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Original Message
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| The pistons are a starting point. |
| By Dave Shoe - 06/30/2004 10:48:58 PM; IP 216.243.176.34 |
You've got 410 pistons in that 390, so compression hangs around 8.5:1. I'd want to bump that up to 9.5:1 with +.030" cast pistons. 9.5:1 is good for a pickup, since they can load the engine down pretty good at highway speeds, heating things up andcausing pinging after a while. If you feel "lucky" (or willing to gamble), 10.0:1 may be fine. Keep in mind that both head gasket thickness and also the head casting (chamber sizes statistically vary) may have an effect on your actual compression. Cast pistons are nice, as you can be fairly sure you won't need to rebalance the engine afterwards, since they are typically all balanced like stock pistons. Note that you'll need to verify the piston/pin combo really do weigh the same, otherwise you'll have to stuff a few extra bucks into a rebalance.
Your connecting rods are great pieces. If the rod bearings look good and they are not excessively out of round, and if the bushings fit the new piston pins with proper slop, you can reuse the rods as is. If you find you need to replace the rod bearings due to out-of-roundness or wear, you might as well buy ARP 3/8" bolts for the FE, install them at the new torque, and then resize(recondition) the rod to make them round at the higher torque.
If the mains are worn, you can just replace them without needing to recondition the main bores, as cast iron mains don't stretch into an oval the same as forged steel connecting rods do over time. If the crank is in fine shape, you can use stock sized bearings.
I'd stick to a stock oiling system, as the FE does have a great setup as it comes from the factory. If you have a front-sump oil pan, you'll need to buy a $96.00 Milodon stock replacement pan, as if your truck becomes too quick, stock front sump pans can be problematic at keeping oil in the sump. Since CJ-type windage trays are available brand new all over the place for about $40.00, I'd install one of them if you have a front sump pan.
You'll want a mild cam profile similar to the GT/CJ, but with modern technology stuffed into it. There are many choices, but you don't want to overdo it, as some cams only work well when you've got more compression.
Obviously, lifters MUST be replaced whenever a new cam is installed, as will the valve springs to match the performance cam requirements, but so will the valve spring retainers and locks, as well as the improperly grooved valve stems. Since you need valves, you might as well stick CJ-sized valves into the head, since good ones are readily available at good prices from FE sources. I would avoid ispending on hardened exhaust valve seats, unless you plan a lot cross country towing which will cause the exhaust valve to glow red for extended periods, allowing the "as cast" exhaust seats to wear. If towing, I'd have hardened exhaust seats installed.
With a modern cam ramp profile, you'll need to upgrade your rockershaft end supports. The center supports are fine, but the end supports are not stiff enough to prevent the end rocker from overflexing at the acceleration ramps of modern cams. Buy a set of four rockershaft end support pedestals and you'll be in fine shape.
I would not worry much about porting. Cast iron is a pain to port, and your engine can make great power without modifying the heads. If, however, you do seek to "improve" the heads a little, simply have the porting shop remove the Thermactor bumps in the ceiling of the exhaust runner. It shuld be good for some extra power as the revs climb. Note that if you do port the thermactor bumps until they disappear, you can run a cam with the same lift and duration on the intake and exhaust. With thermactor bumps intact, it's best to choose a cam that gives the exhaust a little extra lift.
Now you just need an intake, carb, and headers and you're done.
The obvious intake is an Edelbrock "Performer RPM". Do NOT consider a plain "Performer", as they are oinkers. RPM would be perfect for cost, availability, performance, quality, port compatibility, and a slew of other reasons.
Carb should be a 650 to 750 CFM with vacuum secondaries. Mechanical secondaries are nice, too, but gas mileage will drop noticeably and you need to "get used" to the throttle.
Headers should be any type that is compatible with the low-exit exhaust port. Most FE pickup headers are compatible with your C8AE-H or D2TE-AA heads, but you'll want to be sure they properly crush the exhaust gasket at the weld bead of the header tubes, or else the gaskets will likely leak. Headers taylor-made to 427 heads may not match properly, unless the tubes are oversized where they meet the head.
$2K does sound about right, if you do most of the work yourself. If you have a shop do the work, you really need to recheck EVERYTHING, unless you know the builders are qualified specifically on the FE.
Oh, and with these changes, expect it to feel a bit sportier than a 390GT engine, hovering either side of a 428CJ, depending on which choices you made.
I may have left some things out, but this seems about right.
JMO,
Shoe. |
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