Headers first

I've always had headers as my first modification to my new project because evey mod after will be enhanced buy the headers but here is another reason it should be headers first.


I had forgotten the ads for headers in the seventies pushing gas mileage, but they did...

I would like to put headers on, but have never run them.. and hear lots of dissent around the economical ones that go under the steering system. . .

The expensive ones sound great, but the cost to benefit ratio is not close enough to justify on a stock 318.

If there were a mid-range header for something like 5-6 hundred, I might be able to convince myself it is worth the return on investment.

Doug's D453-B black painted, heavier than most other headers. Currently 533.99 from Speedway Motors.
Doug's Headers D453-B Full Length Header, 1-5/8 In, 62-72 Mopar, Blk

They are over the steering, 3/8 flange, 16 gauge tubing. Come with all hardware and gaskets

80mirada said:

Doug's D453-B black painted, heavier than most other headers. Currently 533.99 from Speedway Motors.
Doug's Headers D453-B Full Length Header, 1-5/8 In, 62-72 Mopar, Blk

They are over the steering, 3/8 flange, 16 gauge tubing. Come with all hardware and gaskets

Click to expand...

Oh this is good news!!!

Truth be told I obviously did not look hard enough, b/c I was running under the assumption that all over the steering headers were the high priced ones. .

Thanks 80!

I just got these for my Mirada and they fit so damn well. Biggest thing was having the car high enough.

Depends on the power level I'm chasing after. Anything under 300hp out of a small block and I go manifolds. Even then I prefer shorties now even if it means leaving torque on the table. Just too much of a PITA to me.

>Every time I put headers on an engine, the steady-state fuel economy increased. Now, I can't prove it was the headers that did it. It mightabin that the log manifolds were crap to start with. Or the single-exhaust was not adequate. Or the carb was a pig. etc.
> Every time I put a 4bbl on a 318, the fuel-economy took a dive. Now, I can't prove the carb was to blame. Or the driver just worked it harder, lol. etc.
> headers have the potential to extract quite a bit of power thru the midrange, during the overlap cycle. But the factory 318LA cam only has 20* at the advertised specs, which IMO is too little to bother with. Yet, every time I install long-tubes on mine, with dual 3" full-length pipes; the little 318 surprised the heck out out of me, low-compression and all..
> But the fact remains this;
If your particular car takes 40 horsepower to maintain cruising speed, the car don't much care how she gets it, be it a 4 cylinder, a six or an 8; she just wants the 40 hp.
However; the 4 cylinder has only 4 cylinders with which to make it, so that would be 10hp per cylinder. Whereas the 8 cylinder only needs half as much power per cylinder. And therein lies the problem;
The 4 cylinder will require a much larger throttle opening to make the required power. So it will be on the boosters/mains, which can be very precisely calibrated. Whereas the 8 cylinder will still be on the low-speed circuit, which is, the transferslots and idle mixture screws, which have only a very limited adjustment range, and must be kept rich enough to idle.
And so, it takes a lot of work to get a V8 to challenge a 4-cylinder, as to fuel economy. Of course, the 8 cylinder will lose more power to parasitic loses like friction, as well, and so that has to be covered too.
> However; if the 8-cylinder has to pump it's own exhaust out of the chambers, that costs more than double the power than what the 4 requires. This is where the headers can make the difference. And having a header that is tuned for cruising speed can make a really big difference. Especially if that header doesn't see a restriction in the rest of the exhaust system. And that is one of the reasons that I have double-3inchers on my car. At cruising rpm, the headers can do their job, in every aspect; not just at the top of the power curve.
Using this thinking, I once built an 11.3/1, alloy headed, 330hp 360, that made fuel economy to rival the carburated 4-cylinders. So imagine what can be done with a purpose built 230hp 318.
IMO, Chrysler really missed the mark with the 318LA; it could have been so much better. There is so much untapped potential in that engine, the way that the factory screwed it together. Towards the end, they were just throwing all kinds ofchit at it, trying to see what would stick, instead of attacking the underlying shortcomings. And so, it motored into history, always short of the mark; the little engine that after 1971, in stock form, was never much good at anything, except perhaps, surviving.
But we,
as HotRodders,
can change all that.
The 318, at it's heart, really just needs one thing,(or maybe 2) namely; CCP(Cranking Cylinder Pressure). But getting enough of it, to hit all the bases, and still run a hydraulic cam, is a challenge. And so, low-speed torque is usually sacrificed, and with it goes fuel-economy.
Of course, it doesn't have to be that way. But, 318 HotRodders, do it that way all the time, tanking the CCP down to 100psi even, then running a hi-stall and 3.91s or bigger, in an effort to wake up their lazy 318s. And of course, there is no fuel-economy in that strategy.
The Second thing that a 318 needs is more gears in the transmission and tighter splits. I'm talking splits of around 78%. That would allow you to run a cam at least two sizes smaller than what is usually installed. and then, Fifth or Sixth gear would get you the economy you want.
To that end, I installed a GVod behind my A833od 3+1 trans and got seven usable gears. With 3.23s, that made 65=1450 rpm, and yes the stock 1973 smoggerteen pulled that, with a Thermoquad no less. With the tight splits, and shifting at 4800 rpm, the Rs only dropped about 1060 rpm. That's the way to wake up the stock-cammed engine. And fuel-economy at 1450 rpm; are you kidding! That's a final drive ratio of 1.79. Even better than the 2.20s that some FJM cars got.
So that, IMO, proves my point of more gears.
Now think about it; why did Chrysler spend so much effort on bandaiding the dying 318LA, instead of just giving it more gears and more CCP?
IDK the answer to that, but, IMO,
the 318LA could have been so much more.

