1.6 roller rockers with stock cam?

[Supercharged111]

Felpro changed the coating recently from black to clear but the last set was definately coated when I ran my finger across them. Looks like they are 0.015" compressed now too. Some people copper coat them, but if the deck surface and head face is clean, not badly pitted and straight, I bolt them down and go. Worth a slight bump in compression.

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Thank you!

 

[Schurkey]

The "blueprint" spec for block deck height is 9.025". The pistons should sit .025 in the hole, with a total height of 9" from the main journals. Take that .025 "in the hole", add a .015 head gasket, and the pistons have a .040 quench distance. Nearly perfect.

In fact, the pistons are more-likely to be .027--.030 in the hole, and GM is using a .028 gasket while the aftermarket pushes .040 gaskets. That makes the quench distance around .055, maybe greater. Not so perfect. Tighen up the quench from stock, gain compression, reduce "ping" or "spark knock". Engine makes more power with fewer problems and better fuel economy.

I wanted to use those elastomer-coated steel shim gaskets on my K1500; but the bore size was too small for the width of the combustion chambers on the aftermarket heads I selected. Cost me extra to get the block machined extra to make up for the thicker gaskets I had to use due to the combustion chamber width.

 

[Supercharged111]

In fact, the pistons are more-likely to be .027--.030 in the hole, and GM is using a .028 gasket while the aftermarket pushes .040 gaskets. That makes the quench distance around .055, maybe greater. Not so perfect. Tighen up the quench from stock, gain compression, reduce "ping" or "spark knock". Engine makes more power with fewer problems and better fuel economy.

My 1500 has those dumb .040" gaskets. I didn't know they were thicker than stock until I put them on. I'm itching to do the heads on it and something thinner is going back on to increase the knock threshold.

 

[Frank Enstein]

Yup--first generation Twisted Wedge, not "Gen II". I have a pair on my 'Camino, a pair on the K1500, and another pair "new in the box" that will likely go onto the '77 Nova.

They first-generation TW take a "special" intake rocker arm even though they're advertised as using "stock" rockers. Since I had to buy special rockers for the intakes, I got the comparable set for the exhausts, too.

They're a great entry-level aluminum head. Some have had machining problems that caused rapid valve guide wear; but I haven't noticed that on mine. I think the revised geometry of the "special" rocker arms help.

1st gen 13 degree intake angle. 2nd gen 15 degree intake angle. They lost a bit of flow but the pushrod lengths/rockers were easier to get right.

The twisted wedge had better low and mid lift flow numbers than the 23 degree heads that took their place.

One trick to get the rockers to play nice on the first gen heads is to eliminate the guide plates and use self-aligning rockers.

Also don't be surprised if the intake pushrod and exhaust pushrod are different lengths for the first gen heads.

 

[Schurkey]

I tried to set pushrod length using "ordinary" roller rockers a thousand years ago when I bought my first pair. I was entirely unable to get a good pattern on the intake valve tips no matter where the adjustable pushrod was set.

Called Comp Cams, they knew immediately what the problem was. They had--and still have--four part numbers for intake rocker arms (1.5, 1.6 ratio, 3/8 and 7/16 stud) to fit these goofy Gen 1 heads. Once the special intake rockers showed up, stock pushrod length worked just fine on intake and exhaust.

 

[Supercharged111]

I tried to set pushrod length using "ordinary" roller rockers a thousand years ago when I bought my first pair. I was entirely unable to get a good pattern on the intake valve tips no matter where the adjustable pushrod was set.

Called Comp Cams, they knew immediately what the problem was. They had--and still have--four part numbers for intake rocker arms (1.5, 1.6 ratio, 3/8 and 7/16 stud) to fit these goofy Gen 1 heads. Once the special intake rockers showed up, stock pushrod length worked just fine on intake and exhaust.

And some crappy rockers are just impossible to get a good pattern period. I think it has to do with the height of the pushrod cup and the rocker tip because the ratio itself is just math.

 

[Hipster]

There much more to it then the vale tip pattern, sometimes it can be where the studs and valve guide holes are located. If the fulcrum is too high or low it can effect performance

This is Mopar related but much of the technical aspect pertains to all engines. It's a really good read for anybody trying to gain a better understanding of valvetrain geometry and that there is more to it then just pushrod length.

B3 Racing Engines LLC - Mopar Rocker Arm Geometry Tech

www.b3racingengines.com