Daily Driver Engine 318 vs 360, what one?

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JGC403

JGC403

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Whats going to be the better engine for daily driver duty? Conditions around 425 hp and MPGs. (not expecting to get 30mpg, but better than 10mpg)
I'll be thinking out loud hear.

I was just thinking what engine would be better. Getting 425 hp out of a 318 can be done but, how much will drivability suffer? Since the 360 weights about 25lbs more the 360 would need to produce about 450 hp for the same power to weight ratio.

This is what I was thinking so far:

318 Pros
Smaller displacement would have a better chance at getting decent MPGs. Lighter, less weight on the front of the car. Cheaper.
318 Cons
"Hotter" cam, more of a choppy idle. More difficult to achieve horsepower goal. Power in the high RPM band, less low end torque.

360 Pros
Bigger displacement easier to achieve 450 hp. Less choppy idle. Low end torque, won't need REV it as high.
360 Cons
Weight, bigger displacement, use more fuel.


A 360 should produce more low end torque making it more fun to drive around. Am I on the right track, does anyone else agree with my train of thought hear?

What would you do/ opinion?
 
Kind of an apples to different kind of apples comparison, but...

My 73 Satellite 318 2 barrel, bone stock except for dual exhaust, with 56,000 original miles, weighing 3770 pounds estimated 150 factory NET HP, plus about 20 for the duals, for a total of 170 NET, with a 2.73 gear---average 14 MPG carefully monitored over the last 1500 miles, in mixed driving on 89 octane.

My 2000 Dakota R/T 5.9 (360) MPI, stock (roller cam, molly ring) except for cat back duals and K&N air filter, with 138,000 miles, weighing 4200 pounds listed at 245 factory NET HP, with O/D trans and effective final drive of 2.7x---average 14.1 MPG verified to within .5 MPG by factory EVIC computer in mixed driving on 87 octane.
 
Can't base the idle on displacement, that all has to do with proper cam selection. 425 horse is not something that is achieveable with a couple bolt ons. There are several other factors as far as tranny selection stall rear gears etc.. A 318 at 425 horse is going to take some doing and that is going to translate to dollars. I'm a fan of the 318 but your 425 horse target is going to be up there in the rpm range unless you stroke it. The 360 is going to get you there easier and develop more torque an therefore if you are looking for milage you can run a taller gear and still get adequate performance. There are sacrifices each way but I think a roller motor would be a good bet as suggested above. I'm building a 360 LA roller right now for street and strip use but my target of 400 horse is more attainable without sacrificing drivability.
 
I think N/A your best bet would be to use a 360 roller block and stroke it out to 408. Custom cam grind might be a good idea for best mpgs.

I think the best way to achieve your hp goals and good mpg would be a turbocharger. Get a 318 roller block, beef up the internals, again a custom ground cam might be a good idea here. Slap on an apropriate turbocharger with a good fuel injection setup. Its not cheap but would work very well.
 
If machining from scratch, Roller LA 360. Using a existing short block,the Magnum. Parts ,a TON cheaper on the LA stuff.
 
Yer dreamin. At the HP levels you are imagining, no way will a smaller engine get better mileage. and it won't be cheaper to do get that HP or mileage with a 318 -- I guess you could always hang a turbo on.
 
For a daily driver and decent mileage I'd go a nice mild 318, but there's no need for 425hp in my opinion.
 
How bout a daily driver of 750 hp and around 20mpg? Oh I'm sorry, that's my friend Aaron's Hennessy Camaro, not even my 91 roller 360 LA in the Signet gets that, sorry...


I may be arrogant but not ignorant
 
450 h.p. and gas mileage usually don't go hand in hand.
Your gear ratio in the diff will play a big role in it here as well as your driving style.
The carb size and jetting makes a big difference too.
I would at least think you are looking at a roller cam 360 stroked to 408, fuel injection, and 2:76 gears to achieve your goal.
An overdrive transmission and skinny tires with a hard compound would help you a lot here.
Make the car as light as possible.
 
A 425hp engine doesnt easily translate to 12+mpg. It also doesnt easily translate to daily driver reliability. My best advice is to get a roller 360 from a late 80's truck/van, talk to the guys here about their bolt on builds and come up with the best plan of attck for just doing bolt ons. Don't set your mind on the 425hp mark. Just build it as fast as you can within those guidelines and I promise you. the car will have plenty of go in her.
 