Note-1
the ratios of that 7-gear combo, with gearsplitting were
3.09-2.41-1.67-1.30-1.00-.78-.54 (GV in red); and splits of
.78-.69-.78-.77-.78-.71
I ran this with 2.76s, 3.23s, 3.55s, 4.30s and 4.88s....... cuz with 7 gears, you can run anything.
Note-2
NOT splitting gears, it is now a 4+1 trans running
3.09-1.67-1.00-.78-.54. With a 3.91 rear gear you get a starter gear of 12.08, a second gear of 6.53, and 65=1530rpm, still daym sweet; but your CCP will need to be high enough to pull that wide 1-2 split without falling off the cam.
Note-3
You can't touch the above with an automatic, but you can get close with a hi-stall loc-up A904type combo. Say you run 2.94s for 65= about 2400.
On paper your A904 ratios are 2.45-1.45-1.00. but the convertor acts like a 2-speed with a starter ratio of around 1.8, and a finishing ratio of about 1.1 at top-speed.
So then First gear becomes; 4.41 at zero mph, diminishing to perhaps 3.55 at shift rpm. Second might average 1.67 and third might average 1.1, and then loc-up bringing up the rear for 4+1 ratios of;
4.41-3.55-1.67-1.10-1.00
With 2.94s in the back, your roadgears would appear as;
12.97-10.44-5.70-3.23-2.94,
count 'em.
For convenience and fun, this is hard to beat. And for the 318, cruising at 65= 2400rpm/ 60=2215, wouldn't be half-bad. But that 5.70 Second gear would kind-of suck, lol.
I didn't have a loc-up, so I used a wide-ratio A998 with 2.76s for 60=2150
My 4bbl, 8/1Scr, 140psi CCP, Smoggerteen really liked the 2800stall, which helped cover the lack of starter-gear (2.76 x 2.74 x 1.8=13.61 lol), and helped with the wide 1-2 split (ending at ~5.32). I was reasonably happy, if not ecstatic, with the results.
Note-4
One thing worth mentioning is that my stock but freshened 1973 318LA made reasonable torque at 2800rpm. So, on occasion I would floor it, and manually shift it up into Third gear asap. So the engine kindof hung at 2800 from the get-go to 60 mph...... with the Thermoquad howling the whole way, lol. It was fun for me.......
I guess, With the Wide-ratio A998, my favorite rear gears were the 3.23s, which would have been even better with a loc-up.

