Magnum heads on a 85' 318

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toolmanmike

toolmanmike

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Has anyone put late model Magnum heads on a 318? I have read a couple of articles that said a 30-50 hp. gain could be had (depending on the combination)
 
It's a win win deal. The cost issue is the other factor. Depending, I'd just pocket port what I have.
 
I am just finishing up putting a set of home ported Magnum heads from a 2003 Durango on my 1985 5th Ave 318. What a job......

I am waiting for my pushrods. Everything else is all ready to fire up.

I had use a jig that was made up by a member here to drill the heads for the
LA style intake that I wanted to use. that worked out perfectly.

I had the heads decked 0.020"

I am using the thin MP head gaskets (0.018" thick compressed).

Aftermarket hydraulic lifters for small block mopar that have the oil hole in the center where the pushrod contacts.

The best part is the intake ports match up perfectly with the cast iron intake I am using from a '85 Diplomat Cop car(4 bbl).

The valve size is 1.92 on the intake. Much better than the 1.88 on the original "302"s

59cc Volume compared to the 60cc on the "302"s

I am looking forward to running it.... just waiting for that one last part...

Oh.. btw, the length of the pushrod needed for a set of Magnums decked 0.020 with thin head gaskets for a 318 is the same length as the LS1/LS6 chevy. 7.50"

I sure hope the effort put into this transformation is worth it.
 
Was the jig hard to use and what did it cost?
 
In short, it's worth some power. 50hp I think is a stretch, not without other work, but it's a good swap. Like was said, you need the swap AMC lifters for mopar, and run hollow pushrods because that's how the rockers get oil on Magnums. You gain a modern chamber, some compression, and much better velocity intake and exh ports, plus 1.6:1 rockers instead of the LA 1.5:1. The intake port holes need to be re-angled. A guy has a jig they send around the country..lol. I think it costs $50 plus shipping, and works great. But any machine shop with a TCM or bridgeport can do it.
 
I rented the very same Jig that is going around the country. I beleive i only paid $20 and shipping to the next customer who needed it. Very easy to use. Just be sure to use quality drill bits.

I should be getting the pushrods early next week. I will let you know my impressions as soon as I get her going'
 
PN P4349557 for the Thin Gaskets from Mopar Performance.

Sorry for the huge delay in response. I was just looking at my old posts and realize I never finished this one.

I did get those Magnum Heads on my stock 318. When I pulled the "302"s off I made some deck height measurements.

My '85 318 pistons sat 0.085 in the hole. So far down that I thought I was looking at BTDC.

Nonetheless, I put on the Magnum heads knowing that I wasn't going to gain much in compression as I hoped. At the same time I swapped in a new cam (204/[email protected] .420/[email protected])as I had too since the valve train oiling is thru the pushrods.

So was it worth it? ABSOLUTELY!

At the very first test drive, when I pulled out the driveway....excited of course.... I gave it some gas expecting a total transformation....You know the feeling... tightening the grip on the steering wheel, stiffening your back in preparation and your eyes wide a bit in anticipation... listening to hear the screetch of the radials....BAM...I pressed on the gas pedal, about 3/4 the way and.....BOOOOGGG......At that instant I felt all that effort of, porting, part hunting, cleaning, aligning, bloody knuckles, day dreaming etc. was all for naught. Then it came... and damn, there was no mistaking it. The mid range lifted the front end up a bit. Your peripheral vision blurred as you concentrate on what is in front of you. The push of your back against the seat and the new sound of the 318's exhaust note vibrating the interior cabin.

I was impressed with the new found vigor in the 1800-5000 rpm range. Falls on its face after 5000, function of cam and maybe stock cast iron intake...

With the new Cam that replaced the stock roller(190/[email protected] .391/.391 lift @0.50), the power band moved upwards, taking with it what little low end torque the 318 had. Also, the car has a 2.45 gear and weighs 3800 lbs.

