Engine size recommendation

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JMack

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I'm looking for a little input on what direction I should go in for my 73 Duster. It is a 318 model with a non-original 318 and a 727 transmission in it now. It is tired and in need of a rebuild.

The intent of the vehicle is for me to drive it back and forth to work during the nice part of the year, during rain and snow it will hang out in the garage. It also will never be used to race anyone.

I want an engine that looks and sounds nice and is strong, yet gets decent gas mileage. I assume the 318 is the way to go, but if I use say a 360, will the engine get near the same gas mileage because it also won't have to work as hard and then will everything match up to the 360 (e.g. transmission). If anyone knows a good setup for a nice mix of power and fuel efficiency for this car please share.

Thanks in advance for the input.
 
My 318 does just fine, a little 4bbl, pocket porting of the heads and a mild cam. Sounds good, runs good, decent on gas, and fun to punch the gas pedal! It is in a 65 barracuda formula s.
 
i would look at a 360, especially if its a 3.23 or higher and your going to use a nice tall tire in the rear, you will love the torque over the 318 and mileage will be very close.
 
I made an engine for my brother 3 years ago
he do the same with is than wanna do the engine
is pretty strong and tried to make cost as low as we could

1978 360 block
kb piston final cr. 10.57
915 heads ported at home
750 carb
.509 mp cam(not the best but ¸was cheap
air gap intake
1 5/8 headers you know the real cheap

he is running this engine for the last 3 years have alote of fun
good gas mileage except that he is running premium gas but
a little less compression it could run on 87 octane
 
crazy 340 said:
I made an engine for my brother 3 years ago
he do the same with is than wanna do the engine
is pretty strong and tried to make cost as low as we could

1978 360 block
kb piston final cr. 10.57
915 heads ported at home
750 carb
.509 mp cam(not the best but ¸was cheap
air gap intake
1 5/8 headers you know the real cheap

he is running this engine for the last 3 years have alote of fun
good gas mileage except that he is running premium gas but
a little less compression it could run on 87 octane
Click to expand...



what do you consider "good" gas milage ?? sounds too built for good mileage. my motor wasn't too far off from that and i was lucky to get 10 mpg.
 
JMack said:
I'm looking for a little input on what direction I should go in for my 73 Duster. It is a 318 model with a non-original 318 and a 727 transmission in it now. It is tired and in need of a rebuild.

The intent of the vehicle is for me to drive it back and forth to work during the nice part of the year, during rain and snow it will hang out in the garage. It also will never be used to race anyone.

I want an engine that looks and sounds nice and is strong, yet gets decent gas mileage. I assume the 318 is the way to go, but if I use say a 360, will the engine get near the same gas mileage because it also won't have to work as hard and then will everything match up to the 360 (e.g. transmission). If anyone knows a good setup for a nice mix of power and fuel efficiency for this car please share.

Thanks in advance for the input.
Click to expand...


you sure you have a 727?

just do a 318, small 4bbl headers and a decent set of mufflers. should give ya sound and you should be able to tune for good mileage. thats all your looking for.
 
abodyjoe said:
what do you consider "good" gas milage ?? sounds too built for good mileage. my motor wasn't too far off from that and i was lucky to get 10 mpg.
Click to expand...

2x 10.5 comp! ah geeze for a race car great! besides im worring that there gonna drop another point in octane on us... thats why i didn't go 10:1
 
I would like to have a set-up closer to 15-17mpg, is this possible with a 360? Is it possible with the 318?

I won't be racing anyone, I want a strong reliable engine that will for the most part be a daily driver w/ the exception of bad weather. So in order to invest the money I want to take the fuel efficiency into consideration, especially with climbing gas prices, but would still like a little pep to the gas pedal if I needed to pass someone. If the 318 is the only way to accomplish this, would simply rebuilding it, new bearing, seals, etc. and adding a 4bbl intake/carb (any suggestions for best combo), headers with dual exhaust do the trick. I'd like to have a good idea of what I want to do with the engine before I engage someone to rebuild it so I can explain what I want to have done.

Thanks again for everyone's input, it is much appreciated.
 
I'm not 100% certain what the transmission is, is there a easy surefire way to confirm (or deny) what I have?
 
The 318 will have a mileage edge, no doubt. I'd rather go with a 360 for added brute torque down low.

A basic rebuild with OE pistons or upgraded compresion units for more compresion can be used with gapless rings. No blow by, max compresion.

OE heads simply rebuilt. A upgrade would be 1.60 exhaust valves.

600 cfm carb or a TQ, small primary version on top of a Edel. Performer intake.
Headers a plus, dual exhaust off the manifolds for sure. 2-1/4 min, 2-1/2 max.

