Valve angle to piston?

[Walt Fricke]

I'm having the intake pockets on my J&Es deepened for valve clearance.

At what angle are the valves in 3.2 heads?

That would be the angle of the valve stem to the axis of the cylinder, I guess. I know the RSR 2.8s used something different from the previous motors, but don't know what happened when the bore was opened up to 95mm with the SC and 3.2.

The machinist is probably OK with just using the angle already there - my measurements show the valve getting about the same distance (too close, in fact) to all sides of the valve pocket. But this information might help him.

[MBruns]

If the Je's are recent and un cut they are pretty good, be sure to set one head up with no valves and at TDC and an old valve stem sharpened to a point or a proper transfer punch find the center of the piston pocket as the valve would be aproaching it and make sure you have at least .030 - .040 all the way around the O.D. of the valve to pocket, be sure to have the head aligned by the cam tower.
In most cases they are closer than you think and need machining.

Mike Bruns

[Walt Fricke]

Mike

These were cut to begin with by J&E, then recut by a very reputable shop when I decided on wider intake valves. So I am fairly confident that the local machinist can just adjust his cutter (or whatever you guys use for this)to match the existing flat cut surface, and just machine it deeper (and then carry that width out to the new lip of the flat of the crown.

But I thought telling him that the angle is X would speed up his setup.

The side clearance (as a result of the prior widening) clayed out OK. The problem was that the cam I selected ended up with 0.012-0.015 as minimum clearance when I measured the clay. This was also exactly what the minimum was when I measured by screwing down the valve adjusters at 6 degree intervals to check clearances when I had it all put together. Exhausts were fine, over 0.080 everywhere.

One thing I learned from this is that it is tough to have pistons cut ahead of time and to expect they will work with whatever cam you later choose. Another advantage to the engine builder shops, who can tell customers they know how certain combinations will fit together because they have done all this trial and error before, and can have J&E cut it right to start with.

[MBruns]

Sounds good, its tough to zero in on a pocket depth unless you do a cookie cutter combo, we have it close but I would rather remove it as needed than to give up compression with a pocket too deep. We have our piston vise pinned to the set angles to speed it up but he can just indicate the pocket and cut away.

Mike Bruns

[Flieger]

Xtreme Cylinder Heads for Porsche

Post #8

[Walt Fricke]

Well, from that post the original 901 heads were 59 degrees included angle, with I=27 and E=32.
From Anderson, the 2.8RSR decreased the total angle to 55.75 (the post rounds that up to 56) degrees, with I=25.5 and ex=30.25.
From that post, the 3.0RSR was the same as the 2.8.
From Ludvigesn, the 930 had the same specs.

So one can guess that the 901 specs continued until the 3.0s, and the 2.8 specs continued through the end of the 3.2 era.

Still a guess. My machinist didn't seem to have an issue with using whatever angle is there. I'll see how that came out Monday.

It is tricky trying to calculate just how much this will increase combustion chamber volume. For rough purposes I just measured the width of the existing pocket, used H=0.030, and solved for cubic inches, then converted to cubic ccs.

However, pockets aren't just pockets. The crown on these pistons is flat at the top. The valve pockets aren't round, they are U shaped, with the diameter of the valve continued up to the top where the flat part begins. So you could subtract the voume of the cord subtended by where the flat (now moved upward). But you would be wrong, because the full diameter cutter is just moved up, so there are sort of triangular pieces also cut out.

So I'll have to cc this again. This time I have my tool ready:



It isn't as nice as Cgar's graduated one, but it will let me subtract whatever is above the base of the plug.

[rs-vic]

According to the parts book all cam housings from 68-77 are the same part number. I then measured the valve angles on a 2.0 head and a 2.7 head and both are identical. I got 27.5 degrees on the intakes and 32 on the exhausts. The 3.0 and 3.2 heads have smaller angles due to the wider combustion chamber and larger valves. There's a lot of conflicting information about valve angles. I'm going to try and measure some 3.0 heads sometime this week.

[rs-vic]

I got a chance to measure a 3.0 and 3.2 head. Both are right on spec.
Intake = 25.5 deg and exhaust = 30.25 deg

[VFR750]

My machinist set up the piston using the existing flat surface of the pocket. skimmed .03 off.

Reweighed the pistons and they all got lighter by the same amount! Sweet way to verify the quality of the work. 👍

[cgarr]

In the old days, Walt will remember: we would deepen the piston pockets on the Cadillac motors, take an old valve and braze some cutters on the the face of the valve, bring the piston up to tdc and with a drill and the valve installed in the head, cut the pockets in the pistons. Actually came out pretty damn nice.