I'm getting ready to start playing with my 390. I'm shooting for 400-410 horses at the flywheel, which i figure oughta be pretty easy with where I'm starting from. The only thing I'm not sure of is if stock C8 heads can flow for 400 hp. I've only seen flow ratings on these heads up to .500 lift, and at .500 they're barely moving enough to hit 400 (and that's if everything else is optimized).

I know what it takes to get the exhaust side of FE's doing something, but what does the intake side like and is there anything I need to watch out for? It looks like it would be straight forward enough to straighten the ports out a bit and smooth them up, i'm just wondering if there are any water jackets I really need to be cautious of or anything like that.

I'm also wondering if the stock 4v intake will support 400. I recall hearing the stock 4v actually flowed better than the Performer 390, but not as well as the performer RPM. what truth is there to this?

Right now I'm starting with a recently gone through Z code 390 (315hp/425lbs) with a 'stock plus' type cam in it, dual valve springs, 390 PI rods and a good balance job. I really don't know what kind of power this thing is putting out, but i figure it's about 295 to the ground based on quarter mile trap speed, so about 325 at the flywheel.

I'm looking at this:
10.5:1
750 CFM Quadrajet
ported C8 heads (if need be)
Duraspark II
1 1/2" ID short tube headers (for clearance issues)
dual 2 1/4's with crossover
Custom grind cam by head flow specs

I've already started collecting parts and this thing is by no means a daily driver, so down time is no issue. Figure I should be running about 400 by the end of the summer, sooner if the heads and intake don't need opened up.

Justin

 

You definately want to port the heads. They respond very well to a simple clean up. Polish up the exhaust, remove the emissions bump on the roof. Clean up the casting roughness in both the intake and exhaust, but leave the intake ports slightly rough. Smooth up the short side radius. When you have hardened exhaust valve seats put in, there will be a sharp edge under the seat insert. Smooth that up. Smooth up the area under the valve. Match the intake port opening to the intake manifold opening, using a gasket. They should flow a LOT better after this is all done. Oh, and DO NOT HOG THEM OUT!!!

IIRC the stock S code 390 intake does flow better than the regular Performer intake. If you have one, and have no problem lifting it, go ahead and use it. You'll avoid some potential sealing issues too. For more performance, you could either go to a Performer RPM, or a ported Edelbrock Streetmaster 390 (single plane). When ported correctly, the latter should make significantly more power than any of the previously mentioned dual planes.

 

Heads already have hardened seats, i saw where they've been cut out and new ones installed (i've had one of the heads off to drill out exhaust bolts). whole motor seems like it was gone through right before i picked the car up (mileage wise). From the condition everything appears in I'd say it doesn't have 5,000 miles on it.

But headwise they just like a real nice cleanup on the intake side? Glad to hear that, was hoping I wasn't going to have to go ape on them. As for the other side, I've already ground the bump out of the exhaust ports and got in there with a flap wheel to smooth stuff out.

And as for the intake, it's more of a bear than I like it to be, but if i can pull off the power levels i want without having to drop a couple bills I can put up with 80 lbs of iron. I own an engine hoist for a reason

Justin