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Tech Question
Kevin Seifried, Kitchener ON 1974 Plymouth Satellite Sebring Plus 318
My Satellite is an all original car with the 318 727 trans and I belive 3:55 gears. My question is, how much HP would I gain if I swap the 2 bbl, 318 intake and heads for a 340 4 bbl set up?? Do I need 340 manifolds as well?? Or should I stick with the 318 set up and do a port 'n' polish on my heads, go with some headers and open the exhaust up a little? Any guidance on a mid budget HP boost aside from swaping motors (she's a #'s matching car), would be greatly appreciated
Kev-
You Satellite is a pretty heavy ride. And, unless it has trailer tow, or the axle has been swapped, I'll bet it has more like 2.94 cogs. So you really need to keep the low-end torque up if the car is to have any 'snap' on the street.
I'd go with a set of stock 360 head castings - even the worst smog-era ones will flow lots better than your heads (which are not very good.) Yes, you'll need matching manifolding, including, preferably, a dual-plane aluminum intake and a small 4-Bbl. Headers would help, too, but if you go that route use the smallest pipe ones you can find. Either way, a nice set of 2.25" dual pipes will help tons.
The key to making this work is the cam. Briefly, don't go nuts! The wildest I'd even consider would be a stock 340 repro cam. Something with a few degrees more lobe separation (i.e., less overlap) would be even better. Call one of the major cam houses and tell them your combo, making sure that they know it's a 318 in a heavy car, has tall gears and a stock converter, and is a street driver. If they come up with something close to what I've described, spec-wise (i.e., not over 268/276 deg duration [at 0.008"], not over .4509 lift, less than 45 deg. overlap, I'd go with their recommendation. Otherwise, just a stock 340 repro cam, maybe installed 2 or 3 degrees advanced.
With these changes, you should be adding approximately 40 to 60 HP - a difference that you'll really feel.
Rick
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