Improve my 318!!

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72DartSwingerV8

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Alright guys I'm looking to get my 318 a little more fuel efficient as it has now become my daily driver. Here's my setup:

318 block .030 overbore with standard pistons
318 heads .010 decked
1.88 intake valves
1.60 exhaust valves
340 MP purple shaft cam
Edelbrock Performer Intake
4175 Spreadbore Carb 650 cfm
heddman headers
2.5" exhaust
3.55 gears in the rear
904 automatic tranny
Electronic Ignition conversion

I'm looking at roller rockers, EFI conversion, alternator upgrade, or a throttle body conversion mainly to improve mileage. Maybe even a supercharger? You guys have any other ideas for making this thing run a little better? I want to keep the heads and block the same but I might change the intake for EFI if need be. If you have any ideas that's worth it then I'm all ears.

Thanks guys,
jake
 
Well, if mileage is what you want, there's one thing there that's really gotta go. If you drop the purple shaft for one that has got less duration, and a wider lsa, you'll gain a little low end, lose a little top end, and smile as you pick up quite a bit of mileage.

I'd say also, if you're prepared to start throwing cash at it, and efi conversion is a good way to go. But I wouldn't use a throttle body injection system, You're mileage gains won't be great, but your power loss will. A port injection system is what you might want to go with. I'm personally kinda iffy about EFI unless you build your whole package for it.

Instead of jumping into expensive territory, get yourself an o2 sensor, an air fuel ratio gauge, and either buy a set of jets, power valves and a book on jetting holleys. Or take it to someone who does dyno tuning and tell them what you're trying to accomplish. A holley will run just about anything, but getting them dialed in can be a *****.

Along the carb route, you might also consider a Carter/Edelbrock avs or afb. Not only are they easier to tune than holleys, they're known for all around better mileage at the cost of not screaming as loud.

I'm not sure what you expect to gain from an alternator upgrade, since the power loss from the alternator is related to the load put on it more than its internal structure.

Roller rockers aren't a bad idea, but at this build level, the gains will be miniscule. Switching to rollers makes a bigger difference with big cams, big springs, and big rpm's.

A supercharger will hurt your mileage, period. Not only will it be forcing more air (and therefore, more fuel) into the engine all the time, you've also got the parasitic losses to drive it to consider. Supercharging will only help mileage if you're installing a smaller motor, (like, say, a magnum v6) and making up the power difference with the supercharger.

And although it's less fun, some taller rear gears, 3.23's, 3.08's, 2.73's will make a big difference too, especially down the interstate.
 
ALright thanks for the quick replies. I'd like to stick with the 3.55s because frankly it's too much fun.

Throttle body and supercharger are out.

Looking at EFI I was planning on following a writeup that used Ford stuff. I'd drill the intake for the injectors and use the computer, the works. You think an 02 sensor after the header would really help tuning it? I need to practice my carb tuning anyway. Just a generic sensor will work?

I was thinking that rebuilding the tranny might help it out too. The 200R4 upgrade looks promising.
 
An 02 sensor is a great item to use in the headers collector (not reducer) to aid in tuning the carb. Been there done that with quick and excellent results! IMO, a new AVS style from Edelbrock would be the best new carb while a small primary TQ would be Bette if you can get a good one. Tuning rods are difficult to find. I use modified AFB/AVS rods 3/4 inch shorter.
Edelbrock has a inexpensive 02 sensor.

Cam wise, for this operation, I like a Crane cam. I have also found mileage with Rhodes lifters and custom pushrods depressing the lifter as little as possible. Use a split duration cam 1 step down from what you have now and go with an overdrive trans.
 
Drive it like a grandma.

I don't know about San Diego, but around here, we can pick up 4-bangers for about $1000 all day long. Many of those upgrades you were thinking about are going to cost nearly that much money. Additionally, $1000 will buy about 300 gallons of gas, and I would assume your car gets around 12-15 mpgs. If you avg 12 mpg, you'll be able to drive 3600 miles which depending on the distance you drive could last you the entire year without dropping money up front. Try conserving fuel by combining trips, removing unnecessary travel and by vehicle maintenance (tires 32-35 psi, tune up, etc.) Just a few ideas. Good luck.
 
