1. HectorVenezula

    HectorVenezula Active Member

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    I have the stock 302 heads on my 318 but I have a chance to get 340 x heads would they be better performing heads?
     
  2. Duke5A

    Duke5A Well-Known Member

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    They flow much better than 302 heads, but you'll lose a point of compression on account of them being open chamber. Really, it depends on what your current combo is and plans moving forward. If they are in fact real X heads and you can get them cheap, they're quite valuable and can be sold to the restoration crowd. They don't flow any better than any other 340/360 head opened up to 2.02 valves.
     
  3. BudW

    BudW Moderator Staff Member

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    Stock 340 (and 360) cylinder heads will flow a lot more air than any/all (non-Magnum) 318 cylinder heads will – but there is more to the story.
    318’s was never meant to run more than 4k RPM (or so). They were built for low end torque.
    You can make a 318 run great, but the only item non-replaced/reworked will be the block (and possibly the crankshaft and rods).

    318 intake ports (cylinder head & intake) are much smaller than 340/360 intake ports are. Not measured, but by area, maybe twice the size of the 318. To make use of the 340 cylinder heads, you will need a 340/360 intake and camshaft. To make up for the compression loss (because of the 340/360 open chambers), you will also need taller pistons.

    A Cheaper option would be an older (complete) 360 engine, or a 318/360 Magnum engine.
    I would agree, the 340 “X” cylinder heads can go for big $ to the restore crowd and I have not seen any differences between the 340 “X”, the 340/360 “J” or all of the non-Magnum 360 cylinder heads (once opened up to use 2.02” valves).
    Note: some 2.02” cylinder heads might need some work on some 318 blocks due to machining differences for the valves might touch the cylinder wall in some (or many?) cases).

    I have had friends toss on a set of 360 heads, intake and camshaft on a 318, but left the original pistons alone and was disappointed with the outcome, for the compression loss negated the extra air flow.
    BudW
     
  4. Opticon77

    Opticon77 Well-Known Member

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    Or more precisely, the larger runners/valves lost him a bunch of low rpm port velocity (throttle response and grunt) then his lack of compression kneecapped the improvements in port volume (peak power) at higher RPM. He mismatched the parts in his V8 airpump and therefore dun goofed.

    As for Hector, I suggest sticking with those grunty/efficient 302s until you plan on needing more port volume... usually in the form of a stroker kit or the even more expensive "high RPM" build.
     
  5. XfbodyX

    XfbodyX Well-Known Member

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    I will never understand why so many are open to head swaps but dont want to go further to make things work well.
     
  6. Shorty Thompson

    Shorty Thompson Well-Known Member

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    what the cc'd chamber ? something around 70ish or more ?
     
  7. Duke5A

    Duke5A Well-Known Member

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    72cc if memory serves. All 340/360 LA heads were open chamber and had the same combustion chamber.
     
  8. Shorty Thompson

    Shorty Thompson Well-Known Member

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    Okay . Kinda thought it was around 73ish. For what it's worth I got a set of dart heads that's suppose to be after market x heads . Chamber looks a little smaller. May work for ya.
     
  9. ch1ll

    ch1ll Active Member

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    I did this swap. high flowing heads will not improve a low rpm motor like a 318 very much.
    so I also swapped a stock 4 barrel intake and a 650 Holley. I also swapped a Crower cam in of unknown grind but it was at least 300 advertised duration. the car had a manual valve body on a 727 and 4.56 gears in the rear. I drag raced it, 1/4 mile. it ran 14.02 at 96 mph. it reached full speed at the 1/8 mile cause it didn't have the compression to push faster. I did not mill the heads. if you mill the heads they likely will not be any good to the restoration crowd later down the road. some day these head will be worth alot of money to someone. I also played with a looser torque converter to improve my 60 foot times but kept breaking transmission tail castings. the unibody just was not stiff enough in a 30 year old car. I had a torque strap from the head to the frame and no subframe connectors or roll cage.

    all in all it was a fun car that was quick up to 96 mph. I'm sure that a looser converter and a stiffer frame would have me deep into the 13's.
     
