How polished should the combustion chamber be? I will polish the Exhaust ports. The intake will be rough 36#. Also after final surfacing of the head gasket surface, what edge break should I do around the combustion area? (.005-.010 rad)? Lyle

Machinist here! One of the 'traps' us line and circles guys fall into is making stuff with lines and circles .......
At the base of the combustion chamber wall there has to be a hyperbolic curve leading from the valve seat on up towards the head surface. Notice, too, the mark on the cylinder head face where the gasket edge has stained the surface - this is the line to follow with the unshrouding rather than a circular cut that is concentric to the valve.

Have a look for some of the pics of Bob's heads - 'specially the ones with the tiny 'dimples' ground into the combustion chamber surfaces that the inlet air/fuel mix impinges upon after passing through the intake valve.

Better flow will "beat" static compression ratio as better flow will increase the dynamic compression ratio - the CR that the motor actually sees when operating. So it is better to cut a bit of metal out to increase flow than to worry too much about slightly bigger combustion chamber.

The edge of the combustion chamber should be just 'broken' with a tiny chamfer or radius with care being taken to ensure it does not extend past the edge of the gasket openning. A chamfer is better than a radius as the radius tapers out further and can be harder to gauge the outer edge of it. A quick rub with a bit of fine Crocus cloth .... er! abrasive tape .... will do the job nicely as the head is quite soft cast iron.

[RallyBob]

Originally Posted by GTJIM Better flow will "beat" static compression ratio as better flow will increase the dynamic compression ratio - the CR that the motor actually sees when operating. So it is better to cut a bit of metal out to increase flow than to worry too much about slightly bigger combustion chamber.

Jim, you got that right! I've seen cranking compression changes just by increasing carburetor size! If the intake side is restricted, you can only get so much 'charge' into the engine, but with proper cam timing and balanced airflow in and out of the engine, I have seen serious cylinder pressure numbers.

How does 215 psi sound with 11.2:1 compression but a 266@ .050" duration cam? Normally with that big a cam the cranking compression goes to hell, but with the cam timing figured out and the induction feeding the engine properly, you can get strong cylinder pressures without resorting to 13:1 compression domed pistons which kill flame travel and abolutely choke down high rpm power.

I've even seen 180+ psi with a true 9.5:1 compression ratio, just by a good cam choice and cam timing setup. This is one reason I like the split-duration cams for the 1.9, it's a way to bump the cylinder pressure without resorting to high compression pistons, and you can still run pump gas.

BTW, with the 'big' Chevy valves, the added surface area of the valves will normally compensate for the unshrouding of the chamber, so you usually end up darn near your stock chamber cc's, plus you gain airflow. Which is good...

Bob

[RallyBob]

Originally Posted by Tru-Craft That's a good thought I will cc the chamber when I finish. I should have checked it before I started! I have a real accurate buret I use to check our Go-Kart motors. We use automatic trans fluid and fill it to the top of the plug hole for tech. To check the Opel head what's the best way? Lyle

Lyle, this is the way I normally do it:
http://www.opelgt.com/forums/showpos...&postcount=299
Note the head is tilted slightly upwards so the air can rise and eliminate bubbles. I use small test springs to hold the valves in place, with a touch of grease to seal them up, plus a 'real' sparkplug. I've seen some people use a bolt as a plug here, but a spark plug does have a volume inside the electrode area which affects the cc's.

[RallyBob]

Originally Posted by Tru-Craft So Bob mills the deck at an angle, with the spark plug side lower I would guess. Thats a good idea!! How much angle can we get away with before the head bolts won't go in anymore? 2-3 degrees? Will have to find that post.

I measured an Opel head that was angle-milled .085" and it changed the valve angle just over 1 degree. Not a whole lot, but it's measureable. Flat-milling is generally safer to do, and you don't need to remove a lot to clean the head up flat.

