318 upgrades

Dodge Aspen R/T 318

Active Member
Joined
Feb 23, 2023
Messages
27
Reaction score
8
Location
Bristol, Virginia
hello all,Jim here..where I’m at with my 318 today is where a lot of you were at 25 years ago..I have a 1971 318 engine that runs great,I know it has low compression somewhere in the 8:6:1 range..as of this time I’m going to leave the pistons down in the hole and live with the compression that the engine has now..I do want an engine that performs well,my first upgrade i just purchased was a set of 391 rear gears which will be installed this new week,my 78 aspen has a 8/34 rear and I figured that the lower rear gears would help greatly getting the 318 moving off the line..my next move is to purchase an rpm intake with a 650 Holley,a set of good headers and a good free flowing exhaust,msd distributor and wires..I want to use the stock heads and would like your opinion on the necessary upgrades to the stock heads to help wake the engine up and and make it breath better, also can you please recommend a good performance cam that will work well with the lower compression of the engine and the bolt on upgrades I have I have listed..don’t want to use 360 heads,don’t want to upgrade to a 360 and as of this time would like to work with the lower compression and upgrading the stock 318 heads..i would appreciate any other suggestions you may have on what I’m trying to achieve..I know this isn’t going to be a powerhouse but would like to hear your input on how well you think this will perform..thanks, Jim..
 

Mikes5thAve

Well-Known Member
Joined
Mar 3, 2020
Messages
1,488
Reaction score
606
Location
Canada
Sticking with a 318 you would be better off to get a set of 302 heads from an 85-90 318. They're a better design and should up the compression a bit and affordable since they were on every 2bbl 318 of that time period.
I've always changed my distributor over to the mopar performance one altho I don't know if that's the same as the summit branded one that's available now or if those are more stock. They can be run with msd box also.
 

Dodge Aspen R/T 318

Active Member
Joined
Feb 23, 2023
Messages
27
Reaction score
8
Location
Bristol, Virginia
Jim here, how do you think the setup I described will perform, I know it’s not going to be a 350/400 horse tire shredder but I’m hoping it will perform from light to light rather quickly if needed..
 

Aspen500

Well-Known Member
Joined
Feb 14, 2015
Messages
7,142
Reaction score
2,852
Location
Rib Mountain, WI
Regardless of which heads you use, port matching the intake and exhaust ports and manifold ports to the gaskets helps, especially if using an intake made for a 340/360. Also tapering the guide bosses and opening up the throat area of the ports to eliminate any choke points, and cleaning up any casting flash or bumps in the ports. It'll all help them breath a little better. A set of swirl polished valve isn't a bad idea either to aid air flow past the valves.
 

Aspen500

Well-Known Member
Joined
Feb 14, 2015
Messages
7,142
Reaction score
2,852
Location
Rib Mountain, WI
A 3 angle valve job also helps a bit.

Memory is s bit fuzzy but, don't think there's room in the chamber for bigger valves but don't quote me. Also would have to consider cylinder bore clearance. I recall something about notching the top of the bore for the intake valve on the smaller bore of a 318 when larger valves are used.
 

Aspen500

Well-Known Member
Joined
Feb 14, 2015
Messages
7,142
Reaction score
2,852
Location
Rib Mountain, WI
Should be decent. Kind of need to stick with a "small" cam with 8.6:1 to keep the cylinder pressure up. It's not so much the comprssion ratio as it is cylinder pressure. Too much duration or overlap for a given compression ratio will kill power, especially at lower rpm.
 

Duke5A

Well-Known Member
Joined
Apr 6, 2018
Messages
1,687
Reaction score
900
Location
Michigan
Are you wanting to stay with stock heads for a factory appearance or cost? By the time you get done adding all the costs your into a set of assembled alloy heads and even after upgrades 318 irons will still be turds in comparison.

What you have now is probably the open chamber variety heads. You can gain a considerable amount of compression swapping to a set of 302 casting heads, but they still won't flow great up top. Taking into consideration you're running 3.91 gears the RPM limited motor is probably not going to make for a very optimal combo. If you wanted to stay iron for the factory appearance then reconsider the 340/360 heads. Compression would probably be around the same consider what you have now and you could always mill the heads a bit and run a thinner head gasket. Of course Magnum heads are always an option too.
 

M_Body_Coupe

Well-Known Member
Joined
Aug 19, 2013
Messages
670
Reaction score
314
Location
Windsor, ON, Canada
Hard to recommend a cam w/o first knowing a lot more about how you intend to use the car. If you are willing to tollerate a sloppy low-end, you could go to a bigger cam, but with such low compression it's the wrong way to go. You are sort of in a "no win" situation here if you want this thing to have a bit of punch to it.

What's the convertor stall speed?

Duke is right on the money with his comments: doing anything to the factory heads to unlock some performance (that is meaningful) will very quickly put you in the territory of aftermarket heads. I'd agree, not worth it unless this is necessary.

I had a set of factory '596 heads on my old 360 motor. Heavily ported, intake port had some pretty good flow numbers...but exhaust..well, it still sucked...and the car showed it.
 

XfbodyX

Well-Known Member
Joined
Sep 9, 2015
Messages
1,648
Reaction score
430
Location
Central US
Did you happen to get the gears changed? Wondering what it did vs what was in it?
 
Last edited:

Ele115

Well-Known Member
Joined
Apr 24, 2019
Messages
655
Reaction score
255
Location
Tampa FL
Better heads first, then do something about the compression ration. Otherwise you're still throwing money at a boat anchor
 
Back
Top