Well written AJ/FormS. Makes sense to me and I'm not even a mechanic. That must have taken some time to put all that info down. Thanks.

I'm here to help. and semi-retired. I get Mondays and Fridays off, so if Im not doing Bible-Study, I am usually checking out FABO. and if it's dead over there, then I check in here.

There is a flipside to that;
the factory 318 cam is a good size for most of us. The power peak comes around 4200, but can hang on a long time. The shift rpm could be perhaps as high as 4800. With 3.23s that would get you around 75 mph; and 65=4200 right on the power peak, (both in Second gear). So it's a good combo.
The reasons that a 318 is rather lazy, are threefold;
1) the compression is low, and
2) the log-manifolds kill the measly 20* of overlap, especially when pumping into a factory single exhaust system, and of course,
3) the factory LA heads kill the top end.
But lets have a look at that factory cam. The big picture of all the events, with the cam on split overlap, are;
240intake/130 compression/122 power/248 exhaust/ 20 Overlap,
With the compression degrees of 130, the Ica is a meager 50* which is very early. Because of that, the CCP (Cranking Compression Pressure) ends up fairly high for what it is, sometimes as high as 138psi. And that makes it driveable.
But there is NO room for a later closing intake, and not much room to allow for aging. As soon as the rings lose it, power goes straight into the dumpster.
Lets say you move to the factory 360 cam of 252advertized. The new numbers are;
252 intake/124 compression/116 power/260exhaust/32overlap
With this cam and still 8.0Scr, the pressure falls about 4% to perhaps 132psi.
The power peak will move up to perhaps 4500, and those 300 rpm will bring a few ponies to the table, while the pressure loss at the bottom is actually a much larger loss than the number implies.
Next, lets try the 340 cam. The new numbers are ;
268intake/114 compression/106power/276exhaust/44Overlap
compression is down to 114*, so the Ica is 66*, and pressure has fallen to 120psi. By now the 318 is plenty doggy off the line. The power peak has moved up to about 5000, and of course the heads are way too small to do anything with this. BTW, 5000 rpm is about 80 mph with 3.23s, so even if the engine could make power with this cam, you would be well into speeding-ticket territory.
Guys who do this, invariably install a big hi-stall, and plenty of gear, which renders it a city car.
Now, those numbers are generated with factory hydraulic cams. The first two are ground on 112 Centerlines, while the 340 bad boy is on a 114. The bigger this nimber is, the later the intake closes, and the less CCP the engine will generate.

Ok, we know that to make power with any given engine, you gotta spin it. But the cam has to be able to operate at that new higher rpm.
In other words, you can spin your stock 318LA to the moon, and it will never generate any more power than what it makes in factory trim ...... because the cam is the first limiting factor.
The Second limiting factor is the heads, which are barely adequate for the factory cam.
So, to make power with a 318, you gotta get rid of those heads, and very carefully choose the cam based on what rpm you want the power to peak at. This is where most guys miss the boat. You can easily build a street318 to spin the tires right thru first gear, or at least mostly . That means, on the street, it is easy to choose a cam that, at WOT, is useless in first gear, cuz all it does is spin spin spin. So now, Second gear will become very important, and especially the 2-1 automatic kickdown.
So now, say at 30 mph, you are just cruising around with your factory 2.76 gears, when the urge to nail-it hits you. You might be running 26" tire so your rpm in Second will be 1550 . On the 2-1 KD the rpm will rise to perhaps 3000. Here's the thing, with a beginning Compression ratio of just 8/1 and the factory cam pumping out 138 psi, performance at 3000 rpm is kindof sucky. But if you put a bigger cam in there with a later closing intake, and your engine loses pressure, it will be even suckier! The 340 cam for example, will make your bottom end feel like a 225 slanty, rising with rpm, to about 3500 rpm where it finally starts feeling more like a 318.
So bottom line is this; You gotta bring up the pressure as you go, AND
throw those stinking 2.76s away. As long as they are in there, this problem will never go away ...... with a 318.
So yes, it is possible to make a ripper of a 318 combo, but it takes a well thought-out combination of parts, and a careful assembly of those parts.