The 318 is still a work in progress... I am currently swapping out the rear gears for s set of 3.55 with sure grip. That should solve alot of my low end grunt issue.
 
I am currently swapping out the rear gears for s set of 3.55 with sure grip. That should solve alot of my low end grunt issue.
Click to expand...
It sure will. A tad bit of extra carb and distributor tuning and you'll be good.
It's a huge leap from 2.45's.
Now, the weight issue. That can tuff to solve. Fiberglass isn't out for every car and cost is a bit much for many including me.
 
I still don't what combo to put together. I've got the stock 302 casting heads
which could use a good gasket match and a little pocket porting. I have a set of stock Magnums and a set of ported Magnums( I think I'll save those for a stroker.) I would probably use the stock 273 4-bbl intake with the 302's
just to make it all look stock. I've got a Air Gap intake for the Magnum heads and all the goodies to install them on a LA block. I chose a xe262h-10 Comp cam. 218/224 @.050 262/270...462/470 lift. I would like to keep the stock compression to keep the cost down. This whole project started as a
running engine that I was going to bolt on some goodies as a temporary
powerplant while I was restoring the stock HP273. The closer I looked the more I didn't like. It was a pile of sludge inside. It's a wonder it even ran.
So far ,ridge ream and hone the bores, and send the crank out for grinding. I thought I read somewhere that the mid 80's 318's with the 302 heads had 9/1 compression. Anybody know for sure? I think the Magnum heads have a bit larger chamber than the 302's which might drop compression back to 8.5/1 toolmanmike
 
Mike - you are doing what I did. Havent run mine yet - wont happen till next spring. My motor is a 68 318 bored 60 with 302 ported heads. I'll be hanging all the oem 273 accessories on the thing along with the cast iron single plane 4 bbl intake and the wrinkle valve covers. You can do something similar in as much as the magnum heads can be redrilled to accept the LA intakes, and Ive heard the valve covers from the LA motors will bolt on using 5 of the 8 or 10 valve cover bolt holes - (however many they have) - on the magnum heads. Why not ? If I'd thought more about it I would have ditched the 302's and done the magnum conversion. Live and learn. The combustion chamber volumes are supposed to be very close on the magnum and 302 head, so I dont think you gain or loose a lot of CR that way. I am not sure what the stock CR is on an 85 motor - probably 8.5:1 or so.
 
I've got all the Magnum stuff, I might as well use it. Thanks for the info.
toolmanmike
 
Hey RumbleFish... I have done all that.. with the ignition advance kit and bought a strip kit for the Holley 600. Jets and Springs for the fine tuning. I will hopefully have the gears in by end of today or mid Sunday afternoon. Kids depending......

My '85 came with the 302 but I know that I wanted better flow velocity along with bigger valves( 1.92 compared to 1.88). And even better is the Intake/Exhaust flow ratio of the Mags compared to the 302.

Yes, the 302's and Mag combustion chambers are almost identical in size ~60cc +/- 1cc.

Finally, the pistons in my '85 318 sat 0.085 in the hole making the compression ratio with stock head gaskets and 302 heads 8.90:1.

Toolmanmike....I was thinking about that same cam in my car...I decided to stick to the roller and have it reground to my specs. But don't forget as I often do that cam specs(lift) from the manufacturer are using the 1.5 rocker ratio. Then Magnum heads use the pedistal 1.6 ratio, making your 462/470 a 492/501. The good news is the unported stock Magnum heads flow best @0.500 lift with 28" of h2o. That cam you have there is perfect... the bad news is that the Max lift on a stock Mag head is .520".

Good luck with your build....
 
Here is a supid question.....Can you put in 2.02 intake valves and 1.60 exhaust in the 318 head? Would they fit? Plus, i was wondering putting in a 340 cam in. I have an 89 318 That i want to put it in my Duster. Thanks Rick.
 
