Help me build a 318!

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res1vw21

res1vw21

It's only metal
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Location
Renton Wa
So here is what I am doing, I need a decent gas mileage 318 for the Super Coupe for my cross country (WA-NY and back) road trip next year...

Here is what I have:

'71 318 running and driving in the Swinger right now (OD 4spd and 3.55SG 8 3/4)
Bottom end is stock right now, it has rebuilt 302 heads, a holly 650 4150 (was a 2bbl motor) Edelbrock performer and a set of hooker long tube headers. I think I am getting about 18mpg but I am going to double check that tomorrow.

I have a spread bore Holly 650 DP I am planning on putting on to see if I can bring the millage up a little bit maybe 20mpg?

Now it's got a bit of power but as you all know a stock 318 isn't anything spectacular.

So here is what I am thinking. It needs rings because it's blowing a little right now (a lot less with the head change) so take it to the machine shop and have it hot tanked, checked out and honed, balance a set of '68 318 rods and pistons to give me a lighter rotating assembly and little more compression, add a windage tray, timing chain tensioner, and double roller timing chain and bolt it all back together with new rings bearings and gaskets.
As for cam I was thinking something similar to a stock 340 cam. (Even a used 340 cam would be fine with me, 68 4spd cam being preferred)

Then install in the Super Coupe with the OD 4spd and a 3.55SG 8 1/4.

So how well do you all think this combo would work?
What kind of gas mileage would I be able to pull down?
Should I just rering and bearing the engine to try to keep decent MPG for my cross country roadtrip?
 
How many miles on this engine? Due to it's age (unless it's a low mileage engine which I doubt if the rings are worn out) it's possible it'll need more than just re-ringed. If the piston to wall clearance is too loose the rings won't seal up good and that means less power and fuel mileage. If you do find out you need to bore it get some higher compression pistons. Something that'll get you in the high 8's ~ 9 to 1 comp. More compression will help power and fuel mileage and at high 8's ~ 9 to 1 you will be able to run 87 octane. I highly doubt a 650 double pumper will help fuel mileage because they are generally calibrated for power. For fuel mileage I'd run a Holley 600 vac. sec. or 600 Eddy or if your up to the challenge get a Thermoquad and do some careful tuning. As for the cam a 68 340 4 spd. cam isn't going to help fuel mileage. A newer (71-73) 340 cam might help, or at least equal your stock teen's cam but make more power. But there are so many aftermarket cams designed for fuel mileage I personally would look into them. Get something with lobe centers on 112~114. No more than 260 advertised duration and 208 degrees duration at .050 and .450 lift. Also stay with a straight duration cam, not a split duration. Set up the dist. with as an aggressive spark curve as the engine will allow. Most likely you'll find about 12~14 degrees initial timing with it all in by 2200~2400 will do you good. And make sure to run a vacuum advance and play with the adjustment on it to get it coming in asap without detonation. With all that you should be able to get a good amount more power from it and easily break into the low 20's on the hwy.
 
can also change the diaphragm spring for the vacuum secondaries in your holley carburetor. Lighter spring opens earlier, tighter will limit how far the secondaries open when at full throttle. Everything fishy68 said is dead on the money.
 
This is my current setup using a '85 318 block and 302 heads. Great mpg's and power through the rpm's.

Block bored .030 over, decked, stock rods and crank, .010 under, balanced
ARP rod and head bolts
TRW-8k285ncp30 pistons for about 9.5:1 comp
Heads are stock 302's with a good valve job and back-cut
crane valve springs
lunati voodoo camshaft 60401 lift .454 in./.475 exh.
duration @ .050 213 in./220 exh.
lsa 112 installed straight up
Weiand stealth intake
Edelbrock 1406 carb.
Mallory unilite ignition
TTI headers with magnaflow mufflers 2-1/2''
timing set to 14 initial and 34 total in at about 2,800
 
I have built, literally, dozens of these engines over the years and can tell you that your plan is pretty close to getting you where you want to be. I've had excellent results by doing exactly as you posted, but using 360 heads - with one caveat:

If you dingle-berry hone it (or 400 grit sandpaper) and go for the cheap refresh, run .005 over rings, new chain, brgs, oil pump etc, it will run strong due to it being loose, while sealed up with new rings and cylinder heads, which will also allow it to rev like there's no tomorrow. I've ran many of these engines to 7000 rpms and tried to blow them up, just to give me an excuse to build the next one, but I was never able to "break" one of them. This is where the caveat applies:

