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68WASAGOODYEAR 04-29-2019 07:43 PM

1968 Impala Repower Thread
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Hello all,
Attached is a pic of Gloria. She'll be getting a 496 stroker, T56 Magnum, and a 3.73 posi here in the next few weeks. My plan is to install the engine & trans myself and then take it to a local guy for the rear axle work when I have her running. The T56 will require some fab work (trans tunnel & crossmember) which I also plan to do myself. I thought I would start a thread so I can ask dumb questions as well as post pics and updates which may help someone else in their future build. Thanks in advance for any replies.

68WASAGOODYEAR 04-29-2019 07:47 PM

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Aaaand we're off. Has anyone ever run the coolant bypasses on the back sides of the intake up to the crossover in front? The directions say this results in better cooling performance but I can't find much online...

Big Dave 04-30-2019 09:08 AM

Cheap way is four hose barbs and a length of three quarter inch rubber heater hose. Expensive way is a bunch of AN-10 fittings (at ten bucks or more each), and size ten stainless steel braided hose.

Four elbows at $17 each:

Four 3/8th male NPT to AN10 adapter ($5 ea):

Six Feet of -10 braided stainless steel hose (at $22 for 3'):

Big Dave

68WASAGOODYEAR 04-30-2019 09:48 AM

Thanks for the reply and links Dave. My concern is that this would eliminate the ports in the intake I could easily use for the two temp sensors I need to install (Holley EFI and Dakota Digital). I guess I'll have to see what, if any, coolant ports I can tap into in the block /heads. Two more weeks until I have the engine in from of me.

Big Dave 04-30-2019 10:04 AM

BBC heads do not have temp sensor holes. You have one in the intake and if you use a 1979-'86 and up thermostat housing you get a second temp port.

Big Dave

68WASAGOODYEAR 04-30-2019 12:39 PM

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Thanks Dave. I think this might be the ticket. Will allow me to plumb forward to the crossover via the NPT ports on the spacer and have the two ports in the crossover used for the temp sensors. Exactly as shown:

BA. 04-30-2019 12:52 PM

You've got some serious big plans for the ol' girl! Will be interesting to keep checking in on your progress.

68WASAGOODYEAR 05-07-2019 12:20 PM

A few questions regarding grounds: I want to ensure the new engine is properly grounded.

The water pump is powder coated chevy orange and I will be grounding the battery to it per the original cable routing. Do I need to grind off the powder coating from the pump where it attaches to the block?

I've also got an original ground strap kit from American Autowire. The ones that attach at the valve cover fasteners - do I need to grind the chrome off the valve covers (steel under the chrome)?

Thanks for any replies. The T56 is being delivered today. Will post a pic or two.

Big Dave 05-07-2019 12:49 PM

Chrome and steel (all metals) conduct electricity to one degree or another (there is a table in my Engineering manuals that lists the conductivity of metals (Silver, Copper, Gold, Aluminum, Zinc, Nickel, Brass, Bronze, Iron, Platinum, Steel, Lead, Stainless Steel, etc. for every known alloy, or elemental particle). Your plastic covered water pump is a different story. Plastic is an insulator (why your wires are covered in colored PVC plastic).

You can grind it off, or relocate the cable to a different grounding point like the intake manifold.

Big Dave

68WASAGOODYEAR 05-07-2019 01:34 PM

Thanks Dave. May look into grounding to the intake then.

68WASAGOODYEAR 05-08-2019 08:43 AM

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Got this delivered at 9:30 pm last night by FedEx freight. Neighbors probably weren't too happy about it. Oh well.

68WASAGOODYEAR 05-10-2019 10:17 PM

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I'm trying to drill and tap my intake for the 5/8 line from the heater core. I drilled the correct 45/64" pilot hole and I have a 1/2-14 NPT tap, but the pic shows the furthest I can get the damn thing to go. The black mark on the tap is how far it needs to go. Any tips here? I don't want to crack a $400 intake trying to do this. Thanks for any replies.

Edited to add: I have not been using any kind of lubricant or tap wrench. Wonder if these would help...

Big Dave 05-11-2019 02:37 AM

You must use lube and a proper tool to apply torque. Cut in stages backing it out frequently to clear the tap threads of cut material.

Question I have is are you bottoming out the tap? (does it have a taper or a flat bottom?)

Big Dave

68WASAGOODYEAR 05-11-2019 07:14 AM

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Dave, it is a tapered tap. See pic. Thanks again.

ETA: I bought a 19" trap wrench and cutting lube off Amazon. Will update Monday.

Big Dave 05-11-2019 07:27 AM

Look in hole for marks indicating the tap is hitting back wall of water passage. If clean keep threading in tap with oil on threads. If you are hitting then you need a bottom tap. It will have a flat bottom with full threads from the bottom tip up, like a big screw only having the flutes to hold the material you cut while threading the hole.