I've already had the carb rebuilt professionally and want to stick with it. The 02 sensor sounds like a great place to start so I can look into that. WIll the eddy sensor matter to the Holley carb or is it giving the same info?

I'd like the cam to stay as well because it's what I've wanted for a strong runner. THe mileage is about 15 mpg currently but just looking to get it to 17 or 18.

Whats the best way of getting an overdrive automatic in there or do I need to convert to a stick for overdrive?
 
Tune tune tune. You'll struggle to make up in fuel; saving what you spend in upgrades. Yep,there are better cams,heads,etc but you can do better with tuning. For highway use less gear or OD would be helpful.
 
An overdrive transmission, particularly an A500 transmission (basically, a 904 with a 4th, electronically controlled overdrive gear) out of an early 90's Truck. They'll bolt up, but you will need to shorten your driveshaft and cut your floor to accommodate it. basically it gives you a top gear ratio of .72-1 as opposed to the 904's 1-1. This'll knock as much as 700 rpm off your cruising speed. and you don't lose anything on the bottom end.
 
I agree, Tune it,. It shouldnt be that bad on fuel. Maybe lose the spreadbore Holley for a TQ or an Eddy 600.

That MP 340 purpleshaft isnt that big and is on a 112 or 114lsa.
 
I'm interested in te A500 swap. How much floor do I need to cut and does the corssmember need to be changed as well?
 
lots of things to try
thermoquad( small primaries)
1967 273 2 bbl short duration camshaft or any high lift/short dur.cam
high compression (min. 10.0:1)
302 small valve heads
276:1 gears
any of the above should make a difference,none of which you're willing to change
so your best option would be OD.
you will have to make sure your most efficient maximum torque is your cruise rpm
and that may require 3.91 gears.
 
There's a local (SD area) FABO member here that knows quite a bit about setting up MOPAR Small Blocks. He recently helped me with porting/tuning and cam choices to get my daily driver exactly where I wanted it. Giving him a call might save you some time and money before you start getting into the EFI's etc. Shoot me a PM if you want his contact info.
 
havent been able to read all the replies 'browsing with phone', but i would stay around 600 cfm with the carb, the eddy works good as well as the holley vac secondary.
I would tune the timing/curve, to start
What kind of cranking cylinder psi does this 318 have with those heads?
Are these 360 casting or 318 castings?
Were the bowls blended ?
if this is a 318 head with bigger valves...its even more important to have done some blending/porting.
I live in n.sd, i can check it out and tune what u have along with offer some advice on improving it.
 
The OD and FI mods talked about here are cool and i'm not trying to discourage you from making them. I just want you to run the numbers before you decide. If this is strictly a money saving move, and you want to get 2-3 mpg better, your probably gonna have to put 100k miles on it to recoup your investment. Carb, timing, tuning changes may be a better alternative from a cost standpoint.
 
Even things like oil help my 5.9 Jeep pretty hard on gas it was getting 11.8 mpg switch to Royal Purple now getting 12.3 mpg and I was already running Valvoline synthetic oil. Don't forget get about driving habits my dad used my Jeep for a week and got another 1.5 mpg over what I get. Another OD swap you can do A833 OD standard tranny there fairly cheap.
 
Question NUMBA ONE

With the 3.55 gear, what rear tire you running, and what is your RPM at 60 or 70? I'm betting you have fairly small diameter tires, and are running a fair amount of RPM

NUMBA TEU

Spending tons of money of EFI is not gonna get it. The cost of the EFI will certainly not ever make up for the meager mileage increase.

NUBA THA-REE You may have too much cam. Research the old original 340 cams and compare. Are you using vacuum advance? MANDATORY for any decent mileage.

Here's some real world figures for you, PREFERACED by the fact that yes, back then, we had "real" gas"

Somewhere around 73, "we" had our first "gas shortage" and I thought I was gonna build a drag car so therefore wanted a high mileage street car. My car at the time was this 440sixpack 70 RR, which at the time had a used 440 in, (long story) I bought a low miles 71 (high compression) 340 out of a junker and put in the car

So we have a 70 RR, A-833 hemi box, Dana 60/ 3.54, G-60x15 rear, and headers. Carb varied between original (choke damaged) TQ, QJ, Holley SB. Weighed as I remember about 3860. RPM at 70 was realy close to 3000 on the nose. Stock factory 340 cam.

