Thread: 72elk

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Originally Posted by States

So with the added cost of block work I thinking that roller rockers may not be the best choice. Having vortex heads that require self guiding narrow body rockers I'm thinking about going with the summits sbc rocker arm kit no 12495490. Any comments? I would still be going with a Howard retro fit roller cam.

If I didn't want to spend the money for Scorpions, I'd use the 12495490's. When you do the first mock-up of the motor, pay close attention to the holes in the heads where the pushrods come up through from the tappets and make sure the walls of the pushrods are not rubbing on the iron heads. There are 3 ways to center the rocker over the valve stem tip on a SBC, by using rail rockers or guide plates or the factory production holes in the heads where the pushrods come up from the tappet. You can use ONLY ONE of these methods. Using two or more will give you a headache, trust me. So, if you are using rail rockers, you have to clearance the holes in the heads and NOT use guideplates. You can use a Louis Tool as a guide to cut the holes in the heads a little or you can just get in there with a rat-tail file and enlarge the holes by hand to prevent contact.

Every good build should include making certain that the pushrods are the correct length. Here is the very best guide to accomplishing that.....
https://www.youtube.com/watch?v=o5is9BsH5OU&t=2s

Originally Posted by States

Did some shopping around and picked up a 010 block already bored 30 over and recently honed. Guy totaled his camaro and was parting it out. Came with speed pro hypereutecic H 6180 30 over pistons with stock rods and caps. Guy also threw in a Summit aluminum Cam cover and cam button. All for $280. Looks pretty clean, no ridges on cylinders. Taking to a shop next week to get checked out. This approach will delay completion of my build but will hopefully work out for the best

I'm pretty sure this is the piston you mean, H618CP......
https://www.summitracing.com/parts/s...make/chevrolet
These will do a great job in a street motor and are the correct piston compression height (1.560") to keep the stock dimensions on the factory stack of parts (9.000") Cutting the block to 9.000" and using a Fel-Pro 1003 will put the squish-quench at 0.041" and will also leave the motor ready to accept aluminum heads with a 1003. You have not mentioned aluminum heads, but that is normally the next change that a fellow will make, so I wanted to address it here.

Usually when fellows bolt on a set of aluminum heads, they use the stock block deck height ~(9.025"+) and use a thin steel shim gasket to set the squish at ~0.055"-0.065" or so (not thin enough to generate a good squish/quench). The aluminum heads and the iron block grow and shrink from hot to cold at very different rates and the material on the softer heads can be abraded (called fretting, where material is actually removed from the heads in certain places along their mating surfaces) and the head must be re-surfaced to use it on another build. This can be eliminated by doing it properly in the first place. Every aluminum cylinder head manufacturer that I know of recommends a composition material head gasket for use with their products. This allows a little "give" between the heads and the block as they heat and cool and prevents the fretting of the aluminum material. It's like bolting the head onto a cushion where it is free to move around a little without doing any damage. Pretty cool stuff, huh ? The GO-TO gasket for a SBC is the Fel-Pro 1003 that squeezes down to make a 0.041" squish/quench when used with a 9.000" block deck height and 9.000" stack. Oftentimes, fellows will find that they can drop down one or two grades in octane and still not experience detonation from their motor by following this prescription.

This is why I try to convince every hot rod engine builder that I talk to to cut the block decks for a zero deck and use the gasket thickness as the squish/quench. You'll need to work closely with your machinist though, and make absolutely certain that the heads and intake manifold will bolt together with no gaps top or bottom to make vacuum leaks. Your machinist will have formulas to get everything to fit together like a glove and not leak. The worst scenario is to put the motor together with a gap at the bottom of the head/intake manifold ports. You cannot find this vacuum leak with a combustible material such as spray ether like you can if they are gapped open on the topside, so every time an intake valve opens, that cylinder draws in oily crankcase vapors from the bottom of the ports that make the builder think that it may be rings or valve seals that is causing the motor to oil when it is actually caused by a mis-fitment between the intake manifold and heads.

GET EVERYTHING FLAT AND SQUARE IN THE FIRST PLACE AND YOU WON'T HAVE THESE PROBLEMS. WORK CLOSELY WITH YOUR MACHINIST. if your machinist won't spend time with you addressing these problems, find another machinist who will. This is too important to do in a half-azzed manner.
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