The engine will run fine, but you will not have an engine that is going to last more than about 25-50,000 miles, depending on how much you beat on it (i.e. lifecycle of the engine will decrease), but the best results (when looking for performance and mileage) I've had were with the 360 heads and either the 340 4spd cam or 6 pack cams and, because I couldn't afford new cam kits, I've ran used cams with new lifters... However, while I never blew one up, truth is, the rings would give out after a year or so of beating the snot out of it, and I'd have to find me another "donor" 318 and repeat the process. The more aggressive you build it (more power), the shorter it's lifecycle. No big deal though, as I had plenty of friends that would (almost) pay you to take an old 'teen', and that was a great deal for me at the time...

I've ran multiple 318's, with 360 heads in a 67 Belvedere 4 spd car (back in the '80's), with 3.23 gears, and used the car to commute between NC and WV for many years. It had 1.625 headers, 2.5 inch exhaust, and, as noted, an 833 4 spd trans (no overdrive), and I got 21-22 mpg cruising between 65 and 70 mph - for 7-8 straight hours each way. I had my best results with the 360 heads, since they never hurt bottom end performance, and added significant mid and upper range power that came in hand at times. It wasn't a bullet, but with a quick swap to 4.10's I could hammer most of the 350Shivvie guys with 'em.

It all comes down to personal preference: if you want to do it on the cheap, and you're comfortable with a shortened service life, then go for it. On the other hand, if you're looking for longevity and want it to last you 100K or more, spend the money on pistons, boring, balancing, etc. and you'll be happier in the long run. However, IMHO 318's are the best kept Mopar secret for cheap-reliable power plants and most guys will give them away. That's too bad, as I've had many skeptics refuse to believe I was running 318's due to how strong the cars ran.

If you doubt it, just check out Mopar Actions (cheap) 318 build making 425 HP. It's not hard to do, and that'd be more than enough HP to embarass some 340 and 360 owners out there.

Whatever you decide, have fun with it and let us know how it turns out.

Southernman
 
Groovy this is exactly the advise I was looking for!

I was going to take the block and have it checked to see if it is usable with stock pistons (if I have to bore it I will and am looking for 9ish) and no matter what the rotating assembly will be balanced since it's a 4spd car.

The engine is out of an auto station wagon and had less then 100k on it when I installed it in the swinger last year.

It didn't smoke when I installed it but admittedly I beat the living crap out of it now. I blew the valve stem seals and got a smoking deal (no pun intended:violent1:) on rebuilt 302 heads so I installed them which took care of 95% of the smoking problem but it does still blow a little though It's hard to tell if it's blue or black when I am driving and I haven't had anyone follow me recently to tell me. It does use a bit of oil though (and leaks some too).



Thank you fishy68 for the advise on the cam and carbs, mostly I was thinking 340 cam for the fact that I can get a used one for decently cheap, I will keep my eyes open for a latter one. As for the carb I have a few vac secondary stock holly carbs that I rebuilt and put on the shelf so I will play around with them in the next few months to see what results I can get. I do have a sweet 450cfm primary 750 cfm secondary double pumper that I want to play with as well.

Good to know Southernman I am hoping to get a few more miles out of her but hey 318 blocks are plentiful!


Thanks for all the replies and please keep them coming!

I will let every one know how it turns out.
 
Not trying to hijack your thread and I know you are asking about 318's, but I just built my 71 Charger with the same thought in mind. What I did is a 360 bored .030, 9-1/2 flat top pistons. Windage tray, Melling m72 hv oil pump. Crane energizer cam with 216* duration .454 lift, 3 angle valve job with port matched heads, Eddy RPM intake with a 600 AVS carb, orange box, headers/duals. 727 with factory high stall converter 8-3/4 rear with 2.94 gears. I am getting 16 mpg so far and still have a few more jet/rod changes to make in the carb. and other tuning adjustments. My goal is to match my 09 Ram's milage, which am very close to doing.
I think you are on track with your goal and a good cam will help you bring it closer. You could also call different cam grinders and get their recommendations for your goal. Good luck and look forward to seeing your results!
 