With a 318LA, making pressure is the hardest thing to do. The open-chamber heads have to go.
Pressure also make MPGs. You can make the pressure with any engine, to produce great fuel-economy. But making it also driveable, is a lil tougher. And marrying it to Performance is even trickier.
Doing all three with a 318 auto is pretty tricky. Too expensive for me, so I just went with a 360, which was born with too much bottom-end potential in the first place; so giving some of it up was no big thing.

I agree with most of what @AJ/FormS says, and always, what he says, he backs up with numbers and his thought process.

You can make a 318 run like a scalded cat - but it takes thought and getting the right parts for it. Most people will toss this on it or that on it which makes the car less drivable - and then less likely for one to drive that car (which is a shame). The intent of the 318 was an engine for the masses and have great low end torque.

What have I done to either of my 318's in the last 15 (or so) years? Nothing but maintenance.
What do I have plans on doing to them? I am building a pair of stroked big blocks - but waiting for more money to finish the builds (and not wanting to go into debt in the process).

It is my short term plans to remove both of my 318's in a bit to perform a complete soft parts overhaul. The seals/gaskets are leaking on both engines, bad. The valve seals are shot, as well as the timing chains (both are plastic). I have new chains, chain tensioner's, reseal both engines using newer materials and to install windage trays (it is like free 5 HP, maybe more depending on who you ask).
My plan is to have fuel injection on both big blocks. I'm not a big fan of 4-bbls on 318's - but not opposed to it either. IMO, a stock 318 doesn't need a 4-bbl in the most part. The key word is "stock 318". That said, I need a 4-bbl appearing fuel injection setup for my big blocks - so i will be installing an aluminum 4-bbl intakes while the 318's are out and apart just to make my long term goals easier in the long run. Also, any way to get rid of cast iron is always a good thing.
There are 2-bbl appearing F.I. units out there but I don't need to spend the extra money.
in addition to that, tossing the 2.2 gears as far as I toss 'em (from my '86 Fifth) will be a very good thing, no scratch that, a MOST EXCELLENT THING.

Also, if I didn't already have a lot of investment into my big block deals, I feel building a 360 with decent compression (stroked or not) would result in more bang for the buck than building up a 318.
I am not against 318's nor against building up 318's - for they have their purpose. I just think for modifications needed, money spent and total HP achieved per buck spent, a 360 will get you further and a tad cheaper than what you can spend on a stock 318. Also, you can build your new engine while still driving your car - which is a big issue for some people.

I do have different goals than other people have - so to most here, what I will be doing might not apply.

IF anyone here is planning on making modifications to their 318 - I ask you to FIRST, consider changing out your differential gear ratio first. I think doing that, might satisfy most people. Also, if you are making any major powerplant changes, you will still have to change out the differential gear ratio, anyway. It is a great place to start and who knows - it might be what most people will be happy with and still have all of that way down low torque.
BudW

BudW said:

The intent of the 318 was an engine for the masses and have great low end torque.

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I've owned three 318's in cars over the years. One a 1970, one a 1974, and one a 1987. All were excellent engines which gave me no trouble and performed well with both good power and good economy. I never altured them from stock. I also had a 1970 383 which was very powerful, but also relatively thirsty. Although I am also a great fan of the 225 Slant Six, if I had had a choice, I would have preferred that my OY wagon had a 318 in it instead of the 225SS. Just for that little bit of extra punch. But anyway, I also like the fact that OY is what it is - an old desert survivor that may not be "fast", but is a ton of fun.

