1974 318 duster. Can I port/polish these heads and get enough power out of them?

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supersoap33

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Hey all. I bought this duster and it already had some goodies. Holley 4 barrel street avenger carb and edelbrock low-rise intake with a 3" flow master dual exhaust. The exhaust manifolds are the originals, but I can probably change them out and weld them to the 3" flow masters.

Can I take these heads off, port and polish and keep them? I don't have the money to do much, and keeping things cast is really fine with me. I'm also thinking about putting in new piston rings and an oil pan and rebuilding or just servicing the 904 that came in it so it doesn't leak. And then maybe spending some money and making the rear end a sure grip if they make it with the 8.25. Was also going to put a decent cam in it and change everything to where it works right.

Thoughts? I don't have a big budget at all.
 
You will probably have to define your idea of enough power....to be able to answer the question.
 
Short answer. Unless you have set of templates and experience with a die grinder, proper cutters and a flow bench, more cylinder heads have been ruined than any other engine part.
Buy/borrow as many engine books as possible before you spend a dime on parts or machine work. Know what you are going to do ( Have a plan) before you do it.
To bake a cake you have to know what ingredients you are going to use, what order to mix the ingredients and what proportions of each ingredient you are going to use. How much time mixing and baking.
And then it might come out the way you thought it would.
Just putting different ingredients together without a recipe will get you nothing but something to throw away.
 
3” exhaust is overkill for the 318, you won’t get the proper scavenging effect and actually might be losing power. Carb, intake, cam , exhaust, etc. must match to make a good formula. Bigger isn’t always better if disproportionate.
 
Dave Huth said:
3” exhaust is overkill for the 318, you won’t get the proper scavenging effect and actually might be losing power. Carb, intake, cam , exhaust, etc. must match to make a good formula. Bigger isn’t always better if disproportionate.
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I don't know. I never have supported the "needs a little back pressure" theory. I think if he can afford the 3" system now, it'll be there when he upgrades later on. It's certainly not gonna make the difference between it having good power and not.
 
Dave Huth said:
3” exhaust is overkill for the 318, you won’t get the proper scavenging effect and actually might be losing power. Carb, intake, cam , exhaust, etc. must match to make a good formula. Bigger isn’t always better if disproportionate.
Click to expand...


There is never a scenario where back pressure is a good thing. Tubing diameter and length affect more than scavenging. Cam timing will affect which exhaust sizing will affect combustion chamber scavenging much more than sizing. Get that wrong and the engine will be unaffected by whatever exhaust is bolted to it.
 
448Scamp said:
There is never a scenario where back pressure is a good thing. Tubing diameter and length affect more than scavenging. Cam timing will affect which exhaust sizing will affect combustion chamber scavenging much more than sizing. Get that wrong and the engine will be unaffected by whatever exhaust is bolted to it.
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I'm kinda in agreement. Every single time without fail when I've gone up in header tube size and or exhaust pipe size, I've always gained more power. With no exception.
 
RustyRatRod said:
I'm kinda in agreement. Every single time without fail when I've gone up in header tube size and or exhaust pipe size, I've always gained more power. With no exception.
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Way back when, I put a set of Mickey THompson Try Y's on my 340 in my 73 Challenger and off to the strip I went. With no further tuning or modifications it went slower by a few hundredths. The stock manifolds and exhaust must have been pretty good back them. Good thing I kept all the old parts to put back on. A awful lot of work for no gain.
 
I haven't heard what sort of budget you have here, and what is most important to you. You start adding horsepower, and the rest of the drivetrain might need upgrading too depending on how you plan to drive it.
 
Is it a stock 318 cam? "A bit more" cam might help depending on what is in there. Do NOT go overboard on a cam. Guys on here can advise. "Back in the day" I would have put a 340 cam in

Also just exactly "what is" the intake? What model?
 
supersoap33 said:
Hey all. I bought this duster and it already had some goodies. Holley 4 barrel street avenger carb and edelbrock low-rise intake with a 3" flow master dual exhaust. The exhaust manifolds are the originals, but I can probably change them out and weld them to the 3" flow masters.

Can I take these heads off, port and polish and keep them? I don't have the money to do much, and keeping things cast is really fine with me. I'm also thinking about putting in new piston rings and an oil pan and rebuilding or just servicing the 904 that came in it so it doesn't leak. And then maybe spending some money and making the rear end a sure grip if they make it with the 8.25. Was also going to put a decent cam in it and change everything to where it works right.

Thoughts? I don't have a big budget at all.
Click to expand...