WOW! Great advice and builds. Nice work guy's!
I like fishy's idea's a lot. Build it close to stock cam spec's and give it a free flowing exhaust and decent intake. Best spreadbore carb is the TQ, however, a 600 AFB/Edelbrock will do you real well.
 
There's quite a bit of weight difference between the dart and super coupe it's not going to make near the same mileage.
 
I think if you installed some 2:76 gears in the rear end in conjunction with the 4 speed OD trans, you would get at least 2 more mpg across the board too.
 
Dartnut said:
I think if you installed some 2:76 gears in the rear end in conjunction with the 4 speed OD trans, you would get at least 2 more mpg across the board too.
Click to expand...

My buddy has 2.94 in his Aspen and he can never get it into 4th unless he is doing 70. That would put it into roller cam territory for sure too.
 
res1vw21 said:
So here is what I am doing, I need a decent gas mileage 318 for the Super Coupe for my cross country (WA-NY and back) road trip next year...

Here is what I have:

'71 318 running and driving in the Swinger right now (OD 4spd and 3.55SG 8 3/4)
Bottom end is stock right now, it has rebuilt 302 heads, a holly 650 4150 (was a 2bbl motor) Edelbrock performer and a set of hooker long tube headers. I think I am getting about 18mpg but I am going to double check that tomorrow.

I have a spread bore Holly 650 DP I am planning on putting on to see if I can bring the millage up a little bit maybe 20mpg?

Now it's got a bit of power but as you all know a stock 318 isn't anything spectacular.

So here is what I am thinking. It needs rings because it's blowing a little right now (a lot less with the head change) so take it to the machine shop and have it hot tanked, checked out and honed, balance a set of '68 318 rods and pistons to give me a lighter rotating assembly and little more compression, add a windage tray, timing chain tensioner, and double roller timing chain and bolt it all back together with new rings bearings and gaskets.
As for cam I was thinking something similar to a stock 340 cam. (Even a used 340 cam would be fine with me, 68 4spd cam being preferred)

Then install in the Super Coupe with the OD 4spd and a 3.55SG 8 1/4.

So how well do you all think this combo would work?
What kind of gas mileage would I be able to pull down?
Should I just rering and bearing the engine to try to keep decent MPG for my cross country roadtrip?
Click to expand...


go to moparts and look up hotroddaves 318 super mileage thread
30 mpg highway..lots of good info.
from his thread the key for mileage will be comp( 0 deck kb 167?)
cam w/min over lap but good lift,thermoquad carb ,stock 302 heads
and lots of other info.
 
it's not as simple as low gear and overdrive.
can't quite remember but i think you have to target maximum part throttle torque at cruising speed
which i think was around 1800 - 2000 on his build,going higher or lower hurt mileage.
much info in that thread.
 
I'll call you- I've got a stock 340 cam NIB (Mopar) in my shed I got from Stearns.
 
try this
Super duper MPG 273/318 experiment ! NUMBERS !!!!!!

.. you may not want to duplicate his build but there is a lot of info there
 
Thank you ir3333 I will do some reading.

Sweet V-100 if anything we should at least grab a beer if you drink beer! (Black Raven is a great place)
 
Salty Dog said:
WOW! Great advice and builds. Nice work guy's!
I like fishy's idea's a lot. Build it close to stock cam spec's and give it a free flowing exhaust and decent intake. Best spreadbore carb is the TQ, however, a 600 AFB/Edelbrock will do you real well.
Click to expand...

Another vote for the TQ!! Thermoquads are excellent,both at making power and good gas mileage. As far as I'm concerned,they are the next best option to fuel injection.
 
res1vw21 said:
Thank you ir3333 I will do some reading.

Sweet V-100 if anything we should at least grab a beer if you drink beer! (Black Raven is a great place)[/QUOTE

Left you a VM- sure we could hook up. Sunday is good, re-assembly/detail work on the GS Saturday
Click to expand...
 
defiantly some interesting reading in the moparts thread. Now I just need to figure out what I want to do lol. I am also trying to do this as cheaply as possible so that plays a bit of a roll in some of the choices.
 
Is this a max mileage attempt on a budget? I have an idea or two.
Are you handy/do you have a die grinder? Do you have a air brush for automotive use? Is off set stroking to much out of the way?
 
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