Horsepower with mileage options

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Penstarpurist

Penstarpurist

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Okay guys, here is what I'm wondering. My son and I are bench building options for his bone stock 1971 Plymouth valiant. Current set up is 318 2bbl 904 stock. He loves the car, but has been wanting to give it some pep but wants to retain drivablility and gain some gas mileage. So he is thinking aluminum heads, aluminum 2bbl intake manifold (yes, I said 2bbl aluminum) he says they exist. Dual exhaust and mild cam. Gear change out back. I think that the way to go would be keep the iron heads, stock 340 cam, 4bbl intake either stock steel or aluminum, and carb to match, dual exhaust and a set if 355's out back. Put all the stock parts on the shelf to put back stock if ever wanted. What do you guys think?
 
I wouldn't talk him out of the aluminum heads, but a 2bbl intake is a waste of space.
His money ? aluminum heads, camshaft in the 258 -268 range, dual plane intake with a holley 600.
FWIW 340 camshaft was designed for a little more compression than you have with a 2bbl 318.
I like a 258 @ 050 for the 318
 
Penstarpurist said:
I think that the way to go would be keep the iron heads, stock 340 cam, 4bbl intake either stock steel or aluminum, and carb to match, dual exhaust and a set if 355's out back
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That's pretty much what I did with mine, except I used an HE268 cam. I also added headers.

That's plenty enough to get a young fella in trouble, lol.
 
A nice cam, good dual exhaust, 4:10 gears and a 2004R overdrive trans. He'll have plenty of pep and cruise at 65MPH taching 2000RPM (depending on the size of his rear tires).

Treblig
 
If you really want better mileage, EFI is the way to get it.

3.55's out back won't help your mileage either unless you go with some kind of overdrive.
 
2.73/2.94 rear and go to 13 inch tires when you want to go hunting
 
Google "super duper 273 /318 mileage experiment
I think he hit 30 plus mpg....long read though!
 
72bluNblu said:
If you really want better mileage, EFI is the way to get it.

3.55's out back won't help your mileage either unless you go with some kind of overdrive.
Click to expand...
I definitely like the idea of EFI, I was telling him that would be the way to go. He is just an old school kind of guy. He is running the stock 14" wheels, 2.76 gears. I'm all for going with aluminum heads, lol if he is paying for them. I didn't even think about an overdrive transmission. That would be a great option for it at some point.
 
I don't want to hi jack the thread but the mention of the od trans got my attention // I have a 47 re trans with a lock up torque converter out of a truck //could be an easy cheap /score

any one out there do this ???
what does it take to use this computer trans ??
 
Treblig said:
A nice cam, good dual exhaust, 4:10 gears and a 2004R overdrive trans. He'll have plenty of pep and cruise at 65MPH taching 2000RPM (depending on the size of his rear tires).
In thinking of a 4 and automatic, how well would the old 518 od trans work for It? Direct bolt in, but does it require anything more than linkages and maybe some driveline work?

Treblig
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I'm sorry// looking into this ,the family of 518's (46/47/48) re (electronic) rh (hydraulic) got me thinking that's all !! with a .69 od
and a 2.73 rear stopping would be a issue !!!!!!!:eek:
Bonneville would be the next stop ....
 
Cam and gears are main part to get a balance of performance and mileage.

Theres a sweet spot. EG.. Like the 340 cam over 318 cam will give a good boost in performance with little to no hit in mpg but going a couple steps up from might kill mileage with little useful gain in power.

I wouldn't go 2 bbl. The factory didn't use them for better mileage just cheaper to build. Your only gonna run on the front barrels most of the time anyways.

Modern cars mainly make power from good flowing heads (plus intake/exhaust systems) and mild cam plus OD.
Unlike most modified engines that use lot of cam to try to squeeze all the performance out.

The only problem say puting eddy heads on with a 340 cam is you'll be leaving a lot of power on the table. But you'll have a better behaved and fuel mileage engine then going with poor flowing heads and a big cam to get the same power.

Hydraulic roller and 1.6 rockers are good way to. Since you can get more lift with less duration.
 
Penstarpurist said:
Okay guys, here is what I'm wondering. My son and I are bench building options for his bone stock 1971 Plymouth valiant. Current set up is 318 2bbl 904 stock. He loves the car, but has been wanting to give it some pep but wants to retain drivablility and gain some gas mileage. So he is thinking aluminum heads, aluminum 2bbl intake manifold (yes, I said 2bbl aluminum) he says they exist. Dual exhaust and mild cam. Gear change out back. I think that the way to go would be keep the iron heads, stock 340 cam, 4bbl intake either stock steel or aluminum, and carb to match, dual exhaust and a set if 355's out back. Put all the stock parts on the shelf to put back stock if ever wanted. What do you guys think?
Click to expand...