The bigger advantage to angle milling is you can reduce the cc's a LOT, but you only get half the cam timing change (.080" milled brings the cam about .040" close to the crank). So for that you'd end up with the cam about 3 or so degrees retarded. If you ordered the cam ground advanced a few degrees (which I believe you did), then you're basically home free as long as you install a new timing chain and tensioner rails. You could add a shim on the hydraulic tensionser, but it's probably redundant with that little milling, I usually only add a tensioner extension when I flat-mill .080" or more.
Another benefit to the angle milling is the valve angle changes one degree, which is advantageous for airflow into the cylinder, and the intake manifold tilts a bit more upwards, especially on a GT.

[Tru-Craft]

Originally Posted by GTJIM Machinist here! One of the 'traps' us line and circles guys fall into is making stuff with lines and circles ....... Notice, too, the mark on the cylinder head face where the gasket edge has stained the surface - this is the line to follow with the unshrouding rather than a circular cut that is concentric to the valve.

Jim yep, we machinist's think round and square!!
What I did to un-shroud roughly, was to bore concentric with the valve to within .030" of the gasket scribe mark. Then I moved the mill about a 1/8 toward the plug hole and bored again. I bored 4 arcs this way, this formed the rough parabolic arc you mentioned. I will grind it by hand to blend the arcs into a smooth flow. Hopefully.

The race motor shop that Im working with also said to keep compression to about 9.5:1 and that un-shrouding and flow is more important than high compression for a street car.

Will break edge like you suggested.
Thanks Lyle

[Tru-Craft]

Originally Posted by RallyBob The bigger advantage to angle milling is you can reduce the cc's a LOT, but you only get half the cam timing change (.080" milled brings the cam about .040" close to the crank). So for that you'd end up with the cam about 3 or so degrees retarded. If you ordered the cam ground advanced a few degrees (which I believe you did), then you're basically home free as long as you install a new timing chain and tensioner rails. You could add a shim on the hydraulic tensionser, but it's probably redundant with that little milling, I usually only add a tensioner extension when I flat-mill .080" or more. Another benefit to the angle milling is the valve angle changes one degree, which is advantageous for airflow into the cylinder, and the intake manifold tilts a bit more upwards, especially on a GT.

My head measures 4.055 to 4.060" from deck to valve cover surface, is this stock or has it already been milled?
The head deck is about 5-1/4" wide, so it trigs out to a little less than one degree as you say.
So I will tip my mill head about .87 degrees and angle cut the deck after porting and final valve seat work is completed.
Yep, cam will be ground with 3-4 degree advance.
Will check cc's as you show.
If I get 52.0cc's chamber volume.
head gasket = about .34 cc's
Bore/stroke volume = 498cc's
Compression would be about 9.5:1
Everyone thanks for helping me. I don't do automotive machining, but have found it challenging and fun.
Lyle

[nobody]

The gains you get from porting out the combustion chamber are only effective at high RPM. The other side of it is a loss of low end torque and a problem fitting pistons to get your compression back. In my opinion you break the edges of the combustion chamber after the intake and exhaust is ported. Leave the deck height alone and buy pistons suited for the horsepower range your trying to get to. Or you can spend twice the money and have more time into it for the same outcome. Me personally, I like the idea of buying a stock part and having it fit rather than every part having to be machined before it can be used.

I keep motor design simple so if it breaks it's easily replaced.

[Hiro]

Originally Posted by nobody I keep motor design simple so if it breaks it's easily replaced.

I agree specially for street CIH,
Race CIH is another story,
Each type of engine deserves its own labor!
Hiro

[Tru-Craft]

Originally Posted by nobody The gains you get from porting out the combustion chamber are only effective at high RPM. The other side of it is a loss of low end torque and a problem fitting pistons to get your compression back. In my opinion you break the edges of the combustion chamber after the intake and exhaust is ported. Leave the deck height alone and buy pistons suited for the horsepower range your trying to get to. Or you can spend twice the money and have more time into it for the same outcome. Me personally, I like the idea of buying a stock part and having it fit rather than every part having to be machined before it can be used. I keep motor design simple so if it breaks it's easily replaced.

