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Old 01-16-2013, 04:17 PM
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cobalt327 cobalt327 is offline
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Quote:
Originally Posted by Caballerokid View Post
Ok, so I've got a set of virgin 062 vortec heads and have about $600-$1000 worth of machine and port work set to go with Smithburg Racing and I have an opportunity to pick up a set of 186 Fuelie heads supposedly virgin castings for about $400... plus some machine work probably. I've done some digging on flow rates and such... which should I go with? By looking here Stan Weiss' - Cylinder Head Flow Data at 28 Inches of Water -- DFW / FLW Flow Files for use with Engine Simulation Software at the flow rates, the vortecs kill the fuelie heads. Also the I have a set of worked 882s on my engine currently that I am replacing but it shows the 882's don't even flow that bad. I'm now kind of stumped which way I should go with this. Either the vortec head or the fuelie head (64cc chambers) will give me roughly 11.4:1 static CR on my 360 sbc. Any help is appreciated. Thanks
Are you saying you are about to spend $600-$1000 on the Vortec's? If that's the case, don't. Aftermarket aluminum heads are the best choice to make the domes work using pump gas, unless you have E85 available. But even then, I do not trust that E85 will always be available.

Forget the 186 or any other fuelie heads. They will not work w/the compression you're going to have w/those pistons. The only reason the Vortec heads might be made to work is they're not milled and the chambers/ports are a lot better at resisting detonation- providing you keep the quench distance tight.

A couple points:

As you know, don't use a wide quench in an attempt to lower CR. That's just not how it's done, at least unless you're a hack. And you're not. Moving on...

Using less timing than best max power total timing leaves too much on the table. That is not the way to build an engine. Not saying you're even thinking along those lines, but judging by some of the things I'm reading here, it may come up as a "solution". It's NOT. As little as a -4 degree change in timing from best timing can easily cost 50 hp-plus.

Domed pistons are not generally as efficient as a flat top. They are more prone to detonation if anything, not less. If you are bound to keep them, you need a bigger chamber.

Compression w/a 64cc chamber, all else as you are now (0.040" quench, 3.5cc dome, 0.060" over 350) except the chamber size (64cc instead of 76cc) = 11.7:1 (someone needs to check their math). Way too high to even consider pump gas, even w/aluminum heads.

So either you need ~72cc-plus heads (~10.5:1 CR), or lose the domes.

Using an early style intake on an aftermarket Vortec-type head (from Vortec heads):

Quote:
Many aftermarket Vortec style heads (including Bow Tie Vortec heads) feature dual bolt patterns allowing the use of the early 12-bolt intakes. This has a very limited use.

Commonly available 12 bolt SBC dual plane intakes do not have enough metal above the port to be ported to match the Vortec port, w/o having a vacuum leak or razor thin sealing surfaces above the ports. An early intake would need at least 0.325" of material above the intake port opening to have any chance of sealing, and that doesn't take the difference in the port width/location into account. Because of the height of the Vortec intake port, only the single plane 'raised port' race intakes have enough height to actually mate to the Vortec port- but even then the ports may be too wide or have other port fitment issues.

Because of these differences, a Vortec-specific intake should be used.
A heart shaped chamber will require the piston/chamber be mocked up w/clay and the pistons relieved for clearance where needed. This will drop the CR some, but on a 64cc chamber, you have too much CR anyway. Below is a Vortec-specific domed piston for comparison to your piston. As can be seen, there's a fairly large amount of material that needs removing. The plus side is you can rework them to fit the chamber better than the dome used on the Vortec piston, and the reworking will lower the CR. Just not enough, is all.

Vortec dome piston:

Speed Pro ZH618CP60:

There's a chance that by relieving the piston dome to fit the Vortec chamber, along w/stretching the quench distance a few thou, and unshrouding/relieving the chambers using the cylinder bore and a head gasket as a template, that you might be able to get the CR down to a liveable level.

This will also take some fancy footwork when it comes to selecting the cam specs; a narrow LSA, later intake closing point and (slightly) retarded phasing. I would suggest getting w/the manufacturers w/the combo and see what they can do for you.
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