opt for the higher Voodoo cam , while my truck runs great the idle has very little lope . I wish I would have went with the 62002 .

 

My machinist back when I did my 390 said that the shorter rod in the 390, compared to the 360, helped low-end torque, because the piston velocity was higher near TDC so it could get higher air flow through the intake valve quicker, plus a better angle pushing against the crank pin.

Makes sense, actually. And he did know his stuff, he raced FEs for years.

 

The angle is *worse* with shorter rods because the forces are going more horizontal than vertical. Everything else you said sounds right though -- longer rod = higher RPM benefits in general.

 

The crank pin has to move horizontally (almost) at TDC, so there is more force against the crank pin. More loading of the piston against the cylinder wall though.

 

Makes sense!

 

I'm just about in the same boat- 4.080 bore with a 390 crank and 360 rods. The shop is verifying the piston height as I type. Weird combo. Would a Comp Cams 270 Magnum be considered "mild" with the C8AE-H heads? It's been pretty tedious balancing budget and getting really nice replacement parts in the right combination for decent power and reliability for a daily/cruiser.

 

Crank 1.89
Rod: 6.54
Piston: 1.77
Total: 10.2
Deck: 10.17
CLINK!

If you use pickup 390 pistons you get a piston of about 1.66", thus your total on top of the 360 rod will be about 10.09, still .080 down the hole, a little better than the stock pickup 390.

Do yourself a favor and get 390 (actually "all other FE") rods and pistons with 1.77 compression height.

 

Don't forget the gasket thickness in that math.

Regardless, it didn't really set in with me until I saw the actual rod length. 6.54 vs 6.49 and a weaker rod? I'm not sure why that tiny bit would even be worth bringing up the 360 rods...

 

 

The advice given was that a small cam and the flat tops (very high compression) together is a *terrible* combination. That high of compression will require a big enough cam that stock heads are out of breathing room where it starts to shine, and the bottom end will start to die...the worst of both worlds.

You NEED pistons with a dish and a modestly larger cam (up 1-2 more sizes). Even the 268/276 cam recommends compression down in the 9.1-9.5 range.

Good luck. If it works, let us know. If your machinist is an SBC guy and that's his evidence for what works, you're in deep.

 

460 jared shoot me all the specs of your build , I'll run it on Desktop Dyno 5 to ball park what numbers for HP/TQ

 

 

I've run two 10 to 1 390's with mild cams and they were fine on 87-89 octane. One was a GT390 with a Cam Dynamics 290-something duration (been 35 years since I bought that'n) the other I ran a Crane 272 degree Energizer in a 68 Merc Monterey, it ran fine on 89 octane with the stock flat tops and C8AE-H heads. Not a whole lotta difference in design of the SBC and the FE's in heads, both are 1950's designs, so that's not an issue with a machinist. They even use the same distributor clamp

 

If you want to pick up the power ditch the glass packs and go with turbo mufflers. The HEI distributor ? Fuggly on a Ford.

 

A 10 cc piston will put you at around 10:1. The Speed Pro pistons are 10 cc, and this will likely be your most reasonable priced product available. A true flat 0 cc piston will put you around 11:1. As someone else pointed out, the forged piston is also overkill in this power range.

Ha..."mild cam = 290* duration"...

The stock c8/d2 heads vary widely in combustion chamber size. I've seen 68-72 being most common ranges. If you got some that were 72 cc or maybe even some 74 cc outliers, that makes a world of difference. I quoted compression ratios above with a .050" gasket and a 68 cc chamber.

BOTH of the cams, whether you remember the specs exactly or not, have longer durations than the Lunati cam he has "chosen" which is actually in line with the point I'm trying to make.

Just avoid louvered glass packs and get perforated. A turbo-muff isn't going to give you more power over a perforated glass pack on this planet. Just as importantly, stay reasonable with exhaust pipe size (2-1/4" rather than 2-1/2" +) for your rpm range.

Pertronix makes a nice distributor that looks stock but has modern electronics in it. I love mine. Yes, an actual HEI is a travesty indeed.