I agree stock parts are the best and cheap! I have pretty much stock Chevy everything. For me the machining is kind of free and fun.
This Opel motor has been through alot of machining over the years, mostly not right! But it can be saved.
The block is staying as is for now. It was built about 15 years ago by me, it has 3.75 forged Chevy pistons, everything balanced and has performed fine.
The head is the problem! It has 1.75 intake/1.625 exhaust valves, ported to the max, wrong springs, wrong cam......hey, I had no clue, was reading Chevy race books and built it my way! It ran pretty well!
So now I have another head, and some time for my Opel. This time I want to build a bolt on performance head that will be much better.
Porting will be a challenge, but I have better info and even pictures now.
Im kind of like the guy who painted his car with a spray can, it looks like sh... but he's so proud that he did himself!
So keep sending ideas, so my car doesn't run like sh..!
Im listening!!!
Thanks
Lyle

[Paul]

Lyle,

According to an old post by Bob (Rally), he stated that the stock Opel pistons were typically located .004" to .007" below deck. His recommendation is .005 above deck. According to these numbers you are only looking to deck the block .009" to .012". Thats not enough to hurt anything by decking this small amount. However, removing .010 from the block will raise the compression more than taking .010 from the head.

I say follow Bob's advice and suggestions to get the most results from your efforts. Deck that Block!

Good luck and keep the pictures coming!!!!!!!

[azopelnut]

Originally Posted by RallyBob This is one reason I like the split-duration cams for the 1.9, it's a way to bump the cylinder pressure without resorting to high compression pistons, and you can still run pump gas. Bob

Bob
As an owner of four Opels with dish pistons I would like to here more about split-duration cams, or when you say high compression pistons are you referring to pistons other than flat tops

[Tru-Craft]

Originally Posted by Paul Lyle, According to an old post by Bob (Rally), he stated that the stock Opel pistons were typically located .004" to .007" below deck. His recommendation is .005 above deck. According to these numbers you are only looking to deck the block .009" to .012". Thats not enough to hurt anything by decking this small amount. However, removing .010 from the block will raise the compression more than taking .010 from the head. I say follow Bob's advice and suggestions to get the most results from your efforts. Deck that Block! Good luck and keep the pictures coming!!!!!!!

Thanks Paul, the block is not being re-worked at this time, just pulling the head. The car is still being driven, so I want to just swap the heads and be back on the road in a week or so.
The block was redone (15 years ago) with Chevy pistons and deck machined to let pistons protrude about (.003).
I will follow Bob's blueprint for the head, with added tips from many others!
Should be a big improvement.
The head plan:
Chevy S.S proflow 1.80 intake valves, 1.50 exhaust valves.
Bronze guides, hardened exhaust seats.
Un-shrouded combustion chamber.
Valve guides milled lower (about .200) to match valve under cuts.
Ported and polished ( per Bob).
All sharp edges in the combustion chamber slightly chamfered.
Mill head deck at an angle ( 0 to .080" ).
Titanium spring retainers and keepers.
Head cut for 1-1/4 dia springs, not sure what type yet?
Head cut for Chevy type valve seals. Teflon?
New solid lifters, rocker studs.
Cam from (Cam Techniques) Split profile.
Topped off with a set of Roller Rockers and torque girdle from Gregg.
HP increase?????
Lyle

[Tru-Craft]

Oh, another question.
I have to check the piston to valve head clearance.
Best way?

