scoutcamper

Hey All,

Getting ready to build a new motor for my K5 blazer, I have a build planned out but want to make sure that the community thinks it will be a reasonable combination

Since I do not know if this block is tapped for roller or not I am going to stay Flat Tappet(I have a budget to keep!) Shooting for a pump gas 91 octane at sea level combo, 10:1 with aluminimum heads should be doable i think?

Summit Pistons SUM-17350C-00
Summit Heads: SUM-162108
RVMorseMachine Ported TBI
Port existing OEM Intake Manifold
Comp Cams K12-262-4
1.6:1 Roller Rockers

Plus having my local machine shop resurface crank/rods.

Also looking at swap to the 7427 ECM. After tuning the 7730 for a TPI build I did going to the 7747 ECM is slow and painful.


Want to validate that this cam should be easily tunable and that the combo should work well?

Thanks in advance!

Schurkey

Those pistons have old-style thick rings. At least they've got full compression height. Many aftermarket pistons are deliberately short on compression height, not only do they cheat you out of compression, but they cheat you out of quench.

I'm strongly considering ordering those same aluminum heads for my engine. Ordered EngineQuest cast-iron hybrid Vortec/TBI heads, but they had a crappy valve job, uneven valve tips, and they "forgot" to include some parts that were part of the eBay description. I sent 'em back.

I bought a core Vortec engine. This gives me a guaranteed roller-cam block to start with. I pulled the roller lifters apart for cleaning and inspection, they'll be re-used. I'll re-use the Vortec cam, too. My cylinders have about .0015 taper, so I'm not even boring it. It'll get a dingle-berry brush hone, and I'll reuse the Vortec small-dish pistons with fresh OEM low-friction 1.5mm, 1.5mm, 3mm ring pack. Crank and connecting rods are fine, no need to grind or resize. Heck, even the main bearings look beautiful. It'll get rod bearings and cam bearings, both of which appear to be in tough shape--but without damage to the journals.

That's the advantage to getting a Vortec core short-block in good condition: there's a good chance that the hard-parts will be usable; so you wouldn't have to pay to replace or recondition them. A rings-and-bearings rebuild plus cutting the decks might be all you need to do.

OEM TBI pistons have 2mm, 1.5mm, 4mm ring packs. These are 4-valve relief flat-tops as used in the Caprice.
https://www.summitracing.com/parts/slp-h597dcp
They're .010 short on compression height, you'd probably want to deck the block--but maybe you need to do that anyway.

If you have pushrod guideplates, you'll need hardened pushrods. Guideplates will destroy ordinary OEM pushrods in short order. Get the correct length--pushrods are the LAST thing you buy to complete a long-block.

My original plan was to use thin head gaskets; but that didn't work out. I just got the block back from the machine shop. I had them cut .025 off the deck surfaces so I can use a common .038--.040 head gasket and still have decent quench.

I'm going to use OEM self-guided rocker arms and no guideplates (at least for now.) I expect to use stock pushrods but one never knows until you check the rocker-to-valve contact pattern with an adjustable pushrod.

I would be suspicious of a "ported" throttle body making any better power than stock. Seems to me to be wasted effort, but I have no proof. Some work in the intake manifold could be useful. I haven't really investigated that.

I can't help with camshaft/ECM tuning.

Schurkey

Oh, yeah. I forgot.

You'll absolutely have to have hardened washers on the head bolts. The taper on the ID goes against the bolt head.

I don't have the heads yet, so I can't measure the length of bolts needed. Maybe I can use stock head bolts with hardened washers added, or maybe I have to buy aftermarket bolts that would be a little longer to allow for the thickness of the washers.

Lube the bolt head so it glides on the washer, DO NOT lube the bottom of the washer where it fits against the head.

https://www.summitracing.com/parts/afr-6320

https://www.summitracing.com/parts/man-42102

https://www.summitracing.com/parts/mrg-87