Here's one that I built and got good mileage:

67-68 Cuda Fastback, 72 318 block, TRW 10.5:1 forged pistons (no longer available), stock cam from my bro's 78 Lil Red Express (stock 340 cam), Rhoades lifters, 77 360 heads (important to use the bigger cc - brings compression down to 9.2:1), stock late 60's 340 intake (square bore), Holley 600 vacuum secondary with electric choke and 10.5 power valve, dual snorkel air cleaner, good rebuild 904 trans, 7 1/4 2.76 axle, dual 2 1/4" exhaust with stock 68 exhaust manifolds. I got 17.75 MPG on the highway and probably just under 300 HP.

There were two issues that I had to work out. I originally built it with stock 318 heads and it would overheat when the temperature got above 80° F after 20 minutes of running. It would pull 24" Hg at idle. I found a guy with a set of stock 77 360 heads with intake for $150. I didn't use the intake as it was a spreadbore, but used the heads. The idle vacuum dropped to 22.5" Hg and the compression went to 9.2:1, that solved the overheating issue because the compression was too high with stock 318 heads.

The other issue: The 7 1/4 axle could not handle this combination. I broke 3 axles in 4 years. The last axle break, my left rear tire, drum, and axle came out and passed me on the shoulder of the highway as I was driving at 55 MPH!!! (I slowed down from 70 MPH when I heard the noises from the rear end before it broke). And the gear lube comiong out of the axle caught fire! I doused the fire with a shop towel from the car and had to track my tire with the drum and axle still attached to where it finally stopped rolling. As I waited for the tow truck on the side of the road, I decided to convert to a 8 3/4 axle - no problem after that (it had 3.23 sure grip which reduced mileage a bit). Luckily, I had super stock leaf springs with Mancini racing u-bolts that were a little long, but they prevented the rear quarter panel from getting damaged due to the generous arch of the leaf springs. The 7 1/4 axle can only handle up to a stock 318.
 
Wait, wait wait... are we seriously talking about comparing a couple of MPG difference when it's going to cost big bucks build a 318 that's reliable at that power level?

Also, the 25lb difference is utterly neglegible.

Build a 360, 4spd if possible (or pick up a trans with overdrive) and some "highway" gears. Easier/cheaper to hit the power levels. Neither will provide decent MPG is that 425 horsepower is exploited in any way.
 
What are your goals and what vehicle will be receiving all the power? On a side note, it doesn't take an additional 25HP to move an addtional 25 lbs.
 
DA4AD said:
if your looking for drivabilty, do a 5.7 Hemi swap.
Click to expand...

Hemi is to expensive.


sledger46 said:
What are your goals and what vehicle will be receiving all the power? On a side note, it doesn't take an additional 25HP to move an addtional 25 lbs.
Click to expand...

No I said to keep the same power to weight ratio. The 318 weight in at 525lbs and the 360 at 550lbs. So the 360 would need to make 445hp to be exact.

It would be going in my 1976 Duster, 4 speed car.


What kind of MPG difference would there be between a 318 and 360? I know with early Dakota people report a 1-2 mpg loss when swapping from the 3.9 to (usually) 360.
 
I am just asking here, not trying to be a smartass. First, you throw out "450 HP". Are you familiar with what a car feels like with a TRUE 425 HP? That much power in a properly prepared A body can see some 10 second ETs. Secondly, you are correct. A 318 can be made to produce that power, but streetability will suffer, whether with a roller block or not. Lastly, if you think you would be happy with around 350 HP, you could build a 318 that easily eclipsed that mark AND gets decent mileage too. Just some points to ponder, cause gas AIN'T gettin cheaper.
 
318 plus turbo. Stay out of boost for mileage, boost when power is desired.

Or buy a 4 banger compact and build what you want and don't care about mileage.
 
RustyRatRod said:
I am just asking here, not trying to be a smartass. First, you throw out "450 HP". Are you familiar with what a car feels like with a TRUE 425 HP? .
Click to expand...

My Jeep with a 360 stroker (403c.i.) is over the 400 horsepower mark, (would have more power if I had decent headers for it) but anyways, I would hope a A-body would handle better than my Jeep. The only other vehicle with that much power is my dad's SRT Challenger with the 6.1, that I am car sitting for him and drive that around once a week. Turn off the traction control and that car can get wicked. IDK if you consider the Challenger to have a true 425 hp.
 
awh...those wonderful magazine builds...never seen them run down the track to back up their hp claim...
 
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