390 Rebuild Options

[jingo]

Last oil change found coolant in the pan, bad day. Looking for upgrade suggestions, since I've got to tear it down to fix it...

Existing layout is stock C6, 9" 3.25 axle, medium aluminum riser to generic Edelbrok quad (450 cfm?), electronic igtn, hooker headers, flow masters, 2.5" pipes, Biltstein's, standard tire, stock height. Use is a daily driver, but would like to have some fun too. I guess if I'm going to suck 10 or 12 mpg, I'd like some more bang for the block.

What should I be looking at?

[tnlprt]

Depends on your budget

390engine_004.jpg

[jingo]

True enough. Its a little hard to say what my budget will be for improvements until I find out how much damage and $$$ I need just to get running again. I just pulled the engine yesterday and it will be another week or so before I have those facts. I was hoping to generate some ideas in the meanwhile.

Working back to front, let's assume a full stock rebuild to crate level is somewhere around $2500 - $3000. Let's also assume that 1) head gasket failed, 2) I caught it pretty quick, 3) no overheating or secondary issues, didn't tear up the bearings, etc. I guess somewhere between a full rebuild and just replacing a head gasket is where my upgrade budget sits. More damage and $$$ for base repair, then fewer/no upgrades, and vice versa. That's how I was thinking about it, does that help?

In order of increasing cost, what would be first option, next, and so on? I gather a cam upgrade is useful and relatively inexpensive. Is this a good place to start, what are the options? What would be the next on the list, progressively more costly?

Thanks for helping me get some perspective and any advice you can share.

[tnlprt]

upgrades I would do

Performer RPM intake
650 carb
Headers
2.5 inch dual exhaust
recurve the ignition
10.5 to 1 compression with 93 octane fuel
comp 268H cam
3.50 or 3.70 gears depending on tire diameter and driving habits

[jingo]

@tnlprt - From your list the PO had already installed...

Edelbrock Performer RPM intake, matched to a 1407 4bbl 750CFM carb (manual choke)
Hooker Competition headers, 2.5" dual exhaust (Flowmaster 40's)

I'm afraid these are the only options from your list I have any experience with, so I'll ask some dumb questions on the rest. Hopefully you or others can provide some simple explanations...

Ignition - the PO also replaced points with electronic ignition under the distributor cap (Pertronix?) and a Super Stack coil. Are these components capable of advance timing? Is the advance a one-time process, or will it need to be tweaked, for instance based on extreme weather (sub-freezing to baking hot) or altitude (coastal vs mountain)? Will it run great in the summer but ping in the winter? What do you think is the ideal coil and distributor setup for ignition advance? Mechanical? Vacuum? Both?

Compression - Isn't this a function of piston height, piston rods, cam, and stroke? Did you mean for this to be the result of the other options or standalone? Not sure I want to pay the premium on gas without a significant increase in mileage and performance both. Aren't they mutually exclusive?

Cam - From what I can gather, the 268H cam is pretty aggressive and will have an impact on other components, for instance stall speed in the C6. I don't think I want a super choppy idle or to stall in gear at a stoplight. And I kind of like the 500 RPM rumble I already have. Are there other choices that will get me better acceleration and response without sacrificing a relatively smooth idle.

Axle ratio - I'm running standard 15" tires on 9" vintage Crager rims. With the current 3.25 ratio I get 60MPH at 2700 RPM. I mostly drive around town, not highway. What is the best, most cost effective option for changing the ratio? Replace the whole rear end with salvage/donor parts, rebuild the gears only, etc?

Lastly, since I had to pull the engine, I'm sending the tranny out too...its a little cranky until it warms up, especially in the winter cold, so I'm going to break it down to check seals etc. Are there some options - belts, pistons, torque converter - that make sense for a stock C6, especially in combination with some of these other engine options?

Sorry for the long note, but it seems like there's alot of moving parts here (pardon the pun) and I'm guessing the choices are somewhat dependent on one and other.

Thanks!

[Manny]

upgrades I would do

Performer RPM intake
650 carb
Headers
2.5 inch dual exhaust
recurve the ignition
10.5 to 1 compression with 93 octane fuel
comp 268H cam
3.50 or 3.70 gears depending on tire diameter and driving habits

That's a pretty tough to beat combo. I would say 650 Holley carb as that's my preference. When you pick your cam call comp talk to them tell them what you want they can help you greatly. Tunnel port you got a converter behind that one to speak of or stock?

[tnlprt]

upgrades I would do

Performer RPM intake
650 carb
Headers
2.5 inch dual exhaust
recurve the ignition
10.5 to 1 compression with 93 octane fuel
comp 268H cam
3.50 or 3.70 gears depending on tire diameter and driving habits

That's a pretty tough to beat combo. I would say 650 Holley carb as that's my preference. When you pick your cam call comp talk to them tell them what you want they can help you greatly. Tunnel port you got a converter behind that one to speak of or stock?

That combo should work with a stock convertor

I run a lot more engine than that in my short bed
4.25 bore 3.98 stroke 451CI
2.19 1.71 valves
.674/.308 solid roller
Victor intake
850 race demon
3500 stall
3.50 gears

390engine_004.jpg

[Manny]

Pretty serious Fe. I wanted to build a torque 410. However when a five speed zf showed up for free. Then a dove 429 for $400.00 i kinda am going a different way. Love your build!

[jingo]

Manny, what was your build plan for the 410, a 428 crank? That’s interesting to me, thanks for any details you can share.