318 Long Block Bolt Ons - Tech Articles - Mopar Muscle Magazine

318 Engine Buildup & Dyno Test - Mopar Muscle Magazine

Magazine Builds post #27
 
I'd look for some 360 heads do a little porting and milling.

whatever you do to 318 heads if you do to 360 heads you'll have at least 30-40 hp more.
 
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toolmanmike said:
Way back when, I put a set of Mickey THompson Try Y's on my 340 in my 73 Challenger and off to the strip I went. With no further tuning or modifications it went slower by a few hundredths. The stock manifolds and exhaust must have been pretty good back them. Good thing I kept all the old parts to put back on. A awful lot of work for no gain.
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I've been off by a half second just cuz the air was bad...
 
toolmanmike said:
With no further tuning or modifications
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The reason should be obvious.
To the op leave the stock cam in it for now. Focus on tuning and get it dialed in really well. Timing and carb. Most people don’t spend enough time sorting this stuff out. Build your diff with a sure grip and your choice of street gears 3:23-3:55. Then put a good converter in it, Around 2800 stall. It will surprise you how well your car will run in that state. Especially if you get the tune dialed in.
 
For a cheap and easy upgrade on cylinder heads, get a set of magnum heads and appropriate valve gear from the junk yard. Have them checked out by a machine shop and run em. They’ll be better than the stock heads and much easier than porting yours.
 
273 said:
I'd look for some 360 heads do a little porting and milling.

whatever you do to 318 heads if you do to 360 heads you'll have at least 30-40 hp more.
Click to expand...
You don't want 360 heads on a 318 unless you can do something with the compression. They will drop already low compression to the basement, unless you use something like the 302 heads
 
302 castings are 318 heads. I think you may be referring to the 360 equivalent, which is a 308 casting.
 
I may have recollected wrong no. I was thinking of the small cc heads
 
67Dart273 said:
You don't want 360 heads on a 318 unless you can do something with the compression. They will drop already low compression to the basement, unless you use something like the 302 heads
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Why i said mill, you need to take something like .030-.040" off to have same chamber size as 318 heads, 302 heads are just like any other 318 don't flow enough and the CR advantage get ya like 2% power increase that's like 5hp, 10hp at best, if you want closed chamber magnum would be a better choice and can handle 400hp without porting. LA 360 can handle around 375 hp without porting.
318 heads 300 maybe 325 hp without porting. were talking low cr and reasonable cam sizes here for power output.
 
supersoap33 said:
Hey all. I bought this duster and it already had some goodies. Holley 4 barrel street avenger carb and edelbrock low-rise intake with a 3" flow master dual exhaust. The exhaust manifolds are the originals, but I can probably change them out and weld them to the 3" flow masters.

Can I take these heads off, port and polish and keep them? I don't have the money to do much, and keeping things cast is really fine with me. I'm also thinking about putting in new piston rings and an oil pan and rebuilding or just servicing the 904 that came in it so it doesn't leak. And then maybe spending some money and making the rear end a sure grip if they make it with the 8.25. Was also going to put a decent cam in it and change everything to where it works right.

Thoughts? I don't have a big budget at all.
Click to expand...
I can make a 318 head touch 190's with just a really good .070 wide face 4 angle valve job.
The stock cam is X amount- .395/.400ish of lift..with rocker arms that are advertised @1.5 , but are really less..
Low lift flow would be the focus if staying with the stock cam n only working the heads. Porting will increase flow at all lifts if you know what you're doing... but a good 4 angle valve job is idiot proof.imo

Otherwise...just open the bowl, profile guides, mildly work the straight atop the ssr approach to the turn itself...with the common wall. Leave lip/tiny edge just before it turns on that side of the approach.

Open chamber near seat like a cone, angled to the edge of the chamber. Don't hog it flat to the chamber wall.

If you lay a head gasket on the deck line it up with some spark plugs or what-have-you corks, use a wide tip marker for 318 and that distance of the line you leave should be the bores actual edge and let you know how far to go. With 360s and 340s you just use a regular Sharpie fine point and that's near perfect to show bores actuall boundry line/edge.

Lightly flatten 'not completely' the roof kink in exh ports, lightly roll the ssr over to the floor 'u shape and not flat angled back. Make a venturi if you can in far side bowl/throat.
Snap gauge width at ssr of exh and exit and open them accordingly. Pay attention to the ports design shape and how we're trying to work with that on the exhaust.. 'ends vs the center exh ports' for instance.
 
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273 said:
I'd look for some 360 heads do a little porting and milling.

whatever you do to 318 heads if you do to 360 heads you'll have at least 30-40 hp more.
Click to expand...
More if you also switch out the block for a 360

:poke:

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