Also, if I do have to cut the piston top for valve clearance, I was thinking of using old Chevy valves then grinding cutting notches in the heads.
Then install these "Valve cutters" in the head, mount the head on the block and cut the piston notches with a drill motor!?? Remember I'm not pulling the block, so I will have to do this on the car!
Any other ideas?
Lyle

[Travis]

Lyle,

As long as the valve(cutter) is oversized, you may be able to make it work. Or, you could purchase a tool intended for this purpose.

http://www.iskycams.com/pdfcatalog/2004-05/page17.pdf

-Travis

[Travis]

Checking the underside of the valve is easy. Basically assemble the motor with soft valve springs and check the clearance by pressing the valve or rocker by hand. You can measure with with a dial indicator on the rocker above the valve or on the edge of the lifter(don't forget to compensate for rocker ratio). If you don't have a dial indicator, though I expect you do, you can place a shim between the valve and rocker. You'll want to do this test every few degrees on either side of TDC. I'll be obvious when it's OK to stop.

The side clearance is a bit more of a PITA. It usually involves placing clay or similar on the piston, rotating the motor and measuring the thickness of the clay after disassembly. This will also tell you the clearance under the head...

You could also install an oversized valve and only perform the first test.

-Travis

[Paul]

Lyle,

In another old post Bob gave part numbers of springs and seals he perfered. The Seals he recommended are Viton and require less precise machining than teflon. If you can't find it be searching, I have a hard copy somewhere.

Wait here it is.....
1.85" Intake Cutdown from 1.94" Manley #11522
1.50" Exhaust Manley # 11521
Titanium Retainers Crower # 86031
Springs Inner & Outer Crower # 68106 & # 68208
Keepers Crower #86107
Viton Positive Valve Seals VSI #45341
Valve Guides Chevy .503 OD x 2.375 Long

Piston to valve clearance... modeling clay on the piston tops and an old gasket works well as Travis indicated... just pull the head back off and check the clay...
Exhaust .100" min
Intake .080" min

What else?

[Tru-Craft]

Originally Posted by Paul Lyle, In another old post Bob gave part numbers of springs and seals he perfered. Titanium Retainers Crower # 86031 Springs Inner & Outer Crower # 68106 & # 68208 Keepers Crower #86107 Viton Positive Valve Seals VSI #45341 Piston to valve clearance... modeling clay on the piston tops and an old gasket works well as Travis indicated... just pull the head back off and check the clay... Exhaust .100" min Intake .080" min What else?

Thanks great info, the pieces of the puzzle are coming together!
OK, lets go over the clay method with a little more detail.
I put clay on one piston and bring it to TDC.
Then I put the head and gasket on the block, not bolted down.
Then I open the valves to match the cam lift.
Remove head and check the clay thickness. Correct?

Here is my thought, when the piston is at TDC of the intake stroke the intake valve is not at max lift yet. Why should I cut the piston to clear max valve lift plus (.080 to .100)?
The same with the exhaust stroke, the piston is coming up, exhaust valve is open, as the piston gets near TDC the valve is almost closed.

Or should I install the head completely together, not bolted down. Then install the cam sprocket and chain, rotate the crank through 2 complete turns and then measure the clay?
The less material I remove from the piston the higher my compression will be!
Any thoughts?
Lyle

[jeff denton]

Yes, you aren't making the valve clear the piston at full lift, when the piston is at TDC the valves are moving, but aren't gonna be wide open. The exhaust is closing and the intake is opening, they are in the overlap phase. To me it makes sense to do the clay impression part by running the engine through the strokes and let the camshaft work the valves. I'd have the valves set at zero lash. And it seems it would be safest to give it all some timing leeway, by doing this with the cam advanced one tooth (9 degrees), straight up, and retarded one tooth. Just to make sure. You'll be using solid lifters, but if you weren't, a solid lifter used in place of the hydraulic one would be a good idea in this process.
Since you're using Chevy pistons, I'm speculating that there is just no way the valve notches in the pistons are going to just happen to fit the Opel head/valve specs. I think this step we are discussing is gonna be very important to do.
Hey, I don't suppose you machinist experts have any way to deck the block without stripping it down bare, do you?
I didn't think so, surprise me, OK?

[asdasc]

There is a lot of talk about decking the block, a quick question I have is that in order to do this, I assume you need to remove the 2 studs on the top of the block that align the head. How do you get those out? Can they be reused? Or will I need to order new ones?

Thanks!