Let’s keep it cheap to start with and then add on all the bling later. To be honest, I’d rather start this money spending on best bang for the buck with the ability to add other options later. So, it would be IMO that money well spent now instead of later for the best results for now and later would be in the drive train area.

The A-500 series OD would be costly though a huge bennifit overall later. Coupled with the 3.55’s, this would equal a 2.45 final drive feel ratio. Finding a non lock up converter can be a pain but at least at that point, converters are cheaper than lock up converters.

Engine wise, a decent mileage cam with some power would be in the 210 - 216 intake duration @.050 range. Add a LD4B or Performer or on the very cheap a OE iron 4bbl. intake, 600 Holley/AFB and headers w/a 2-1/2 exhaust.
Keep the stock heads stock for now.
Use a good ignition system and IMO, you’ll be in good shape with a mid 13 second car that gets good mileage when at cruise.
 
I've always read that Mopar OD transmission require extensive trans tunnel modification plus the problem with finding a non-lock converter. The 200R4 requires minimal (many threads on FABO) mods to the upper cross member and non lock up converter are easily found. I did it to my '69 Barracuda so I know, I have an extensive thread on everything I did to my car (did it all myself).

treblig
 
If you want power and mileage, 318s need all the help they can get.
Start looking at making your engine run efficient throughout the rpm-range and make good torque at low rpms. Power comes naturally then.

A 2-bbl intake... come on, really? Thinking about aluminium heads and then choke it right down again with a wimpy manifold doesn't sound like a plan.
Aluminium heads mainly help at higher rpms.
Mileage comes from making good torque at lower rpms, where you do the most driving (<3000 rpm).

Costwise I think you're still miles ahead even with 'extensive tunnel mods' and a A500/A518 transmission. Consider the costs of beefing up a small GM transmission, getting a proper adapter and flexplate to match it all up, linkage adapter.
 
A four barrel intake and carb with dual exhaust will make more power and gas mileage could even improve if he keeps his foot out of it.
 
My son was very receptive to the thought of an od transmission. Definitely gave him some things to think about.
 
Please don't hate me, but: this story has a simple solution.
Here are your options;
For more performance; moreTM (Torque Multiplication),bigger engine,more air thru-put, more compression.
>For more fuel economy; Smaller engine, lower rpm, more compression
>notice more compression is on both lists.
If you want to spend money, get the compression up.That's a triple whammy; More torque, more power, and more mpgs.
this story has a simple solution;
a bone stock LA360 with a 318 cam and no more than 3.23s. I'd even put the 318heads on her.
It costs pretty much the same to repiston a 360 as it does a 318,and it's way easier to make compression with the larger swept volume of the 360.
A big engine operating at a lower rpm might make at least as much economy as a smaller engine operating at a higher rpm. The problem often is that the smaller engine suffers in the performance arena.
A 360 has no problem pulling even 2.76s with the tallest tires you can fit. But 2.94s will get you about 50mph@5000 rpm,in first gear, so I like those.And yes the 318 cam will go to 5000, even 5500. but it's kindof done at 4500 to 4800 with the stock 318 heads.
Then a matching port-size intake,a metering-rod carb,a free-flowing exhaust, plus I'm a huge fan of fresh cold air into the carb.
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Aluminum heads on a low compression teener with a stock cam is IMO; now how do I say this delicately?, um, not the best engineering. Whatever you might gain in the compression is lost to the increased heat loss from the chamber. And since the stock cam is in there, The advertised head flow will never be achieved, or at least not for very long. And if you upsize the cam, then the cylinder pressure drops, and the low-rpm torque falls into the basement. So no matter how you slice that pie, it will leave you with a bad memory. Aluminum heads work best with high compression; they are a match made in heaven.
Those are my opinions.
loosly based on my experiences.
 
