Should I leave it Stock?

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I am tempted. I have considered pulling the heads and doing a port/polish job and some decking. Once I start taking away material though is when things become non reversible. I can see myself sending the heads off the machine shop for a simple clean up and "accidentally" having some other work done.
As long as the intake surface is machined too the intake will be untouched and work in any correct head. Keep an eye peeled for a pair of heads. You can pick them up cheap.
 
I say enjoy your car and make it yours. Your needs and pinion in the end is what counts.
Like said, most any mod can be reversed if the next owner wishes. Hi nickle.
I car less about taking a car to a show and Iam not a racer, but I have alway enjoyed the seat of my pants feel of torque and the sound of a healthy "at least" sounding engine!
I have some slant cars I just enjoy driving too, the snail that it is!!
For many years I tended to gauge my respet for a certain model by how others regarded it, then it hit me, only time it matters is when I sell.
 
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At 4000 ft you might be in a bit of a pickle.
Your 8/1, 2bbl 273 is feeling like a slanty would at sealevel.
All the bolt-ons you can name cannot solve your problem; except supercharging.

Is it possible you have an incomplete idea about headers.
Firstly headers are tuned over a very narrow rpm range, usually working best at the typical torque peak in the mid-3000s.
But they are inertially tuned. They need a slug of hot exhaust gasses moving down the pipe at high-speed, to perform their function. In your case, this presents some problems;
1) because of your altitude, and your very low effective compression ratio, there will never exist a slug of hot exhaust gasses moving down the store-bought header pipes at high-speed. You will get a warm slow-moving loosely knit doughy thing, and
2) it won't pick up speed until much later in the rpm band. This does not help you off the line; not even a tiny bit. Furthermore,
3) the 4bbl cannot help you if the tires will not spin, the rpm just stays too low for too long, with the factory lo-po rear gears. It will be ~40mph with 2.76s before the headers start to work.
Secondly, headers have a secondary function, related to the first. Beginning at just before peak torque and continuing until you shift, that slug of fast-moving very hot exhaust gasses, is supposed to help your engine create the low pressure in the chamber, so that atmosphere will be encouraged to start moving into there, a tiny fraction of time sooner. It does this during the overlap cycle, when both valves are a tiny bit open.In your case, the overlap cycle is too short to be effective.
For you; the only advantage headers can provide is a low pressure place for the warm combusted exhaust gases to exit into, so at least the pistons don't have to pump them out. IMO, at 4000ft, this is flogging a dead horse. Considering the difficulty of fitting headers in your chassis, and the meager benefit of them, IMO, you can achieve similar results with HP logs and a free-flowing dual exhaust, with a well-placed cross-over.
Hang-on; I'm not saying headers won't allow your engine to make horsepower; not saying that. What I am saying is that at 4000ft with a 273, it's gonna take a lotta rpm to measure it, and for the cost of them, and the trouble involved in the installation in your particular chassis; to me, I could not justify it. If your pockets are deeper than mine, and you are 20 years younger than me, or have a drive-on hoist, then have at it.

But I gotta re-iterate;
for a 273@4000ft
Your biggest bang for the buck is gonna be a higher stall TC, followed hotly by 30 to 40% more rear gear, depending on your starting point.On the plains 3.55s are considered the go-to gear. At 4000ft that is not gonna cut it.

IMO, your best bet is to, as already stated, mothball that 273, and drop a stock Magnum in there.
As for me; on that Magnum, I would;
>install HP log manifolds, and any 4bbl induction system.
>install very large dual exhaust pipes to very large in/out, 3-pass mufflers, and anything easy to fit after that, with turn-downs at or just after, the bumper. Crossover recommended but optional.
>Convert the serpentine to the 273 V-belts including the waterpump!
>leave the Magnum cam in there, but retime it to not less than 4* advanced,
That is what I would do.
Furthemore; I would;
>convert to an isolated field electronically regulated charging system, and to electronic ignition.
> with that torquey Magnum, I would swap in an A999, loc-up with the 2.74/1.54/1.00 ratios, and with that, just maybe the 2.76s can stay.At least until the Magnum breaks the 7.25.

Of course a supercharger would neatly bypass all the hassles, of this swapping business. Bolt it on a Shazzam yur done. Drive it into the shop Friday night, Go for a Sunday drive. OOps, yur gonna need bigger tires.
 
F98851CC-A961-4BA6-BAE4-6F9CC94B48B3.jpeg

This was an all original 30k mile 65 Gt
Slant 6 car. Go for it !
 
I've got a very good Mopar Friend in Cedar Hills, that if you ever need help or a place to wrench...
 
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