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  10. Shorty Thompson

    Shorty Thompson Well-Known Member

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    Did you try less taller gear ?
     
  11. XfbodyX

    XfbodyX Well-Known Member

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    Still confused why some cant grasp a piston swap or even cheat with oem pistons and offset grind the crank. Ive on lil 318 that is 339.6 cubic inches and runs harder then a 340 does due to a small stroke increase. The only thing making a 318 a low rpm short block is the low compression pistons.

    I have posted this before, if you must use the low comp pistons another good cheat is fast bleed lifters to give you 4-6 less degrees duration till about 3500 rpm.

    People will swap heads, cams, rear gears, verts but yet still skiddish of a piston and balance job. Unless running a T brake a cast crank can live forever at 450hp.
     
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  12. Oldiron440

    Oldiron440 Well-Known Member

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    I think the block is a big black hole and there scared to go in.:)
     
  13. ch1ll

    ch1ll Active Member

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    no, not enough torque at low rpm with that combination. the gears were a bit steep(swap meet parts). 4.10 or 4.30 may have improved the times a bit but with that combination higher compression was the missing key.
     
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  14. Opticon77

    Opticon77 Well-Known Member

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    To be fair, all other LA build combinations considered, buying pistons for a 318 crosses that old "might as well pick up a 360" line. And knowing the compression/port velocity problems I think any 318 head swaps (outside of 302s) cross that same line. Not worth it unless you are committed to fully building what is effectively a de-bored 340... presumably for nostalgic reasons.
     
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  15. XfbodyX

    XfbodyX Well-Known Member

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    I love 318 topics.

    So your saying lets foolishly dump x amount of money and effort to this point knowing its not going to have the greatest results, is that what im reading. But it can be productive and have good returns if done well and it dont take alot of fancy parts.

    But im still not buying it, you can still find 318 forged replacement pistons cheap, if you bide your time. Cheaper then even a set of cast replacements at $100. I just found and bought another set for $62 shipped. And guess what, they have the same comp height of the 69 318 at 1.759. Which was rated at 230hp to the 340-s 275. And that was with open chamber heads, what 302-s could net you 20-25hp, dump this junk on a hydro roller cam block and pull another 20-25hp. (But id ask this, how many here have really ever broke a cast piston in a street car with an occasional trip to the track?) Dont rattle them and keep them under 5500 and you never will.

    You can also hunt around and find some hyper domed pistons for about $200 if your timing is correct.

    Back to the replacement pistons they do not need to be balanced although I would.

    So with them being approx .060-.065 in the hole with the thin head gasket you can pull an real world 9.6 to 1 comp ratio. Better yet weld and grind a crank from 3.31 to 3.45 nets you .140 then divide that by 2 and and you gain .070 which puts that factory replacement piston at zero deck with enough room for a .450 lift cam and more if you take a little from the already preset eyelets on the pistons. You stomping

    Heads are simple, you need 200 cfm to pull off approx 400hp and you can gain a substantial jump in the csa of the pinch point to easily achieve enough port volume. This is a low cost move too because you can use already existing larger mopar valves. Add valves, bowl work and work on the throat ect.

    Anyway, honestly if one had zero parts to start with, yes a 360 will net a bit more. Say a 425/425 J headed 360 is as simple as it gets, a 400/400 318 requires a bit of work (not money if you can do some of it) and attention to detail but as ive wrote before even if you pulled 500hp out of either your still gonna get smoked by the majority of new performance cars sold today.

    Look back at the old chevy 327, the ford 302 performance versions, ect.... and the most hypocritical thing I read is (A 318 was never meant.....) well what was the best factory 360 rated at? The mean E58 360 at 225hp and 300tq that would net you mid 15s in the 1/4. So the 360 was never really a high output performance motor until we made them that way. Factory it was a low comp smogger just like the 318 and even the smogger so called performance 360 had restrictive heads.

    I guess my point is people are just simply biased on 318-s and vs complaining I think folks should just buck up and stop complaining and focus on making there 318 run right with a set of well matched parts.

    OR one could just pop a tiny $1300 to turn there 318 into a 390 but why? Most would keep the oem gear and wonder why they cant hook or are still getting beat by the ones with well match combos, but thats another rant for another rainy day.