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AJ/FormS said:
Please don't hate me, but: this story has a simple solution.
Here are your options;
For more performance; moreTM (Torque Multiplication),bigger engine,more air thru-put, more compression.
>For more fuel economy; Smaller engine, lower rpm, more compression
>notice more compression is on both lists.
If you want to spend money, get the compression up.That's a triple whammy; More torque, more power, and more mpgs.
this story has a simple solution;
a bone stock LA360 with a 318 cam and no more than 3.23s. I'd even put the 318heads on her.
It costs pretty much the same to repiston a 360 as it does a 318,and it's way easier to make compression with the larger swept volume of the 360.
A big engine operating at a lower rpm might make at least as much economy as a smaller engine operating at a higher rpm. The problem often is that the smaller engine suffers in the performance arena.
A 360 has no problem pulling even 2.76s with the tallest tires you can fit. But 2.94s will get you about 50mph@5000 rpm,in first gear, so I like those.And yes the 318 cam will go to 5000, even 5500. but it's kindof done at 4500 to 4800 with the stock 318 heads.
Then a matching port-size intake,a metering-rod carb,a free-flowing exhaust, plus I'm a huge fan of fresh cold air into the carb.
Click to expand...

While it is hard to disagree that a bigger engine is better for this and even more so since I have done 360’s with excellent results with just basic bolt on parts with and without camshaft changes. He does have a 318 and did ask about a 318 so why don’t you help him build the engine he is asking about rather than add to the equation and possible confusion due to the added contemplation?

Again, not that I disagree with the use of a 360.
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Aluminum heads on a low compression teener with a stock cam is IMO; now how do I say this delicately?, um, not the best engineering. Whatever you might gain in the compression is lost to the increased heat loss from the chamber. And since the stock cam is in there, The advertised head flow will never be achieved, or at least not for very long. And if you upsize the cam, then the cylinder pressure drops, and the low-rpm torque falls into the basement. So no matter how you slice that pie, it will leave you with a bad memory. Aluminum heads work best with high compression; they are a match made in heaven.
Those are my opinions.
loosly based on my experiences.
Click to expand...
It has been proven otherwise. But with upgraded cam and compression. Aluminum is not a power maker or looser, but allower. In the form of allowing more compression.

The power loss due to heat escape through aluminum has been disproven.

And as shown by members, flow over compression.
(But Ma MoPar already told you that years ago. 360 heads on a 318.)
 
A lot will depend on the type of driving this is intendend for. A lot of idling time and stop and go is different than improving mpg on the county roads and interstates. Some will also depend on the climate. Since emissions are not a condideration, carb and timing is fine.

I think the 318 is very decent base. In stock form, using a timing curve from 67 or 68 non-CAP, should pull 21-22 mpg highway with the current drivetrain and provide good pep.
Reducing weight is always a plus for both goals. (feather duster for factory example amed at milage)
A four barrel carb will help power in the rpm range. As others have said it should not hurt mpg. The extra two barrels allow it to operate with more efficency over a wider rpm range. If trying to improve 1/4 mile times and mph - this is what is needed. Horsepower is all in the top rpm - its not the same as pep.
Small tube headers will help the upper rpm and possible the entire range. These will need to be custom for what you want to do.

Changing intake to aftermarket is sometimes better for mid and top power (2500 - 6000 rpm) and often worse for idle to mid. A lot has to do with fuel distribution during part throttle. With good vacuum this is (part thrtottle/low throttle distribution) less of a problem but it still can be worse than many stock intakes. Losing weight is good of course.
Aluminum heads. Losing weight is good. Others have already commented on other impacts. This change will require some time working on part throttle timing and fueling.
 
Penstarpurist said:
I think that the way to go would be keep the iron heads, stock 340 cam, 4bbl intake either stock steel or aluminum, and carb to match, dual exhaust and a set if 355's out back. Put all the stock parts on the shelf to put back stock if ever wanted. What do you guys think?
Click to expand...

I think this will be a good plan...

The aluminum heads and 2 bbl intake are not worth the expense vs power gained for your application...
 
Oh hey! There is always a super charger! A TorqStorm is reasonable in cost and your only looking at two other expenses to make it work. A boost reference fuel pump and MSD ignition with retarding the timing. This in addition to basic breakfast or on parts and a well thought out cam would yield excellent results.
 
The trick to build power with the least amount of overlap you can get away with. Overlap kills mileage but its great at building mid high power. Rhoads lifters can help, same with roller cam wide lsa and high ratio rockers good flowing heads etc...

Compression matters but really our hands are tied with how much we can have.
For a mileage cam squeezing more the 9:1 can be a chore and you definitely don't want less than 8.5:1 if you can help it. So you got a narrow window not to much be done here.
There is things you can do to increase this but you better know what your doing. Going up to 10:1 from 9:1 is only gonna get you an increase of 10-15 hp on your build.

And overdrive is number 1 way to increase mileage on highway. But it also allows the number 1 way of making your car a street terror is allowing deeper gears. Deeper 1st and 2nd might also help.
 
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