THAT THING GOT 17.5 mpg and was and am not that careful a driver. I'm not a guy who idles out onto the freeway doing 45 at the end of a ramp!!! If I'm on a two lane road and you are being stupid, YOU are gonna get PASSED. The car had aftermarket "hang on" A/C, and would guess that "careful" driving could have done better.

(Even the original 6-pak engine, with headers, Edelbrock, and a Holley 800 DP managed to get just under 14.)

http://moparforums.com/forums/f62/my-old-ride-back-day-596/

81sruds.jpg
 
ALright, to answer everyone's questions and ask some more:

What kind of Thermoquad should I be looking for? and do these come in spreadbores?

Is the only way of increasing compression by decking the heads? I took .010 off the head already.

1w&cg
I still need to measure cylinder pressure. Heads are 318 castings that I had 360 valves put in. I don't think the bowls were blended but I'm not positive.

I'm running 17" wheels so the RPMs aren't too high but could always be a little lower.
 
Is that a new OE replacement 340 cam or the upgraded 340 cam?

Every TQ is a spreadbore. Look for one with the small primaries at 1.38 inch.
Increasing compression now that the engine is built happens on two ways. Minorly with a thin head gasket, a little bit with a head milling. .010 milled is a very very small amount milled.

The carb and/or the 02 sensor do not care about each other And will not effect each other. The carb doesn't give info to the sensor. The sensor reads the amount of 02 in the exhaust

Do you have a MSD or like unit on the car now? I have found them to be very good at getting mileage from our old rides.
 
I think most questions asked are great ones.

Id love to hear what the tire size is on your 17 inch rims, to help figure out what the ratio to the road is.

It would be nice to know what mpg your getting to begin with.

If your cam isn't huge i think you should try and tune your carb "if possible" to try and get the best mpg. like said a o2 sensor helps a lot. Wideband would be best for an o2 sensor. You could even make it able to swap from car to car for tuning if you got clever.

From what I've heard about thermoqauds is they can be great but are hard to tune, maybe not a good carb for a first time tuner?
 
Tire size,most likely a 245/45r//17.X2,on the wideband.If you really want more mileage cheaply,install and use a vacuum guage. A multispark box will slightly increase mpg,and drivability and kaintenece intervals.
 
I do not have an MSD unit, only an Electronic Ignition from a late 70s Mopar. I was considering putting my CDI on there but heard that you shouldnt run CDI on electronic ignition. That true?

If I were to get the heads remilled how much more could I comfortably take off?

Tire size is 245/45r/17 as guessed.

Mileage is about 14mpg

Could you guys explain the difference between a wideband and a normal 02 sensor?

Vacuum gauge already installed.
 
You could spend 5-10 grand on the thing your posting to get better gas mileage which if you did every thing you said may give you a 20-30% increase of 3-5 mpg, money not well spent. Pick a budget and do the things with the most reward.
 
72DartSwingerV8 said:
I do not have an MSD unit, only an Electronic Ignition from a late 70s Mopar. I was considering putting my CDI on there but heard that you shouldnt run CDI on electronic ignition. That true?
Click to expand...

My turn for a question. What the heck is a CDI ignition?
(I should know this, but it is really late for me and a couple of double shifts under the belt, well, my head hurts right now, so I'll just ask.....)

If I were to get the heads remilled how much more could I comfortably take off?
Click to expand...
Genealy, .060. Talk to your machinist before milling the head blindly.

Could you guys explain the difference between a wideband and a normal 02 sensor?
Click to expand...

A very basic way to explain this is that a wide band 02 will tell you the air fuel ratio on a wide scale. From a ratio probably to rich and to lean for your engine to run on.

A narrow band is just that, a very narrow window. Normaly just a point or two off of a perfect condition.

You want a wide band sensor if your new to this. (Carb tuning)
And I think you are via the questions your asking.

Vacuum gauge already installed.
Click to expand...

Also a good tool to use.
 
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