Posted By: alpha727
318 LA block with magnum heads compression ratio? - 01/23/09 04:08 AM
What would the compression ratio be in a 86' 318 LA block with stock pistons and a set of factory magnum heads?
Posted By: 70AARcuda
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 04:14 AM
unless you know what the deck height is on the pistons...head cc...pistons cc.. head gasket cc..
you would be guess....
Posted By: GO_Fish
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 04:15 AM
you will pick up about 1/2 point compression, maybe a little more doing only the Mag head swap.
Posted By: volaredon
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 03:52 PM
thats what I was thinking about 1/2 a point as well. Whats funny is that for what seemed like "forever" I kept hearing that stock Magnum heads had 59-60 CC chambers and here recently it seems that everyone says that they are actually 63CC as are the current (stock/original) '163 heads that are on my 83 318are "supposed" to be.
Also I have seen most posts about ANY stock Mopar head say that for those that took the time to CC their heads, that most are actually larger than recognized published figures. Without measuring everything it is a crap shoot. Anyone done a CC job and seen a set of stock heads come out LESS than advertised combustion chamber volume?
Posted By: Wedgeman
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 03:55 PM
I have heard 59-60 cc too ! I tought they were...
Dan
Posted By: patrick
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 05:11 PM
the open chamber 318 heads actually run closer to 68cc. the closed chamber 302's usually run in the 58-62cc range.
Posted By: alpha727
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 05:49 PM
Thanks for the info. I've been trying to decide whether I should use the 302's or swap to the magnum heads I think I'm leaning towards the 302's
Posted By: kick_the_reverb
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 06:13 PM
My stock open chamber 675 type 318 heads were 64 cc
Ran
Posted By: alpha727
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 06:36 PM
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.
Posted By: alpha727
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 07:01 PM
it will be around 700 to set up the 302's the way that I'd want. I'll have to look deeper into the magnums. I'll check the link you gave me to compare prices.
Posted By: alpha727
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 07:18 PM
ok so, would the magnums with the stock valves still outflow the 302's with 2.02 / 1.60's with intake runners enlarged to 360 size, exhaust ports gasket matched and port work done?
Posted By: alpha727
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 07:19 PM
I'm sorry let's assume that the lift is exactly the same for both sets of heads.
Posted By: patrick
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 08:44 PM
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.
Posted By: patrick
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 08:49 PM
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.
Posted By: goldduster318
Re: 318 LA block with magnum heads compression ratio? - 01/23/09 10:44 PM
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.
Posted By: alpha727
Re: 318 LA block with magnum heads compression ratio? - 01/24/09 04:27 AM
ok, I'm convinced I'll go magnum. Thanks for all of the info.
Posted By: tpabayflyer
Re: 318 LA block with magnum heads compression ratio? - 01/24/09 04:21 PM
I would go for the magnum heads... actually the EQ heads.
With a 2.03 intake valve and porting they got flow numbers of 275/int -- 229ex at .600 lift........
that is pretty decent for some cheap cast iron heads.... TBF