BudW said:

IF anyone here is planning on making modifications to their 318 - I ask you to FIRST, consider changing out your differential gear ratio first. I think doing that, might satisfy most people. Also, if you are making any major powerplant changes, you will still have to change out the differential gear ratio, anyway. It is a great place to start and who knows - it might be what most people will be happy with and still have all of that way down low torque.
BudW

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I have been preaching this same thing since the 70s, and no one who ever started with gears and/or a Convertor, ever came back afterward to argue bad advice on my part. My own gutless 1973 Smoggerteen took on a whole new personality with exactly those two things.
Yet Every guy I ever knew who installed the 340stuff into his 318LA, with no other changes; without exception, was a very disappointed guy, including myself, before I understood about the pressure thing.
You just keep on preaching it!, brother.

BTW
as to the 4bbl thing:
the 318 has a bore and stroke that make one cylinder have a capacity to contain a maximum of ~652 cc or about 3/4 of a US quart. With the engine off and the piston at the bottom, at least two cylinders will have that much air in them, plus whatever fits in the chamber.
But as soon as the engine is idling, the closed throttle blades together with the rpm controlling the time-factor, there is no way for this much air to enter the cylinder.
Now, when you open the throttle blades as far as they go (WOT), only the rpm and upstream restrictions can limit how much air can actually pass thru the engine on every revolution.
If the heads are a restriction, or the cam events are, or the exhaust piles up; then all the carburation in the World, will not increase the power after the engine hits that wall.
The TORQUE curve is a good visual indicator of at what rpm your particular combo hits the wall. Below is an example in which the wall is hit at 3200rpm. You can see the sharp drop-off in torque after that. The only reason that the engine continues to make additional power is by virtue of rpm. But by 4400rpm, it is completely choked and the power begins to fall.
Getting back to the one-cylinder capacity of 652cc; In one revolution, of a 4-stroke 8cylinder engine, 4 cylinders will attempt to be filled at WOT. So the maximum capacity is 4 X 652 cc=2608cc which converts to .09 cubic feet. At 4400rpm when this example hits the wall, that would be 4400 x.09=404.8 cubic feet. So your carb has to be that big. Or does it?
However, this engine stopped being able to ingest even close to the max, at 3200rpm. By 4400 it might be down to less than 70% so
70% x405cubic feet is 283cubic feet, and since we are talking revolutions per minute, this equates to 283cfm.
Back at 3200,say if this engine was able to fill 100% of its capacity, this would math to 100% x .09 x 3200=288cfm.Therefore, anything bigger than 288 cfm is just bragging rights...... on this example.
If you want this particular example to make more power, it will first need to be able to process more air; and that usually starts with a bigger cam. But, almost right away, the heads will become the restriction.
Therefore, in the search for absolute power, when starting with a stock low-rpm 318 engine, you need to cam it up AND get rid of the low-rpm heads.
Lets say you built it, and it torque peaks at 4000. Your new carb requirement at 100% is; 100% x .09 x 4000=360 cfm. With good heads, say the power peaks at 5300 and the VE ( Volumetric Efficiency) has only dropped to 82%. Now your carb requirement is; 82% x.09 x 5300=391cfm.

Now, your stock 2bbl might be rated at 250cfm. But this is based on it being measured on a lo-performance engine and uses a different measuring system. When your 250cfm 2bbl-rated number is converted to a 4bbl number, it becomes about 177cfm; so you want to get rid of that thing.
However. whatever 4bbl carb you put on there, your stock engine cannot pull hard enough on it to even tickle it's rating.
The simple conversion factor is 1.414; so
For example a 500cfm 4-bbl rated carb, rated as a 2bbl is a 500/1.414=707... and that means the front half is about 707/2=353 ........ which is already 353/288=1.226 or PLUS 22.6% bigger than your stock 318 can ever pull no matter what and
353/391=.903 or Short only 10% of what your heavily modified 318 can pull.

