Mopar Action On-line – Tech Questions
Kevin Seifried, Kitchener ON 1974 Plymouth Satellite Sebring Plus 318
My Satellite is an all original car with the 318 727 transand I belive 3:55 gears. My question is, how much HP would I gain if I swapthe 2 bbl, 318 intake and heads for a 340 4 bbl set up?? Do I need 340manifolds 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 #’smatching car), would be greatly appreciated
You Satellite is a pretty heavy ride. And, unless it has trailer tow, or theaxle has been swapped, I’ll bet it has more like 2.94 cogs. So you reallyneed to keep the low-end torque up if the car is to have any ‘snap’ on thestreet.
I’d go with a set of stock 360 head castings – even the worst smog-era oneswill flow lots better than your heads (which are not very good.) Yes, you’llneed matching manifolding, including, preferably, a dual-plane aluminumintake and a small 4-Bbl. Headers would help, too, but if you go that routeuse 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 wildestI’d even consider would be a stock 340 repro cam. Something with a fewdegrees more lobe separation (i.e., less overlap) would be even better. Callone of the major cam houses and tell them your combo, making sure that theyknow it’s a 318 in a heavy car, has tall gears and a stock converter, and isa street driver. If they come up with something close to what I’vedescribed, spec-wise (i.e., not over 268/276 deg duration [at 0.008″], notover .4509 lift, less than 45 deg. overlap, I’d go with theirrecommendation. Otherwise, just a stock 340 repro cam, maybe installed 2 or3 degrees advanced.
With these changes, you should be adding approximately 40 to 60 HP – adifference that you’ll really feel.