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Re: 318 LA block with magnum heads compression ratio?
[Re: alpha727]
#201646
01/23/09 12:14 AM
01/23/09 12:14 AM
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Joined: Jan 2003
Posts: 9,826
las vegas
70AARcuda
master
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master
Joined: Jan 2003
Posts: 9,826
las vegas
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unless you know what the deck height is on the pistons...head cc...pistons cc.. head gasket cc..
you would be guess....
Tony
70 AARCuda Vitamin C
71 Dart Swinger 360 10.318 @ 128.22(10-04-14 Bakersfield)
71 Demon 360 10.666 @122.41 (01-29-17 @ Las Vegas)
71 Duster 408 (10.29 @ 127.86 3/16/19 Las Vegas)
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Re: 318 LA block with magnum heads compression ratio?
[Re: alpha727]
#201647
01/23/09 12:15 AM
01/23/09 12:15 AM
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Joined: Jul 2003
Posts: 6,167
Maryland
GO_Fish
master
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master
Joined: Jul 2003
Posts: 6,167
Maryland
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you will pick up about 1/2 point compression, maybe a little more doing only the Mag head swap.
Scott B.
"I'm a self-made man... I started with nothing, and I still have most of it!"
68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph
69 340 GTS stock 14.18@ 95.60 mph
01 5.9L Ram 1500 Quad Cab 4x4
01 3.5L 300M 16.23@ 86.97 mph
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Re: 318 LA block with magnum heads compression ratio?
[Re: GO_Fish]
#201648
01/23/09 09:50 AM
01/23/09 09:50 AM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
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Posts: 16,123
Grand Haven, MI
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Quote:
you will pick up about 1/2 point compression, maybe a little more doing only the Mag head swap.
no you won't if it's a 2bbl...OEM magnums usually run in the 63cc chamber range, the stock 302 heads usually run in the 58-63cc range, so your compression won't change dramatically, adn might decrease slightly..
I have an '86 318 out of my 5th ave and measured it, at TDC the pistons are about .085 in the hole. with this measurement, if you use a thin head gasket (say, a .028", 4.06" bore), you're looking at 8.6:1 compression with a 63cc chamber. using a .040" gasket drops it to 8.4, using a head gasket that comes in a kit (most that come in the fel-pro kits are .054" compressed thickness) will take you south of 8.2:1.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: 318 LA block with magnum heads compression ratio?
[Re: Wedgeman]
#201651
01/23/09 01:11 PM
01/23/09 01:11 PM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
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Grand Haven, MI
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the open chamber 318 heads actually run closer to 68cc. the closed chamber 302's usually run in the 58-62cc range.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: 318 LA block with magnum heads compression ratio?
[Re: alpha727]
#201653
01/23/09 02:13 PM
01/23/09 02:13 PM
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Joined: Sep 2007
Posts: 576
Escondido, CA
kick_the_reverb
mopar
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mopar
Joined: Sep 2007
Posts: 576
Escondido, CA
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My stock open chamber 675 type 318 heads were 64 cc
Ran
"Hey mister, something's wrong with your car, it idles roughly" - number one comment I got in Israel when daily driving a 70 Barracuda with a lopey cam.
Currently working on - 1966 Dodge A100 van 318/auto
Finally - disc brakes on the front.
In the plans - rear disc brakes, B&M 250 blower
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Re: 318 LA block with magnum heads compression ratio?
[Re: alpha727]
#201656
01/23/09 02:53 PM
01/23/09 02:53 PM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
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I Live Here
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Grand Haven, MI
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Quote:
If I get the magnum heads than more than likely I will have to get new pistons to raise the compression ratio to where I want it to be and all of the other things that go with the magnum swap. But, if I go 302's I can keep the stock pistons and mill the heads put in bigger valves and do a port job they would probably end up costing close to the same amount but, I think the 302's would outflow the magnums when compared.
sorry, wrong answer. a nearly max ported 302 with bigger valves will flow about the same as an OOTB magnum head on the intake side, and be down about 30cfm on the exhaust. chamber volume on the 302's is very close to a magnum, within about 3-5cc, which will be about the same amount of volume (and compression) difference as a .028 vs. a .054" thick head gasket. which why not just mill the magnum heads a bit?
if you're paying for port work, enginequest magnums will be significantly cheaper. 318B's have the LA intake bolt pattern. Carolina Machine Engines (www.cmengines.com) is a distributor and will set them up for $650-900 depending on what you want for valves and springs. just getting a used set of 302 heads done with new valves, springs, and machine work (no port work), you're probably up in the $500 range.
another option would be to disassemble the short block and deck the block .050 or so if the bores are in good shape and you don't want to buy pistons.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: 318 LA block with magnum heads compression ratio?