If your not sticking to the stock cam, I would go no larger than a 216/218 intake duration and 8 - 10* more exhaust duration with stock port heads.

I ran this cam in a Duster with 3.21 gears and 225/70/14 tires. The engine was a stock '79 - 318 with a LD4B intake and 600 carb, headers w/2-1/2 exhaust.

You should be able to get 18 mpg's with added compresion, use of a MSD 6 box for making sure all the fuel is burned and taller tires would help in mileage as well.
 
Another example I did was a 360 in my '79 Dodge Magnum. A simple bolt on part upgrades. The car was basicly 3700 lbs. The 360 got 20 mpg's. I did the following to the drive train;

360 dead stock
JY iron 4bbl intake
Carter 625 AFB MP distributor fired by a MSD 6
Dual exhaust w/ H-pipe and Thrush mufflers @ 2-1/4 to the rear bumper
The air cleaner was a factory 340 "Trap Door" w/ a K&N filter

Thae trans recieved a basic shift kit and deep pan

The rear remained stock with 2.76 gears while the car road on 235/60/15 on all 4 corners.

Headers would have helped mileage, but I never got there.

No matter which engine you build, keep it simple and mello. You will get good results and mileage from the engines. Another thing you may want to consider is an overdrive trans. The ratio of MoPars ODtrannys are .69.

.69 X 4.10 = 2.829 or 2.83 final gear ratio feel. You can accelerate quickly and shift into OD for a Hwy. gear ratio. Just food for thought.
 
JMack said:
I'm not 100% certain what the transmission is, is there a easy surefire way to confirm (or deny) what I have?
Click to expand...


trans%20pans%20difference.jpg
 
JMack said:
I would like to have a set-up closer to 15-17mpg, is this possible with a 360? Is it possible with the 318?

I won't be racing anyone, I want a strong reliable engine that will for the most part be a daily driver w/ the exception of bad weather. So in order to invest the money I want to take the fuel efficiency into consideration, especially with climbing gas prices, but would still like a little pep to the gas pedal if I needed to pass someone. If the 318 is the only way to accomplish this, would simply rebuilding it, new bearing, seals, etc. and adding a 4bbl intake/carb (any suggestions for best combo), headers with dual exhaust do the trick. I'd like to have a good idea of what I want to do with the engine before I engage someone to rebuild it so I can explain what I want to have done.

Thanks again for everyone's input, it is much appreciated.
Click to expand...



15 - 17 mpg should be no problem with a 360. my all stock 360 with headers and a 780 carb and 2.94 gear gets that and i never even tried to tune for better mileage.
 
I like the 318 myself...Only because I am in the middle of building one...They have low compression, so you'll need to mill the heads or get a aftermarket closed chamber head like RHS. On mine I'm using a stock bottom end with RHS heads, with hughes 1.5 roller rockers edelbrock RPM cam and lifters & an RPM manifold with a holley 600 spreadbore carb, and dougs headers...I hope this cobbled together parts engine makes 300 HP. I'd be happy with that. lol
 
I'd just run the 318. Yes, the 360 will make a little more hp/torque, but a well built 318 should have no problem making 300 hp and still get 18 mpg or more. Get the compression up around 9.5:1, put 1.88/1.60 valves in the heads, run a 600 cfm carb, Edelbrock performer intake and a set of headers with dual exhaust to make it sound good. Go with a fairly mild cam, I like the Lunati 60402. Sounds good but still very manageable.

My Challenger has a rebuilt 318 in it, built before I bought the car so I don't know the specs. Its a pretty mild build though, runs fine on 87 octane, idles really smooth, I doubt the compression is even 9:1 or that the cam is anything more than a step above stock. I run a Edelbrock streetmaster intake, 600 cfm Carter, and Hooker Super Comp headers into glass packs and 3.23 gears. It sounds good and pulls pretty well considering the weight of the car. Its not a tire shredder, but its no slouch either. And even though I know the headers are too big and it runs a touch rich I still usually get 15-17mpg on the freeway.
 
Thanks to all for the time and input, this information is exactly what I needed to know. It sounds like I can accomplish this feat with either set-up. I think I will go with the 318 since 1) I already have one and 2) I like the idea of keeping the same size the car came stock with.

I haven't been a member of this forum long, but I'm very pleased with how active and helpful everyone has been.
 
abodyjoe said:
what do you consider "good" gas milage ?? sounds too built for good mileage. my motor wasn't too far off from that and i was lucky to get 10 mpg.
Click to expand...


on a trip where I need to get 60$ of gas
he only need 45$

4.10 gear in mine 3.90 in his car
biggest diference 4 speed for him 727 for me
 
YES! A lean tune will help with mileage. Mine were lean. You can richen up the secondary side for WOT blasts. A Carter carb uses a rod to richen up the primary side of the carb for moderate acceleration. Choose carefuly when trying to balnce the tune between lean running and a lightly richer mix on a moderate accelration.
 
