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Opel Rallier since 1977
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The cam is .504” lift, 257 degrees @ .050” duration, 112 degree lobe separation. But your grandma could drive it to church. Gotta love the big displacement engines!
Can I ask on this engine:
  • Static CR?
  • Solid cam or hydraulic?
  • Installed ICL?
Tnx.
 

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13,485 Posts
Can I ask on this engine:
  • Static CR?
  • Solid cam or hydraulic?
  • Installed ICL?
Tnx.
I only ported the head and spec’d the camshaft.

But I know it has custom forged 97 mm pistons (flat tops with two valve reliefs), 45 DCOE’s, 2.4 exhaust manifold, 2.5” exhaust system.

Figure on the chamber volume being 56 cc’s or so.

The cam is a solid lifter grind. I’m also unsure of the intake centerline, I didn't assemble it.

But it pulls like crazy.
 

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Opel Rallier since 1977
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1,710 Posts
Found this today and if you click on the specs for each cam it gives a pretty good level of detailed info. Hope it helps....


Eric
Tnx Eric. At least they list what looks like an advertised duration spec.... but it helps to know at what lift that duration is taken, which I don't see. Hydraulic or solid? IDK. No .050" lift durations. No LSA numbers but you can deduce it from the ICL (Intake CenterLine angle) and valve timing; turns out that the LSA equals the ICL number.

Notice how that ICL/LSA parameter gets smaller and smaller but the lower end of the main torque band goes higher and higher? That is where the rules that you cited don't typically work out 100% as advertised; they are not what ususally happens with how standard series cams like these get made: you don't get a narrower LSA without also getting a bigger duration in most standard series cams.

The overlap is there to create the exhaust scavenging effect, and it works well when it works, but at lower RPM's when the exhaust scavenging dies off, then the overlap works against you. Below that lower end of the main RPM range, the exhaust scavenging is crapping out and you get more and more reversion of exhaust gasses back up the intake from the large overlap and large duration, narrow LSA cam. That drops torque as you gets lower in RPM, makes for a rougher idle, and lowers fuel mileage . A very high compression ratio to helps some.... but that is what causes the rumpity-rump rough idle of a big cammed engine and the drop-off of torque.
 

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Opel Rallier since 1977
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1,710 Posts
I only ported the head and spec’d the camshaft.

But I know it has custom forged 97 mm pistons (flat tops with two valve reliefs), 45 DCOE’s, 2.4 exhaust manifold, 2.5” exhaust system.

Figure on the chamber volume being 56 cc’s or so.

The cam is a solid lifter grind. I’m also unsure of the intake centerline, I didn't assemble it.

But it pulls like crazy.
Thanks.... gotta plug that one in to the 'Brainac machine' and see what numbers pop out...LOL. Not looking like a particularly high SCR, though, without pop-ups. Lots of unanswered variables.... like rear gear ratio.
 

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Thanks.... gotta plug that one in to the 'Brainac machine' and see what numbers pop out...LOL. Not looking like a particularly high SCR, though, without pop-ups. Lots of unanswered variables.... like rear gear ratio.
Well, it’s 97 x 85 mm displacement. Flat tops mean a lot more than on a 1.9!

I had pistons with small dish on another friend’s 2.5 and it had 9.8:1 compression.

His car runs a Getrag 240 with a 3.67 LSD rear axle.
 

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Here are his pistons BTW.

Followed by the dished pistons for my father’s 2.5 turbo engine. It took a 21.3 cc dish to get down to 8.5:1 compression
428032
428033
428034
 

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Opeler
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466 Posts
Discussion Starter #108
Bob, would you happen to have a preferred technique to add or deepen valve reliefs in the tops of pistons?
 

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Bob, would you happen to have a preferred technique to add or deepen valve reliefs in the tops of pistons?
Send it to my machinist!
That’s after calculating diameter and depth needed. Angle is 23 degrees for CIH engines.

The valve notch locations are NOT symmetrical, they are off center in the cylinder to allow for the larger intake valves.
 

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Opeler
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Discussion Starter #111
Thanks Bob, I was going to base my depth based on the stock 2.4 and cam lift as a reference and then compute any delta in my setup. What method do you recommend for proper clearance calculations?
 

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Thanks Bob, I was going to base my depth based on the stock 2.4 and cam lift as a reference and then compute any delta in my setup. What method do you recommend for proper clearance calculations?
Stock cam doesn’t even really need notches. Long stroke engine helps in this matter since the piston acceleratefrom TDC faster than a short stroke engine.

Maximum valve lift really doesn’t factor in for two reasons. One: the piston is never at TDC when the valves are fully open, unless you break a timing chain. And two, valve duration/overlap are far more crucial in determining clearance.

I have a piston mocked up with the valve reliefs machined out over 3/8”deep, which I then put clay into. I use that with the head /cam combo I’m running to determine valve relief depths and locations. Bigger valves and more overlap put the notch diameters ‘further out’ than a small duration cam, as the valves are opening sooner and closing later relative to piston location.
 

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Here’s a 2.0 piston with large valve reliefs, 1.84”/1.5” valves, .435” lift, 242 @ .050” cam with 108 LSA. Head was also angle-milled .080”.

428108
I used the clay method to check clearance.

Plenty of clearance.
428109
428110


A long stroke 2.4 would have even more clearance.
 

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Opeler
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Discussion Starter #114
Pretty cool Bob. was that done with the valves set to full open and then the crank turned with the cam in the same place? I understand that the valves are not open at TDC but that would present the worse case condition, right?
 

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Pretty cool Bob. was that done with the valves set to full open and then the crank turned with the cam in the same place? I understand that the valves are not open at TDC but that would present the worse case condition, right?
That is with camshaft timed correctly relative to crank. Full lift at TDC would end up needing deeper notches than what I already had.

.435” lift, with the valves already .030” below the head surface plus expansion clearance would require notches .525” deep to create a ’non interference’ design. Trouble is, the pistons aren’t even .525” thick....
 

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Do not forget about the exhaust valve rotators being eliminated and installed spring heights on all valves.
 
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