Now here's the clincher;
with 2.20 gears you can't hit 5300 until 64 mph in 2.74 low gear with 27" tires, and 10% convertor slip..
to restate it another way, and
IMO,
Installing a 4bbl on an otherwise stock 318, and with 2.20 gears, is a big fat waste of time and money. Your 4bbl will wail and moan and sound terrifying, but the stock 318 will only pull what the combo will allow, and with 2.20gears, this is way up in the roadspeed range.

Ok now what about with 3.91s? Well now yer talking; the big-cam/big-headed 318 with 3.91s and the 2.74 low gear will now hit 5300 at 36 mph oh yeah. And 5300 in 1.54 Second comes to .......64 mph about as perfect a combo as it gets.
So now, the 4bbl is gonna wake it up at favorable roadspeeds, BUT she still don't need as much as a 500; remember the math points to just 391 4-bbl rated cfm.

Having said all that;
You might have noticed that the 318 makes only .092 cubic feet per revolution, at 100%VE.. All calculations are based on that number, and on rpm.
There are three ways to make more absolute power 1) more rpm, and 2) more VE, and 3) a bigger displacement
The fastest way by far, is more displacement, which comes with the bonus having more inherent power at low-rpm, and in the midrange. The 360, for example has the potential to displace .104 cubic feet at 100% VE which is 13.22% more than a 318. So for the 360 to make the same absolute power as a 318, you can rev it lower,which means a smaller cam, smaller carb, smaller everything, and including a smaller rear gear. And the additional displacement means, that for the same take-off power, the 360 can use less stall. And the additional inherent midrange power means you can build it to a lower compression ratio . That's a lot of wiggle room.
I agree with Bud who said;

BudW said:

I am not against 318's nor against building up 318's - for they have their purpose. I just think for modifications needed, money spent and total HP achieved per buck spent, a 360 will get you further and a tad cheaper than what you can spend on a stock 318. Also, you can build your new engine while still driving your car - which is a big issue for some people.

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@AJ/FormS, the above chart is for a 1997 318 which would be a Magnum and they do flow more CFM than a non-Magnum 318 does - BUT that is a minor detail as to what you are trying to say.

This is an older thread that I thought I'd bring up: Second time entering into a Car Show.
The rated torque converter stall for my car is 1700-2000 RPM - so not sure why they started measuring at a higher RPM. Either way, you can see the flat torque and HP curves.

Yes and this 5.2M graph appears to be from a truck engine, which has the "beerkeg intake which pumps up the low-rpm torque, as can be seen by the odd shaped torque line.
I use that graph all the time because it's handy, and clear, and clearly marked as to what it is.

BudW said:

This is an older thread that I thought I'd bring up: Second time entering into a Car Show.
The rated torque converter stall for my car is 1700-2000 RPM - so not sure why they started measuring at a higher RPM. Either way, you can see the flat torque and HP curves.

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I notice that they do that all the time; probably in an effort to keep the engine out of low-rpm detonation.
On your graph, notice that at the end of the test, at ~4750, she is still making 120 hp...... which is 88.8% of the peak, or down just 11.2%

I used to install a Smoggerteen into my Barracuda every winter, about 5 or 6 winters in a row until my son made me an offer on it that I couldn't refuse. That was a stock 1973 longblock, with an addition of a 4bbl and headers. Oh, and some valvesprings that allowed the valvetrain to hang together to past 5400. In that shape, she was regularly spun up to 5000, and I gotta say that the power did not seem to be all that choked up. I ran her with a 2800TC and she was a hoot!
Now, on your chart, @4750 being only down 11.2%, (probably into a single exhaust/no headers) that makes perfect sense. My numbers mightabin a lil higher with the 4bbl and headers/ dual 3" sewer pipes, but the shape would remain similar. Flat is good!
I really liked that lil hummer.