JMack said:
Thanks to all for the time and input, this information is exactly what I needed to know. It sounds like I can accomplish this feat with either set-up. I think I will go with the 318 since 1) I already have one and 2) I like the idea of keeping the same size the car came stock with.

I haven't been a member of this forum long, but I'm very pleased with how active and helpful everyone has been.
Click to expand...

There's a ton of info on 318 builds on here. The basic formula I mentioned above, but there's quite a few different threads on here for specific builds. There's are a couple magazine builds too, one by Hot Rod and one by Mopar Muscle, both were 400 hp 318 builds. Surprisingly, neither build was really that extreme, and a slight cam downgrade for either would be a very streetable build. Both did use something other than stock LA 318 heads, mopar muscle used stock magnum heads, hot rod ported a set of 302's. Head work is needed to get to 400 hp, but not necessary for 300hp except for maybe the larger 1.88/1.60 valves and the port matching for mating to the slightly larger intake ports.

http://www.moparmusclemagazine.com/techarticles/mopp_0409_318_engine_build/machining_process.html

http://www.hotrod.com/howto/113_0304_318_small_block_build/index.html

But outside the headwork, the bottom end of both builds was pretty similar and is a good base for a 300hp build. The extra horsepower in the articles is due to primarily better flowing heads (and a cam choice to take advantage of it), which is probably the biggest bottleneck on a SB mopar, especially a 318.
 
JMack said:
I would like to have a set-up closer to 15-17mpg, is this possible with a 360? Is it possible with the 318?
Click to expand...

I get 16.5 to 18 mpg around town and 21-22mpg on the hiway with my 360. BUT, I also have an A833OD tranny, this combined with 3.55 gears and a 27" tall tire has it turning a tick over 2000 rpm at 65 mph and when I am crusing at anything over 40 mph its in OD.

This engine is far from stock and I have spent a fair amount of time getting the carb dialed in for great mileage. When I first dropped it in the car I was getting 12 mpg. Based on 102 mph trap speeds it is making approximately 370 HP.

Here is my build;

Bottom End: zero decked block with 30 over KB107 pistons.

Heads: Stock magnum heads with 64cc chambers and MP R/T valve springs. Combined with an 0.040 head gasket I have a static compression ratio of 10.6:1. The closed chamber magnum heads provide excellent quench allowing the engine to run on 89 octane and I have used 87 in a pinch but have to be careful getting on it at the lower rpms with 87.

Cam: Comp XE268H. 224/230 duration at 50 with .509/.512 lift (this is more than advertised because of the magnum 1.6:1 rocker ratio). Engine pulls strong from 1500 rpm to 6000+ rpm.

Intake, Exhaust and Carb : I have a Professional Products Crosswind high rise dual plane intake, 1 5/8 headers, 2.5" exhaust with turbo mufflers and an X-pipe. After trying a bunch of different carbs I have settled on a Holley 670 Street Avenger, this carb more than any thing else contributed the most to the decent mileage (it picked up 5 mpg with no tuning compared to a Road Demon 725 or a Holley 3310 750). Also, there is no loss of power as measured by the butt dyno compared to the bigger carbs I tried, the smaller carbs I tried did have a noticeable drop off in power on the top end. BTW, the 370 HP estimate was derived from 1/4 mile runs with a 600 CFM carb.

My Barracuda is a nice weather daily driver between April and the first time the roads are salted in the late fall. I typically put 7-8k miles per year on it. My other vehicle is a Dakota 4x4 which with a v6 gets about the same mileage.
 
I say go with the 318. Almost as someone said above, i'd add flowmasters, headers, and just to make some of the Mopar guys here groan.... A ThermoQuad. You'll love the gas mileage and you'll also love it when those secondarys open. :) Keep it cheap and simple till you can afford to blow cash on gas for fun.

P.s. The more you change, the more it will cost you to build.
 
If your just putt putting around on the street the little 318 is perfect for it...
 
The rear end ratio is going to make more of a difference than either engine.

I got 26 inch tires and 3.91 gears in a 3,700 car with a 10 inch converter. I get 8 to 12 mpg, yuk. I getting taller tires next time for it.

2.94 gears at good on the freeways, traffic seems to be going 75 mph now.

I recall the drive 55 days, U went 62 mph and got 20 mpg with 2.71 gears. If U were not winding it out, lol No cell phones were great
 
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