Big Dave

68WASAGOODYEAR 05-12-2019 10:15 AM

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Dave, the boss on the intake I'm tapping is at least 1" thick and I'm at most maybe 1/3 of the way thru it. Not bottoming out for sure.

I got this bugger installed in the meantime. Clutch master cylinder. Had to remove the wiper motor and brake booster / master cylinder to make room. Also installed the pedal linkage. I'm hoping this was the worst part.

68WASAGOODYEAR 05-17-2019 02:47 PM

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Someone make me feel better about taking the hoist off! Being an engineer, I'm very aware of moments, and this looks like a big one. Hard to believe that dinky engine stand will hold it...

Big Dave 05-17-2019 03:24 PM

With aluminum heads and intake and water pump your BBC weighs the same as an all cast Iron small block. So yes that engine stand will hold it up. Whether you can rotate it freely to work on it; well ... that would be questionable. Other issue is with the trangular legs and it being very top heavy (center of gravity very close to the edge of the base; well as you studied in engineering I would be very cautious pushing it around the shop). Any thing that gets stuck under a wheel and it will probably flip over (with a leg rising rapidly off the floor following an arc that could hook you if you are standing near it).

Engine stands are rated by weight (same as jacks and cranes). A good engineer always has a 50% safety factor in mind so a 630 pound BBC like you have probably needs an engine stand rated for a thousand pounds (945 pound load with safety factor). It is why I had in my shop a seven ton floor jack and a five ton engine crane (that and I liked the air over hydraulic cylinder), and all four of my engine stands had four legs rated at a thousand pounds with my favorite having a gear head to rotate the engine.

Big Dave

68WASAGOODYEAR 05-17-2019 05:13 PM

Its a 1000 lb stand that is brand new and has 4.5/5 stars on Summit. Should be fine.

68WASAGOODYEAR 05-18-2019 08:03 AM

PCV plumbing idea

Plumb both PCVs to this:

Route the clean air back to a vacuum fitting on the Holley and plumb the oil drain to a hose - barb fitting I would install in the mechanical fuel pump block - off.

Big Dave 05-18-2019 10:05 AM


Originally Posted by 68WASAGOODYEAR (Post 224060)
PCV plumbing idea

Plumb both PCVs to this:

Route the clean air back to a vacuum fitting on the Holley and plumb the oil drain to a hose - barb fitting I would install in the mechanical fuel pump block - off.

PCV is a thermal plastic. It isn't used on water heaters because it turns soft at 170° degrees and start st flow at 220° degrees. Coolant and engine oil exceed this temp easily.

I used to order custom plumbing from a company in Clearwater, FL that bent PCV pipe to order by immersing the pipe (capped at both ends and filled with compressed air) in a long thin tank of hot cooking oil, and then pulling it out and putting it on a wooden table with hundreds of holes in it to hold pins and cylinders of different diameters. Once bent around the rollers it was sprayed with cold water and the ends cut off. Voilą a custom bent pipe to fit a complex device we were building.

68WASAGOODYEAR 05-19-2019 12:16 PM

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Installing the intake manifold. I have extra fasteners, which set off alarm bells. Holes 5,10,11, & 16 on the intake torque sequence diagram (see attached images) do not have matching threaded holes in the Dart Pro 1 heads. Is this normal? Thanks for any replies.

Big Dave 05-19-2019 03:43 PM

If you had a SBC I could understand it, due to the difference between an early SBC head and the Vortec head. But that doesn't apply to a BBC. Every Dart head I have ever seen was fully machined for installation of an intake manifold.

Only difference in a BBC manifold is between a tall deck manifold and a standard height manifold (a bit more than three eighths inch difference in bolt spacings). A tall deck is too wide to fit between the heads of a standard deck height (kind of what you are experiencing).

Big Dave

68WASAGOODYEAR 05-20-2019 10:29 AM

Confirmed with the manufacturer that this is not an issue.

For new engines, is it common to use some quantity of ATF fluid mixed with the oil?

Big Dave 05-20-2019 12:50 PM


Originally Posted by 68WASAGOODYEAR (Post 224116)
For new engines, is it common to use some quantity of ATF fluid mixed with the oil?


ATF is 10 weight hydraulic oil. You can run 10 weight motor oil in an engine but it will be subject to ambient air temps as it can become too thin to pump at high temperatures.

I run 10W30 high Zinc/Phosphate motor oil with GM EOS for break in and off the shelf motor oil afterwards as I run only roller lifters. If you run the cheaper to buy initially flat tappet cam then you must run high Zinc/Phosphate motor oil all of the time or risk loosing an engine.

Big Dave

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