[Re: patrick]
#201658
01/23/09 03:09 PM
01/23/09 03:09 PM
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Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
goldduster318
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
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Quote:
Quote:
If I get the magnum heads than more than likely I will have to get new pistons to raise the compression ratio to where I want it to be and all of the other things that go with the magnum swap. But, if I go 302's I can keep the stock pistons and mill the heads put in bigger valves and do a port job they would probably end up costing close to the same amount but, I think the 302's would outflow the magnums when compared.
sorry, wrong answer. a nearly max ported 302 with bigger valves will flow about the same as an OOTB magnum head on the intake side, and be down about 30cfm on the exhaust. chamber volume on the 302's is very close to a magnum, within about 3-5cc, which will be about the same amount of volume (and compression) difference as a .028 vs. a .054" thick head gasket. which why not just mill the magnum heads a bit?
if you're paying for port work, enginequest magnums will be significantly cheaper. 318B's have the LA intake bolt pattern. Carolina Machine Engines (www.cmengines.com) is a distributor and will set them up for $650-900 depending on what you want for valves and springs. just getting a used set of 302 heads done with new valves, springs, and machine work (no port work), you're probably up in the $500 range.
another option would be to disassemble the short block and deck the block .050 or so if the bores are in good shape and you don't want to buy pistons.
notice how I said in stock form. A lot of people would not want to port them themselves, and it costs $$$ to have that done. Either one of these head sets are fairly prone to cracking so I'd be worried about going hog wild on these heads. Plus, to be at the magnum's flow you need to buy new valves and have machining done for that.
my entire magnum conversion, including heads didn't even cost $450 and I even bought the MP R/T springs and retainers.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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Re: 318 LA block with magnum heads compression ratio?
[Re: alpha727]
#201661
01/23/09 04:44 PM
01/23/09 04:44 PM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
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Grand Haven, MI
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the flow for a max effort 302 and OOTB enginequest heads will be comparable on the intake, but the 302 will be down about 30cfm on the exhaust.
when Dulcich built the "junkyard jewel" 318, IIRC his flow results after extensive porting, 2.02/1.60 valves maxed out in the 200/150 (int/ex) range. IIRC RyanJ maxed ported a set of 302's and installed bigger valves, and he got ~240/150 (int/ex) on his bench. but these are basically professional porters with a flow bench at their disposal, not a backyard hack (no offense).
most tests I've seen on the enginequests (sold by Hughes as "iron rams") place the peak flow at 215-230/170-180 (int/ex) out of the box with stock valves.
also, if you hog out the 302's to near 360 size, you will probably run into issues--the set Dulcich did on his 400HP "junkyard jewel" motor cracked and sprung a coolant leak in one of the intake ports about 6 months after that article was published because the casting was too thin after porting.
also, what size cam are you planning on running? with stock pistons (no valve reliefs) you may start getting into valve-to-piston clearance at lifts greater than ~.480" lift.
when I contacted CME about a year ago, they quoted me $650/pr + ship for EQ318B's, 3 angle valve job, OEM valves, seals, & keepers, and GM3100 springs & retainers set up at 1.65" IH. those springs installed at that height should be good for a cam to about .51" lift or so. they also quoted me $850/pr for the same heads, but with 2.02/1.625 SB chev valves .1" longer than stock, 5 angle valve job, and springs for a hydraulic roller cam good for .55" lift.
and if you wanted more power down the road, the EQ mag heads max out in the 280/220 range for int/ex flow max ported.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: 318 LA block with magnum heads compression ratio?
[Re: patrick]
#201662
01/23/09 04:49 PM
01/23/09 04:49 PM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
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Grand Haven, MI
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it's hard to say. honestly, it'll probably be a wash. max ported 302's might make a little more torque because the runner will still be about 20cc smaller than a magnums, so they'll have a little bit more velocity at low RPMS. but they might run out of breath sooner, too.
on the flip side, the magnum has a little better chamber, which will help it more....but unless you're near 0 deck for good quench, the slight improvement in chamber design probably won't be significant.
also, the poor exhaust port of the 302's might hurt some too.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: 318 LA block with magnum heads compression ratio?
[Re: patrick]
#201663
01/23/09 06:44 PM
01/23/09 06:44 PM
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Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
goldduster318
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
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here's an article using a 318 with zero deck pistons and stock and ported magnum heads: http://www.popularhotrodding.com/tech/0810phr_chrysler_318_engine/index.htmlI run box stock magnum heads on an under 9:1 (probably more like 8.6:1) 360...I know its a bigger engine, but its got great torque and horsepower. you can't feel it "lay down" at all anywhere from idle to 5500 (I don't spin it over that since its a somewhat loose used short block). I actually am able to get "too much" ignition advance so it will start missing at idle and won't start easily with this engine. I doubt it will change your 318's compression much at all. I had the same heads that are on my 360 on an 89 318 with stock pistons that ran decent (had minor carb issues though before it had a bearing spin). Obviously, the 360 is going to be stronger, but if you've ever driven a 318 magnum powered pickup, you'll know they make good torque as well.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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