Ricksdust said:
Here is a supid question.....Can you put in 2.02 intake valves and 1.60 exhaust in the 318 head? Would they fit? Plus, i was wondering putting in a 340 cam in. I have an 89 318 That i want to put it in my Duster. Thanks Rick.
Click to expand...

Not a stupid question at all. However, I have found from others who have down that and read even more posts and tech articles that suggest going to a 2.02 with Magnum Heads on a 318 wouldn't gain much and possibly hurt flow. The stock '89 318 came with 1.78 intakes. Magnums have 1.92, that in itself is a huge step up in flow.

All I did was blend the bowls and ground the guides just a tad.
 
Port matching seems pretty straight-foreward but I'd like to see some photos of what bowl blending looks like when done correctly. Any help?
toolmanmike
 
bschubarg said:
Hey RumbleFish... I have done all that.. with the ignition advance kit and bought a strip kit for the Holley 600. Jets and Springs for the fine tuning. I will hopefully have the gears in by end of today or mid Sunday afternoon. Kids depending......

My '85 came with the 302 but I know that I wanted better flow velocity along with bigger valves( 1.92 compared to 1.88). And even better is the Intake/Exhaust flow ratio of the Mags compared to the 302.

Yes, the 302's and Mag combustion chambers are almost identical in size ~60cc +/- 1cc.

Finally, the pistons in my '85 318 sat 0.085 in the hole making the compression ratio with stock head gaskets and 302 heads 8.90:1.
Click to expand...

Kids depending, LOL, I'm in the same boat! Good luck.

Ricksdust; A 2.02 - 1.60 valve set up will fit. I did this on a teen a long time ago. You will be happier with a stock intake valve and a 1.60 exhaust valve with pocket porting gasket match set up on a mild engine, or, 1.88 intake valve on a street striper set up. The idea is to keep port velocity up, not drop it.
The 2.02 has a place of a 318 when you start to hunt for some serious power on a street strip car or a drag racer. And I would seriously save that move for a long time.
On the cam, while the 340 cam has been done alot with good results, todays bump sticks have a better edge. You can get similar cams with less advertised duration with similar or more duration @ .050 and more lift while mantaining a good idle and vaccum.
 
bschubarg said:
Yes, the 302's and Mag combustion chambers are almost identical in size ~60cc +/- 1cc.
Click to expand...

Did you actually cc the heads? I cc'd the magnum heads I am using on my 360 and they were 64cc which agrees with what most people that have measured them have found.
 
Yes I did. Albeit, not all chambers, just a few so I could get an idea. I honestly never heard of anyone saying 64cc., but know a few ppl who have actually measured and read anywhere from 57 to 60....

http://www.moparchat.com/forums/showthread.php?t=99313&page=3

Check that out for instance. You can even look at some articles Mopar Muscle have done. All say 59 cc.

You used alcohol right? I also hear that the water there in Pemboke, MA does funny things!!!! LOL
 
Well I guess the magnum heads vary like the open chamber heads (vary about 4cc's). FWIW, I have heard of more incidences of people measuring and getting closer to 64 than 60 but anyway just a number you need to know when setting up your engine to get the compression you want. Unless Mopar Muscle actually stated they measured the head volume I would expect it's just a number they were told.

BTW, I used Pembroke water! ;)
 
bschubarg said:
The valve size is 1.92 on the intake. Much better than the 1.88 on the original "302"s

59cc Volume compared to the 60cc on the "302"s
Click to expand...

#302 castings have 1.78" intakes IIRC. And FWIW, my #302's cc'd 57cc....magnums cc'd ~62 cc.
 
I stand corrected.. indeed the 302's came with 1.78 stock intakes... so many numbers... so little time. however, I did measure for myself my chambers just fir giggles and got just about 60cc straight across. Manufacuturing tolerances....?
 
308 heads are some of the last of the old LA rocker shaft heads used on 360's. They used 1.88/1.60's. Supposed to be the best of that series with a improved exh port and a pretty standard intake port.
 
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