[jingo]

My engine is now torn down, but no obvious source for the oil coolant mix. Engine had a full rebuild .020 over when I got it, less than 5k miles ago. Shop says cross hatch still fresh, gaskets good, pistons/valves good, pressure test good. The only anomaly was the bolts “didn’t feel right” when the intake manifold was removed. Best guess is the PO installed the intake (Performer RPM) at home after the engine came back and screwed it up somehow, creating a coolant leak. Is there a common “gotcha” for an FE intake install that the P.O. missed?

Didn’t hear back from Manny, but after reading many posts here, DIY, 54, FTE, etc, I’m landing on a budget 410 stroker as a good fit for a high torque, low RPM street engine. I want to keep CR in the 9.5 range for pump gas, but the only affordable piston I can find is the KB silvolite dish (KB 3193-20). I would appreciate if someone can check my math.

With a 428 crank (Eagle?), a 3.98 stroke at .020 over gives me 848cc. On a stock 10.17 deck the piston will be .032 in the hole (6.8cc), with four valve reliefs (8cc), compressed .039 gasket/4.4 bore (1.4cc), 2.62x.075 dish (6.6cc), and 68cc head chamber totals 99cc compressed volume. So (848+99)/99 gives a static CR of 9.55:1

That would be great except for all the posts that say quench should be in the .040-.060 range. I’d be at .071 (.039+.032). Squaring up the deck by .010, or a .027 metal gasket could help, but a 1.67 piston would be better. Unfortunately the only other piston options for a 4.07 bore are custom or race gear. Which sort of defeats the whole budget angle ...crank plus pistons on this build are less than $600.

Thanks for any thoughts or suggestions!

[jingo]

So the build is done and going on the dyno this week.

By design this was a pretty mild build compared to other suggestions above. I wanted a relatively low RPM, long-life, high torque motor, quick off the line, for a daily driver around town. Not much highway use around here.

Went with a new rotating assembly using the Eagle 428 crank, paired with a XE256H cam and MSD RTR distributor. Bored the block to .030 over and added ‘410’ style 381NP30 dish pistons. Kept the stock 390 piston rods, valve stems, 68cc heads, as well as the Edelbrock RPM Performer intake, 750cfm carb, Hooker Competition headers, and 2.5” Flowmaster 40 dual exhaust from the PO’s old build.

The heads and block were honed, and the new crank was balanced both at the flywheel and also shaved a smidge on a couple lobes internally. The only ‘surprise’ machine work was line honing the crank. Clearance was .0001 out of the box, a little too tight I’m told (?), took it to .0002 I believe.

Used Cometic .051 SS gaskets...with the longer stroke and shorter pistons yields an SCR around 9.6, which should keep me in pump gas. Ideally I’d like to make all my HP at or below 4800 RPM, max torque around 2800 RPM. I believe this was spec for the ‘66-67 410 (Fairlane), the closest fit to my build, although CR was supposedly around 10.5.

I’d really like to get the most out of my dyno time. Can anyone tell me how much advance, mechanical/vacuum, I should set up initially? Other than the cam sheet, is there a ‘best practice’ to tweak my setup between pulls to get the engine tuned up right, before I put it back in the truck?

Thanks for any suggestions...dyno data to follow for anyone interested in a street tame 416 build. Hoping for 400HP and 450+ lbs torque when the dust settles.

-Jack

[jingo]

Final Build Data - 416FE stroker

428 crank, XE256H cam, .030 over, NP381 pistons, RPM intake, 750 CFM 4bbl, MSD All-in-One, Hooker Comp Headers, 2.5" dual exhaust -

336 HP @4600 RPM (*Net)
455 ft-lbs @2800 RPM
Timing @34 deg, all in

SCR 9.7:1, 190 psi in all cylinders

My pump gas, stump puller. Perfect for hauling the camper on grades, or popping around town on the flats.

Thanks for all the advice, hoping to be on the road again next week.

[8ton]

Looks good to me! It will be interesting to see what the mileage is.
Did you do any work to the heads and are they stock c8aeh?
What squish did you end up with?

[jingo]

Not sure mileage will be 'interesting', more like 'depressing'.
Hoping for 12 or 13mpg if I baby it unloaded <50mph...highway/loaded/towing/goofing off, probably no better than 10.

Stock heads, no port work, measured 68cc. Simple budget choice, rotating assembly or new heads, not both.
I put the money into replacing the rotating assembly, crank to cam, to get more torque on lower RPM and long life.

Squish/quench sucks, another trade-off to keep SCR less than 10:1, used .051 SS gaskets. After decking the NPs were .030 in the hole.
Pulled real good on the dyno up to 4600, which is fine by me. I don't think I've ever run it much past 3500 anyway. 3.25 rear end on 15" tire (for now).

[8ton]

You mentioned earlier that you were having the trans redone at the same time, what all is being done to that? I have heard that converting to roller bearings reduces friction in the c6. Are you changing the torque converter?
I tried one of the low stall 'mileage' converters, but didn't see much difference.

12-13 mpg would be pretty decent, really. After all, it is a 416" 330hp beast in a 4200# brick.
I would suspect that with so much torque down low, mileage won't fluctuate a ton.

If you end up with the heads off again in a few years, you could do some valve deshrouding in the chambers and run a .021 gasket to tighten up your quench while keeping your Cr the same.
I have been bench racing a very similar build so I have spent alot of time thinking about it.