    Speaking of well matched combos, the only ones in the fmj world who are happy with a factory or highway gear and can make it work are the guys with the stroked big blocks where 500 pounds of tq make highway gears part of a well matched combo.
    Notice stressing well matched combos here?

    Just so no one gets butt hurt, at the end of the day all that matters is were happy with what we got. I think setting a goal for you and your car weather a /6 or a hemi is important and if you meat that goal then you have been successful and no one should stress too hard on what others think.
     
    Last edited: May 23, 2019
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  16. Opticon77

    Opticon77 Well-Known Member

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    Yeah but by the time you add up that carb, intake, port work, cam, pistons, block refresh machining/parts, high stall converter, and 4.10s ... you should have already picked up that $300 craigslist 360 core with forged crank instead.

    Here's one you can start with... Mopar 360
     
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  17. XfbodyX

    XfbodyX Well-Known Member

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    that $300 craigslist 360 core with forged crank instead

    Im sorry to inform you there was never a factory steel crank 360, thats a low compression stock 360.
    This CL 360 still is going to need heads, intake, carb, machine work....ect.

    If this here were close to me for $250 and if you could local pickup you cant beat it, a real forged steel crank and forged trw replacement slugs. This here id turn the crank, get some fresh rods, hone it, ring it, a decent cam and cruise anyplace and have a 250 shot plate kit on it since its a true forged assembly.

    1970 Mopar 318 Engine Short Block 030 Over Date 3-13-70 Chrysler Dodge Plymouth | eBay

    I have some really nice machined 360 blocks if anyone is looking. Also a nice set of bare 2.02 J heads that need nothing.
     
    Last edited: May 23, 2019
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  18. XfbodyX

    XfbodyX Well-Known Member

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    But since this is about heads, mopar put alot of thought in the 302 and 308 smog heads. These are not for sale but here is a set of mopar performance smog race head, big intakes, ported and chamber work right out of the box. It would not be hard to copy these.

    thumbnail_15.jpg

    thumbnail_14.jpg

    8.jpg

    9.jpg
     
  19. AJ/FormS

    AJ/FormS Well-Known Member

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    For me,a streeter;
    a 318/rebore is a money pit. If I'm gonna spend my hard-to-come-by coinage, I'm gonna go all the way to 360. Especially when there are plenty of Magnums to chose from that already have far better than 7.8/1 Scr, to start with and the cylinders waaay outlast LAs.
    Sure a smogger-teen can do pretty well with big gears and loose TCs, but you gotta also factor the cost of those in, when you hotrod the teener. Whereas, at the same power-level, a 360 can easily get by with 3.23s and a stock TC, I mean 96mph is easy peasy for just about any 4bbl 360, even with the stock cam.
    96mph is a W/P of 13.8 with an auto, so at 3400lbs is just 246hp. That's about what a 73/74 Dart-Sport was advertised to be; 8/1Scr, log-manifolds, and all. So, basically, drop in the 360 and 96 is a given.
    But if you transfer all the 318 go-fast stuff onto the 360 and it will eclipse the 318 in a hurry, and you still haven't opened the 360 up.
    The teener, IMO, just has too little swept area (652cc) to make any real low-rpm torque, especially when hot-rodded . And until recently, making compression was a tough thing to do. So the poor teener always needed gears and TC to help it jump off the line, and generally performance drops off rapidly with wind-resistance.
    But if you open up the 360;then you instantly have ~737 cc of swept volume to work with, or 13% more volume. That's almost like swapping out a 383 for a 440 (14.9%).. So whatever coinage I spend on the 360 is gonna net me ~13% better results, than if I had spent it on a 318.
     
    Last edited: May 23, 2019
  20. Shorty Thompson

    Shorty Thompson Well-Known Member

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    Currently on my back porch that will be worked on this summer is a 318 w/360 crank with a set of cast pistons on stock 360 rods . Now with a total agreement with on C/P height accompanied the greater stroke of the 360 I came out with a 350 or so , the hard way at .060 over. Take your time and build yourself a nice teen. Btw , with the CP391 I was still below deck at TDC.